環氧樹脂與雙馬來醯亞胺樹脂轉注成型高性能複合材料-材料特性與製程

Abstract

連續纖維補強的高分子複合材料具有高比強度、剛硬性、耐腐蝕等優點，近年來已應用於太空飛行載具、飛機結構及其他高級運輸工具上，以取代金屬材料，達到減輕重量及提昇性能的目的。樹脂轉注成型是一種具經濟效益的複合材料製程技術，它係預先將乾燥的纖維織物置於模具中，然後以低壓輔助灌注樹脂於模具內並加熱硬化而成，它省略了傳統熱壓釜製程中的預浸布裁切、冷藏與手積層等步驟，適於一次成形大型與外形複雜的零件，具有可減少零件數目與降低生產成本等優點。樹脂轉注成型的製程與成品性能會受到許多參數的影響，本研究係探討樹脂在轉注成型製程中的硬化反應與黏度行為，以及主要製程參數對注模行為與複材機械性能之影響，作為選定最適化注模製程條件之參考。研究出的高性能複合材料纖維含量達55﹪以上、空孔率低於1﹪。1581/PR500環氧樹脂玻璃纖維複合材料的玻璃轉移溫度達208℃、彎曲強度585 MPa。1581/CPA-2350雙馬來醯亞胺(BMI)樹脂玻璃纖維複合材料的玻璃轉移溫度達316℃、彎曲強度613 Mpa；碳纖維/BMI複合材料的彎曲強度可達808 MPa。 在本研究中，使用一修正的Kamal動力學模式可以合理描述PR500環氧樹脂在160-197℃溫度範圍、LY564/HY2954環氧樹脂在50-80℃溫度範圍的自催化與擴散控制硬化反應行為，LY564/HY2954樹脂的黏度與溫度及硬化程度成一函數關係，並可使用一實驗模式描述其關係。CPA-2350 BMI樹脂反應速率為硬化程度與溫度的函數，在115-145℃溫度範圍內硬化反應初期為一級動力學反應，使用動力學模式與流變模式可合理描述125-135℃範圍內轉注成型注模階段的硬化行為與黏度變化。 在PR500樹脂轉注成型中，在溫度160℃與壓力392kPa 條件下，可獲致具有最佳物理與機械性質的玻璃纖維強化PR500複合材料；在150℃樹脂溫度時，由於樹脂中硬化劑顆粒的濾除效應，致使樹脂流動受到限制，複合材料機械性質下降；相較於1581織布，使用高滲透性織布EF420的注模時間較短，複合材料的彎曲強度及儲存模數亦較低。在LY564/HY2954樹脂轉注成型中，相較於使用新樹脂與55﹪纖維含量的複材，使用老化樹脂需要兩倍的注模時間，其成品的層間剪切強度與彎曲強度下降7-15﹪；使用老化樹脂與55﹪纖維含量的複材較使用44﹪纖維含量與相同樹脂者之注模時間增加35﹪、層間剪切強度與彎曲強度下降4-12﹪。週邊注模及中央注模兩種不同的流動安排，會產生完全不同的流動模式，以及成品機械性質的差異；相較於中央注模者，使用周邊注模時，注模時間減少65﹪，複材空孔含量降低28﹪，彎曲強度提昇6﹪。 相較於航空級環氧樹脂PR500，LY564/HY2954環氧樹脂轉注成形複合材料之彎曲強度較低(585Mpa vs. 394MPa)、空孔含量較高( 0.37﹪vs. 0.83﹪)、玻璃轉移溫度亦較低(208℃ vs. 153℃)。 在使用耐高溫CPA-2350 BMI樹脂轉注成型中，於125℃與135℃注模的碳纖維複合材料較在115℃與145℃注模者具有較佳的機械性質與較低的空孔含量。在125℃下注模，增加注模壓力可以縮短注模時間，減少空孔含量與改進複材機械性質。相較於周邊注模者，使用中央注模時，會造成注模時間增加3.8倍，複材空孔含量增加3.7﹪，彎曲強度降低3.3﹪。52﹪碳纖維複合材料較58﹪纖維含量者，空孔含量低且機械性質高。對照於玻璃纖維複材，高強度、高模數的碳纖維提供了碳纖複材優異的機械性質。在不同纖維含量與織布構造情形下，我們發現高纖維含量是造成複合材料高空孔含量的主要因素。

