E-PBT-Bead foaming of poly(butylene terephthalate) by underwater pelletizing
E-PBT-Bead foaming of poly(butylene terephthalate) by underwater pelletizing
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DOI：
10.1177/0021955x14528524
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发表时间：
2014-09-01
影响因子：
2.5
通讯作者：
Altstaedt, V.
中科院分区：
文献类型：
--
作者：
Koeppl, T.;Raps, D.;Altstaedt, V.
由聚对苯二甲酸丁二醇酯（PBT）等工程热塑性塑料制成的泡沫是新一代聚合物泡沫，可能是轻质、绝缘和阻尼材料的未来。通过泡沫挤出或珠粒发泡，可以获得低至中等密度的泡沫（< 500 kg/m3）。然而，PBT的泡沫挤出是相当具有挑战性的，这是由于其低熔体强度和可拉伸性与小的温度加工窗口相结合，这是半结晶热塑性塑料的特征。这项工作证明，通过选择合适的材料和水下造粒泡沫挤出工艺参数，可以减少泡孔聚结和泡孔稳定性不足的问题。因此，使用CO2作为超临界发泡剂可以首次实现膨胀PBT珠粒。为了获得具有均匀泡沫结构的球形低密度PBT珠粒，系统地研究了两种不同商业挤出等级和不同发泡剂浓度的不同工艺参数。研究了水下切粒机的水压和切粒速度对E-PBT泡沫形态和珠粒结构的影响。结果表明，使用具有足够高熔体粘度的聚合物等级有助于减少泡孔聚结。达到的最低密度为230 kg/m（3）。发泡剂浓度的增加无助于降低密度。通过差示扫描量热法研究熔融范围，并得到205-215 ℃的合理模塑温度。这对应于蒸汽模制机中17-21巴的蒸汽压力。
Foams from engineering thermoplastics like poly(butylene terephthalate) (PBT) are a new generation of polymer foams and, probably, the future for lightweight, insulation and damping materials. By means of foam extrusion or bead foaming, it is possible to achieve low-to-medium density foams (< 500 kg/m(3)). However, foam extrusion of PBT is quite challenging due to its low melt strength and drawability combined with a small temperature-processing window, which is a characteristic of semi-crystalline thermoplastics. This work proves that the problem of cell coalescence and insufficient cell stabilisation can be reduced by choosing the right material and processing parameters in foam extrusion with underwater pelletizing. Therefore, expanded PBT beads could be realised for the first time using CO2 as supercritical blowing agent. To obtain spherical low-density PBT beads with a homogenous foam structure, different process parameters were systematically studied with two different commercial extrusion grades and different blowing agent concentrations. The influence of water pressure and cutting speed of the underwater pelletizer on foam morphology of E-PBT and bead structure was studied. It was shown that using a polymer grade with a sufficiently high-melt viscosity helps to reduce cell coalescence. The lowest achieved density was 230 kg/m(3). An increase of the blowing agent concentration did not help in reducing the density. The melting range was investigated by differential scanning calorimetry and yielded reasonable moulding temperatures of 205-215 degrees C. This corresponds to steam pressures of 17-21 bar in a steam-moulding machine.