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Environmental impact plays an ever-increasing role in the industrial production of materials, and because of its importance, the scientific community is examining a wide variety of new materials that are more environmentally friendly. Bioplastics are characterized by the fact that the usual petrochemical resins (polypropylene, polyethylene etc.) are replaced by bio-sourced resins and the reinforcements (glass fibers, carbon fibers etc.) are replaced by natural fibers (bamboo, flax, cotton, etc.). Polylactic acid (PLA) is a biodegradable polymer that is increasingly used in biomedical applications and in packaging. Additionally, bamboo is a promising source of fibers that could be used as reinforcement. In fact, bamboos are grasses with rigid, woody stems, which grow extremely fast and profusely. By virtue of these properties, bamboo is a good candidate as a natural fiber source. Therefore, composites made of a PLA matrix which are reinforced by bamboo fibers may offer many potential advantages as a replacement for less biodegradable alternatives. The mechanical performance of polymer-based composites is often dominated by the interfacial properties between the fibers and matrix, especially with respect to mechanical failure. In this thesis, both untreated fibers and those modified with a NaOH treatment were examined. The shear strength at the interface between a bamboo fiber and the surrounding PLA matrix is quantified. A novel method for processing pull-out-test samples and the details of a test procedure are described. Electron and optical microscopy are both used to examine the failure mode and to quantify the geometry of the fiber-matrix interface. The value of the interfacial shear strength is reported, and its statistical variations are discussed. The results provide important information regarding the future design of natural composites.
Advisor: Joseph Turner