Miscible polymethyl methacrylate/polylactide blend with enhanced foaming behavior and foam mechanical properties

High-performance foams play significant roles in many industries. Microcellular foaming with carbon dioxide as blowing agents is an advanced and environmentally friendly technology to prepare polymeric foams with significantly refined cellular morphology. The manipulation of polymer microstructure and rheological behavior is the key to tailor its foaming behavior. In this study, polymethyl methacrylate (PMMA) was blended with polylactide (PLA) to improve its foaming behavior in one-step batch foaming with carbon dioxide as blowing agents. It was demonstrated that PMMA and PLA are fully miscible in molecular level. The presence of PLA can lead to decreased glass transition temperature of PMMA, and PMMA can suppress the crystallization of PLA. PLA can enhance the melt elasticity of PMMA at low shear oscillation frequencies but decrease the melt elasticity of PMMA at high shear oscillation frequencies. Thanks to the plasticity effect and heterogeneous nucleation effect of PLA, adding an appropriate amount of PLA can significantly broaden the foaming window of PMMA and refine cellular morphology. Microcellular PMMA/PLA foams with cell sizes less than 10 µm and expansion ratio up to 18.4 were fabricated under a foaming pressure of 17.24 MPa with 10 wt% PLA. Nanocellular PMMA/PLA foam can be achieved with the presence of 25 wt% PLA under a foaming pressure of only 6.90 MPa. The PMMA/PLA blend foams show significantly enhanced compression modulus and strength compared with neat PMMA foams. Moreover, reducing cell sizes can significantly enhance the compression modulus and strength of foams.