CELLULOSE FIBERS FOR CEMENT REINFORCEMENT

Abstract: Cellulose fibers such as wood pulp are made more suitable for reinforcement of cement products by a treatment which reduces their swelling in aqueous and alkaline mediums. The fibers are dispersed in water, allowed to swell, and impregnated with a solution of a titanium and/or zirconium chelate compound. After drying, the fibers are heated to react the chelate compound(s) with the hydroxyl on the cellulose fibers, preferably to produce cross-linking between hydroxyl group residues. The treated fibers are more stable in cement media, and, despite their increased hydrophobicity, are dispersible in cement slurries to give good web formation in the manufacture of cement products such as sheet. They impart improved flexural strength and modulus to cement products compared with untreated cellulose reinforcing fibers.

Description: Cellulose fibres for cement reinforcement This invention relates to cellulose fibres suitable for cement reinforcement, and is concerned with a process for making cellulose fibres more suitable for that purpose and with fibre-reinforced cement products incorporating such fibres. Substantial activity is being directed to developing reinforcing fibres for cement which replace the asbestos fibres formerly used. Cellulose fibres are being used for this purpose because of their capacity for dispersing in cement slurries to form webs in the manufacture of fibre-reinforced cement products. However, cellulose fibres are susceptible to swelling and degradation in the alkaline cement medium and this tends to reduce their performance as a reinforcement. According to this invention, a process for making cellulose fibres more suitable for cement reinforcement is characterised by dispersing the fibres in an aqueous medium which swells the fibres, impregnating the swollen fibres with a titanium chelate compound and/or a zirconium chelate compound in solution, drying the fibres, and then effecting reaction between the chelate compound(s) and the hydroxyl groups on the cellulose fibres to link titanium and/or zirconium radicals to residues of said groups. Preferably the aforesaid chelate compound(s) react with the hydroxyl groups on the cellulose fibres to form cross-links between residues of hydroxyl groups. The cellulose fibres are preferably wood pulp fibres, but other natural or regenerated cellulose fibres, for example viscose fibres, may also benefit from treatment by the process of the invention. _O PI The invention includes cellulose fibres having an improved suitability for cement reinforcement after treatment by the process of the invention. Cellulose fibres treated by the process of the invention have an enhanced stability against swelling, particularly if cross-linked as described. Moreover, the stabilising effect is apparent not just on the surface of the fibres but throughout the body of the fibres. This is the result of dispersing the fibres in an aqueous medium and allowing them to separate and to swell so that the chelate compound(s) can thoroughly impregnate the fibres. The chelate compound(s) may be added to the same aqueous medium used to disperse and swell the cellulose fibres and may be added at the same time as the fibres or later, after they have been dispersed. Preferably the chelate compound(s) are already in. solution before being added to the aqueous dispersion medium. The use of the chelated form of compound makes it possible to use an aqueous medium to disperse and swell the cellulose fibres and to act as a vehicle for impregnation because, unlike other titanates or zirconates, the chelated compounds resist hydrolysis by water at ambient temperatures. Thus, it is possible to control the conditions during impregnation and the subsequent drying step so that there is minimal hydrolysis of the chelate compound(s) by the water, and subsequently ' to treat the dried fibres to effect the desired reaction with the hydroxyl groups of the cellulose fibres when there is little or no water present to effect preferential hydrolysis. Conditions which minimise hydrolysis during impregnation are the maintenance of the aqueous impregnation medium at ambient temperature and preferably at a low solution pH. If alkaline conditions are to be used to enhance the swelling of the cellulose fibres,, then it is preferable to inhibit water hydrolysis of the chelate compound(s) by incorporation, for example, of a polyhydroxy compound such as sorbitol in the aqueous medium. The aqueous medium may be mechanically extracted from the impregnated fibres, suitably to a solids concen- tration