摘要
聚丙烯(PP)是一种在生产和生活中常见的重要塑料,广泛应用于产品包装、汽车附件、电子产品、室内装修、绝缘材料和建筑材料等领域。但由于聚丙烯易燃,且燃烧时释放出大量的烟雾及有毒气体而使其应用范围受到了很大限制,特别是在汽车制造和电子产品领域。因此赋予PP良好的阻燃性能对于扩大其应用范围具有重要意义。
采用硅烷偶联剂KH-550对阻燃剂进行表面改性,以提高其在PP基体中的分散性和相容性。采用机械球磨法对原始粒径较大的氢氧化镁(约2μm)和氢氧化铝(约10μm)进行表面改性,分析讨论了改性对阻燃剂粒径大小、形貌及分散性的影响。结果表明：球磨改性更有利于粉体的细化和分散；当介质为酸性条件时,KH-550对氢氧化物粉体的改性效果最佳,并对反应机理进行了分析和探讨。因聚磷酸铵(APP)阻燃剂的平均粒径(<1μm)较小而采用常规方法对其进行表面改性,改性后的APP其分散性、热稳定性及与有机相的相容性都得到了很大的提高。
通过比较不同阻燃剂的改性效果和对聚丙烯燃烧特点的分析,选用APP作为阻燃剂将其应用于聚丙烯,获得阻燃聚丙烯(APP/PP)复合材料。采用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)、热重-差热分析仪(TGA-DTA)、熔体流动速率仪(MFR)和极限氧指数仪(LOI)分别对阻燃复合材料的晶体结构、断面形貌、热稳定性、结晶行为、熔体流动速率和阻燃性能进行了分析测试,并测定了复合材料的力学性能。
研究结果表明：随着APP添加量的增加,复合材料的热力学稳定性增加,MFR值先降低后增加；APP的添加对PP基体有异相成核作用,当添加量达到13%后,这种异相成核作用更加明显,使得复合材料的力学性能不会随APP添加量的增大而继续下降,同时还增强了APP与PP基体间的界面结合；复合材料的阻燃性能和热稳定性亦随之提高,当添加量为20%时,LOI值达到30%；阻燃复合材料在燃烧时实现自熄,APP起到了催化成炭和防融滴的作用；表面改性后的APP提高了阻燃复合材料的拉伸强度、冲击强度和断裂伸长率。
综上所述,APP不但可以同时作为酸源和气源,还兼具催化成碳的作用,与三相膨胀阻燃体系相比,APP单独使用不仅提高了PP的阻燃效率,同时还可降低生产成本、优化工艺条件。
As an important plastic in our life, polypropylene (PP) are widely used in such fields as electric casings, cars, electronics, interior decorations, insulation materials, architectural materials and so on. However, it is easy to flame, accompanying the emission of thick smoke and poisonous gases, which restricts its application range, especially for the automotive manufacture and the electronic industry. Therefore, it is important and necessary to improve the fire retardant behavior of PP so as to expand its applications.
Magnesium hydroxide (about 2μm) and aluminum hydroxide (about 10μm) flame retardant powders in large sizes were modified with silane coupling agent KH-550 by mechanical ball-milling. The effects of surface modification on the particle size, morphology and dispersibility were discussed. The results showed that the mechanical ball-milling was more conducive to the size refinement and dispersibility of particles, and the optimum modification condition was achieved in acidic medium. The reaction mechanism was analyzed and discussed too. In view of ammonium polyphosphate (APP) in relatively small size (<1μm), the conventional surface modification was carried out on APP particles. The dispersability, compatibility and thermal stability of modified APP were greatly enhanced.
By comparison of the modification effects of different flame retardants, APP was finally choosed to be added in PP. The flame retardant APP/PP composite was obtained. X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), thermo gravimetric-differential thermal analysis (TGA-DTA), melting flow rate (MFR) and Limiting oxygen index (LOI) were used to analysis and characterize APP/PP composites in terms of the crystal structures, section morphologies, thermal stability, crystallization behavior, melt flow rate and the flame retardant performance. The mechanical properties of composite were also tested. The results indicated that the thermal stability of APP/PP composites was increased with the addition of APP, with a result of MFR decreasing at first and then increasing. The interfacial binding force between APP and the matrix had been improved due to heterogeneous nucleation of APP, which also inhibited the drop of the mechanical properties of composites when APP loading greater than 13%. With the increase of APP loading, the LOI value and the thermal stability of the composites obviously increased. When APP loading was up to 20 wt.%, the LOI value reached 30%. The composites could be self-extinguished after ignited, due to the char formation and droplet resistance of APP. The modified APP brought good mechanical properties to the composites, with the tensile strength, impact strength and elongation all improved.
In summary, APP could be used as an acid source and a gas supplier at the same time, combined with promoting char formation. Compared with three-phase intumescent flame retardant system, the exclusive use of APP as flame retardant enhanced the flame retardant efficiency, and decreased the production cost and simplified the processing condition.
引文
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