ISSN:
0032-3888
Keywords:
Chemistry
;
Chemical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Measurements were made of linear viscoelastic properties and nonlinear stress-strain properties of phase-separated styrene-butadiene-styrene (SBS) copolymers and their blends with several homopolymer polystyrenes (PS) and one random copolymer (SBR). Torsion pendulum testing yielded shear moduli G′, G″, and Rheovibron experiments produced tensile moduli E′, E″, over a 220°K range of temperature, both at low frequencies. For pure copolymers and their PS blends, G′ and E′ correlated quite well with the total PS content, but G″ and E″ were more sensitive to how the additive was distributed. Results suggest that a PS additive whose molecular weight (M) is less than that of the copolymer PS-block (Ms) causes expansion of both the interphase and the homogeneous PS-rich phase, while an additive with M 〉 Ms mixes less well with these phases (probably forming separate domains of pure PS) and is less effective in enhancing the linear moduli. The blending with SBB produced reduction in G′ but a broad midrange peak in G″, suggesting that SBR was localized almost entirely within an expanded interphase. Tensile stress-strain data were obtained with an Material Testing System at room temperature. For PS blends, properties did not correlate well with the total PS content, the blends being always weaker than the SBS of the same overall composition. The amount of set also increased with PS content in the blends. Cyclic tests to increasing strain showed progressive structural alterations (as for the host SBS), with blend behavior resembling host properties more closely with each new cycle. When SBR was the additive, amounts as small as 1 percent reduced the curves by 15 percent. The yield stress was eliminated entirely with an addition of 10 percent SBR, but for all cases the set was the same. Results are discussed in terms of interphase force barriers to chain flow.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pen.760221104
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