FI89719B - Method for production of a starch-based polymer dispersion, and a dispersion produced by the method - Google Patents

Description

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The invention relates to a process for preparing an aqueous polymer dispersion comprising a graft copolymer of starch and an unsaturated monomer. The solids content of the dispersion is high, but the viscosity level can be adjusted to the level required by the technical application - e.g. use as a binder in the paper industry. The invention also relates to a polymer dispersion prepared by the process.

The preparation of graft copolymers from starch and unsaturated monomers by radical polymerization is known per se. An overview of the current state of the art is presented e.g. in O.B. Wurtzburg: Modified starches: Properties and Uses (CRC press, 1986). In the patent literature, e.g. U.S. Pat. No. 3,061,571, U.S. Pat. No. 20,306,1472, U.S. Pat. No. 3,138,564, GB 869,501 and U.S. Pat.

However, these known methods have drawbacks which result in the product graft polymer being stable in solution only at low dry matter concentrations, or that the product dispersion has weaknesses in the intended applications, e.g., U.S. Pat. No. 4,301,177 describes an aqueous the use of a starch graft copolymer dispersion as a binder for a paper coating, however, the bond strength of the dispersion prepared according to the teachings of said patent has been deficient.

The polymer dispersion prepared according to our application has been found to be stable for long periods of time at high dry matter contents of at least 25% by weight, but typically 40-55% by weight. The main field of application of the polymer dispersion according to the invention is intended to be the use of a binder in the paper industry, in which case it has been found to provide good bonding strength in addition to its advantageous handling properties.

In the process of the invention, the starch or starch derivative in granule form 5 is grafted with a monomer containing unsaturated double bonds using a suitable radical initiator as a catalyst. The characteristic features of the method appear from the appended claim 1.

The starch used may be any starch isolated from natural raw materials (native starch), e.g. potato, barley, wheat, oat, corn, tapioca, sago, rice, etc. tuber or cereal starch. In addition to native starches, variously modified starches can also be used as starting material. Examples are starches which have been oxidized, acid-cleaved, cationized, etherified with ethylene or propylene oxide, variously esterified (e.g. acetylated and phosphatized) and variously cross-linked starches.

Any known initiation method useful in grafting can be used as the radical initiator. These include e.g. hydrogen peroxide either as such or as an oxidation-reduction pair together with a suitable iron, copper, manganese, or the like salt, ascorbic acid or other suitable oxidizing compound; ammonium, potassium and the like. persulfates; cerium salts (e.g. cerium ammonium nitrate) and electron and UV irradiation.

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A large number of polymer chain-forming monomers useful in grafting are available. Examples which may be mentioned are styrene, butadiene, esters of acrylic acid with alcohols, acrylic acid, acrylonitrile, acrylamide, vinyl acetate, N-vinylpyrrolidone, 2-ethylhexyl acrylate and methacrylic acid and its esters with alcohols. Mixtures of various unsaturated monomers, e.g. the above-mentioned compounds, are also useful.

Grafting is preferred, and in most cases necessary under oxygen-free conditions, e.g., a nitrogen atmosphere as a shielding gas.

However, if the hydrolytic cleavage carried out at a later stage of the preparation process according to the invention is carried out acid-catalytically, which is the preferred cleavage method, it is most preferred to use monomers which do not contain acid-degradable groups (e.g. ). Thus, e.g., styrene, butadiene, and acrylic and methacrylic acids are preferred grafting monomers.

The above does not in any way preclude the use of e.g. acrylic acid barriers or the like in the first step of preparing the dispersion. In such cases, it is only sufficient that the subsequent cleavage procedure be carried out in another way (e.g. enzymatically) so as not to achieve a stable dispersion. . ·. 25 easily reach equal solids content of the dispersion. ···. than the most efficient cleavage methods (acid talc).

