WO1996023104A1 - Paper containing thermally-inhibited starches - Google Patents

Abstract

Thermally-inhibited starches and flours, preferably cationic or amphoteric starches which are optionally chemically crosslinked, are added, primarily as wet end additives, to paper stock. The starch or flour is inhibited by dehydrating to anhydrous or substantailly anhydrous and then heat treating the dehydrated starch or flour for a time and at a temperature sufficient to inhibit the starch or flour and improve its viscosity stability when dispersed in water. The dehydration may be a termal or non-thermal dehydration (e.g., by alcohol extraction or freeze-drying). Preferably, the pH of the starch or flour is adjusted to neutral or above prior to dehydration.

Description

PAPER CONTAINING THERMALLY-INHIBITED STARCHES Technical Field

This invention relates to paper and its

manufacture using starches or flours.

Background Art

Heat Treatment of Starches and Flours Heat/moisture treatment and annealing of starches and/or flours are taught in the literature and distinguished by the amount of water present.

"Annealing" involves slurrying a granular starch with excess water at temperatures below the starch's or flour's gelatinization temperature. "Heat/moisture-treatment" involves a semi-dry treatment at temperatures below the starch's or flour's gelatinization temperature, with no added moisture and with the only moisture present being that normally present in a starch granule (which is typically 10% or more).

In the following discussion, a history of the various heat/moisture and annealing treatments of starch and/or flour is set out.

GB 263,897 (accepted Dec. 24, 1926) discloses an improvement in the heat treatment process of GB

228,829. The process of the '829 patent involves dry heating flour or wheat to a point at which substantially all of the gluten is rendered non-retainable in a washing test and then blending the treated flour or wheat with untreated flour or wheat to provide a blend having superior strength. The improvement of the '897 patent is continuing the dry heating, without, however,

gelatinizing the starch, for a considerable time beyond that necessary to render all of the gluten non-retainable. "Dry-heating" excludes heating in a steam atmosphere or an atmosphere containing considerable quantities of water vapor which would tend to gelatinize the starch. The wheat or flour may contain the usual amount of moisture, preferably not greater than 15%. The heat treatment may exceed 7 hours at 77-93°C (170-200°F), e.g., 8 to 14 hours at 82°C (180ºF) or 6 hours at 100°C (212°F).

GB 530,226 (accepted Dec. 6, 1940) discloses a method for drying a starch cake containing about 40-50% water with hot air or another gas at 149°c (300°F) or above without gelatinizing the starch. The starch cake is disintegrated by milling it to a finely divided state prior to drying.

GB-595,552 (accepted December 9, 1947) discloses treatment of starch, more particularly a corn starch, which involves drying the starch to a relatively low moisture content of 1-2%, not exceeding 3%, and subsequently dry heating the substantially moisture-free starch at 115-126°C for 1 to 3 hours. The treatment is intended to render the starch free from thermophilic bacteria. The starch should not be heated longer than necessary to effect the desired sterilization.

U.S. 3,490,917 (issued January 20, 1970 to C.A.F. Doe et al.) discloses a process for preparing a non-chlorinated cake flour suitable for use in cakes and sponges having a high sugar to flour ratio. The starch or a flour in which the gluten is substantially or completely detached from the starch granules is heated to a temperature of from 100-140ºC and then cooled. The conditions are selected so that dextrinization does not occur, e.g., about 15 minutes at 100-115°C and no hold and rapid cooling at the higher temperatures. The heat treatment should be carried out under conditions which allow the water vapor to escape. The reduction in moisture content due to the heat treatment depends upon the temperature employed. At treatment temperatures of 100-105ºC, the moisture content is reduced from 10-12% to 8-9%, by weight, while at medium and high temperatures the moisture content is typically reduced to 7% or less. Preferably, during cooling the moisture is allowed to reach moisture equilibrium with the atmosphere. The gelatinization temperature of the heat treated starch or flour is approximately 0.5-1ºC higher than that of a comparable chlorinated flour or starch. The heating can be carried out in many ways, including heating in a hot air fluidized bed.

U.S. 3,578,497 (issued May 11, 1971 to E. T. Hjermstad) discloses a process for non-chemically

improving the paste and gel properties of potato starch and imparting a swelling temperature as much as -7 to -1°C (20 to 30°F) higher. A concentrated suspension (20-40% dry solids) at a neutral pH (5.5-8.0, preferably 6-7.5) is heated either for a long time at a relatively low temperature or for a short time at successively higher temperatures. The suspension is first heated at a temperature below the incipient swelling temperature of the particular batch of starch being treated (preferably 49°C - 120°F). Then the temperature is gradually raised until a temperature well above the original swelling temperature is attained. It is essential that swelling be avoided during the different heating periods so that gelatinization does not occur. After this steeping treatment the starch has a higher degree of granular stability. It resists rapid gelatinization and produces a rising or fairly flat viscosity curve on cooling. The pastes are very short textured, non-gumming, non-slimy, cloudy and non-cohesive. They form firm gels on cooling and aging.

U.S. 3,977,897 (issued August 31, 1976 to

Wurzburg et al.) discloses a method for preparing non- chemically inhibited amylose-containing starches. Both cereal and root starches can be inhibited, but the inhibition effects are more observable with root

starches. Amylose-free starches, such as waxy corn starch, show no or very slight inhibition. The Brabender viscosity of cooked pastes derived from the treated starch was used to determine the inhibition level.

Inhibition was indicated by a delayed peak time in the case of the treated corn starch, by the lack of a peak and a higher final viscosity in the case of the treated achira starch, and by the loss of cohesiveness in the case of the treated tapioca starch. The granular starch is suspended in water in the presence of salts which raise the starch's gelatinization temperature so that the suspension may be heated to high temperatures without causing the starch granules to swell and rupture yielding a gelatinized product. The preferred salts are sodium, ammonium, magnesium or potassium sulfate; sodium,

potassium or ammonium chloride; and sodium, potassium or ammonium phosphate. About 10-60 parts of salt are used per 100 parts by weight of starch. Preferably, about 110 to 220 parts of water are used per 100 parts by weight of starch. The suspension is heated at 50-100°C, preferably 60-90°C, for about 0.5 to 30 hours. The pH of the suspension is maintained at about 3-9, preferably 4-7. Highly alkaline systems, i.e., pH levels above 9 retard inhibition.

U.S. 4,013,799 (issued March 22, 1977, to

Smalligan et al.) discloses heating a tapioca starch above its gelatinization temperature with insufficient moisture (15 to 35% by total weight) to produce

gelatinization. The starch is heated to 70-130°C for 1 to 72 hours. The starch is used as a thickener in wet, pre-cooked baby foods having a pH below about 4.5. U.S. 4,303,451 (issued December 1, 1981 to Seidel et al.) discloses a method for preparing a

pregelatinized waxy maize starch having improved flavor characteristics reminiscent of a tapioca starch. The starch is heat treated at 120-200°C for 15 to 20 minutes. The pregelatinized starch has gel strength and viscosity characteristics suitable for use in pudding mixes.

U.S. 4 , 303 , 452 (issued Dec. 1, 1981 to Ohira et al.) discloses smoking a waxy maize starch to improve gel strength and impart a smoky taste. In order to

counteract the smoke's acidity and to obtain a final product with a pH of 4-7, the pH of the starch is raised to pH 9-11 before smoking. The preferred water content of the starch during smoking is 10-20%

The article "Differential Scanning Calorimetry of Heat-Moisture Treated Wheat and Potato Starches" by J.W. Donovan et al. in Cereal Chemistry. Vol. 60, No. 5, pp. 381-387 (1983) discloses that the gelatinization temperature of the starches increased as a result of the heat/moisture treatment or annealing. See also the article "A DSC Study Of The Effect Annealing On

Gelatinization Behavior Of Corn Starch" by B.R. Krueger et al. in Journal of Food Science, Vol. 52, No. 3, pp. 715-718 (1987).

U.S. 4,391,836 (issued July 5, 1983 to C.-W.

Chiu) discloses instant gelling tapioca and potato starches which are non-granular and which have a reduced viscosity. Unmodified potato and tapioca starches do not normally gel. The starches of the patent are rendered non-granular and cold-water-dispersible by forming an aqueous slurry of the native starch at a pH of about 5-12 and then drum-drying the slurry. The starches are rendered gelling by heat treating the drum-dried starch for about 1.5 to 24 hours at 125-180ºC to reduce the viscosity to within defined Brabender viscosity

limitations.

U.S. 4,491,483 (issued January 1, 1985 to W.E. Dudacek et al.) discloses subjecting a semi-moist blend of a granular starch with at least 0.25 wt. % of a fatty acid surfactant and sufficient water (about 10-40 wt. %) to a heat-moisture treatment at from about 50-120°C, followed by drying to about 5-15 wt. %, preferably 10 wt. %, moisture. The heat-moisture treated starch-surfactant product is characterized by a hot water dispersibility of from about 60-100% and a higher pasting temperature than the granular starch from which it is derived.

Preferably, the treatment takes place in a closed

container so that the moisture can be maintained at a constant level. The preferred conditions are 3 to 16 hours at 60-90°C. Degradation and dextrinization

reactions are undesirable as they destroy the thickening ability of the starch. The use of conditions, such as, e.g., 35% moisture at 90°C for 16 hours results in reduced paste viscosity. It is believed the presence of the surfactant during the treatment permits formation of a complex within the partially swollen starch matrix with straight chain portions of the starch molecules. The limited moisture environment allows complex formation without gelatinization.

Japanese Patent Publication No. 61-254602.

(published December 11, 1987) discloses a wet and dry method for heating waxy corn starch and derivatives thereof to impart emulsification properties. The wet or dry starch is heated at 100-200°C, preferably 130-150°C, for 0.5 to 6 hours. In the dry method, the water content is 10%, preferably 5%, or less. In the wet method, the water content is 5 to 50%, preferably 20-30%. The pH is 3.5-8, preferably 4-5. The article "Hydrothermal Modification of Starches: The Difference between Annealing and

Heat/Moisture-Treatment", by Rolf Stute, Starch/Stärke Vol. 44, No. 6, pp. 205-214 (1992) reports almost

identical modifications in the properties of potato starch with annealing and heat/moisture treatments even through the alteration of the granular structure is different. The Brabender curves of the heat/moisture-treated and annealed potato starches show the same typical changes, including a higher gelatinization temperature and a lower peak viscosity or no peak. The DSC curves also show a shift to higher gelatinization temperatures for both treatments. A combined treatment involving annealing a heat/moisture-treated potato starch leads to a further increase in gelatinization temperature without detectable changes in gelatinization enthalapy and with retention of the viscosity changes caused by the heat treatment. A combined treatment involving annealing a heat/moisture-treat potato starch does not lower the gelatinization temperature, when compared to the base starch, and increases the gelatinization temperature at higher heat/moisture treatment levels.

