EQUIBIAXIAL DEFORMATION OF POLY(4-METHYL-1-PENTENE) BY A FORGING PROCESS

Poly(4-methyl-1-pentene) (PMP) has been uniaxially compressed by a forging (equibiaxial) process. The rheology of the process has been examined for this semicrystalline polyolefin, melting point about 235-degrees-C. The yield energy, area under the compressive stress-strain curve up to the yield point, as a function of temperature was found to consist of two linear components of different slope. These two linear relations arise from the glassy and crystalline phases of PMP. The intercept temperature (T(i)) at zero yield energy for the glassy phase has been evaluated. The attainable maximum compression ratio without sample rupture (CR(max)) increased steadily on increasing forging temperature above T(i), and below T(m). In this range, the crystalline relaxation temperature (T(c)), evaluated from an Arrhenius plot of yield stress was 160-degrees-C. Above T(c), a CR(max) of 240 was reached. This value is five times higher than that attained for isotactic polypropylene (i-PP). However, the draw efficiency evaluated by elastic recovery in the plane direction of PMP (0.76) is lower than for i-PP (0.97). Differential scanning calorimetry analyses showed that the melting peak became a complex doublet on increasing compression ratio (> 100). The drawing and stress-strain behavior of PMP are compared with i-PP. (C) 1994 John Wiley & Sons, Inc.