【作者】 彭娅；

【导师】 傅强；

【作者基本信息】 四川大学 ， 材料学， 2004， 博士

【摘要】 硅橡胶具有耐高温、耐低温、防潮、绝缘、耐老化等优异性能,被广泛应用于国民经济众多领域,尤其是室温硫化硅橡胶。由于纯室温硫化硅橡胶力学性能较差,因此加入补强填料才具有使用价值。通常采用白炭黑作为补强填料,而碳酸钙在橡胶中仅作为普通的增容填料。随着纳米技术的发展,由于碳酸钙粒子的纳米级超细化,其晶体结构和表面电子结构发生变化,产生了普通碳酸钙所不具有的量子尺寸效应、小尺寸效应、表面效应和宏观量子效应,从而可以部分或是全部代替价格昂贵的白炭黑作为橡胶的补强填料。目前大量的研究工作主要集中在纳米碳酸钙填充橡胶的工程应用上,然而对碳酸钙在橡胶中所起的补强作用在国内外都没有进行深入的研究。由于纳米碳酸钙的产生使得碳酸钙自身的结构特点发生了根本的变化,存在粒径大小不同,粒子的形状不同,表面处理剂也有不同。纳米碳酸钙填充室温硫化硅橡胶补强效果与粒子的粒径、晶型、表面活性等因素有关,但是除此之外是否还受其它因素的影响。为了理解纳米碳酸钙的补强特性需要对纳米碳酸钙与室温硫化硅橡胶之间是否存在相互作用以及相互作用的特征进行研究,而且对于纳米碳酸钙在室温硫化硅橡胶中的补强机理是与炭黑或白炭黑的补强机理相似或是完全不同,对此也研究甚少。本论文将针对以上存在的问题对纳米碳酸钙填充脱醇型室温硫化硅橡胶进行深入的研究。首先研究了粒径不同、表面处理剂不同的纳米碳酸钙填充室温硫化硅橡胶的拉伸强度、断裂伸长率和定伸模量等力学性能,与纯胶相比都有一定程度的增加,说明纳米碳酸钙填充到室温硫化硅橡胶中明显体现了补强作用。通过三<WP=3>种不同种类纳米碳酸钙填充室温硫化硅橡胶力学性能的比较可知:粒径越小,补强作用也越强;而表面处理剂的差异对纳米碳酸钙在硅橡胶中补强效果影响并不大。除了粒径和表面活性以外,纳米碳酸钙含量的变化对纳米碳酸钙在RTV硅橡胶中补强作用也存在较大的影响,并且分为两个阶段:当纳米碳酸钙的含量低于80 phr时,其最大拉伸应力、断裂伸长率和100%定伸模量与纯硫化胶相比提高较小;当填充量增加至80 phr时,填充胶的力学性能都有较大幅度的增加,表现出明显的补强作用;继续增加填料含量,尽管100%定伸模量有所增加,但最大拉伸应力不再提高且断裂伸长率大大降低。填充量在80 phr填充胶的力学性能达到最佳。故纳米碳酸钙填充到室温硫化硅橡胶体系中具有双重作用,它既可用作提高力学性能的补强剂也可作为降低产品成本的增容剂。而采用气相法二氧化硅补强硅橡胶所需加入较小的填充量,如10%就能达到较明显的补强效果。纳米碳酸钙填充室温硫化硅橡胶的应力软化效应也表现出与力学性能相同的变化趋势:与未填充室温硫化硅橡胶应力软化程度相比,纳米碳酸钙填充硫化胶的应力软化程度随着填充量的增加应力软化程度增加。但是当填料含量低于80 phr时,随填料含量的增加应力软化程度增加幅度较小,当填料含量达到80 phr时,应力软化程度有明显的陡升。而气相法二氧化硅填充室温硫化硅橡胶的应力软化效应变化趋势同纳米碳酸钙相反:补强效果越明显,其应力软化程度反而降低。可见纳米碳酸钙与气相法二氧化硅的补强机理有所不同。为了弄清纳米碳酸钙在室温硫化硅橡胶中的补强机理,我们对纳米碳酸钙与室温硫化硅橡胶之间的相互作用进行研究,并与气相法二氧化硅与基体的相互作用进行对比。首先研究了纳米碳酸钙填充胶的粘度随填料含量的变化情况,发现在基料中加入不同含量的纳米碳酸钙表现出增粘作用,其粘度随填充量的变化同填充胶的力学性能和应力软化效应变化相同,也存在两个阶段:当填料浓度较低时,填充胶的粘度增加幅度较小;当填料含量增加至80 phr时,其胶体粘度陡增,为未填充胶料的65倍。而粘度的增加有利于纳米粒子团聚体在剪切作用下得以破碎,从而以较小的尺度均匀分散。所以通过SEM观察到对于同种纳米碳酸钙在基体中分散情况与纳米粒子的含量有关,填料含量越高,粒子的分散越均匀,在基体中分散尺度也越小。DMA和DSC表征结果说明加入纳米碳酸钙对室温硫化硅橡胶的玻璃化温<WP=4>度影响较小,但熔点随着含量的增加而明显移向低温,即填料与室温硫化胶分子链的相互作用使得聚二甲基硅氧烷在受限空间下结晶,从而使得高聚物晶体不完善所致;Kraus曲线的变化趋势也显示纳米碳酸钙于室温硫化硅橡胶之间存在着相互作用。为了研究纳米碳酸钙与室温硫化硅橡胶相互作用的本质,采用了IR和动态激光光散射对未硫化胶料进行表征,结果表明纳米碳酸钙表面处理剂的羰基与室温硫化硅橡胶分子链端的羟基发生了化学吸附反应,但是在甲苯特别是在氨气氛下甲苯溶液中遭到破坏。而气相法二氧化硅与室温硫化硅橡胶之间的相互作用较强,二氧化硅与聚二甲基硅氧烷的强相互作用是由于两者的结构相似,并且二氧化硅表面的Si-OH可与聚二甲基硅氧烷的Si-O形成氢键所致。而TG测试显示在室温硫化硅橡胶中填充纳米碳酸钙可以提高胶体的耐热性。通过对不同含量纳米碳酸钙填充硫化胶的热降解活化能的计算可知,随着纳米碳酸钙含量的增加热降解活化能增加。主要是在室温硫化硅橡胶中填充纳米碳酸钙的表面处理剂的羰基与硅橡胶末端的硅羟基相互作用而使得残余的羟基数目更多还原

