Title of Invention

"A PROCESS FOR PREPARATION OF AN EPOXY-MODIFIED PHENOL-FURFURAL AND COMPOSITES THEREOF"

Abstract

This invention relates to a process for preparation of an epoxy-modified phenol-furfural resin wherein pehnol-furfural resin is prepared by condensation polymerisation of phenol with furfural at a temperature of for example 140°C in presence of anhydrous potassium carbonate as condensation catalyst to obtain phenol-furfural resin wherein the mole ratio of phenol to furfural is 1.4:1.04, blending of powder phenol-furfural resin dissolved in ethyl alcohol with epoxy-resin dissolved in a solvent which is methyl ethyl acetone taken in a ratio of 80:20 with a variation of 3-5% to obtain Epoxy modified phenol-furfural resin.

Full Text

FIELD OF INVENTION This invention relates to a process for preparation of an epoxy-modified phenol-furfural resin and composites thereof. PRIOR ART Phenol-furfural resin are used for reinforcement of carbon fibre or glass fibre. These resins, owing to presence of an aromatic ring in them, provide good thermal protection. The composites made therefrom, are light weight and have high strength which make them suitable for airborne and commercial applications. During the impregnation of fabric with resin, no structural change takes place in the resin and the resin is referred to as B-stage resin. However, when the reinforced fabric is subjected to heat and pressure in a hydraulic press, the resin acquires a cross-linked structure and is referred to a C-stage resin. According to a process known in the art, (B-stage) epoxidised phenol-furfural resin is prepared by the reaction of novalac and epichlorohydrin in the presence of acid or base as catalyst. The disadvantage of the above process is that product some times gets cross-linked during preparation of B-staged resin and becomes useless. Another disadvantage of the above process is that during reaction, heat is liberated which causes increase in the reaction temperature which leads to uneven distribution of molecular weight in the product which is not desirable as the resin obtained thereby does not have uniform properties. Still another disadvantage of the above process is that during purification, the complete specification of the base, which is used to the extend of 40%, as a catalyst in the preparation of resin, is difficult. The presence of traces of base in the resin, which may be left after purification, may initiate local growth/cross-linking in the final product during storage and thus reduce the life of the product. OBJECTS OF THE INVENTION The primary object of the present invention is to propose a process for preparation of epoxy-modified phenol-furfural resin and their composites. Another object of the present invention is to propose a process for preparation of epoxy-modified phenol-furfural resin with improved inter-laminar shear strength. Still another object of the present invention is to propose a process for preparation of epoxy-modified phenol-furfural resin with improved flexural strength. Further object of the present invention is to propose a process for preparation of epoxy-modified phenol-furfural resin with improved char yield so that the reinforced carbon composite prepared there from has superior integrity of structure at higher temperatures. Still further object of the present invention is to propose a process for preparation of epoxidised phenol-furfural resin with superior flow properties which leads to better impregnation of fabric during reinforcement of carbon or glass fabric. Yet further object of the present invention is to propose a process for preparation of epoxidised phenol-furfural resin which provides reinforced composites with improved impact strength. Still further object of the present invention is to propose a process which provides a stable epoxidised phenol-furfural resin which does not undergo any cross-linking in structure unless heated to 170°C with cross linker. Even further object of the present invention is to provide a process which avoids cross-linking of polymeric chain when there is no-uniform heating during preparation with the result that the resin remains soluble and fusible. Still further object of the present invention is to provide a process which eliminates the use of base NaOH as catalyst which in the known processes causes cross-linking even if traces of it is left after preparation. Yet further object of the present invention is to propose a process which uses phenol-furfural resin in which there is narrow range of molecular weight distribution due to which the mechanical and thermal properties of the product obtained are uniform. STATEMENT OF INVENTION According to this invention there is provided a process for preparation of an epoxy-modified phenol-furfural resin wherein pehnol-furfural resin is prepared