氢氧化镁/可膨胀石墨/聚丙烯复合材料的热降解过程与燃烧行为

以可膨胀石墨(EG)和氢氧化镁(MH)为无卤阻燃剂,通过熔融共混法制备了无卤阻燃聚丙烯(PP)复合材料(EG/PP、MH/PP和MH/EG/PP),采用热重法研究了复合材料的热降解过程,以氧指数(LOI)和垂直燃烧(UL-94)评价研究了复合材料的阻燃性能,采用锥形量热仪研究了复合材料的燃烧行为.结果表明:MH和EG间存在显著的协同阻燃作用,在阻燃剂质量分数为60%时,MH与EG质量比为5∶1的MH/EG/PP材料其氧指数可以达到29.7,与MH/PP复合材料相比提高了11.2%; EG与MH协同具有良好的降低热释放作用,与PP和MH/PP相比,MH/EG/PP复合材料的热释放速率峰值(peak-HRR)分别降低了73.9%和34.2%; EG和MH的协同作用大幅度降低了MH/EG/PP的质量损失速率;结合残炭的形貌结果,揭示了EG和MH协同阻燃机理的关键在于增强了炭层的隔热和隔氧作用.

Thermal Degradation and Combustion Behavior of Flame Retardant Polypropylene with Expandable Graphite and Magnesium Hydroxide

Expandable graphite (EG) and magnesium hydroxide (MH) were used to prepare halogen-free flame-retardant polypropylene(PP) composites (EG/PP, MH/PP and MH/EG/PP) through melt blending. The thermal degradation process was investigated with the thermogravimetric analysis (TGA). The flame retardant properties were evaluated in terms of limiting oxygen index (LOI) and vertical testing UL-94. The combustion behavior was studied with cone calorimeter. As a result, the significant synergistic flame retardant effect between MH and EG was revealed. When the mass fraction of flame retardant was 60%, the LOI value of the composites with MH/EG at a mass ratio of 5 : 1 reached 29.7, which showed an increase of 11.2% in comparison with the composites with MH. MH/EG exerted a synergistic effect in reducing heat release rate (HRR). The peak-HRR of MH/EG/PP composites was decreased by 73.9% and 34.2% respectively in comparison with that of PP and MH/PP. The thermal weight loss rate of the composites was greatly depressed when EG and MH were applied together in PP. Combined with the results of the residue morphology, the flame retardant mechanism of the enhanced effects of char layer in the barrier effects of heat and O₂ transfer was revealed.