【Abstract】 Silicone rubbers have taken an important role in a variety of applications for almost 40 years. Among them the moisture-curable room-temperature vulcanizable (RTV) silicone rubber represents one of the largest volume and commercially most successful silicone technologies. The networks have excellent primerless adhesion to substrates, such as, glass, metal, wood, masonry and plastics. Additional benefits include excellent weatherability, durability, electrical insulation, chemical resistance, stability at high temperature. It is well known that fumed silica is the well-reinforcing filler for RTV silicone rubber, for silica filled rubbers show an increase in modulus, hardness, tensile strength, abrasion as well as resistance to fatigue and cracking. Calcium carbonate has been long time considered as mineral fillers that extended and cheapened the rubbers. Nowadays, nano-calcium carbonate has attracted considerable interest because of its raw materials abundance in nature, low cost compared with fumed silica and the presence of activity by treatment of the surface. The nano-size, larger specific surface area and active points of nano-calcium carbonate make it possible to be used as reinforcing agent just like carbon black or <WP=8>silica. Although a number of investigations have been devoted to the analysis of silica-filled rubber networks, little work has been done on the reinforcement of calcium carbonate filled rubber network. Therefore, it is our purpose in this work to study the relationship of reinforcement RTV silicone rubber by using nano-calcium carbonate and filler characteristics such as filler size, structure, surface activity, and to carry out a systematically investigation on interaction between RTV silicone rubber and nano-calcium carbonate compared with silica filled RTV silicone rubber.It have been found that there is a simultaneously increase of tensile strength, modulus and elongation of nano-CaCO3 filled RTV silicone rubbers no matter what the kinds of nano-CaCO3 compared with unfilled silicone rubber. The mechanical properties can be improved slightly with increasing the filler content which is lower than 80 phr while these properties of 80 phr nano-CaCO3 filled RTV silicone rubbers greatly increase whereafter little decline with adding more fillers. The same trendence has been observed in the stress-softening effect of different filler content of RTV silicone rubbers. It is concluded that the trend of effect on the reinforcement of the nano-CaCO3 appears two-step.The dispersion of nano-CaCO3 particles in rubber was studied via SEM after the samples were fractured in liquid nitrogen. It is revealed that the three kinds of nano-CaCO3 can disperse evenly in rubber matrix. The indistinct interface of filler and rubber shows that there has been interaction between filler and rubber. At the same time, the more the content of filler is, the smaller the size of the agglomerate, For viscosity of 80 phr nano-CaCO3 filled rubber is much higher than that of pure rubber, which conduces to the even dispersion of filler in the matrix.The interaction between nano-CaCO3 and RTV silicone rubber has been characterized by DSC, stress relaxation, DMA, balance swelling and TG. DMA and DSC results showed that the interaction can decrease the melting temperature for filler might hold the rubber molecular chain crystallization for the interaction <WP=9>between filler and rubber. The results of IR and Dynamic Laser Light exhibit that the interactions between filler and rubber are chemical adsorptions, which is consistent with TG results that are revealed that this chemical interaction between nano-CaCO3 and RTV silicone rubber could improve the thermal stability of filled rubbers. Stress relaxation results showed that both the stress relaxation rate and relaxation degree augment, which indicated that the interaction between filler and rubber concludes physical adsorption. The crosslinking degree obtained by balance swelling illustrated that interaction can increase the crosslinking degree and the int更多还原