HIGH SPEED MELT SPINNING OF POLYETHYLENETEREPHTHALATE (PET); EFFECT OF MOLECULAR WEIGHT

Abstract

PET filaments have been produced by the high speed melt spinning method in the range of take-up velocity, 1, 000-8, 000m/min for the three different molecular weight PET (_??_η=18, 400, 20, 500, 29, 800).The physical and mechanical properties of these filaments were studied as a function of molecular weight. The following results were obtained.(1) Until the take-up velocity reaches 4, 000-5, 000m/min, the fiber structure formation by oriented crystallization develops at lower take-up velocity for the higher molecular weight sample. It is suggested that the elongational viscosity varied by the molecular weight affects the crystallization of PET under the orientation in the high speed melt spinning.(2) The degree of molecular orientation and the degree of crystallization show levelling off after the spinning velocity reaches 4, 000-5, 000m/min. The values of these levels are lower for the higher molecular weight sample, indicating that the increase in the molecular weight does not lead to the development of the fiber structure in the melt spinning. Decreased molecular motion of the higher molecular weight PET may give rise to this fact.(3) For the fibers spun at the take up velocity near the critical spinnability, the decrease in the densities, the reduction of the birefringences, the development of crimps and the appearance of a shoulder melting peak in the DSC thermograms, were found. These may be due to the sliding or the scission of the chain molecules or to the increase in the void content. Further investigations are aimed at these problems.