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Cimteclab S.p.A. has developed innovative bio-based composites using jute fibres as reinforcement and a cardanol-based thermosetting resin as the matrix. The use of a matrix derived from a natural resource increases the renewable portion of natural-fibre-reinforced composite materials.
P. CAMPANER (1), D. D’AMICO(2), L. LONGO (3), C. STIFANI (4), A. TARZIA (5), R&D CIMTECLAB S.P.A. (published on April 2010 - JEC Magazine #56)
At the moment, the automotive industry is one of the most prominent consumers of bio-based composites. Its main motivations are weight reduction (about 10- 30%), day-to-day fuel efficiency, and CO2 emission reduction. Researchers have developed natural-fibrereinforced composites for both interior and exterior structural applications mainly because of the added advantages of natural fibres, such as high strength-to-weight ratios, low cost, ease of processing, environmental benefits and worldwide availability.
Moreover, unlike glass fibres, natural fibres cause no harm to workers during handling and less wear to the processing equipment. Researchers are trying to explore the technical applications of various natural fibres such as hemp, flax, kenaf and jute. In the automotive industry, applications include door and instrument panels, body panels, underbody panels, roof tops and front-end fenders. Natural-fibrereinforced automotive components are currently used by several vehicle manufacturers including Ford, Opel, Daimler Chrysler, BMW, Fiat, Audi, Peugeot, Renault, Mercedes Benz and Volvo.
Besides the fibres, the matrix has a strong influence on the properties of composites. In fact, the properties of naturalfibre- reinforced composites not only strongly depend on the type of fibre, but also on the type of matrix and the fibrematrix combination. At the moment, composites prepared using conventional thermosetting resins such as epoxy or phenolic resins fulfil the requirements for higher performance applications. They provide adequate mechanical properties, in particular stiffness and strength, at acceptable price levels. In addition, thermosetting compounds have higher thermal stability and lower water absorption than materials based on thermoplastic polymers such as polypropylene (PP). Even though the demand for improved recycling concepts is expected to result in the substitution of thermosetting polymers by thermoplastics, the use of thermosetting matrices based on renewable raw materials could meet the need to reduce the environmental impact of industrial processes and products, promoting a preference for natural-reinforced thermosetting composites over thermoplastic alternatives.
Therefore, the substitution of synthetic fibres by natural fibres is only the first step in the development of new renewable resource-based materials. The growing demand is driven by the pressure to reduce the emission of greenhouse gases such as CO2 into the atmosphere and by an increasing awareness of our finite fossil resources.
Cimteclab S.p.A. has developed novel bio-based composites that can meet the requirements of automotive structural components. In particular, recently-launched cardanol-based novolac-type phenolic resins have been used in the formulation of thermosetting resins, blended with a conventional epoxy resin. Composites using jute fibres as reinforcement and the cardanolbased thermosetting resin as the matrix were produced.
Cardanol-based epoxy curing agents
Cimteclab S.p.A. recently launched innovative bio-based epoxy curing agents. These agents are novolac-type phenolic resins made from cardanol, which is a natural phenol derivative obtained from cashew nut shell liquid (CNSL). CNSL is an abundant agricultural by-product of the cashew (Anacardium occidentale L.) industry, obtained traditionally as a by-product of the processes used to remove the cashew kernel from the nut (Figure 1). This is an inedible product, which means that a vegetable material source can be used, leaving edible oils for human consumption.
Cardanol-based novolacs are especially designed to be used as curing agents in the formulation of heat-cured epoxies, using a tertiary amine as catalyst. In addition to be compatible with conventional bisphenol A and bisphenol F epoxy resins, they are liquid at room temperature and impart flexibility and hydrophobicity in cured epoxy resins. Moreover, they have key properties such as chemical and water resistance.”
Innovative bio-based composites
Innovative bio-based composites using jute fibres as reinforcement and a cardanol-based thermosetting resin as the matrix have been developed. Coupling natural fibres with cardanol-based matrices has resulted in composites characterized by a natural component content above 50% by weight.
Representative composite laminates were produced by hand lay-up of jute fabrics using a mixture of a conventional diglycidyl ether of bisphenol A (DGEBA) epoxy resin, a cardanol-based novolac as curing agent and a tertiary amine catalyst. To serve as a reference, composite laminates were prepared using a thermosetting resin obtained from reacting a DGEBA with a conventional amine curing agent such as diethylene triamine (DETA). The composites were obtained combining the resin with about 34% jute fibres by weight.
As shown in Table 1, the natural-based matrix performs like a composite matrix. The resulting laminates are characterized by a modulus and strength comparable to those measured when using the DGEBA/DETA resin but with a higher ductility. In addition to their comparable or better performance, cardanol-based resins are price competitive with conventional products.
It was also observed that appropriate surface treatments could effectively remove impurities from the fibres, low moisture sorption and improve matrix-reinforcement interactions. Therefore, the use of fibre surface treatments and an appropriate matrix could increase the environmental resistance of the composites and enhance the fibre-polymer interface. This could open up a whole spectrum of interesting new applications, allowing the use of bio-based composites for exterior car components.
Renewable resource-based materials are currently gaining in importance worldwide. The instability of the crude oil market and discussions on CO2 emissions did not favoured conventional materials which are constantly under the microscope, thus preparing the way for natural alternatives. Cimteclab S.p.A. has developed innovative bio-based composites containing more than 50% renewable resources by weight. The use of a matrix derived from a natural resource has increased the renewable portion of naturalfibre- reinforced composite materials.