FI74309B - MICROFIBRILLATORS OF CELLULOSE AND FOUNDATION FOR FRAMSTAELLNING AV DENSAMMA. - Google Patents

Description

1 74309

This invention relates to microfibrillated pulp and a process for its production.

Methods have long been known for opening, i.e. grinding, pulp fibers for fibrillation, for increasing surface area, increasing accessibility, and achieving small particle size. Different types of ball mills are used to make pulp with several tens of microns in size. Studies have shown that during such a comminution process, ball mill grinding breaks the chemical bonds of the pulp.

It is also known to grind pulp under pressure in water to obtain microcellulose with a particle size of less than one micron. In the case of pulp derivatives, cold milling methods for derivatives in liquid nitrogen have also been disclosed in the prior art. Acoustic comminution in a ball mill is also a known method for producing pulp with an extremely small particle size. Such finely divided pulps have been used as low-calorie food additives and as thickeners in pharmaceutical products. They also have extensive use as thickeners, extenders and carriers in the cosmetics and detergents industry.

Fine pulps can also be produced by conventional methods in the production of mechanical pulps, paperboard and pulp. But normally these traditional methods additionally use the

30 chemical treatment of the pulps, such as acid hydrolysis or mercerization, which chemically modify or degrade the pulps produced.

It is known in the paper industry that the strength of paper is directly proportional to the degree of grinding and refining applied to the fibers prior to formation.

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But the milling and cleaning used in the paper industry are relatively inefficient processes because a lot of energy has to be consumed to achieve relatively low fiber opening and fibrillation.

Special forms of pulp, such as microcrystalline pulps, are also known. In microcrystalline pulp, the amorphous, accessible regions of the pulp are either cleaved or removed by dissolution, leaving less-than-10 m accessible axial regions of a few tens of microns in size. In order to produce microcrystalline pulp, it is necessary to destroy a significant part of the pulp to obtain the final product, and thus the process is quite expensive. In addition, the distilled, amorphous reactive part of the fiber is removed and cleaved, leaving only microcrystals in which the surface is mainly reactive.

The main object of the present invention is to produce a new type of pulp, the properties and characteristics of which differ from all previously known pulps.

It is a further object of the present invention to provide a finely divided pulp having a significantly increased surface area, a greatly improved absorption properties, and a significant improvement in reactivity and binding capacity.

It is a further object of the present invention to provide microfibrillated pulp without significant chemical alteration or degradation of the pulp feedstock.

It is a further object of the present invention to provide a process for producing a very fine pulp material having a number of unusual properties and uses.

The above and other objects of the present invention are achieved by feeding a fibrous pulp liquid suspension through a small diameter orifice in which the suspension is subjected to a pressure drop of at least 20,760 kPa and high velocity friction followed by high velocity braking impact flattening and repeating said suspension through the orifice. that the pulp suspension forms a sufficiently stable suspension. In the process, the pulp is converted to microfibrillated pulp without significant chemical transformation.

The microfibrillated pulp of the invention has a water retention value of more than 280%, a settling volume after 60 minutes as a 0.5% by weight aqueous suspension of more than 60% and, when hydrolysed at 60 ° C in 1M hydrochloric acid, has a growth rate of at least twice that of pulp. has been ground to a Canadian freeness of 50.

The invention will be more readily understood from the accompanying drawing, in which Figure 1 shows a cross-sectional diagram of an apparatus suitable for carrying out the present invention and Figure 2 shows the rate of growth of digestion by acid hydrolysis of microtibrillated pulp samples of the invention compared to a pulverized pulp.

Figures 3, 4 and 5 are photomicrographs showing unground pulp fibers (Figure 3) and microfibre-25 interlaced fibers after five feeds (Figure 4) and 20 feeds (Figure 5).

