Chen Xi, Li Lingqiao, Wei Tong, Venerus David C, Torkelson John M
Department of Chemical and Biological Engineering , Illinois Institute of Technology , Chicago , Illinois 60616 , United States.
ACS Appl Mater Interfaces. 2019 Jan 16;11(2):2398-2407. doi: 10.1021/acsami.8b19100. Epub 2019 Jan 4.
Conventional polymer network composites cannot be recycled for high-value applications because of the presence of permanent covalent cross-links. We have developed reprocessable polyhydroxyurethane network nanocomposites using silica nanoparticles with different surface functionalities as reinforcing fillers. The property recovery after reprocessing is a function of the interaction between the filler surface and the network matrix during the network rearrangement process. When nonreactive silica nanoparticles lacking significant levels of surface functional groups are used at 4 wt % (2 vol %) loading, the resulting network composite exhibits substantial enhancement in mechanical properties relative to the neat network and based on values of rubbery plateau modulus is able to fully recover its cross-link density after a reprocessing step. When nanoparticles have surface functional groups that can participate in dynamic chemistries with the reprocessable network matrix, reprocessing leads to losses in mechanical properties associated with cross-link density at potential use temperatures, along with faster rates and lower apparent activation energies of stress relaxation at elevated temperature. This work reveals the importance of appropriate filler selection when polymer network composites are designed with dynamic covalent bonds to achieve both mechanical reinforcement and excellent reprocessability, which are needed for the development of recyclable polymer network composites for advanced applications.
由于存在永久性共价交联，传统的聚合物网络复合材料无法回收用于高价值应用。我们使用具有不同表面功能的二氧化硅纳米颗粒作为增强填料，开发了可再加工的聚羟基聚氨酯网络纳米复合材料。再加工后的性能恢复是网络重排过程中填料表面与网络基体之间相互作用的函数。当使用4 wt%（2 vol%）负载量、缺乏显著表面官能团水平的非反应性二氧化硅纳米颗粒时，所得网络复合材料相对于纯网络在机械性能上有显著增强，并且基于橡胶态平台模量的值，在经过再加工步骤后能够完全恢复其交联密度。当纳米颗粒具有可与可再加工网络基体参与动态化学作用的表面官能团时，再加工会导致在潜在使用温度下与交联密度相关的机械性能损失，以及在高温下应力松弛的更快速率和更低表观活化能。这项工作揭示了在设计具有动态共价键的聚合物网络复合材料以实现机械增强和优异的可再加工性时，选择合适填料的重要性，这对于开发用于先进应用的可回收聚合物网络复合材料是必需的。
