GB1585074A

GB1585074A - Process for the manufacture of cellulose-polyurethane materials

Info

Publication number: GB1585074A
Application number: GB2272976A
Authority: GB
Original assignee: Wadeson F P
Current assignee: Wadeson F P
Priority date: 1977-05-16
Filing date: 1977-05-16
Publication date: 1981-02-25

Description

(54) PROCESS FOR THE MANUFACTURE OF CELLULOSE POLYURETHANE MATERIALS (71) I, FRANK PETER WADESON, a British Subject of 19 Sevington Park, Maidstone, Kent, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly des- cribbed in and by the following statement: This invention relates to the manufacture Of cellulose-polyurethane materials.

A wide range of plastics materials can be obtained by reacting diisocyanates with dihydric alcohols, and the use of polyfunctional isocyanates and/or polyhydric. alcohols generally results in the formation d cross-linked materials. Various catalysts can be used to increase the rate and extent of reaction. These polyurethane plastics have a great variety of uses.

Over the years, various proposals have been made for reacting the hydroxyl groups of the cellulose molecule with isocyanates. Since the first suggestion of this reaction in 1920, many applications of this reaction have been investigated and can be classified into processes involving cotton-based textile fibres, paper-based products and timber products.

Work in the field of cotton based textile fibres has been reviewed by various workers but it is interesting to note that the results obtained have not yet been used commercially to any significant degree.

The chemistry of the reaction of monoand di4socyanates has been studied in detail by Bayer, Angew. Chem. A 59 257 (1974).

He concluded that although urethane derivatives could be prepared by reaction of isocyanates with cellulose derivatives for example, nitrocellulose, ethyl cellulose and cellulose acetate, it was doubtful if a reaction was effected between the isocyanate and the hydroxyl groups of cellulose itself. He contended that reaction of the isocyanate with residual water in the cellulose structure, which was very difficult to remove, led to the formation fo substituted ureas and polymeric ureas on the fibres, even in the presence of a large excess of isocyanate.

Subsequent work using octadecyl iso cyanate tol improve the water repellency of cotton fibres tends ro support this view.

Since then however, many workers have claimed complete reaction of cellulose with mono-isocyanates but in the context of textile treatments this is considered undesirable as there is a tendency to destroy completely the character of the fibre.

In various work in this field undertaken by Gaissedet and Schneebeli U.S. Patent No.

1,357,450, Compt. Rend. 234, 738 (1952) and 236, 1034 (1953) and Assoc. Tech. Ind.

Papetriere, Bull 223 (1953), dried cotton cellulose was reacted with a large excess of phenol isocyanate in the presence of pyridine to give a colloidal suspension of a carbonate derivative. Treatment of various cotton fibres with a smaller proportion of reactant resulted in an improvement in the water repellent properties. It was stated however that the reaction with the hydroxyl groups of the ce11u- lose was only made possible by the swelling action of the pyridine, and that with other solvents, for example toluene, they were inaccessible. The influence of the solvent was confirmed by various research workers and the use of pyridine, dimethyl formamide and dimethyl sulphoxide was found to greatly enhance the extent of the isocyanate-cellulose reaction.

The improvement of properties of textile fibres has also been attempted by the application of water soluble bisulphite addition products of isocyanates. These materials fall into the classification of "capped" or "blocked" isocyanates which are stable and unreactive under normal ambient conditions but the isocyanate reactivity is released by their decomposition at an elevated temperature. Fabrics were treated by aqueous solutions of these derivatives and heated and dried at 1500C.

The development of isocyanate-treatments with paper has been largely directed towards coating processes and few significant attempts have been made in this area to achieve a chemical bond with the cellulose, the adhesion between paper and resin relying primarily on a good mechanical key.

Some work however has been carried out involving the direct application of isocyanates to paper with the aim of effecting improvements in wet strength and reducing its water absorption properties. The results obtained are analogous to the isocyanate modification of cotton textiles and have. not been com- mercially exploited to any significant extent.

The outstanding contribution to this field has been the work of Trout (U.S. Patent No.

3,485,575). His investigations were directed toward the improvement in stiffness of paperboard by graft polymerization. His studies covered a variety of materials and techniques which included radiation grafting of acrylonitrile and the application of a range od isocyanates in the vapour phase, in solution, and the use of "blocked" isocyanates.