by condensation polymerisation of phenol with furfural at a temperature of for example 140°C in presence of anhydrous potassium carbonate as condensation catalyst to obtain phenol-furfural resin wherein the mole ratio of phenol to furfural is 1.4:1.04, blending of powder phenol-furfural resin dissolved in ethyl alcohol with epoxy-resin dissolved in a solvent which is methyl ethyl acetone taken in a ratio of 80:20 with a variation of 3-5% to obtain Epoxy modified phenol-furfural resin. According to the present invention there is provided a process for preparation of an epoxy-moditled phenol-furfural resin wherein phenol-furfural resin is prepared by condenstaion polymerisation of phenol with furfural in presence of anhydrous potassium carbonate as condensation catalyst as against the known process which uses sodium-hydroxide (NaOH) to the extent of 40% as a catalyst. In these known processes, elimination of NaOH used as catalyst poses difficulty and even traces of NaOH left after purification, lead to cross-linking which reduces the shelf life of the product. Further, in the conventional polymerisation process, the number of -OH groups or epoxy groups present in an average molecule or the length of aliphatic chain which imparts flexibility and toughness, can not be controlled precisely whereas in the present process, the number of average -OH groups present in phenolic resin can be predetermined and then blended with epoxy resin with known molecular weight or epoxide equivalent. Thus aliphatic moiety, epoxide groups and phenolic- OH groups can be controlled in this process effectively. In preparation of phenol-furfunal resin the mole ratio of phenol to furfural is kept to the order of 1.4 : 1.04. The ratio can be varied in order to get resin of desired composition. The final product is characterized with melting point, IR, viscosity in solution, phenolic group present and molecular weight wherein the molecular weight of phenol-furfunal resin is in the range of 500-600. The above resin can be blended with desired epoxy resin in different proportion in order to get rein with the required properties. The blended resin is mixed with 10% hexamethylene diamine as cross linker. For preparation of composite, carbon fibre is impregnated with resin. When phenol furfunal resin is blended with 20% of high molecular weight epoxy resin (molecular weith 2000) and impregnated on carbon fabric and cured, there is a 100% increase in flexural strength and 60% increase in interlaminar shear strength with respect to conventional phenolic resin. DESCRIPTION OF ACCOMPANYING DRAWINGS Fig. 1 (a): shows the synthesis of B-stage phenol-furfural resin. Fig. l(b): shows the formation of cross linked epoxy modified phenol-furfural resin. DESCRIPTION OF THE PROCESS According to the present invention, the epoxy modified phenol-furfural resin and their composites are prepared by the process involving following steps: a. Preparation of phenol-furfural resin Phenol furfural resin is prepared by taking 50 to 60% preferably 55 to 59% by weight of phenol, 0.5 to 2.0% preferably 1.0 to 1.2% by weight of anhydrous potassium carbonate and 40% to 45% preferably 41 to 43% by weight of furfural. After the reaction is complete, which can be noticed when evolution of water has ceased, heating is discontinued. The melting point of the product obtained, is checked. If the melting point of the product is less than 85°C, then heating is continued at about 140°C for some more time and checked again till the melting point of the product obtained is in the range of 85-90°. b. Preparation of epoxy-modified phenol-furfural resin The resin obtained as above is grinded to a fine powder. The powder resin is dissolved in ethyl alcohol to get a solution of 25 to 30% preferably 30-32%. A separate solution of epoxy resin like araldite 6097 is prepared in a solvent like methyl ethyl ketone so as to get 6-15% preferably 10-12% of resin in the solution under reflux. The two solutions of phenol-furfural resin and epoxy resin are then blended together thoroughly so that pehnol-furfural so that phenol-furfural resin to epoxy-resin is in the ratio of 80:20 with variation in the ratio of about 3 to 5%. The mixture of two solvents is then cooled to room temperature and to this cooled blend, is added, a cross-linked preferably hexamethylene tetramine also known in the art as hexamine to the extent of 8 to 12% preferably 10-11% by weight with respect to solid content in the blend. The composition thus prepared is diluted to get around 40% solid. The composition thus prepared is ready for fibrous reinforcement. e. Curing The resin composition prepared as above is curved by heating at about 150-170°C%. the extent of cross linking is determined from the quantity of insoluble fraction remaining after extraction with methyl ethyl ketone. The