Preparation and modification of layered double hydroxides and application in polypropylene as flame retardant
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摘要: 采用共沉淀法制备了镁铝类水滑石（LDHs）前驱体，加入少量聚磷酸铵（APP）制得APP-LDHs，探讨了不同质量分数APP对LDHs晶体生长的影响；当APP在LDHs前驱浆液中添加量为0.8wt%时，将APP-LDHs与季戊四醇（PER）、硅烷偶联剂KH-550进行球磨混合，制备插层包覆改性的LDHs；通过XRD、FTIR、SEM和TG等对改性前后的LDHs进行了表征；采用极限氧指数（LOI）、垂直燃烧测试（UL-94）、缺口冲击和弯曲实验等方法研究了LDHs改性前后LDHs/聚丙烯（PP）复合材料的阻燃性能及力学性能的差异。研究结果表明：APP的加入，未显著影响LDHs的层板生长，但其层板堆叠受到抑制；SEM观察表明，所制备的LDHs为片状，且经插层包覆改性后的LDHs粉体形貌较为规整，颗粒粒径为100~250 nm；改性LDHs在较高温度下的热稳定性显著优于未改性的LDHs；当PP中加入质量分数为20%的LDHs及改性LDHs时，可抑制PP燃烧时产生的熔滴，并促使LDHs/PP复合材料表面形成炭层；改性LDHs/PP复合材料具有更好的阻燃性能，且其冲击强度、弯曲强度等力学性能下降不明显。Abstract: Mg-Al layered double hydroxides (LDHs) precursor was synthesized by coprecipitation method under mild conditions. The crystallization of LDHs was modulated with a small amount of ammonium polyphosphate (APP) to prepare APP-LDHs and the influence of APP at different mass fraction on the crystallization was investigated. When the addition of APP in LDHs suspension was 0.8wt%, the APP-LDHs was mixed with pentaerythritol (PER) and silane coupling agent KH-550 via ball milling and the modified LDHs (modified-LDHs) was completed ultimately. XRD, FTIR, SEM, TG were utilized to characterize the structure, morphology and thermal stability of the LDHs. The fire retardancy of LDHs/PP composites were evaluated by UL-94 test and limiting oxygen index (LOI), as well as the mechanical behavior was assessed, using flexural strength and notch impact strength. The results demonstrate that the crystal growth of LDHs is inhibited along the stacking direction in the presence of APP, but the grain size which represents layer growth remains unchanged. SEM images of the LDHs indicates sheet-like structure of the as-prepared LDHs, while the APP-LDHs modified by PER and KH-550 via ball milling shows that the modified-LDHs formed a regular powder with particle size of 100 nm to 250 nm. The modified-LDHs performs a better thermal stability at higher temperature. PP fills with 20 % mass fraction of LDHs burnt without droplet and the surface of LDHs/PP composites residue are covered with an expanded char network. Modified-LDHs/PP composite has superior flexural strength and notch impact strength compares with LDHs/PP and APP-LDHs/PP composites.
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