Unidirectional Rubber-Toughened Green Composites Based on PHBV

Abstract

The large-scale entry of bio-based polymers, such as poly(hydroxybutyrate-co-valerate) (PHBV), in applications commonly occupied by petroleum-based plastics is heavily limited by their poorer mechanical properties, thus, hindering efforts to reduce harmful plastic waste. Prior work to improve these properties has involved short natural fibre reinforcements, which do not produce substantial improvements. In this work, PHBV was simultaneously reinforced with unidirectional flax and toughened with poly(butylene adipate-co-terephthalate) (PBAT) or epoxidized natural rubber (ENR) to produce well-rounded composites. Toughened unidirectional composites were prepared by cryogenic grinding, powder layup and compression moulding. Unidirectional flax addition resulted in 4-fold increases in tensile properties, 3-fold increases in flexural properties and 20-fold increases in impact properties, whilst producing minimal change in the thermal properties. PBAT and ENR phases appeared well bonded to the PHBV within the composite. The addition of PBAT did not cause any significant changes in thermal or mechanical properties. The addition of ENR, however, reduced the tensile modulus and the flexural properties but produced a significant increase in impact strength, attributed to the coarse particle size of ENR. Unidirectional flax reinforcement of PHBV widens the scope of application of PHBV considerably where mechanical properties are of concern, while ENR has significant potential as a bio-based toughening agent for biocomposites.

Soil Biodegradation of Unidirectional Polyhydroxybutyrate-Co-Valerate (PHBV) Biocomposites Toughened With Polybutylene-Adipate-Co-Terephthalate (PBAT) and Epoxidized Natural Rubber (ENR)

“…As noted above the composites developed surface cracking during soil burial but this was not observed for the neat PHBV. This difference is attributed to the higher level of PHBV crystallinity in the composites induced by nucleation at the fibers, as discussed in earlier work by Zaidi and Crosky (2019).The increased level of crystallinity would result in increased brittleness.…”

“…In this work, PHBV was simultaneously reinforced with unidirectional flax and toughened with PBAT or ENR50. The mechanical, thermal, and morphological properties of the resulting composites have been reported previously in Zaidi and Crosky (2019). This study focuses on the biodegradation properties of those composites and elucidates the effect of PBAT and ENR on the biodegradation of PHBV/flax composites.…”

“…In contrast, biodegradation of PBAT has been reported to be minimal (Tsutsumi et al, 2003;Trinh Tan et al, 2008;Ali Shah et al, 2013). It is noted, however, that the ENR particles were much coarser than the PBAT particles (Zaidi and Crosky, 2019) and this may also have affected the degradation rate. Pantani and Sorrentino (2013) conducted biodegradation studies on PLA and reported that crystallinity is a factor that affects the biodegradation rate of PLA, with the rate being faster for amorphous samples compared to crystalline samples.…”

“…The authors attributed this to crystallinity affecting the diffusion of water into the sample and presenting difficulty in access to the polymer chains for enzymatic attack by the microorganisms. Differences in time of saturation for PHBV/flax and the toughened composites might therefore be due to differences in crystallinity between the two types of samples, as the toughened composites would have had a much lesser crystallinity as a result of addition of amorphous PBAT and ENR, as discussed in Zaidi and Crosky (2019).…”

“…The localized pitted regions, which were seen as lightcolored regions when viewed using SEM, were more pronounced on the PHBV/ENR/flax and PHBV/PBAT/flax samples than on the PHBV/flax composite. This is attributed to lower crystallinity caused by the addition of the toughening agents (Zaidi and Crosky, 2019), since amorphous regions are known to degrade preferentially to crystalline regions (Abe and Doi, 1999;Woolnough et al, 2010).…”