Stress and strain oscillations in syndiotactic polypropylene and in poly(ethyleneterephthalate)

Stress-oscillation behaviour of semi-crystalline polymers: the case of poly(butylene succinate)

“…For the samples tested at a higher rates from 50 to 200 mm min À1 , the periodic stress oscillation is absent, where increasing the testing rate shifts the onset of the oscillations. 8 The increase in strain rate tends to reduce localized load in a certain velocity range. 5,8,9 The decrease in SO behavior only occurs where the velocity is in a critical range, heat dissipation occurs and hence softening of the polymer, excess heat dissipation at high strain rates increases further and thus softening increases and SO attenuates, which has been observed in PET and sPP polymers.…”

“…8 The increase in strain rate tends to reduce localized load in a certain velocity range. 5,8,9 The decrease in SO behavior only occurs where the velocity is in a critical range, heat dissipation occurs and hence softening of the polymer, excess heat dissipation at high strain rates increases further and thus softening increases and SO attenuates, which has been observed in PET and sPP polymers. 8,9 In PBS, a second yielding appears independent of the elongation rate.…”

“…Toda proposed that the effect of crystallization which occurs due to a temperature rise or high drawing rates, accounts for the self-excited SO behavior. Ebener 8 also demonstrated that the magnitude of SO is related to the tensile conditions, such as strain rate, temperature, thickness and length of polymer samples. The SO behavior was observed only when the sample length was above a critical level, and higher strain rates also promoted the magnitude of oscillation.…”

“…It can be seen in amorphous and semi-crystalline polymers during cold drawing and is characterised by obvious periodic formation of transparent and opaque banding perpendicular to the deformation direction. The SO and instability of necking have been observed in a number of thermoplastic polymers, such as amorphous polyethyleneterephthalate (aPET), 2,5-9 copolyesters, 10 high density polyethylene (HDPE), 1,11 syndiotactic polypropylene (sPP) 8,[12][13][14] and polyamide 1,15,16 at room temperature, and polycarbonate (PC) at elevated temperatures. 17 The SO mechanism is under debate although, it was proposed that the mechanical work was converted into thermal energy which generated local heat instability in the neck region of the polymer sample.…”

An infrared spectroscopic approach to the polymorphic behavior of syndiotactic polypropylene and its crystal–crystal transformations during mechanical stretching

“…The phenomenon of stress-oscillation has been observed in amorphous but crystallizable polymers, e.g., PET [34], semicrystalline polymers, e.g., sPP [34], trans-polyisoprene [35], sPP [34,36] and in amorphous but not crystallisable polymers, such as polyvinyl chloride.…”