Foaming Poly(vinyl alcohol)/Microfibrillated Cellulose Composites with CO₂ and Water as Co-blowing Agents

We investigated the continuous extrusion foaming of poly(vinyl alcohol) (PVOH)/microfibrillated cellulose (MFC) composites using supercritical carbon dioxide (scCO 2 ) as the blowing agent. First, the as-received PVOH pellets were compounded with water to decrease their melting point. Then, they were compounded with an MFC solution to prepare the sample. Both scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM) showed that the MFC dispersed well in the PVOH/MFC composites. Differential scanning calorimetry (DSC) results showed that adding MFC affected the thermal behavior. This, in turn, affected cell nucleation and cell growth phenomena during foam extrusion. Water also acted as a co-blowing agent, together with scCO 2, in creating biodegradable polymer foams with a uniform cell structure and a high cell density. The effects of the MFC content, scCO 2 content, and die temperature variations on the cell density and cellular morphology of the PVOH/MFC composite foams were examined systematically.