Study On The Preparation And Selective Laser Sintering Of Polypropylene/graphene Nancomposite Powders

Selective laser sintering(SLS)is a kind of technology which uses laser as heat source to sinter and stack powders layer by layer to build parts.Polymer powders are currently the most widely used SLS materials.It can be used for forming polymers,ceramics,metals and composites.Polypropylene(PP)is a kind of thermoplastic polymer,which has the advantages of low density,high toughness,high impact strength and stable chemical properties.It is widely used in automobile manufacturing,electrical and electronic construction and medical treatment.It is one of the fastest developing polymer materials in the world.PP has been applied in the SLS process.However,no external driving force exists during the SLS process,resulting in lower performance of fabricated parts than the conventional molded parts.Therefore,domestic and foreign scholars are using nano-materials to enhance the performance of SLS parts,and have achieved good results.This has become a hot spot in the field of SLS.In this study,graphene is used to enhance SLS parts of polypropylene.The preparation and SLS process of polypropylene/graphene composite powders,and the properties of sintered parts were studied.In this study,polypropylene/graphene composite powders with graphene content of 0.1 wt.%,0.5 wt.%,1.0 wt.% and 2.0 wt.% were prepared by a stirring evaporation method.The results show that the particle size of polypropylene and four composite powders is ranging of 20-100 μm.Their powder shapes are spherical or nearly spherical,and graphene is adsorbed on the surfaces of the polypropylene particles.Graphene reduces the crystallization rate of polypropylen and improves the thermal stability of polypropylene.On the other hand,graphene increases the melt viscosity of polypropylene,and the higher the content of graphene,the greater the melt viscosity of the composite powder.This behavior is not conducive to the flow of polypropylene melt during the SLS process.The SLS mechanism of polypropylene/graphene composite powders was studied,and the influence of the process parameters on the properties of polypropylene/graphene composite SLS parts was analyzed in this study.The preheating temperature in the SLS process was determined by the DSC curves of the five kinds of powders.The laser power,scanning speed and thickness of the polypropylene/graphene composite powders were determined by 10 groups of experiments.Then a set of optimal process parameters is determined as follows: the preheat temperature is 110 ℃,the scanning distance is 0.2 mm,the layer thickness is 0.12 mm,the scanning speed is 2000 mm / s,and the laser power is 9 W.Measurements were carried out on the pure polypropylene and polypropylene/graphene SLS parts.It is found that after the SLS of the pure polypropylene and polypropylene/graphene composite powders,α phase of polypropylene matrix partially changes to γ phase.When 0.1 wt.% content of graphene is added,the tensile strength and toughness of the sintered parts are enhanced,but the tensile modulus is reduced.When the graphene content is more than 0.1 wt.%,the tensile strength and toughness of the sintered parts are reduced,but the tensile modulus is improved.On the other hand,it is found that the addition of excessive graphene reduces the flexural strength and surface quality of the sintered parts.The addition of graphene enhances the thermal stability of the sintered parts of polypropylene,and changes the way that the sintered parts of polypropylene are broken.