Title of Invention	An improved process for the manufacture of natural fibre based composite laminates useful for making plain/corrugated sheets and products thereof
Abstract	An improved process for the manufacture of natural fibers based composite laminates useful for making plain/corrugated sheets and products thereof which comprises washing of natural fibers such as herein described to remove foreign materials, surface modifying the said washed fibers by immersing in a coupling agent solution such as herein described, followed by chopping to the required length, preparing non-woven strand mats using the said chopped surface modified fibers and mat forming water based polymeric agents such as herein described, impregnating the mats so obtained with hybrid resign, stacking a plurality of mats using adhesive to bond plain and corrugated core and sandwiching between two glass fabrics and compressing under gel coated brass plates at a pressure in the range of 1-2 MPa to obtain laminates, curing of laminates so obtained at room temperature for at least two hours followed by post-curing at a temperature in the range of 80°C-105°C for a period of at least one hour at a pressure of 0.5-1.5 MPa.

Title of Invention

An improved process for the manufacture of natural fibre based composite laminates useful for making plain/corrugated sheets and products thereof

Abstract

An improved process for the manufacture of natural fibers based composite laminates useful for making plain/corrugated sheets and products thereof which comprises washing of natural fibers such as herein described to remove foreign materials, surface modifying the said washed fibers by immersing in a coupling agent solution such as herein described, followed by chopping to the required length, preparing non-woven strand mats using the said chopped surface modified fibers and mat forming water based polymeric agents such as herein described, impregnating the mats so obtained with hybrid resign, stacking a plurality of mats using adhesive to bond plain and corrugated core and sandwiching between two glass fabrics and compressing under gel coated brass plates at a pressure in the range of 1-2 MPa to obtain laminates, curing of laminates so obtained at room temperature for at least two hours followed by post-curing at a temperature in the range of 80°C-105°C for a period of at least one hour at a pressure of 0.5-1.5 MPa.