A particularly suitable device for carrying out the invention is a high-pressure homogenizer of the type commercially available and used for preparing emulsions and dispersions. In such a device, energy is applied to the low viscosity suspension by allowing it to flow at high speed through a limited orifice. The most important part of such a device is a combination of a homogenizer valve and a seat connected to the outlet of 35 high pressure pumps. A typical valve assembly 4 74 309 seen in drawing Figure 1. In a liquid suspension of an arrow shown in the valve assembly which is indicated by the numeral 1, and gets into the valve seat 2. At this point the liquid pressure is high and the speed of five small. As the liquid progresses to the small diameter opening 3, which is a small clearance formed by the valve 4 and the valve seat 2, the velocity increases sharply up to 213 m / s depending on the operating pressure. The pressure drop is calculated from the inlet of the orifice 3 to its outlet. When the Sus-10 pension discharges between the valve and its seat, it collides with the impact ring 5 surrounding the opening and results in a high-speed braking impact. The opening 3 must be small enough to create the necessary massage, but it must be larger than 15 fibers in diameter. Normally this means a diameter of about 0.397 to 6.35 mm (1/64 "to 1/4"). Such homogenizers and their use have been described in several contexts in the literature, e.g. in L.H.Rees, "Evaluating Homogenizers for Chemical Processing", Chemical Engineering, May 13, 1974, pp. 86-92. A more detailed description of such devices can be found in the above literature.

The microfibrillated product of the invention and the untreated pulp are compared in full scale photographs 3, 4 and 5 taken with a scanning electron microscope. The magnification is 500 times in all cases. In all cases, the pulp is in the hemlock sulfite pulp. In Figure 3, the untreated pulp fibers are almost completely smooth and flattened cylindrical in shape and have loops or folds. In Figure 4, the fibers have been torn into component layers and fibrils through the five homogenizers after the feed. In Fig. 5, after twenty feeds through the homogenizer, the fiber fiber happiness can no longer be identified. The lamellar layers have exploded into fibrils.

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The microfibrillated pulp product of the invention has a number of characteristics that uniquely distinguish it from other known pulp products.

It has not been chemically cleaved in the process and its degree of polymerization has remained almost unchanged. On the other hand, it has a higher degree of fibrillation and better accessibility than any previously known pulp product. In addition, microfibrillated pulp reaches a "coagulation point" in both water and organic solvents when fed several times through the fibrillation process. The clotting point is a critical point in the process where the pulp suspension rapidly thickens and becomes a viscous castle. Thereafter, the suspension is sufficiently stable even after long-term storage.

By a sufficiently stable suspension is meant an aqueous suspension which, when diluted to 0.5% and left to stand for one hour, retains at least 60% of its original volume, i.e. the amount of clear liquid is not more than 40%. Normally, the suspensions to be treated retain at least 80% of their original volume. Such a stable suspension, i.e. the clotting point, is known for starch, but is not known to have been observed previously with pulp. The microfibrillated pulp of the invention also has a significantly greater ability to retain water than the closest prior art pulp products. The water retention capacity is more than 280% by weight of the pulp, usually more than 300% and in many cases considerably higher. The increase in cleavage caused by acid hydrolysis, a recognized measure of pulp access, is at least twice that of pulp. When comparing the properties of the pulps discussed herein and the pulp of the prior art, pulps of the same origin are compared, i. 35 pulps produced mainly by the same defibering methods. The above and other features of the product 6 74309 make it uniquely suited for a wide variety of purposes, some of which are new and include use in paper products and fibrous sheets to improve strength.

