Effect of hydrogen bonding on the crystallization behavior of poly(3-hydroxybutyrate- co-3-hydroxyhexanoate)/silica hybrid composites

Biodegradable poly(3-hydroxybutyrate- co-3-hydroxyhexanoate) (PHB-HHx)/hydrophobically modified silica hybrid composites were prepared using simple melt compounding and the effect of hydrogen bonding on their crystallization behavior was observed. The intermolecular hydrogen bonding between PHB-HHx and silica increased gradually with the increase of silica content of the hybrid composites. However, the extent of intermolecular hydrogen bonding was not directly proportional to the silica content. Although, the crystallization rates of the PHB-HHx/silica hybrids decreased as the strength of intermolecular hydrogen bonding increased, the constant value of the Avrami exponent indicates that the presence of silica does not alter the nucleation mechanism or the geometry of the crystal growth of the PHB-HHx hybrids. The calculated crystallization activation energy increased with the addition of silica, suggesting that silica retards the overall crystallization rate of the PHB-HHx hybrid composites as a result of the existence of intermolecular hydrogen bonding. The relationship between the extent of intermolecular hydrogen bond and crystallization rate is described by the empirical second-order equation.