Accelerated weathering studies on the bioplastic, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Abstract

The effect of accelerated weathering exposure time on the bioplastic, poly(3-hydroxybutyrateco-3-hydroxyvalerate) (PHBV) was studied. The chemical structure and thermophysical property changes of solvent cast PHBV films were examined by a combination of optical microscopy, size exclusion chromatography, FTIR and 1 H-NMR spectroscopies, tensile testing, and differential scanning calorimetry (DSC). The exposed PHBV surfaces experienced surface crazing upon weathering. The molar mass of weathered PHBV was shown to decrease due to chain scission which was dominant over the crosslinking reaction mechanism, and compositional analysis showed the polymer degradation was non-random between the hydroxybutyratehydroxyvalerate units. The degree of crystallinity for PHBV was shown to increase significantly (by 20%) upon weathering. Tensile tests showed that the weathered PHBV exhibited reduced ultimate strength and elongation to break, while the Young's modulus increased ascribing to an increase in crystallinity. Different degradation mechanisms (Norrish I/II, radical initiation, crosslinking, and hydrolysis) of PHBV are proposed and confirmed based on the experimental

Development of bio-derived and biodegradable polyhydroxyalkanoate (PHA)-based wood plastic composites (WPCs)

“…Similar mechanical changes were also reported in an accelerated weathering study on PHBV under longwave irradiation (UVA, at 340 nm) [Wei & Mcdonald, 2016]. UV-induced cross-linking was usually associated with the above mechanical changes for PE [Hussein, 2007;Raab et al, 1982].…”

“…The tensile modulus increased and the tensile strain at break decreased for the first 2 months and were maintained after 2 months. The increase in tensile modulus and brittleness of PHA have been associated with the secondary crystallisation of PHA which was commonly observed [Wei & Mcdonald, 2016]. When wood was added, the mechanical stability of the samples under soil deteriorated: both the strength and stiffness of PHA20W decreased, although the samples were still intact after 12 months.…”

“…It has already been shown that the bulk properties of PHBV such as melting point were stable upon UV exposure even with an observed decrease in molecular weight from 350 to 130 kDa [Wei & Mcdonald, 2016] unless the polymer was exposed to high energy sources such as gamma [Mitomo et al, 1994] or electron irradiation [Bergmann et al, 2007]. The UV exposure to sunlight may not be sufficient to influence the lamellar structure of PHBV and thus the melting temperature [Wei & Mcdonald, 2016]. Under stronger energy sources, PHBV could undergo chain scission, accompanied by cross-linking mainly in the amorphous region, which led to change in the bulk crystal structure and lower the melting temperature [Bergmann et al, 2007].…”

“…It is proposed that any surface changes induced by crosslinking may affect the mechanical properties but the bulk properties will remain unchanged. It has already been shown that the bulk properties of PHBV such as melting point were stable upon UV exposure even with an observed decrease in molecular weight from 350 to 130 kDa [Wei & Mcdonald, 2016] unless the polymer was exposed to high energy sources such as gamma [Mitomo et al, 1994] or electron irradiation [Bergmann et al, 2007]. The UV exposure to sunlight may not be sufficient to influence the lamellar structure of PHBV and thus the melting temperature [Wei & Mcdonald, 2016].…”

Surface characterization of weathered and heat‐treated wood‐based composites reinforced by styrene maleic anhydride

“…Many scientists have experimented with different behaviors of WPC materials under different weather conditions. [23][24][25][26][27][28] Scientists continue their studies using special chambers in laboratories that can be made more suitable for weather conditions.…”