Chemical Crosslinking of Starches and Flours Starches and flours are chemically modified with difunctional reagents such as phosphorus

oxychloride, sodium trimetaphosphate, adipic anhydride, acetic anhydride and epichlorohydrin to produce

chemically crosslinked starches having excellent

tolerance to processing variables such as heat, shear, and pH extremes. Such chemically crosslinked starches (also referred to as "inhibited starches") provide a desirable smooth texture and possess viscosity stability throughout processing operations and normal shelf life.

In contrast, when unmodified (i.e., non-crosslinked) starches, particularly waxy-based starches, are gelatinized, they reach a peak viscosity which soon begins to breakdown, loose thickening capacity and textural qualities, and behave unpredictably during storage as a result of the stresses encountered during processing. Heat, shear, and/or an extreme pH,

especially an acidic pH, tend to fully disrupt the starch granules and disperse the starch.

Papermaking

Papermaking, as it is conventionally known, is a process of forming an aqueous slurry of pulp or wood cellulosic fibers, introducing the fibers onto a screen or wire to form an interlocking mat and to allow the water to drain through the screen or wire, squeezing the mat between rollers, drying it, and processing it into a dry roll or sheets.

Most paper is made on a Fourdrinier machine or a cylinder machine. In the Fourdrinier and multi-cylinder operations, and in other machine operations typical in papermaking, the aqueous slurry of the pulp or wood cellulosic fibers is formed at the feed or inlet to the machine, called the wet end. In the wet end, the pulp or wood cellulosic fibers are subjected to

mechanical beating or chemical refining to promote fiber-to-fiber bonding and ultimately strengthen the final paper product. However, a practical limit exists in the amount of refining that can be used for strength

development. Excessive refining causes the sheet to lose other desirable characteristics, such as porosity, flexibility, brightness, and opacity. The addition of starch to the wet end obviates the need for excessive refining and improves the strength of the paper stock.

Historically, starch has been used in papermaking processes in a solubilized form so that the starch molecules are accessible for bonding to the cellulosic fibers. Starch retention on cellulosic fibers is increased by making the starch cationic or amphoteric. Both starch and cellulosic fibers are anionic. Attracted to the negatively charged cellulosic fiber, and also to any of the common negatively charged fillers added to the wet end system, the cationic or amphoteric starch

increases fiber-to-fiber and fiber-to-filler bonding, promoting a high degree of filler retention as well as strength.

Various cationic starches are known and used in the paper industry, with the tertiary amino and

quaternary ammonium starch ethers being the most

commercially significant derivatives. These and other cationic starches, as well as a method for their

preparation, are described in "Cationic Starches" by D.B. Solarek, Modified Starches: Properties and Uses. Chapter 8, pp. 113-129 (1986).

While unmodified or modified chemically crosslinked starches have been used in a number of applications, they have not been used to a large extent in papermaking. The following publications disclose the use of chemically crosslinked starches in papermaking. U.S. 3,417,078 (issued December 7, 1968 to C. Patel) discloses the use of a cationic starch imidazoline derivative which is reacted with a crosslinking agent such as dichlorobutene. European Patent No. 097,371

(published January 4, 1984 to S. Frey) discloses the use of a nongelatinized starch which is cationized and partly crosslinked. U.S. 5,122,231 (issued June 16, 1992 to K. Anderson) discloses the use of a cationic starch as a wet crosslinked end additive to produce increased starch loading capacity. Japanese Patent No. 2-133695

(published May 22, 1990 to K. Maeda) discloses the use of a cationic crosslinked starch having specified, but broad, degrees of crosslinking. U.S. 5,368,690 (issued November 29, 1994 to D. Solarek et al.) discloses the addition of jet-cooked chemically-crosslinked cationic or amphoteric starches having a viscosity breakdown of about 2-85% for improving calcium carbonate retention.

Disclosure of Invention

This invention is directed to paper comprising, as an additive, a starch or flour that is thermally inhibited. The starches and flours may be non-pregelatinized granular starches and flours or

pregelatinized granular or nongranular starches and flours. The starches or flours are thermally inhibited to impart the functionality previously provided by chemical crosslinking with a multifunctional crosslinking agent. The thermally-inhibited starches and flours can be used wherever starches are conventionally used in paper manufacture, for example, as wet end additives, coatings, and sizes.

Preferably, the starch is derivatized with cationic, anionic, non-ionic, or amphoteric substituents. When anionic or non-ionic starches are used as wet end additives, they are typically used in combination with cationic or amphoteric starches.

The starches and flours are thermally inhibited, without the addition of chemical reagents, in a heat treatment process that results in the starch or flour becoming and remaining inhibited. The starches and flours are referred to as "inhibited" or "thermally-inhibited (abbreviated "T-I"). When these thermally-inhibited starches and flours are dispersed and/or cooked in water, they exhibit the textural and viscosity

properties characteristic of a chemically-crosslinked starch. The starch granules are more resistant to viscosity breakdown. This resistance to breakdown results in what is subjectively considered a non-cohesive or "short" textured paste, meaning that the gelatinized starch or flour tends to be salve-like and heavy in viscosity rather than runny or gummy.

When the thermally-inhibited starches and flours are non-pregelatinized granular starches or flours, the starches or flours exhibit an unchanged or reduced gelatinization temperature. In contrast, most annealed and heat/moisture treated starches show an increased gelatinization temperature. Chemically-crosslinked starches show an unchanged gelatinization temperature. It is believed the overall granular

structure of the thermally-inhibited starches and flours has been altered.

The starches and flours that are substantially completely thermally inhibited will resist

gelatinization. The starches and flours that are highly inhibited will gelatinize to a limited extent and show a continuing rise in viscosity but will not attain a peak viscosity. The starches and flours that are moderately inhibited will exhibit a lower peak viscosity and a lower percentage breakdown in viscosity compared to the same starch that is not inhibited. The starches and flours that are lightly inhibited will show a slight increase in peak viscosity and a lower percentage breakdown in viscosity compared to the same starch that is not

inhibited.

The starches and flours are inhibited by a process which comprises the steps of dehydrating the starch or flour until it is anhydrous or substantially anhydrous and then heat treating the anhydrous or

substantially anhydrous starch or flour at a temperature and for a period of time sufficient to inhibit the starch or flour. As used herein, "substantially anhydrous" means containing less than 1% moisture by weight. The dehydration may be a thermal dehydration or a non-thermal dehydration such as alcohol extraction or freeze drying. An optional, but preferred, step is adjusting the pH of the starch or flour to neutral or greater prior to the dehydration step.

The amount of thermal inhibition required will depend on the reason the starch or flour is included in the paper, as well as the particular processing

conditions used to prepare the paper. Paper pulps prepared with the thermally-inhibited starches and flours will possess viscosity stability, and process tolerance such as resistance to heat, acid and shear. In addition, the viscosity of the jet-cooked thermally-inhibited starches is lower than the viscosity of jet-cooked chemically-crosslinked starches. This lower viscosity is a significant processing advantage.

Depending on the extent of the heat treatment, various levels of inhibition can be achieved. For example, lightly inhibited, higher viscosity products with little breakdown, as well as highly inhibited, low viscosity products with no breakdown, can be prepared by the thermal inhibition processes described herein.

For making paper having an alkaline pH, a thermally-inhibited, cationic, anionic, amphoteric, or non-ionic starch or flour is added to the wet end of the papermaking system. If a non-pregelatinized starch or flour is used, it is preferably cooked, e.g., by jet cooking, before addition. When used to improve the calcium carbonate retention, non-pregelatinized granular starch or flour will be thermally inhibited to a level such that, when the starch or flour is dispersed in water at 5% solids at 95°C, it will show a breakdown from peak viscosity in the range of 15-65%, preferably 25-45%.

Mode(s) For Carrying Out the Invention All starches and flours are suitable for use herein. The thermally-inhibited starches and flours are used in these compositions for their strength, retention. thickening/bindings and surface modifying properties, which will depend on the starch or flour base selected as well as its modification.

The thermally-inhibited starches and flours can be derived from any native source. A "native" starch or flour is one as it is found in nature in unmodified form. Typical sources for the starches and flours are cereals, tubers, roots, legumes and fruits. The native source can be corn, pea, potato, sweet potato, banana, barley, wheat, rice, sago, amaranth, tapioca, sorghum, waxy maize, waxy tapioca, waxy rice, waxy barley, waxy potato, waxy sorghum, starches having an amylose content of 40% or greater and the like. Preferred starches are waxy starches, potato, tapioca and corn.

The thermal inhibition process may be carried out prior to or after other starch or flour reactions are used to modify starch or flour. The starches may be modified by conversion (i.e., acid-, enzyme-, and/or heat-conversion), oxidation, phosphorylation,

etherification (e.g., by reaction with propylene oxide), esterification (e.g., by reaction with acetic anhydride or octenylsuccinic anhydride), and/or chemical

crosslinking (e.g., by reaction with phosphorus

oxychloride or sodium trimetaphosphate). The flours may be modified by bleaching or enzyme conversion.

Procedures for modifying starches are described in the Chapter "Starch and Its Modification" by M.W. Rutenberg, pages 22-26 to 22-47, Handbook of Water Soluble Gums and Resins, R.L. Davidson, Editor (McGraw-Hill, Inc., New York, NY 1980).

Native granular starches have a natural pH of about 5.0-6.5. When such starches are heated to

temperatures above about 125 'C in the presence of water, acid hydrolysis (i.e., degradation) of the starch occurs. This degradation impedes or prevents inhibition. Therefore, the dehydration conditions need to be chosen so that degradation is avoided. Suitable conditions are dehydrating at low temperatures and the starch's natural pH or dehydrating at higher temperatures after increasing the pH of the starch to neutral or above. As used herein, "neutral" covers the range of pH values around pH 7 and is meant to include from about pH 6.5-7.5. A pH of at least 7 is preferred. More preferably, the pH is 7.5-10.5. The most preferred pH range is above 8 to below 10. At a pH above 12, gelatinization more easily occurs. Therefore, pH adjustments below 12 are more effective. It should be noted that the textural and viscosity benefits of the thermal inhibition process tend to be enhanced as the pH is increased, although higher pHs tend to increase browning of the starch or flour during the heat treating step.

To adjust the pH, the non-pregelatinized granular starch or flour is typically slurried in water or another aqueous medium, in a ratio of 1.5 to 2.0 parts of water to 1.0 part of starch or flour, and the pH is raised by the addition of any suitable base. Buffers, such as sodium phosphate, may be used to maintain the pH if needed. Alternatively, a solution of a base may be sprayed onto the powdered starch or flour until the starch or flour attains the desired pH, or an alkaline gas such as ammonia can be infused into the starch or flour. After the pH adjustment, the slurry is then either dewatered and dried, or dried directly, typically to a 2-15% moisture content. These drying procedures are to be distinguished from the thermal inhibition process steps in which the starch or flour is dehydrated to anhydrous or substantially anhydrous and then heat treated.

