Study On The Relationship Between Microphase Structure And Compressibility Of Oil-extended SBS/LLDPE/EVA Blends

In order to develop a new type of sealing material with excellent sealing performance and high practicality,oil-extended polystyrene-polybutadiene-polystyrene(SBS)and linear low-density polyethylene(LLDPE)were used as the main raw materials and ethylene-vinyl acetate copolymer(EVA)as an auxiliary material to prepare the oil-extended SBS/LLDPE/EVA blends by melt mixing method,and the influences of each component on the mechanical properties,processing properties and microstructure of the blends system were explored.The results indicated that:(1)The compressive stress of the oil-extended SBS/LLDPE/EVA mass ratio of 50/35/15at a fixed strain of 40%(Refer to the actual deformation value during gasket packaging)could meet the requirements as a bottle cap gasket,and after three cycles of compression there was no obvious change in its resilience performance;And its stress-strain curve could also be used into practical industrial production.Besides,the hardness and compression modulus of the blends decreased with the increase of the oil-extended SBS content as well as increased with the increase of the LLDPE content,while the melt flow rate(MFR)reacted in an opposite way.And the content of EVA has no significant effect on the hardness or MFR of the blends.(2)The content of oil-extended SBS or LLDPE didn’t show significant effect on the transparency of the blends while the addition of EVA could improve the transparency of blends and made the change significantly when its content was in low level.The increase of oil-extended SBS content would reduce the compatibility of the blends while LLDPE increased it.And the increase of EVA content would promote the phase separation of the system as well as move the glass transition temperature of the blends to a higher temperature and increase its internal friction.(3)Under the condition of constant strain compression,the stress of the blends decayed with time passing by,and the attenuation rate was faster at first and getting slow as times went by.The higher the temperature,the lower the initial stress.According to the Time-Temperature superposition principle(TTS),the stress relaxation curves at different temperatures were superimposed into a total stress relaxation modulus curve,which could predict the stress relaxation behavior of the blends for 1.5×10~8s(about 4.7 years),at which time the stress could still meet the sealing requirements;And at the same time,the corresponding WLF equation was obtained in a quite good fitting degree.The generalized Maxwell model had a better fitting effect on the stress relaxation curve of the system:the larger the value of n,the better the fitting effect,but also the more fitting parameters.