There are several types of unsaturated polyester resin - general purpose, flexible, resilient, low-shrinkage (low profile), weather resistant, chemical resistant and fire resistant varieties. These polyester resins are prepared from a blend of phthalic anhydride and maleic anhydride esterified with propylene glycol to form linear polyester chains having molecular weights in the range of 1000-3000. For Curing of such unsaturated polyester resin with fibre, azo type initiators (R-N=N-R) and organic peroxides (R-O-O-R) are generally used.
Fabrication of composites
Hybrid composite of glass and jute fibre can be fabricated by the hand lay-up technique using a laboratory compression moulding machine. 10-ply hybrid laminates containing 8 inner plies of untreated/silane/ titanate/TDI treated jute fibre sandwiched between two outer plies of glass fibre (weight content of jute: 25-27%) are made. Curing is done at 80°C under a pressure of approx 2x105 N/m2 for a period of 90 min. Jute composites are at present being used commercially in India for applications like automobile interiors. There are also some temporary outdoor applications like low cost housing for defence etc. However, use of jute alone as reinforcing fibre would not be suitable for high strength applications. Jute-glass fibre combination can be well suited to such applications. Incorporation of glass with jute brings about large increases in mechanical properties of composites. Although there exists a good potential of jute-glass hybrid composites, nobody is practicing commercially in India. A substantial amount of development work is required for its commercial exploitation. A report from National Institute of Research on Jute and Allied Fibre Technology (NIRJAFT) reveals that, usually for moulded jute composites with polyester resin, the resin intake is up to 40% maximum. Both hot press moulding and hand lay-up technique can be used for its fabrication. In the latter process, the resin take up may go up to 300-400% on the basis of jute fibre used which is not economical. Also, it is seen that some pre-processing of jute/treatment of fibre is required so that the interface problem could be solved. Generally, when unsaturated polyester resin is used with glass fibre, the ratio maintained is 2.5:1. Whereas, for resin with jute, the ratio maintained is 3.5-4:1. However, increase in temperature increases the productivity. Even with unsaturated polyester resin, hot condition impregnation is usually done for higher productivity.
The characteristics of natural fibre composite boards are as follows:
· Attractive natural look as it can be painted, polished or laminated at will
· Water-proof with minimum surface absorption
· Economical
· Strong and rigid
· Environment-friendly
· Can be nailed, screwed and cut sharply.
A composite has three entities that are susceptible to failure - the reinforcement, the matrix and the interface. The failure of one can initiate failure of the others, and the actual process that takes place in any particular case is determined by the stress required to activate each individual mechanism. The mechanism activated by the lowest stress will normally govern composite failure. Thus, in order to increase the potential application area of jute fibres as reinforcement in composites, it is necessary to concentrate more on three major aspects (a) fibre modification (b) resin matrix and (c) coupling agents.
Jute composites: potential applications
The jute composites can be very cost-effective material especially for building and construction industry (panels, false ceilings, partition boards etc), packaging, automobile and railway coach interiors and storage devices. A survey of international patents establishes the potential applications of jute composites in various sectors. These are summarised in the following sections:
A US patent (# 5663216) granted in 1997 to a German company describes the process of fabricating a bio-degradable composite. This involves using a thermoplastic starch and a hydrophobic biologically degradable polymer reinforced with natural fibres such as ramie, cotton, etc. Pradom Ltd, London, UK, in its patent (US patent # 5218012) granted in 1993 described an innovative approach to electrical pre-treatment of reinforcing fibres for their application in composite. The treatment involves coating the fibre with a conductive or semi-conductive material and then subjecting it to an electric field with a DC supply (50-150,000 V) or AC (10,000-30,000 V; frequency: 50-1000 Hz). The process of moulding thermoset composite reinforced with natural fibres was patented (US patent # 5231121) by a German company in 1993. The inventors used a resin mixture comprising unsaturated polyester with styrene and acrylic acid esters.
The process involves impregnating the natural fibre with the aforesaid resin formulation and hot pressing it to a desired shape. In their application dating back to 1974, M/s Care Inc, NY, USA, patented (# 3819466) double-wall reinforced and insulating building panel with a combination of glass and jute composites. The panels comprise of an inner skin of woven jute layers saturated in polyester resin and an outer skin of woven jute with an exterior coating of chopped glass fibre both impregnated with polyester resin. The intermediate layer bonding inner and outer skin is made of corrugated woven jute composite. The panel is of light weight and has high durability even in extreme temperature conditions.
In a US patent (# 5285957) of 1994, The Mead Corporation Dayton, Ohio, USA, described the use of jute mesh as the intermediate reinforcing material for a corrugated container such as bulk storage bins. The reinforcing material may be placed in between the outer and inner lines of two-faced corrugated board construction.
A US patent (# 5037690) granted in 1991 to M/s De Groot Automotives BV of Netherlands describes the process of fabricating a sheet material. The sheet comprises polyurethane resin reinforced with binder-free natural fibres such as jute, flax, hemp, coir, ramie, cotton, etc possibly combined with polypropylene, polyethylene and/or glass fibre. The preferred natural fibre is jute in the form of needled jute felt. The application lies in fabricating a sandwich panel with two outer walls made of jute composite sheets. The Marlo Company Inc, Newton, Connecticut, USA, in their patent (US patent # 4559862) in 1985 describe a packing material comprising glass in combination with organic fibre such as sintered polytetrafluroethylene (TFE) with or without impregnant. A preferred impregnant could be a lubricant with a binder. The process also talks of substitution of sintered TFE fibre by natural and other fibres.