Full Text	The present invention relates to an improved process for the manufacture of. natural fibres based composite laminates useful for making plain/corrugated sheets and products thereof. Emphasis on developing alternate building materials, especially wood substitute has been considered an active area of current material research because of acute shortage of timber and -rorsni t -y to connorvo the environment. Keeping this in view, investigation on role of natural fibres in polyester resin was undertaken. The product so developed can be used as wall panel, partition, door panel, roofing, table tops etc. Natural fibres such as jute, sisal, coir etc. are abundantly available in developing countries like India, China, Bangladesh, Srilanka, South Africa etc. They are ligno-cellulosic in nature consisting of helically wound cellulosic microfibrils in a matrix of lignin and hemicellulose. The strength of these fibres varies from fibre to fibre depending on their origin and physico -mechanical properties. Traditionally, these fibres are used for the manufacture of carpets, ropes, sacks, wall hangings, yarn handbags etc. However,because; of the advent of synthetic fibres and plastics, there is a steady decline in the use of natural fibres in their conventional markets. This necessitated the attention of scientists/technologists to search for new diversified applications of these fibres. The high tensile modulus and low elongation at break of these fibres indicate their reinforcing potentiality in composite matrices (St.John, D.A. and Kelli, J.M., "The flexural behaviour of fibrous plaster sheets", Cem. Conor. Res., vol.5, 1975, p. 347; Swift, D.G. and Smith, R.B.L.,"Sisal-cement composites as low cost construction materials," Appropriate Technol., vol.6, No.3, 1979, p. 6; Gram, H.E., "Durability of natural fibre in cement-based roofing sheets," J. Ferrocem., vol.17, No.4, 1987, p. 321). Various attempts have been made to use natural fibres as reinforcement in the form of strands, chopped, coarse needled pad and woven/non-woven chopped strand mat in polymer matrices for property improvement as well as applications development in various sectors (Chand, N., Verma, S. and Rohatgi, P.K., "Mechanical behaviour of sisal-polyester system," Internal Report, RRL, Bhopal, 1986; Owolabi, O., Czvikovszky, T. and Kovacs, " Coconut fibre reinforced thermosetting plastics", J. Appl. Polym. Sci. , Vol. 30, 1985, p. 1827; Pal, P.K., " Jute reinforced plastics: a low cost composite material," Plast.& Rubber Proc. Appl., Vol.4, No.3, 1984, p.215; Prasad, S.V., "Natural fibre based composites," Encyclopaedia of Composite Materials, Pergamon Press Pic., Headigton Hill Hall, Oxford U.K., 1989, p.197;Ranganathan, S.R., Pal, P.K., Raina, A.K., and Mitra, B.C., "A process for preparing jute based laminates and jute based laminates manufactured thereby," Patent Application No. 23/Cal/1989 dated 9.1.1989; Singh, B., Gupta, M., Verma, A. and Hajela, R.B., "Studies on Polymer composites based on sisal/polyester and glass/modified sisal fibre, fillers and polyester", Res. & Ind., Vol.39, 1994, p. 38). The advantages of using chopped strand mat are their light in weight, ability to provide good wetting & resin flow and easy adaptability in all forms of pressure moulding. Unidirectional sisal fibre/epoxy cylindrical tube and flat sheets (Paramasivam, T. and Abulkalam, A.P.J., "On the study of natural fibre composites", Fib., Sci. Technol., 7, 1974, p. 85), chopped sisal/polyester sheets (Satyanarayana, K.G. et al," Possibility of using natural fibre composites as building m,it;.ori aln" , Proc . Int. 1 . Conf . on Low cost housing for developing countries, India, 1984, p. 177), sisal mat-CNSL plain and corrugated laminates for roofing application (Bisanda, E.T.N. and Ansell, M.P., "Properties of sisal-CNSL composites", J. Mater. Sci., vol.27, 1992, p. 1690), Jute reinforced polyester for primary school buildings, grain silos and low cost housing (Winsfield, A.G., "Jute reinforced polyester projects for UNIDO/Government of India". Plast Rubber Intl., 4, 1979, p. 23), bagasse-phenolic composites for wall panels, roofing, door shutters, furnitures etc. (Salyer, I.O., and Usmani, A.M., " Utilisation of bagasse in new composite building materials," Ind. Eng. Prod. Res. Dev.,Vol 21, 1982, p.17) are some of the products described in the literature. Belmares et al . , ("New composite materials from natural hard fibres", Ind.Eng. Chem. Prod. Res. Dev., vol. 20, 1981, p. 555) have suggested the findings of palm/polyester composites extendable to other similar fibres such as sisal for making low cost composite building materials such as roofs, silos, low cost housing elements etc. However, lack of good interfacial bonding between the fibre and the matrix, poor resistance to moisture and susceptibility to environment make; these composites less attractive. In an effort to combat some of these aforementioned disadvantages, the methods for protecting the composites either by providing hydrophobicity to the natural fibre or by applying a gelcoat/glass fibre as a surfacing layer is a continuous subject of debate. Attempts have been made to prepare hybrid laminates with combination of glass and natural fibres in polyester resin to improve the impact properties, warping and environmental resistance (Pavithran, C., et al, "Impact properties of sisal-glass hybrid laminates", J. Mater.Sci., Vol.26, No.2, 1991, p. 455; Shah, A.N. and Lakkad, S.C., "Mechanical properties of jute reinforced plastics", Fibre Sci. Technol. , 45, 1981, pTM5) . In view of reducing the cost and improvement of stiffness properties of hybrid, the inclusion of particulate filler has been made to prepare particulate hybrid laminates as panelling materials (Singh, B., Gupta, M. and Verma, A., "Mechanical behaviour of particulate hybrid composite laminates as potential building materials", Const. & Build. Mater., 9, 1995, p. 39) . Viewing the importance of interfacial bonding, surface chemical modification of natural fibre was carried out by alkali treatment (Chand, N. and Rohatgi, P.K., "Adhesion of sisal fibre-polyester system", Polym. Commun. , Vol.27, 1986, p. 157), isocyanate modified cardanol (Joseph, K., Thomas, S. and Pavithran, C., "Effect of ageing on the physical and mechanical properties of sisal fibre-reinforced polyethylene composites," Comp. Sci. Technol., Vol.53, 1995, p. 99), resin treatments (Varma, D.S., Varma, M. and Varma, I.K.,"Coir fibre-3 Effect of resin treatment on properties of fibres and composites, "Ind. Eng. Chem. Prod. Res. Dev. , Vol. 25, 1986, p. 282), vinyl polymer grafting (Barkakati, B.C. and Robson, A., "Polymer deposition in sisal fibre : A structural investigation", J. Appl. Polym. Sci., Vol. 24, 1979, p. 269) and coupling agents treatment (Bisanda E.T.N. and Ansell, M. P. , "The effect of silane treatment on the mechanical and physical properties of sisal-epoxy composites", Comp. Sci., Technol., Vol.41, 1991, p. 165; Singh, B., Gupta, M. and Verma, A., "Influence of fibre surface treatment on the properties of sisal-polyester composites", Polym. Compos. Vol.17, No.6, 1996, p. 910; Varma, I.K., Ananthakrishnan, S.R. and Krishnamoorthy, S. , "Composites of glass/modified jute fabric and unsaturated polyester resin," Composites, Vol. 11, 1990, p. 77) . These treatments provide improved physico-mechanical properties and hygrothermal stability to the resultant composites as a consequence of enhanced interfacial adhesion. Choice of surface treatment depends on its specificity for a particular ressin. However, the benefits made by improving wetting or interfacial bonding are limited. Experimental studies have indicated that compatibility of surface-modified natural fibres with resin matrix is also a critical factor in obtaining the best mechanical properties of the resultant composites. In addition, literature has not revealed any information on the use of modified conventional resin matrix for natural fibre reinforcement to cope with moisture-induced degradation. Therefore, searching of new surface modification procedure based on water enriched coating compatible with resin matrix, easy method for producing a light weight chopped natural fibre strand mat and modification of conventional resin matrix against hydrolytic stability are imperative to obtain various performance based properties as well as commercial exploitation. The main object of the present invention is to provide an improved process for the manufacture of natural fibres based composite laminates useful for making plain/corrugated sheets and products thereof which obviates the drawbacks as detailed above. Another object of the present invention is to provide a process wherein the natural fibres have been used may be such as sisal, jute, coir, sunhemp etc. Another object of the present invention is to provide composite laminates of surface- modified natural fibres. Still another object of the present invention is to provide natural fibres based composite laminates using polyester- urethane hybrid resin. Yet another object of the present invention is to provide composite laminates useful