of 20 to 50, preferably 30 to 35, per cent by weight, prior to final drying. The usual equipment for hydroextraction may be used including porous screens, squeeze rollers and rotary extractors. The hydroextracted fibres may be dried as a fixed or fluidised bed of fibres using a current of warm air as the drying medium. Hydroly¬ sis of the impregnant chelate compound(s) by residual water is minimised during drying by keeping the temperature sufficiently low. Generally a temperature of about 40°C. to 60°C. is satisfactory, although with selected chelate compounds such as titanium dilactate higher drying tempera¬ tures can be used safely. After the impregnated fibres have been dried, then the desired reaction between the chelate compound(s) and the hydroxyl groups on the cellulose fibres may be effected, conveniently by heating the fibres, preferably at a temperature of at least 100 β C. Titanium chelate compounds are the preferred compounds, and a number of suitable compounds are commercially available. These include those formed by reacting a titanate with the following chelating agents:- alkanolamines (for example, triethanolamine and diethanol- amine) ; -diketones (for example, acetylacetone) ; keto esters (for example, ethylacetoacetate) ; hydroxy acids (for example, lactic acid) and certain glycols (for O FI example, octylene glycol) . The preferred titanium chelate compounds are titanium lactate, triethanolamine titanate and titanium acetylacetonate. The concentration of the chelate compound(s) impregnated into the cellulose fibres does not need to be greater than 10 per cent by weight based upon the dry weight of the cellulose fibres; indeed greater concentrations may have a deleterious effect by embrittling the fibres. A preferred range of concentration is 0.1 to 5 per cent by weight based upon the dry weight of the cellulose fibres, and within this range the optimum concentration varies according to the reactivity of the particular chelate compound and the process conditions employed. The desired concentration of the impregnant may be obtained by appropriate settings of the impregnating solution concentration and of the solids concentration to which the impregnated fibres are hydroextracted before drying. An aqueous medium is used to disperse and swell the cellulose fibres and, preferably) to impregnate them with the chelate compounds, and, as aqueous processes are invariably used in the processing of cellulose fibres, the process of the invention is readily accommodated into existing process and equipment schemes. Wood pulp is a basic and inexpensive source of cellulose fibres and its manufacture involves aqueous processing. The process of the present invention may be carried out in a pulp mill on wet pulp prior to the final drying and baling stages, with suitable- modification and/or addition to the drying plant so that the treated pulp can be first dried under non- reactive conditions and then heated to effect reaction. Cellulose fibres treated by the process of the invention have increased hydrophobicity but, possibly because the effect is not concentrated at the surface of the fibres, they remain wettable by water. This is important for even dispersion of the fibres in aqueous cement slurries so that uniform webs may be formed from the slurries for making fibre-reinforced cement products such as sheet and board. The invention includes a fibre-reinforced cement product in which the reinforcing fibres comprise cellulose fibres which have titanium and/or zirconium radicals linked to residues of hydroxyl groups on the cellulose fibres, preferably with the titanium and/or zirconium radicals forming cross-links between said hydroxyl group residues. The cellulose reinforcing fibres suitably incorporate up to 1.0 per cent by weight, preferably 0.01 to 0.5 per cent by weight, of titanium, or zirconium or titanium and zirconium together, based upon the dry weight of cellulose fibres. The fibre-reinforced cement product may incorporate up to 10 per cent by weight of the treated cellulose fibres based upon the dry weight of the product. It may also incorporate other reinforcing fibres, especially high modulus fibres, that is fibres having a modulus in excess of 10 G Pa, such as high modulus poly(vinyl alcohol) fibres and high modulus acrylic fibres. Usually the latter are incorporated in the cement product in lower concentration than the treated cellulose fibres. The invention is illustrated by the following examples:- Example 1 100 gms of compressed bleached Kraft pulp (" apponia" pulp) was defibrated with a mechanical blender in 4 