Crystalline Forms Modulation Strategy Of Polypropylene Powder For Selective Laser Sintering

?-crystalline form polypropylene is widely used in automobile,household appliances,building materials and other fields due to its excellent toughness and high thermal deformation temperature.At present,addition of specific?nucleating agents is the main method to produce?-crystalline form polypropylene products in industry because of its advantages of operating simply and taking effect rapidly.Furthermore,it is significant that with the use of selective laser sintering technology to produce polypropylene parts with?-crystalline form for enriching the types of polypropylene products and expanding the application scope of polypropylene.Therefore,the development of?nucleating agents suitable for the of selective laser sintering powder preparation technology is the focus and difficulty of research.In order to solve these problems and application requirements,the research on the crystalline forms modulation strategy of polypropylene powder for selective laser sintering was studied.The research content and results are as follows:(1)The effects of different?nucleating agents on the crystallization properties and non-isothermal crystallization kinetics of polypropylene were investigated.Two kinds of aliphatic dicarboxylic salt?nucleating agent were synthesized:zinc adipate and calcium pimelate.Differential scanning calorimetry(DSC),X-ray diffraction(XRD)and polarized microscopy(POM)were used to compare the melting and crystallization behavior,relative content of?-crystals,and microscopic crystal morphology of polypropylene nucleated by zinc adipate,calcium pimelate and TMB-5.Non-isothermal crystallization kinetics of Pure-i PP and three kinds of nucleated polypropylene was studied by the Mo method.The result showed that all three kinds of?-nucleating agents have good nucleation ability,which can significantly reduce the grain size of polypropylene,increase the crystallization temperature and increase relative content of?-crystals of polypropylene.The result of XRD showed that when the amount of nucleating agent added is 0.05wt%-0.2wt%,K_?value of polypropylene nucleated by zinc adipate basically remained at 80%,the K_?values of polypropylene nucleated by calcium pimelate and TMB-5 were both greater than 92%.The results of non-isothermal crystallization kinetic studies showed that when the amount of nucleating agent added was 0.1wt%,zinc adipate accelerated the crystallization rate of polypropylene.calcium pimelate and TMB-5 can accelerate the crystallization rate of polypropylene in the early stage,with the progress of the crystallization process,the overall crystallization rate of nucleated polypropylene decreases.The reason may be related to the different dispersity of nucleating agents in polypropylene.(2)The synergistic effect of different components of the compound?-nucleating agent in inducing the crystallization of polypropylene was studied.Two kinds of low cost and high efficiency compound?nucleating agents with zinc adipate as the main component and calcium pimelate or TMB-5 as the secondary component were prepared.The result of DSC showed that the crystallization peak temperature of polypropylene nucleated by 0.1wt%zinc adipate/calcium pimelate compound?nucleating agent is between the crystallization peak temperatures of polypropylene nucleated by 0.1wt%zinc adipate and 0.1wt%calcium pimelate separately.When the mass ratio of zinc adipate to calcium pimelate is 8:2,the K_?value of nucleated polypropylene reaches 94.3%.Zinc adipate/calcium pimelate compound nucleating agent reduces the crystalline grain size of polypropylene and improves the uniformity of?-crystalline form distribution.The crystallization peak temperature of polypropylene nucleated by zinc adipate/TMB5 compound?nucleating agent is between the polypropylene nucleated by 0.1wt%zinc adipate and Pure-i PP.This phenomenon may be related to the agglomeration of the nucleating agent component in the polypropylene matrix.When the mass ratio of zinc adipate to TMB-5 is 9:1,the K_?value reaches 92.0%,it was increased by 8.3%compared with polypropylene nucleated by 0.1wt%zinc adipate,but the K_?value is 2.9%lower than polypropylene nucleated by 0.1wt%TMB-5.Zinc adipate/TMB-5 compound nucleating agent induced polypropylene to form?-crystal and branch-like?-crystal.(3)The crystalline form and sintering window of polypropylene powder for selective laser sintering were modulated with nucleating agents.The polypropylene powders nucleated with zinc adipate or?nucleating agent HPN-20E were prepared respectively,and the properties was compared with the polypropylene powder without nucleating agent.The result of XRD showed that the polypropylene powder containing?-crystals was prepared by melt extrusion combined with cryogenic grinding through zinc adipate as nucleating agent.The crystalline form of the polypropylene powder nucleated by HPN-20E and the Pure-Powder are both?-crystal.The result of DSC showed that sintering window of polypropylene was narrowed by nucleating agents.The result of SEM showed that the morphology of polypropylene powder after cryogenic grinding process is irregular,and the filamentous structures appears on the surface of?-Powder and?-Powder,which leads to the reduction of its loose bulk density.In conclusion,the?-crystalline form polypropylene powder for selective laser sintering can be prepared by adding?-nucleating agents,and this method has the characteristics of high efficiency,stability and low cost.