後輻射退火於聚乙烯其硬度之探討

Hardness Evolution of Post-irradiated Polyethylene during Annealing

陳姵澐(Chen, Pei Yun)

指導教授 ： 李三保

國立清華大學/工學院/材料科學工程學系/碩士(2012年)

摘要

高能輻射是目前已知非常便利的一個方法用來改善高分子的機械性質。然而，經加馬射線輻射處理過後的高分子，在高於玻璃轉換溫度退火的機制目前還未被釐清。在本實驗中會探討後輻射退火於聚乙烯之效應。在此提出理論模型來分析市售的高密度聚乙烯及低密度聚乙烯。
微硬度在不同輻射劑量照射後隨著退火時間的變化相當明顯。高密度及低密度聚乙烯皆以鈷-60加馬輻射源以劑量率5 千戈雷/小時照射並在絕對溫度313-393 K空氣氣氛下進行後輻射退火。0 千戈雷的高密度及低密度聚乙烯作為實驗對照組。無論樣品是否經過輻射，高密度聚乙烯的微硬度皆大於低密度聚乙烯，這是因為結晶度的緣故。結晶度可由X射線繞射儀與示差掃描熱卡計而得。高密度及低密度聚乙烯皆會在四十小時內微硬度達到飽和，硬度會隨著輻射劑量增加而有明顯上升。高密度聚乙烯在輻射劑量800 千戈雷時有最佳的硬度特性。硬度在低於軟化點的時高溫時會上升，此實驗結果與時效溫度大於玻璃轉換溫度的聚碳酸酯相符。然而此現象與聚甲基丙烯酸-2-羥基乙酯及聚甲基丙烯酸甲酯相反。
理論上硬化過程的速率常數遵守阿瑞尼士方程式。硬度受加馬射線照射後產生的缺陷所控制。較高的輻射劑量所需的活化能比較低的輻射劑量還低，而此過程的焓的變化量大於零，代表此反應為一個吸熱反應的過程。

關鍵字

硬度 ； 聚乙烯 ； 後輻射退火 ； 退火

並列摘要

It is known that the high energy irradiation is a convenient method to improve the mechanical property of polymer. Nevertheless, the kinetic mechanism of the gamma rays-irradiated polymer at annealing temperature above the glass temperature is still unknown. The effect of post-irradiation annealing on polyethylene is studied. We propose the theoretical model to analyze the commercial polyethylene which are HDPE(high density polyethylene) and LDPE(low density polyethylene).
The variation of the microhardness with time and different irradiation doses reveal significantly. The HDPE and LDPE samples were exposed in Cobalt-60 gamma rays source at a dose rate of 5 kGy/hr and post annealed at 313-393 K in air condition. The 0 kGy HDPE and 0 kGy LDPE are the control specimens. No matter what the samples are treated before or after irradiation, the microhardness of HDPE is greater than that of LDPE due to the crystallinity. The crystallinity was obtained from XRD(X-Ray Diffraction) and DSC(Differential Scanning Calorimetry). Both the microhardness of HDPE and LDPE achieve saturation below 40 hours. The hardness increases significantly with the irradiation dose. The HDPE exposed in 800 kGy has the best performance in microhardness. The hardness are greater when the PE annealed in the elevated temperature below the Vicant softening point. The result is the same as the PC (polycarbonate) whose glass transition temperature is below the aging temperature. However, the phenomena of PE is opposite to those of PHEMA(Poly(2-Hydroxyethyl Methacrylate)) and PMMA(Poly(methyl methacrylate)).
Theoretically, the rate constant of the hardening process obeys the Arrhenius equation. The hardness is controlled by the defect induced by the gamma-rays irradiation. The activation energy of higher irradiation dose is lower than the activation energy of lower irradiation dose. The enthalpy change is larger than zero, and it satisfies endothermic process.

並列關鍵字

microhardness ； polyethylene ； post-irradiation annealing ； annealing

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