However, the use of acid-sensitive compounds as grafting monomers according to the invention provides another and more advantageous possibility than described above. Accordingly, as can be seen from the application examples below, grafting is performed in several steps as follows:

Grafting onto the starch in granular form is first carried out with acid-resistant monomers (styrene, butadiene, etc.). · Then the cleavage and gelatinization of the starch grains are carried out in an optimal manner (the suitable technique is explained in detail below). The pre-grafted, cleaved and gelatinized starch derivative is then re-grafted with a monomer or monomer mixture giving the desired properties.

It should be emphasized that relevant to the invention and the improvements it provides over the prior art (e.g., surface strength in paper applications) is specifically the treatment sequence in which the first grafting occurs to the starch in granular form and dispersing the reaction mixture to a suitable viscosity level. after this. The quality properties of the dispersion can then be further modified by further grafting.

The total amount of monomer or monomer mixture used in the grafting can vary within quite wide limits. By varying the amount and quality of the monomer / mixture, the optimal polymer dispersion quality for each application can be selected. For example, in surface sizing and coating of paper, the printability properties of the paper product can be affected by optimizing these binder parameters. Theoretically, the amount of synthetic monomer can range from 1 to> 300% based on the amount of dry starch. In practice, however, it is appropriate; 30 lanes to remain below 200% for both production economic and technical reasons. It is preferred that in the process according to the invention, in the grafting onto the starch in granular form, the amount of monomers is less than 50% of the total amount of dry starch, and any additional amount of monomer is grafted only after the cleavage step.

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As already indicated above, in the process according to the invention, the starch graft in granular form is catalytically cleaved and, either simultaneously or after the cleavage step, is dispersed by dispersing the graft grains by heating the aqueous mixture of starch graft from of the support monomers and the cleavage method varies from n.

Between 40 and 95 ° C. In the graft cleavage event 10, the glucose chains of the starch polymers are cleaved by a suitable catalyst. By controlling the reaction time, temperature and catalyst concentration, the properties of the final dispersion product can be varied so as to obtain a polymer dispersion suitable for the particular application. The dispersion is characterized by what appears from the appended claim 10.

All the same 20 cleavage methods can be used for grafting, which are generally useful in starch cleavage processes. Thus, various oxidation methods (e.g. with hypochlorite, ozone or peroxides), cleavage by radiation (gamma, electron or UV radiation) and enzymatic cleavage (especially by alpha-amylases) are possible.

However, a particularly preferred method of cleavage in the process according to the invention is acid-catalyzed hydrolysis; 30 which allows precise monitoring of the degree of hydrolysis and adjustment of the viscosity level. Suitable catalyst acids are strong acids in general and hydrochloric acid or sulfuric acid in particular. From the point of view of product quality and reaction control, it is preferable that the amount of catalyst acid be limited so that the pH of the reaction mixture is not substantially lower than 0.5.

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It is also advantageous and to speed up the preparation process that the graft grains are dispersed, i.e. gelatinized, simultaneously with the acid hydrolysis by raising the temperature of the reaction mixture above the gelatinization temperature.

It should be noted that enzymatic cleavage by alpha-Amy glasses occurs in process processing in exactly the same way as acid hydrolytic cleavage. The only limitation is that in the grafting step, the amount of monomer (degree of substitution) cannot be very high, because then the activity of the enzymes is inhibited or slowed down too much.

15 After digestion steps and cooling, the product is ready for use without pH adjustment, unless further grafting is required to achieve the desired properties in the application. If further grafting is desired, the procedure is preferably identical to the first grafting step: the mixture is deoxygenated with a shielding gas, the catalyst is added and the desired amount of monomer is gradually added at a suitable grafting temperature with stirring (20-100 ° C, typical reaction time 1-2 h ).

