TITLE: "PROCESS FOR PREPARING AQUEOUS SUSPENSIONS OR SLURRIES FROM CELLULOSE MICROFIBRILS, CELLULOSE MICROFIBRIL AQUEOUS SUSPENSION OR SLURRY AND ITS USE"

Cellulosic products and cellulose derivatives" are widely employed in daily life.

Although wood was probably the first raw material used by man, and apparently all possible products derived from native cellulose have already been developed, current technological progress has frequently made it possible to develop new products, pointing out a new industrial age.

Brazilian patent PI 8404937 in the name of the present applicant describes a new kind of material which has been used as a temporary substitute for human skin. It is a cellulosic film formed by a network of microfibrils resulting from bacteri- al fermentation. This same material, since it is found in a dif¬ ferent physical state from all other cellulosic materials so far used, opens up possibilities for developing new products for a vast range of applications.

Cellulose is found in nature as one of the most abun- dant renewable materials. Produced by a number of organisms, it exists in greatest availability in the stem of trees, in a physical state adequate for various kinds of use . Other natural sources used, such as ramie (leaves) or cotton (isolated fibers), occur in minor proportions, but have basically the same features at microscopic level as far as the formation of cellulosic fi¬ bers is concerned.

The walls of plant fibers are composed mainly of cel¬ lulose, the degree of purity of which varies from plant to plant and between the layers forming the cellular walls . Cellulose produced by bacteria shows a loose microfi- bril network, microfibrils being kept isolated from one another

by the liquid culture medium before drying the cellulosic materi¬ al. In this case, there are ways to avoid the occurence of chemi cal bonding among them or to allow the same only at the desired moment. 5 In the formation of cellulosic material constituting wood, glucose molecules are chemically bonded to form cellulose macromolecules and through secondary valency forces, form together so called crystalline molecular sets which become lon¬ gitudinally bonded to form elementary fibrils. However, the

10 crystalline areas are not formed continuously, there being amor¬ phous regions among them.

Crystalline areas become hidrophobic through the forma tion of hydrogen bonds between cellulose molecules, followed by the formation of microfibrils, which orm the lamellas constitut -*-5 ing the cellular wall.

Thus , there are no isolated microfibrils in the cellu¬ losic material constituting the wall of wood fibers , but an aggregate strongly bonded by hydrogen bonds that keeps it in this form in a practically irreversible way. The cellular wall is formed by a primary (P) and a secondary wall (S) , which is subdivided in three discrete layers.

The primary wall contains firstly pectins , proteins and a little cellulose (about 5%) , the proportion of which grad¬ ually increases during the cell development. ⁵ In the secondary wall, the fibrils form a mesh, which gradually forms discrete lamellas, in which:

- Layer S-, is constituted by a number of lamellas of highly spiralled intersecting microfibrils , with a thickness of 0,2 - 0,35 microns .

30 - Layer S ₂ has a thickness of several microns (1,8 - 3,7 microns) and is constituted mainly by cellulose, it being extremely compact and oriented with sets of slightly spiralled microfibrils, forming a number of concentric lamellas.

-Layer S ₃ has a thickness of 0,1 - 0,15 microns,

35 contains cellulose and its fibrils are spiralled and intersect¬ ing.

Although the chemical bonds among microfibrils are theoretically irreversible, the partial fibrillation of the cellular wall may be carried out by mechanical means. This is

the usual way to obtain certain advantages in some properties of the paper to be produced from wood fibers, but to a limited degree because of the excessive mechanical work required to dis¬ rupt and delaminate cellular walls, which causes losses in other properties of the paper as well.

