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。

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.

1. K.H. Ng, Non-ionizing radiations–sources, biological effects, emissions and exposures, Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN(ICNIR2003), Electromagnetic Fields and Our Health, 16 (2003).
2. S. Massey, Action of water in the degradation of low-density polyethylene studied by x-ray photoelectron spectroscopy, Express Polym. Lett., 1, 506-511 (2007).
3. V. Plaek, B. Bartoniek, V. Hnat, and B. Otahal, Dose rate effects in radiation degradation of polymer-based cable materials, Nucl. Instrum. Meth. B, 208, 448-453 (2003).
4. M. Goldman, R. Gronsky, R. Ranganathan, and L. Pruitt, The effects of gamma radiation sterilization and ageing on the structure and morphology of medical grade ultra high molecular weight polyethylene, Polym. Plast. Technol. Eng., 37, 2909–2913 (1996).
5. V. Premnath, A. Bellare, E.W. Merrill, M. Jasty, and W.H. Harris, Molecular rearrangements in ultrahigh molecular weight polyethylene after irradiation and long-term storage in air, Polymer, 40, 2215–2229 (1999).
6. V. Premnath, W.H. Harris, M. Jasty, and E. Merrill, Gamma sterilization of uhmwpe articular implants: An analysis of the oxidation problem , Biomaterials, 17, 1741-1753 (1996).
7. D.A. Baker, R.S. Hastings, and L. Pruitt, Study of fatigue resistance of chemical and radiation crosslinked medical grade ultrahigh molecular weight polyethylene, J Biomed. Mater. Res., 46, 573-581 (1999).
8. K.S. Simis, A. Bistolfi, A. Bellare, and L.A. Pruitt, The combined effects of crosslinking and high crystallinity on the microstructural and mechanical properties of ultra high molecular weight polyethylene, Biomaterials, 27, 1688-1694 (2006).
9. C.J. Perez, E.M. Vallés, and M.D. Failla, The effect of post-irradiation annealing on the crosslinking of high-density polyethylene induced by gamma-radiation, Radiat. Phys. Chem., 79, 710-717 (2010).
10. C. Laurent, C. Mayoux, and S. Noel, Mechanisms of electroluminescence during aging of polyethylene, J. Appl. Phys., 58, 4346-4353 (1985).
11. A. Yamanaka, Y. Izumi, T. Kitagawa, T. Terada, H. Hirahata, K. Ema, H. Fujishiro, and S. Nishijima, The effect of γ-irradiation on thermal strain of high strength polyethylene fiber at low temperature, J. Appl. Polym. Sci., 102, 204-209 (2006).
12. A. Yamanaka, Y. Izumi, T. Kitagawa, T. Terada, H. Sugihara, H. Hirahata, K. Ema, H. Fujishiro, and S. Nishijima, The radiation effect on thermal conductivity of high strength ultra-high-molecular-weight polyethylene fiber by γ-rays, J. Appl. Polym. Sci., 101, 2619-2626 (2006).
13. L.H. Sperling, Introduction to physical polymer science, Fourth edition ,John Wiley & Sons, Inc. Publication, Hoboken, NJ, USA, (2006).
14. J.E. Mark, Polymer data handbook (2nd edition), Oxford University Press, Oxford, UK, (2009).
15. S.M. Rowland, K. Kopsidas, and X. Zhang, Aging of polyethylene adss sheath by low currents, IEEE Trans. Power Deliv., 25, 947-952 (2010).
16. G. Chen, M. Fu, X.Z. Liu, and L.S. Zhong, Ac aging and space-charge characteristics in low-density polyethylene polymeric insulation, J. Appl. Phys., 97, 083713 (2005).
17. S. Wojtas, Influence of aging by partial discharges on resistivity of polyethylene, Dielectric Materials, Measurements and Applications, 1988., Fifth International Conference 191-193 (1988).
18. B. Tajeddin, R.A. Rahman, L.C. Abdulah, N.A. Ibrahim, and Y.A. Yusof, Thermal properties of low density polyethylene-filled kenaf cellulose composites., Eur. J. Sci. Res., 32, 223-230 (2009).
19. F. Vilaplana, V. Morera-Escrich, P. del Hierro-Navarro, B. Monrabal, and A. Ribes-Greus, Performance of crystallization analysis fractionation and preparative fractionation on the characterization of g-irradiated low-density polyethylene, J. Appl. Polym. Sci., 94, 1803-1814 (2004).
