聚倍半硅氧烷以不同方式改性纤维素绝缘纸的机理研究

本文运用分子动力学方法，建立了纯纤维素模型和一系列聚倍半硅氧烷以不同方式改性的纤维素绝缘纸模型，并对其热力学性能进行了计算、对比和讨论. 实验结果表明，各聚倍半硅氧烷纤维素改性模型的性能均优于未改性模型，并且当两条纤维素分子链作为取代基通过化学键接枝在聚倍半硅氧烷分子上(M2模型)时，改性效果最佳，其内聚能密度与溶解度参数的值相较于未改性模型提高了9%，拉伸模量、体积模量、剪切模量、柯西压的值分别提升了38.6%、29.5%、41.1%和29.5%，此外本文还计算并分析了各模型的自由体积分数和均方位移，结果显示，相较于其他模型，M2模型中的化学键在避免使纤维损失强度的同时，增加了分子链间的纠缠，使纤维素分子链占据了更多自由体积，从而使体系具有更小的自由体积分数，抑制了纤维素的链运动，进而提升了纤维素绝缘纸的热稳定性，这从微观角度解释了化学处理影响改性效果的机理.

A Comparative Simulation: Di erence between Chemical Grafting and Physical Doping of Cellulose by Using Polysilsesquioxane

In order to study the effect of different modification methods on polysilsesquioxane (POSS) modified cellulose, a molecular dynamics method was used to establish a pure cellulose model and a series of modified models modified by polysilsesquioxane in different ways. And their thermodynamic properties were calculated. The results showed that the performance of cellulose models was better than that of unmodified model, and the modified effect was the best when two cellulose chains were grafted onto polysilsesquioxane by chemical bond (M2 model). Compared with pure cellulose model, the cohesive energy density and solubility parameters of M2 model are increased by 9%, and the values of tensile modulus, bulk modulus, shear modulus and Cauchy pressure increased by 38.6%, 29.5%, 41.1% and 29.5%, respectively. In addition, the free volume fraction and mean square displacement of each model were calculated and analyzed in this work. Compared with the pure cellulose model, the molecular chain entanglement of cellulose was increased due to the existence of the chemical bonds in the M2 model, which made the cellulose molecular chains occupy more free volume, so that the system had a smaller free volume fraction, inhibited the chain movement of cellulose chains, and thus improved the thermal stability of cellulose.