Study On The Preparation And Properties Of Polypropylene Powder For Selective Laser Sintering

With the development and application of selective laser sintering(SLS)technology,the demand for various polymer powders compatible for this technology has increased accordingly.To solve this problem as well as warping and shrinkage of SLS parts,we modifed polypropylene(PP)powder using high-temperature induced crystallization method.By dispersing PP powder in its poor solvent at appropriate temperature,a PP powder with high sphericity,small particle and wide sintering window was obtained,which is found to more suitable for SLS process.This method has advantages including simple process,lower cost and eco-friendly medium,which may provide a new way for the preparation of SLS materials.The main researches are as follows:(1)The raw material powder was modified by high-temperature induced crystallization method.The effects of the modified process conditions on the properties of PP powders,including sizes and morphology were analyzed.By several trials,the optimal conditions were determined:processing temperature 170℃,processing time 6h,stirring speed 1000 r/min,mixture of glycerol and silicone oil(volume ratio 2:1)as dispersing medium.Under these parameters,PP powder with high sphericity and smooth surface was obtained.The modified PP powder exhibited sintering window of 50.3℃ and the average particle size of 132.2μm.Due to its spherical morphology and small size,modified PP powder demonstrated LBD and CBD being 0.501g/cm3 and 0.411g/cm3.respectively,which is better than raw PP powder.Also,the reasons accounting for the wide sintering window of PP powders were explored by means of Differential Scanning Calorimeter(DSC)and X-ray diffraction(XRD).(2)By varying the processing parameters of SLS technique,3D parts printed with different PP powders were prepared.And the dimensional accuracy of 3D parts were evaluated to explore the effect of material properties on 3D parts properties.It is found that processing parameters exerted influences on the warpage and shrinkage behavior of 3D parts in the order of laser power>sintering temperature>scanning mode.The preheat temperature 110℃,laser power 40W,scanning spacing 0.10mm,scanning speed 200mm/s,the size shrinkage mean value and the standard deviation of X direction sintered PP modified powder sample were 0.7mm and 0.4mm respectively;Y direction were 1.0mm and 0.5mm respectively.Moreover,the surface precision of these samples were better than that of the raw material powder samples due to the lower melt viscosity and better material flow during sintering process.The dimensional accuracy is essentially improved compared to the raw material counterparts.