Balancing Melt Solubility and Morphology in Epitaxial Nucleation: The Case of Nicotinic Acid and Poly(hydroxybutyrate-co-hydroxyhexanoate)

• Published in: ACS applied polymer materials 2023-10, Vol.5 (10), p.8600-8607
• Main Authors: Bledsoe, Joshua, Crane, Grant, Drewke, Jessica, Casey, James, Klepov, Vladislav, Locklin, Jason
• Format: Article
• Language: English
• ISSN: 2637-6105; 2637-6105
• DOI: 10.1021/acsapm.3c01692

Nicotinic acid was evaluated as a melt-soluble nucleator for a poly­(hydroxy­butyrate-co-hydroxy­hexanoate) (PHBHHx) copolymer for melt-processing applications. A series of nicotinic acid concentrations (1–5 wt %) were analyzed to determine the best concentration for overall nucleation performance. 2 w/w% nicotinic acid was found to be the optimal concentration, successfully crystallizing PHBHHx at a peak temperature of 73 °C under nonisothermal conditions. When extrusion is performed at 150 °C, 2 w/w% of nicotinic acid occupies an optimal concentration within the polymer where all the nicotinic acid is dissolved in the PHBHHx matrix, which is not the case at higher concentrations. 2 w/w% also recrystallizes rapidly to produce many fine, needle-like crystals that are highly active toward PHBHHx nucleation, which is not observed with other concentrations. Powder X-ray diffraction (PXRD) analysis of the differing nicotinic acid crystals determined that the (110) and (120) faces are likely responsible for nucleation. Gel permeation chromatography (GPC) analysis revealed a modest degradation of molecular weight, likely due to the E1cb degradation mechanism common in PHAs.