Facile One-Step Approach to Manufacture Environmentally Friendly Poly(vinyl alcohol) Bead Foam Products

Bead foaming is a burgeoning technology for manufacturing lightweight polymer parts with complex geometrical structures. Currently, only a few polymers can meet the requirements for bead foaming, which is the critical obstacle facing polymer bead foams for some special applications. Poly(vinyl alcohol) (PVA) bead foaming is of great significance for eco-packaging materials because of its low cost, good biodegradability, and excellent mechanical properties. However, due to its water solubility, the bead foaming of PVA has not yet realized by conventional steam-chest welding. Herein, a facile and efficient method was proposed to manufacture environmentally friendly PVA bead foams by combining thermal processing and supercritical carbon dioxide (scCO2) foaming. The expansion of plasticized PVA beads and welding of foamed beads were simultaneously completed in our homemade mold. The unique foaming behavior of plasticized PVA bead in the confined space was studied using different plasticizers at various filling contents and foaming temperatures. The macrovoids and boundaries among neighboring beads became indistinct and thus vanished, along with the increase of filling content or welding temperature. At the relatively high temperature, the bimodal cellular structure comprising small cells ranging from 20 to 40 μm and large cells in the range of 60–90 μm are formed in the plasticized PVA bead foams, as well as the formation mechanism was clarified. Benefitting from the uniform structure and high-quality welding, the biodegradable PVA bead foams were provided with high compressive strength and resilience, which might be a promising alternative to traditional polystyrene bead foams.