自回收聚碳酸酯合成可再加工之熱固性樹脂

Abstract

本研究以聚碳酸酯之化學回收出發，以簡單、無催化劑、溫和的反應製程轉換廢棄高分子塑料成高價值的低分子量回收中間體產物hydroxyl N,N’-diphenylene-isopylidenyl biscarbamate (DP-biscarbamate)，並以此為單體重新聚合製備出一系列可重複加工的熱固性聚氨酯或環氧樹脂，成功達到廢棄塑料的低碳循環高值化利用。熱固性樹脂的重複加工性質是由於動態共價適應性網絡(Covalent adaptable networks, CANs)的引入，在適當的熱刺激下能產生鍵結重組並伴隨顯著的黏流性值變化。其中，DP-biscarbamate具備複數個苯酚-胺基甲酸酯官能基能做為反應活性中心，在聚氨酯與環氧樹脂的系統中分別參與裂解-重組反應或是親核加成反應以達到網絡重組的目的。樣品的重複加工能力利用粉碎-熱壓的方式測量回復後的機械性質變化，發現聚氨酯及環氧樹脂能分別達到90 %及100 %的初始機械性質回復，證明回收材料亦能達到良好的再回收性質。本研究亦透過流變性質分析、線性膨脹測量法、小分子模型研究等多種技術了解樣品於加工環境產生的物理及化學性質變化，證實可以透過催化劑選擇及精準的結構設計避免動態反應發生的同時伴隨副產物的生成。此外，引進含有柔軟醚基的胺解試劑提升材料的排列能力，並在微差掃描熱分析及X光散射圖譜中皆觀察到材料之微觀相分離。根據上述基礎再透過化學交聯的方式進一步提升材料的熱性能及機械性質。簡言之，本研究經由化學交聯改善回收材料性質普遍不如新製樣品的問題，並利用苯酚-胺基甲酸酯官能基使化學交聯樣品具備重複回收利用的能力，提供了一個循環材料的嶄新設計概念，期望能減緩塑膠廢棄物對生態環境造成的衝擊。

This work demonstrates a simple, straightforward, and practical insight into a novel closed-loop material recycling strategy by converting poly(carbonate) (PC) into malleable thermosets. These strategies start with the chemical recycling of PC to obtain high value-added intermediate hydroxyl N,N’-diphenylene-isopylidenyl biscarbamate (DP-biscarbamate), followed by repolymerization of DP-biscarbamate into commonly used thermosets such as polyurethane (PU) or epoxy resin (EP). The recyclability of these repolymerized samples was enhanced by incorporating the notion of covalent adaptable networks (CANs), from which topology can rearrange upon experiencing thermal stimuli. As a result, PU and EP recovered 90 % and 100 % of their tensile strength after multiple rounds of compression molding treatments, respectively. This is due to the phenolic-carbamate functional groups from recycling moiety that can act as active site for network rearrangement. Stress relaxation analysis, dilatometric measurements, and small-molecule study were also conducted to realize the influence of CAN on physical or chemical properties. Besides, all samples exhibited excellent thermal and mechanical properties due to the incorporation of flexible ether linkage, which can promote crystallinity and form micro-phase separation morphology. Therefore, all PUs and EPs can meet the necessary standard compared to those prepared from commercial feedstocks.