Abstract
Objectives. Determination of the influence of molecular weight on the modulus of elasticity, yield, strength, and retardation processes in polyethylene. Methods. We used vane samples (thickness: 4 mm; length: 100 mm; width.: 10 mm) made by injection molding at p = 60 MPa, T = 210 °C, τ = 15 s from the following polyethylenes: HDPE 27773 (Stavrolen, Lukoil, Russia); BorSafe HE3490-IM (Borealis, Austria; black); CRP 100 Hostalen (Basell Polyolefins, Netherlands; black); Stavrolen PE4PP-25B (Stavrolen, Lukoil, Russia; black). The samples were in accordance with the defined standards for the AL 7000 LA-5 tensile testing machine. The study of relaxation characteristics was carried out in two modes: relaxation and retardation. Results. We obtained stress-strain diagrams at various temperatures under isothermal conditions (T = const) and determined the influence of polyethylene molecular weights on the modulus of elasticity, yield, and strength of polyethylenes. We have shown that under isothermal conditions, when the stress equals the yield strength, the removal of the external action results in a two-stage response. The first stage is the stress relaxation. The second stage characterizes the elastic features of the studied materials under the external action e = const. Conclusions. We have established that temperature increase affects the physicomechanical characteristics of polyethylenes differently, depending on their molecular weights. The experiments have shown that when the stress exceeds the yield strength, at constant deformation, there is a complex response of the polyethylenes to external action. This response is characterized by two stress stages throughout the course of time. The first stage is characterized by asymptotic decrease in stress down to a constant value; the second stage is characterized by constant stress throughout the course of time. We have determined relaxation times for the relaxation stage (stage I) and calculated activation energy. We have also established that the activation energy depends on molecular weights of the polyethylenes. It has been shown that an increase in polyethylene molecular weight leads to a decrease in relaxation time and activation energy.
Highlights
We have shown that under isothermal conditions, when the stress equals the yield strength, the removal of the external action results in a twostage response
The experiments have shown that when the stress exceeds the yield strength, at constant deformation, there is a complex response of the polyethylenes to external action
It has been shown that an increase in polyethylene molecular weight leads to a decrease in relaxation time and activation energy
Summary
Определение влияния молекулярной массы полиэтиленов на модуль упругости, текучесть, прочность и процессы ретардации. В результате проведения экспериментов были получены диаграммы «напряжение–деформация» при различных температурах в изотермических режимах (Т = const) и определено влияние молекулярной массы на модуль упругости, текучесть и прочность полиэтиленов. Установлено, что повышение температуры неодинаково отражается на физико-механических характеристиках полиэтиленов различной молекулярной массы. Эксперименты показали, что при напряжениях выше предела текучести при постоянстве деформации наблюдается сложная реакция исследуемых полиэтиленов на внешнее воздействие. Рассчитаны времена релаксации для релаксационной области (участок I), а также рассчитана величина энергии активации. Что увеличение молекулярной массы полиэтиленов ведет к снижению времени релаксации и уменьшению энергии активации. Релаксационные и физико-механические характеристики полиэтиленов с различной молекулярной массой. Тонкие химические технологии = Fine Chemical Technologies.
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