20. C. Albano, R. Perera, P. Silva, and Y. Sánchez, Characterization of gamma irradiated pes using esr, ftir and dsc techniques, Polym. Bull., 51, 135-142 (2003).
21. M.D. Ridley and M.S. Jahan, Effects of packaging environments on free radicals in γ-irradiated uhmwpe resin powder blend with vitamin e, J. Biomed. Mater. Res. A, 88A, 1097-1103 (2009).
22. X. Colin, C. Monchyleroy, L. Audouin, and J. Verdu, Lifetime prediction of polyethylene in nuclear plants, Nucl. Instrum. Meth. B, 265, 251-255 (2007).
23. K.J. Kim, Y.H. Kim, J.H. Song, Y.N. Jo, J.S. Kim, and Y.J. Kim, Effect of gamma ray irradiation on thermal and electrochemical properties of polyethylene separator for li ion batteries, J. Power Sourc., 195, 6075-6080 (2010).
24. L. Minkova, Dsc of γ-irradiated ultra-high molecular weight polyethylene and high density polyethylene of normal molecular weight, Colloid. Polym. Sci., 266, 6-10 (1988).
25. J.G. Fatou, C. Marco, and L. Mandelkern, The influence of molecularweight on the regime crystallization of linear polyethylene, Polymer, 31, 1685–1693 (1990).
26. J. Xu, P. Ji, J. Wu, M. Ye, L. Shi, and C. Wan, Study on the determination of the molecular weight of polyethylene with ultrahigh temperature gpc, Macromol. Rapid Commun., 19, 115–118 (1998).
27. E.P. Otocka, R.J. Roe, M.Y. Hellman, and P.M. Muglia, Distribution of long and short branches in low-density polyethylenes, Macromolecules, 4, 507-512 (1971).
28. D. Person, G. Strate, E. Vonmeerwall, and F. Schilling, Viscosity and self-diffusion coefficient of linear polyethylene, Macromolecules, 20, 1133-1141 (1987).
29. A. Toda, T. Oda, M. Hikosaka, and Y. Saruyama, A new analyzing method of temperature modulated dsc of exo- or endo-thermic process: Application to polyethylene crystallization, Thermochim. Acta, 293, 47-63 (1997).
30. G. Biglione, E. Baer, and S.V. Radcliffe, Effect of high hydrostatic pressure on the mechanical behaviour of homogeneous and rubber reinforced amorphous polymers, proc. 2nd. Intern. Conf. On fracture, Fracture 1969, April, Bristol, England, (1969).
31. D.R. Mears, Effects of hydrostatic pressure on the mechanical behavior of polyethylene and polypropylene, J. Appl. Phys., 40, 4229-4273 (1969).
32. A. Keller and J.G. Rider, On the tensile behaviour of oriented polyethylene J. Mater. Sci., 1, 389-398 (1966).
33. W. Wu, G.D. Wignall, and L. Mandelkern, A sans study of the plastic deformation mechanism in polyethylene, Polymer, 33, 4137–4140 (1992).
34. I.M. Ward, Review: The yield behaviour of polymers, J. Mater. Sci., 6, 1397-1417 (1971).
35. D. Constantin, Coupling of gelpermeation chromatography and automatic viscometry. Application to the study of long chain branched polyethylene, Eur. Polym. J., 13, 907–913 (1977).
36. S.G. Burnay and G.W. Groves, The lamellar structure of oriented high- density polyethylene, J. Mater. Sci., 12, 1139-1142 (1977).
37. N.S. Murthy, Recent developments in polymer characterization using x-ray diffraction, Rigaku J., 21, 15-24 (2004).
38. G.B. McKenna, K.L. Ngai, and D.J. Plazek, Differences in the molecular weight and the temperature dependences of self-diffusion and zero shear viscosity in linear polyethylene and hydrogenated polybutadiene, Polymer, 26, 1651–1653 (1985).
39. C. Tanford, Intrinsic viscosity and kinematic viscosity, J. Phys. Chem., 59, 798-799 (1955).
40. S. Sasaki, H. Masunaga, K. Itou, K. Tashiro, H. Okuda, A. Takahara, and M. Takata, Crystallization behavior of polyethylene on silicon wafers in solution casting processes traced by time-resolved measurements of synchrotron grazing-incidence small-angle and wide-angle x-ray scattering, J. Phys. Conf. Ser., 184, 012015 (2009).
