ISSN:
1435-1528
Keywords:
Key words Elongational flow
;
polymer melt elongation
;
elongational viscosity
;
birefringence
;
elongational flow opto-rheometry
;
stress-optical
;
coefficient
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Abstract Polymer melt elongation is one of the most important procedures in polymer processing. To understand its molecular mechanisms, we constructed an elongational flow opto-rheometer (EFOR) in which a high precision birefringence apparatus of reflection-double path type was installed into a Meissner‘s new elongational rheometer of a gas cushion type (commercialized as RME from Rheometric Scientific) just by mounting a small reflecting mirror at the center of the RME‘s sample supporting table. The EFOR enabled us to achieve simultaneous measurements of tensile stress and birefringence as a function of time t under a given constant strain rate within the range of 0.001 to 1.0s–1. can be monitored upto the maximum Hencky strain of 7 as attained, in principle, with RME, while the measurable range of the phase difference in the birefringence was 0 to 250 (0 to 79100nm for He-Ne laser light) within the accuracy of ±0.1 (±31.6nm) up to . The performance was tested on an anionically polymerized polystyrene (PS) and a low density polyethylene (LDPE). For both polymers first followed the linear viscoelasticity rule in that the elongational viscosity, , is three times the steady shear viscosity, , at low shear rate , but the tended to deviate upward after a certain Hencky strain was attained. The birefringence was a function of both Hencky strain and strain rate in such a way that the stress-optical law holds with the stress-optical coefficient being equal to the ones reported from shear flow experiments. Interestingly, however, for PS elongated at low strain rates the vs relation exhibited a strong nonlinearity as soon as reached steady state. This implies that the tensile stress reaches the steady state but the birefringence continues to increase in the low strain-rate elongation. For the PS melt elongated at high strain rates, on the other hand, was nearly a constant in the entire range observed. For LDPE with long-chain branchings, exhibited tendency of strain-induced hardening after certain critical strain, but was nearly a constant in the entire range of observed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00367361
Permalink
