| Polymer materials are the earliest and most widely used materials for selective laser sintering(SLS)molding technology.As one of the four general-purpose plastics,polypropylene(PP)has many advantages such as abundant raw material sources,low production cost,low density,chemical stability,good electrical insulation and heat resistance,and easy processing.However,its application in the field of SLS is still very insufficient,and the preparation of its powder is one of the major problems that need to be solved.A new method,water dispersion method,was used to prepare PP powder for selective laser sintering.The principle is that the PP and water in the viscous flow state under high temperature and high pressure are under the action of certain emulsifiers,so that the PP is uniformly present in the water,and then through cooling and other processes,the PP cools and crystallizes into micron-sized powders.The final result was that Plenic F108 was successfully used as a surfactant to disperse the PP,and PP particles with uneven particle size distribution were obtained,the feasibility of the water dispersion method was verified.In order to obtain a polymer powder material that can be used for SLS,several factors of the dispersion effect of PP in water had been intensively studied,including the amount of surfactant added,the amount of PP added,the amount of nucleating agent added,the melt index,Effect of temperature,speed,etc.The result of the study was that if the amount of surfactant added was less than 10g,no powder could be obtained.In the range of 10g-60g,it was proportional to the rate of powder formation.When the amount of surfactant was 60g or more,the rate of powder formation becomes stable;When the addition amount of PP reaches 10g or more,the obtained powder quality was stable at about 7g;Carbon-white as a nucleating agent has a great influence on the dispersion effect,and the rate of powder formation was maximum when the addition amount of carbon-white was 0.15g.The change of heating temperature and cooling rate had little effect on the rate of powder formation,while the rotation speed had a significant effect.The rotation speed was directly proportional to the powder formation rate.The maximum powder formation rate was72.5%at 1500 rpm.The melt index of PP was proportional to the powdering rate.When the melt index of PP was from 20g/10min to 41.3g/10min,the powder forming ratio was from 48.6%to 56.4%.The properties of the product(PP powder)under the best preparation conditions were studied from four aspects.In the macroscopic morphology analysis,the PP powder was smooth to the touch,had good fluidity,high sphericity,no aging and yellowing.In the performance analysis of SLS process conditions,the powder has a certain degree of sphericity,good dispersion between the powders,high density of the powder,pore-like voids on the surface of the powder,particle size range of75μm-100μm,average apparent density was 0.523g/cm~3,which was in line with the performance requirements of the SLS process for PP powder;In the crystallinity and thermal analysis of PP powder,no obvious black cross phenomenon was observed under the polarizing microscope.The XRD analysis concluded that the crystallinity of the powder was 80.56%,which is a single crystalline PP powder of alpha crystal type.The melt index of the powder is 23.7g/10min.The conclusion of DSC is that the sintering window temperature of the PP powder in the SLS process is126.10℃-159.25℃;The test bar obtained by injection molding has a tensile strength of 21.965 MPa,a flexural strength of 27.77 MPa,a flexural modulus of 1297 MPa,and a notched impact strength of 10.64 KJ/m~2. |
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