41. R. Bercia, M. Tirnovan, C. Bercia, and N. Popescu-Pogrion, Electron microscopy of γ-irradiated polyethylene, Surf. Interface Anal., 38, 552-556 (2006).
42. E.A. Zubova, N.K. Balabaev, and L.I. Manevitch, Molecular mechanisms of the chain diffusion between crystalline and amorphous fractions in polyethylene, Polymer, 48, 1802-1813 (2007).
43. M.C. Sobieraj and C.M. Rimnac, Ultra high molecular weight polyethylene: Mechanics, morphology, and clinical behavior, J Mech. Behav. Biomed. Mater., 2, 433-443 (2009).
44. W.F. Msuya and C.Y. Yue, The correlation between the lamellar thickness and the degree of crystallinity in semicrystalline polymers, J. Mater. Sci. Lett., 8, 1266-1268 (1989).
45. I. Kamel and L. Finegold, A model for radiation-induced changes in ultrahigh-molecular-weight polyethylene, J. Polymer Sci. Polymer Phys. Ed., 23, 2407-2409 (1985).
46. T. Kawai, A. Keller, A. Charlesby, and M.G. Ormerod, The effect of crystallization conditions on radiation-induced crosslink formation in polyethylene, Philos. Mag., 12, 657-671 (1965).
47. M. Failla, R.G. Alamo, and L. Mandelkern, On the analysis of the raman internal modes of crystalline polyethylene, Polym. Test., 11, 151–159 (1992).
48. F.J.B. Calleja, Microhardness relating to crystalline polymers, Adv. Polym. Sci., 66, 117-148 (1985).
49. F. Carrasco, P. Pagès, S. Pascual, and X. Colom, Artificial aging of high-density polyethylene by ultraviolet irradiation, Eur. Polym. J., 37, 1457-1464 (2001).
50. V.A. Soloukhin, J.C.M. Brokken-Zijp, O.L.J.v. Asselen, and G.d. With, Physical aging of polycarbonate: Elastic modulus, hardness, creep, endothermic peak, molecular weight distribution, and infrared data, Macromolecules, 36, 7585–7597 (2003 ).
51. Y. Zhou, X. Wang, P. Yan, X. Liang, Z. Guan, and N. Yoshimura, Annealing effect on the morphology of polyethylene materials and the tree initiation voltage, 2001 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, Kitchener, Ontario, Canada, 241-244 (2001).
52. D. Rueda, J. Martinezsalazar, and F. Baltacalleja, Annealing effects in lamellar linear polyethylene as revealed by microhardness, J. Mater. Sci., 20, 834-838 (1985).
53. S. Zalwert, Attempt of a super-molecular interpretation of glass-transition relaxation processes in amorphous polystyrene, Makromol. Chem., 177, 3083-3088 (1976).
54. J.G. Fatou, C.H. Baker, and L. Mandelkern, The effect of crystallization conditions and temperature on the polymorphic forms of polyethylene, Polymer, 6, 243–248 (1965).
55. K.P. Lu, Y.K. Fu, and S. Lee, Hardness of irradiated hydroxyethyl methacrylate copolymer at elevated temperatures, J. Appl. Polym. Sci., 113, 657-661 (2009).
56. K.P. Lu, S. Lee, and C.P. Cheng, Hardness of irradiated poly(methyl methacrylate) at elevated temperatures, J. Appl. Phys., 90, 1745-1749 (2001).
57. L.H. Gabriel, Chapter 1 history of physical chemistry of hdpe, Physical Chemistry and Mechanical Properties of HDPE, National Academy Press, Washington, DC, 5 (2007).
58. S. Levin, Tools for polymer characterization, Medtechnica, Petach-Tikva, Israel, (2006).
59. Standard test method for microindentation hardness of materials, ASTM designation E384-99, West Conshohocken, USA, (2000).
60. S.H. Yeh, Evolution of hardness and transmittance in irradiated polycarbonate, Department of Materials Science and Engineering, Master Thesis, National Tsing Hua University, (2001).
61. P. Atkins and J.D. Paula, Physical chemistry, Oxford University Press, Oxford, UK, 212 (2006).