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The following embodiments further illustrate the method of preparing a polymer dispersion according to the invention:

Example 1: 212 g of hypochlorite oxidized potato starch with a dry matter content of 82% and a carboxyl content of 1.5% were slurried in 228 g of water in a 3 liter reaction vessel. A nitrogen flow below the liquid surface was provided in the reaction vessel to provide an inert atmosphere. 0.05 g, copper sulfate 35 and 0.5 ml of 30% hydrogen peroxide were added to the vessel, and styrene was added dropwise to the mixture with stirring. The temperature of the reaction vessel was maintained at 40 ° C by means of a water bath. The total amount of styrene 17.6 g was added over 1 hour, after which a further 0.5 ml of hydrogen peroxide was added and the reaction was allowed to proceed for a further hour. Based on the gas chromatographic analysis performed, the free styrene content of the mixture was then less than 0.02% (below the detection limit of the analytical equipment used). The pH of the reaction mixture was lowered to 1.03 with 30% hydrochloric acid and then the temperature was slowly raised. At a temperature of about 60 ° C, as the viscosity of the reaction mixture began to increase with the onset of gelatinization of the graft grains, the temperature rise was stopped until the viscosity of the mixture clearly decreased again as the hydrolysis proceeded. The temperature was then raised to 83 ° C and the hydrolysis was allowed to continue at this temperature for 3 h. The resulting white dispersion was cooled to room temperature and neutralized with 15% NaOH to pH 6.5. The Brookfield viscosity at 20 ° C was 380 cP.

Example 2: 75 kg of native potato starch with a fiber content of 85.5% was slurried in 91 kg of water.

20 g of ferrous sulfate was added to the reactor and it was thoroughly purged with nitrogen. 0.2 L of 30% hydrogen peroxide was then added and styrene was gradually added dropwise to the reaction mixture. The total amount of styrene (8.8 kg) was added within 1.5 h. Another 100 ml of hydrogen peroxide was added over 45 min. after the start of the styrene addition and another 100 ml after all the styrene had been added to the reaction mixture. The reaction was allowed to proceed for a further 1.5 h, after which the mixture was acidified with 30% hydrochloric acid (pH 0.6) and hydrolysed and gelatinized according to Example 1. The highest hydrolysis temperature was 89 ° C, and the hydrolysis time was 2 h 45 min. The reaction mixture was cooled and neutralized with 15% NaOH to pH 5.9. The product had a Brookfield viscosity of 790 cP ---- 35 at 20 ° C.

Example 3: The preparation of the product was carried out according to Example 1.

β 8971 9 with the following amounts: 244 g of oxidized potato starch in 450 g of water was reacted with 50 g of styrene. In the hydrolysis step, the pH was 0.5 and the reaction temperature was 94 ° C for 2 h. After neutralization, a white dispersion with a Brookfield viscosity of 120 cP at 25 ° C was obtained. The grafting was then continued as follows: 1 ml of 30% hydrogen peroxide was added to the reaction mixture under a nitrogen atmosphere and 150 g of butyl acrylate were added dropwise to the reaction mixture over 2 h. An additional 1 mL of hydrogen peroxide was then added and allowed to stir for 2 h. The resulting yellowish dispersion had a viscosity of 480 cP.

Example 4: The product was prepared according to Example 3, but in the second grafting step 50 g of vinyl acetate were used instead of butyl acrylate. The temperature during the second grafting was maintained at 50 ° C for three hours. The viscosity of the off-white dispersion at room temperature was 270 cP.

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Example 5: The product was prepared as in Example 1. but instead of styrene, 25 g of butadiene washed with an alkali solution was introduced into the reaction mixture. The starch was 212 g of the oxidized potato starch of Example 1. After the hydrolysis and gelatinization steps, a yellowish dispersion with a Brookfield viscosity of 340 cP was obtained.

Example 6: The product was prepared as in Example 4, 30 but before grafting butadiene into starch grains, 15 g of styrene were grafted. The product, which was an almost white dispersion, had a viscosity of 490 cP.

