Isothermal and nonisothermal crystallization of polymers: Analysis with a shear differential thermal analyzer

Abstract

Design and application of differential thermal analysis apparatus in high magnetic fields Rev. Sci. Instrum. 80, 073907 (2009);The working principle of an instrument developed for studying the effects of controlled shear pulses on the isothermal and nonisothermal solidification of polymers is presented. The device combines a capillary rheometer and a differential thermal analyzer ͑DTA͒. The capillary rheometer part of the system allows the production of shear pulses with controlled duration and intensity at any prescribed temperature up to 300°C, and the DTA records the thermal effects resulting from the solidification. Results obtained for quiescent isothermal and nonisothermal crystallizations compare well with those obtained from power compensation differential scanning calorimetry. The effect of controlled shear pulses on the overall isothermal crystallization kinetics enables the evaluation of a critical strain responsible for the saturation of crystallization in sheared polymer melts. Additional shear ͑increase of the shear rate or of the shearing time͒ does not accelerate the crystallization kinetics. The shear-induced nonisothermal crystallization of polyethylene filled with talc shows the acceleration of the crystallization kinetics with the shear rate increase, thus confirming this device as a valuable experimental tool for studying the effect of shear on the solidification of fast crystallizing materials.

Evaluation of the Effect of Melt Memory on Shear‐Induced Crystallization of Low‐Density Polyethylene

“…Further increase in the shear rate, or the shearing time, does not lead to an acceleration of the process. Similarly to the results obtained for isotactic poly(propylene),14 the results in Figure 1 confirm the strain applied to the molten polymer as the controlling factor for saturating the crystallization from a sheared melt. As mentioned previously, strains with similar magnitude (≈10 3 s.u.)…”

“…By evaluating the strain at the onset of the steady‐state, one can find that, at a specific temperature, the viscosity of polymer solution18 or melt19 always reaches the steady‐state with the same strain, irrespective of the magnitude of the shear rate. Further, a strain of ≈10 3 s.u., similar to that needed for stabilizing the anisotropy of sheared polymer melts11 and to saturate the crystallization from sheared melts,13,14 defines the onset of the steady‐state in shear‐stress growth experiments of a low‐density polyethylene melt 19. However, a proof that the same strains are responsible for those effects was not given so far and it is important for identifying unequivocally the melt state responsible for the saturation of crystallization.…”

“…Analysis of shear‐induced crystallization of i‐PP with a shear DTA allowed the evaluation of strain ≈1 800 s.u. for saturating the crystallization 14. It was also reported that the anisotropy of PE and PP melts with DBS increases with shear strain, and saturates at about 10 3 s.u 11…”

“…For comparison, similar experiments were also performed with a new shear DTA instrument,14 which was also used for analyzing the effect of the melt memory on shear‐induced crystallization experiments. The shear DTA combines a capillary rheometer and a differential thermal analyzer.…”

RheoDSC: A hyphenated technique for the simultaneous measurement of calorimetric and rheological evolutions

“…A similar concept was put forward by Martins et al, 3 Rheometric Scientific ͑currently TA Instruments͒, 4 and Nagatake et al 5 However, the drawbacks associated with their approaches limit the applicability of the instruments. Martins et al 3 developed a shear differential thermal analyzer that allowed studying the effect of controlled shear pulses on the isothermal and nonisothermal solidifications of polymers. For this purpose, a capillary rheometer and a differential thermal analyzer were combined into a single instrument.…”