水滑石类化合物的制备、改性及其在PVC中的应用

【作者】 朱健；

【导师】 周建良；

【作者基本信息】 中南大学 ， 无机化学， 2011， 硕士

【摘要】 水滑石类化合物(LDHs)是一类阴离子型层状材料,层间具有可交换的阴离子。LDHs特殊的层状结构和化学组成使其有望替代传统热稳定剂,成为无毒、廉价、高效的PVC热稳定剂新品种。本文本着降低原料成本、简化制备工艺和提高产品性能的原则,研究了恒定pH值法合成MgAl-CO3-LDHs的相关条件,改进了湿法表面改性工艺对MgAl-CO3-LDHs进行表面改性,探索了阴离子交换法合成ZnAlLa-CO3-LDHs的相关条件,并将MgAl-CO3-LDHs与ZnAlLa-CO3-LDHs复配后应用到PVC中。实验以LDHs对PVC的热稳定时间(刚果红测试)作为产品的性能指标,采用X射线衍射(XRD)、傅立叶变换红外光谱(FT-IR)、扫描电镜(SEM)、电感耦合等离子体原子发射光谱(ICP)、热重-差示(TG-DSC)、粒度分析等检测手段对LDHs进行测试和表征。论文考察了pH值、原料种类对合成MgAl-CO3-LDHs的影响；采用硬脂酸钠为表面改性剂,对比了常规湿法改性工艺和改进湿法改性工艺对MgAl-CO3-LDHs表面改性效果的影响；研究了pH值、初始溶液中n(La3+)/n(Al3+)、陈化时间对合成前驱体ZnAlLa-NO3-LDHs的影响；探索了阴离子交换时间对制备ZnAlLa-CO3-LDHs的影响。并考察了MgAl-CO3-LDHs与ZnAlLa-CO3-LDHs的复配比例对PVC热稳定性能的影响。结果表明：以氯化镁和硫酸铝为原料合成MgAl-CO3-LDHs的优选pH值为10.0；原料种类会影响MgAl-CO3-LDHs的结晶度、微观形貌、红外特征及对PVC的热稳定效果；常规湿法改性工艺中硬脂酸钠的较佳用量为LDHs质量的6%,改进湿法改性工艺中硬脂酸钠的较佳用量为LDHs质量的7%,后者改性的LDHs比前者的平均粒径更小、粒径分布更集中、对PVC的热稳定效果更好；合成前驱体ZnAlLa-NO3-LDHs的优选条件为：反应pH值=8.0,初始溶液n(La3+)/n(Al3+)=1/8,陈化时间24h；阴离子交换时间为1～2h合成的ZnAlLa-CO3-LDHs的结晶度和纯度较高；MgAl-CO3-LDHs和ZnAlLa-CO3-LDHs按质量比1：0.2复配后,对PVC的热稳定时间可达49.3min,优于单一类水滑石对PVC的热稳定效果,复合水滑石体系具有“协同效应”。综上所述,以氯化镁和硫酸铝为原料合成MgAl-CO3-LDHs,在保证产品性能的前提下节约了原料成本；改进了湿法改性工艺,缩短了LDHs表面改性的工艺流程,并取得较好的表面改性效果；采用阴离子交换法合成ZnAlLa-CO3-LDHs,并将MgAl-CO3-LDHs与ZnAlLa-CO3-LDHs复配使用,提高了LDHs对PVC的热稳定性能。论文为水滑石类热稳定剂的生产和应用提供了重要的理论依据。更多还原

【Abstract】 Layered Double Hydroxides (LDHs) or hydrotalcite-like compounds (HTLcs) are a category of anionic layered materials, which contain exchangeable anions in the interlayer. LDHs will replace traditional heat stabilizers to become a new kind of PVC heat stabilizer which have the advantage of non-toxic, inexpensive, efficient due to their special layer structure and chemical composition.In this thesis, on the principle of reducing cost, simplifying preparation process and improving the properties of products, synthetic conditions of MgAl-CO3-LDHs with constant pH method were studied. MgAl-CO3-LDHs were modified by the improved wet surface modification process, related conditions of ZnAlLa-CO3-LDHs with anion-exchange method were also investigated and the composites of MgAl-CO3-LDHs/ZnAlLa-CO3-LDHs were applied in PVC.The thermal stable time for PVC (congo red test) as the main performance index of LDHs, the samples were tested and characterized by XRD, FT-IR, SEM, ICP, TG-DSC and grading analysis. In this thesis, effects of pH values and materials types on the synthesis of MgAl-CO3-LDHs were investigated; surface modification effects of MgAl-CO3-LDHs prepared with routine wet modification process and improved wet modification process were compared when sodium stearate was used as surface modifier; effects of pH values, n(La3+)/n(Al3+) values of initial solution and aging time on the synthesis of precursor ZnAlLa-NO3-LDHs were discussed; influences of anion-exchange time on the preparation of ZnAlLa-CO3-LDHs were also explored. Besides, effects of composite ratios of MgAl-CO3-LDHs and ZnAlLa-CO3-LDHs on PVC thermal stabilities were investigated.The results showed that the optimal pH value was 10.0 when MgAl-CO3-LDHs were prepared with MgCl2 and A12(SO4)3 as the raw materials; the materials types had influences on crystallinity, micro-morphology, infrared feature and thermal stabilities of PVC; the optimum dosage of sodium stearate was 6% of the LDHs weight in routine wet modification process while 7% in improved wet modification process, the later had smaller average diameter, narrower particle distribution and better thermal stabilities of PVC than the former; the optimum reaction conditions of precursor ZnAlLa-NO3-LDHs were:the reaction pH was 8.0, the molar ration of n(La3+)/n(Al3+) was 1/8 in the initial solution, aging time was 24h; the crystallinity and purity of ZnAlLa-CO3-LDHs were higher when anion-exchange time was 1～2h; the heat-stable time for PVC could reach to 49.3min when MgAl-CO3-LDHs and ZnAlLa-CO3-LDHs were composited at mass ratio of 1:0.2, and had better thermal stabilities of PVC than single LDHs, which all suggested there was "synergistic effect" in composite LDHs system.In conclusion, MgAl-CO3-LDHs were synthesized using MgCl2 and A12(SO4)3 as materials, which could reduce costs on the base of guaranteeing the properties of products; the surface modification process of LDHs was simplified and surface modification effects was improved by improved wet modification process. ZnAlLa-CO3-LDHs were synthesized with anion exchange method and thermal stabilities of LDHs for PVC were improved when MgAl-CO3-LDHs and ZnAlLa-CO3-LDHs were composited. This thesis provided important theoretical basis for production and application of LDHs as heat stabilizers.更多还原