The treatment of paperbcard by isocyanates in the vapour phase was carried out using reduced pressure and elevated tern- perature. The di-isocyanates used were toluene di-isocyanate (TDI), 1 ,6-hexamethylene diisocyanate (HMDI) and - trans-vinylene diisocyanate (TVDI). Increases in stiffness were observed for most samples, the best results being obtained with TVDI. The water content of the fibre before treatment was found to be critical. With a higher water content a higher degree of reaction with the isocyanate was obtained but the increase in stiffness of the samples relative to the extent of reaction was lower than with samples of a lower initial water content. This can be explained by the greater tendency for reaction of the isocyanate with water to form polyureas in preference to the urethane grafting reactions in the case of the samples of higher water content.

Experiments on the treatment d paperboard with "blocked" isocyanates involved the preparation of adducts of TDI and HMDI with alcohols, for example cyclohexanol, with phenols, for example p-methoxyphenol and p-cresol, with acetic acid and with sodium and ammonium bisuiphites. The sheets of paperboard impregnated with the adduct were then air-dried and cured at 1470C i.e., 300C above the dissociation point of the adduct.

Increase in stiffness was observed for most treated samples with the exception od the bisulphite adduct samples.

The investigation of the effect of treatment of paperboard by solutions of isocyanates covered the use of a range of diand tri-isocyanates in benzene, dimethyl sulphoxide (DMSO) or mixtures of these solvents. It was found that the most effective result was obtained using trifunctional isocyanates and it was concluded that both crosslinking and mechanical reinforcement mechanisms were involved, and the optimum effect was achieved by a mixture of DMSO : benzene of 1 : 5. A maximum increase in weight of 10 % was observed for this technique.

Further work has been reported on the treatment of pulp paper in the form of linear board by solutions od toluene di-isocyanate with the aim of improving wet strength and stiffness properties by crosslinking. It was found that treatment of pulp materials re sulted in great difficulties in subsequent papermaking processes.

The reaction of isocyanates in solution with paper has been applied to the production ob unusually low power factor capacitor materials. In U.S. Patent No. 2,806,190 the paper pulp was first dried by heating with benzene, and then refluxed in the presence of a solution of toluene di-isocyanate in trichloroethane. The finished paper sheet was then produced by normal production methods.

There have been many attempts to pro duce improved or reconstituted products from the treatment of wood waste products with iso cyanates or polyurethane compositions.

They cover a wide range of different approaches but differ from the work previously described in that the investigations are mainly directed towards a fairly crude technological process with a superficial technical basis.

A process developed in Japan (Chem. Abs.

7969822) involves the treatment ob wood pulp with suitably catalyzed solution of methanediplhenyldtisocyanate (MDI). If the pulp is ob a sufficiently high water content i.e., for Japanese cedar greater than 29 %, an expanded material is produced which is of value as an insulation board.

French Patent No. 1,522,491 describes a process whereby wood chips or waste fibres are first coated with MDI, then mixed with a polyol and moulded by the application of pressure and heat to produce structural panels.

The present invention is based on the observation that cellulose-polyurethane materials possessing advantageous properties can be produced by heating cellulose fibres impregnated with a blocked polyisocyanate and a catalyst, under compression.

The present invention therefore provides a process for the manufacture of a cellulosepolyurethane material which comprises the steps of impregnating a cellulose fibre material with a blocked polyisocyanate and a catalyst, and compressing the impregnated material and heating it to unblock the polyisocyanate and to cause the polyisocyanate to react with the cellulose.

Cellulose fibre materials which can be used in the process of the present invention are suitably those discussed above, that is to say wood and similar vegetable fibres, paper products and cotton textile materials. Materials which have proved to result in especially advantageous products are unbleached mech anically ground softwood, bleached kraft pulp, woven cotton textile fabrics and pulped waste paper products. The last of these has the additional advantage that it is a relatively inexpensive material.

It is preferred in the process of the present invention that the cellulose fibre material is substantially dry immediately prior to the heating step. As noted above, the presence of more than minor amounts of free water in the fibre material during heating will result in the selective formation of various ureas and polyureas on the surface od the fibres, instead of the desired formation od a cellulose-iso- cyanate bond. For the purposes of the present invention, the cellulose fibres should generally not contain more than about 5 % by weight of water, although substantially dry fibres are preferred.