for making plain/corrugated sheets and products thereof. Accordingly, the present invention provides an improved process for the manufacture of natural fibers based composite laminates useful for making plain/corrugated sheets and products thereof which comprises washing of natural fibers such as herein described to remove foreign materials, surface modifying the said washed fibers by immersing in a coupling agent solution such as herein described, followed by chopping to the required length, preparing non-woven strand mats using the said chopped surface modified fibers and mat forming water based polymeric agents such as herein described, impregnating the mats so obtained with hybrid resign, stacking a plurality of mats using adhesive to bond plain and corrugated core and sandwiching between two glass fabrics and compressing under gel coated brass plates at a pressure in the range of 1-2 MPa to obtain laminates, curing of laminates so obtained at room temperature for at least two hours followed by post-curing at a temperature in the range of 80°C - 105°C for a period of at least one hour at a pressure of 0.5 -1.5 MPa. In an embodiment of the present invention, the surface modification of fibers may be effected by immersing in 0.5 - 2% (by weight of fibers) aqueous solution of coupling agents such as organosilane, organotitanate, organozirconate and methacrylamide functional amine adduct of pyro-phosphato titanate. In another embodiment of the present invention, 8-15% (by weight of fibers) emulsion such as poly (vinyl acetate) emulsion is used for making chopped strand mats. In yet another embodiment of the present invention, 20-55% (by weight of fibres) hybrid resin used for impregnating the mats may be such as polyester-urethane hybrid resin prepared from refluxing diethylene glycol (2-5 moles), isophthalic acid (1-2 moles) and maleic anhydride (1-2 moles) under nitrogen atmosphere using conventional synthesis route which was then reacted with 5-20 weight % diphenyl methane 4,4' diisocynate. Still in another embodiment of the present invention, the curing of pressed laminate£3 may be effected at room temperature for a period of atleast 2 hours. Accordingly, the present invention provides products such as corrugated core composite panels for door materials, panelling, partitioning and roofing materials using the natural fibre laminates of the present invention. The process for making composite panel consists of several steps. First step involves surface modification procedure of fibres. Natural fibres were immersed and washed in water for 24 hours to ensure maximum removal of water solubles from the surface. These are air dried and heated at 105 ^ 5 C in an oven to a constant weight. The surface modification of natural fibres was carried out by immersing them in 0.5-2 % (by weight of fibres) aqueous solution of organotitanate, organosilane, organozirconate and methacrylamide functional amine adduct of pyro-phosphato titanate coupling agent and stirred continuously. The treated fibres were washed with respective solvent to remove physisorbed compounds from the fibre surface. The treatment conditions for optimum adsorption ot coupling agent onto natural fibres was selected on the basis of experiments performed under variation of certain parameters such as concentration (0.5-3 weight %) , pH(3-12), treatment time (15-240 minutes) , curing time - (30 - 240 minutes) and curing temperature (60-100°C). The choice of methacrylamide functional amine adduct of pyro-phosphato titanate surface modifier is due to its solubility in water eliminating risk of toxicity associated with the use of solvent besides providing good compatibility with polyester matrix and fire retardancy to the fibre. In the second step, a light weight chopped natural fibre strand mat was prepared by randomly arranged surface-modified fibres (3-6 cm) in the desired size. About 6-15 weight % of poly (vinyl acetate) emulsion in water was sprayed uniformly to the fibre entanglements. Evaporating excess water, the air dried sprayed sample was kept at 80°C for 4 hours. The hardened fibre entanglement was compressed in a hydraulic press between two cellophene lined brass plates at 80-100 C under a pressure of 1-2 MPa for 5-10 minutes to obtain smooth finished non-woven mat. The mats have moisture content in the range of 2-5 %. The main objective of using chopped strand mat over woven mat is to minimise resin consumption, easy removal of entrapped air on the mat surface, avoiding tenacity loss during weaving and good wetting out of all fibre strands through easy penetration of resin. The third step comprises preparation of laminating resin. The basic polyester is prepared by condensing diethylene -llycol (2-5 tnolc.M) and isophthalic acid (1-2 moles) at 200-215°C under nitrogen atmosphere until the acid number was reduced to approximately 40-70 (I) . Maleic anhydride (1-2 moles) was added to (I) after cooling down to 100-120°C. After the complete addition, the temperature- of the flask was again increased to 150-200°C to obtain acid value at the level of 12-24 (II). This polyester containing styrene(30-40 %) reacted with 5-20 weight % diphenyl methane 4,4' diisocyanate (MDI) to form polyester-urethane hybrid resin (III) . This resin was catalysed before laminate moulding. Excess of diethylene glycol is used to adjust acid number/viscosity relationship and provide more flexibility to the resultant resin as compared to higher molecular weight glycol. MDI is used to enhance tensile elongation of the hybrid resin. Benzoyl peroxide is selected as initiator over methyl ethyl ketone percftcide due to its effectiveness with isocyanate on long contact. N,N diethyl aniline is used as promoter for urethane reaction. The fourth step involves preparation of laminates. The chopped natural fibre strand mats were cut to the desired size and wetted with polyester-urethane hybrid resin containing 0.5-1 % benzoyl peroxide and 0.2 - 0.5 % N,N diethylaniline. The excess of resin was squeezed out through roller. The desired thickness of wetted mats ( 4-6 layers) were sandwiched between resin rich/ gel coated brass/steel plates and compressed in a hydraulic press for 2-4 hours at a pressure of 1-3 MPa.Glass fabric surfacing mat (30 g m ) was used on exterior surface. Gel coated glass fabric is used to provide environmentally resistant composite. Poly (vinyl alcohol) was used as a mould releasing agent.Corrugated sheet (3-4 layers natural fibre mats) was prepared on a matched pair of cast iron/ seasoned wooden block moulds having corrugated face. The laminates were cured at room temperature for 24 hours and then post-cured at 80-100°C for 3-5 hours at a pressure of 1-2 MPa. The demoulded sheets are saw cut and trimmed to form panels of desired size. In the fifth and final step, sandwich panel using natural fibre-hybrid resin corrugation as core (2-3 mm) and gel coated glass/natural fibre-hybrid resin plain sheet as face material' (3-4 mm) was prepared. The rough surface at the contact point of face panel and corrugation was created by sanding. Jointing of panels was done using isocyanate-modified polyester resin adhesive and then placed under a nominal pressure for 2'hours to ensure strength development at joints. In the light of background discussions on prior art, a concerted effort on identified gaps such as surface treatment of fibres, chopped strand mat alternative to woven mat and modification of conventional polyester resin matrix against hydrolytic conditions have been made. Exploiting the drawbacks of natural fibres towards moisture absorption, coupling agent in aqueous medium was applied, which masks the moisture attracting surface hydroxyl and other oxygen containing groups by long chain hydrocarbon attachment besides depositing in the lumen of cell wall. This reduces surface free energy of fibre closer to the resin matrix. The methacryl functionality of coupling agent provides good compatibility with resin matrix and formed strong fibre-matrix interface. Using polyester-urethane hybrid resin with chopped natural fibre strand mat not only allows higher fibre loading but also provides benefit of resistance towards moisture. Certain drawbacks associated with conventional polyester resin such as brittleness and delamination in composites due to poor toughness are overcome by the use of polyester-urethane hybrid as laminating resin. Comparing with single wall plain board of similar thickness/mass per unit area, corrugated core sandwich panel resulted in light weight, better rigidity, low 'thermal conductivity, good sound insulation characteristics, etc. The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention. Example-1 Sisal fibre (440 gm) was washed with distilled water. For preparing a chopped strand mat, 40 gms of chopped fibre (aspect ratio 323) was immersed in 1 % (by weight of fibres) aqueous solution of methacrylamide functional amine adduct of pyro-phosphato titanate coupling agent (0.40 gm in 600 ml distilled water) and stirred constantly for 30 minutes at pH 9. The immersed fibres were drained off followed by washing with distilled water. Thereafter, these fibres were cured at 100 C for 1 hour to complete the reaction. The treated fibres were randomly arranged in 30 cm x 30 cm area and sprayed with 15 weight % aqueous solution of poly (vinyl acetate) emulsion. The sample was stored for 24 hours at room temperature, subsequently placed in air circulating oven at 80°C for 4 hours and then sandwiched between cellophene lined brass plate in a hydraulic press at 100 C for 5 minutes under 1 MPa pressure. Similar procedure was adopted for preparing other 10 mats (weigh 440 4 +10 g m-2 ) . To synthesize polyester resin, 0.234 moles; 39 gms of isophthalic acid and 1.13 moles; 120 gms of diethylene glycol were taken in a four necked round bottom flask equipped with stirrer, inlet tube for inert gas, reflux condenser and thermometer. The condensation reaction was carried out under nitrogen atmosphere. The mixture was refluxed for 10 hours and stirred continuously for 1 hour at 210^C. The acid value of contents was 40. The water content generated during condensation reaction was distilled off. The temperature of mixture was cooled down to 110°C and then added 0.706 moles; ' 70 gms of maleic anhydride. The temperature of mixture was again raised to 175°C and refluxed for 2 hours to get an acid value of 15.50. 