A flax-reinforced sandwich structure suitable for replacing wood in the top plates of string musical instruments was developed. The mechanical properties of Sitka spruce, the most widely used wood species for this application, were taken as a benchmark when the new materials were developed. The materials were characterized by static and dynamic methods to determine the dynamic Young’s modulus, shear modulus, internal friction, and static mechanical properties. Based on the material characterization, a hand lay-up process with a two-part closed mold and internal pressure bladder was developed and six prototype ukuleles were manufactured. The results show that the flax-reinforced sandwich structure can successfully act as a top plate and that an efficient manufacturing process can be developed to produce monocoque string musical instruments out of composite materials.

Understanding the fatigue performance of biocomposites is critical in order to increase their acceptance, but current literature in this area is mostly limited to nonwoven reinforcements. This paper considers the tension-tension fatigue of three different woven flax/epoxy composites, for which two of them are prepreg-based and the other is manufactured using the Vacuum Assisted Resin Transfer Moulding (VARTM) process. Good fatigue performance of flax fibres comparable to those exhibited by glass fibres has shown the potential of this material to be implemented in load-bearing applications. The results suggest that minimizing the crimp in the yarns is a major concern to increase the resistance to fatigue damage in this class of materials. In addition to the three mentioned composites, two hybrids of flax/glass/ epoxy were manufactured using the same VARTM process to check if the fatigue stability of flax fibre is extendable to its hybrids. The results show that an increase in the strength is possible, while maintaining similar fatigue behaviour as the plain flax/epoxy composites.

This paper aims to better understand the nature of flax/epoxy hot melt prepreg systems as well as the mechanical properties of their cured composites. Two uncured systems were subjected to thermal gravimetric analysis and compaction experiments. Composites were then produced in an autoclave at pressures of 1, 3 and 5 bars. Void analysis was carried out on the cured laminates by optical microscopy and void contents ranging from below 1% to over 20% were obtained by image analysis. The primary source of voids was shown to be resin starvation based on the results of the compaction tests. Tensile properties were shown to be strongly degraded by fabric crimp. Short beam tests revealed a 16% decrease in interlaminar shear strength with a 3.5% increase in void content. Similarly, water absorption tests showed a significant increase in rate of absorption likely due to the presence of voids. The results suggest that in order for flax/epoxy prepregs to reach their full potential, the level of crimp and the evacuation of moisture during cure should be of primary concern.

The characteristics of waste oil palm empty fruit bunch fiber (OPEFB) including fiber morphology and mechanical properties were investigated for use as reinforcement in polymer composites. The mechanical properties of the OPEFB fiber were determined by the single fiber tensile test which was carried out at different span lengths (20, 40, and 60 mm) to obtain the reliable strength and stiffness of the fiber. The extrapolated E‐modulus at infinite fiber length was found to be around 4.36 GPa. The fiber strength was in the range of 150–190 MPa. The unidirectional (UD) composite of OPEFB fibers in various polymer matrices, namely polypropylene, poly(lactic acid), and epoxy, were prepared and characterized. Three‐point bending test (3PBT) was performed on the UD composites in both fiber transverse and longitudinal directions to determine fiber‐matrix interfacial adhesion and composite flexural properties, respectively. Besides, It was found that the efficiency factors achieved for OPEFB in poly(lactic acid) and epoxy were 0.72 and 0.87, respectively, which were significantly higher than that of OPEFB in polypropylene. This result was consistent with the interfacial strength measured by transverse 3PBT. The study provides fundamental understanding for design and application of OPEFB in polymer composites. POLYM. COMPOS., 40:1158–1164, 2019. © 2018 Society of Plastics Engineers