Shear‐induced crystallization of isotactic polypropylene studied by simultaneous light intensity and rheological measurements

Abstract

We investigate the effects of high shear rate and a melt‐insensitive, organophosphate nucleating agent on shear‐induced crystallization of four isotactic polypropylenes using a sliding plate rheometer under isothermal, low‐supercooling conditions. We used a bifurcated optical fiber probe to measure light intensity and a shear stress transducer to monitor the simultaneous viscoelastic response to small‐amplitude oscillatory shear. The two techniques complement each other; at early times of crystallization, large attenuation in the light intensity is observed, whereas during the later stages, a major change in the viscoelastic response occurs due to the growing volume fraction of spherulites. In contrast to quiescent crystallization, the nucleation pathway of nucleated polymers after a brief, strong shear is little influenced by the nucleating agent but strongly affected by molecular weight. The early kinetics of non‐nucleated polymers is more strongly enhanced by shear than that of nucleated polymers. Increasing either shear rate or strain accelerates crystallization, and we found the product of shear rate and strain to be useful for correlating our data. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

The rheo-Raman microscope: Simultaneous chemical, conformational, mechanical, and microstructural measures of soft materials

“…We have shown previously that the appearance of birefringent light-scattering material precedes crystallinity as measured by the Raman spectroscopy. 17 Prior results have also shown that light scattering appears well before crystallinity as measured by dilatometry, 41 rheology, 42 and x-ray scattering. 43 The explanation for the appearance of light scattering prior to other crystallinity measurements is not resolved, but certainly the relative sensitivity of each technique to crystallization must be taken into account.…”

Flow Induced Crystallization of Poly(ether‐block‐amide) from the Microinjection Molding Process and its Effect on Mechanical Properties

“…When “thread‐like” nuclei become denser, cylindrulites impinge prior to significant noncrystallographic branching and a highly oriented morphology forms. Currently, studies of flow conditions on the onset of oriented structures are mainly based on using laboratory plate‐plate rheometer, sliding plate rheometer or customized pressure driven flow cell; very few attempts have been made to study or validate such thresholds under non‐isothermal industrial processing conditions …”

Quiescent crystallization of polypropylene: Experiments and modeling

“…In general, flow enhances the kinetics of crystallization immensely compared to that of quiescent crystallization by stretching and orienting molecules in the direction of flow. Flow parameters such as strain and strain rate have been found to play a critical role in this phenomenon …”

“…Flow parameters such as strain and strain rate have been found to play a critical role in this phenomenon. 1,[7][8][9][10][11][12][13][14][15][16][17] The effect of flow on the kinetics of crystallization was studied previously. [18][19][20][21][22][23][24][25][26][27] In particular, Coccorullo et al 23 used optical microscopy to determine nucleation and growth rate of iPP under weak shear deformation (_ c 5 020.3 s 21 ) using the Linkam shearing cell (CSS 450).…”