0.02 % (by weight of resin) hydroquinone was added to inhibit premature gelation. The resin so prepared was cooled to 140 C and refluxed with 40 % (by weight of resin) styrene for 1 hour. Excess of styrene and unreacted acid/glycol were drived out through vacuum. The resin so prepared was blended with 20 weight% diphenyl methane 4,4' diisocyanate and stirred well for 10 minutes under nitrogen atmosphere. The resin was catalyzed with 0.5 % benzoyl peroxide and 0.2 % N,N diethyl aniline. For laminate preparation, gel coat was applied on one part of mould. When it becomes tacky, a coat of catalyzed resin is brushed over it and the first layer of resin wetted glass fabric is applied followed by four layers of wetted chopped sisal strand mats. Excess of resin was squeezed out by roller/hand. Thereafter, it was closed by second part of mould and compressed at a pressure of 2 MPa for 2 hours in a hydraulic press to form 1'xl' plain sheet (4 mm thick). Accordingly, corrugated sheet (pitch length = 76.2 mm, pitch'depth = 19.0 mm, thickness =2.5 mm) was prepared from three layers of resin wetted chopped sisal strand mats using wooden block mould with corrugated face. Poly (vinyl alcohol) was used as mould releasing agent. After demoulding, the plain and corrugated sheets were cured at room temperature for 24 hours and post-cured at 80 C for 4 hours at a pressure of 1 MPa. For preparation of sandwich panel (size=llxll, thickness=30mm), corrugated sheet (2.5 mm) was used as core material and plain sheet (4 mm) as face material. At the contact point of face and corrugation, the surface of sheets was roughened by sanding to improve its adhesiveness. Isocyanate-modified polyester resin adhesive was then applied on the rough surface of sheets. Corrugated core was sandwiched between two plain sheets and compressed together at nominal pressure till the green strength has developed. Details of parameters for composite laminates are given below : A. Ingredients related to fibre and resin: Sisal fibre for one mat 40 gm Coupling agent(by weight of fibres) 1% Aspect ratio of fibres 323 PVA Emulsion (by weight of fibres) 15% Chopped strand mat (weight) 440 + lOg m2 Isocynate content in hybrid resin 20% Composite Laminates Sisal mat content (by weight) 60% Hybrid resin content (by weight) 40% Glass surfacing mat(weight) 30 g m Gel coat Pressure used 2 MPa Curing time 24 Hours at room temperature 4 hours at 80 °C Size of panel . 30 cm x 30 cm Thickness 30 mm Example 2_ Sisal fibres (1.43 kg) were taken for preparation of 11 mats. Qut of this quantity, 130 gm of the fibres was washed with (distilled water, dried in air and kept at 105°C to constant moisture. The chopped sisal fibres (aspect ratio 323)were treated with O.fe% (by weight of fibres) aqueous solution (1.8 litre) of methacrylamide functional amine adduct of pyro-phosphato titanate. The constant stirring during the treatment was done. After 15 minutes, the treated fibres were emersed out, washed with distilled water and dried in an oven at 80 C for 4 hours to complete the reaction at the surface. The non-woven mat was prepared by randomly arranged surface modified fibres in 100cm x 30 cm area and sprayed with 8% aqueous solution of film forming grade poly(vinyl acetate) emulsion. This entanglement was air dried for 24 hours and then placed in an oven for 2 hours at 100 C. The hardened dry mass was then sandwiched between two cellophene lined brass plates in a hydraulic press at 120 C for 5 minutes under 1.5 MPa pressure. Thus one mat is ready. Similar procedure was adopted for preparing other 10 mats. To synthesise polyester resin, isophthalic acid, ethylene glycol and maleic anhydride were taken in the molar ratio of 1:2.64:1 using the procedure as described in example 1. The prepared resin was blended with 10 weight % diphenyl methane 4,4' diisocynate to form hybrid resin. The composite laminates (1m x 1m) were prepared firstly by impregnating the mat in resin followed by stacking between two mould plates and then pressing in a hydraulic press at a pressure of 1 MPa for 4 hours. Accordingly, a corrugated sheet (1m x 1m size) with a pitch length 76.2 mm and pitch depth 19 mm and thickness 3 mm was prepared by sisal mat (3 layers) and wollastonite filled hybrid resin. Gel coat with glass surfacing mat was used on exterior side. Procedure of laminate prepration is same as described in Example 1. The curing of the laminate was done at room temperature for 36 hours followed by post curing at 105 C for 2 hours at a pressure of 0.5 MPa. For preparing sandwich composite panel of size 1m x 1m, thickness 30 mm, corrugated core was bonded with face plain sheet using isocynate modified polyester adhesive. Procedure for fabrication of composite panels is same as given in Example 1. Details of parameters for composite laminates are given below : B. Ingredients related to fibre and resin: Sisal fibre for one mat 130 gm Coupling agent(by weight of fibres) 0.5% Aspect ratio of fibres 323 PVA Emulsion (by weight of fibres) 8% Chopped strand mat (weight) 415 4 + lOg m"2 Isocynate content in hybrid resin 10% Composite Laminates Sisal mat content (by weight) 50% Hybrid resin content (by weight) 30% Wollastonite(by weight) 20% Glass surfacing mat(weight) 30g m-2 Gel coat Pressure used 1 MPa Curing time 36 Hours at room temperature 2 hour at 105 °C Size of panel 100 cm x 100 cm Thickness 30 mm In conclusion, natural fibres are a renewable source and could have promising prospect in low pressure moulding. It can be helpful for finding alternate building materials for various applications. The main advantages of the present invention are that they provide a process for making natural fibres based composite panels with the following properties: 1. Light weight 2. High rigidity 3. Low thermal conductivity and sound insulation 4. Easy mounting and maintenance 5. Good weatherability 6. No lamination or painting is required 7. Alternative to pressed single wall boards We Claim: 1. An improved process for the manufacture of natural fibers based composite laminates useful for making plain/corrugated sheets and products thereof which comprises washing of natural fibers such as herein described to remove foreign materials, surface modifying the said washed fibers by immersing in a coupling agent solution such as herein described, followed by chopping to the required length, preparing non-woven strand mats using the said chopped surface modified fibers and mat forming water based polymeric agents such as herein described, impregnating the mats so obtained with hybrid resign, stacking a plurality of mats using adhesive to bond plain and corrugated core and sandwiching between two glass fabrics and compressing under gel coated brass plates at a pressure in the range of 1-2 MPa to obtain laminates, curing of laminates so obtained at room temperature for at least two hours followed by post-curing at a temperature in the range of 80°C - 105°C for a period of at least one hour at a pressure of 0.5 -1.5 MPa. 2. A process as claimed in claim 1, wherein coupling agent such as methacrylamide functional amine adduct of Neo pentlyl diallyl oxy tri (dioctyl) pyro-phosphato titanate is used. 3. A process as claimed in claim 1 and 2 wherein polymeric agents such as poly (vinyl acetate) emulsion is used for making chopped strand mats. 4. A process as claimed in claim 1-3 wherein hybrid resign is essentially constitutes diphenyl methane 4,4' diisocynate (MDI). 5. A process as claimed in claim 1-4 wherein adhesive used for constructing sandwich composite panels such as isocyanate modified polyester resin (propylene glycol based) is used . 6. An improved process for the manufacture of natural fibers based composite laminates useful for making plain/corrugated sheets and products thereof substantially as herein described with reference to the examples.

