求翻译：但由于PP自身结构的原因，其氧指数((LOI)只有17.4左右，属于易燃材料，遇火易燃烧、且发热量高、燃烧速度快、并伴有发烟、滴落现象，容易发生火灾，火焰传播速度快，不易熄灭，给人们的生命、财产安全造成极大的威胁，这就使得其应用领域受到了极大的限制。因此，对PP的阻燃改性具有非常重要的目的和意义。性能优异的无卤阻、低烟、低毒的膨胀型阻燃剂的开发与应用将成为21世纪PP阻燃剂最活跃的研究领域。本文解决的关键问题是自制无卤、低烟、低毒的膨胀型阻燃剂MPOP，添加到PP中后明显改善PP了的阻燃性能，并没有明显地影响PP的加工性能和破坏PP的物理、机械性能。是什么意思？

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However, because the reason PP structure itself, the oxygen index (LOI) is only about 17.4 and flammable materials, fire-burning, and produce less heat, burning high-speed, and with the smoke, drop-off in case of a fire, it is easy, fast, and flame spread is not easy to turn off, to the lives of peo

But due to PP itself structure of causes, its oxygen index ((LOI) only 17.4 around, belonging to flammable material, case fire easy combustion, and and heat high, and combustion speed fast, and and with mad