A multiscale chemomechanics theory for the solvent – Assisted recycling of covalent adaptable network polymers
A multiscale chemomechanics theory for the solvent – Assisted recycling of covalent adaptable network polymers
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DOI：
10.1016/j.jmps.2020.103918
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发表时间：
2020-05
影响因子：
5.3
通讯作者：
Xiaojuan Shi;D. Soule;Yiqi Mao;C. M. Yakacki;Haibao Lu;Kai Yu
中科院分区：
文献类型：
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作者：
Xiaojuan Shi;D. Soule;Yiqi Mao;C. M. Yakacki;Haibao Lu;Kai Yu
热固性聚合物由于其永久交联网络而难以使用常规方法回收。最近报道了共价自适应网络（CAN）聚合物可以利用键交换反应（BER）在有机溶剂中完全分解。通过加热分解的溶液以蒸发溶剂来发生再聚合。CAN的这一显著特征为热固性材料的绿色和可持续回收利用提供了令人兴奋的机会。在本文中，我们发展了一个多尺度化学力学理论来研究CAN的再聚合过程，其中可溶性链段通过BER在尾部连接。在大分子水平上，通过考虑反应物种的距离和扩散率来制定化学反应速率，这决定了平均链段长度和网络固化度（DoC）。然后将DoC的演化规律输入到连续水平的多分支模型中，以捕获不同固化状态下CAN的热机械性能。所建立的理论可以预测再聚合CAN的官能团转化率、溶液粘度、体积收缩率和玻璃化转变行为。揭示了各种材料和工艺条件对热固性材料性能的影响机理，为热固性材料及其复合材料的绿色可持续回收利用技术的直接工程应用奠定了基础。
Thermosetting polymers are hard to be recycled using conventional methods due to their permanently crosslinked networks. It was recently reported that covalent adaptable network (CAN) polymers could be fully decomposed in organic solvents utilizing bond-exchange reactions (BERs). Re-polymerization occurs by heating the decomposed solution to evaporate the solvent. This prominent feature of CANs provides exciting opportunities to enable the green and sustainable recycling of thermosets. In this paper, we develop a multiscale chemomechanics theory to study the re-polymerization process of CANs, where the soluble chain segments connect at the tails via BERs. At the macromolecular level, the chemical reaction rates are formulated by considering the distance and diffusivity of reactive species, which determine the average chain segment length and network degree of curing (DoC). The evolution rule of DoC is then fed into the continuum-level multi-branched model to capture the thermomechanical properties of CANs at different curing states. The established theory can predict the conversion ratio of functional groups, solution viscosity, volume shrinkage, and glass transition behaviors of re-polymerizing CANs. It also reveals the influencing mechanisms of various material and processing conditions, which paves the road for the immediate engineering applications of the green and sustainable recycling approach for thermosets and their composites.