When dry fibres are used, the stage at which drying is carried out will depend upon the method used to impregnate the fibre material with the blocked polyisocyanate and the catalyst. Clearly, if the blocked polyisocyanate and the catalyst are water soluble and if the fibre material is impregnated with the blocked polyisocyanate and the catalyst from aqueous solution, then drying will be carried out after impregnation. However, if impregnation is carried out from a nonaqueous system, drying may be carried out either prior to or subsequent to the impregnation step, although prior drying is preferred in order to avoid the possibility of premature unblocking od the polyisocyanate.

The precise nature of the polyisocyanate is of no great importance (the term polyiso cyanate being used herein to mean a compound having at least two isocyanate groups).

Good results can be obtained with any of the diisocyanates mentioned above, for example toluene diisocyanate, 1,6-hexamethylene diisocyanate; trans-vinylene diisocyanate and methanediphenyldiisocyanate. Methanediphe- nyldusocyanate is especially preferred.

The polyisocyanate is used in the process of the present invention as its adduct with a blocking agent, in order to prevent its reaction with any water present in the fibres and with atmospheric moisture. Blocked polyisocyanates, also known as "capped" polyisocyanates, are well known and can be produced simply by reacting the polyisocyanate with the blocking agent; for example, when a polyisocyanate is reacted with phenol in the presence od aluminium chloride, there is obtained a phenol urethane which dissociates into phenol and the original polyisocyanate upon heating to about 1 600C. These blocked polyisocyanates are highly stable at room temperature, but dissociate at elevated tem peratures, the precise temperature depending on the particular polyisocyanate and the precise blocking agent. The blocking agent can be any of those mentioned above i.e. alcohols, phenols and bisulphites, although bisuiphites are the only useful blocking agents forming water-soluble adducts. It is important to bear in mind, however, that whatever the nature of the blocking agent, it must neither interfere with the chemistry of the cellulose/iso cyanate reaction nor impart undesirable pro- perties to the final material.

An especially preferred blocked polyisocyanate is that manufactured by Bayer and sold under the name "Desmodur AP stable", which is described generally as a phenolmasked polyisocyanate (the word 'Desmodur' is a registered Trade Mark).

The catalyst can be any one of a number of compounds which are known to catalyse the formation of polyurethanes from hydroxylcontaining compounds and polyisocyanates, including various amines, stanneus salts, zinc salts and organo-metallic compounds, for example di-n-butyl tin acetate, provided that it is compatible with the solvent in which it is to be dissolved or dispersed for ins- pregnation of the cellulose fibres. Zinc octoate is preferred, especially when the blocked polyisocyanate is "Desmodur AP stable".

The solvent in which the blocked polyisolcyanate and catalyst are suitably dissolved or dispersed for impregnauon of the cellulose fibres must be capable of being evaporated from the impregnated fibres at a temperature well below the dissociation temperature of the blocked polyisocyanate, if necessary under reduced pressure. Whilst water can be used as the solvent when the blocked isocyanate is a bisulphite adduct, an organic solvent will generally be used. Blocked polyisocyanates are soluble in the majority od readily available volatile organic solvents, for example esters, ketones, giycolethers and sone alcohols and halogenated hydrocarbons, although they may be insoluble in aliphatic and aromatic hydrocarbons. In the process of the present invention, suitable solvents are, for example methanol, beryl alcohol, farfuryl alcohol, diacetone alcohol, ethyl, propyl, butyl and amyl acetates, acetone, methyl ethyl and methyl isobutyl ketones, cyclohexanone, methylcycloc hexanone, butyl glycol, bibenzyl ether, methyl glycol acetate, ethyl glycol acetate, 3-inethoicy- n-butyl acetate, cresol, xylenoil, methylene chloride and chlorobenzene.

In order to obtain a greater degree of cross-linking in the final cellulose-polyurethane material, a cross-linking agent can be included in the blocked polyisocyanate/cata lyst solution with which the cellulose fibres are impregnated. Trifunctional compounds, for example triethanolamine and glycerol, are preferred.

The blocked isocyanate/catalyst solution can also include a polyol, which serves to improve the flow properties and also to react with any excess polyisocyanate which does not react with the cellulose or with the cross linking agent, when present.

