Thickening process of polyethylene single crystals at an early stage of annealing

Abstract

By the use of a position sensitive proportional counter, changes in small and wide angle X-ray scattering during annealing of polyethylene single crystal mats were measured from the start in successive spans of very short measuring time. At high temperatures, the long period relating to stacking of lamellae rapidly increased at an early stage, passed through a plateau, and thereafter again increased gradually. With a decrease in annealing temperature, the amount of its first rapid increase was reduced and the plateau changed into an ascending slope. At much lower annealing temperatures, the long period increased following the log t law after an induction time. The integral breadth of a peak corresponding to the long period first increased rapidly, simukaneously with the rapid increase in the long period, and thereafter decreased. Wide angle X-ray measurement showed that the integrated intensity of 110 reflection first decreased and then increased during annealing at high temperatures. This fall and rise process was more marked, when the annealing temperature is higher and the initial thickness of lamellae is smaller. From these observations, it was inferred that in the thickening process, stacking order of lamellae at first decreased because of rapid reorganization due to partial reeking or melt-recrystallization and subsequently increased through increasing evenness of IameHar thickness.

Melting behavior of poly(butylene succinate) during heating scan by DSC

“…Similar results have already been discussed in PE single crystal systems. 34,35 In Figure 11, the two melt temperatures for PBS single crystals were plotted with T c . The high endotherm is almost constant in temperature, and low endotherms fall on a line with a slope, becoming close to the T m ϭ T c line as T c increases.…”

Drawing and extrusion of semi-crystalline polymers

“…The slope B rapidly increases with :ira [211]. The explanation of the more complicated effect [212] is partly based on melting the too-thin lamellae or blocks and recrystallizing them according to the new temperature which may be higher than the Tc at which the crystallization of the sample has occurred, and partly on the sliding chain motion in the crystals depending linearly on log (t~l + C) [213]. In this manner one can initially obtain two [216] populations of crystals, the unmelted crystals yielding a large L and the new crystals yielding a smaller L. After a long annealing both populations merge.…”

Crystallization Behavior of Amorphous Poly(l-Lactide)

“…5). It is well known that when polymer crystallites are subjected to isothermal annealing, or even isothermal crystallization, they become increasingly perfect, and thicken, with time, [15] leading to an increased melting point. When amorphous PLLA is annealed at a temperature as high as 1108C, the crystallized PLLA could undergo thermal annealing concurrently as crystallization proceeds.…”