Full Text

The present invention relates to an improved process for the manufacture of. natural fibres based composite laminates useful for making plain/corrugated sheets and products thereof.
Emphasis on developing alternate building materials, especially wood substitute has been considered an active area of current material research because of acute shortage of timber and -rorsni t -y to connorvo the environment. Keeping this in view, investigation on role of natural fibres in polyester resin was undertaken. The product so developed can be used as wall panel, partition, door panel, roofing, table tops etc.
Natural fibres such as jute, sisal, coir etc. are abundantly available in developing countries like India, China, Bangladesh, Srilanka, South Africa etc. They are ligno-cellulosic in nature consisting of helically wound cellulosic microfibrils in a matrix of lignin and hemicellulose. The strength of these fibres varies from fibre to fibre depending on their origin and physico -mechanical properties. Traditionally, these fibres are used for the manufacture of carpets, ropes, sacks, wall hangings, yarn handbags etc. However,because; of the advent of synthetic fibres and plastics, there is a steady decline in the use of natural fibres in their conventional markets. This necessitated the attention of scientists/technologists to search for new diversified applications of these fibres. The high tensile modulus and low elongation at break of these fibres indicate their reinforcing potentiality in composite matrices (St.John,
D.A. and Kelli, J.M., "The flexural behaviour of fibrous plaster sheets", Cem. Conor. Res., vol.5, 1975, p. 347; Swift, D.G. and Smith, R.B.L.,"Sisal-cement composites as low cost construction materials," Appropriate Technol., vol.6, No.3, 1979, p. 6; Gram, H.E., "Durability of natural fibre in cement-based roofing sheets," J. Ferrocem., vol.17, No.4, 1987, p. 321). Various attempts have been made to use natural fibres as reinforcement in the form of strands, chopped, coarse needled pad and woven/non-woven chopped strand mat in polymer matrices for property improvement as well as applications development in various sectors (Chand, N., Verma, S. and Rohatgi, P.K., "Mechanical behaviour of sisal-polyester system," Internal Report, RRL, Bhopal, 1986; Owolabi, O., Czvikovszky, T. and Kovacs, " Coconut fibre reinforced thermosetting plastics", J. Appl. Polym. Sci. , Vol. 30, 1985, p. 1827; Pal, P.K., " Jute reinforced plastics: a low cost composite material," Plast.& Rubber Proc. Appl., Vol.4, No.3, 1984, p.215; Prasad, S.V., "Natural fibre based composites," Encyclopaedia of Composite Materials, Pergamon Press Pic., Headigton Hill Hall, Oxford U.K., 1989, p.197;Ranganathan, S.R., Pal, P.K., Raina, A.K., and Mitra, B.C., "A process for preparing jute based laminates and jute based laminates manufactured thereby," Patent Application No. 23/Cal/1989 dated 9.1.1989; Singh, B., Gupta, M., Verma, A. and Hajela, R.B., "Studies on Polymer composites based on sisal/polyester and glass/modified sisal fibre, fillers and polyester", Res. & Ind., Vol.39, 1994, p. 38). The advantages of using chopped strand mat
are their light in weight, ability to provide good wetting & resin flow and easy adaptability in all forms of pressure moulding. Unidirectional sisal fibre/epoxy cylindrical tube and flat sheets (Paramasivam, T. and Abulkalam, A.P.J., "On the study of natural fibre composites", Fib., Sci. Technol., 7, 1974, p. 85), chopped sisal/polyester sheets (Satyanarayana, K.G. et al," Possibility of using natural fibre composites as building m,it;.ori aln" , Proc . Int. 1 . Conf . on Low cost housing for developing countries, India, 1984, p. 177), sisal mat-CNSL plain and corrugated laminates for roofing application (Bisanda, E.T.N. and Ansell, M.P., "Properties of sisal-CNSL composites", J. Mater. Sci., vol.27, 1992, p. 1690), Jute reinforced polyester for primary school buildings, grain silos and low cost housing (Winsfield, A.G., "Jute reinforced polyester projects for UNIDO/Government of India". Plast Rubber Intl., 4, 1979, p. 23), bagasse-phenolic composites for wall panels, roofing, door shutters, furnitures etc. (Salyer, I.O., and Usmani, A.M., " Utilisation of bagasse in new composite building materials," Ind. Eng. Prod. Res. Dev.,Vol 21, 1982, p.17) are some of the products described in the literature. Belmares et al . , ("New composite materials from natural hard fibres", Ind.Eng. Chem. Prod. Res. Dev., vol. 20, 1981, p. 555) have suggested the findings of palm/polyester composites extendable to other similar fibres such as sisal for making low cost composite building materials such as roofs, silos, low cost housing elements etc. However, lack of good interfacial bonding between the fibre and the matrix,
poor resistance to moisture and susceptibility to environment make; these composites less attractive. In an effort to combat some of these aforementioned disadvantages, the methods for protecting the composites either by providing hydrophobicity to the natural fibre or by applying a gelcoat/glass fibre as a surfacing layer is a continuous subject of debate. Attempts have been made to prepare hybrid laminates with combination of glass and natural fibres in polyester resin to improve the impact properties, warping and environmental resistance (Pavithran, C., et al, "Impact properties of sisal-glass hybrid laminates", J. Mater.Sci., Vol.26, No.2, 1991, p. 455; Shah, A.N. and Lakkad, S.C., "Mechanical properties of jute reinforced plastics", Fibre Sci. Technol. , 45, 1981, pTM5) . In view of reducing the cost and improvement of stiffness properties of hybrid, the inclusion of particulate filler has been made to prepare particulate hybrid laminates as panelling materials (Singh, B., Gupta, M. and Verma, A., "Mechanical behaviour of particulate hybrid composite laminates as potential building materials", Const. & Build. Mater., 9, 1995, p. 39) . Viewing the importance of interfacial bonding, surface chemical modification of natural fibre was carried out by alkali treatment (Chand, N. and Rohatgi, P.K., "Adhesion of sisal fibre-polyester system", Polym. Commun. , Vol.27, 1986, p. 157), isocyanate modified cardanol (Joseph, K., Thomas, S. and Pavithran, C., "Effect of ageing on the physical and mechanical properties of sisal fibre-reinforced polyethylene composites," Comp. Sci. Technol., Vol.53, 1995, p. 99), resin
treatments (Varma, D.S., Varma, M. and Varma, I.K.,"Coir fibre-3 Effect of resin treatment on properties of fibres and composites, "Ind. Eng. Chem. Prod. Res. Dev. , Vol. 25, 1986, p. 282), vinyl polymer grafting (Barkakati, B.C. and Robson, A., "Polymer deposition in sisal fibre : A structural investigation", J. Appl. Polym. Sci., Vol. 24, 1979, p. 269) and coupling agents treatment (Bisanda E.T.N. and Ansell, M. P. , "The effect of silane treatment on the mechanical and physical properties of sisal-epoxy composites", Comp. Sci., Technol., Vol.41, 1991, p. 165; Singh, B., Gupta, M. and Verma, A., "Influence of fibre surface treatment on the properties of sisal-polyester composites", Polym. Compos. Vol.17, No.6, 1996, p. 910; Varma, I.K., Ananthakrishnan, S.R. and Krishnamoorthy, S. , "Composites of glass/modified jute fabric and unsaturated polyester resin," Composites, Vol. 11, 1990, p. 77) . These treatments provide improved physico-mechanical properties and hygrothermal stability to the resultant composites as a consequence of enhanced interfacial adhesion. Choice of surface treatment depends on its specificity for a particular ressin. However, the benefits made by improving wetting or interfacial bonding are limited. Experimental studies have indicated that compatibility of surface-modified natural fibres with resin matrix is also a critical factor in obtaining the best mechanical properties of the resultant composites. In addition, literature has not revealed any information on the use of modified conventional resin matrix for natural fibre reinforcement to cope with
moisture-induced degradation. Therefore, searching of new surface modification procedure based on water enriched coating compatible with resin matrix, easy method for producing a light weight chopped natural fibre strand mat and modification of conventional resin matrix against hydrolytic stability are imperative to obtain various performance based properties as well as commercial exploitation.