The starches or flours can be pregelatinized prior to or after the thermal inhibition process using methods known in the art. The amount of

pregelatinization, and consequently, whether the starch will display a high or a low initial viscosity when dispersed in water, can be regulated by the

pregelatinization procedure used, as is known in the art. The resulting pregelatinized starches are useful in applications where cold-water-soluble or cold-water-dispersible starches are used.

Pregelatinized granular starches and flours have retained their granular structure but lost their polarization crosses. They are pregelatinized in such a way that a majority of the starch granules are swollen, but remain intact. Exemplary processes for preparing pregelatinized granular starches are disclosed in U.S. 4,280,851 (issued July 28, 1981 to E. Pitchon et al.),

U.S. 4,465,702 (issued August 14, 1984 to J.E. Eastman et al.), U.S. 5,037,929 (issued August 6, 1991 to S.

Rajagopalan), and U.S. 5,149,799 (issued September 22, 1992 to Roger W. Rubens), the disclosures of which are incorporated by reference.

Pregelatinized non-granular starches and flours have also lost their polarization crosses and have become so swollen that the starches have lost their granular structure and broken into fragments. They can be

prepared according to any of the known physical, chemical or thermal pregelatinization processes that destroy the granule such as drum drying, extrusion, or jet-cooking. See U.S. 1,516,512 (issued Nov. 25, 1924 to R.W. G.

Stutzke); U.S. 1,901,109. (issued March 14, 1933 to W. Maier); US. 2.314.459 (issued March 23, 1943 to A.A.

Salzburg; US. 2,582,198 (issued January 8, 1957 to O.R. Ethridge); us. 2.805.966 (issued September 10, 1957 to O.R. Ethridge); US. 2,919,214 (issued December 29, 1959 to O.R. Ethridge); U.S. 2,940,876 (issued June 14, 1960 to N.E. Elsas); U.S. 3,086,890 (issued April 23, 1963 to A. Sarko et al.); U.S. 3,133,836 (issued May 19, 1964 to U.L. Winfrey); U.S. 3,137,592 (issued June 16, 1964 to T.F. Pratzman et al.); U.S. 3.234.046 (issued February 8, 1966 to G.R. Etchison); U.S. 3,607,394 (issued September 21, 1971 to F.J. Germino); U.S. 3,630,775 (issued

December 18, 1971 to A.A. Winkler); and U.S. 5,131,953 (issued July 21, 1992 to J.J. Kasica et al.); the

disclosures of which are incorporated by reference.

If the pregelatinization process is performed first and the pregelatinized starch or flour is granular, the pH is adjusted by slurrying the pregelatinized granular starch or flour in water in a ratio of 1.5-2.0 parts to 1.0 part starch, and optionally, the pH is adjusted to neutral or greater. In another embodiment, the slurry is simultaneously pregelatinized and dried and the dried, starch or flour is thermally inhibited. If the thermal inhibition process is performed first, the starch or flour is slurried in water, the pH of the starch or flour is adjusted to neutral or greater, and the starch or flour is dried to about 2-15% moisture.

The dried starch or flour is then dehydrated and heat treated. The inhibited starch or flour is reslurried in water, optionally pH adjusted, and simultaneously

pregelatinized and dried.

For non-granular pregelatinized starches or flours prepared by drum drying, the pH is raised by slurrying the starch or flour in water at 30-40% solids and adding a sufficient amount of a solution of a base until the desired pH is reached.

For non-granular pregelatinized starches or flours prepared by the continuous coupled jet-cooking/spray-drying process of U.S. 5.131.953 or the dual atomization/spray-drying process of U.S. 4,280,851. the starch or flour is slurred at 6-10% solids in water and the pH is adjusted to the desired pH by adding a sufficient amount of a solution of a base until the desired pH is reached.

Suitable bases for use in the pH adjustment step include, but are not limited to, sodium hydroxide, sodium carbonate, tetrasodium pyrophosphate, ammonium orthophosphate, disodium orthophosphate, trisodium phosphate, calcium carbonate, calcium hydroxide,

potassium carbonate, and potassium hydroxide, and any other bases approved for use under the applicable

regulatory laws. The preferred base is sodium carbonate. It may be possible to use bases not approved provided they can be washed from the starch or flour so that the final product conforms to good manufacturing practices for desired end use.

A thermal dehydration is carried out by heating the starch or flour in a heating device for a time and at a temperature sufficient to reduce the moisture content to less than 1%, preferably 0%. Preferably, the

temperatures used are 125°C or less, more preferably 100-120ºC. The dehydrating temperature can be lower than

100°C, but a temperature of at least 100°C will be more efficient for removing moisture.

Representative processes for carrying out a non-thermal dehydration include freeze drying or

extracting the water from the starch or flour using a solvent, preferably a hydrophilic solvent, more

preferably a hydrophilic solvent which forms an

azeotropic mixture with water (e.g., ethanol).

For a laboratory scale dehydration with a solvent, the starch or flour (about 4-5% moisture) is placed in a Soxhlet thimble which is then placed in a Soxhlet apparatus. A suitable solvent is placed in the apparatus, heated to its reflux temperature, and refluxed for a time sufficient to dehydrate the starch or flour. Since during the refluxing the solvent is condensed onto the starch or flour, the starch or flour is exposed to a lower temperature than the solvent's boiling point. For example, during ethanol extraction the temperature of the starch is only about 40-50°C even though ethanol's boiling point is about 78°C. When ethanol is used as the solvent, the refluxing is continued for about 17 hours. The extracted starch or flour is removed from the

thimble, spread out on a tray, and the excess solvent is allowed to flash off. The time required for ethanol to flash off is about 20-30 minutes. The dehydrated starch or flour is immediately placed in a suitable heating apparatus for the heat treatment. For a commercial scale dehydration any continuous extraction apparatus is suitable.

For dehydration by freeze drying, the starch or flour (4-5% moisture) is placed on a tray and put into a freeze dryer. A suitable bulk tray freeze dryer is available from FTS Systems of Stone Ridge, New York under the trademark Dura-Tap. The freeze dryer is run through a programmed cycle to remove the moisture. The

temperature is held constant at about 20°C and a vacuum is drawn to about 50 milliTorr (mT). The starch or flour is removed from the freeze dryer and immediately placed into a suitable heating apparatus for the heat treatment.

After it is dehydrated, the starch or flour is heat treated for a time and at a temperature sufficient to inhibit the starch or flour. The preferred heating temperatures are greater than about 100°C. For practical purposes, the upper limit of the heat treating

temperature is about 200°C. Typical temperatures are

120-180°C, preferably 140-160°C, most preferably 160°C. The temperature selected will depend upon the amount of inhibition desired and the rate at which it is to be achieved. The time at the final heating temperature will depend upon the level of inhibition desired. When a conventional oven is used, the time ranges from 1 to 20 hours, typically 2 to 5 hours, usually 3.5 to 4.5 hours. When a fluidized bed is used, the times range from 0 minutes to 20 hours, typically 0.5 to 3.0 hours. Longer times are required at lower temperatures to obtain more inhibited starches.

For most applications, the thermal dehydrating and heat treating steps will be continuous and

accomplished by the application of heat to the starch or flour beginning from ambient temperature. The moisture will be driven off during the heating and the starch will become anhydrous or substantially anhydrous. Usually, at these initial levels of inhibition, the peak viscosities are higher than the peak viscosities of starches heated for longer times, although there will be greater

breakdown in viscosity from the peak viscosity. With continued heat treating, the peak viscosities are lower, but the viscosity breakdowns are less.

Although starches with a wide range of inhibition can be obtained by the thermal inhibition process, the preferred starches for use in papermaking will have a level of inhibition which results in the starch, after dispersion in an aqueous medium, having a balance of both intact granules and solubilized starch molecules.

The process may be carried out as part of a continuous process involving the extraction of the starch from a plant material.

As will be seen in the following examples, the source of the starch or flour, the initial pH, the dehydrating conditions, the heating time and temperature, and the equipment used are all interrelated variables that affect the amount of inhibition. The heating steps may be performed at normal pressures, under vacuum or under pressure, and may be accomplished by conventional means known in the art. The preferred method is by the application of dry heat in dry air or in an inert gaseous environment.

The heat treating step can be carried out in the same apparatus in which the thermal dehydration occurs. Most conveniently the process is continuous with the thermal dehydration and heat treating occurring in the same apparatus, as when a fluidized bed reactor is used.

The dehydrating and heat treating apparatus can be any industrial ovens, conventional ovens, microwave ovens, dextrinizers, dryers, mixers and blenders equipped with heating devices and other types of heaters, provided that the apparatus is fitted with a vent to the

atmosphere so that moisture does not accumulate and precipitate onto the starch or flour. The preferred apparatus is a fluidized bed. Preferably, the apparatus is equipped with a means for removing water vapor, such as, a vacuum or a blower to sweep air or the fluidizing gas from the head-space of the fluidized bed. Suitable fluidizing gases are air and nitrogen. For safety reasons, it is preferable to use a gas containing less than 12% oxygen.

Superior inhibited starches having high

viscosities with low percentage breakdown in viscosity are obtained in shorter times in the fluidized bed reactor than can be achieved using other conventional heating ovens or dryers.

The starches or flours may be inhibited

individually or more than one may be inhibited at the same time. They may be inhibited in the presence of other materials or ingredients that would not interfere with the thermal inhibition process or alter the

properties of the starch or flour product.

Industrial Applicability

The thermally-inhibited starches and flours can be used wherever starches and flours are conventionally used in papermaking, e.g., as wet end additives, sizes, or coatings.

When used as wet end additives, they increase the dry strength and the retention of fillers or pigments and minimize or overcome strength losses due to the incorporation of fillers. They are usually added as an aqueous dispersion which is prepared by cooking a

thermally-inhibited non-pregelatinized granular starch or flour or dispersing a thermally-inhibited pregelatinized starch or flour.

Converted starches, as well as starch ethers and starch esters, are useful as surface sizing agents, or coatings for providing barriers for water vapor, grease, and solvents.

Non-converted starches are useful as thickeners in surface sizings.

Cationic starches are useful as flocculants for suspensions or inorganic or organic matter having a negative charge. When used as surface sizes, they provide pick-up and penetration for inks and the like. When used as coatings, they act as water vapor, grease, and solvents barriers.

Cationization of starch can be carried out by well known chemical reactions with reagents containing primary, secondary, tertiary or quaternary amines

attached through an ether or ester linkage, as disclosed, for example, in Solarek, "Cationic Starches".

Typical cationic and cationogenic groups include the diethylaminoethyl ether groups introduced by reaction with 2-diethylaminoethylchloride hydrochloride or 3-(trimethyl ammonium chloride)-2-hydroxypropyl ether groups introduced by reaction with 3-chloro-2-hydroxypropyl trimethylammonium chloride. See, U.S.

