Mechanical properties of compression moulded fibre composite sheets

Abstract: This master thesis project was carried out at a large international company in the forest industry. The company is currently interested in producing sheet formed composite materials with high wood fibre content that can be further processed and formed using conventional compression moulding. The goal of this project was to investigate how the compression moulding temperature and compression moulding hold time influence the mechanical properties of the material, as well as comparing different compositions of the composite material. By a series of preparation tests, an appropriate pre-heating method was developed and the compression moulding parameters to be tested were determined. The mechanical properties to evaluate were tensile properties, flexural properties, short bend test properties and impact strength. Testing was based on ISO- standards with minor adjustments. The tests showed that the mechanical properties increased with a higher moulding temperature. An increased moulding hold time led to increased mechanical properties as well, but not as significantly as the temperature. The density of the compression moulded composite was the most important factor for the mechanical properties. Comparisons between the tested composite compositions showed that a higher polymer content is favourable. Additionally, using long wood fibres with low lignin content had some advantages compared to short fibres with high lignin content.