The main object of the present invention is to provide an improved process for the manufacture of natural fibres based composite laminates useful for making plain/corrugated sheets and products thereof which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a process wherein the natural fibres have been used may be such as sisal, jute, coir, sunhemp etc.
Another object of the present invention is to provide composite laminates of surface- modified natural fibres.
Still another object of the present invention is to provide natural fibres based composite laminates using polyester-
urethane hybrid resin.
Yet another object of the present invention is to provide composite laminates useful for making plain/corrugated
sheets and products thereof.
Accordingly, the present invention provides an improved process for the manufacture of natural fibers based composite laminates useful for making plain/corrugated sheets and products thereof which comprises washing of natural fibers such as herein described to remove foreign materials, surface modifying the said washed fibers by immersing in a coupling agent solution such as herein described, followed by chopping to the required length, preparing non-woven strand mats using the said chopped surface modified fibers and mat forming water based polymeric agents such as herein described, impregnating the mats so obtained with hybrid resign, stacking a plurality of mats using adhesive to bond plain and corrugated core and sandwiching between two glass fabrics and compressing under gel coated brass plates at a pressure in the range of 1-2 MPa to obtain laminates, curing of laminates so obtained at room temperature for at least two hours followed by post-curing at a temperature in the range of 80°C - 105°C for a period of at least one hour at a pressure of 0.5 -1.5 MPa.
In an embodiment of the present invention, the surface modification of fibers may be effected by immersing in 0.5 - 2% (by weight of fibers) aqueous solution of coupling agents such as organosilane, organotitanate, organozirconate and methacrylamide functional amine adduct of pyro-phosphato titanate.
In another embodiment of the present invention, 8-15% (by weight of fibers) emulsion such as poly (vinyl acetate) emulsion is used for making chopped strand mats.
In yet another embodiment of the present invention, 20-55% (by weight of fibres) hybrid resin used for impregnating the mats may be such as polyester-urethane hybrid resin prepared from refluxing diethylene glycol (2-5 moles), isophthalic acid (1-2 moles) and maleic anhydride (1-2 moles) under nitrogen atmosphere using conventional synthesis route which was then reacted with 5-20 weight % diphenyl methane 4,4' diisocynate.
Still in another embodiment of the present invention, the curing of pressed laminate£3 may be effected at room temperature for a period of atleast 2 hours.
Accordingly, the present invention provides products such as corrugated core composite panels for door materials, panelling, partitioning and roofing materials using the natural fibre laminates of the present invention.
The process for making composite panel consists of several steps. First step involves surface modification procedure of fibres. Natural fibres were immersed and washed in water for 24 hours to ensure maximum removal of water solubles from the surface. These are air dried and heated at 105 ^ 5 C in an oven to a constant weight. The surface modification of natural fibres was carried out by immersing them in 0.5-2 % (by weight of fibres) aqueous solution of organotitanate, organosilane, organozirconate and methacrylamide functional amine adduct of pyro-phosphato titanate coupling agent and stirred continuously. The treated fibres were washed with respective
solvent to remove physisorbed compounds from the fibre surface. The treatment conditions for optimum adsorption ot coupling agent onto natural fibres was selected on the basis of experiments performed under variation of certain parameters such as concentration (0.5-3 weight %) , pH(3-12), treatment time (15-240 minutes) , curing time - (30 - 240 minutes) and curing temperature (60-100°C). The choice of methacrylamide functional amine adduct of pyro-phosphato titanate surface modifier is due to its solubility in water eliminating risk of toxicity associated with the use of solvent besides providing good compatibility with polyester matrix and fire retardancy to the fibre. In the second step, a light weight chopped natural fibre strand mat was prepared by randomly arranged surface-modified fibres (3-6 cm) in the desired size. About 6-15 weight % of poly (vinyl acetate) emulsion in water was sprayed uniformly to the fibre entanglements. Evaporating excess water, the air dried sprayed sample was kept at 80°C for 4 hours. The hardened fibre entanglement was compressed in a hydraulic press between two cellophene lined brass plates at 80-100 C under a pressure of 1-2 MPa for 5-10 minutes to obtain smooth finished non-woven mat. The mats have moisture content in the range of 2-5 %. The main objective of using chopped strand mat over woven mat is to minimise resin consumption, easy removal of entrapped air on the mat surface, avoiding tenacity loss during weaving and good wetting out of all fibre strands through easy penetration of resin. The third step comprises preparation of laminating
resin. The basic polyester is prepared by condensing diethylene -llycol (2-5 tnolc.M) and isophthalic acid (1-2 moles) at 200-215°C under nitrogen atmosphere until the acid number was reduced to approximately 40-70 (I) . Maleic anhydride (1-2 moles) was added to (I) after cooling down to 100-120°C. After the complete addition, the temperature- of the flask was again increased to 150-200°C to obtain acid value at the level of 12-24 (II). This polyester containing styrene(30-40 %) reacted with 5-20 weight % diphenyl methane 4,4' diisocyanate (MDI) to form polyester-urethane hybrid resin (III) . This resin was catalysed before laminate moulding. Excess of diethylene glycol is used to adjust acid number/viscosity relationship and provide more flexibility to the resultant resin as compared to higher molecular weight glycol. MDI is used to enhance tensile elongation of the hybrid resin. Benzoyl peroxide is selected as initiator over methyl ethyl ketone percftcide due to its effectiveness with isocyanate on long contact. N,N diethyl aniline is used as promoter for urethane reaction. The fourth step involves preparation of laminates. The chopped natural fibre strand mats were cut to the desired size and wetted with polyester-urethane hybrid resin containing 0.5-1 % benzoyl peroxide and 0.2 - 0.5 % N,N diethylaniline. The excess of resin was squeezed out through roller. The desired thickness of wetted mats ( 4-6 layers) were sandwiched between resin rich/ gel coated brass/steel plates and compressed in a hydraulic press for 2-4 hours at a pressure of 1-3 MPa.Glass fabric surfacing mat (30 g m )
was used on exterior surface. Gel coated glass fabric is used to provide environmentally resistant composite. Poly (vinyl alcohol) was used as a mould releasing agent.Corrugated sheet (3-4 layers natural fibre mats) was prepared on a matched pair of cast iron/ seasoned wooden block moulds having corrugated face. The laminates were cured at room temperature for 24 hours and then post-cured at 80-100°C for 3-5 hours at a pressure of 1-2 MPa. The demoulded sheets are saw cut and trimmed to form panels of desired size. In the fifth and final step, sandwich panel using natural fibre-hybrid resin corrugation as core (2-3 mm) and gel coated glass/natural fibre-hybrid resin plain sheet as face material' (3-4 mm) was prepared. The rough surface at the contact point of face panel and corrugation was created by sanding. Jointing of panels was done using isocyanate-modified polyester resin adhesive and then placed under a nominal pressure for 2'hours to ensure strength development at joints.
In the light of background discussions on prior art, a concerted effort on identified gaps such as surface treatment of fibres, chopped strand mat alternative to woven mat and modification of conventional polyester resin matrix against hydrolytic conditions have been made. Exploiting the drawbacks of natural fibres towards moisture absorption, coupling agent in aqueous medium was applied, which masks the moisture attracting surface hydroxyl and other oxygen containing groups by long chain hydrocarbon attachment besides depositing in the lumen of cell wall. This reduces surface free energy of fibre closer to the