2,813,093 (issued November 12, 1957 to Caldwell, et al.) for reactions with dialkylaminoalkyl halides to introduce tertiary amino groups which can then quaternized to ammonium groups; U.S. 2,876,217 (issued March 3, 1959 to Paschal1) for gelatinizable cationic starch ethers; U.S. 2,970,140 (issued January 31, 1961 to Hullenger et al.) for granular starches containing alkyl amine groups; U.S. 2,989,520 (issued June 20, 1961 to Rutenberg, et al.) for reactions with beta-halogeno akylsulfonium-, vinyl sulfonium-, or epoxyalkyl-sulfonium salts U.S. 3,077,469 (issued February 12, 1963 to A. Aszalos) for reactions with beta-halogenoalkyl phosphonium salts; U.S. 4,119,487 (issued October 10, 1978 to Tessler) for epihalohydrin-tertiary amino or tertiary amine salt reaction products; U.S. 4,260,738 (issued April 7, 1981), U.S. 4,278,573

(issued July 14, 1981 to Tessler), and U.S. 4,387,221

(issued June 7, 1983 to Tessler) for alkyl- or alkenylsulfosuccinates; and U.S. 4,675,394 (issued January 23, 1987 to D. Solarek, et al.) for reactions with aminoalkyl anhydrides, amino epoxides, amino halides, or aryl amines. The disclosures of the above patents are

incorporated herein by reference.

Converted starches containing cationic or cationogenic groups and sulfo-succinate groups, useful as pigment retention aids, are described in U.S. 4,029,544 (issued June 14, 1977 to Jarowenko et al.).

Amphoteric starches are also useful herein.

Dual treatments of starch with cationic and anionic modifying reagents have been used to prepare amphoteric derivatives for use in different applications, including as wet end additives. Cationic derivatization,

particularly with tertiary amino or quaternary ammonium ether groups has been combined with further derivatization with anionic groups such as phosphate, phosphonate, sulfate, sulfonate or carboxyl groups. The resulting amphoteric starches and methods for their preparation are disclosed in Solarek, "Cationic

Starches", supra, pp. 120-121. See also, U.S. 3,459,632 (issued August 5, 1969 to Caldwell, et al.) for the preparation of starch derivatives containing anionic phosphate groups and cationic groups; U.S. 3,562,103

(issued February 9, 1971 to Moser et al.); and U.S.

4,876,336 (issued October 24, 1987 to Solarek, et al.) for the preparation of starch derivatives containing anionic phosphate groups and cationic tertiary amino or quaternary ammonium groups. The disclosures of the above patents are incorporated herein by reference.

Anionic starches are prepared by substitution with anionic groups such as those discussed above

according to the procedures previously disclosed for preparing amphoteric starches but without the use of cationic reagents.

When anionic or non-ionic starches are used in the papermaking process, they are used in conjunction with cationic additives, such as a synthetic polymer containing the residues of cationic monomers or a

cationic or amphoteric starch. Alternatively, the anionic or nonionic starch may be thermally inhibited in combination with a cationic or amphoteric starch, and this thermally inhibited starch blend used as an additive in the papermaking.

Aldehyde-containing starches, useful as

strength aids starches, are described in U.S. 4,675,394 (issued June 23, 1987 to Jobe et al.), the disclosure of which is incorporated herein by reference.

Recovery of the starch derivatives may be readily accomplished, with the particular method employed being dependent on the form of the starch base. Thus, a granular starch is recovered by filtration, optionally washed with water to remove any residual salts, and dried. The granular starch products may also be drum-dried, jet-cooked and spray-dried, or gelatinized and isolated by alcohol precipitation or freeze drying to form non-granular products. If the starch derivative is non-granular, it may be purified by dialysis to remove residual salts and isolated by alcohol precipitation, freeze drying, or spray drying.

The amount of a substituent on the starch is defined as the degree of substitution (DS) which means the average number of substituent groups per

anhydroglucose unit of the starch molecule. The degree of substitution can be varied, although generally a degree of substitution (DS) from about 0.005 to 0.2, and preferably from about 0.01 to 0.05, will be used. Higher degrees of substitution may be used, but this makes the starch more costly and difficult to make, and therefore, is not economically attractive.

When the starch is to be used in the wet end system of papermaking, it is derivatized, optionally pregelatinized, and then thermally inhibited. It may then be subjected again to controlled gelatinization.

Jet cooking provides a continuous process for gelatinizating the starch. It is well known in the art. By varying the temperature, pressure, flow rate, solids content of the starch slurry, and equipment configuration (e.g., haffles and mixers) it is possible to provide gelatinization conditions where a proportion of the thermally-inhibited starch granules will hydrate and partially swell without fragmenting and a portion of the granules will disperse and solubilize. Gelatinization and dispersion of the starch occurs in a very short period of time, from a few seconds to a few minutes. Suitable conditions are temperatures of about 90-165°C, preferably about 100-160°C, more preferably about 105-122°C, and an applied back pressure of at least 5 psi, preferably about 5-20 psi, although the pressure can be as high as 100 psi. The starch concentration in the cooking chamber should be at least 3%, preferably from 3-7% solids.

The derivatized and thermally-inhibited

starches, optionally pregelatinized, may be effectively added to pulp prepared from any type and combination of cellulosic fibers and/or synthetic fibers. Cellulosic materials include bleached and unbleached sulfate

(kraft), bleached and unbleached sulfite, bleached and unbleached soda, neutral sulfite, semi-chemical,

chemiground wood, and ground wood. Synthetic fibers include polyamides, polyesters, rayon and polyacrylic resins, as well as fibers from minerals, such as asbestos and glass. Viscose rayon or regenerated cellulose fibers can also be used for the pulp.

Inert mineral fillers, such as, clay, titanium dioxide, talc, calcium carbonate, calcium sulfate, and diatomaceous earths, rosin, and other additives commonly introduced into paper, such as, dyes, pigments, sizing additives, alum, and anionic retention aids, may be added to the pulp or furnish.

The amount of thermally-inhibited starch that is added to the wet end or paper pulp will be an

effective amount, typically from about 0.05-5%,

preferably from about 0.1-2%, by weight based on the dry weight of the pulp.

In a preferred embodiment, the thermally-inhibited starch is added to a simple alkaline

papermaking system (i.e., one containing mainly pulp, alum and starch), or to a microparticle colloidal

papermaking system. Suitable microparticles for inclusion in the alkaline systems include colloidal silica, bentonite and anionic alum, which are usually incorporated in amounts of at least 0.001%, more

typically about 0.01-1% by weight based on the weight of dry pulp. Further description of such microparticle inorganic materials may be found in U.S. 4,388,150

(issued June 14, 1983 to Batelson et al.); U.S. 4,643,801 (issued February 17, 1987 to Johnson); U.S. 4,753,710

(issued June 28, 1988 to Holroyd et al.); and U.S.

4,913,775 (issued April 3, 1990 to Holroyd et al.).

It has been determined that significantly improved performance in papermaking is produced when the starch is thermally inhibited to a level sufficient to provide a percentage breakdown in viscosity of about 2- 60% calculated according to the formula:

,

where Peak is the peak viscosity in Brabender Units and is the viscosity after holding at 95°C for 30 minutes.

Sample Preparation

Unless indicated otherwise, all the starches and flours used were granular and were provided by

National Starch and Chemical Company of Bridgewater, New Jersey.

The controls for the test samples were from the same native sources as the test samples, were unmodified or modified in the same manner as the test samples, and were at the same pH, unless otherwise indicated.

All starches and flours, both test and control samples, were prepared and tested individually.

The pH of the samples was raised by slurrying the starch or flour in water at 30-40% solids and adding a sufficient amount of a 5% sodium carbonate solution until the desired pH was reached.

Measurements of pH, either on samples before or after the thermal inhibition steps, were made on samples consisting of one part starch or flour to four parts water.

After the pH adjustments, if any, all non-pregelatinized granular samples were spray-dried or flash-dried as conventional in the art (without

gelatinization) to about 2-15% moisture.

After the pH adjustment, if any, slurries of the starches to be pregelatinized to granular

pregelatinized starches were introduced into a pilot spray dryer, Type 1-KA#4F, from APV Crepaco, Inc., Dryer Division, Attleboro Falls, Massachusetts, using a spray nozzle, Type 1/2J, from Spraying Systems Company of Wheaton, Ill. The spray nozzle had the following

configurations: fluid cap 251376, air cap 4691312. The low initial cold viscosity samples were sprayed at a steam:starch ratio of 3.5-4.5:1, and the high initial cold viscosity samples were sprayed at a steam:starch ratio of 5.5-6.5:1. Moisture content of all

pregelatinized samples after spray drying and before the dehydration step in the thermal inhibition process was 4-10%.

For the samples pregelatinized by drum drying the pH was raised by slurrying the starch or flour in water at 30-40% solids and adding a sufficient amount of a 5% sodium carbonate solution until the desired pH was reached. A single steam-heated steel drum at about 142-145°C was used for the drum drying.

For the samples pregelatinized by the continuous coupled jet-cooking/spray-drying process of U.S. 5 , 131 , 953 or the dual atomization/spray-drying process of U.S. 4,280,851, the starch or flour was slurred at 6-10% solids in water and the pH was adjusted to the desired pH by adding a sufficient amount of 5% sodium carbonate solution until the desired pH was reached. Except where a conventional oven or dextrinizer is specified, the test samples were dehydrated and heat treated in a fluidized bed reactor, model number FDR-100, manufactured by Procedyne Corporation of New Brunswick, New Jersey. The cross-sectional area of the fluidized bed reactor was 0.05 sq meter. The starting bed height was 0.3-0.8 meter, but usually 0.77 meter. The

fluidizing gas was air except where otherwise indicated. When granular non-pregelatinized starches were being heat treated, the gas was used at a velocity of 5-15

meter/min. When pregelatinized granular starches were being heat treated, the gas was used at a velocity of 15-21 meter/min. The side walls of the reactor were heated with hot oil, and the fluidizing gas was heated with an electric heater. The samples were loaded into the reactor and then the fluidizing gas was introduced, or the samples were loaded while the fluidizing gas was being introduced. No difference was noted in the samples in the order of loading. Unless otherwise specified, the samples were brought from ambient temperature up to no more than 125°C until the samples became anhydrous and were further heated to the specified heat treating temperatures. When the heating temperature was 160°C, the time to reach that temperature was less than three hours.

The moisture level of the samples at the final heating temperature was 0%, except where otherwise stated. Portions of the samples were removed and tested for inhibition at the temperatures and times indicated in the tables.

