冷凍鑄造技術(Freeze Casting)是近年來興起的仿生製程，用於合成具有結構異向性的多孔材料。目前大多數的研究集中於陶瓷基多孔材，然而陶瓷多孔材需經高溫燒結且易碎裂。為了改善製程且增加應用潛力，本研究以聚乙烯醇(Polyvinyl Alcohol)取代陶瓷作為多孔支架的主材料，結合冷凍鑄造技術與高分子醚化反應成功地在170C製備聚乙烯醇多孔支架，並探討溶液濃度、冷卻速率、及高溫醚化條件等參數對其微結構與機械性質的影響。透過掃描式電子顯微鏡(SEM)的觀察，證實此材料具有序層狀多孔結構，而孔洞大小、孔隙率及孔洞形狀則可利用冷凍鑄造製程中的參數去調控。以壓應力測試量測此高分子多孔材的機械性質，結果發現經醚化交聯反應後，可得到具足夠機械強度及韌性且高孔隙率的多孔材。此外，本研究證實了水氣含量對聚乙烯醇支架機械性質的影響，因此可以透過調節濕度得到具有截然不同力學性質的聚乙烯醇支架。此具有異向性結構的聚乙烯醇多孔材，在徑向上具有極低的熱傳導係數，具有優異的熱絕緣性質且具有優異的回復性能，在經歷壓縮形變之後，亦能恢復到原來的形狀，經過多次壓應力循環後，仍具有足夠的強度及良好的回復性能。整體而言，此具備輕量化結構的聚乙烯醇多孔材料具有良好的熱絕緣性質及機械性質，且具有形變後回復能力，期待未來能應用於綠能建材或生醫領域。

Freeze casting is a novel technique to synthesize bio-inspired porous scaffold with unidirectional porous structure. Extensive studies have focused on ceramic-based porous materials, but ceramic materials need to be sintered in high temperature and are easily fractured. In this study, PVA (Polyvinyl alcohol) was utilized as the main materials to improve the process and increase the potential applications. The PVA porous scaffolds were successfully synthesized at 170C by combination of freeze casting and polymeric etherification reaction. The effect of parameters, such as solid loading, cooling rate and heat treatment condition, on microstructural and mechanical properties were discussed. The well aligned cellular structure of the scaffolds were revealed by SEM, meanwhile, the pore size, porosity and pore shape can be tailored by tuning the experimental parameters. The mechanical properties were measured by compression tests. Results showed that the scaffolds possessed good mechanical strength and toughness after etherification. In addition, the effect of moisture contents on mechanical properties was confirmed. The PVA scaffolds with distinct mechanical properties can be obtained by adjusting humidities. The anisotropic PVA scaffolds possessed low thermal conductivity in the radial direction and provided excellent thermal insulation property. Cyclic tests showed that PVA scaffolds exhibited extraordinary recovery after compression test and can still provide enough strength and good recovery after multiple cycles under compression. In summary, the lightweight PVA porous scaffolds provided good thermal insulation and mechanical properties, and exhibited recovery ability after deformation, which can be potentially applied in green building materials or biomedical fields in the future.

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