Effect of Plasticizer on the Morphology and Foaming Properties of Poly(vinyl alcohol) Foams by Supercritical CO2 Foaming Agents

As an environment-friendly polymer, polyvinyl alcohol (PVA) foams have attracted increasing attention due to their excellent thermal insulation and cushioning properties. However, the main drawback of PVA is its difficulty in melt processing (due to strong inter-/intrahydrogen bonds) and to control the cell morphology. To overcome the processing limits and realize the control of cell morphology, environmentally friendly PVA microcellular foams were prepared by two-step foaming method, using ethylene glycol (EG) as a plasticizer and supercritical carbon dioxide (Sc-CO2) as foaming agent. The melting behavior and rheological properties of plasticized PVA foams were investigated by differential scanning calorimetry (DSC) and rheometer. The effect of EG content on cell morphology was studied by scanning electron microscopy (SEM). It was demonstrated that EG plasticizer exhibited good plasticizing effect, which decreased the melting point and widened the processing window of PVA. Moreover, the plasticizer could affect the melt strength and crystallization of samples, thus, affecting the foaming process and the cell morphology. The foaming effect of PVA foams was obviously improved after adding plasticizer. With the increase of plasticizer content, the cell size of the foam increased from 9.30 μm (10 phr) to 12.75 μm (30 phr), and the expansion ratio increased from 2.33 (10 phr) to 3.36 (30 phr). This work has reference significance for the study of the regulation of cell morphology in the subsequent polymer foaming process.