Unless specified otherwise, the samples were tested for inhibition using the following Brabender

Procedures. Brabender Procedure - Non-Pregelatinized Granular Starches

Unless other stated, the following Brabender procedure was used. All samples, except for corn, tapioca and waxy rice flour, were slurried in a

sufficient amount of distilled water to give a 5%

anhydrous solids starch slurry. Corn, tapioca, and waxy rice flour were slurried at 6.3% anhydrous solids. The pH was adjusted to pH 3.0 with a sodium citrate, citric acid buffer and the slurry was introduced into the sample cup of a Brabender VISCO/Amylo/GRAPH (manufactured by C.W. Brabender Instruments, Inc., Hackensack, NJ) fitted with a 350 cm/gram cartridge. The VISCO\Amylo\GRAPH records the torque required to balance the viscosity that develops when a starch slurry is subjected to a

programmed heating cycle. The record consists of a curve tracing the viscosity through the heating cycle in arbitrary units of measurement termed Brabender Units (BU).

The starch slurry is heated rapidly to 92°C and held for 10 minutes. The peak viscosity and viscosity ten minutes after peak viscosity were recorded in

Brabender Units (BU). The percentage breakdown in viscosity (± 2%) was calculated according to the formula:

,

where "peak" is the peak viscosity in Brabender units, and "(peak + 10')" is the viscosity in Brabender Units at ten minutes after peak viscosity. If no peak viscosity was reached, i.e., the data indicate a rising (ris.) curve or a flat curve, the viscosity at 92°C and the viscosity at 30 minutes after attaining 92°C were

recorded.

Using data from the Brabender curves, inhibition was determined to be present if, when

dispersed at 5% or 6.3% solids in water at 92-95°C and pH 3, during the Brabender heating cycle, the Brabender data showed (i) no or almost no viscosity, indicating the starch was so inhibited it did not gelatinize or strongly resisted gelatinization; (ii) a continuous rising

viscosity with no peak viscosity, indicating the starch was highly inhibited and gelatinized to a limited extent; (iii) a lower peak viscosity and a lower percentage breakdown in viscosity from peak viscosity compared to a control, indicating a moderate level of inhibition; or (iv) a slight increase in peak viscosity and a lower percentage breakdown compared to a control, indicating a low level of inhibition.

Characterization Of Inhibition of Non-Pregelatinized

Granular Starches By Brabender Curves

Characterization of a thermally-inhibited starch is made more conclusively by reference to a measurement of its Brabender viscosity after it is dispersed in water and gelatinized.

For non-inhibited starches, the cycle passes through the initiation of viscosity, usually at about 60-70°C, the development of a peak viscosity in the range of 67-95°C, and any breakdown in viscosity when the starch is held at an elevated temperature, usually 92-95°C.

Inhibited starches will show a Brabender curve different from the curve of the same starch that has not been inhibited (hereinafter the control starch). At low levels of inhibition, an inhibited starch will attain a peak viscosity somewhat higher than the peak viscosity of the control, and there may be no decrease in percentage breakdown in viscosity compared to the control. As the amount of inhibition increases, the peak viscosity and the breakdown in viscosity decrease. At high levels of inhibition, the rate of gelatinization and swelling of the granules decreases, the peak viscosity disappears, and with prolonged cooking the Brabender trace becomes a rising curve indicating a slow continuing increase in viscosity. At very high levels of inhibition, starch granules no longer gelatinize, and the Brabender curve remains flat.

Brabender Procedure - Pregelatinized

Granular and Non-Granular Starches

The pregelatinized thermally-inhibited starch to be tested was slurried in a sufficient amount of distilled water to give a 4.6% anhydrous solids starch slurry at pH 3 as follows: 132.75 g sucrose, 26.55 g starch, 10.8 g acetic acid, and 405.9 g water were mixed for three minutes in a standard home Mixmaster at setting #1. The slurry was then introduced to the sample cup of a Brabender VISCO/Amylo/GRAPH fitted with a 350 cm/gram cartridge and the viscosity measured as the slurry was heated to 30°C and held for 10 minutes. The viscosity at 30°C and 10 minutes after hold at 30°C were recorded. The viscosity data at these temperatures are a

measurement of the extent of pregelatinization. The higher the viscosity at 30°C, the grater the extent of granular swelling and hydration during the

pregelatinization process.

Heating was continued to 95°C and held at that temperature for 10 minutes.

The peak viscosity and viscosity 10 minutes after 95°C were recorded in Brabender Units (BU). The percentage breakdown was calculated using the previous formula.

If no peak viscosity was reached, that is, the data indicated a rising curve or a flat curve, the viscosity at 95°C and the viscosity at 10 minutes after attaining 95°C were recorded. Characterization of Inhibition of

Pregelatinized Granular Starches by Brabender Curves

As discussed above, characterization of a thermally-inhibited starch is made more conclusively by reference to a measurement of its viscosity after it is dispersed in water and gelatinized using the instrument described above.

For pregelatinized granular starches, the level of viscosity when dispersed in cold water will be

dependent on the extent to which the starch was initially cooked out during the pregelatinization process. If the granules were not fully swollen and hydrated during pregelatinization, gelatinization will continue when the starch is dispersed in water and heated. Inhibition was determined by a measurement of the starch viscosity when the starch was dispersed at 4.6% solids in water at pH 3 and heated to 95°C.

When the pregelatinized granular starch had a high initial cold viscosity, meaning it was highly cooked out in the pregelatinization process, the resulting

Brabender traces will be as follows: for a highly

inhibited that the starch, the trace will be a flat curve, indicating that the starch is already very swollen and is so inhibited starch it is resisting any further gelatinization or the trace will be a rising curve, indicating that further gelatinization is occurring at a slow rate and to a limited extent; for a less inhibited starch, the trace will he a dropping curve, indicating that some of the granules are fragmenting, but the overall breakdown in viscosity will be lower than that for a non-inhibited control or the trace will show a second peak but the breakdown in viscosity will be lower than that for a non-inhibited control.

When the pregelatinized starch had a low initial cold viscosity, meaning it was not highly cooked out in the pregelatinization process and more cooking is needed to reach the initial peak viscosity, the resulting

Brabender traces will be as follows: for a highly

inhibited starch, the trace will be a rising curve, indicating that further gelatinization is occurring at a slow rate and to a limited extent; for a less inhibited starch, the trace will show a peak viscosity as

gelatinization occurs and then a drop in viscosity, but with a lower percentage breakdown in viscosity than for a non-inhibited control.

If no peak viscosity was reached, that is, the data indicated a rising curve or a flat curve, the viscosity at 95°C and the viscosity at 10 minutes after attaining 95°C were recorded.

Characterization of Inhibition of Pregelatinized

Non-Granular Starches by Brabender Curves

The resulting Brabender traces will be as follows: for a highly inhibited starch the trace will be flat, indicating that the starch is so inhibited that it is resisting any further gelatinization or the trace will be a rising curve, indicating that further gelatinization is occurring at a slow rate and to a limited extent; for a less inhibited starch, the trace will show a dropping curve, but the overall breakdown in viscosity from the peak viscosity will be lower than that for a non-inhibited control.

Brabender Procedure— Crosslinked Starches

The crosslinked, thermally-inhibited cationic and amphoteric starches (23.0 g) to be tested was

combined with 30 ml of an aqueous solution of citric acid monohydrate (prepared by diluting 210.2 g of citric acid monohydrate to 1000 ml in a volumetric flask) and

sufficient water was added to make the total charge weight 460.0 g. The slurry is added to the cooking chamber of the Brabender VISCO amylo GRAPH fitted with a 700 cm/gram cartridge and rapidly heated from room temperature to 95°C. The peak viscosity (highest

viscosity observed) and the viscosity after 30 minutes at 95°C were recorded. The percentage breakdown in viscosity (±2%) was calculated according to the formula

Characterization of Inhibition by Cooks A dry blend of 7 g of starch or flour (anhydrous basis) and 14 g of sugar were added to 91 ml of water in a Waring blender cup at low speed, then transferred to a cook-up beaker, allowed to stand for 10 minutes, and then evaluated for viscosity, color, clarity and texture.

Some of the granular non-pregelatinized starch samples were tested for pasting temperature and/or gelatinization temperature using the following

procedures.

Rapid Visco Analyzer (RVA)

This test is used to determine the onset of gelatinization, i.e., the pasting temperature. The onset of gelatinization is indicated by an increase in the viscosity of the starch slurry as the starch granules begin to swell.

A 5 g starch sample (anhydrous basis) is placed in the analysis cup of a Model RVA-4 Analyzer and

slurried in water at 20% solids. The total charge is 25 g. The cup is placed into the analyzer, rotated at 160 rpm, and heated from an initial temperature of 50°C up to a final temperature of 80°C at a rate of 3°C/minute. A plot is generated showing time, temperature, and

viscosity in centipoises (cP). The pasting temperature is the temperature at which the viscosity reaches 500 cP. Both pasting temperature and pasting time are recorded. Differential Scanning Calorimetry (DSC)

This test provides a quantitative measurement of the enthalapy ( H) of the energy transformation that occurs during the gelatinization of the starch granule. The peak temperature and time required for gelatinization are recorded. A Perkin-Elmer DSC-4 differential scanning calorimeter with data station and large volume high pressure sample cells is used. The cells are prepared by weighing accurately 10 mg of starch (dry basis) and the appropriate amount of distilled water to approximately equal 40 mg of total water weight (moisture of starch and distilled water). The cells are then sealed and allowed to equilibrate overnight at 4°C before being scanned at from 25-150°C at the rate of 10°C/minute. An empty cell is used as the blank.

Brookfield Viscometer Procedure

Test samples are measured using a Model RVT Brookfield Viscometer and the appropriate spindle (the spindle is selected based on the anticipated viscosity of the material). The test sample, usually a cooked starch paste, is placed in position and the spindle is lowered into the sample to the appropriate height. The

viscometer is turned on and the spindle is rotated at a constant speed (e.g., 10 or 20 rpm) for at least 3 revolutions before a reading is taken. Using the

appropriate conversion factors, the viscosity (in

centipoises) of the sample is recorded.

Calcium Carbonate Retention

The various samples were tested an alkaline Dynamic Retention Evaluation using a Britt Jar (modified TAPPI T26 pm 79 method) at 0.75% addition level. The retention was compared with that of a cationic waxy corn starch reacted with diethylaminoethyl chloride

hydrochloride or an amphoteric waxy corn starch reacted with diethyl aminoethyl chloride hydrochloride and sodium tripolyphosphate. The test was run while mixing and agitating using a Britt Jar with a screen having holes 76 microns in diameter.

To simulate a simple papermaking system, a sample of 500 ml of 0.5% by weight pulp stock was placed in the jar and agitated at about 800 rpm. Alum, at 0.5 wt. % of dry fiber in the pulp stock, was added and mixed at 400 rpm for one minute and then the mixing was

increased to 1000 rpm. The starch, at 0.75 wt. % of dry fiber, was then added and mixing was continued for another minute.

