Study On The Relationship Between Crystallinity And Transparency Of Random Copolymers

Polypropylene random copolymer（PPR）has been widely used in various transparent products due to its good optical properties.On the basis of good clarifying ability of NX8000,the effects of NX8000 on the crystallinity,transparency and mechanical properties of PPR were in detail studied.The main research contents and conclusions of this study include:Firstly,the effect of NX8000 on the thermodynamic behavior of PPR was investigated.During non-isothermal crystallization,the increasing adding amount of NX8000 can raise the crystallization temperature（T_c）of PPR apparently and reach the maximum value at 119.1℃,so does the melting point（T_m）.PPR/NX8000 composites exhibit the multiple melting behavior,which can be ascribed to the coexistence ofαandγcrystal forms,and melting-recrystallization-remelting phenomenon.In the subsequently heating process,γform crystals would transform toαform crystals in the PPR composites with high NX8000 content,while theα_I toα_II crystal transformation occurs in the PPR composites with low NX8000.Study of isothermal crystallization further reveals that PPR crystals grow in a two-dimensional manner.The more adding NX8000,the higher PPR crystallization rate（Z_t）,and the Z_t value of PPR composites with 0.5 wt%NX8000 can achieve 309 times than that of PPR composites with 0.3 wt%NX8000.Secondly,the effect of NX8000 on the crystal structure of PPR was systematically studied.Spherulites of PPR significantly refine and homogenize more and more with increasing NX8000 content in composites.The speherlite diameter of PPR in composites with 0.5 wt%NX8000 can be reduced 100 times than in neat PPR.Meanwhile,the relative content ofγform crystals（K_γ）in composites increases with increasing NX8000 content and reaches the maximum value at 64.9%,which is in accordance with the fact thatγcrystal is able to grow faster thanαcrystal in high T_c range.Finally,the effect of NX8000 on the optical properties and mechanical properties of PPR was examined.The haze value of PPR composites with 0.5wt%NX8000 drops to only 5.2%.When increasing NX8000,the content ofγcrystal raises,but the transparency of PPR declines.However,the smaller and more uniform spherulite size of PPR,the transparency of it performs higher.The comprehensive effect shows that NX8000 can greatly improve the optical performance of PPR materials.At the same time,NX8000 helps enhance the yield strength,flexural modulus,elongation at break,and notch impact strength of PPR,indicating the ability of NX8000 on improving the rigidity and toughness of PPR.