The object of this invention refers to a process for obtaining an aqueous suspension of cellulose microfibrils, the cellulose being produced by bacterial fermentation, and to its uses. The said process is characterized by the elimination of the culture medium used in the bacterial fermentation from the cellulose microfibrils by washing, the further grinding and macerating of said cellulose microfibrils through mechanical means and the reduction of the water from the product obtained in aqueous suspension so as to make it pasty. The product obtained by said process, in its physical form, consists of particles of cellulose microfibril networks and fragmented individual filaments measuring about 0,14 microns in diameter, in aqueous suspension or slurry form. Its chemical composition consists mainly of alpha cellulose. An analysed sample of said product showed the follow¬ ing data:

A) Total hydrolysis (Seaman) a. total sugar 81,3%

B) Ash content 1,8% C) Gas chromatography (GLC) of hydrolysates

(in the form of auditols) a. glucose 98,0% b. mannose, galactose and xylose 2,0% D) Treatment with 17,5% NaOH solution and NaBH ₄ for 72 hours a. insoluble material (alpha cellulose) 86,5% .a.l glucose 98,0% a.2 mannose, galactose and xylose + 2,0% b. soluble material in 17,5% NaOH, but insoluble at pH 5 2,5% b.l glucose 93,0% b.2 xylose 6,0% b.3 mannose and galactose traces c. soluble material in 17,5% NaOH and

also at pH 5 c.l total sugar 2,4%

This invention has demonstrated that, in order to obtain better results in terms of use of the cellulose microfi- brils, the elimination of the culture medium from the biological material produced by the bacteria is critical. Thus, when a greater efficiency in the cleaning of the material is needed, said material may optionally be first subjected to a bath in an alkaline aqueous solution, for a variable period of time as a ^' function of the thickness and humidity content of the microfi- bril network. In this case, after diffusing said alkaline solu¬ tion into the biological material, the latter is washed in run¬ ning water or merely in successive immersion and changes of water. Be it for the alkaline solution treated material or for the untreated, the washing in water should be done to ensure maximum elimination of the culture medium in which the microfi- bril network developed.

As a supplementary step, the biological material may e subjected to another stage of washing w th oxidants, such as, for example, in sodium hypochlorite solution and water, respecti vel .

An adequate cleaned cellulose microfibril network is then ground and macerated by mechanical means. This operation is extremely simple to carry out, it being possible to use a wide range of different equipment. Among the device that process the material in a single operation, there are those provided with sharp high speed rotating blades and those of isolated operation, grinders, refiners and mills, besides the possibility of combining them with the above mentioned rotating blades. Since the macerated cellulosic material has a high- water retention capacity, water must be added when practicing maceration with a rotating blade equipment, in a proportion of about 99,5% (weight/weight) . The use of other equipment may reduce this proportion significantly.

In order to reduce storage space as well as packaging and transportation costs, excessive water may then be drained by means of filters or fine mesh screens, through the action of gravity and/or vacuum applied to the system.

The resulting material then should be kept moist for use, since the drying action will promote the formation of hydrogen bonds between microfibrils, to the detriment of the quality of the product of the invention.

Consistences of 5,3 to 5,5% (humidity of 94,7 to 94,5%) are adequate for storage and transportation, resulting in a reduction in volume and weight greater than 10,5 times that of a suspension with 99,5% humidity.

The entire process of preparation described above may optionally be effected with a roughly water washed and dehidrat- ed material, leading to an economy in the chemicals used for further cleaning. Contrary to this, there is an increase of time and costs because of the additional drying of microfibril net¬ works and alterations in the quality of the product obtained. The product obtained by the process of this invention lends it¬ self to applications in several industrial sectors, which can be better understood from the following table:

PURPOSES AREAS OF APPLICATION . Promotion of wood fibers floc- culation during papermaking; . Better fines, colouring filler materials and solubles reten¬ tion; . Promotion of a great number and Papermaking better distribution of bonds between wood fibers; . Control of surface gluing quality in highly absorbent substrates ; . Better sheet surface quality, independent of surface sizing; . Longer humidity absorption time by paper.

As thickening agent, thickens Industrialization of food¬ products to be marketed, pro¬ stuffs, sweets and candies viding a better appearance and/ Industrialization of or better physical properties for resins, paints, drinks,

use . detergents, shampoos , waxes soaps and cosmetics.