To practice the invention, pulp or other non-regenerated pulp fiber is added to the liquid to form a pulp suspension. A particularly suitable pulp source is conventional pulp of either hardwood or softwood pulp, which is normally obtained by a defibering process or, if desired, pre-cut. Known cooking methods can be used to make the pulp and both chemical and mechanical defibering are involved. Almost any liquid can be used, provided that it is reactive in the process and is liquid enough to act as a pulp carrier. In addition to water, organic liquids such as dimethyl sulfoxide, glycerin and lower alcohols can be used. The concentration of pulp in the suspension may vary, among other factors, depending on the size of the homogenizer or other equipment used for micro-fibrillation of the pulp. More pulp-containing suspensions can be used in large or commercial scale homogenizers. The smaller particle size or shorter fibers of the starting pulp also allow for higher concentrations of pulp. Normally the suspension contains less than about 10% by weight of pulp and preferably the amount of pulp in commercial scale production is 4-7% by weight.

The above-mentioned liquid suspension or stock is fed to a homogenizer and pressurized to at least 20670 kPa, preferably 34450-55120 kPa. The stock is then repeatedly fed through a homogenizer until it forms a sufficiently stable pulp suspension. The temperature of the stock rises as it passes through the homogenizer 35. It is believed that the combined effect of both high pressure drop and elevated temperature is necessary to obtain the microfibrillated pulp of the invention. To minimize the number of feeds required through the homogenizer, the pulp stock must first be heated to a temperature of at least 50 ° C 5 and preferably at least 80 ° C before the feed is finally fed to the homogenizer. When the pressure is less than about 20670 kPa, no heating or processing produces a stable suspension.

The following examples illustrate the practice of the invention. Unless otherwise stated, all parts and percentages are by weight.

Example 1

A 2% pulp stock was prepared in about 11.4 liters of water using a prehydrolysed sulfate pulp truncated to pass through a 3.175 mm (0.125 ") screen. The stock was divided into four portions and each portion was processed separately. The starting temperatures of the pulps were 25 ° C ( room temperature), 60 ° C, 75 ° C and 85 ° C. The stock was fed through a Manton-Gaul (trademark) homogenizer 20 at a pressure of 55,120 kPa two or more times until a stable suspension was obtained, i.e. the clotting point was reached.

The stock at room temperature had to be fed 11 times through a homogenizer. At the end of the seventh feed-25, the temperature had risen to 70 ° C and at the end of the eleventh feed, the temperature was 95 ° C. The stock with an outlet temperature of 8iiPc reached the desired end point after two feeds and the final temperature was 96 ° C.

30 These experiments show that in the production of commercially microfibrillated pulp, it is more economical to preheat the system than to feed it repeatedly through a homogenizer.

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Example 2

The entire set of experiments of Example 1 was repeated, except that 20% glycerin based on the total weight of the stock was added to the stock to determine the effect of the plasticizer on the process. Glycerin did not significantly reduce clotting point formation conditions, i. it was found that gelation occurred with approximately the same amount of feeds through the homogenizer at the same outlet pressures and temperatures.

10 Example 3

All the experiments of Example 1 were repeated, however, replacing water with an organic support, dimethyl sulfoxide. No significant difference in behavior could be observed, i.e. gelation occurred with the same number of feeds at the same outlet pressures and temperatures.

Example 4

A series of experiments were performed to compare the water retention properties of microfibrillated pulp, microcrystalline pulp and highly ground pulp prepared in accordance with the invention. The microcrystalline pulp used was of a commercial grade sold under the trademark Avicel PH-105. The ground pulp was a pulp ground in a standard PFX refiner to various free-25 ness numbers. (The PFI grinder is a device developed by the Papirindustriens Forsknings Institutt, the Norwegian pulp and paper research institute. It is known worldwide as the PFI grinder). Table I shows the water retention results obtained with the test series of the above pulps. The water retention capacity of a pulp material refers to its ability to retain water when centrifuged under conditions in which most of the surface water is removed. Thus, the amount of water retained within the fiber is primarily measured, which indicates the degree of swelling of the fiber in the water. The water retention values in Table I are expressed as weight percent of 9 74309 centimeters water from the original weight of the pulp. For comparison, Table I also shows the water retention values for the prehydrolyzed sulfate pulp used as the starting material, from which both the microfibrillated pulp and the pulp were prepared. Microtibrillated pulps were prepared at a pressure of 55,120 kPa. CSF (Canadian Standard Freeness) figures indicate (in milliliters) the rate at which water seeps through the sieve in the stock. The measurement took place according to TAPPI Bulletin T227 M-58, May 1943, kor-10 continued in August 1958, according to. CSF number 182 means highly ground pulp and CSF number 749 means almost unground pulp.

