Natural fiber composites optimization of microstructure and processing parameters

Abstract: Natural fiber composites, (NFC) are defined in this work as a group of materials where at least the fibers originates from renewable and CO2 neutral resources. NFC consists of a polymer matrix and a natural fiber. The fibers which originate from wood or plants can replace non-renewable fibers or fillers or simply replace part of the plastic. If plastics from renewable resources are used, NFC is a 100% renewable material. Even though there is very large variety of fibers, matrices and manufacturing techniques used to produce NFC, these materials are often separated as its own material class. However, the variety of constituents and processing methods result in completely different materials with very diverse properties. NFC could thus be suitable for an extremely wide area of applications. We believe that it is important to distinguish different types of NFC and classify them based on matrix (thermoplastic or thermoset), fiber (long or short/orientation) and manufacturing techniques. For instance compression molded composites are very different from injection molded materials. Therefore it is important to find the limits of their performance in connection to the processing parameters. The focus of this work is on the compounding and injection molding techniques. Although extensive research has been done on injection molded NFC, this is one area where the natural fibers still have not made a market breakthrough. We believe that the reason for the limited use of natural fiber compound in injection molded products is partly due to uncertainties about the influence of different constituents on the final properties and lack of defined framework for product design and manufacturing in order to optimize the material and assure consistent quality. Although deep knowledge about these materials have been accumulated among producers and researchers in this area, guidelines or simple rules of thumb for NFC development and processing are quite hard to find in literature. Thus, in order to make natural fiber compounds a more interesting alternative for the injection molding industry, this work is focused on finding limitations on important properties and giving general guidelines for material optimization and processing of natural fiber composites.

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