Enhanced crystallization kinetics of bacterially synthesized poly(3-hydroxybutyrate-co-3-hydroxyhexanate) with structural optimization of oxalamide compounds as nucleators

Bacterially synthesized poly (3-hydroxybutyrate-co-3-hydroxyhexanate) (PHBH) has attracted much attention as biodegradable plastics and potential biomaterials. However, the crystallization rate of PHBH is very low, which limits its application in plastic field. Herein, oxalamide compounds (OXAn) with a formula of C6H5NHCOCONH(CH2)nNHCOCONHC6H5 (n = 2, 4, 8, 12) were tailor-made as nucleators to improve the crystallization behaviors of PHBH. The effect of aliphatic spacer length of OXAn, i.e., -(CH2)n-on the nucleation behavior was investigated. The OXAn would assemble into shish-like superstructures and PHBH crystals preferred to grow on the surfaces of the shish. The crystallization rate of PHBH/OXAn blends increased with the spacer length of OXAn up to n = 8 and then leveled off, which trend was consistent with the nucleation activity (Ψ) and the nucleation constant (Kg) of the OXAn. Meanwhile, the OXAn increased the nuclei density of the PHBH while inhibited its secondary crystallization, resulting in a superior and steady mechanical performance of PHBH materials. This work provides a scientific approach to design the optimal structure of OXAn as nucleators for PHBH materials, which may broaden the application range of PHBH materials.