MELTING BEHAVIOR OF COMPRESSED MATS OF POLYETHYLENE SINGLE-CRYSTALS

Abstract

Structural change of Polyethylene single crystal mats by hot pressing was investigated by means of x-ray diffraction and differential scanning calorimetry. X-ray data showed that the deformation of the mat proceeded through the following stages. For a specimen pressed with lower compression ratios (C. R.) 1-5.3, the intra-lamellar<001> slip or the chain tilting developed resulting in a decrease of the lamellar thickness. With higher C. R. 5.3-11.7, locally concentated slips occurred in the mat and blocks of lamellar fragments rotated so as to decrease the angle between the chain axis and the direction of the deformation.
In melting experiments, (1) a remarkable increase of the melting points occurred at higher compression stages (C. R.>5.3), (2) both of minimum half width of melting peak and minimum heat of fusion appeared at intermediate stages (C. R.=3.0_??_5.3), and (3) superheating effects became obvious at higher compression stages (C. R.>5.3).
These results suggested that the structural and melting behaviors of compressed mats differed from that of drawn mats. The discussion was made on the assumption that a small number of tiechains in compressed mats mainly existed in the lamellar slip bands.