The drawing behavior of linear polyethylene. I. Rate of drawing as a function of polymer molecular weight and initial thermal treatment

Abstract

The drawing behavior of a series of linear polyethylene homopolymers with weight‐average molecular weight (M̄w) ranging from 67,800 to ∼3,500,000 and variable distribution (M̄w/M̄n = 5.1−20.9) has been studied. Sheets were prepared by two distinct routes: either by quenching the molten polymer into cold water or by slow cooling below the crystallization temperature (∼120°C) followed by quenching into cold water.When the samples (2 cm long) were drawn in air at 75°C using a crosshead speed of 10 cm/min it was found that for low M̄w polymers the initial thermal treatment has a dramatic effect on the rate at which the local deformation proceeds in the necked region. At high M̄w such effects are negligible. An important result was that comparatively high draw ratios (λ > 17) and correspondingly high Young's moduli could be obtained for a polymer with M̄w as high as 312,000. It is shown how some of the structural features of the initial materials (mainly studied by optical microscopy, small‐angle x‐ray scattering and low‐frequency laser Raman spectroscopy) can be interpreted in terms of the molecular weight and molecular weight distribution of the polymers. Although crystallization and morphology can be important at low M̄w, it suggested that the concept of a molecular network which embraces both crystalline and noncrystalline material is more helpful in understanding the drawing behavior over the whole range of molecular weights.

On Ultra-High Tensile Modulus by Drawing Single Crystal Mats of High Molecular Weight Polyethylene

“…The modulus was determined from the tangent to the stress-strain curve at a low strain ( < 0.1 %). The cross-sectional area of a sample (10-1 10-3 mm 2 ) was calculated from the sample weight, length, and measured density.…”

Gel-spun polyethylene fibres

“…Spinning from semidilute solutions [4][5][6][7][8] results in fibres with improved properties compared to more concentrated systems [9][10][11] due to a reduction in the number of entanglements. On the other hand, some entanglements are necessary to warrant sufficient coherence of the starting structure to allow drawing without premature breakage [12,13].…”

Composite modeling for the effective elastic properties of semicrystalline polymers

“…Davidse et al [1962] have determined the Young's modulus by measuring the sound velocity, ν, and density, ρ, of various polyethylene samples. The Young's modulus According to [Janzen 1992a;1992b;1997], the experimental results of Davidse et al [1962] cannot be uncritically accepted because their measurements are about three times greater than those obtained from bending and tensile tests. Though this difference was attributed to larger deformations in the bending and tensile tests, the anomaly needs to looked into with a deeper perspective.…”

“…Experimental data from [Janzen 1992b] and[Davidse et al 1962] are compared to our predicted results in Figure 6 for the Young's and shear moduli. These results show that the experimental results lie within the composite inclusion bounds.…”

“…It is well established that small-strain tensile deformation properties, such as Young's modulus, yield stress, and yield strain are directly related to percent crystallinity, independently of molecular weight; [Jordens et al 2000]. However for low and medium density, Nakayama et al [1991] and Capaccio et al [1976] have shown that the crystallinity decreases with increasing molecular weight of PE. This is the case for PE processed following the standard procedure based on slow cooling from the melt, according to this last reference.…”