Water retention tests were performed by allowing a sample of the aqueous pulp suspension to drain in a cup with a torn bottom, centrifuged at 3600 rpm (sample force 1000 g) for 10 minutes, and the pulp sample was collected and weighed. The sample was then dried in an oven at 105 ° C for at least four hours and reweighed. Water-20 retention values were obtained by subtracting the weight of the sample after oven drying from the wet weight after centrifugation, dividing by the oven dry weight and multiplying by one hundred.

Table I

25 Sample No. Pulp Water retention values (%) 1 untreated pulp 57 2 microcrystalline pulp 112

Ground pulp 3 CSF 749 57 30 4 CSF 500 77 5 CSF 385 84 6 CSF 182 104

Microfibrillated pulp 7 unheated - 8 feeds 331 35 8 preheated to 75 ° C - 4 feeds 385 10 74309

Example 5

An important distinguishing feature of the finely divided pulp product of the invention is its ability to form a sufficiently stable suspension. A series of tests were performed to determine the rate of settling of aqueous suspensions of microfibril-5 pulp. The microfibrillated pulp was prepared from a prehydrolyzed sulfate pulp that had been truncated to pass through a 3.175 mm (0.125 ") screen. A 2% aqueous stock of the pulp was fed both at the starting room temperature and preheated through a homogenizer as in Example 1 at 55 to 120 kPa. the suspension of the rolled pulp was diluted to give a 0.5% aqueous dispersion of the microfibrillated pulp The stability of the suspensions was determined by measuring the settling volume as a percentage of the original volume after standing for one hour at ambient temperature.Before feeding to the homogenizer, the untreated pulp immediately settled. The results of the others are shown in Table 20 II.

Table II

Sample Number of feeds Pulp Landing state hhmogene through the conveyor% density [_la ° C_ 25 1 1 50 10 (after 10 minutes) 2 1 (preheated to 75 ° C) 86 38 33 68 42 45 77 98 30 58 100 100 6 4 (preheated.

75 ° C) 100 100 11 74309 Sample 1 was for the most part only slightly fibrillated, as it reached a settling volume of 10% after only 10 minutes of standing. Samples 2 and 3 had incomplete fibrillation because they reached a settling volume of 42% or less after one hour.

Example 6

In order to compare the behavior of the pulps obtained by different defibering methods, samples of sulphite-10 pulps, sulphate pulps and prehydrolysed sulphate pulps were compared in terms of water retention values after comparable preparation. All samples were prepared by passing them 1 to 8 times through a homogenizer at an initial pressure of 55120 kPa and an ambient temperature. The results are shown in Table III.

Table III

Sample Mass type Number of feeds Water No._number_Reservation 1 sulphite 0 60 20 2 sulphite 5 340 3 sulphite 8 397 4 sulphate 0 100 5 sulphate 5 395 6 prehydrolysed sulphate 0 60 ^ 7 prehydrolysed sulphate 5 310 8 prehydrolysed sulphate 8 330

It can be seen from Table III that, although there are differences, the water retention values of all three pulps have clearly increased and in a relatively similar manner when fed 5-8 times through the homogenizer.

Example 7

In order to compare the water retention values of the microfibrillated pulp 35 with the pulps 12 74309 ground in a standard paper grinder to different freeness numbers, a series of tests were performed. Different pulps were ground in a standard PFI plate grinder to different Canadian-Freeness numbers (defined in Example 5 4 above) until the maximum possible grinding was achieved. The water retention values of the pulps were measured at different freeness levels. The results are shown in Table IV.