extraction is carried out by boiling the cured resin in methyl ethyl ketone for 20-30 minutes. The solvent is removed by filtration. The insoluble resin is washed several times with methyl ethyl ketone and dried at 150-160°C till constant weight of insoluble fraction is obtained. PREPARATION OF COMPOSITES Carbon fabric or glass fabric is cut into suitable size pieces. It is impregnated with resin solution by means of one inch brush. The heated fabric is allowed to dry to room temperature for 48 hours. The dry treated fabric is cut into suitable size for lamination. These layers are stacked together to get required thickness of composite. These layers are taken between two mild steel plates. The composite is prepared by-keeping the plates first at about 120°C at contact pressure between platens of hydraulic press. Successive contact and release of pressure of press plate ensures removal of air pockets etc. The operation is carried out for five minutes. Platen temperature is increased to about 170°C and composite is cured for one hour at about 50 psi pressure. The synergistic property of the epoxy-modified phenol-furfunal resin over its ingredients is its property of imparting flexibility to the composite prepared therefrom. The invention will now be illustrated with respect to an example which is intended to be an illustrative specific example and is not intended to be taken restrictively to imply any limitation on the scope of the present invention. WORKING EXAMPLE 133g of phenol was taken in a reaction vessel equipped with stirrer and condenser and the bath temperature was raised to 140"C. 2.7 g of anhydrous potassium carbonate was dissolved into it. 100 g of furfural was added, maintaining bath temperature 10 about 140°C for about 4 hours. When evolution of water has stopped, heating was discontinued. The melting point was checked. Heating and cooling was repeated till the melting point of the product obtained was in the range of 85-90°C. The resin was dissolved in ethyl alcohol after grinding to a fine powder and was blended with a 12% solution of epoxy resin in methyl ethyl ketone. Keeping ratio of phenol-furfural resin to epoxy resin to 80:20. 12% hexaminc, with respect to phenol-furfural resin was mixed thoroughly and composition was diluted to about 40%. For preparation of composite, carbon fabric was cut into suitable size pieces and these pieces were impregnated with resin by application with a brush to get about 30% resin fabric ratio. The impregnated carbon fabric pieces were stacked together and taken in a hydraulic press and cured The physical properties of the composite obtained are as in Table-I below: (Table Removed) Carbon char yield : between 51 to 61% at 700°C. pbw - Parts by weight. It is understood that the process of the above invention is susceptible to modifications, adaptations, changes by those skilled in the art. It is to be understood that such modifications, adaptations, changes are within the scope of the present invention which is set forth by the following claims: WE CLAIM;- 1. A process for preparation of an epoxy-modified phenol-furfural resin wherein pehnol-furfural resin is prepared by condensation polymerisation of phenol with furfural at a temperature of for example 140°C in presence of anhydrous potassium carbonate as condensation catalyst to obtain phenol-furfural resin wherein the mole ratio of phenol to furfural is 1.4:1.04, blending of powder phenol-furfural resin dissolved in ethyl alcohol with epoxy-resin dissolved in a solvent which is methyl ethyl acetone taken in a ratio of 80:20 with a variation of 3-5% to obtain Epoxy modified phenol-furfural resin. 2. A process for preparation of an epoxy-modified phenol-furfural resin as claimed in claim 1 wherein the said synthesis of phenol-furfural resin is carried out by taking 50 to 60% preferably 55 to 59% by weight of phenol, 0.5 to 2% preferably 1.0 to 1.2% by weight of anhydrous potassium carbonate and 40 to 45% preferably 41 to 43% by weight of furfural. 3. A process for preparation of an epoxy-modified phenol-furfural resin as claimed in claim 1 wherein the said epoxy-modified phenol-furfural resin, is mixed with 10 to 12% of hexamine as cross-linker. 4. A process for preparation of an epoxy-modifed phenol-furfural resin and composites thereof substantially as herein described. 5. Epoxy modified phenol-furfural resin and composites thereof as prepared by the process as claimed in claim 1 substantially described and illustrated herein.

Documents:

785-del-1999-abstract.pdf

785-del-1999-claims.pdf

785-del-1999-correspondence-others.pdf

785-del-1999-correspondence-po.pdf

785-del-1999-description (complete).pdf

785-del-1999-drawings.pdf

785-del-1999-form-1.pdf

785-del-1999-form-19.pdf

785-del-1999-form-2.pdf

785-del-1999-form-26.pdf

785-del-1999-form-3.pdf