Evaluation of spherulite growth in PHB‐based systems – a DoE approach

Formulations based on poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate‐co‐valerate) were studied to statistically assess the importance of process parameters (temperature) and chemistry in filled and/or plasticized PHB‐based formulations on spherulite growth rate (SGR) and nucleation density (ND). It was found that in binary systems, addition of a plasticizer results in shift of the maximum SGR towards lower temperatures, with the value of the shift dependent on polymer‐plasticizer compatibility. The presence of the filler does not significantly influence SGR, instead resulting in ND changes dependent on filler chemistry, with Cloisite Ca++ showing the strongest nucleating action in all formulations among fillers studied. In ternary systems, statistical analysis shows that SGR strongly depends on the crystallization temperature (Tc), plasticizer type and concentration, and hydroxyvalerate content in the polymer chain while being independent of the presence and chemistry of the filler in the system. ND has, however, proven to be dependent on all investigated parameters, including both filler type and its concentration, with Tc being the most important factor. These results expand the understanding of factors controlling crystallization in polymer systems and provide an initial set of design tools that can be used to control mechanical properties in new generations of packaging materials.