To carry out the process of the present invention, the cellulose fibre material is generally first dried to remove all residual moisture when the impregnation solution is nonaqueous. This can be achieved by drying in air at a temperature of about 105 C, to constant weight. The generally dried cellulose fibres are then impregnated with a solution of the blocked polyisocyanate and the catalyst and, if desired, a polyol. In genral, the impregnation solution will be mechanically homogenously mixed with loose cellulose fibres, for example ground wood fibres or pulp, whereas fibres in sheet form, for example a paper product or a cotton textile material, will be placed in and allowed to soak up the solution. Depending on the absorbtivity of the fibres, the amount of solution will usually be from about 2 to 10 times the weight od the fibres, preferably about 4 times the weight of the fibres. The solution will generally contain from 5 to 40 % by weight, preferably from 8 to 30 % by weight, based on the total solution, of the blocked polyisocyanate, and from 0.25 to 2 % by weight of the catalyst relative to the amount of blocked polyisocyanate. When a polyol is also included, this is suitably present in the solution in an amount of from 2 to 10 % by weight, preferably about 5 % by weight.

Similarly, the cross-linking agent, when present, is suitably contained in the solution in an amount of from 2 to 10 % by weight, preferably about 5 % by weight After impregnation excess solution, if any, can be allowed to drain off and the solvent can be removed by the application of gentle heat and, if necessary, a slightly reduced pressure until constant weight is attained.

In order to form the final cellulose-polyurethane material, the fibres are compressed and heated for a period and to a temperature which is sufficient to cause dissociation of the blocked polyisocyanate, and to permit the free polyisocyanate to react with the cellulose.

This temperature will generally be from about 10 to 500C above the dissociation temperature of the blocked polyisocyanate. The time and temperature will od course depend on the particular blocked polyisocyanate employed and can be determined by simple preliminary experiments. In the case of the preferred "Desmodur AP stable", the impregmated fibres are preferably heated to a temperature of from 145 to 1600C preferably for from 10 to 30 minutes, more preferably from 10 to 20 minutes.

When the fibres are in sheet or web form, they are suitably heated in a conventional hydraulic press with heated platens. The platens may be plain or provided with any desired surface pattern to provide the final material with a decorative or other relief sur face. In the case od loose fibres, it is neces sary to contain the fibres within a mould between the press platens or in a conventional compression mould. This mould may be such as to provide a simple sheet structure of any desired dimensions, or any desired shape.

The pressure applied to the fibres may vary considerably depending on the nature d the fibres and on the nature of the desired product Pressures of from 200 to 1000 psi are generally suitable.

The materials produced in accordance with the present invention have excellent mechani cal properties; more especially they possess extremely high flexural strengths and tensile strengths, which compare favourably with conventional fibre-reinforced plastics materials 'and plastics-laminated materials. These pro perties enable the composite to be used, for example in sheet or bar form as a wood substitute, or as machine parts, for example gear wheels.

The following Example illustrates the invention.

EXAMPLE.

The following materials were selected for use in the Example: (a) Unbleached, mechanically ground soft wood which has been flash dried, and has a relatively short fibre length.

(b) Prime bleached kraft pulp.

(c) Waste paper products which approxi mate in properties to product (a) above, re covered from high quality paper-plastics film laminates. (Recovered newsprint possesses similar fibre properties to (a) above).

(d) Cotton cloth.

Solutions of Desmodur AP Stable were prepared by reducing the crystals of material to a fine powder in a pestle and mortar and allowing the requisite - quantity to dissolve overnight in methylene chloride (previously dried over anhydrous MgSO4). The catalyst, zinc octoate, was added to the solution im mediately before the impregnation stage.

Three solutions were prepared having the following compositions (parts by weight)

Solution A B C Desmodur AP stable 250 125 75 Zinc octoate 2.5 1.25 1.25 Methylene chloride 750 875 875 Polyol 50 One part by weight of fibres (a) and four parts by weight of solution were brought into contact and mixed thoroughly to ensure homogeneity. In the case of the cloth (d) and pulp board (bathe cellulosic component was allowed to soak up the requisite quantity od solution in a metal dish. Excess solvent was then removed from the impregnated fibre by the application of gentle heat and vacuum until a constant weight situation was achieved.

All moulding operations were carried out using a hydraulic press with electrically heated, water cooled pllatens to produce product samples od area 36 square inches. The curing cycle for all moulding operations was 15 minutes at 150-1550C. The pressure ap plied depended upon the nature of the pro; duct desired and the mould being used.

Results (a) Wood pulp fibre Wood pulp fibre was impregnated with the three different solutions detailed above and the excess solvent removed as described above.