To simulate a microparticle papermaking system, a sample of 500 ml of 0.5 wt. % by weight pulp stock was placed in the jar and agitated at about 800 rpm. Alum, at 0.25 wt. % of the of the dry fiber in the pulp stock, was added and mixed at 400 rpm for one minute and then the mixing was increased to 1000 rpm. The starch at 0.75 wt. % of the dry fiber, was then added and mixing was continued for another minute. Colloidal silica was added at 0.15 wt. % of the dry fiber and the sample was mixed for another minute.

After the addition/mixing sequence, a 100 ml sample was collected by removing the clamp. The sample was acidified with 5 N hydrochloric acid to solubilize the calcium carbonate and then filtered onto tared filter paper to recover the fine solids. A standard water hardness titration was run by adding Eriochrome Black "T" indicator and titrating with 0.1 N of the disodium salt (EDTA) ethylene diamine tetra-acetic acid, disodium salt) standard solution to a blue endpoint, using a calibrated burette. Identical titrations were made on an acidified portion of the starting pulp sample and a 25 ml sample of 100 ppm hardness water used and with this information the percent retention of calcium carbonate (CaCO₃) was determined using the following formula: ,

where P is ml EDTA for pulp stock W is ml EDTA for raw water blank, and S is ml EDTA for sample.

Drainage Resistance

The drainage resistance test was performed on the furnish using a turbulent pulse sheet former (TPSF), which is a modified Britt jar that incorporates air and vacuum to simulate the dynamics of an industrial paper making machine. Furnish (200 ml) at 0.5% consistency was diluted to one liter with water and added to the TPSF to simulate a 80 lb/3330 sq ft fine paper grade. The following were then added to the furnish in the order recited and mixed for 30 seconds at 1000 rpm after each addition: alum (0.25 wt. % of dry fiber used in the pulp stock), starch (0.75 wt. % dry fiber), colloidal silica (0.15 wt. % dry fiber). The conditions for the paper formation were: air pressure of 20 in. of vacuum

pressure of 10 in. Hg; total pulse count for drawing air and vacuum, 3. The resistance of water drainage from the furnish and additives was measured for each sample and a comparison made using the cationic starch as the control. Comparative values are given in the following table measured against the cationic starch as a control with a value of 100.

Bond Strength

After the drainage resistance test, the sheets formed on the TPSF were pressed and dried tested for Scott Bond strength. The sheets were conditioned

overnight at 21.5°C and 50% relative humidity. TAPPI test procedure T 541 om-89 were used. Comparative values are set out in the following tables measured against the cationic starch as a control with a value of 100. EXAMPLES

The following examples will more fully illustrate the embodiments of the invention. In the examples, all parts are given by weight and temperature are in degrees Celsius unless otherwise noted. The thermally-inhibited starches and controls in the

following examples were prepared as described above and are defined by textural characteristics or in relation to data taken from Brabender curves using the above

described procedures. The thermally-inhibited starches and flours are referred to as "T-I" starches and flours and the conditions used for their preparation (i.e., pH to which the starch is adjusted and heat treatment temperature and time at that temperature are included in parenthesis - (pH; temperature/hoId time at that

temperature). All pH adjustments are done with sodium carbonate unless specified otherwise. Unless otherwise specified, the thermally-inhibited starches and flours referred to as "granular" starches are non-pregelatinized granular starches and flours.

In the first three examples, the moisture indicated is the moisture of the starch before the dehydration and heat treating steps. As indicated above, as the starches were brought from ambient temperature up to the heating temperature, the starches became anhydrous or substantially anhydrous.

In the tables the abbreviations"sl.", "mod.", "v.", "ris." and "N.D." stand for slight or slightly, moderate or moderatly, very, rising, and not determined.

EXAMPLE 1

This example illustrates the preparation of the starches of this invention from a commercial granular waxy maize base starch by the heat treatment process of this invention. Processing conditions and their effects on viscosity and texture of waxy maize starch are set forth in the Tables below.

To obtain a heat-stable, non-cohesive thickener, samples of granular starch were slurried in 1.5 parts of water, the pH of the slurry was adjusted with the addition of a 5% Na₂CO₃ solution and the slurry was agitated for 1 hour, then filtered, dried, and ground. The dry starch samples (150 g) were placed into an aluminum foil pan (4" × 5" × 1-1/2") and heated in a conventional oven under the conditions described in

Tables I and II. Brabender viscosity measurements demonstrated that the most heat-stable starches were obtained by heating at 160'C and a pH of at least 8.0 for about 3.5 to 6.0 hours.

EXAMPLE 2

This example illustrates that a variety of granular starches may be processed by the method of this invention to provide a non-cohesive thickener with properties similar to chemically crosslinked starches.

Processing conditions and their effects on the viscosity and texture of waxy barley, tapioca, V.O.

hybrid and waxy rice starches are set forth in the tables below.

The viscosity and texture evaluation results show that a non-cohesive, heat-stable starch thickener may be prepared from waxy barley, V.O. hybrid, tapioca and waxy rice starches by the process of this invention. The amount of inhibition (non-cohesive, thickening character in cooked aqueous dispersion) increased with increasing time of heat treatment.

EXAMPLE 3

This example illustrates the effects of

temperature, the pH, and starch moisture content on the viscosity and texture of the treated starch.

Part A

A waxy maize starch sample (100 g) containing 20.4% moisture was heated in an oven at 100"C for 16 hours in a sealed glass jar. A second sample was heated for 4 hours and a third sample was heated for 7 hours under the same conditions. The product viscosity and texture were compared to a 12.1% moisture granular waxy maize starch control using the cook evaluation method of Example 1, Table I. Results are shown in Table V, below.

The results demonstrate that moisture added during the process yields a product which is as cohesive and undesirable as a control starch which had not been heated.

Part B

Samples (900 g) of a commercial granular waxy maize starch (obtained from National Starch and Chemical Company, Bridgewater, New Jersey) were placed in a 10" × 15" × 0.75" aluminum tray and heated in an oven at 180ºC for 15, 30, 45 and 60 minutes. The pH of the starch was not adjusted and remained at about 5.2 during the heating process. Sample viscosity and texture were evaluated by the method of Example 1.

As shown in Table VI, below, the pH 5.2 samples were characterized by an undesirable, cohesive texture similar to that of a waxy maize starch control which had not been heat treated.

Thus, a combination of selected factors, including the pH, moisture content and the type of native starch, determine whether a desirable, non-cohesive, heat-stable starch thickener is produced by the process of this invention.

EXAMPLE 4

This example shows carrying out the thermal inhibition in the fluidized bed previously described. The effects of temperature and time at the indicated temperature on the level of inhibition of waxy maize granular starch at pH 9.5 are shown below.

The data shows that inhibited anhydrous or substantially anhydrous samples can be obtained at heat treating temperatures between 100-200°C, with more inhibition obtained at higher temperatures or at longer times at lower temperatures. The starch samples heated at 200°C were highly inhibited (rising curves) or

completely inhibited (no gelatinization).

EXAMPLE 5

Samples of a high amylose starch (Hylon V - 50% amylose) at its natural pH and pH 9.5 were evaluated for the effect of the high amylose content on inhibition. The starches were thermally-inhibited at 160°C in the fluidized bed for the indicated time. Due to the high levels of amylose, it was necessary to use a pressurized Visco/amylo/Graph (C.W. Brabender, Hackensack, NJ) to obtain Brabender curves. Samples were slurried at 10% starch solids, heated to 120°C, and held for 30 minutes.

The data show that inhibition was obtained only on the high pH sample.

EXAMPLE 6

This example shows the preparation of pregelatinized granular, thermally-inhibited waxy maize starches. The pregelatinization step was carried out prior to the thermal inhibition. The fluidized bed described previously was used.

Starch slurries (30-40% solids), pH adjusted to 6, 8, and 10, were pregelatinized in a pilot size spray drier (Type-1-KA#4F, from APV Crepaco, Inc., Dryer

Division, of Attle Boro Falls, Massachusetts) using a spray nozzle, Type 1/2 J, from Spraying Systems Company of Wheaton, Illinois. The spray nozzle had the following configuration: fluid cap, 251376, and air cap, 4691312.

The resulting high and low viscosity pregelatinized granular starches were dehydrated and heat treated at the temperature and time indicated. The thermally-inhibited starches were evaluated for

inhibition using the Brabender procedure previously described.

The results are shown below:

The results show some thermal inhibition was attained in all the dehydrated and heat treated

pregelatinized granular starches and that increasing the initial pH and the heat treatment time increased the level of inhibition. For the samples at pH 6.0, at 0 and 30 minutes, the recorded peak was actually a second peak obtained after the initial high viscosity began to breakdown. For some of the samples at pH 10, no peak viscosity was reached, indicating a highly inhibited starch.

EXAMPLE 7

This example describes the preparation of thermally-inhibited pregelatinized granular starches from additional starch bases as well as a waxy maize starch. The granular starches were adjusted to the indicated pH, pregelatinized using the procedure previously described, and heat treated in an oven at 140°C for the indicated time. The cook evaluation and Brabender results are shown below.

The results show that thermally-inhibited pregelatinized granular starches can be prepared using other starch bases and that for non-cohesive starches longer times and/or higher pHs are required when an oveno rather than a fluidized bed is used for the dehydration and heat treatment.

EXAMPLE 8

This example shows the preparation of pregelatinized, non-granular starches which were

pregelatinized by drum-drying and then thermally

inhibited. Samples of waxy maize, tapioca and potato starches, at pH 6, 8, and 10, were pregelatinized by drum-drying. The samples were placed in a 140°C oven, dehydrated to anhydrous, and heat treated at 140°C for the indicated times.

The viscosity and textural characteristics of the thermally-inhibited starches are set out below.

Brabenders were run on some of the above starches. The results are shown below.

The results show that longer heating times and/or higher pHs are required to prepare non-cohesive starches at 140°C. It is expected that heating at 160°C, preferably in a fluidized bed, will provide non-cohesive starches.

EXAMPLE 9

This example shows the preparation of another pregelatinized non-granular starch which was jet-cooked, spray-dried, and then thermally inhibited.

A granular high amylose starch (50% amylose) was jet-cooked and spray-dried using the continuous coupled jet-cooking/spray-drying process described in

U.S. 5,131,953 and then thermally inhibited for 8 hours at 140°C. The jet-cooking/spray-drying conditions used were as follows: slurry - pH 8.5-9.0; cook solids - 10%; moyno setting - about 1.5; cooking temperature - about 145°C; excess steam - 20%; boiler pressure - about 85 psi; back pressure - 65 psi; spray-dryer - Niro dryer; inlet temperature - 245°C; outlet temperature - 115°C; atomizer - centrifugal wheel. The pregelatinized non-granular starch was adjusted to pH 8.7 and dehydrated and heat treated for 8 hours in an oven at 140°C. The characteristics of the resulting thermally-inhibited starches are set out below.

