Natural Fibre Composites (NFC) as Building Materials Natural fibres, as a substitute for glass fibres in composite components, have gained interest in the last decade, especially in the housing sector. Fibres like jute, sisal, coconut fibre (coir), ramie, banana, flax, hemp etc. are cheap and have better stiffness per unit weight and also have a lower impact on the environment. Structural applications are rare since existing production techniques are not applicable for such NFC products and non-availability of semi-finished materials with adequate quality. The moderate mechanical properties of natural fibres prevent them from being used in high-performance applications (e.g. where carbon reinforced composites would be utilized), but for many reasons they can compete with glass fibres. Advantages and disadvantages determine the choice of their consideration. Lower specific weight of NFCs results in higher specific strength & stiffness compared to glass fibre and is a benefit especially in parts designed for bending stiffness. Many components are now produced in natural composites, mainly based on polyester or polypropylene and fibres like flax, jute, sisal, banana or ramie. Until now however, the introduction in this industry is lead by motives of price and marketing (‘processing renewable resources’) rather than technical demands. It can be moulded into sheets, boards, gratings, pallets, frames, sections and many other shapes. They can be used as a substitute for wood, metal or masonry for partitions, false ceilings, facades, barricades, fences, railings, flooring, roofing, wall tiles etc. The wide usage of ligno-cellulosic fibres as reinforcement in thermoplastic such as polyethylene, polypropylene is due to their low cost, low density, high specific strength, flexibility and reduced wear of processing machinery. Studies have been carried out by the Indian Jute Industries’ Research Association (IJIRA), Kolkata on the effect of compatibilizers, impact modifiers and fibre loading on jute-fibre reinforced polypropylene composites. In an attempt to improve the impact strength of composites, it was found that olefinic based impact modifier (containing carboxylic functions) resulted in increase in mechanical, flexural and impact strengths than the elastomer based modifier. This has been due to presence of carboxylic functional group having better bonding with jute fibre and homogeneity with polypropylene matrix. Regional Research Laboratory, Thiruvananthapuram carried out detailed analysis of the effect of fibre length, fibre content on the tensile properties of coir fibre reinforced polyethylene composites. It was observed that the strength modulus and failure strain of the composites increased with fibre length upto the maximum fibre length of 20 mm and fibre volume fraction of 0.26. Further increase of fibre length resulted in decrease in fibre-fibre interaction and poor compaction of fibre in the matrix. Although coir fibre processes 60-70% low tensile strength than sisal & pineapple fibres, coir-polyethylene composites show comparable tensile strength and higher failure strain to those of sisal & pineapple fibre based composites. This is due to presence of natural waxy layer on the fibre resulting in better interfacial bonding between coir and polyethylene. Due to the inherent advantages of these composites, some composite products such as natural fibre based panels, corrugated/foamed core sandwich door materials & frames, pultruded GRP shuttering system, roofing sheet & tiles, artificial marble, repair materials for strengthening concrete structures etc. have been developed by Central Building Research Institute (CBRI), Roorkee. A systematic study has been carried out at CBRI on sisal & jute fibre composites for their application in construction sector. Various coupling agents (silane, titanate, N-substituted methacrylamide) have been used to improve the wettability of these fibres. Process know-how for fabricating these natural fibre composites has been established by CBRI. The sandwich composite panels are lightweight and have excellent bending stiffness besides good thermal & sound insulation. For semi-structural applications hybrid composites have been developed with glass fibre, sisal fibre & polyester resin. The tensile strength of hybrid composites is 56 MPa with an elastic modulus of approx. 2 GPa. Further, CBRI has carried out developmental efforts using sisal fibre and wollastonite as synergistic reinforcement alternative to glass fibres in dough & bulk moulding compounds to widen their usage in the housing sector. The physico-mechanical properties such as thickeners, monomer type, sisal/wollastonite/glass fibre content of the moulding are studied as a function of various constituents. Sisal based dough moulding compound can be used for developing building materials such as checker floor plate, roof tile, sanitary ware etc. An attempt has also been made by CBRI to fabricate jute pultruded doorframes using woven jute cloth and phenolic resin. Phenolic resins is often used for fabrication of jute-composite products mainly because of its high heat resistance, low smoke emissions excellent fire retardance properties and compatibility with jute fibres. The pultruded doorframe (2140 x 920 mm) can accommodate 35 mm thick door. The density of these profiles fabricated has been 873 ± 10 Kg./m3. CBRI has also evaluated the mechanical properties of these pultruded doorframes. It was observed that the variation in tensile & flexural strength of profiles at low humidity condition has been marginal while a progressive deterioration is observed at high humidity levels. The pultruded doorframe was performance tested for 2-3 years. There was no sign of warping, bulging, discolouration etc. CBRI has developed another technology for production of coir-cement roofing sheet having a thickness of 6-8 mm. The manufacturing process involves soaking of coir fibre in mineralized water and then mixing with dry cement in the ratio of 1:5 by weight. A sheet is made with this wet mix of cement coated fibres and is held under pressure for 4-8 hrs. The long-term performance under actual conditions has been ascertained. Another type of roofing sheets with a thickness of 3-4 mm fabricated using chopped fibre strand mats, fibrous reinforcing filler, anti-aging agent and unsaturated polyester resin. CBRI has developed medium density composite doors containing coir fibre, cashew nut shell liquid (CNSL) as natural resin and paraformaldehyde as major constituents. Coir fibre contributes mechanical strength to the composite while the CNSL with paraformaldehyde act as a binder. Coir is impregnated with CNSL and is compression moulded under high temperature. The pressure required during casting of the board/sheet depends upon the required density of the final product. These boards can be used as wood substitute for paneling, cladding, surfacing and partitioning and other interior applications. The boards have density between 0.5 – 0.9 gms/cm3 and can be cut, sawed, nailed & screwed. The boards have very low water absorption and negligible swelling.
