(Received 4 May 1993; accepted 26 October 1994)
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Tensile stress relaxation is shown to be an experimental way to quantify the short-term elastic recovery of linear low-density polyethylenes (LLDPEs). The evolution of the force decrement ΔF with the logarithm of time is described by two linear equations on both sides of a critical time value tc = 100 s.
The slope p1 of the ΔF − ln(t) plot below tc increases linearly with the percentage of elongation ε up to the critical εc value associated with the onset of the yielding plateau; beyond εc, p1 remains almost constant with ε. This constant plp value is a linear function of the Tensile Residual Deformation (TRD) measured at the end of the relaxation: the lower the plp value, the lower the TRD. The determination of ptp thus appears as a predictive tool of the short-term elastic recovery of a material. Results show that the plp slope is slightly more sensitive to density evolutions than the TRD value. Assessing the elastic recovery capability through a stress relaxation analysis offers the following advantages: operator-independence, time-saving, and possibility of information storage for further data treatment.
ECP, Enichem Polymères France S.A., Centre de Recherches Polymères, Mazingarbe,
Laboratoire de Structure et Propriétés de l'Etat Solide, URA CNRS 234, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq,
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