Table IV

10 Sample Mass type Canadian Water No._Freeness dätys_ 1 sulphite 625 170 2 sulphite 470 210 3 sulphite 235 220 15 4 sulphite 50 265 5 sulphate 580 165 6 sulphate 380 185 7 sulphate 215 190 8 sulphate 50 195 20 9 prehydrolysed sulphate 540 165 10 prehydrolysed 315 195 11 prehydrolysed sulphate 100 220 25 12 prehydrolysed 50 245 sulphate

It can be seen from Table IV that the known pulp milling methods, taking into account the different and extreme levels, do not give microfibrillated pulp-like products. In addition, the highly ground pulps differ from the microfibrillated pulp in question in another important respect, i.e. their chemical reactivity, as can be seen from the example below.

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Example 8 A useful way to measure pulp accessibility is known as the "Cuen residue" test. Cue, or copper-ethylenediamine, completely dissolves all pulps from cotton in the unpolished pulp at a single molar concentration of 5. As the concentration of Cuen decreases, more and more unreadable residue remains, depending on the relative insolubility. Cuen dilution tests were performed on ground, freeness-varying massoil-10a (ground as in Example 7 in a PFI grinder to the corresponding freeness values) and microtibrillated pulp. All pulps tested were prehydrolysed sulfate pulps. The microtibrillated pulp was fed through a homogenizer at an initial pressure of 55,120 kPa. Table V shows the residual percentages of the different masses in the Cuen dilution test. The temperature was 25 ° C and the Cuen concentrations are shown in the table.

Table V Residual percentage 2 0 Cuen concentrates CSF figures for ground pulp Traction of microfibrillated pulp (g / ml) Number of feeds _ 535 309 89 60_1 5 8 12 98.2 98.2 95.5 88.2 79.1 69.1 14 92.7 86.3 79.1 77.3 68.2 41.8 30.0 25 16 33.6 19.1 11.8 17 9.1 7.2 5.4

It can be seen from the table above that the ground pulps leave significantly more residue and dissolve to a much lesser extent than microfibrillated pulp. These values indicate that the accessibility changes a lot when the mass is hanogenated according to the invention. Optical photomicrographs taken from various pulp samples in this example show that the structure of the hcmogenated pulps is clearly more transparent than with the most strongly ground pulps.

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The microfibrillated pulp of the invention comes from the homogenizer as a sufficiently stable suspension. The above examples have addressed the preparation and testing of such microfibrillated pulp suspensions. It has been found that drying microfiber-treated pulp alters its properties and is also relatively expensive. Thus, it is recommended that the microfibrillated pulp be used in undried form as a suspension of an aqueous or organic liquid. But in some cases, it may be desirable to use dried microfibrillated pulp. The following examples illustrate the preparation of microfibrillated pulp and the drying and testing of the product thus prepared.

Example 9 A wet sulphite pulp (370 g wet = 100 g oven dry) which had not been dried after defibering was dispersed in 10 liters of deionized water in a counter-rotating mixer. The stock was fed through a homogenizer at a pressure of 55,120 kPa and a temperature below 40 ° C 5, 10 and 20 times. The resulting stock was freeze-dried. The reactivity of the microfibrillated pulp was determined by measuring the solubility in dilute Cuen and comparing the results to the corresponding results with starting material and starting material truncated to pass through a 3.175 mm (0.125 ") sieve. Cuen solubility tests were performed at 0.125 Cuen the table shows the percent residues of microfibrillated pulp and control samples in the diluted Cuen when tested.

