Polyethylene fiber formation in tubular flow. II. Discussion of precursor formation and nucleation time analysis

Abstract

This is a continuation of the preceeding paper, Part I, and presents a discussion of the nature of the precursor structure formation process observed in the flow‐induced crystallization experiments described in I. A discussion of stress‐induced crystallization theory as applied to these experiments is also given and a first‐order analysis of crystal nucleation rates is presented. Conclusions regarding the nature of flow‐induced crystallization and our current ability to quantitatively model the overall process are also presented.

Time Evolution of Structures under Shear-Induced Phase Separation and Crystallization in Semidilute Solution of Ultrahigh Molecular Weight Polyethylene

“…It is well-known that the fibrous crystalline superstructure having a characteristic morphology of so-called “shish kebab” was grown in stirred dilute or semidilute solutions of polyethylene. , Many efforts have been made to elucidate the mechanism of formation of the shish-kebab structure, but it is still not completely clarified. It should be emphasized that there are few researches concerning relationships between the shear-induced phase separation and the shear-induced crystallization, except for the extensive works reported by McHugh and co-workers. − …”

“…It should be emphasized that there are few researches concerning relationships between the shearinduced phase separation and the shear-induced crystallization, except for the extensive works reported by McHugh and co-workers. [13][14][15][16][17] McHugh and co-workers reported a series of interesting and important rheooptical works of polyethylene and polypropylene solutions in tubular shear flow geometry. [13][14][15] Their studies elucidated phenomena of liquidliquid "precursor formation" (phase separation) and subsequent fibrillar shish-kebab crystallization.…”

“…[13][14][15][16][17] McHugh and co-workers reported a series of interesting and important rheooptical works of polyethylene and polypropylene solutions in tubular shear flow geometry. [13][14][15] Their studies elucidated phenomena of liquidliquid "precursor formation" (phase separation) and subsequent fibrillar shish-kebab crystallization. Although our work is directed along the same line as these preceding works, there is an important difference between our works and these previous works.…”

Formation of fibrous crystals in flowing blends of polyethylene melts

“…The importance of extensional flows in the formation of extended-chain, fibrillar polymer crystals has been extensively discussed in a number of reviews [1][2][3][4][5][6]. However, since most of the fundamental studies in this area have focused on the use of solutions in various flow geometries, relatively little work has been reported on the corresponding fiber growth phenomenon in melts.…”

A technique for monitoring the kinetics of flow-induced crystallization

“…Induction times for the amorphous precursor formation and birefringence development, which characterize this mode of growth show qualitative trends with flow rate and temperature consistent with the development of oriented crystallinity according to a nucleation-controlled rate process? * 3 We have analyzed our video tapes of the growth process using an image processing technique to convert the analog signal for the light intensity associated with the video image of a fiber to a digital signal. This allows conversion of the images to intensity versus time data which can then be analyzed to obtain quantitative information on the in sztu transformation kinetics.…”