熱遮蔽EPDM複材設計與加工及使用特性探討

Abstract

近年來合成橡膠複合材料逐漸被研究以應用於航太領域的結構上，這些材料往往受到側向壓力和熱負荷，而結構應具有低比重、高耐氧化性及卓越的耐燒蝕特性。研究指出，如EPDM、FKM之類的合成橡膠，若利用填充物強化後足以成為保護太空載具的熱遮蔽複材。 本研究的目的為探討EPDM複合材料中各類型的填充物，如kelvar、cork與silica對於熱遮蔽效果的影響，並與相關的耐燒蝕材料的效果進行比較。 本研究應用精密壓床和特製模具製作EPDM複材板，並參考ASTM規範的設備及步驟進行燒蝕測試。實驗試片的準備係將Kevlar、cork和silica等填充物均勻混合後，進行熱壓成型，其過程中按照步驟添加活化劑、硫化劑和促進劑，並藉由改變EPDM複合材料的成分比例，製作不同試片。 研究結果顯示，S10K5C10複材(EPDM為100 phr)相對於其它比例的EDPM複材有更好的絕熱效果。Silica在熱遮蔽材料受熱分解時對形成碳化層過程扮演重要角色。Kevlar的添加使複材熱穩定性明顯提升。Cork對於熱遮蔽特性雖沒有顯著影響，但可降低複材密度及熱傳導率。材料製作過程中混合的均勻性亦會影響效果與穩定性。 由於EPDM複材的機械強度、傳導率及熱穩定性等性質符合做為航太領域中絕熱層的條件，取代了以往對人體有致癌風險的石棉纖維，是現有最佳絕熱層材料之一。利用EPDM的高填充性，可針對填充物成分與比例進行調整以開發新複材。

In recent years, composites are being increasingly studied to use in aerospace constructions, which often subjected to the combinations of lateral pressure and thermal loading. Thermal insulation composite structures should have low specific gravity, high oxidation resistance, and superior thermal and ablation properties. Research shows synthetic rubbers like EPDM, FKM are capable of being ablation materials to protect the space vehicles by reinforcing with adding fillers. This study is going to observe the effect of various types of fillers such as cork, silica, Kevlar on thermal and ablation characteristics, and compare it to relative ablation materials. After the experiments were performed using a precision press machine and customized mold, ASTM standard equipment and procedures were used in the ablation test. The samples were fabricated by thermoforming after mixing Kevlar, cork and silica fillers. Activator, vulcanizing agent and accelerator were added in accordance with the schedule. Different EPDM-filler composites were used in each sample. The result shows that S10K5C10 composites have better thermal and ablation characteristics. Silica is the main factor in char forming when thermal decomposition. Kevlar loadings enhance the thermal stability of composites ablation. Cork loadings marginally affect the thermal and ablation characteristics but decrease specific gravity and thermal conductivity. Homogeneity also affects ablation characteristics and stability. The physico-mechanical properties, conductivity and thermal stability of EPDM-filler composites make them suitable materials for aerospace applications. Therefore, EPDM-filler composites have been used to avoid the health hazards of asbestos. Because they can accommodate large amounts of fillers, further study of EPDM-filler composites is warranted.