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

Abstract

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.

Submission to Journal of Polymers and the Environment Evaluation of Thermal Properties and Crystallinity in PHB-Based Systems – A DoE Approach

“…Together with CCa ++ , it was the only filler showing nucleating action despite system plasticisation. This result is consistent with observations noted in our study of spherulite nucleation and growth in PHBbased systems where CCa ++ was better nucleant than CNa + or CaCO 3 [20]. BN was also the only filler that consistently increased X c in the plasticised PHB matrix (Figure S3 d,h in the Supporting Information).…”

“…3a, Figure S2a in the Supporting Information). CCa ++ shown the most significant nucleating action among CCa ++ , CNa + and CaCO 3 group, in line with results obtained for spherulitic growth measurements [20]. Further, PHB/5CaCO 3 sample has shown anti-nucleating action (reducing T c ), showing that at higher contents, restriction of polymer mobility due to filler presence might be dominant over presence of additional nucleation centres [70,71].…”

“…The samples were melted during first DSC run as described below and were run in duplicates (powder samples prepared twice rather than running two experiments on the same batch to ensure no systematic error). For the presented set of data, the repeatability for all samples was good (error ± 2%), with no significant clustering of the filler within PHB matrix observed [18,20].…”

“…This conclusion is in line with theoretical investigations based on Hansen solubility parameters and results obtained for spherulitic crystallisation presented previously. [20] Upon introducing plasticiser to the system, T cc changes in a manner similar to T c and decreases with increasing plasticiser content, with more significant changes noted for TA addition compared to ATBC addition. Alike pure PHB samples, ∆H cc values are noted at ca.…”

“…We have shown in our previous work [20] that DoE can be successfully applied to assess the effect of each individual factor on spherulitic growth in PHB-based systems. Here, we are applying DoE to study the effect of formulation (HV content, plasticiser content and type, filler content and type) on thermal properties and crystallisation in PHB-based systems performed by Dynamic Scanning Calorimetry (DSC) to probe the importance of different length scales while investigating crystallisation and providing a natural extension to previous work.…”