Rheological behaviors and foaming behaviors of crosslinked ethylene–vinyl acetate with polyfunctional monomers

Abstract

To produce ethylene–vinyl acetate (EVA) foams with a higher foaming ratio and stable cell size, the efficiency of the crosslinking reaction is required to conduct simultaneously with the blowing reaction. Hence, the multifunctional monomer trimethylolpropane trimethacrylate (TMP) as a crosslinking promoter and a crosslinking agent dicumyl peroxide are used together as a crosslinking system to EVA foaming, when chemical blowing agent azodicarbonamide (ADC) is used. The TMP concentration of approximately 1.0 phr (per hundred resin) is most effective for balancing the expansion ratio and fine cell size. In the SEM diagram and expansion ratio results, it can be found that when the concentration of TMP ranges from 0 to 1.0 phr, the cell mean size is reduced from 360.3 to 140.5 μm and the expansion ratio is reduced from 13.6 to 9.1 at 170°C. The results of time-sweep experiment of thermogravimetric analysis (TGA) show that the foaming time of ADC in the melt increases with the addition of TMP. Capillary rheometer and rotational rheometer tests show that the viscosity and the crosslinking efficiency of the melt are improved with the TMP addition. The curing time has been reduced from 2.93 to 2.22 min for 170°C.