Changes in orientation of crystallites during stretching and relaxation of polyethylene films

Abstract

A microbeam camera has been used in x‐ray diffraction studies of the changes which occur in orientation of crystallites in polyethylene film when the film is stretched and later relaxed. The collimator of the microbeam camera, 100 μ in diameter, allows one to follow the orientation changes very closely in the necked‐down region of a stretched sample. The stretching of polyethylene proceeds by alignment of the a‐axes of the crystallites perpendicular to the stretching direction with the planes containing b‐ and c‐axes perpendicular to the a‐axis but randomly oriented, followed by a gradual change to a state in which the c‐axes become more nearly aligned in the stretching direction although perfect alignment is not achieved. On relaxation, either the orientation of the c‐axis parallel to the original stretching direction becomes less perfect, or folding of the oriented crystallites about the b‐axis takes place. In the latter case the preferred crystallographic directions parallel to the stretching direction have indices such as [u0w]. These orientation changes during stretching and relaxation of the stretched samples suggest that crystallites in polyethylene films consist of parallel arrangements of platelets containing b‐ and c‐axes. The distinction between directions in the reciprocal lattice and the crystal lattice is clarified. A number of x‐ray diffraction patterns and charts of dimensional changes illustrate the paper.

A real-time drawing study on solution-crystallized UHMW-polyethylene — comparison with conventional x-ray results

“…This is in line with findings for melt-crystallized PE samples at very low draw ratios [21][22][23][24][25][26]. 1.1, the 200 reflection almost immediately exhibits an equatorial maximum in addition to two reflection arcs on both sides of the equator.…”

Structural evolution of OBC/carbon nanotube bundle nanocomposites under uniaxial deformation

“…Aggarwal has given the explanation that the splitting of the (110) reection is due to imperfect orientation of b-and c-axis with respect to the stretching direction, i.e., there are considerable wobble of the b-and c-axis. 51 The four-arc pattern is not very obvious in our results, but the splitting of (110) reection and subsequent approaching can also be observed, which is presented and discussed in detail later. At the onset strain of 600%, (010) reection of the strain-induced monoclinic crystals emerges on the equator between amorphous ring and (110) reection in WAXD patterns, exhibiting a highly ordered but relatively diffuse point-like reection.…”

Effect of Alignment on Enhancement of Thermal Conductivity of Polyethylene–Graphene Nanocomposites and Comparison with Effective Medium Theory

“…Different approaches like mechanical stretching [ 28 ], electric field [ 29 , 30 , 31 ] and magnetic field [ 32 , 33 , 34 ] have been used for orientation of nanofillers. Mechanical stretching has been used for alignment of both the polymer matrix [ 35 , 36 ] and dispersed filler material [ 37 , 38 ]. Amy et al reported an enhancement in k by a factor of 18 in epoxy-CNT composites with densely aligned arrays of CNTs [ 39 ].…”