resin matrix. The methacryl functionality of coupling agent provides good compatibility with resin matrix and formed strong fibre-matrix interface. Using polyester-urethane hybrid resin with chopped natural fibre strand mat not only allows higher fibre loading but also provides benefit of resistance towards moisture. Certain drawbacks associated with conventional polyester resin such as brittleness and delamination in composites due to poor toughness are overcome by the use of polyester-urethane hybrid as laminating resin. Comparing with single wall plain board of similar thickness/mass per unit area, corrugated core sandwich panel resulted in light weight, better rigidity, low 'thermal conductivity, good sound insulation characteristics, etc.
The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.
Example-1
Sisal fibre (440 gm) was washed with distilled water. For preparing a chopped strand mat, 40 gms of chopped fibre (aspect ratio 323) was immersed in 1 % (by weight of fibres) aqueous solution of methacrylamide functional amine adduct of pyro-phosphato titanate coupling agent (0.40 gm in 600 ml distilled water) and stirred constantly for 30 minutes at pH 9. The immersed fibres were drained off followed by washing with
distilled water. Thereafter, these fibres were cured at 100 C for 1 hour to complete the reaction. The treated fibres were randomly arranged in 30 cm x 30 cm area and sprayed with 15 weight % aqueous solution of poly (vinyl acetate) emulsion. The sample was stored for 24 hours at room temperature, subsequently placed in air circulating oven at 80°C for 4 hours and then sandwiched between cellophene lined brass plate in a hydraulic press at 100 C for 5 minutes under 1 MPa pressure.
Similar procedure was adopted for preparing other 10 mats (weigh
440 4 +10 g m-2 ) . To synthesize polyester resin, 0.234 moles; 39
gms of isophthalic acid and 1.13 moles; 120 gms of diethylene glycol were taken in a four necked round bottom flask equipped with stirrer, inlet tube for inert gas, reflux condenser and thermometer. The condensation reaction was carried out under nitrogen atmosphere. The mixture was refluxed for 10 hours and stirred continuously for 1 hour at 210^C. The acid value of contents was 40. The water content generated during condensation reaction was distilled off. The temperature of mixture was cooled down to 110°C and then added 0.706 moles; ' 70 gms of maleic anhydride. The temperature of mixture was again raised to 175°C and refluxed for 2 hours to get an acid value of 15.50. 0.02 % (by weight of resin) hydroquinone was added to inhibit premature gelation. The resin so prepared was cooled to 140 C and refluxed with 40 % (by weight of resin) styrene for 1 hour. Excess of styrene and unreacted acid/glycol were drived out through vacuum. The resin so prepared was blended with 20 weight%
diphenyl methane 4,4' diisocyanate and stirred well for 10 minutes under nitrogen atmosphere. The resin was catalyzed with 0.5 % benzoyl peroxide and 0.2 % N,N diethyl aniline. For laminate preparation, gel coat was applied on one part of mould. When it becomes tacky, a coat of catalyzed resin is brushed over it and the first layer of resin wetted glass fabric is applied followed by four layers of wetted chopped sisal strand mats. Excess of resin was squeezed out by roller/hand. Thereafter, it was closed by second part of mould and compressed at a pressure of 2 MPa for 2 hours in a hydraulic press to form 1'xl' plain sheet (4 mm thick). Accordingly, corrugated sheet (pitch length = 76.2 mm, pitch'depth = 19.0 mm, thickness =2.5 mm) was prepared from three layers of resin wetted chopped sisal strand mats using wooden block mould with corrugated face. Poly (vinyl alcohol) was used as mould releasing agent. After demoulding, the plain and corrugated sheets were cured at room temperature for 24 hours and post-cured at 80 C for 4 hours at a pressure of 1 MPa. For preparation of sandwich panel (size=llxll, thickness=30mm), corrugated sheet (2.5 mm) was used as core material and plain sheet (4 mm) as face material. At the contact point of face and corrugation, the surface of sheets was roughened by sanding to improve its adhesiveness. Isocyanate-modified polyester resin adhesive was then applied on the rough surface of sheets. Corrugated core was sandwiched between two plain sheets and compressed together at nominal pressure till the green strength has developed. Details of parameters for composite laminates are
given below :
A. Ingredients related to fibre and resin:
Sisal fibre for one mat 40 gm
Coupling agent(by weight of fibres) 1%
Aspect ratio of fibres 323
PVA Emulsion (by weight of fibres) 15%
Chopped strand mat (weight) 440 + lOg m2
Isocynate content in hybrid resin 20%
Composite Laminates
Sisal mat content (by weight) 60%
Hybrid resin content (by weight) 40%
Glass surfacing mat(weight) 30 g m
Gel coat
Pressure used 2 MPa
Curing time 24 Hours at room temperature
4 hours at 80 °C
Size of panel . 30 cm x 30 cm
Thickness 30 mm
Example 2_
Sisal fibres (1.43 kg) were taken for preparation of 11 mats. Qut of this quantity, 130 gm of the fibres was washed with (distilled water, dried in air and kept at 105°C to constant moisture. The chopped sisal fibres (aspect ratio 323)were treated
with O.fe% (by weight of fibres) aqueous solution (1.8 litre) of methacrylamide functional amine adduct of pyro-phosphato
titanate. The constant stirring during the treatment was done. After 15 minutes, the treated fibres were emersed out, washed with distilled water and dried in an oven at 80 C for 4 hours to complete the reaction at the surface. The non-woven mat was prepared by randomly arranged surface modified fibres in 100cm x 30 cm area and sprayed with 8% aqueous solution of film forming grade poly(vinyl acetate) emulsion. This entanglement was air dried for 24 hours and then placed in an oven for 2 hours at 100 C. The hardened dry mass was then sandwiched between two cellophene lined brass plates in a hydraulic press at 120 C for 5 minutes under 1.5 MPa pressure. Thus one mat is ready. Similar procedure was adopted for preparing other 10 mats. To synthesise polyester resin, isophthalic acid, ethylene glycol and maleic anhydride were taken in the molar ratio of 1:2.64:1 using the procedure as described in example 1. The prepared resin was blended with 10 weight % diphenyl methane 4,4' diisocynate to form hybrid resin. The composite laminates (1m x 1m) were prepared firstly by impregnating the mat in resin followed by stacking between two mould plates and then pressing in a hydraulic press at a pressure of 1 MPa for 4 hours. Accordingly, a corrugated sheet (1m x 1m size) with a pitch length 76.2 mm and pitch depth 19 mm and thickness 3 mm was prepared by sisal mat (3 layers) and wollastonite filled hybrid resin. Gel coat with glass surfacing mat was used on exterior side. Procedure of laminate prepration is same as described in Example 1. The curing of the laminate was done at room temperature for 36 hours followed by
post curing at 105 C for 2 hours at a pressure of 0.5 MPa. For preparing sandwich composite panel of size 1m x 1m, thickness 30 mm, corrugated core was bonded with face plain sheet using isocynate modified polyester adhesive. Procedure for fabrication of composite panels is same as given in Example 1. Details of parameters for composite laminates are given below :
B. Ingredients related to fibre and resin:
Sisal fibre for one mat 130 gm
Coupling agent(by weight of fibres) 0.5%
Aspect ratio of fibres 323
PVA Emulsion (by weight of fibres) 8%
Chopped strand mat (weight) 415 4 + lOg m"2
Isocynate content in hybrid resin 10%
Composite Laminates
Sisal mat content (by weight) 50%
Hybrid resin content (by weight) 30%
Wollastonite(by weight) 20%
Glass surfacing mat(weight) 30g m-2
Gel coat
Pressure used 1 MPa
Curing time 36 Hours at room temperature
2 hour at 105 °C
Size of panel 100 cm x 100 cm
Thickness 30 mm
In conclusion, natural fibres are a renewable source
and could have promising prospect in low pressure moulding. It can be helpful for finding alternate building materials for various applications.
The main advantages of the present invention are that they provide a process for making natural fibres based composite panels with the following properties:
1. Light weight
2. High rigidity
3. Low thermal conductivity and sound insulation
4. Easy mounting and maintenance
5. Good weatherability
6. No lamination or painting is required
7. Alternative to pressed single wall boards

