Recently, biodegradable plastic materials that can be decomposed by living organisms have attracted significant attention because of the great demand for the safe disposal of plastics. Recycling has failed to provide a practical solution for plastic waste disposal (60% of all plastics produced are discarded). It is difficult to achieve both durability and biodegradability in biodegradable plastics. In additive manufacturing processes, polylactic acid (PLA), one of the biodegradable plastics, is typically used, but it presents strength and durability problems. We developed novel additive manufactured biodegradable composite plastics by inserting continuous natural fibers (cotton, hemp, jute, etc.) into fabricated layers of PLA. The composite had a greater strength than normal additive manufactured PLA materials and could be used like a normal PLA filament in fused deposition modeling to create free-form three-dimensional objects. In this study, we performed experiments to evaluate the durability and biodegradability of the composite (PLA as matrix and hemp fibers as reinforcement). Specimens made from the composite were exposed to a normal indoor environment and to severe environments that products might encounter during use (presence of water and UV light (300–400 nm)). The decrease in strength over time was compared with that of PLA, and the durability was evaluated. The results indicated that the strength of the manufactured composite material exceeded that of PLA under all conditions. Whereas the stiffness of PLA exposed to UV light reduced significantly, that of the composite material remained constant, suggesting the significant effect of fiber reinforcement. In addition, test specimens were buried in a simulated soil environment, and their biodegradability was evaluated. The strength of the composite material decreased rapidly, and the biodegradability was confirmed to be at an acceptable level.

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