The results show that even a high amylose starch can be inhibited. There was less breakdown for the thermally-inhibited starch and the overall viscosity was higher.

EXAMPLE 10

This example shows that thermally-inhibited waxy maize starches can be prepared by drum drying the starches prior to thermal inhibition. The resulting non-granular thermally-inhibited drum-dried starches are compared with the non-granular thermally-inhibited waxy maize starches prepared by the continuous coupled jet-cooking and spray-drying process used in Example 8 and with granular thermally-inhibited starches prepared by the dual atomization/spray drying process described in U.S. 4,280,251 (which was used in Example 6). The conditions used for the oven dehydration and heat

treatment were 8 hours at 140°C.

The characterization of the resulting thermally-inhibited pregelatinized starches is shown below.

The results show that after 8 hours heat treatment at 140°C all the pregelatinized thermally-inhibited starches showed much less breakdown. The results also show that a higher degree of inhibition along with a higher peak viscosity can be obtained if the starch granules are completely disrupted as by drum drying or jet cooking.

EXAMPLE 11

This example shows that a granular starch can be dehydrated by ethanol extraction and that a better tasting starch is obtained.

A granular waxy maize starch was slurried in 1.5 parts water based on the weight of the starch and adjusted to pH 7 and 9.5 with 5% sodium carbonate, held for 30 minutes, filtered, and dried on a tray to a moisture content of about 5-6% moisture. The starch having the pH of 5.3 was a native starch which was not pH adjusted.

For the dehydration, the dried pH 5.3, pH 7.0, and pH 9.5 starches were each separated into two samples. One sample was dried on trays in a forced draft oven at 80°C overnight to thermally dehydrate the starch to <1% (0%) moisture. The other sample was placed in a Soxhlet extractor and allowed to reflux overnight (about 17 hours) with anhydrous ethanol (boiling point 78.32°C). The ethanol-extracted sample was placed on paper so that the excess alcohol could flash off which took about 30 minutes. The ethanol-extracted starch was a free flowing powder which was dry to the touch.

For the heat treatment, the oven-dehydrated starches and ethanol-extracted starches were placed on trays in a forced draft oven and heated for 3, 5, and 7 hours at 160°C.

The thermally-inhibited (T-I) starches and the controls were evaluated using the Brabender Procedure previously described was used. The results are shown below:

The results show that the starches can be dehydrated by ethanol extraction. The results also show that dehydration without the subsequent heat treatment did not inhibit the starch. The viscosity breakdown was not significantly different from that of the native waxy maize starch. Both of the thermally-inhibited pH 7 starches were higher in viscosity than the pH 5.3 (as is) thermally-inhibited starches. The starches which were thermally-inhibited at pH 9.5 were moderately highly inhibited or highly inhibited (rising curve).

EXAMPLE 12

Granular tapioca, corn, and waxy rice starches and waxy rice flour were adjusted to pH 9.5, dehydrated in an oven and by extraction with ethanol, and heat treated at 160°C for the indicated time. They were evaluated for Brabender viscosity using the procedure previously described.

The results show that pH 9.5-adjusted, ethanol- extracted, heat-treated tapioca and corn starches had viscosity profiles generally similar to those of the same thermally-inhibited starches which were oven-dehydrated. The 7 hours heat-treated samples were more inhibited than the 5 hour heat-treated samples.

EXAMPLE 13

This example compares ethanol extracted

granular waxy maize starches and oven-dehydrated granular waxy maize starches heat treated in an oven for 5 and 7 hours at 160°C at the same pH, i.e., pH 8.03.

The thermally-inhibited starches were slurried at 6.6% solids (anhydrous basis), pH adjusted to 6.0-6.5, and then cooked out in a boiling water bath for 20 minutes. The resulting cooks were allowed to cool and then evaluated for viscosity, texture, and color.

These Brabender results show that highly inhibited starches can be obtained by both thermal and non-thermal dehydration. The cook evaluation results show that there is a benefit for the ethanol-dehydrated, thermally-inhibited starches in terms of reduced color. As will be shown hereafter, there is also a flavor improvement with ethanol dehydration. EXAMPLE 14

A granular waxy maize starch was pH adjusted to pH 9.5 as previously described. The starch was then placed in a freeze dryer and dried for 3 days until it was anhydrous (0% moisture). The freeze-dried (FD) starch was heat treated for 6 and 8 hours at 160°C in a forced draft oven.

Brabender evaluations were run. The results are shown below:

The results show that the starch can be dehydrated by freeze drying and that the subsequent heat treatment is necessary to inhibit the starch. The starches are highly inhibited as shown by their rising viscosity.

EXAMPLE 15

This example shows that thermal inhibition reduced the gelatinization temperature of the granular waxy maize starches.

The gelatinization temperature of an untreated waxy maize, a thermally-inhibited (T-I) waxy maize (pH adjusted and not pH adjusted), and chemically-crosslinked (X-linked) waxy maize starches (0.02%, 0.04%, and 0.06% phosphorus oxychloride) were determined by Differential Scanning Calorimetry. The starches were thermally dehydrated and heat treated in an oven for the indicated time and temperature.

The results show that there was a significant reduction in peak gelatinization temperature of the thermally inhibited (T-I) starches. The heat treatment reduced the enthalpy ( H) from 4.3 cal/g for the

unmodified starch to 2.8 - 2.9 cal/g for the thermally- inhibited starch. The chemically crosslinked (X-linked) starches are essentially identical to the unmodified waxy starch in peak temperature (72-74°C vs. 74°C) and

enthalpy (4.2-4.4 vs 4.3 cal/g). The reduced gelatinization temperature and decrease in enthalpy suggest that the overall granular structure has been altered by the dehydration and heat treatment. EXAMPLE 16

This example shows that the thermal inhibition may begin as early as 110°C (230ºF), that it is

substantially noticeable at 160° (320°F), and that the gelatinization is unchanged or reduced. Granular waxy maize starches were pH adjusted to 7.0 and 9.5 and dehydrated and heat treated using air having a Dew point below 9.4°C (15°F) in the fluidized bed previously described at the indicated temperature and time. The Brabender and DSC results are shown below.

The DSC results show that at the onset of inhibition there was a slight reduction in the peak gelatinization temperature and that as the inhibition temperature and time increased there was a reduction in peak gelatinization temperature. The enthalpy is unchanged or slightly higher, unlike the enthalpy of the more highly inhibited starches of the prior example.

EXAMPLE 17

This example shows the correlation between the RVA pasting temperature and time and DSC peak

gelatinization temperature and time and the reduction in Brabender viscosity breakdown for various granular starch bases and for granular waxy maize starches dehydrated by various methods including heating, ethanol extraction, and freeze drying. The base starches were unmodified. The starches were all adjusted to pH 9.5 before

dehydration. The ethanol-extracted and freeze-dried controls were pH adjusted and dehydrated but not heat treated. The dehydrated starches were all heat treated in an oven at 160°C for the indicated time except for the starches chemically crosslinked with sodium

trimetaphosphate (STMP) which were heat treated at 160°C for the indicated time in the fluidized bed previously described.

The results show that heat treatment of thermally and non-thermally dehydrated granular starches reduced the pasting and peak gelatinization temperatures while at the same time inhibiting the viscosity

breakdown. Because the gelatinization temperature has been lowered by the heat treatment of the dehydrated starch, less time is required to reach the pasting and gelatinization temperatures. The more highly inhibited starches showed a lower pasting temperature and less breakdown in viscosity.

EXAMPLE 19

A granular waxy maize starch which had been lightly crosslinked with 0.04% phosphorous oxychloride was thermally-inhibited. The granular starch was jet- cooked and spray-dried using the coupled continuous jet-cooking/spray-drying process and conditions described in Example 8. The spray-dried starch was oven dehydrated and heat treated for 8 hours at 140°C.

The Brabender results and viscosity and textural characteristics of the resulting thermally- inhibited starch are set out below.

The results show that after the dehydration and heat treatment steps the crosslinked starch was very highly inhibited.

EXAMPLE 19

This example shows the thermal inhibition of converted starches.

Samples of waxy maize and tapioca starch were slurried in 1.5 parts water. The slurries were placed in a 52ºC water bath, with agitation, and allowed to equilibrate for one hour. Concentrated hydrochloric acid (HCl) was added at 0.8% on the weight of the samples.

The samples were allowed to convert at 52°C for one hour. The pH was then adjusted to 5.5 with sodium carbonate, then to pH 8.5 with sodium hydroxide. The samples were recovered by filtering and air drying (approximately 11% moisture). The starches in 50g amounts were placed in an aluminum tray, covered and placed into a forced draft oven at 140°C for 5.5 hours. The starches were evaluated for inhibition.

The results show that converted starches can be thermally inhibited by this process.

EXAMPLE 20

Waxy maize samples reacted with 7% and at 3% by weight propylene oxide (PO), at the naturally occurring pH and at pH 9.5, were evaluated for inhibtion.

The results set out in the following tables.

The data show that derivatized starches, in this case etherified starches, can be thermally inhibited by this process and that higher inhibition can be

achieved at higher pH.

EXAMPLE 21

A converted hydroxypropylated waxy maize starch (25 WF starch reacted with 2% propylene oxide) was adjusted to pH 9.5 and thermally inhibited using the fluidized bed previously described. Samples were taken at 110°C, 125°C, and 140°C, all for 0 minutes.

The thermally-inhibited starch samples were cooked in tap water at 88-93ºC (190-200ºF) bath

temperature for 30-60 minutes to yield solutions having a Brookfield viscosity of approximately 3000 cps. The viscosity stability at room temperature was evaluated. The control was a hydroxy-propylated waxy maize starch which was not thermally-inhibited.

EXAMPLE 22

Waxy maize samples at the naturally occurring pH and at pH 8.5, were reacted with 1% by weight acetic anhydride (Ac₂O) and thermally-inhibited. The control was the non-thermally-inhibited waxy maize starch acetate.

The data show that derivatized starches, in this case esterified starches, can be inhibited to varying degrees and that higher inhibition can be

obtained at higher pH.

EXAMPLE 23

This example shows the preparation and use of a thermally-inhibited cationic starch in a simple

papermaking system and a microparticle papermaking system.

A granular waxy corn starch (1000 g) was slurried in 1500 cc water, 175 g of 4% sodium hydroxide were added, and the slurry was heated to 40°C. One hundred (100) g of a 50% aqueous solution of 3-chloro-2-hydroxypropyl trimethyl ammonium chloride was added while maintaining the pH at 11.5 by adding 4% sodium hydroxide. The mixture was allowed to react overnight at 40°C. The slurry was adjusted to pH 6.5 with hydrochloric acid, filtered, washed and air dried to about 8-15% moisture. The degree of substition was of 0.04.