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Table VI

Sample Pulp type_Pulp residue% No. 1 Untreated pulp 71.0 5 2 Untreated pulp (cut to pass through a 3.175 mm sieve) 52.4 3 microfibrillated 5 feeds 33.1 4 microfibrillated - 10 feeds 14.9 10 5 microfibrillated - 20 feeds 5.7

By intrinsic viscosity of a long chain compound such as pulp is meant a viscosity proportional to the average degree of polymerization (DP) of the long chain compound. The intrinsic viscosity of pulp in a copper-ethylenediamine solution is known as the intrinsic viscosity of Cuen. It is obtained by measuring the gradual increase in the viscosity of the solvent due to the dissolved pulp (i.e., the intrinsic viscosity) at a solute content of 20 to 0.5% and extrapolating the viscosity-concentration function to a concentration of zero. The following example compares the Cuen viscosities of several pulp samples both before and after homogenization.

Example 10 An aqueous stock having a total solids content of 1% was prepared from a sulphite pulp which had not been dried after defibering. The stock was homogenized at a pressure of 55,120 kPa and a temperature of 20 ° C and 90 ° C by feeding 1-20 times. The resulting stock was then freeze-dried and their Cuen viscosities determined. The results are shown in Table VII.

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Table VII

Sample Hcmogenoin £ i- Number of feeds Cuen boundary viscosity No. temperature ° C number of binding 1 20 0 8.83 2 20 1 8.81 3 20 5 8.46 4 20 10 8.15 5 20 20 7.55 10 6 90 0 8.66 7 90 1 8.65 8 90 5 8.30 9 90 10 7.86 10 90 20 7.10 15 It can be seen from Table VII that, according to the Cuen intrinsic viscosity measurements, the pulp is almost chemically unchanged due to the hanogenation treatment.

The microfibrillated pulp of the invention can be further characterized by the acid hydrolysis rates of the material formed as compared to the PFI-ground or highly ground material. The following examples deal with the relative acid hydrolysis rates of microfibrillated pulp and pulp ground in a PFI grinder.

Example 11 25 Preheated hydrolyzed sulphate pulp was ground in a standard PFI grinder using water as the grinding medium. Grinding took place up to 10,000 revolutions, at which time the Canadian freeness number was measured to be 50 ml. In the paper industry, this far exceeds the need to form paper-30 and approaches the extreme limit of PFI machine performance.

The prehydrolysed sulfate pulp was fed through a Manton-Gaul homogenizer using water as a carrier. The pressure drop was 55,120 kPa and homogenized by feeding 35 nine times at 100 ° C. Acid hydrolysis of these samples was performed by hydrolysis of 1, 2, 3 and 17 74309 for 5 hours at 60 ° C in 1M hydrochloric acid. Ko. at the end of time the hydrolysis was stopped and the material formed was taken up in acetone and dried in vacuo and at room temperature overnight. Cuen intrinsic viscosity measurements allowed the growth rate of cleavage to be calculated. The increase in cleavage is directly proportional to the number of bonds broken in the hydrolysis. The rate of bond breakage is a measure of the open structure of the pulp, i.e. the accessibility. In Fig. 2, the two solid lines 10 show the growth rate of the decomposition of microfibrillated pulp of this example compared to the corresponding value in the highly ground pulp. It can be seen from the figure that for microfibrillated pulp this value is n.

3.5 times larger.

15 Example 12

The prehydrolysed sulfate mass was ground in a PFI grinder using glycerin as the grinding medium. Grinding took place for 5,000 revolutions to give a Canadian freeness number of 137 ml. The prehydrolysed sulfate mass was homogenized as in Example 11 but using glycerin as a medium and the reference hydrolysis rates were determined in aqueous acid. Again, in the case of acid hydrolysis, it was found that the growth rate of the cleavage of the homogenized pulp was significantly, i.e. 3.2 times higher, than that of the pulverized pulp when both were prepared in glycerol medium. The growth rates of the cleavage of these two masses appear in Figure 2 as two dense dashed lines.

