Mechanical and thermal behavior of natural fiber-polymer composites without compatibilizers

The present study aims at understanding the mechanical and thermal properties of natural fibers in a polymer matrix without strong adhesion between the two constitutes. For this purpose, four types of pulps, which are refined and unrefined pine and birch kraft pulps, were used together with polypropylene without any compatibilizer. One constituent pulp based and composite pulp fiber-polypropylene handsheets were prepared by standard laboratory sheet preparation method followed by hot pressing process. In addition to these handsheets, pure polypropylene sheets were also formed as the reference. The produced handsheets were tested to determine their tensile properties following the ISO 1924-2 standard for paper and board. During these tests, infrared thermal imaging was also carried out with FLIR A655SC thermal camera with frame rate of 200 Hz and thermal resolution of 50 mK so as to investigate the thermal behavior. As a result of the experiments, it was deduced that the chosen methods produced composites with unsatisfactory properties. In addition, microstructures of the investigated handsheets were analyzed with scanning electron microscopy (SEM) indicating the heterogeneous mixing of constituents and existence of material defects, which was mainly due to the inherent incompatibility of hydrophilic natural fibers and hydrophobic thermoplastics. The study aims at paving a way for improved natural fiber-polymer composite manufacturing methods, a requirement for better understanding the natural fiber and polymer matrix bonding practices.