| As an important thermoplastic resin,polyethylene(PE)is widely used in food,medical,electronic appliances and new energy due to its advantages of good molding and processing properties,light weight and low price.However,with the development of high technology,conventional polyethylene materials could not well meet the requirements of high-tech products.Therefore,the modification of pure polymer materials has become a research focus in the field of polymer materials.In this paper,polyethylene was modified by two different methods: heat treatment and graphene filling,so as to make its performance more excellent.Biaxially oriented polyethylene(BOPE)films were heat treated at different temperatures and times.The changes of crystallization behavior,microstructure,optical and mechanical properties of BOPE films under different heat treatment conditions were investigated.The results showed that compared with before heat treatment,the crystallinity of BOPE film increased by 0.4% when the heat treatment time was 15 min and the heat treatment temperature was 100℃;However,when the heat treatment temperature was higher than 105℃,the crystallinity of BOPE film decreased.When the heat treatment temperature was 100℃,the crystallinity of BOPE film increased first and then decreased with the extension of heat treatment time.With the increase of heat treatment temperature and the extension of heat treatment time,the transverse orientation of BOPE films increased,resulting in the decrease of elongation at break in this direction.When the heat treatment temperature was 100℃,the heat treatment time was 15 min and40 min,the transmittance of BOPE film was small,the haze was large,and the transverse(TD)and longitudinal(MD)fracture strength was large.Therefore,the optimal heat treatment condition of BOPE film was 100℃ heat treatment for 15 min,with less time and the best comprehensive performance.Linear low density polyethylene grafted maleic anhydride/graphene(LLDPE-g-MAH/G)nanocomposites were prepared by melt blending.The effects of different G content on the crystallization behavior,microstructure,mechanical and rheological properties of the nanocomposites were investigated.DSC results showed that the addition of G with different content all led to an increase in crystallization temperature and crystallinity of LLDPE-g-MAH,indicated that G played a heterogeneous nucleation role on LLDPE-gMAH matrix.SAXS results showed that LLDPE-g-MAH/G nanocomposites produced microphase separation structure after adding G.The mechanical properties test showed that the addition of a small amount of G could improve the tensile strength and elongation at break of LLDPE-g-MAH,which were 3.8 MPa and 29% higher than pure LLDPE-gMAH,respectively.The rheological property test showed that when the nanocomposites were in the molten state,the addition of G led to the increase of storage modulus,loss modulus and complex viscosity.For LLDPE-g-MAH/G0.5% nanocomposites were hot drawing,and the effect of simultaneous orientation of polyethylene crystal and graphene along the draw direction on the thermal conductivity of nanocomposites was investigated.The test results showed that the thermal conductivity of LLDPE-g-MAH/G nanocomposites along the draw direction after drawing was 3.6 times higher than before drawing,indicated that the simultaneous orientation of polyethylene crystals and graphene along the draw direction has an obvious enhancement effect on the thermal conductivity.SAXS and XRD confirmed that polyethylene crystals and graphene in LLDPE-g-MAH/G nanocomposites were oriented along the draw direction at the same time.DSC results showed that the original crystals in the nanocomposites were damaged and broken by drawing,the crystal size was reduced and the melting point was decreased.At the same time,drawing could promote the crystallization and orientation of polyethylene molecular chain along the draw direction,so as to improve the crystallinity of nanocomposites. |
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