As a friction reducing agent. Drilling/cutting of materi¬ als.

As a binding agent for the Industrialization of drugs manufacture of tablets.

As adhering agent for Industrialization of agri¬ maintaining products on a cultural and forest defen¬ substrate. sives . Ceramics.

As an humidity retention Civil construction agent in concretes and for producing concretes, ceramics and light porous plasters.

. As a raw material for produc¬ Individual protection/ ing high mechanical strength snielding. materials.

The following examples disclose the invention in greater detail but do not limit the same. EXAMPLES

Example 1 - Obtaining of cellulose microfibrils a. Cleaning of the cellulosic material.

Cellulose microfibril networks, with a thickness of 0,25 cm and a humidity content of 99%, obtained by the fermenta¬ tion in nutrient medium of Acetobaterxylinum bacteria, were subjected to a bath of an alkaline aqueous solution ^' at 5% concen tration (pH 11) , for a period of three hours at room temperature.

After diffusion of the alkaline solution into the biological material, the microfibril networks were washed in running water for a period of four hours to ensure total elimina

tion of alkaline solution.

The microfibril networks were then immersed in a so¬ dium hypochlorite solution at 1% concentration, for three hours at room temperature and washed in running water until no more chlorine odour could be detected, this taking five hours, b. Maceration of the microfibril networks The duly cleaned cellulose microfibril networks were ground and macerated by means of a device provided with rotating blades driven at 1400 revolutions per minute, with the addition of a volume of water approximately equal to the volume of the microfibril network (having a humidity content of about 99%) .

Since the cellulose microfibrils obtained by the process of this invention have excellent properties for a variety of applications, such as papermaking and as a raw mater_i al for film forming, adhering agents, thickeners, binding agents and humidity retention agents for aqueous solutions, the tests hereinafter described were effected to determine the microfibril behaviour in certain kinds of uses .

1 - Influence of the microfibrils on the paper proper- ties and on the retention of fines and other additives.

2 - Influence of the microfibrils on the mechanical properties of the paper.

When applied to wood fiber pulp, the microfibrils provided a greater adhesion between fibers for a material of similar chemical nature, according to the greater number of hydrogen bonds developed during the drying of the paper.

A more intimate contact of the fibers, promoted by the surface tension action of evaporated water and the presence of a greater amount of cellulose in fibriiar form, allowed better chemical adhesion of the pulps and provided greater mechanical strength during the use of the paper produced. Considerable increases in strength over papers without the addition of this product were observed during more critical uses of the paper (100% relative humidity) at high humidity content. Other important factors for the use of cellulose mi¬ crofibrils as a paper additive, which are not observed with a great number of products employed in internal sizing are the simultaneous gains in tensile strength, tearing and bursting properties .

In order to determine the effect of the microfibrils on paper strength, paper sheets with/without the addition of microfibrils were prepared at different concentration levels, that is : 0%, 2%, 4% and 6% (weight/weight) .

The microfibrils were added to the homogenizer of the fiber suspension, before forming the paper sheet, in non mechan¬ ically treated wood fibers after the wood chips cooking process for their preparation. Paper sheets were then prepared in a Type F/SS2 Regmed sheet forming machine and dried at 90 C for 30 minutes. One third of said sheets, representing all microfibril concentration levels, was then placed in a weathering chamber for four days, at 65% relative humidity and 20°C, until reaching the equilibri- um humidity with the ambient.

The other two thirds of said sheets were stored at 100% of Rfi and 20 C, half of them staying under these condi¬ tions for four days and the other half for fourteen days, thus permitting partial and total adsorption of ambient humidity by the sheets, respectively.

