Abstract
In this paper, for the first time, positron annihilation lifetime spectroscopy, after an appropriate adaptation, was used to analyze the plastic deformation process of high-density polyethylene as a representative semicrystalline polymer. It was shown that the average size of the free volume pores of the amorphous phase in the studied strain range decreased in comparison with the undeformed polyethylene, even after the initiation of the cavitation phenomenon due to highly anisotropic, ellipsoidal shape of cavities with the aspect ratio amounting to ∼45. The mean positron lifetime was practically constant in the analyzed range of strains even after activation of the micromechanisms of plastic deformation of crystals due to the mutually compensating effects activated in the crystalline phase. A clear change of the dispersion of positron lifetime as a function of local strain was observed. This effect was correlated with the reduction of the crystallites length by the relative displacement (slips) of adjacent crystalline blocks within individual lamellae.
Highlights
Plastic deformation of semicrystalline polymers is a complex process, including the cooperative response of a crystalline and an amorphous component
We demonstrated that the modification of the interlamellar regions at a free volume level can lead to a significant change of the intensity of the cavitation phenomenon:
The results presented in Figures 1Sa and 2S are a clear evidence of the lack of relaxation processes in the deformed sample clamped in the frame with a selected screw tightening torque
Summary
Plastic deformation of semicrystalline polymers is a complex process, including the cooperative response of a crystalline and an amorphous component. The initial stages of deformation of the crystalline component are usually analyzed with the X-ray techniques (WAXS (wide-angle X-ray scattering) or SAXS).[8,27] no studies on deformation-induced changes in the size of free spaces or defects of the crystalline component have been undertaken so far; for a complete and reliable description of the deformation process of polymer crystals, this issue seems to be very important. In this paper, we adapted the PALS technique in a way that enabled tracking of the deformation-induced changes of the structure of the amorphous and crystalline component of the polymeric material We performed such analysis for a representative semicrystalline polymer: high-density polyethylene, deformed to the yield point for better understanding of the micromechanisms activated in both phases (crystalline and amorphous)
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