Ulrich Riedel

Natural fibre-reinforced biopolymers as construction materials - new discoveries

Originally coming from aerospace technology, fibre reinforced plastics (FRP) are successfully used for various applications, today because of their excellent specific properties, e.g. high strength and stiffness, low weight and the potential of optimisation by orientating (esp. Continuous) fibres along the load paths. In order to successfully meet the environmental problems of these classic composites, the DLR Institute of Structural Mechanics developed an innovative idea in 1989: By embedding natural and near natural reinforcing fibres e.g. flax, hemp, ramie, cellulose etc. into a biopolymeric matrix from cellulose, starch or lactic acid derivatives etc. (thermoplastics as well as thermosets), new fibre reinforced materials, called biocomposites, were created and are still being developed. In terms of mechanical properties being comparable to glass fibre reinforced plastics (GFRP), latest developments on new fibre/matrix combinations and environmentally compatible flame retardants enable biocomposites to replace GFRP in most cases. Biocomposites are designed to meet the processing requirements for commonly used manufacturing techniques, e.g. pressing, injection moulding, filament winding, BMC, SMC etc. Apart from anisotropic and specially tailored lightweight structural parts with continuous fibre reinforcements, biocomposites are very well suited for panelling elements in cars, railways and aeroplanes, etc. using different kinds of nonwovens from single fibres (needlefelt nonwovens, fleeces etc.) to be easily adapted to the usually curved shapes of panellings, fairings etc.

Nanoscaled Boehmites’ Modes of Action in a Polymer and its Carbon Fiber Reinforced Plastic

Laminates of carbon fiber reinforced plastic (CFRP), which are manufactured by injection technology, are reinforced with boehmite particles. This doping strengthens the laminates, whose original properties are weaker than those of prepregs. Besides the shear strength, compression strength and the damage tolerance, the mode of action of the nanoparticles in resin and in CFRP is also analyzed. It thereby reveals that the hydroxyl groups and even more a taurine modification of the boehmites’ surface alter the elementary polymer morphology. Consequently a new flow and reaction comportment, lower glass transition temperatures and shrinkage, as well as a changed mechanical behavior occur. Due to a structural upgrading of the matrix (higher shear stiffness, reduced residual stress), a better fiber-matrix adhesion, and differing crack paths, the boehmite nanoparticles move the degradation barrier of the material to higher loadings, thus resulting in considerably upgraded new CFRP.

Bessere Eigenschaften von CFK durch Integration keramischer Füller

Hohere Eigenspannungen von im Injektionsverfahren hergestellten kohlenstofffaserverstarkten Verbundkunststoffen (CFK) bringen, verglichen mit Kennwerten, die mittels Prepreg-Verfahren erzielt werden, in puncto Druckkennwerte Defizite mit sich. Diese gehen in erster Linie auf geringere Steifigkeiten sowie eine erhohte Schwindung der CF-Laminate zuruck. Durch Zugabe von Nanopartikeln zu dem Epoxidharz konnen hier Verbesserungen der mechanischen sowie thermischen Kennwerte erzielt werden.

Structural Materials Made Of Renewable Resources (Biocomposites)

In view of the increasing shortage of resources as well as growing ecological damage, the aspects of the exploitation of raw materials and the recovery after the end of the lifetime of products have to increasingly be taken into consideration. In addition, the aspect of saving energy by means of lightweight constructions must also be regarded. The use of conventional, i.e. petrochemically-based plastics and fibre-reinforced polymers, the production process, as well as usage and recovery are often very difficult and demand considerable technical resources. An answer to solve all these problems may be provided by natural fibre-reinforced biopolymers based upon renewable resources, called biocomposites in the following. By embedding plant fibres, e.g. from flax, hemp, or ramie (cellulose fibres) into biopolymeric matrices, e.g. derivatives from cellulose, starch, shellac, or plant oils, fibre-reinforced polymers are obtained that can be integrated into natural cycles in an environmentally-friendly manner, e.g. by classic recycling, by CO2-neutral incineration (including recovery of energy), and possibly by composting.