Relaxation transitions polyethylene

HDPE High-density polyethylene Ta, Tp, Ty a, fi, y are relaxation transition... 

Other low temperature relaxation processes are also detected in polymers (142,144,158-162). The interpretation of these transitions is, however, highly ambiguous, as regard to the kinetic units of motion involved in each relaxation process. For instance, for polyethylene (PE) the observed relaxation transitions in 150 to 170 K (S- or /-transitions) is most frequently attributed to a local rotation event within about two monomer units in the vicinity of the defects in crystallites, or in amorphous region, while the relaxation processes in the temperature... 

The wide bands of dielectric losses occur in the region from 10 Hz to 10 MHz for many organic species doped into a predeuterated polyethylene matrix at 4.2 K [Gilchrist, 1991]. The relaxation is caused by tunneling transitions between several equilibrium positions of OH or NH2 groups. The bandwidth is determined by the distribution of barrier parameters in amorphous matrix. 

Recently Moore and Petrie (5) have demonstrated that control of sample thermal history can result in transition from ductile to brittle behavior for polyethylene terephthalate. This transition in behavior was related to volume relaxation of the glassy state. 

The y relaxation of polyethylene, expressed in terms of tan 5, is centered in the vicinity of — 120°C at 1 Hz. This relaxation is believed to be caused by molecular motions occurring in the amorphous phase as indicated by the fact that the relaxation is very weak in highly crystalline polyethylene crystallized from dilute solutions (39,40). The relatively high intensity and universality of the y relaxation in polyethylenes, independent of whether they do or do not have branches in their structure, seems to suggest that the y relaxation may be associated with the glass transition. According to this interpretation, the glass transition temperature of polyethylene would be located in the vicinity of — 120°C. 

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