Open access publications in the SLU publication database

Abstract

The increasing demand for environmentally friendly materials has ushered in a new generation of bio plastics and plant fibre based composite materials. The quality of the raw components is very important when manufacturing a bio based material. For example, many plant fibres are hygroscopic, which means that moisture becomes an important quality determining factor. Therefore, a better understanding and knowledge of moisture adsorption equilibrium is of importance. The moisture adsorption equilibrium of several different plant fibres is examined in paper I. Differences in moisture adsorption equilibrium was found between unretted and retted hemp fibres, while differences between varieties were small. An example of a renewable composite material, investigated in this thesis, is a wheat gluten plastic reinforced with hemp fibres. Paper II shows the effect of hemp fibre reinforcement on the mechanical properties of a wheat gluten based plastic film. Different fibre contents and fibre quality levels were tested. It was found that the fibres did improve the mechanical properties of the plastic and that fibre content was the most important factor in creating a stronger material. However, there were problems encountered with regards to fibre distribution in the material, poor adhesion between the fibres and plastic and a large variation in the material properties. In paper III, we attempted to improve the fibre distribution by using a high speed grinder to mix the fibres and the plastic. Further a diamine was used as a cross linker between the fibres and the plastic to improve the bonding. It was found that the grinder did improve the fibre distribution but not sufficiently to avoid clusters of fibres. The diamine did not improve the interaction between the fibres and the plastic but it did strengthen the plastic itself to a certain degree. It is concluded that hemp fibres can be used to improve the mechanical properties of wheat gluten plastics. However, the fibre distribution and interaction with the plastic needs to be much improved. A possible solution for the fibre distribution problem might be to decrease the viscosity if the wheat gluten dough while the fibre-plastic interaction might be improved by selecting a different cross linking substance.