A US patent (# 9831626 A1) granted to a US company in 1998 describes the method for fabricating wet-laid non-woven webs using jute fibre as reinforcement. Composites of the unpulped fibre webs with cellulosic and spun bonded sheets find applications as thermoformed trim products for vehicle interiors.
The process for making a multi-layer composite body comprising a thermoplastic layer and layers of natural fibre bonded to thermoplastic resin was patented (# 9836900 A1) by a German company in 1998. The composite body has at least one reinforcing layer made of an open-cell fabric of melting fibres penetrated on one or both sides of the melting thermoplastic materials. The composite body has excellent mechanical properties particularly bending stress and impact resistance.
Indian scenario
Due to an occurrence of a wide variety of natural fibres in the country, Indian researchers have directed efforts for quite some time in developing innovative natural fibre composites for various applications. The national institutions such as National Institute of Research on Jute and Allied Fibre Technology (NIRJAFT), Indian Jute Industrys Research Association (IJIRA), Central Glass and Ceramic Research Institute (CGCRI), Department of Textile Technology - IIT Delhi, Regional Research Laboratory (RRL) - Bhopal, Institute of Jute Technology - Calcutta University especially merit the mention for their long standing research activities. IJIRA carried out extensive work on pre-treatment of jute fibres with acrylonitrile for improving their compatibility with thermoset plastics.
NIRJAFT has developed a whole set of novel jute and other natural fibre composite products based on hot press moulding and hand lay-up technique. A lot of efforts has gone into the studies on resin/fibre ratio, physical and chemical characteri-sation of jute composites, water absorption properties, etc apart from developing products such as panels, boards, packaging material, etc. The grading of raw material and its implementation for the benefit of both cultivators and industry has been one of the significant contributions of NIRJAFT. A commercially viable technology has been developed by them for the manufacture of particle boards from jute stick, which is an agro-waste. IIT - Delhi has been quite active in developing jute-based geo-textiles for applications in prevention of soil erosion, leaching etc. CGCRI - Calcutta has worked on jute-glass hybrid components for cost-reduction without sacrificing the mechanical properties. An excellent example for commercial exploitation of jute composites has been the fabrication of automobile interiors (door panels) by Birla Jute Industries Ltd. While the national research agencies in India have excellent scientific achievements to their credit for development of jute composites, efforts on their commercialisation have been limited so far. In order to improve upon the laboratory-industry linkages towards application development and commercialisation. The Advanced Composites Mission was conceptualised by Department of Science & Technology and Defence Research & Development Organisation. The Mission mode activities are being implemented by Technology Information, Forecasting & Assessment Council (TIFAC), an autonomous organisation under DST. Among a wide array of composite product development, the Mission has launched a few projects focussing on jute composites.
The project on Jute-based Composites - An Alternative to Wood Products has been launched in collaboration with M/s Duroflex Limited, Bangalore, a leading manufacturing industry in rubberised coir materials. The project aims at development of oriented jute face layer for coir-ply board. Natural hard fibres such as coir and jute impregnated with phenolic resins are used for its manufacture. The project activities will enable the production of coir-ply boards with proper orientation of jute having a very similar appearance of wood. The average production capacity of coir-ply plant planned under the project would be around 1000 sheets of 2.4 m x 1.2 m of 12 mm thickness. In this project, 80% of the material used in the composite are natural fibres such as jute and coir. Such a composite will be a good alternative for wood and wood products using 100% indigenous technology, which in turn saves the foreign exchange of our country. These natural materials have all the properties required for a general purpose board and can be used in the place of wood or MDF synthetic resin boards for surface panelling, partitioning, false ceiling, etc.
The Mission is actively considering a project proposal in collaboration with M/s Fabtech Industries, Calcutta, with technology support from CGCRI - Calcutta for manufacturing a cost-effective Jute-glass hybrid composite for glass shutter assembly and louver shutter assembly for railway coaches. The products made of jute-glass hybrid composites can be used as a replacement of high-cost sheet moulding compound and low-strength dough moulding compound based glass-fibre composites. The technology for the fabrication and evaluation of hybrid composites incorporating jute felt and glass fibre using polyester resin as a matrix has been developed successfully by CGCRI. In these hybrid composites, jute can play the role of filler fibre where strength and modulus requirement are not demanding. Moisture absorption limits can also be reduced from 25% to 2% by weight using glass layer on either side of the jute fibre layer. Another proposal on developing Jute composite as packaging material by complete utilisation of jute plant from NIRJAFT along with an industry partner is also under active consideration by the Mission.
Conclusion
It can thus be inferred that jute fibres can be a very potential candidate in making of composites, especially for partial replacement of high-cost glass fibres for low-load bearing applications. As such, commercial exploitation of jute composites for non-structural applications promises excellent potential. From the point of view of wood substitution, jute composites could be an ideal solution. With ever depleting forest reserves, a composite based on renewable resources such as jute, coir, sisal, etc is poised to penetrate the market. Indigenous wood supply for plywood industry having been stopped virtually and with increasing landed cost of imported plywood veneers, the jute composite boards provide very good value for the customers without any compromise in properties. With ever increasing emphasis on fuel efficiency, jute composites would enjoy wider applications in automobiles and railway coaches. In fact, the market segment for railway coaches in India has a vast potential which is yet to be tapped to a good extent. India would always have an edge for natural availability of jute and manpower intensity in its cultivation. Value-added novel applications such as jute composites would not only go a long way in improving the quality of life of people engaged in jute cultivation, but would also ensure international market for cheaper substitution.
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