Behavior of Bamboo Fiber Reinforced Composites: Pristine and Damaged

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Abstract Natural fiber composites have proven elusive to large scale use in industry due to their lower mechanical properties than glass or carbon fibers despite their low cost, natural availability, and sustainable sourcing. The large variance in quality, behavior, necessary processing, compatibility with a thermoset matrix and longevity between the different types of natural fibers makes it challenging to descern the optimal formulation of natural fiber to be used as the reinforcing substrate in composite materials. The lack of uniformity in fiber quality within single strands of natural fiber can create challenges for their use in high strength applications where there are high standards for conformity to an ideal material behavior. Accordingly, for those applications it is common practice to use weaved fibers with high levels of homogeniety over large lengths, which is a requirement that can only be met when the fibers are subjected to the same processing parameters in their synthesis, such as E-Glass and PAN Carbon fibers. However, there is still considerably wide use for composites in applications with medium to low strength requirements, such as panelling, framing and brakets. It is in this area that chopped strand mats find wide use and adoption. In this study we investigate the behavior of different types and mixtures of chopped strand bamboo fiber reinforced thermoset composites, where the reinforcing bamboo fiber extraction, processing and their resin infusion have been performed using different techinques. The study covers the bamboo fibers that are extracted both mechanically and chemically, as it also covers resin infusion through VARTM and by manual mixing and consolidating using compression molding. Two different mechanically extracted fiber types are studied. One is extracted by manually seperating individual fibrils from the culm of the fresh bamboo stalk. The other type is extracted using the manner performed in the textile industry, by crushing the stalk and combing the viscose top. The chemically extracted bamboo fiber is processed by delignifying the bamboo stalk, by submerging it in acid, leaving the cellulose fibers intact. These different fiber types are then prepared into chopped strand mats and infused with a thermoset resin containing recycled polyester. Glass Fiber (GF) is also used as the baseline for understanding the standard perfromance of this application. Samples are also drilled to evaluate their response to damage similar to what can be expected for the materials to undergo in joining operations. Results of the study show that industrially prepared GF performs significanlty better than the bamboo fibers when prepared with VARTM, even though the bamboo fibers theoretically have a similar stiffness. Bamboo fibers are however, able to bridge this gap, when prepared in the compression mold, as matrix dominated behavior allows for equalization of contribution across the different fiber regimes. There seems to be minimumal variation in the response of the bamboo fibers to damage by drilling, similar to what is witnessed from GF as well. This shows that for the applications of medium and low strength requirements, bamboo fiber can be a truly competitive alternative to synthetic fibers.