锥形量热仪中聚合物的熔融现象及其对燃烧行为的影响

Melting Phenomena and Their Infl uences on Burning Behaviors of Polymers in Cone Calorimeter

采用锥形量热仪研究几种聚合物的燃烧行为并观察熔融现象,发现聚合物的熔融现象与其加工温度下的熔体流动速率几乎无相关性,与裂解机理相关性较大。结果表明,以解聚为主要裂解机理的聚甲基丙烯酸甲酯、聚甲醛和高抗冲聚苯乙烯仅出现熔融软化现象,其质量损失速率(MLR)和热释放速率(HRR)曲线只有一个燃烧增长阶段,而以随机裂解为主要裂解机理的低密度聚乙烯、聚丙烯、聚酰胺和乙烯–醋酸乙烯共聚物不仅存在物理熔融软化现象而且会因裂解而出现流淌熔体并最终形成池火,导致MLR和HRR曲线出现两个增长阶段。第二增长阶段的MLR和HRR较大,燃烧消耗掉大部分聚合物,且该阶段可能与池火燃烧有关。

The melting phenomena and the buming behaviors of several polymers in the cone calorimeter were studied. It was found that the melting phenomena depended on the pyrolysis mechanism, but nearly had nothing to do with the melt flow rate. The results show that polymers with dominant pyrolysis mechanism of depolymerization, including polymethylmethacylate, polyoxymethylene and high impact polystyrene, become soft due to melting and their mass loss rate（MLR） and heat release rate （HRR） curves have only one increasing period. Polymers with dominant pyrolysis mechanism of randoms scission, including low density polyethylene, polypropylene, polyamide and ethyl-vinylacetate copolymer, not only become soft before ignition due to physical melting but also formed flowing melts after ignition due to pyrolysis, leading to two increasing periods of their MLR and HRR curves. Most fuels, probably in the form of flowing melts, are combusted during the second period with relatively high MLR and HRR.