The effect of γ‐irradiation on thermal strain of high strength polyethylene fiber at low temperature

Abstract To understand the contribution to negative thermal expansion by the length of the molecular chains in high‐strength ultra‐high‐molecular‐weight polyethylene (UHMW‐PE) fiber, the thermal expansion coefficient in the range of low temperature was investigated for high‐strength UHMW‐PE fiber (Toyobo, Dyneema®; hereinafter abbreviated to DF), irradiated by γ‐rays (γ‐rays treatment) that induce the molecular scission. The molecular weight of DF decreased by γ‐ray treatment. X‐ray diffraction behavior did not change by γ‐ray treatment. The melting behavior observed by DSC showed the main chain scission of DF by γ‐ray treatment. The DFs, with and without γ‐ray treatment, expand by cooling down (negative thermal expansion). The change of negative thermal expansion of DF by γ‐ray treatment was small. It is suggested that negative thermal expansion does not change by only the molecular chain scission. These results suggested that the effect of negative thermal expansion of DF in the temperature range from 213 to 303 K by the molecular chain scissions is small and that the length of extended molecular chains contributes to a negative thermal expansion a little. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 204–209, 2006