Resin transfer process (RTM) is being considered as an alternate to the traditional prepreg lay-up/autoclave curing process for the manufacture of high performance composites because of its economics and flexibility. In RTM, a pre-catalyzed resin is injected under pressure into a fibrous preform in a hot closed die mold, then in-situ curing the resin to form the final parts. This study involves a resin transfer molding (RTM) process for making advanced composites based on high performance epoxies and high temperature resistant bismaleimide (BMI) resins. The curing kinetics and viscosity change of resins during the mold filling stage were studied and simulated with appropriate kinetic and rheological models. The effects of processing variables including injection temperature, injection pressure, gating arrangement, fiber volume fraction and fabric structure on the processing and performance of the resulting composites were investigated. The produced composites possess fiber volume fraction higher than 55﹪and void content lower than 1﹪. The glass transition temperature (Tg) is 208℃ and flexural strength reaches 585Mpa for 1581/PR500 fiberglass epoxy composites. For 1581/CPA-2350 fiberglass bismaleimide (BMI) composites, the Tg is 316℃ and flexural strength reaches 613Mpa. Moreover, the flexural strength of carbon fiber BMI composites approaches 808Mpa. A modified Kamal's kinetic model was adapted to describe the autocatalytic and diffusion-controlled curing behavior of PR500 epoxy resin over the temperature range of 160-197℃and of LY564/HY2954 epoxy resin over the temperature range 50-80℃for resin transfer molding (RTM) process. The cure reaction of CPA-2350 BMI resin follows first order kinetics over the temperature range of 115-145℃ in the initial stage of the cure reaction. An empirical model correlated the resin viscosity with temperature and the degree of cure for LY564/HY2954 epoxy and CPA-2350 BMI was obtained. Predictions of rate of reaction and resulting viscosity change by the modified Kamal's model, first order kinetics and the empirical rheological model agreed well with the experimental data for the mold filling stage of the RTM process. The optimized physical and mechanical performance of PR 500 epoxy based glass composites was obtained by processing the resin at 160℃under 392 kPa pressure. At 150℃resin temperature, restriction of resin flow and reduction in mechanical performance of the resulting composites were found due to particulate filtration of the hardener from resin matrix. Molding of highly permeable EF420 fabric required shorter mold filling time, but resulted in reduced flexural strength and storage modulus as compared to those of 1581 fabric. In RTM process of LY564/HY2954 two-part epoxy, molding aged resin with 55﹪fiber exhibited twice mold filling time and caused a 7-15﹪deterioration in the interlaminar shear strength(ILSS) and in the flexural strength of the composites as compared to that of the composites molded with fresh resin. At 55﹪fiber volume fraction, composites molded with aged resin resulted in 35﹪longer filling time, and 4-12﹪decreased ILSS and flexural strength as compared to that of the composites at 44﹪fiber volume fraction. Moldings with the perimeter inlet exhibited 65﹪shorter mold filling time, 28﹪reduced void content and 6﹪improved flexural strength as compared to that of the composites molded with the center inlet. As compared with those of PR500 epoxy, composites based on LY564/HY2954 epoxy resin behaved lower flexural strength (585Mpa vs. 394MPa), higher void content (0.37﹪vs. 0.83﹪) and lower Tg (208℃ vs. 153℃). For CPA-2350 BMI based carbon composites, better mechanical properties and less void content were obtained for moldings at 125℃ and 135℃ as compared to moldings at 115℃ and 145℃. Decreased mold filling time, lowered void content and improved mechanical properties were observed with increasing injection pressure for moldings processed at 125℃. Moldings with a center inlet resulted in 3.8 times increase in mold filling time, 3.7﹪increase in void content and 3.3﹪decrease in flexural strength as compared with a perimeter inlet. Composites with 52﹪carbon fiber exhibited lower void content and higher mechanical properties as compared to those of 58﹪carbon fiber. In contrast to glass fiber counterpart, carbon fiber contributes to the superior mechanical performance of their composites due to the exceptional strength and modulus. Among moldings of varied fiber fraction and fabric structure, the higher fiber volume fraction is the key factor that resulted in the higher voids trapped in the resulting composites.