Chen Wana, Gangwei Sunb, Feng Gaoa, Tao Liua,∗, Mohamed Esseghirc,∗, Ling Zhaoa,Weikang Yuanaa
Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East China University of Science and Technology, Shanghai 200237, PR Chinab
Dow Chemical China Co. Ltd., Elastomers, Electrical & Telecommunication R&D, Shanghai 201203, PR Chinac
Dow Chemical Company, Elastomers, Electrical & Telecommunication R&D, Collegeville, PA 19426, USAa
Low Density Polyethylene (LDPE) is blended with High Density Polyethylene (HDPE) and three typesof Polypropylene (PP) having different melting index (MI), respectively. The compatibility of LDPE/HDPEblends is characterized by using thermal analysis and rheology methods. Differential scanning calorimeter(DSC) traces and rheology methods confirmed their good compatibility. For LDPE/PP blends, the incom-patibility has been widely acknowledged in the literature. The distribution of the PP phase in the blendis investigated using polarized optical microscopy (POM). It is found that the phase structure is closelyrelated to the blend composition and the viscosity ratio of the blend components. Extrusion foaming ofthe blends is conducted using a single extruder fitted with a CO2gas injection system. Under similar foam-ing conditions, the compatible LDPE/HDPE blends all generated a uniform cell morphology and achievedroughly the same expansion ratio. Although the incompatible interface is beneficial to cell nucleation, theLDPE/PP blends did not achieve satisfactory foaming performance. To determine the differences in thefoaming behavior of the two blends, the viscoelastic properties and diffusion coefficients of supercriticalCO2in the blends, were accurately measured via rheology and magnetic suspension balance (MSB) meth-ods. The results indicate that the viscoelastic properties did not show a dominant role in determining thefoaming behavior, by contrast, CO2 diffusion is found to be the key factor affecting foaming performanceespecially in the case of a co-continuous phase structure.