Example 13 A prehydrolyzed sulfate pulp was ground in a PFI grinder using propylene glycol as the grinding medium. Grinding was performed up to 10,000 revolutions, at which time the CSF was measured to be 129 ml. The prehydrolysed sulfate pulp was also homogenized in propylene glycol 35 at a pressure drop of 55,120 kPa. Relative hydrolysis 1 !! 74309 sine velocities are shown as two sparse dashed lines in Figure 2. Again, the growth rate of degradation of the homogenized pulp caused by hydrolysis was 2.1 times higher than the corresponding value of the highly ground pulp.

Thus, it can be stated that in all cases the pulps treated by homogenization were quantitatively more transparent, i.e. more accessible, than the pulp prepared by grinding in the PFI grinder.

The chemical and physical accessibility of pulp can also be measured by reaction with cellulase, an enzyme that hydrolyzes pulp to glucose. Thus, experiments were performed comparing the accessibility of microfibrillated pulp as well as several other finely divided pulps to the cellulase enzyme. The experiments were performed with Trichoderma viride enzyme.

This is a cellulase complex capable of quantitatively converting crystalline, amorphous and chemically derived pulps to glucose (or, when derivatives are used, to substituted glucose). The system is multi-enzymatic and contains at least three enzyme components, all of which play an important role in the overall process.

Example 14 A 1% stock was prepared from a sulphite pulp which had not been dried after defibering by suspending 50 g of pulp in 5 liters of deionized water. The stock was homogenized by passing it 0, 5 or 10 times through a homogenizer at a pressure of 55120 kPa and a temperature of 30 ° C. The stock suspensions were freeze-dried.

Samples of lyophilized microfibrilated pulp were then tested for cellulase reactivity. For comparison, the cellulase reactivity of a control sample of microcrystalline Avicel pulp, ball mill-milled Solka-Floc pulp, PFI-ground pulp and non-homogenized sulfite pulp was also tested. Solka-Flock is a trademark of 19 74309 for finely divided pulp powder produced by ball-mill-dried pulp. The PFI-ground pulp was ground at 12,500 revolutions to a Canadian freeness number of 100, which was the same value as the microtibrillated pulp after 5 to 10 feeds.

Samples (0.5000 g oven-dried) were placed in flasks and 50 ml of acetate buffer was added. 0.0800 g of cellulase enzyme was then added. The flasks were placed in a constant temperature shaking bath at 37 ° C + 1 ° C. After 70 and 170 hours, the samples were filtered through a sinter filter and the filtrates were analyzed for free sugars by paper chronatography. Only glucose was detectable. The results of the Cuen intrinsic viscosity and cellulase tests are shown in Table VIII of tau-15.

Table VIII

Pulp sample Feed- Cuen limit- Viscosity-released glucose numer. tea (mg / 50 ml) 20 _ (dl / g) 70 h_170 h_ control mass 0 8.83 37.5 41.0 microtibrillated δ 8.46 77.0 107 microns ibrillated 10 8.15 92.5 157 microcrystalline - 1 , 16 15 18.5 25 ball mill ground - 4.08 36 4 7 PFI ground - 8.44 66 91

Despite the small particle size and lower intrinsic viscosity of the microcrystalline and ball milled samples, both had lower reactivity than both microtibrillated samples and released less than one-third of the glucose in the microtibrillated pulp after 10 feeds. Similarly, the fibers in the PFI-milled sample were not as open as microtibrillated 20 7 4 3 0 9 pulp, although both had the same Canadian freeness numbers and only about 60% of the glucose in the micro-fibrillated pulp after 10 feeds was released.

Example 15 The microtibrillated pulp of the invention can be used to significantly improve the strength of a paper sheet structure. To demonstrate this, a 2% aqueous stock of microtibrillated pulp was prepared from a prehydrolysed sulfate pulp that had been truncated to pass through a 3.175 mm (0.125 ") sieve and fed five times through a homogenizer at 55120 kPa. 60% microtibrillated pulp as a suspension with said percentages based on the total weight of the sheet and dispersed for 15 seconds in a mixer.

