Tailoring Biocomposites with Reduced Water Uptake for 3D Printing
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In this study, two different grades of bioPE, with a varying melt flow index (MFI) were tested for making biocomposites reinforced with wood fibre. A low MFI was found to be more adequate for the manufacturing. Filaments were produced and further used for additive manufacturing (3D printing). Different types of pulp fibres (thermomechanical pulp, bleached and unbleached kraft fibre) were used in the manufacturing and the effect of these were further tested with respect to mechanical properties and water absorption. TMP generally showed a slightly better performance than kraft fibres in regard to decreasing water uptake and improving mechanical properties. Composites with a surface modified version of the fibres were also manufactured and tested in the same manner as the original composites. This surface modification has an aim to improve the hydrophobic properties to the fibers, hence it is of great interest to examine water uptake in the manufactured composites and whether this modification affects the compatibility between fibre and matrix. With regard to the modifications, TMP was found to perform better than kraft fibre with the modification. Two treatments were assessed for the TMP fibres, an LG (lauryl gallate) treatment and an OG (octyl gallate). The OG modification overall showed the greatest decrease in water uptake and improvement in mechanical properties. The microstructure, dispersion of fibre and fracture surfaces of the filaments were further examined through SEM assessment, and the performance of the samples in regard to 3D printing was assessed. Fibre dispersion was found roughly similar in all samples, however, the void fraction and roughness of the filament varied throughout the samples, especially showing poor results with a bioPE with a high MFI. TMP showed a greater ability to 3D print, and a better print quality. The modified TMP fibres also gave improved results in 3D printing compared to the modified kraft fibres.