Study On Novel Materials From EVM/POM Blends

In this paper,polyoxymethylene(POM)and ethylene-vinyl acetate copolymer(EVM)were selected as the research objects,and the toughening modification of POM and the preparation of dynamically vulcanized EVM / POM thermoplastic elastomer(TPV)were studied,respectively.In the first part,three grades of EVM(Levapren 500,Levapren 700,Levapren700 pxl)were used as toughening modifiers for POM.The mechanical properties,dynamic mechanical properties,crystallization behavior and morphology of POM /EVM blends were studied.The notched impact strength of POM was effectively improved by the three grades of EVM,while the Levapren 700 pxl was the optimal candidate.The results of the dynamic mechanical analysis(DMA)indicated that the compatibility between EVM and POM is not good,which was consistent with the results of microstructure of blends.The addition of EVM reduced the crystallinity,crystallization temperature and melting temperature of POM,and the VA content and pre-crosslinking structure of EVM had an effect on the crystallization behavior of the blends.The processing technology parameters had a certain influence on the mechanical properties of the blends,but the effect was not obvious.The screw rotation speed was200 rpm,processing temperature from 150 to 180 ?,injection pressure at 8 MPa,the POM / EVM500 blends possessed best mechanical properties.In the second part,EVM / POM TPV was prepared by dynamic vulcanization method using Luperox231 / HVA-2 as vulcanization system.Compared with EVM /POM blends,the comprehensive mechanical properties of EVM / POM TPV can be improved obviously.Tensile strength can reach about 12 MPa,but elongation at break is low.The results showed that the screw rotation speed and processing temperature of extruder had an effect on the mechanical properties of EVM / POM TPV.In order to prepare the EVM / POM TPV with good performance,the screw rotation speed was set at 250 rpm and the temperature of extruder ranged from 145 to 175 ?.Themechanical properties of TPV decreased with the increase in Luperox231,and the tensile strength and tensile set of TPV increased first and then increased with the increase in HVA-2.In this part,the effects of castor oil and dioctyl sebacate(DOS)on the processability,mechanical properties,thermal behavior and dynamic mechanical properties of EVM / POM TPV were also studied.Both of these plasticizers reduced the mechanical properties of the EVM / POM TPV and effectively improved its processing performance.After adding the plasticizers,a decrease in storage modulus and loss modulus can be observed.Plasticizers decreased the glass transition temperature of EVM and the crystallinity of the POM,but had little effect on the POM.EVM / POM TPV had good aging resistance and poor oil resistance.Plasticizers had an effect on the aging resistance and oil resistance of EVM / POM TPV.Comparing with castor oil,DOS had better plasticizing effect on EVM / POM TPV.When the amount of DOS was 10 %,the performance of TPV was equivalent to that with 20 % castor oil.