耐衝擊聚苯乙烯及聚丙烯發泡加工之研究

Abstract

在木材日益短缺的今天，押出結構發泡產品可說是天然木料的最佳替代品，可取代木材成為各式的建材。押出結構發泡產品在以往是以PVC為主流，但是PVC燃燒時易生有毒氣體且回收不易。在環保意識高漲的現代、已漸漸的被較無此類問題且價格低廉的PS及PP所取代。 本研究除了以向核心發泡的方法來探討耐衝擊聚苯乙烯押出結構發泡其加工條件對發泡結構及機械性質之影響外，更以高熔融強度之分枝型聚丙烯為材料，探討其出模發泡結構與加工條件之關連，以作為日後進一步研究時之參考。在耐衝擊聚苯乙烯方面，根據研究結果顯示，隨著引取速率、發泡劑濃度、模頭溫度及定型模溫度的增加會導致成核速率增加及引取速度加快，使得產品皮層變薄及氣泡數目增多，而且其抗折屈服強度、抗折模數及耐衝擊強度也隨之下降。至於高熔融強度之聚丙烯方面，由實驗結果可得知，隨著發泡劑濃度、模頭溫度、模唇長度的增加及分流管孔徑的縮小，會導致成核速率的增加，使得氣泡數目增多，且氣泡尺寸變小。至於增加成核劑濃度則導致氣泡數目增加，但氣泡尺寸則呈先減後增之趨勢。

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.