During the weathering times above mentioned, the masses of the sheets were determined in an analytical balance (0,001 g precision) and the laboratory assays were carried out to determine the strength of the manufactured sheets , the results of which are disclosed in table 1. '

After the tests, all pieces of each paper sheet were dried at 0% humidity (103 + 2°C) and weighed at 0,001 g preci¬ sion to determine the humidity content. The humidity content of the sheets at the time of testing was calculated by the formula given below: ϋ% = ^{ml " m2} X 100 ml wherei :

U% = percentage humidity content ml = mass at the test m2 = dry mass at 0% humidity

The gains in paper strength, due to the addition of microfibrils to the cellulosic pulp, are shown in table 2.

All evaluations effected conform to the standards established by ABNT - Brazilian Association of Technical

Standards - utilizing the following mechanical assay equipment:

Evaluated Equipment Type of

Strength Manufacturer Equipment

Tensile Regmed RE/A-30

Bursting Regmed MT/MOT-A

Tearing Regmed ED-1600 ,

TABLE 1 - INFLUENCE OF ADDING CELLULOSE MICROFIBRILS TO KRAFT PROCESS CHEMICAL PULP*, WITH PINUS SP. WOOD, ON THE TENSILE, TEARING AND BURSTING FACTORS, AT DIFFERENT LEVELS OF PAPER HUMIDITY CONTENT.

*NON MECHANICALLY PROCESSED PULP (SR° = 15, 17,17 AND 20, FOR ADDITIVE LEVELS OF 0%, 2%, 4% AND 6%, RESPECTIVELY)

TABLE 2 - GAINS IN TENSILE, TEARING AND BURSTING FACTORS DUE TO ADDING CELLULOSE MICROFIBRILS TO PINUS SP. KRAFT PROCESS CHEMICAL PULP* - IN PERCENTAGE

*NON MECHANICALLY PROCESSED PULP (SR° = 15, 17, 17 AND 20, FOR ADDITIVE LEVELS OF 0%, 2%, 4% AND 6%, RESPECTIVELY)

3 - Influence of microfibrils of the physical proper¬ ties of the paper.

By evaluating paper sheets manufactured from Eucalyp¬ tus sp. bleached wood pulp, obtained by a Kraft process, increases in the whiteness of the formed sheet were observed with the addition of cellulose microfibrils to a wood fibers pulp, as hereinbefore described.

By using this material at 6% on a sheet dry weight basis, a whiteness increase of 1,5° GE without other additives was obtained, and when combined with calcium carbonate, the whiteness was significantly increased by increasing the proportion of this water soluble product. The excellent reten¬ tion of the calcium carbonate applied, in its turn, was provid¬ ed by the high water and aqueous solution retention capacity of the material of the present invention. In table 3 below, the values obtained experimentally for this purpose are given.

TABLE 3 ^" - INFLUENCE OF THE ADDITION OF CELLULOSE MICROFIBRILS

ON PAPER WHITENESS AND RETENTION OF CALCIUM CARBONATE.

CaCo added to WHITENESS DEGREE (°GE) (a) fiber suspension (%) Controls Samples made from Gains 6% cellulose microfibrils

0,00 70,5 72,0 1,5 0,06 71,5 74,6 ³ ,1 0,09 71,3 74,0 ³ ,7

(a) Regmed Type AL/OP - Dig whiteness meter

The opacity of the paper, due to the small amount of calcium carbonate used in the cellulosic pulp, has apparently not been effected within the individual groups presented in table 4. However, a reduction of said property is observed ■ between the groups for a material with 6% cellulose microfibrils when compared with the controls. This is due to the fact that microfibrils better occupy the inner space of formed sheets, reducing their thickness and,thus their opacity.

TABLE 4 - INFLUENCE OF THE ADDITION OF CELLULOSE MICROFIBRILS ON PAPER OPACITY.

CaCθ3 added to OPACITY (%) (a) fiber suspension (%) Controls Samples made from Loss 6% cellulose microfibrils

0,00 33,8 28,1 6,7 0,06 33,6 27,6 6,0 0,09 35,9 29,0 4,9

(a) Regmed Type AL/OP-Dig whiteness meter

The gradual reduction in the percentage of loss of opacity by increasing the calcium carbonate content was however again an indication of the high capacity of aqueous solution retention of the inventive material. Consequently, the expected results when applying cellulose microfibrils to a fiber pulp will be an excellent gain in opacity, at higher levels of con¬ centration of calcium carbonate or other water soluble products to be employed for this purpose.

