Long-term irradiation effects on gamma-irradiated Nylon 6,12 fibers
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onzalo Martínez-Barrera Laboratorio de Investigación y Desarrollo de Materiales Avanzados (LIDMA), Facultad de Química, Universidad Autónoma del Estado de México, Km. 12 de la carretera Toluca-Atlacomulco, San Cayetano 50200, Mexico
M.C. Resendiz Centro de Investigación en Ingeniería y Ciencias Aplicadas (CIICAp), Universidad Autónoma del Estado de Morelos, Cuernavaca 62210, Morelos, Mexico
V.H. Lara Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, Iztapalapa 09340, México
Witold Brostow Laboratory of Advanced Polymers & Optimized Materials (LAPOM), Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203-5310 (Received 31 October 2007; accepted 4 January 2008)
Long-term effects on Nylon 6,12 crystalline fibers irradiated six years ago have been determined, including chemical structure and morphology, and their relationship with storage time. Results from x-ray diffraction, small-angle x-ray scattering, scanning electron microscopy, and atomic force microscopy are reported for those fibers and for freshly irradiated ones. Some results for non-irradiated samples are included for comparison. Changes in the shape and size of the crystals (crystallinity degree) are found; the crystallite size increases with storage time. Both surface and bulk changes are seen in the morphology. Surface damage increases with storage time. Changes observed can be attributed to irradiation causing chain scission, which, in turn, causes crystal reorganization. The present results reinforce interpretation of earlier results obtained for concretes reinforced with irradiated Nylon fibers.
I. INTRODUCTION
Effects of irradiation on morphology and structure of polymeric materials have been investigated since the mid 20th century.1–3 Generally, chemical bonds are affected. The resulting changes are irreversible, and they do not differ from those produced by conventional means. Highenergy radiation has the advantage of applicability in the solid state, thus resulting in savings in time and cost. Polymers are quite sensitive to even slight variations in their chemical bonding. This is why a variety of modification techniques is used, including corona charging,4 photo inscription,5 or modification of interactions by magnetic fields.6 If the bond structure geometry is modified by using ␥ radiation, the characteristics of the long a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0152 1276 J. Mater. Res., Vol. 23, No. 5, May 2008 http://journals.cambridge.org Downloaded: 24 Mar 2015
chains of polymers vary. The material property changes can be explained in terms of irradiation effects on chain strength, chain orientation, and crystallinity. Depending on the applied dose, chain crosslinking and/or chain scission may occur. In the long history of the problem, chain scission either in the amorphous regions7–9 or inside of the crystallites10,11 has been reported. In a number of cases, polymer properties are enhanced by gamma radiation.11–2
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