Browsing by Author "Parkkinen, Hanna"

Reducing the use of plastic has become an important topic and at the same time the forest industry is looking for new opportunities for fiber use. Increased environmental awareness, together with environmental regulations and legislation, have forced manufacturers and industry to choose environmentally friendly solutions for products. Natural fiber reinforced composites have great potential because they are biodegradable, environmentally friendly, abundant and cost-effective when compared to synthetic reinforcements. Natural fibers also have favorable mechanical properties such as low density and good tensile strength and elastic modulus. The aim of this study is to examine the use of natural fibers in composites and how fiber properties affect the properties of natural fiber composites. In the experimental part of the research handsheets of birch and eucalyptus pulp were prepared. In addition, composites were prepared combining handsheets and two polymers. The differences between the birch and eucalyptus fibers were studied and also the effect of refining on the properties. In addition, the mechanical properties of sheets and composites were compared and also differences between polypropylene (PP) and polylactide (PLA). The mechanical properties tested were tensile strength, bending stiffness, elastic modulus and break elongation. In addition, the structure of composites and sheets were examined with optical microscopy. Composites made from polylactide had a better tensile strength and higher elastic modulus when comparing to polypropylene composites. Elongation and bending stiffness were improved with the polypropylene composites. On the sheets there is a clearly better elastic modulus than in the case of polypropylene. When the sheets and polypropylene are combined, the elastic modulus decreases when compared to the fibers. In addition, the elongation of the sheets was good, especially when comparing the polylactide composites. By refining the fibers, the mechanical properties of the sheets were improved. The refining of the fibers was generally seen to have the same effects on the composite results. The differences between birch and eucalyptus fibers are relatively small. With the birch fibers slightly better tensile strength and elongation are obtained but the eucalyptus sheets are stiffer. The results show that when combining fibers and plastic as a composite, many good mechanical properties are obtained in comparison with the properties of the sheets or the pure polymer.