| Summary: | 碩士 === 國立交通大學 === 應用化學系 === 87 === Recently, due to the shortage supply of the natural wood, the extruded structural foams gradually become the most suitable materials for replacing the natural wood. Previously, PVC is the main processing materials for the structural foams. However, PVC has the disadvantage of generation of the toxic gases during combustion and difficulty of recycling. Owing to the global concerns of environmental protection, structural foam products made with polystyrene (PS) and polypropylene (PP) which don’t have much problem and also posses low price, are gradually replacing the polyvinyl chloride foam products.
This study aims to investigate the effect of processing conditions on the foam structure and mechanical properties of high impact polystyrene structural foams. In addition, the branch polypropylene with high melt strength was used to study the relationship between processing condition and foam structure exiting from the die. The results can provide useful information for further study of the processing of the extruded PP structural foam. The experimental results for HIPS showed that higher nucleation rate and take-off speed were obtained under either one of the following conditions: higher take-off speed, higher blowing agent concentration, higher die temperature, higher calibrator temperature, which would lead to a thinner skin layer and a larger bubble count. Meanwhile, flexural yield strength, flexural modulus and impact strength also decrease under these processing conditions. Regarding to the study of PP foams, the experimental results demonstrated that higher nucleation rate can be obtained under either one of the following conditions: higher blowing agent concentration, higher die temperature, larger die land length or smaller diameters of flow connector, Consequently leading to a larger bubble count and smaller bubble size. With regard to the increase of nucleation agent concentration, the results illustrated that the bubble count would increase. However, the bubble size showed the trend of increase first and subsequent decrease.
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