In situ crystallization of native poly(3-hydroxybutyrate) granules in varying environmental conditions

Abstract

Poly(3-hydroxybutyrate) (PHB) is a microbial biopolyester that can be produced from renewable feedstocks as an eco-friendly bioplastic. PHB in vivo exists as amorphous, intracellular granules that contain a small amount of water and are surrounded by a membrane of lipids and proteins. The native granules undergo varying degrees of crystallization when subjected to changes in environment such as dehydration, temperature, pH, and other mild conditions. For the first time, the in situ crystallization of native PHB granules was monitored via ATR-FTIR. Empirical models describing the crystallization of PHB granules in different environments were developed from Avrami's equation. The extent of granule crystallization is governed by granule size, number of nucleation points, and spherulitic geometry. The primary stabilizing factors of amorphous PHB granules are water, membrane lipids and proteins. Removing any of these factors may induce partial crystallization of PHB, which toughens the granules against extensive molecule degradation and granule aggregation.