We Claim:
1. An improved process for the manufacture of natural fibers based
composite laminates useful for making plain/corrugated sheets and products thereof which comprises washing of natural fibers such as herein described to remove foreign materials, surface modifying the said washed fibers by immersing in a coupling agent solution such as herein described, followed by chopping to the required length, preparing non-woven strand mats using the said chopped surface modified fibers and mat forming water based polymeric agents such as herein described, impregnating the mats so obtained with hybrid resign, stacking a plurality of mats using adhesive to bond plain and corrugated core and sandwiching between two glass fabrics and compressing under gel coated brass plates at a pressure in the range of 1-2 MPa to obtain laminates, curing of laminates so obtained at room temperature for at least two hours followed by post-curing at a temperature in the range of 80°C - 105°C for a period of at least one hour at a pressure of 0.5 -1.5 MPa.
2. A process as claimed in claim 1, wherein coupling agent such as
methacrylamide functional amine adduct of Neo pentlyl diallyl oxy tri
(dioctyl) pyro-phosphato titanate is used.
3. A process as claimed in claim 1 and 2 wherein polymeric agents such as
poly (vinyl acetate) emulsion is used for making chopped strand mats.
4. A process as claimed in claim 1-3 wherein hybrid resign is essentially
constitutes diphenyl methane 4,4' diisocynate (MDI).
5. A process as claimed in claim 1-4 wherein adhesive used for constructing
sandwich composite panels such as isocyanate modified polyester resin
(propylene glycol based) is used .
6. An improved process for the manufacture of natural fibers based
composite laminates useful for making plain/corrugated sheets and
products thereof substantially as herein described with reference to the
examples.

Documents:

2445-del-1997-abstract.pdf

2445-del-1997-claims.pdf

2445-del-1997-correspondence-others.pdf

2445-del-1997-correspondence-po.pdf

2445-del-1997-description (complete).pdf

2445-del-1997-form-1.pdf

2445-del-1997-form-19.pdf

2445-del-1997-form-2.pdf

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Patent Number

195175

Indian Patent Application Number

2445/DEL/1997

PG Journal Number

38/2008

Publication Date

19-Sep-2008

Grant Date

29-Dec-2006

Date of Filing

28-Aug-1997

Name of Patentee

Council of Scientific & Industrial Research,

Applicant Address

Rafi Marg, New Delhi-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	Manorama Gupta	Central Building Research Institute, Roorkee .INDIA.
2	Anchal Verma	Central Building Research Institute, Roorkee .INDIA.
3	Brajeshwar Singh	Central Building Research Institute, Roorkee .INDIA.

PCT International Classification Number

B 28 B1/52

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA