Morphology And Mechanical Properties Of Micro-injection Molded IPP Parts

The polymer melt undergoes high temperature, high pressure and high shear inthe micro-injection molding process. The flow behavior performances rheologicalphenomena which is different from that of macro-injection molding such as wall slip,surface tension and size dependence of viscosity. The morphology of iPP productssuch as skin-core structure, skin layer thickness, orientation, Crystallinity and βcrystal content are strongly influenced by the special rheological behavior. Themechanical properties are determined by the morphology of the micro-injectionproducts. Therefore, it has important meaning to study the relationship between theprocessing conditions, the morphology and the mechanical properties of the microinjection molding. The main work and conclusions are as follows:1. The Influence law and significance of the process parameters on themorphology of the micro-injection products. The Orthogonal experiment of sixfactors and five levels was selected, the six factors were melt temperature, moldtemperature, injection speed, packing pressure, packing time, cooling time. The layerthickness, orientation, Crystallinity and β crystal content were choosed as indicatorsof micro injection molding products. Influence law and significance of the processparameters on the morphology of the micro-injection products were studied. Then theInfluence law of scale effect on the morphology was explored. The result showed that:the importance and influence of process parameters on different structural indicatorswere different from each other. As for1.0mm and0.5mm micro-injection products,the most important factor on skin layer thickness and orientation was injection speed.With the injection speed increasing, the skin layer thickness and orientation reduced.The influence of process parameters on the morphology is different because of scaleeffect. As the thickness decreased, the percentage of skin layer thickness, orientationand β crystal content increased but Crystallinity decreased.2. The Influence law and significance of the process parameters on themechanical properties of the micro-injection products. Yield stress, modulus and elongation at break were selected as mechanical properties indexes. Influence law andsignificance of the process parameters on the mechanical properties of themicro-injection products were studied. Then the Influence law of scale effect on themechanical properties was explored. The result showed that: the importance andinfluence of process parameters on different mechanical properties indexes aredifferent from each other. As for1.0mm,0.5mm and0.2mm micro-injectionmolding products, the melt temperature is an important factor affecting the elongationat break.with the melt temperature increasing, the elongation at break increases. Theinfluence of process parameters on the morphology is different because of scale effect.With the size reducing, the yield stress and elastic modulus increase, but theelongation at break decreases.3. The relationship between morphological and mechanical properties of themicro injection molded parts. With the processing conditions changing, therelationships between skin layer thickness, orientation, Crystallinity, β crystal contentand yield stress, modulus, elongation at break were analyzed.The result showed that:As for the1.0mm micro-injection products, the orientation has the same trend as theyield stress. The skin layer thickness and the elongation at break follow the same rule.But the crystallization in skin layer and the elongation at break has the oppositerelationship. As for the0.5mm micro-injection products, the skin layer thickness andorientation has the same relationship.