litres of an aqueous solution containing 125 gms of a 50 " per cent by weight aqueous solution of titanium dilactate ["Tilcom" TL (Registered Trade Mark) produced by Titanium Intermediates Limited] . After steeping for 1 hour, the impregnated pulp fibres were separated from the liquor in a hydroextractor to a solids concentration of 26 per cent by weight, and had a pick—up of titanium dilactate of 4.4 per cent by weight based upon the dry weight of the pulp fibres. The wet pulp was dried to a constant weight in air at a temperature of 105°C. over a period of 1 hour and then heating was continued at a temperature of 105°C. for 15 hours to ' effect reaction between the impregnated titanium dilactate and the hydroxyl groups on the cellulose of the pulp fibres. The moisture regain of the treated pulp fibres at a temperature at 20 β C. and a relative humidity of 90 per cent was 12.0 per cent by weight compared with 15.3 per cent by weight for untreated pulp fibres. The liability of the treated fibres to swell was assessed in water and normal (N/l) sodium hydroxide solution by steeping samples of the treated pulp fibres in such solutions at a temperature of 15°C. for 1 hour, and comparing the weight increases with those obtained for untreated pulp fibres given the same test. Weights were measured after identical 10 minute centrifuging of the steeped fibres to remove free liquid. The results were as follows:- Sample Weight Increase (per cent) Untreated pulp in water (Control) 139 Treated " " n (Example) " 78 untreated " " NaOH (Control) 227 Treated " " B (Example) 126 In order to test the performance of the treated fibres as OMH a reinforcement for cement as compared with the untreated fibres, composite cement bars were made. The fibres were dispersed in an aqueous slurry of Portland cement at a concentration of 6 per cent by weight based upon the weight of the dry composite. The fibre- containing slurry was compressed into bar moulds and cured for a period of 14 days, at 100 per cent relative humidity for the first 7 days and under ambient conditions thereafter. The bars were than tested for flexural strength and flexural modulus, both dry and wet, using the method of British Standard No. 4024-1981. The results are shown as follows:- Sample Flexural Strength Flexural Modulus M Pa G Pa Dry Wet Dry Wet Untreated Pulp (Control) 14.4 10.4 (70.0) 12.5 9.4 (75.2) Treated Pulp (Example) 16.5 12.3 (74.5) 16.7 15.4 (92.2) The figures in brackets are the percentage retention of properties in the wet state compared with the dry and show a significant improvement for the treated pulp, particularly with respect to flexural modulus. Example 2 The procedure of Example 1 was repeated but using 70 gms of zirconium acetylacetonate powder dissolved in a water/acetone mixture instead of titanium dilactate. The treated pulp fibres had a moisture regain at a temperature of 20°C. and 90 per cent relative humidity, equal to 12.3 per cent by weight compared with 15.3 per cent for the uπreated pulp fibres. Example 3 Staple fibres of regenerated cellulose made by the viscose process ("Fibro" - Registered Trade Mark) were dispersed in an aqueous solution of titanium dilactate ("Tilcom" TL) . The solution concentration was adjusted to give an impregnation level of titanium dilactate after hydroextraction of 5 per cent by weight based upon the dry weight of cellulose. Another sample of the same fibres was similarly impregnated but at the 10 per cent level. Both fibre samples were dried in air at 60°C. and then heated for 1 hour at a temperature of 105°C. to effect reaction between the titanium dilactate and the hydroxyl groups on the regenerated cellulose fibres. The treated fibres showed considerably reduced swelling in water, and in normal (N/i) sodium hydroxide solution compared with untreated fibres when assessed as described in Example 1. The results were as follows:- Sample Weight Increase (per cent) untreated fibres in water 82 , . 2 Treated " ( 5% chelate) 36 , .1 (10% chelate) 32 , . 3 Untreated fibres in NaOH 159 , . 2 Treated ■ " ( 5% chelate) 115 , . 2 " (10% chelate) 111 , . 