Investigation of the foaming behavior in ultra-high molecular weight polyethylene (UHMWPE) and low-density polyethylene (LDPE) blends with varying molecular weights prepared by compression molding

Ultra-high molecular weight polyethene ( UHMWPE) has demonstrated significant potential in the field of foaming materials due to its unique chain entanglement structure and exceptional properties. However, its high melt viscosity and complex rheological behavior present challenges in controlling foaming processes. This study utilizes UHMWPE with number-average molecular weights Mn of 2×10 6 g/mol, 4 ×10 6 g/mol, and 6 ×10 6 g/mol as the primary raw material. It is combined with modified materials, such as low-density polyethylene ( LDPE), Ethylene Vinyl Acetate ( EVA), and styrene-maleic anhydride copolymer ( SMA). To prepare the pre-foamed materials, we start by controlling the variables and mixing them evenly in a double-roll open mill at a temperature of 95 ℃. Next, we transfer the mixture into a hot press machine set at temperatures of 200 ℃, 215 ℃, and 230 ℃ for molding and foaming. After this process, we conduct density measurements, scanning electron microscopy ( SEM), and tests of the mechanical properties and rheological behavior of the blended material before foaming. The rheological analysis demonstrates that temperature significantly affects the viscoelasticity of the pure materials, and materials with higher molecular weights exhibit a stronger relaxation spectrum intensity. After mixing UHMWPE with LDPE, no interface relaxation peak was observed in the blend. The Han curve displayed a slope ranging from 2.56 to 2.68, which is close to the ideal value of 2, indicating that the modified blend exhibits good compatibility. The Han curve indicates that UHMWPE /EVA has poor compatibility, while UHMWPE /SMA shows the worst compatibility. Scanning electron microscopy images revealed that among the UHMWPE foam materials modified with LDPE, EVA, and SMA, the average pore size ranged from 106.2 to 126.7 μm, with LDPE resulting in the smallest pore size and narrow pore size distribution. The foaming experiment yielded a relatively optimized formula and process: UHMWPE with Mn=4×10 6 g/mol was blended with 50 parts of LDPE at a foaming temperature of 200 ℃. The apparent density of the UHMWPE / LDPE modified foaming material was 0.427 g/cm³, with a tensile strength of 6.6 MPa and an elongation at break of 11%. • The addition of LDPE significantly reduces the high viscosity of UHMWPE and provides good compatibility, which enhances the foaming of the blended material. • The foam made of UHMWPE and LDPE (50/50 wt) has a relatively low density, with UHMWPE having a molecular weight of Mn 4×10 6 at a foaming temperature of 200 °C. • The modified foam sample F8, which comprises 4 million UHMWPE at a mass fraction of 50 and was foamed at a temperature of 200 °C, exhibits the highest tensile strength, greatest elongation at break, and smallest average pore size.