自我修復材料能透過外界的刺激來修復因機械損傷引起的裂紋，具有增加材料安全性、延長使用壽命及節省翻新成本等優點。聚氨酯 (Polyurethane, PU)為具有軟硬分子鏈的區段共聚物，物性多變從剛硬到柔軟並廣泛應用於日常生活中，熱可逆狄-阿 (Diels-Alder, DA)反應具有反應溫度適中及可逆回復率高的優點，導入DA可逆共價鍵於PU分子鏈中能具有優異的自我修復能力，藉由retro-DA斷鍵反應可使分子鏈變短以填補裂紋，經DA再鍵結反應可使分子鏈變長以回復機械性質，然而於修復材料裂紋期間為黏流態會使機械性質大幅下降，缺乏彈性使材料容易受外力產生形變。本實驗以含有熱可逆Diels-Alder鍵的線性PU分子鏈 (簡稱DAPU)作為修復劑，並以熱固性交聯PU (Crosslinked PU, CPU)作為骨架，兩者以重量比1:1進行物理混摻，藉由retro-DA斷鍵反應使DAPU分子鏈變短以提升流動性並填補裂紋，而熱固性CPU的網狀結構於斷鍵期間可維持材料彈性。由光學顯微鏡觀察可得，填補裂紋所需的溫度因CPU網狀結構會束縛線性DAPU分子熱運動而上升，而由拉伸測試可知，熱固性CPU為非可逆共價鍵組成，材料裂紋由線性DAPU分子鏈填補，其拉伸強度回復率與純DAPU相比由92.1 %下降至68.2 %，藉由動態熱機械分析可知線性DAPU與熱固性CPU混摻後，於裂紋修復期間能維持一定的彈性模數，可拓展自我修復材料之應用，如燃料儲藏囊、充氣膜結構以及建築外殼塗層等持續受力之材料。

Self-healing materials can repair cracks caused by mechanical damage through external stimuli. and have the advantages of increasing material safety, extending service life and saving renovation costs. Polyurethane (PU) is a kind of copolymer with soft and hard segment. The physical properties can behave from rigid to soft and widely use in daily life. The advantage of Diels-Alder (DA) reaction is moderate reaction temperature and well reversibility. The introduction of DA reversible covalent bond in PU molecular chain can have excellent self-repairing ability. The retro-DA bond-breaking reaction can shorten the molecular chain to fill the crack. Then the DA re-bonding reaction can increase the molecular chain to restore the mechanical properties. However, during the crack healing the viscous flow state causes a significant drop in mechanical properties. The lack of elasticity makes the material susceptible to deformation by external forces. In this experiment, a linear PU molecular chain containing a thermally reversible Diels-Alder bond (DAPU) was used as a healing agent can healing the crack of bulk material. Moreover, a thermosetting crosslinked PU (CPU) was used as a backbone to enhance the elasticity during crack healing. Both component blend together with a weight ratio of 1:1. Observed by optical microscopy, the temperature required to fill the crack increases because the CPU network structure will constrain the thermal motion of the linear DAPU molecules. From the tensile test, the thermosetting CPU is composed of non-reversible covalent bonds, and the material crack is filled by linear DAPU. The tensile strength recovery rate decreased from 96.7 % to 68.2 % compared with pure DAPU. According to dynamic thermomechanical analysis, the blend of DAPU and CPU can let the material maintain a certain elastic modulus during the crack repairing. This kind of self-healing material can extend applications such as fuel storage bladders, inflatable structure membrane and architectural building envelopes.

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