4 - Retention of fines

The retention of fines was also observed as a conse¬ quence of the ability of the cellulosic microfibrils to promote flocculation of fibers in suspension.

In experiments with no other additive employed, the inventive material retained most of the fines contained in a chemical pulp ground from Eucalyptus sp. at mesh 180.

Table 5 below discloses weight per area and dry mass values for formed sheets , which show the effect of added cellu¬ lose microfibrils.

TABLE 5 - INFLUENCE OF ADDED CELLULOSE MICROFIBRILS ON FINES

RETENTION, IN A PAPER FORMED FROM EUCALYPTUS sp. CHEM¬ ICAL PULP.

PULP CONDITION UNGROUND . GROUND (a)

Percentage of cellulose microfibrils employed 0% 6% 0% 6%

Weight per area value (g/m ² ) 62,84 62,61 61,44 62,88

Dry mass (g) 4,330 4,332 4,169 4,311

(a) Grinding in Jokro mill for 22 minutes

According to the values in table 5, it is seen that there were practically no changes in the weight per area and mass for paper sheets made from unground pulp, because no significant amount of fines was present in this condition.

On the other hand, for a paper made from ground pulp,

a significant loss was observed when the inventive product was not added.

A cellulose microfibrils addition of 6% (mass/mass) retained almost all fines in the ground pulp, resulting in paper sheets with weight per area and mass values similar to those produced as unground cellulosic pulps .

Since fines retention occurs in mechanical form, due to interlacing thereof with individual particles and fibrils in the inventive product, other kinds of particles can also be confined in the paper sheet. Thus, by using cellulose microfi¬ brils in the pulp, an advantage is found not only in fines retention, but also in the retention of other solid additives employed in producing paper, such as fillers and pigments. An amount of 2% microfibrils (the lowest percentage tested) in the wood fibers in suspension was deemed able to produce a high degree of flocculation.

Example 2 - Use of microfibrils for forming films . Like papermaking with wood fibers , cellulose micro¬ fibrils may be used. for producing special films. From a cellulose microfibrils suspension of known consistency, volumes allowing the manufacture of films with a weight per area value of 10 g/m ² were used.

Three different methods for forming films were employed: a) a simple drying of a suspension of microfibrils in vessels having a known surface area; b) forming films in a paper sheet forming machine - Regmed Type F/SS2-e; c) applying microfibrils to paper surfaces and then drying.

2.a - Film forming by the simple drying of a cellulo¬ se microfibril suspension.

Suspension volumes containing 3 grams of microfibrils (mass at 0% humidity content) were poured into vessels with a 300 cm ² surface, previously paraffined to avoid adherence of the dry films to the vessels .

Drying of the microfibril suspension 'was effected in a laboratory oven at 40 + 2°C until total elimination of humidi- ty.

The films obtained were then taken for microscopic examination, where a completely homogeneous structure was observed, with no visible porosity at 400 times magnification.

As a further test, the films were subjected to water and aqueous solution permeability tests. For this purpose, a microfiltering support and films cut to a size compatible with said support were used.

The tests demonstrated that the material did not allow free flow (through pores) of water and aqueous solutions, although it did allow flow via diffusion through the film, wet¬ ting a surface opposite to that in contact with the liquid.

This result shows that the cellulose film can be used for special purposes, allowing a given amount of liquids, fatty materials and oils or salts to pass to a liquid phase in a controlled manner (as a function of time and the film surface area) , permitting its use in several fields of application, such as in the production of films for automatic titration machines, in controlling the feed rate of drugs to wounds, of nutrients to plants and animals, among others. 2.b - Formation of films in a paper sheet forming machine.

