Heterogeneous Nucleation of Poly(hydroxybutyrate-co-hydroxyhexanoate)

_{Nucleation comprises the initial step of polymer crystallization, wherein the polymer melt stabilizes into ordered local structures, allowing for points from which polymer crystals can begin to grow. Nucleation quality can significantly impact the materials properties and processability of a polymer and is therefore of high importance to the materials science community. However, the collective understanding of polymer nucleation remains largely empirical. Poly(hydroxybutyrate-co-hexanoate (PHBH) is a biopolymer whose industrial implementations are limited, despite its impressive biological degradability, because of its slow crystallization rate and exceptionally low homogeneous nucleation density. Especially given the growing importance of biopolymers in the reduction of plastic pollution, a more comprehensive understanding of heterogeneous PHBH nucleation is needed to improve the practicality of PHBH processing. In an initial study, xanthine and a series of its methylated derivatives were investigated as potential nucleators for PHBH.}¹ _{Xanthine and theobromine were effective as nucleating agents, whereas caffeine and theophylline were not. A kinetic investigation of the efficiency of the successful candidates was supplemented by a rationalization of nucleation performance involving the periodic alignment of crystal features with hydrogen bond-accepting carbonyl oxygen in the polymer backbone. A second study evaluated nicotinic acid (a biobased, biodegradable, and non-toxic B-vitamin) as a melt-soluble PHBH nucleating agent exhibiting concentration-dependent performance.}

_References:

1. _{Beyond Lattice Matching: The Role of Hydrogen Bonding in Epitaxial Nucleation of Poly(hydroxyalkanoates) by Methylxanthines, J. Bledsoe, G. Crane, J. Locklin, ACS Applied Polymer Materials 2023, 5, 5, 3858-3865.}