Laboratory sheets were then prepared from the stock according to the method TAPPI 7504 to obtain laboratory sheets weighing 1.25 g. The properties of the formed laboratory sheets were:

20 Table IX

Sample MicrotibroTreatment sheet Mullen puncture barrier pulp pro- weight pulp (g) cheese dry (kPa) centimeter_addition_ 1 0 1.21 56 (control) 2 20 1.14 99 3 40 1.02 104 4 60 0.82 64

Example 16 A second set of sheets was prepared using 12.7 mm (1/2 ") staple viscose fiber to obtain a fibrous sheet. Adding 20, 40 and 60% of an aqueous suspension of microtibrated pulp prepared according to Example 15 gave the following results: 2i 74309 Sample Microfibrillary Sheet Weight ELB + ^ Pull strength of Mullen-no. Pulp centum (g) dry _addition_ (kPa) _ 1 sheet did not stay together enough 5 (due to uncontaminated adhesion role) υ 2 20 0.64 53 129 3 40 0.70 60 180 4 60 0.68 57 116 X) 10 'Elrepho brightness on a black background to indicate sheet formation.

The results show that microfibrillated pulp is a useful binder for paper and fibrous structures. Although the amount of use can vary widely, the amount of normal-15 li is 0.5 to 40% of microfibrillated cellulose based on the weight of the paper product or fibrous sheet formed.

Embodiments illustrating the invention have been described above, and it is intended by the applicants that the appended claims cover all forms which fall within the scope of the invention.

Claims (16)

74309 A method for producing microfibrillated pulp, characterized in that a liquid suspension of fibrous pulp 5 is fed through a high-pressure homogenizer with a small-diameter orifice in which the suspension is subjected to a pressure drop of at least 20670 kPa and high-velocity friction followed by high-velocity braking repeating the feed of said suspension through the orifice so many times that the pulp suspension forms a sufficiently stable suspension, whereby the pulp is converted into microfibrillated pulp in the process without significant chemical change of the pulp feedstock. A method according to claim 1, characterized in that the liquid suspension is heated to a temperature of at least 50 ° C before being fed through the orifice. Process according to Claim 2, characterized in that the liquid suspension is heated to a temperature of at least 80 ° C. Method according to Claim 1, characterized in that a pressure drop of at least 34450 kPa is applied to the suspension. Process according to Claim 1, characterized in that the suspension contains at most 10% by weight of pulp. Process according to Claim 5, characterized in that the suspension contains 4 to 7% by weight of pulp. Process according to Claim 1, characterized in that the suspension is an aqueous suspension. Process according to Claim 1, characterized in that the suspension is an organic suspension. Method according to Claim 1, characterized in that the friction takes place at right angles. 74309 10. Microfibrillated pulp, characterized in that it is prepared by feeding a liquid suspension of fibrous pulp through a high-pressure homogenizer with a small-diameter orifice in which the suspension is subjected to a pressure drop of at least 20670 kPa and high-velocity friction followed by high-velocity braking against the surface, and possibly by repeating the supply of said suspension through the orifice with a water retention value of microfibrillated pulp of more than 280%, a settling volume after 60 minutes as a 0.5% by weight aqueous suspension of more than 60% and a growth rate of hydrolysis at 60 ° C of 1 m in hydrochloric acid at least twice as large as pulp ground to a Canadian standard grind of 15 ml at 50 ml. Microfibrillated pulp according to Claim 10, characterized in that it is in the form of an aqueous suspension. Microfibrillated pulp according to Claim 10, characterized in that it is in the form of an organic suspension. Microfibrillated pulp according to Claim 10, characterized in that it has a settling volume of more than 80%. Microfibrillated pulp according to Claim 10, characterized in that it has a water retention value of more than 300%. A paper product with improved strength, characterized in that it contains microfibrillated pulp according to claim 30. Fiber sheets with improved strength, characterized in that they contain microfibrillated pulp according to claim 10. 74309