酸性介质环境中橡胶的热-化学-力耦合行为及本构关系研究

With development of chemical industry and energy resource, more and more the vulcanizates have been used in acidic medium environment. The conditions of the vulcanizates worked in hot acid are different from the environment of hot air, ozone, salt and alkali in that, on one hand, the rubber macromolecule can be aged and eroded by heat and acid and there is a complex changes for the crosslinking and chain scission of rubber macromolecules, on the other hand, the acid ease to react to inorganic materials and lead to the failure of interface between rubber matrix and filler. These can result in that decreased the mechanical properties and reliability of the rubber product. Compared with the environment of hot air, ozone, salt and alkali, the effects of acid on the rubber are more complex, and can play an important role for the vulcanizates uses. This is a typical thermo-chemo-mechanical multi-fields coupling behavior. This project can provide the parameters and internal variable of materials and analyze the impacting mechanism between hot acid and vulcanizates. According to the theory of thermodynamics and micromechanics, we can built up the constitutive relation of thermo-chemo-mechanical coupling and be verified it by experiments and FEM. This work has an important economic value and significance of the practical applications for instructing design of rubber formula and enhancing the reliability and safe service of the rubber seal for the large chemical reactors and the fuel cell.

随着化工、能源工业的发展，硫化橡胶越来越多应用在热酸性介质环境下。硫化橡胶在热酸环境下服役，不同于在热氧、臭氧和盐碱的化学介质中，一方面，橡胶大分子受到热的老化作用和酸的侵蚀，存在着断链与交联交替进行的复杂变化；另一方面，酸易于和体系中补强无机物产生化学反应，导致无机物与橡胶基体界面损伤，使得硫化橡胶在热酸环境下，力学性能下降，可靠性降低。相对热氧、臭氧和盐碱的化学介质环境，其作用更为复杂，更具代表性，是典型的热-化学-力多场耦合作用。此课题通过对填充无机物的饱和硫化橡胶，在热酸环境中的化学与粘弹行为研究，确定材料本构变量与内变量，分析热酸对硫化橡胶的作用机理，依据热力学定律与细观力学理论，提出热-化学-力多场耦合作用下的本构方程，并通过实验与有限元分析加以验证。对指导耐热酸橡胶材料配方设计，分析大型化工反应器、燃料电池橡胶密封件可靠使用寿命，保证设备安全，具有重要经济价值和实际应用意义。

以氟橡胶为例，制备了有填充和无填充硫化橡胶。依据相应的工程应用背景，通过选择硫酸、盐酸和硝酸介质，在自行设计的酸环境蠕变与应力松弛仪上，开展了酸环境下硫化氟橡胶及其复合材料的粘弹性实验，完成了不同温度和和浓度，在静载下的橡胶试件在热酸中的蠕变与松弛实验，用于考察酸介质下硫化氟橡胶粘弹性行为的温度依赖性，获得了材料常数和材料函数随温度的变化规律。在理论研究方面，基于实验结果和现有模型的分析，建立了更有简单有效的四原件粘弹性热力耦合本构模型，计算结果与实验结果具有较好的一致性；通过数据拟合建立起腐蚀速率方程，计算结果与实验结果具有较高的吻合度；通过试件质量变化，不同实验温度和不同浓度条件下各类酸介质的扩散规律和Fick定律，得到了相应的扩散常数。利用Fick定律模拟质量增加与实验结果具有较好的一致性。同时通过实验观测，获得了扩散距离和硝酸浓度之间的关系；采用红外与X射线能谱多种分析手段，确定了热酸环境下的橡胶主链结构的变化，给出了硫化氟橡胶中酸扩散与腐蚀机理。