Example 7: The product was prepared as in Example 4, 35 but the monomer used was 25 g of a mixture containing 80% styrene and 20% acrylic acid. The product obtained when the reaction mixture was neutralized with NaOH to pH 6.3, 9 B9719 was a white dispersion with a Brookfield viscosity of 690 CP.

Example 8: In accordance with Example 1, 215 g of 13 g of butyl acrylate were grafted onto 5 g of 5 g of hypochlorite-oxidized potato starch slurried in 270 ml of water. The pH was adjusted to 6.0, and 0.01 U / gram of thermostable Bacillus licheniformis alpha-amylase was added to the reaction mixture. The temperature was raised to 90 ° C for 2 hours 10, after which the pH was lowered to 3.5 to stop the enzyme activity. A translucent dispersion with a viscosity of 600 cp at 25 ° C was obtained.

Example 9: This example illustrates the use of dispersions prepared by the process of the invention in paper coating pastes. The kaolin pastes, the recipes of which are shown in Table 1, were applied to a 40 g / m2 basis weight LWC base paper containing 80% mechanical pulp in three different amounts of coating using a Helicoater laboratory coating machine.

Table 1. Recipes for test pastes. The amounts of substances in the table as parts by weight of solids. The paste has a total dry matter content of 60% and a pH of 7.0.

"25 recipe pasta 1 pasta 2 pasta 3 kaolin 100 100 100 SB latex 6 6 6 30 SH300E 1) 6 SH350E 2) - 6 US4301017 3) - - 6 glyoxal 0.6 0.6 0.6

Ca stearate 0.4 0.4 0.4 35 1) dispersion prepared according to Example 1 2) dispersion prepared according to Example 3 10 B 9 71 9 3) Dispersion prepared according to Example 3 of U.S. Patent 4301017

The resulting coated papers were calendered with a laboratory lanther and measured for surface strength by IGT as well as Hunter gloss and brightness. The results were interpolated with respect to the amount of coating to 9 g / m 2. The results are shown in Table 2.

10 Table 2. Paper technical properties of papers coated with test pastes.

15 IGT, cm gloss% lightness% paste 105 74 73.0 pasta2 115 72 72.5 pasta3 70 70 72.5 20

Claims (10)

A process for preparing an aqueous, high solids, viscosity-adjustable polymer dispersion from native or modified starch, which process comprises grafting to the starch by grafting polymer chains of unsaturated double-bonded structural monomers, characterized in that by digestion and heating the starch to at least the gelatinization temperature. Process according to Claim 1, characterized in that the cleavage of the grafted starch is carried out before heating to a temperature above the gelatinization temperature. Process according to Claim 1, characterized in that the cleavage of the grafted starch is carried out simultaneously with the gelatinization heating. Process according to one of the preceding claims 1 to 3, characterized in that the cleavage of the grafted starch 25 is carried out with a strong mineral acid. Process according to one of the preceding claims 1 to 3, characterized in that the cleavage of the grafted starch is carried out enzymatically. ': 30 Process according to Claim 4, characterized in that butadiene, styrene or a mixture thereof is used as monomer in the grafting of the starch. - 35 7. A process for the preparation of an aqueous, high solids, viscosity-adjustable polymer dispersion from native or modified starch, which process comprises grafting starch by grafting unsaturated double-bonded monomers and polymer chains consisting of monomers having a double bond. dispersing the structure of the starch by catalytic cleavage and heating the starch to at least the gelatinization temperature, and subjecting the gelatinized starch to further grafting. Method according to Claim 7, characterized in that the subsequent grafting is carried out under pre-grafting conditions. Process according to Claim 7, characterized in that a different monomer is used in the subsequent grafting than in the pre-grafting. Aqueous dispersion prepared by a process according to any one of the preceding claims, characterized in that it has a solids content of at least 25% by weight and a Brookfield viscosity at 20 ° C of 340 to 790 cP. 13 8 971 9