Natural Fibre Composites
Natural Fibre Composites Fig. 1. Three different types of forest residues used on Forestcar project. From top to bottom: crushed remains of heather shrubs, remnants of pine and eucalyptus. Forestry wastes as fillers automotive plastics In recent decades, great efforts are being made towards the development of new materials with less environmental impact, coming as far as possible from renewable sources and with a high level of biodegradability. The CTAG (Galician Automotive Technological Centre) is strongly committed to the environmental preservation and is currently investigating the creation of new plastic materials in which the inclusion of environmentally friendly source materials takes a more relevant role. The location of CTAG, in the northwest of the Iberian Peninsula, where the timber industry represents one of the most important sectors in the region, led to the choice of these materials. Thus, Forestcar project, in collaboration with CIS Madeira (Galician Timber Technological Innovation and Services Centre), focuses on the use of forest residues as reinforcement for manufacturing plastic parts for the automotive industry, minimizing its environmental impact and greatly reducing costs. By A. Tielas, D. García, M. de Dios Plastic Product / Process Area Engineering & Development Department Galician Automotive Technological Centre (CTAG), Spain and G. Piñeiro Galician Timber Technological Innovation and Services Centre (CIS-Madeira), Spain Five different types of residues were used, two of them from charred wood of eucalyptus and pine, and the other three from shrubs or bushes (gorse, heather and broom) (Figure 1), in order to achieve a minimum concentration of 40 wt% of natural reinforcement within a polymer matrix of commercial polypropylene. Several factors must be taken into account when incorporating the natural reinforcement to the polymer matrix. First, forest debris should fit to plastic processing conditions. Compatibility between filler and polymer, the potential release of odor-generating volatile or the lower resistance to high temperatures and pressures of such natural substances can hinder the compounding and injection processes. Furthermore, 40 bioplastics MAGAZINE [03/12] Vol. 7
Fig. 2. Processed residues through mechanical refining (left) and thermo-mechanical defibering (right) final material should improve, or at least preserve, the mechanical properties of the original matrix and its structural toughness under environmental conditions to meet the minimum requirements of automotive industry. The selected residues (CIS Madeira) were chipped with a cutter unit and then granulometrically sorted to discard finest and thickest items, giving priority to those particles with the higher aspect ratio. Two types of fiber processing were performed for each residue, thermo-mechanical defibering and mechanical refining. In the case of thermo-mechanical defibering, materials are subjected to prior digestion before going to the pulping mill. On the other hand, mechanical refining does not involve any chemical stage and the process is performed exclusively by a mechanical procedure. This method produces larger particles than thermo-mechanical defibering (Figure 2). After treating the forest residues, the processes of compounding and injection molding take place (CTAG). An Engel Victory VC 2550/350 injection machine was used with the settings normally employed for the injection of commercial polypropylene (injection temperature 190°C, mold temperature 20°C and injection speed = 45 mm/s) (Figure 3). Injected probes underwent a series of standard tests in order to check the mechanical properties of the composite material and its suitability to the specific requirements of the automotive industry (CTAG). Tensile, bending and density tests were performed as well as tests of resistance to climatic factors (humidity, temperature and solar radiation) and emission of volatiles, comparing bioplastics MAGAZINE [03/12] Vol. 7 41