5 Example 4 450 gms of compressed bleached Kraft pulp ("Lapponia" pulp) was defibrated with a mechanical blender OMH in 15 litres of an aqueous solution containing 225 gms of an 80 per cent by weight solution of triethanolamiήe titanate in isopropyl alcohol ("Tilcom" TET) , 225 gms of a 65 per cent by weight solution of ethoxy isopropoxy 5 titanium bisacetoxyacetonate in isopropyl alcohol ("Tilcom" Pl-2) and 225 gms of acetic acid. The dispersed pulp was steeped for 1 hour in the solution and was then filtered off from the solution and squeezed to a solids content of 30 per cent. The pick-up 10 of the titanium chelate compounds was 7.1 per cent by weight based upon the dry weight of the pulp fibres. The wet pulp was dried to a constant weight in air at a temperature of 40°C. over a period of 16 hours. It was then heated in an oven at a temperature of 140°C. for 15 2 hours to effect reaction between the titanium chelate compounds and the hydroxyl groups on the cellulose of the pulp fibres. A comparison was made between the performance of the treated pulp fibres and untreated pulp fibres as web 20 formers in the production of cement composites reinforced by high modulus poly(vinyl alcohol) fibres. Each sample of pulp was disc refined to a freeness of 40° Schopper Riegler and dispersed in an aqueous cement slurry. The solids content of the slurry comprised:- 25 Portland cement 85.5 parts by weight Bowl clay (Hy od AT) 10.0 " " " High Modulus PVA Fibre 1.0 " " " (Unitika HM1 grade 10 mm staple) Refined pulp fibres 3.5 " " " The slurry was formed into composite cement bars as 30. in.Example 1, and the wet flexural strengths and the dry densities of the bars were measured. The results were as follows:- Sample Wet Flexural Strength Dry Density (M Pa) 3 Untreated Pulp (Control) 14.1 1,836 Treated Pulp (Example) 14.8 1,742 If allowance is made on a linear scale for the different densities of the bars, then the wet flexural strength of the bar incorporating the treated pulp is about 11.0 per cent greater than that of the bar incorporating the ntreated pulp. Example 5 "Lapponia" pulp was treated by the procedure of Example 1 but to a pick—up of titanium dilactate on the pulp of 2.2 per cent by weight based upon the dry weight of the pulp fibres. The pulp was dried as before at a temperature of 105°C. over 1 hour and then split into five samples which were heated to effect reaction between the titanium dilactate and the hydroxyl groups on the cellulose of the pulp fibres at five different conditions. Each treated sample of pulp was beaten in a "Lampen" mill for 40,000 revolutions and then made into a paper according to Standard T.A.P.P.I procedure T 200. The papers were produced purely as a method of testing the pulp fibre properties in relation to the treatment conditions and, as the results in the following Table show, there is no intention to demonstrate the suitability of the treated fibres for making paper. The tests used to " measure the various properties of the papers are indicated in brackets. OHH TABLE The reduction in pulp freeness, breaking strength and porosity in conjunction with the increased capillary rise, are consistent with an increasing extent of .cross- linking as the reaction conditions are increased in severity. Example 6 300 gms of compressed bleached Kraft pulp (Lapponia pulp) were introduced into a mechanical blender together with 10 litres of an aqueous solution containing 150 gms of an 80 per cent by weight solution of triethanolamine titanate in isopropyl alcohol ("Tilcom" T.E.T.), 150 gms of a 65 per cent by weight solution of ethoxy isopropoxy titanium bisacetoxyacetonate in isopropyl alcohol ("Tilcom" Pl-2) , and 60 gms acetic acid. The blender was operated so that the pulp was defibrated in the solution over a period of one hour. After this treatment, the pulp was filtered off from the solution and squeezed to remove excess liquid. The pick up of the titanium compounds was 4.3 per cent by weight based on the dry weight of the cellulose. The wet pulp was dried to a constant weight in air at a temperature of 40"C. over a period of 12 hours, and was then heated in an oven in air at a temperature of 140° C. for two hours to effect reaction between the titanium chelate compounds and the hydroxyl groups on the cellulose. The resulting fibres had an increased hydrophobicity and a reduced swelling in water and in alkaline solutions, the extent of the reduction being greater in the latter case. The fibres remained sufficiently water wettable to be readily dispersible in aqueous media. In order to test their performance as a reinforcement for cement, they were beaten to a freeness level of 55° Schopper Riegler and then dispersed in an aqueous slurry of Portland cement in amount of 5 per cent by weight based upon the dry weight of the cement plus fibre. The fibre-containing slurry was poured into bar moulds and allowed to set at room temperature in an atmosphere at 100 per cent relative humidity over a period of three days. Each set bar had a water content of 15 per cent by weight based upon the total weight of the bar. Drying of the bars was then effected in air at 80°C. over a further 24 hours. The cement bars were tested for flexural strength and for flexural modulus, under both dry and wet conditions, using the method of British Standard No. 4624- 1981. The results are shown as follows:- Flexural Strength Flexural Modulus (M Pa) (G Pa) Dry Test 17.1 12.0 Wet Test 10.5 9.7

