Crystallization Kinetics of Poly(3-hydroxybutyrate) Granules in Different Environmental Conditions

Abstract

Poly(3-hydroxybutyrate) (PHB) is a natural biopolyester accumulated in microbial cells as tiny amorphous granules. The nano- micro-particles have a variety of potential applications and behave differently in different environments. In this work, the in situ crystallization of native PHB granules was investigated under different environmental conditions. The isothermal crystallization kinetics of the granules was shown to follow Avrami’s equation. The model parameter describing crystal growth is a function of temperature or pH and estimated from in situ crystallization measurements with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Empirical equations describing crystal growth are derived for the parameter values. PHB granules heated at 80-140°C in acidic solution (pH 2) up to 4 hr showed an increase in crystallinity from about 5% to 35% and moderate particle aggregation. PHB granules suspended in alkaline solutions (pH 9-12) at room temperature up to 4 hr showed an increase in crystallinity up to 45% and very little particle aggregation. It was found that the amorphousness of PHB granules in vivo is stabilized by water, lipids and proteins. Upon removal of these impurities, partial crystallization is induced which may inhibit extensive particle aggregation

Polyhydroxybutyrate Composites with Random Mats of Sisal and Coconut Fibers

“…Another paper 54 reports that the crystallinity of PHB can vary 35 to 45% depending on the experimental parameters. However, these results are considered relatively low compared with other published studies 16,51 .…”

What Changes in Poly(3-Hydroxybutyrate) (PHB) When Processed as Electrospun Nanofibers or Thermo-Compression Molded Film?

“…In vivo PHB granules are fully amorphous, but during recovery, the amorphous granules environment changes and may cause the crystallization of the particles 4 . When pure PHB is heated above its melting point (~180°C), it becomes a fully amorphous melt.…”

“…When pure PHB is heated above its melting point (~180°C), it becomes a fully amorphous melt. Upon cooling, the PHB molecules crystallize, forming antiparallel helical chains linked by C -H•••O hydrogen bonds between the carbonyl (C=O) and methyl (CH 3 ) groups of the polyester backbone 4 . The final PHB polymer properties depend on the crystallization degree, which depends on the PHB processing conditions.…”

Blends of ethylene-co-vinyl acetate and poly(3-hydroxybutyrate) with adhesion property

“…Furthermore, the two melting peaks of pure PHB shift to higher temperatures in all blends (from 131 to 138-156°C and from 147 to 154-167°C), this indicating better miscibility which can be favoured by the reduction in molecular mass of PHB during melting. The increase is less important in the blends containing 40 wt% or less PHB (EVA/PHB (70:30) is an exception); furthermore, the melting temperatures of the blends containing more than 50 wt% PHB are very similar ( [29] proposed the existence of physical crosslinking between PHB and different polymers (PLA, polypropylene carbonate -PPC -, polyvinyl acetate -PVAc), and the existence of interactions between the carbonyl (C=O) and methyl (CH 3 ) groups between PHB and PLA, and between PHB and PVAc in polymer blends have been supported in several studies [30][31][32][33][34][35][36]. The crystallinity of EVA, PHB and EVA/PHB blends was determined by X-ray diffraction.…”

“…The existence of physical interactions between EVA and PHB phases in EVA/PHB blends is evidenced by changes in compatibility, crystallinity and viscoelastic properties. The interactions between EVA or PVAc and PHB or PLA or PPC in polymer blends have been ascribed to the disruption of the interactions between the carbonyl (C=O) and methyl (CH 3 ) groups by weak physical interactions with C=O and CH 3 groups of PVAc [28][29][30][31][32][33][34][35][36]. Because of CH 3 and C=O groups also exists in the vinyl acetate domains in EVA, weak interfacial interactions between C=O and CH 3 groups of PHB and CH 3 and C=O groups of EVA can be produced.…”