Fibre reinforced plastics (FRP) have been a standard in lightweight construction for a while now. Now a new trend is making itself felt: the use of natural fibres, which can be produced with lower energy costs and are biodegradable.
The thermoset specialists at Lorenz Kunststofftechnik have developed a Bulk Moulding Compound (BMC) reinforced with jute, cotton or sisal fibre, that exhibits, depending on the composition, properties similar to traditional FRP. Fibre length can be adjusted as needed and the material can accordingly be compression or injection moulded. Moreover, the use of biobased fibres open up new possibilities for use: the cotton thermoset, for example, is easy to paint, laminate or finish and is therefore suitable for design applications.
This new development is based on the tried and tested material, BMC 0204, which already contained two eco-friendly materials: calcium-carbonate as a bulking agent and ATH as a flame retardant. The new natural fibres also replace the glass fibres, which leads to a lower energy consumption during production, reducing the carbon footprint of the process. The type and length of fibre to be used is chosen according to the intended use; for instance, compounds with sisal are characterised by a degree of shrinkage of -0.1 to -0.3 percent, while cotton-reinforced thermosets have a high elasticity modulus of over 8,000 MPa and low abrasion. They all have a very low density of between 1.65 and 1.7 g/cm3, making them lighter even in comparison with FRP. This makes the produced parts ideal for lightweight construction.
Natural fibre-reinforced plastics (biocomposites) generally offer good thermal and acoustic insulation. By changing the actual composition of the BMC, the specific properties can also be adjusted individually, for example to endow the normally highly flammable natural fibres with excellent fire-resistant properties. In UL94 flammability tests, a 1.5 mm thick sample could be put out within ten seconds. This result corresponds to the best classification, V0. The problem of moisture absorption, very common in biocomposites, could also be solved using the appropriate material composition so that, measured according to ISO 62, it is only ≤ 0,5% for the eco-friendly BMC with cotton, ≤ 1,3 % with jute and ≤ 1,8 % with sisal.
Unlike the traditional, often thermoplastic biocomposite panels, bio-reinforced BMC also opens up different processing options, as parts can now be either compression moulded or injection moulded. This means that more complex and delicate parts, which up until now could only be produced from FRP, can be produced from biocomposites as well. The required moulding temperature in the cylinder is 20 to 40 °C and, in the mould itself, 140 to 170 °C. This means that the material is suitable for various fields of application; from large parts, for instance in car interiors, to tiny components, for example in electronics.
The complete range of natural fibre thermosets produced by Lorenz can be recycled; 100 percent of cutting and punching waste can be reused, in accordance with their material composition. Energy recovery of the fibres is carbon-neutral and they burn without residue. The composites are compliant with RoHS, containing neither halogens nor any heavy-metal compounds, are overall highly ecologically friendly and harmless to humans and the ecosystem. The experts at Lorenz, however, intend to take this a step further: they are currently working on an organic resin matrix to replace the polyester resin currently used, yielding a composite material that will ultimately consist wholly of non-fossil-based material.