Thermal stability enhancement of poly(hydroxybutyrate-co-hydroxyvalerate) through in situ reaction

Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) has recently caught more and more attention due to its renewability, good mechanical and barrier properties, as well as marine biodegradability. However, the severe thermal degradation during processing is a major drawback and limits its application. In this work, the thermal stability of PHBV during melt-processing was investigated by incorporating reactive agents. Various contents of Di(tert-butylperoxyisopropyl)benzene (DB), Triallyl isocyanurate (TAIC) and multi-functional epoxy chain extender (ECE) were used. The mixing torque, mechanical and thermal properties were studied. The results revealed that the mixing torque of PHBV gradually decreased during 10 min of melting time and eventually dropped to 2 N.m. Upon adding ECE, the mixing torque slightly increased but still decreased during 10 min period. For the system consisting of DB/TAIC or DB/TAIC/ECE, the mixing torque reached the equilibrium and their values were roughly twofold higher than PHBV alone. The possible crosslinking reaction and torque reversion were predominantly observed when adding high contents of DB and TAIC. 1 H NMR spectra suggested the reaction of DB/TAIC and PHBV. Young’s modulus and tensile strength of system consisting of DB at 0.3 phr, TAIC at 0.1 phr and ECE at 0.5 phr increased from 1440 and 40.4 MPa to 1803 and 55.5 MPa, respectively. TGA thermograms showed that the onset temperature and inflection point were improved when adding DB/TAIC and ECE. From the findings, it indicated that the combination of DB/TAIC and ECE was one of the simplest and effective ways to improve the melt viscosity without sacrificing the mechanical properties