Abstract: Aggregates of single-, a few- and multi-chain crystals with folded-chain structure were prepared by a freeze-drying procedure from dilute solution of ultra-high molar mass polyethylene in para-xylene with mass concentration ranged from 10^-3 to 10^-5 g/mL. The chains in UHPE are very long (10⁴ nm); they can form several lamellae themselves or enter many lamellae to crystallize together with other chains. By means of DSC, the thermal analysis of the freeze-dried samples indicated that their melting temperature and crystallinity decreased as the solution concentration decreased. Average crystal volume and the number of chain per crystal were estimated according to the melting point of samples, and also they decreased with the decrease of the solution mass concentration. Because of lower entanglement concentration in the freeze-dried samples, the resulted crystals would have a higher perfection. Crystal dimensions normal to (110) and (200) were measured by using WAXD, and the average crystal volume was estimated on the basis of the measured dimensions and it is in agreement with the data from the DSC measurement.

Key words: Ultra high molecular mass weight polyethylene, Freeze drying, Crystallization