Claims: CLAIMS 1. A process for making cellulose fibres- more suitable for cement reinforcement, characterised by dispersing the fibres in an aqueous medium which swells the fibres, impregnating the swollen fibres with a titanium chelate compound and/or a zirconium chelate compound in solution, drying the fibres, and then effecting reaction between the chelate compound(s) and the hydroxyl groups on the cellulose fibres to link titanium and/or zirconium radicals to residues of said groups. 2. A process as claimed in claim 1, characterised in that the chelate compound(s) react with the hydroxyl groups on the cellulose fibres to form cross-links between residues of hydroxyl groups. 3. A process as claimed in claim 1, characterised in that the dried cellulose fibres incorporate up to 10 per cent by weight of the chelate compound(s) based upon the dry weight of the cellulose fibres. 4. A process as claimed in claim 1, characterised in that the dried cellulose fibres incorporate 0.1 to 5 per cent by weight of the chelate compound(s) based upon the dry weight of the cellulose fibres. 5. A process as claimed in claim 1 5 characterised in that the chelate compound is a titanium chelate compound formed by the reaction of a titanate and a chelating agent selected from the group comprising alkanolamines, diketones, keto esters, hydroxy acids and glycols. 6. A process as claimed in claim 5, characterised in that the titanium chelate compound is selected from the group comprising titanium lactate, triethanolamine ' titanate and titanium acetylacetonate. 7. A process as claimed in claim 1, characterised in that the aqueous medium is mechanically extracted from the impregnated fibres to give a solids concentration of 20 to 50 per cent by weight prior to drying. 8. A process as claimed in claim 1, characterised in that the dried fibres are heated to effect reaction between the chelate compound(s) and the hydroxyl groups on the cellulose fibres. 9. A process as claimed in claim 8, characterised in that the dried fibres are heated at a temperature of at least 100°C. 10. Cellulose fibres characterised by an improved suitability for cement reinforcement after treatment by a process as claimed in claim 1. 11. Cellulose fibres as claimed in claim 10 characterised in that the fibres comprise wood pulp fibres. 12. A fibre-reinforced cement product in which the reinforcing fibres comprise cellulose fibres,characterised in that the cellulose fibres have titanium and/or zirconium radicals linked to residues of hydroxyl groups on the cellulose fibres. 13. A fibre-reinforced cement product as claimed in claim 12, characterised in that the titanium and/or zirconium radicals form cross-links between residues of hydroxyl groups on the cellulose fibres. 14. A fibre-reinforced cement product as claimed in claim 12, characterised in that the cellulose fibres incorporate up to 1.0 per cent by weight of titanium or zirconium or titanium and zirconium together, based upon the dry weight of cellulose fibres. 15. A fibre-reinforced cement product as claimed in claim 14, characterised in that the cellulose fibres incor¬ porate 0.01 to 0.5 per cent by weight of titanium or zirconium or titanium and zirconium together, based upon the dry weight of cellulose fibres. 16. A fibre-reinforced cement product as claimed in claim 12, characterised in that the cellulose fibres are incorporated in a concentration up to 10 per cent by weight based upon the dry weight of the product. 17. A fibre-reinforced cement product as claimed in claimt 1122,, cchhaarraacctteerriisseedd in that the cellulose fibres comprise wood pulp fibres. 18. A fibre-ϊ-reinforced cement product as claimed in claim 12, characterised in that the cement product incorporates high modulus fibres having a modulus in excess of 10 G Pa, in addition to the cellulose fibres. 19. A fibre-reinforced cement product as claimed in claim 18, characterised in that the high modulus fibres comprise high modulus poly(vinyl alcohol) fibres and/or high modulus acrylic fibres.

Inventors: BLACKIE MERRICK STUART, POYNTON DAVID JOHN, BLACKIE, MERRICK, STUART, POYNTON, DAVID, JOHN
Applicants: COURTAULDS PLC
Application year: 1984
Main classification: C04B31
IPC codes: C04B16, C04B18, C04B20