To suspension volumes containing 1, 2 and 3 grams of cellulose microfibrils, water was added up to a total volume of seven liters (15 repetitions for mass level used) , which were then drained in the Regmed F/SS2 sheet forming machine (mesh 180), with vacuum assistance in the final phase.

The wet films were then dried under the effect of vacuum and temperature (.40 kgf/cm - 90°C) .

The films formed were weathered to 65% relative humi- dity and 20°C and then evaluated as to structure and permeabili¬ ty, according to the method used in example 2.a.

All films, independent of their thickness, had no pores and did not allow the free flow of water or aqueous solu¬ tions . However, the passage of liquids was allowed via diffusion through the film.

Although the films were produced under the effect of vacuum, there was no significant change of thickness among the sheets, these having the same mass of microfibrils made by the methods described in this and the previous example. This shows

that in both cases there occurs a total accomodation of micro¬ fibrils forming the sheets, with the maximum chemical adhesion possible.

Since these are films having properties identical to those produced by the method of the previous example, they may be used to control the diffusion of liquids, fatty materials, oils or salts .

2.c - Formation of films on the surface of papers.

A water suspension, containing 1% cellulose microfi- brils, was prepared for application to the surface of papers.

Two kinds of paper were used to receive the microfi¬ brils : a) one having high water absorbency; and b) one having low water absorbency. On the surface of the two kinds of paper, 1000 ml of suspension per square meter of paper were spread evenly. After applying said suspension, the sheets were dried in an oven at 35°C until total elimination of excess humidity.

The surface treatment of said paper sheets resulted n the formation of films 0,02 mm thick, which remained adhered to the paper surface.

The more absorbent paper, which was the least mechan ically treated to promote surface smoothness and having the lowest internal sizing, allowed greater adherence to the film than the less absorbent paper.

The two kinds of paper were tested to evaluate water absorbency and paper printing quality by comparing their indivi dual surfaces,- that is, the one that received the microfibril film and that of the untreated opposite side. The adsorbency test evaluated the time consumed for the paper to absorb a water drop and demonstrated that the treated surface of the more absorbent paper had its absorption reduced by more than 10.000%, while the less absorbent one had a reduction of about 7.000%. Evaluation for printing quality of the paper was done after printing both paper surfaces with conventional print ing machines .

The evaluation considered individually the printing quality by itself and the occurence or not of ink migration

from one surface to the other.

As a result, a significant improvement of the print¬ ing quality was observed in both kinds of paper covered with microfibrils. The ink migration, which occured in the more absorbent paper from the untreated surface to the microfibril treated one, was not found in the opposite direction

The results obtained show that the cellulose micro¬ fibrils may be used to improve the properties of that surface of paper, so as to make it less liquid absorbent and to give it a finer texture, which is directly related to the printing qualit .

Example 3 - Use of cellulose microfibrils to make a material with high impact resistance properties.

A microfibril suspension obtained by a maceration process was filtered and centrifuged to reduce humidity, reach¬ ing about 5% of solid material.

The pasty material was then placed in a vessel for oven drying until reaching a humidity content of 90% (mass/mass) when it started to show a hardened surface. It was then manually blended to become homogeneous and spread over the tray, where it was dried in a ventilated oven (50°C) until total drying.

The dry material volume corresponded to approximately 1:30 of the paste obtained by centrifugation. This material, in the form of a flat board 8 mm thick, was subjected to impact tests, by shooting the same with 22 and 38 caliber bullets.

The action of impact on the board made from microfi¬ brils showed the high resistance of said material and its damp¬ ing ability due to its plasticity.

When shooting three meters away from the material, it was pierced to a depth of only 2 mm with 22 caliber bullets and of only 3,5 mm with 38 caliber bullets.

Other types of mechanical strength were not tested, since the main purpose of this experiment was to evaluate the performance of the board as a protection material, particularly for shielding and bulletproof vests. In that respect, the results show that a material made from cellulose microfibrils has excellentimpact resistance and enough plasticity for the intend¬ ed purpose.