This yielded samples od various fibre : polyisocyanate ratios which were then subjected to moulding. In each case a simple metal frame mould was used and the pressure varied to produce optimum results.

In each case the moulding pressure was about that normally used for the moulding of phenolic resin laminates.

In order to investigate the extent of reaction of the, polyisocyanate with the cellulosic fibre, a sample of material was taken from the centre of one of the moulded sheets having an initial composition of 50 % fibre, 50 % polyisocyanate, and subjected to a prolonged solvent extraction procedure. A soxhlet apparatus was used and the sample was exposed to methylene chloride for 20 hours.

During this period a loss of weight of only 5 % was observed. This result can be considered as strong evidence for the presence of a high degree of reaction.

Tensile strength, and flexural strength and modulus determinations carried out on samples of the moulded material resulted in values substantially greater than those for the kraft pulp and cotton materials shown in Table I.

(b) Prime bleached kraft pulp This material was used in sheet form and the impregnation process was carried out on the sheet material after drying to constant weight. Only impregnation solution B was used for these experiments to obtain a material with a fibre to polyisocyanate ratio by weight of around 2 : 1.

The moulding cycle used was the same as for the wood pulp fibre but samples were prepared from two sheets of impregnated material crossplyed and moulded wtihout a frame mould. This produced excellent quality sheet mouldings 1.92 mm thick having a density of 1.27 g/ml.

Tensile strength, and flexural strength and modulus determinations were carried out on these samples and the results obtained are shown in the following Table I.

The procedures adopted were in accordance with BS 2782 Methods and 302D respectively.

(d) Cotton cloith laminates The cotton cloth had a weight of 38 g/m2 and was impregnated using solution B to give a fibre to polyisocyanate ratio by weight d around 2 : 1.

Samples were produced by moulding 4 ply, and 8 ply samples of impregnated sheet crossplied using the standard moulding cycle and no frame mould. Mouldings of excellent quality were obtained and the thicker samples subjected to tensile strength and flexural strength and modulus determinations. The results obtained are shown in the following Table I.

Typical values of these properties for phenolic laminates are included in Table I for comparison purposes.

Other Tests Samples of the kraft pulp materials were also subjected to a series of simple environmental tests.

(i) Dry heat Samples were subjected to 40 hours exposure in an air circulating oven maintained at 105 0C with no observed de terioration. The fact that no softening was detected confirmed that the bulk d the blocked polyisocyanate originally present had been reacted.

(ii) Low temperature After a 2 hour period of conditioning of a samll sample at - 25 C no deterioration was observed. Although the sample was not subjected to the formal flexural testing procedure in this state, it was shown that it could be flexed to a low radius of curvature without brittle failure even at this low temperature.

(iii) Water In water at normal ambient temperature, there was virtually no softening effect and no significatnt absorbtion of water.

Following Table II summarizes the experimental conditions described above.

TABLE I

Laminate Composition Tensile Flexural Flexural Wt % Density Thickness Strength Strength Modulus Sample Polyisocyanate g/ml mm Kg/mm2 Kg/mm2 Kg/mm2 Kraft Pulp 26.2 1.27 1.92 8.90 7.22 18.7 18.5 1057 7.20 17.1 7.50 18.4 6.43 18.4 6.68 18.9 6.58 Cotton 28.8 1.13 2.50 5.83 5.65 12.6 12.0 557 5.53 11.0 5.80 11.8 5.58 11.8 5.45 12.6 5.75 Phenolic 50 1.30 - 1.46 5 - 15 7 - 10 500 - 1500 Laminates TABLE II

Moulding Conditions Nominal Impregnating Fibre : Time Temp. Ram Pressure Density Fibre Solution Polyisocyanate Ratio (min) ( C) (tonnes) g/ml Wood pulp A 1 1 15 150-155 5 (a) A 1 1 10 1.39 A 1 1 10 1.34 Wood pulp C 2 1 15 150-155 4 - 6 1.34 (a) C 2 1 40 C + 1% H2O 2 1 10 C + 1% H2O 2 1 25 Wood pulp B 2 1 15 150-155 20 (a) Kraft 2 ply B 2 1 15 150-155 5 1.19 (b) B 2 1 10 1.23 B 2 @ 1 25 1.27 Cotton Cloth B 2 1 15 150-155 10 0.98 (d) 4 ply B 2 1 20 0.98 8 ply B 2 : 1 25 1.13

Claims

WHAT I CLAIM IS:

1. A process for the manufacture of a cellulose-polyurethane material which com- prises the steps of impregnating a cellulose fibre material with a blocked polyisocyanate and a catalyst, and compressing the impregnated material and heating it to unblock the polyisocyanate and to cause the polyisocyanate to react with the cellulose.

