Controlled Degradation of Biodegradable Polymers for Use in Melt-Blown Nonwovens

Abstract

Nonwovens have many applications; however, they are typically made from petroleum-based polymers that are unsustainable and release microplastics upon breakdown that pose a risk to the health of both us and the environment. As such, it is necessary to shift to more environmentally benign materials such as biodegradable polymers. Unfortunately, readily available biodegradable polymers do not have the properties required, namely high melt flow index (MFI), for use in melt blowing, a common method for producing nonwovens. Therefore, this thesis aims to modify biodegradable polymers through aqueous hydrogen peroxide-induced controlled degradation to make them compatible with the melt blowing process. Two different biodegradable polymers are subjected to this treatment: poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT). Both systems demonstrated clear evidence of molecular weight reduction due to random chain scission induced by the peroxide radicals with additional contributions from thermal degradation and hydrolysis. PLA was also shown to begin crosslinking once a critical processing time was reached, while processing time appeared to have little effect on PBAT. The degraded products were then melt-blown to produce nonwoven mats with much finer and more uniform fibers compared to their untreated counterparts. The degraded PBAT from the second study was then blended with untreated PLA to develop a final melt-blown nonwoven with more balanced tensile properties than either material alone. Finally, since PLA and PBAT are immiscible when both are present in large quantities, maleation was used as a compatibilization technique to successfully enhance the quality of the melt-blown blends. Overall, reactive batch mixing with aqueous hydrogen peroxide is demonstrated to be a sustainable method for the molecular weight reduction of low MFI biodegradable polymers, allowing them to be well suited for use in melt-blown nonwovens.