Mechanical properties of modulus‐graded bamboo fiber‐reinforced PHBV composites and their thermal stability properties

Abstract In this study, bamboo fibers (BFs) were classified into high‐modulus fiber (HMBF), medium‐modulus fiber (MMBF), and low‐modulus fiber (LMBF) based on modulus grading from the source, and then these fibers were added as a reinforcement phase to poly‐3‐hydroxybutyrate‐co‐3‐hydroxyvalerate (PHBV) to fabricate BF/PHBV composites. To improve the interfacial compatibility, BFs were surface modified with a silane coupling agent and a rare‐earth coupling agent. The performance of graded BFs and bamboo powder/PHBV composites was investigated. The findings revealed that the HMBFs significantly enhanced the mechanical strength and heat resistance of the composites, where the high modulus fiber/PHBV composite (HMBPC10) showed an increase in tensile strength, tensile modulus, flexural strength, and flexural modulus by 12.36%, 7.99%, 8.77%, and 17.10%, respectively, compared with the low modulus fiber/PHBV composite (LMBPC10). Moreover, the thermal stability of HMBPC and the middle modulus fiber/PHBV composite (MMBPC) was also superior to that of LMBPC. Further studies showed that the silane coupling agent has the potential to enhance the interfacial adhesion between the fiber and the PHBV, while the treatment with the rare‐earth coupling agent further enhanced the overall characteristics of the composites. After the silane coupling agent treatment, the flexural strength of the three modulus‐graded BF/PHBV composites increased by 10.37%, 16.72%, and 16.17%, respectively. Furthermore, the flexural modulus of these three composites increased significantly by 45.96%, 46.81%, and 67.93%, respectively, after the rare‐earth coupling agent treatment. The graded‐BF reinforcement method proposed in this research offers a fresh perspective for the efficient use of BFs and widens its application prospects in the field of degradable composites. Highlights BF/PHBV composites are sustainable and low‐cost composites. HMBF significantly improved the mechanical properties of BF/PHBV composites. Modulus grading of bamboo helps to utilize the main material at a higher value. Rare‐earth and silane coupling agents enhance the performance of BPCs.