2. A process according to' claim 1, wherein the cellulose fibre material is wood fibres, a paper product or a cotton textile material.

3. A process according to claim 2, wherein the cellulose fibre material is wood pulp.

4. A process according to claim 2, wherein the cellulose fibre material is kraft pulp.

5. A process according to claim 2, wherein the cellulose fibre material is pulped waste paper. A

6. A process according to any one of claims 1 to 5, wherein the cellulose fibres contain not more than 5 % by weight of water.

7. A process according to any one of claims 1 to 6, wherein the cellulose fibres are impregnated with a solution of the blocked polyisocyanate and the catalyst in an organic solvent.

8. A process according to claim 7, wherein the blocked polyisocyanate is an adduct of an isocyanate and an alcohol or a phenol.

9. A process according to claim 7 or claim 8, wherein the solvent is removed from the cellulose fibres prior to the heating step.

10. A process according to any one of claims 7 to 9, wherein the solvent is an ester, a ketone, a glycol ether, an alcohol or a halogenated hydrocarbon.

11. A process according to any one of claims 1 to 6, wherein the cellulose fibres are impregnated with an aqueous solution of the blocked polyisocyanate and the catalyst and wherein the cellulose fibres are subsequently dried or substantially dried.

12. A process according to claim 11, wherein the blocked polyisocyanate is an adduct of an isocyanate and a bisulphite.

13. A process according to any one of claims 1 to 12, wherein the polyisocyanate is a diisocyanate.

14. A process according to claim 13, wherein the diisocyanate is toluene diisocyanate, 1,6-hexamethylene diisocyanate or transvinylene diisocyanate.

15. A process according to claim 13, wherein the dllsocyanate is methanediphenyl- diisocyanate.

16. A process according to any one of claims 1 to 15, wherein the catalyst is an amine, a stannous salt, a zinc salt or an organometallic compound.

17. A process according to claim 16, wherein the catalyst is zinc octoate.

18. A process according to any one of claims 1 to 17, wherein the cellulose fibres are impregnated with from 2 to 10 times their weight of a solution of the blocked polyisocyanate and the catalyst.

19. A process according to any one od claims 1 to 18, wherein the cellulose fibres are impregnated with a solution ob the blocked polyisocyanate and the catalyst which con tains from 5 to 40 % by weight, relative to the total solution, of the blocked polyiso cyanate and from 0.25 to 2 % by weight, relative to rhe blocked polyisocyanate, od the catalyst.

20. A process according to any one of claims 1 to 19, wherein the cellulose fibres are impregnated with a solution of the blocked polyisocyanate and the catalyst which also contains a polyol.

21. A process according to claim 20, wherein the solution contains from 2 to 10 % by weight of the polyel.

22. A process according to any one of claims 1 to 21, wherein the cellulose fibres are impregnated with a solution of the blocked polyisocyanate and the catalyst which also contains a crossAinking agent.

23. A process according to claim 22, wherein the solution contains from 2 to 10 % by weight of the cross-linking agent.

24. A process according to claim 22 or claim 23, wherein the cross-linking agent is triethanolam ine or glycerol.

25. A process according to any one of claims 1 to 24, wherein the impregnated cellulose fibres are heated to a temperature of from 10 to 50 C above the dissociation temperature of the blocked polyisocyanate.

26. A process according to any one of claims 1 to 25, wherein the impregnated cellulose fibres are heated for a period of from 10 to 30 minutes.

27. A process according to any one d claims 1 to 26, wherein the impregnated cellulose fibres are heated under a pressure of from 200 to 1000 psi.

28. A process according to any one of claims 1 to 27, wherein the cellulose fibres are loose fibres and are heated under pressure in a mould.

29. A process according toany one of claims 1 to 27, wherein the cellulose fibres are in sheet or web form and are heated under pressure between the platens of a press.

30. A process according to claim 1 carried out substantially as hereinbefore described.

31. A cellulose-polyurethane material when ever manufactured by a process according to any one of claims 1 to 30.