Study On The Properties And Crystallization Behavior Of PP-R Material By Composite Nucleating Agent

Polypropylene random copolymer（PP-R）is a new type of polypropylene developed in recent years.It takes polypropylene as the matrix,with a small amount of ethylene monomer randomly inserted into the polypropylene macromolecular chain,formed under a series of reaction conditions.Because PP-R has the excellent characteristics of low thermal conductivity,strong creep resistance and long service life,it occupies a place in the pipeline market competition.However,due to the poor toughness of PP-R,especially when it is impacted at low temperature,PP-R pipes are more likely to crack,which will eventually lead to material damage.Therefore,how to improve the impact strength and other mechanical properties and crystallization properties of PP-R materials at normal temperature and low temperature（-15℃）,which has become the focus of this research project.In this paper,PP-R was modified by adding three different nano-fillers（hydrophobic nano SiO₂,nano Ca CO₃,and hydrophilic nano SiO₂）to select nano-fillers with excellent comprehensive performance.Then it was compounded with rare earthβnucleating agent and the optimum experimental formula was obtained by designing orthogonal experiment.Use universal tensile testing machine、impact testing machine、DSC、PLM、SEM and other research methods for analysis and characterization.The main conclusions of the experiment are as follows:（1）Among the three different PP-R/nanoparticle composite materials,the comprehensive performance of the PP-R/hydrophobic nano-SiO₂composite material is better.The results show that when the content of hydrophobic nano-SiO₂is 2%,the low-temperature impact strength of PP-R/hydrophobic nano-SiO₂is 16.4KJ/m²,which is the highest among the three.Observed under a polarizing microscope,the effect of hydrophobic nano-SiO₂in refining crystal grains and increasing the crystallization rate is more obvious than that of nano-Ca CO₃and hydrophilic nano-SiO₂.（2）Using rare earth nucleating agent WBG-2 to modify PP-R as a comparative experiment.The material can be observed under a polarized light microscope to"vertical"βcrystals,indicating WBG-2 promoted the production ofβcrystals;from the DSC curve analysis,the addition of WBG-2 increased the crystallization temperature and another peak appeared at a melting temperature of about 131℃.Combined with XRD analysis,the new peak isβpeak,indicating that the crystal form inside PP-R is transformed fromαcrystal toβcrystal.（3）From conclusion 1,it is concluded that the hydrophobic nano-SiO₂has the highest cost performance and the best overall performance.Therefore,the hydrophobic nano-SiO₂is compounded with WBG-2.The results show that at-15℃,the maximum impact strength of the composite material is nearly 4 times higher than that of pure PP-R;the maximum tensile strength is 15.2%higher than that of pure PP-R.The Avrami equation was used to compare the isothermal crystallization kinetics of the composite materials.The results show that the crystallization rate K value of PP-R/hydrophobic nano SiO₂,PP-R/WBG-2 and PP-R/hydrophobic nano SiO₂/WBG-2 composite materials is larger than that of pure PP-R material,and the half crystallization time t_1/2is smaller than that of pure PP-R material;And it is concluded that the PP-R/hydrophobic nano-SiO₂/WBG-2 composite material has the best effect.