A portion of the above cationic starch derivative was chemically crosslinked with 0.01 wt. % of epichlorohydrin at 40°C for 16 hours, neutralized to pH 6.0, filtered, water washed (2 parts water per part of starch), and air dried to about 8-15% moisture.

A portion of the above chemically-crosslinked, cationic starch was thermally inhibited by adjusting the pH to 9.5 with a 5% solution of sodium carbonate, spray-drying without gelatinization to between 3-15% moisture, and thermally dehydrating and heat treating the cationic, chemically-crosslinked granular starch in the fluidized bed previously described.

Prior to addition to the papermaking furnish, the starch samples were slurried at 4-6% solids and cooked in a mini-jet cooker (scaled down jet cooker to simulate a commercial jet cooker) at a temperature of 105-122°C and an applied back pressure of 5-20 psi using controlled live steam. The mini-jet cooker had a cooking chamber capacity or volume of 5.0 ml. The starch was passed through the cooking chamber at a flow rate of about 130 ml/min with a retention time of about 2.3 seconds.

A standard papermaking furnish was prepared using a pulp stock which comprised an aqueous slurry of bleached hardwood kraft pulp (BHWK) and bleached softwood kraft pulp (BSWK). The pulp stock (80 wt. % BHWK and 20 wt. % BSWK) was refined in an aqueous solution to about 400 CSF (Canadian Standard Freeness) and a pH of 7.8-8.2. The pulp stock contained precipitated calcium carbonate filler (30% by weight of fiber) with 8-10 wt. % fiber fines and 37-42 wt. % total fines.

Calcium carbonate retention, dry strength, and drainage resistance in both simple and microparticle papermaking systems were evaluated. The non-thermally-inhibited cationic starch was used as the control.

The results show that in the simple papermaking system the lightly inhibited starches (120°C for 0 min. and 125°C for 15 min.) were better than the cationic control in both calcium carbonate retention and dry bond strength and were as good as the thermally-inhibited, chemically crosslinked cationic starch in dry bond strength but not in calcium carbonate retention.

In the microparticle system, the very lightly inhibited starch (120°C for 0 min.) was better than the non-inhibited control in dry hand strength and drainage resistance and as good as the control in calcium

carbonate retention. The lightly inhibited starches (125°C for 15 min. and 130°C for 0 min.) were better than the non-thermally inhibited control in calcium carbonate retention, dry bond strength, drainage resistance. The highly inhibited starches (160°C) were unsatisfactory in both calcium carbonate retention and dry bond strength.

The samples of starches were tested for

Brookfield viscosity at 3% solids at 20 rpm with a No. 5 spindle.

The results show that the thermally-inhibited starches are much lower in viscosity (<60 to 1900 cps) than the thermally-inhibited chemically crosslinked starch (3650 cps.). This is a significant advantage in papermaking since the pulp slurrier must be pumped. A Brabender analysis run on the starch which thermally inhibited at 160°C for 120 minutes. It showed a percentage breakdown of 2%.

EXAMPLE 24

A cationic waxy maize starch was prepared using sufficient 3-chloro-2-hydroxypropyl trimethyl ammonium chloride to give about 0.30-0.36% bound nitrogen as quaternary ammonium groups. The cationic starches were thermally inhibited in the fluidized bed previously described at the indicated temperature and time. The thermally-inhibited cationic starches were cooked at 4% solids, a temperature of 104°C (220°F), a pressure of 20 psi, and pump speed of 3.1 in the mini-jet cooker

previously described.

The cooked starches were evaluated in two alkaline retention systems using a standard 80/20

hardwood:softwood bleached Kraft pulp (pH 7.8) with 30% calcium carbonate. The microparticle system contained 5 lbs./ton alum, 15 lbs./ton starch, and 3 lbs. /ton silica. The polymer system contained 10 lbs./ton alum, 15

lbs./ton starch, and 1 lb./ton of a 33% emulsion of polyacrylamide (Nalco 625) as a retention aid. A non-thermally inhibited cationic starch was used as the control.

The results show that the more lightly inhibited starches (130°C for 0 and 15 min. and 140°C for 0 min.) had better calcium carbonate retention than the non-inhibited cationic starch. The more inhibited starch (140°C for 15 min.) had lower calcium carbonate retention than the non-inhibited cationic starch.

EXAMPLE 25

This example shows the use of thermally-inhibited cationic and amphoteric waxy maize starches in alkaline fine papers.

The cationic waxy maize starch was prepared as above.

The amphoteric waxy maize starch was prepared by reacting a granular anionic waxy maize starch

containing about 0.08-0.12% bound phosphate (provided by reaction with a sufficient amount of sodium

tripolyphosphate) with a sufficient amount of 3-chloro-2-hydroxpropyl trimethyl ammonium chloride to give about 0.25-0.32% bound nitrogen.

The cationic and amphoteric starches were adjusted to pH 9.5 and dehydrated and heat treated in the fluidized bed previously described for the indicated time at the indicated temperature.

The thermally-inhibited starches were jet cooked as previously described and evaluated in the microparticle paper making system containing 5 lbs./ton alum, 15 lbs. /ton starch, and 3 lbs. /ton silica and in a polymer system containing 10 lbs. /ton alum, 15 lbs./ton starch, and 1 lb./ton of an anionic polyacrylamide (Nalco 625) as a retention aid.

The calcium carbonate retention data for the cationic starches are shown below. A non-thermally- inhibited cationic starch was used as the control.

The results show that the more lightly inhibited cationic starches (130°C for 15 min. and 140°C for 0 min.) were better than the control in the

microparticle system and that all the lightly inhibited starches were better than the control in the polymer system.

The calcium carbonate retention data for the amphoteric starches are shown below. A non-thermally-inhibited amphoteric starch was used as the control.

The results show that the inhibited starches were better than the control.

The TPSF drainage data in the Microparticle and Polymer Systems are shown below.

The results show that the drainage performance was satisfactory.

Now that the preferred embodiments of the present invention have been described in detail, various modifications and improvements thereto will become readily apparent to those skilled in the art.

Accordingly, the spirit and scope of the invention are to be limited only by the appended claims and foregoing specification.

Claims

WE CLAIM:

1. A paper comprising, as a wet end additive, an effective amount of a thermally-inhibited starch or flour homogeneously dispersed therein, which starch or flour, after dispersion in water, is

characterized by its improved viscosity stability in comparison to the non-thermally-inhibited base starch or flour.

2. The paper of Claim 1, wherein the starch or flour is a non-pregelatinized granular starch or flour which has an unchanged or reduced gelatinization

temperature or a pregelatinized granular or non-granular starch or flour.

3. The paper of Claim 1, wherein the thermally-inhibited starch or flour is prepared by thermally or non-thermally dehydrating the starch or flour to anhydrous or substantially anhydrous and heat treating the anhydrous or substantially anhydrous starch or flour for a time and at a temperature sufficient to inhibit the starch or flour and improve its viscosity stability.

4. The paper of Claim 3, wherein the starch or flour is adjusted to a pH of neutral or greater prior to the dehydrating.

5. The paper of Claim 1, wherein the starch or flour is a cereal starch or flour, a tuber starch or flour, a root starch or flour, a legume starch or flour, or a fruit starch or flour.

6. The paper of Claim 4, wherein the

thermally-inhibited starch or flour is selected from the group consisting of corn, pea, oat, potato, sweet potato, banana, barley, wheat, rice, sago, amaranth, tapioca, sorghum, waxy maize, waxy tapioca, waxy rice, waxy barley, waxy potato, waxy sorghum, and a starch or flour having an amylose content of 40% or greater.

7. The paper of Claim 6, wherein the starch is a derivatized starch selected from the group

consisting of a cationic starch, an anionic starch, a non-ionic starch, and an amphoteric starch, which

derivatized starch is optionally chemically crosslinked.

8. The paper of Claim 7, wherein the derivatized starch or derivatized, chemically-crosslinked starch, after dispersion in water, has a breakdown in Brabender viscosity of only from about 15-65%.

9. The paper of Claim 8, wherein the breakdown in Brabender viscosity is from about 25-45%.

10. The paper of Claim 8, wherein the cationic or amphoteric starches contain tertiary amino or

quaternary ammonium groups.

11. The paper of Claim 10, wherein the cationic starch contains at least about 0.15% by weight of bound nitrogen and wherein the amphoteric starch contains at least about 0.15% by weight of bound nitrogen and at least about 0.04-1% bound phosphate groups.

12. The paper of Claim 11, wherein the cationic starch is a waxy maize starch containing

diethylaminoethyl chloride hydrochloride groups and/or 2- hydroxypropyl trimethyl ammonium chloride groups in an amount sufficient to provide about 0.2-0.45% by weight of bound nitrogen; or an amphoteric waxy maize starch containing diethylaminoethyl chloride hydrochloride groups and/or 2-hydroxypropyl trimethyl ammonium chloride groups in an amount sufficient to provide about 0.2-0.45% by weight of bound nitrogen and phosphate groups in an amount sufficient to provide about 0.1-0.3% by weight of bound phosphate.

13. The paper of Claim 7, wherein the starch is cooked at a temperature of from about 220-250ºF and at a pressure of at least 15 psi.

14. The paper of Claim 1, wherein the wet end system further comprises an alkaline microparticle system containing an aluminum donor, an aluminum donor and colloidal silica or silicic acid, or an aluminum donor and bentonite and optionally a polyacrylamide.

15. In a method for making paper, the step which comprises adding to the stock, at any stage prior to passing the stock onto the wire, a dispersed

thermally-inhibited cationic or amphoteric starch or flour which starch or flour, after dispersion in water, is characterized by its improved viscosity stability in comparison to the non-thermally-inhibited cationic or amphoteric base starch.

16. In the method of Claim 15, wherein the cationic or amphoteric starch is chemically-crosslinked prior to or after the thermal inhibition and wherein the thermally-inhibited and chemically-crosslinked starch is dispersed by cooking at a temperature of 220-250°F and a pressure of at least 15 psi.

17. A paper stock comprising (a) water, (b) cellulose fibers, (c) mineral fillers, and (d) a

thermally-inhibited starch or flour homogeneously

dispersed therein, which thermally-inhibited starch or flour is characterized by its improved viscosity

stability in comparison to the non-thermally-inhibited base starch or flour.

18. The paper stock of Claim 17, further comprising (e) an aluminum donor, (f) colloidal silica or silicic acid or bentonite optionally together with a polyacrylamide as retention and drainage aids, and (g) optionally a sizing agent.

19. The paper stock of Claim 18, the aluminum donor is aluminum sulfate and/or polyaluminum chloride, wherein the mineral filler is calcium carbonate, and wherein the sizing agent is an alkenyl succinic anhydride and/or an alkyl ketene dimer.

20. A paper prepared from the stock of Claim 18.