Effect of plasticizers on thermal and physical properties of compression-moulded poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] films

Abstract

a b s t r a c tPoly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) is a promising bio-based, biodegradable polymer for replacing synthetic polymers, but its brittleness limits its application range. With the aim of improving the mechanical properties of PHBV films, different plasticizers (polyethylene glycol (PEG 200, 1000 and 4000), lauric acid (LA) and stearic acid (SA)) were incorporated into the film formulation at 10 wt%. All plasticized films showed lower melting temperature and crystallization degree than pure PHBV films. All plasticizers, except SA, reduced film stiffness and resistance to break, and increased the films' water sorption capacity and solubility as well as their water vapour permeability, but only PEG1000 yielded more extensible films. PEG1000 and PEG4000 gave rise to the most heat-resistant plasticized films, while LA and SA highly promoted the heat-sensitivity of PHBV. PEG1000 was the most effective at plasticizing PHBV films, and it was the only plasticizer that partially mitigated the ageing effects. However, a greater ratio of plasticizer would be required to adapt PHBV mechanical properties to some packaging requirements.

Control of the secondary crystallisation process in poly(hydroxybutyrate-co-hydroxyvalerate) through the incorporation of poly(ethylene glycol)

“…The molecular weight of PEG was found to have a negligible effect on the melting point of PHB-co-HV in line with results reported by Requena et al [21]. As this current investigation shows the molecular weight to have little effect on the melting point it is believed that the number of PEG chains is the dominating factor in melting point reduction.…”

“…Given the presence of hydroxyl groups separated by long aliphatic chains biodegradable [19,20] poly(ethylene glycol) may be a suitable alternative to BPA. Previous work has analysed the blending of PHB-co-HV and PEG over a range of molecular weights and concentrations and the resulting effects on the initial thermal and mechanical properties [21][22][23][24][25]. Miscible blends have been reported with PEG containing a molecular weight of 400 Da, however partial miscibility was found when the molecular weight exceeded 1500 Da [22].…”

“…In addition Li et al observed that smaller PEG molecular weights were more favourable during blending with poly(lactic acid) as their smaller size facilitates their insertion into the free volume of the molten state [26]. To date, only Requena et al [21] has reported the effect of PEG on the secondary crystallisation of PHB-co-HV, however, the study only evaluated one concentration and was performed over a relatively short time scale (5 weeks). Therefore, this study aims to extend both the range of PEG molecular weights and concentrations and the length of storage time to assess the longterm effectiveness of the use of PEG as a means to hinder the secondary crystallisation process and resulting embrittlement.…”

Recent Advances in Bioplastics: Application and Biodegradation

“…Inclusion of 3-hydroxyvalerate (PHBV) and 3-hydroxyhexanoate (PHBH) during biosynthesis [281,282], the addition of low molecular weight polypropylene glycol [283] or polyethylene glycol [284], blending with other polymers [278,285], and cross-linking [286] are some of the strategies used to improve the thermal processability of PHB. The addition of PEG1000 to PHBV-based matrices significantly lowered the stiffness of films which also became more extensible, thermo resistant, improved regarding water vapour permeability, and more resistance to aging [287]. The choice of a plasticiser will clearly depend on its effectiveness; on the rate of its volatility or migration during use; on the storage, toxicity, and renewability; and on how it affects the biodegradability of the final material.…”

Starch-protein active films for food preservation

“…PHB shows good processability, yielding materials with a high degree of transparency and stiffness, since it presents physical properties (melting points, degrees of crystallinity and glass transition temperatures) that are very similar to polypropylene (Requena et al, 2016b). However, its high degree of crystallinity makes it stiffer and more brittle than PP.…”