Courtesy of The Textile Journal (La Revue du Textile)
                                                                
During the last 10 years, natural fibre composites with thermoplastic and thermoset matrices have been identified by car manufacturers and suppliers, mainly in Europe, for manufacturing several types of parts like door panels, seat backs, headliners, package trays, dashboards, and also interior parts. The main incentive for the use natural fibres such as hemp, flax and sisal are providing automobile part reinforcement with reductions in weight, cost, and CO2 emissions, less reliance on petroleum resources, recyclability, biodegradability— and most importantly the fact that natural fibres are seen as “green” or ecofriendly. Ecological evaluation, or eco-balance of natural fibre mats as compared to glass fibre mats for development of automotive applications presents a real opportunity for bio-based composites. For example, the energy consumption to produce a flax fibre mat including cultivation, harvesting, straw decortication and fibre isolation is evaluated to approximately 17% of the energy required to produce mat from glass fibre.

While the United States has less strict regulations concerning automotive end-of-life requirements, European Union and Asian countries have released stringent guidelines. European Union legislation implemented in 2006 has expedited recent natural fibre composites in automotive sector; by 2006, 80% of a vehicle must be reused or recycled and by 2015 it must reach 85%. Japan requires 88% of a vehicle to be recovered (which includes incineration of some components) by 2005, rising to 95% by 2015. As a result, most automakers are evaluating the environmental impact of a vehicle’s entire lifecycle, from raw materials to manufacturing to disposal.

The idea of using bio-based materials in automotive applications is not new. In the 1930s, Henry Ford strongly supported the use of such material. Hemp was used to produce reinforced soy resin composites in the manufacturing of exterior body panels. But, at that time technologies were not at all mature and given processing difficulties, dimensional stabilities, performance limitations and the arrival of low cost petroleum products, this idea was abandoned.

Glass fibre composites are very good candidates to meet the structural and durability demands of automobile interior and exterior parts. Excellent mechanical properties and good manufacturing facilities have permitted the introduction of glass fibre composites within the automotive industry. However, glass fibre composites present non-negligible limitations such as their relatively high fibre density, difficulty to machine, poor recycling and the potential health hazard of glass fibre dust. It is now well recognized that natural fibre composites offer many advantages compared to traditional glass fibre composites, but several major technical issues must be addressed before the engineering and the industrial communities adopt this new class of materials. The main challenges faced are:

• homogenization and improvement of the fibre’s properties by controlling the straw processing and fibre surface treatment
• control of the effect of natural fibres on the polymer matrix properties
• fibre/matrix properties
• moisture sensitivity
• flammability

Recently, the National Research Council of Canada (NRC) has launched a National Program on Bioproducts that includes a project entitled ‘’Biomaterials and bio-polyols for the production of environmentally-friendly products for the automotive, aerospace, construction and plastics industries’’. This project led by the Biotechnology Research Institute (BRI) includes participation of several NRC institutes and the Industrial Material Institute (IMI) is mainly responsible for the development of technologies to optimize properties and manufacturing of natural fibre composites. The main objectives of this part of the project are to find solutions to optimize the quality of fibres, the fibre/matrix properties and to decrease moisture sensitivity as well as natural fibre flammability. Another important point to mention is that natural fibre composites represent a very good opportunity for Canada since it is the first producer of flax seed oil in the world.

Natural fibre composites in the automotive industry include the use of either a thermoset or thermoplastic polymer binder system combined with the natural fibre performance, mat or loose fibres. However, optimum performance and structural components will be achieved only with the development of technical textiles, as currently done for glass and carbon reinforcement. In automotive applications, the most common system is thermoplastic polypropylene because thermoplastic is easier to recycle. Polypropylene is also favored due to its low cost, excellent mechanical properties, good dimensional stability and impact strength. The development of thermoplastic natural fibre composites is mainly limited by two factors: the upper temperature at which the fibres can be processed and the incompatibility between the fibres and the polymer matrix. The generally perceived upper limit for processing natural fibres for short-term exposures is around 220 °C. The result of prolonged high-temperature exposure may be discoloration, volatile release, poor interfacial adhesion, and cellulose components can become brittle and premature degradation of polymer matrix can occur. Currently, surface treatments (enzymes, chemicals, nanoparticles) and compatibility strategies to obtain high performance and high service temperature of natural fibres are in development at NRC (BRI-IMI).

• Good interface

• Bad interface

       Figure 1. Natural fibre surface treatments and compatibilization
       strategy has permit to improve interfacial properties in polypropylene
       composites.

The implementation of natural fibre composites into interior trim continues to be developed by automotive suppliers mainly based on short fibres or natural fibre mats processed by compression molding, injection molding, thermoforming, and structural reaction injection molding. The primary drivers for the selection of the appropriate process technology for natural fibre composites are the size and geometry of the part’s performance, cost, and ease of manufacturing. Several factors must be considered in selecting a process. The process must allow good dispersion or distribution of the fibres in the composite, good compatibility between the hydrophobic matrix and hydrophilic fibres, minimum fibre degradation to insure optimum performance, control of fibre orientation. The control of moisture in natural fibre composites is of prime importance because it can result in significant performance reduction. It is quite costly to dry natural cellulose fibre and the ability to control and minimize energy input during this process is one opportunity foreseen with the processing of natural fibre materials. Similarly, the ability to eliminate water absorption during the servicing of natural fibre composite components is paramount in industrial applications.


Patel M, Bastioili C, Marini L, Wurdinger, E. 2002. Environmental assessment of bio-based polymers and natural fibres. Netherlands: Utrecht University.