The Research On Effect Of Lubricants On The Performance Of Modified Polypropylene With Sorbitol-based Nucleating Agents For Transparence Enhancement

Polypropylene（PP）is widely used in medical equipment,household appliances,daily necessities and packaging materials because of its good mechanical properties,non-toxic and non-hazardous,good chemical stability,good heat resistance and easy processing and molding,and has achieved significant economic and social benefits.The large size of spherical crystals generated by ordinary PP and the existence of both crystalline and amorphous regions inside the material make the optical properties of PP materials poor,which limits their applications in transparent packaging and engineering materials.Therefore,it is of great practical importance to modify ordinary PP to make it have good optical properties through transparent modification.Transparent modification of PP with nucleating agents is by far the simplest and most economical method.Among them,sorbitol nucleating agents are most effective in enhancing transparency,but sorbitol nucleating agents have certain polarity and limited compatibility with PP matrix,resulting in their poor dispersion in PP,which affects the final effect of increasing transparency.In this work,1,2,3-trideoxy-4,6:5,7-bis-O-[（4-propylphenyl）methylene]-nonanol（TBPMN）,the main component of the latest generation sorbitol nucleating agent NX 8000,was used as a nucleating agent and compounded with different lubricants（stearate,low molecular weight wax）,followed by blending,extrusion and pelletizing injection molding with PP.The effect of lubricants on the performance of TBPMN transparent modified PP was investigated.The details are as follows:（1）The nucleating agent TBPMN was used to modify PP with increased transparence.The results showed that TBPMN could effectively improve the optical and mechanical properties of PP with the best effect at 0.4 wt%addition.Compared with the pure PP specimens,the haze decreased by 41.7%,the transmittance increased by 6.3%,and the impact strength and tensile strength increased by 40.0%and 23.0%,respectively.（2）The effects of stearates on the performance of PP transparentl y modified by TBPMN were investigated by using different stearates（Calcium,Zinc,Aluminum,Lithium,Sodium and Potassium）as lubricants at the optimum addition of nucleating agents.The results showed that calcium stearate（Ca St）,zinc stearate（Zn St）and aluminum stearate（Al St）could improve the performance of PP transparently modified by TBPMN in the order of Ca St>Zn St>Al St.The best results were obtained with the addition of Ca St.At the optimum addition of 0.03 wt%,the haze decreased by 3.4%,the melt index increased by 17.4%,and the impact strength and tensile strength increased by9.0%and 20.5%,respectively,compared to the specimens without Ca St addition.The crystallization behavior of the modified PP was subsequently characterized by Scanning Electron Microscopy（SEM）,Polarizing Microscopy（POM）,and X-Ray Diffraction analysis（XRD）,and the results showed that Ca St,Zn St,and Al St could improve the dispersion of TBPMN in PP,reduce the grain size and enhance the crystallinity.Finally,the melting and non-isothermal crystalliza-tion properties of the modified PP were investigated by Differential Scanning Calorimetry（DSC）,which showed that the melting enthalpy（ΔH）of the modified PP became larger and the melting peak（T_f）temperature increased.The non-isothermal crystallization kinetics study showed that the addition of TBPMN and stearate could increase the crystallization peak temperature（T_p）and shorten the semi-crystallization time(T_1/2)of PP.The magnitude of crystallization activation energy（ΔE）was 0.4-TBPMN>0.03-Zn St>0.03-Ca St>Pure PP in order of magnitude.（3）Polypropylene wax（PP wax）,Polyethylene wax（PE wax）,Oxidized Polyethylene wax（OPE wax）,and Fischer-Tropsch wax（FT wax）were used as lubricants at the optimum nucleating agent addition.The effects of low molecular weight waxes on the performance of PP transparently modified by TBPMN were investigated.The results showed that PP wax,PE wax and FT wax can improve the performance of PP modified by TBPMN transparently,and the effect was PP wax>PE wax>FT wax in order,while OPE wax had certain polarity and poor compatibility with PP substrate,which would reduce the performance of modified PP specimens.The best result was obtained by adding PP wax with the optimal addition of 1.1 wt%.Compared with the specimens without PP wax,the haze decreased by 10.0%,the melt index increas ed by 6.0%,and the impact strength and tensile strength increased by 7.3%and 23.7%,respectively.The crystallization behavior of the modified PP was subsequently characterized by Scanning Electron Microscopy（SEM）,Polarizing Microscopy（POM）,and X-Ray Diffraction analysis（XRD）,and the results showed that PP wax,PE wax and FT wax could improve the dispersion of TBPMN in PP,reduce the grain size and enhance the crystallinity.Finally,the melting and non-isothermal crystallization properties of the modified PP were investigated by Differential Scanning Calorimetry（DSC）,which showed that the melting enthalpy（ΔH）of the modified PP became larger and the melting peak（T_f）temperature increased.The non-isothermal crystallization kinetics study showed that the addition of TBPMN and stearate could increase the crystallization peak temperature（T_p）and shorten the semi-crystallization time(T_1/2)of PP.The magnitude of crystallization activation energy（ΔE）was 1.1-PP wax>0.7-PE wax>0.4-TBPMN>0.5-FT wax in order of magnitude.