Physical aging in the mechanical properties of miscible polymer blends
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Case Western Reserve University School of Graduate Studies / OhioLINK
1993
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=case1056644954 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-case10566449542021-08-03T05:30:45Z Physical aging in the mechanical properties of miscible polymer blends Chang, Geng-Wen Physical aging mechanical properties miscible polymer blends <p>Changes in mechanical properties during isothermal physical aging were investigated for three miscible blends: polystyrene(PS)/poly(2,4-dimethyl 1,6-phenylene oxide)(PPO), PS/poly(vinyl methyl ether)(PVME), and poly(methyl methacrylate)(PMMA)/poly(ethylene oxide)(PEO). The aim was to compare the kinetics of the physical aging process between blends and pure components, using tensile stress relaxation and dynamic mechanical measurements. Positron annihilation lifetime (PAL) spectroscopy was used as a probe for structural disorder (free volume) to aid interpretation of the physical aging studies. Analysis of the aging stress relaxation data by generation of a stretched exponential master function, as proposed by Struik, was possible for both blends and homopolymers.</p><p>Discrepancies in the scaling of the characteristic stress relaxation time τ with respect to the temperature distance Tg-T between PS/PPO, PS/PVME and the PS homopolymer were resolved by invoking the presence of concentration fluctuations in the blends. By selecting the onset glass transition temperature (Tg<sub>i</sub>) as a reference point, the relaxation times for PS/PPO and PS/PVME glasses can be scaling to those of pure PS. This indicates that the initial stress decay is determined by the more mobile regions in the b lends. However, this temperature scaling does not apply to the PMMA/PEO blend for which the τ values at fixed Tg<sub>i</sub>-T are larger than for pure PMMA, suggesting that, in this system, the interaction between the blend components produces a more dense matrix.</p><p>Using the coupling theory of Ngai as a guide, we infer that the width of the spectrum of stress relaxation times in the blend may be increased by the presence of concentration fluctuations, or by an increase in matrix density (lower free volume). Thus, the increase observed in the spectral widths for both blends and homopolymers at lower temperatures indicates that the relaxing elements become more strongly coupled to the surrounding matrix. For the PS/PPO blend, the spectral width is narrower than for pure PS suggesting that increased free volume from dissolved PPO dominates over the effect of concentration fluctuations. By contrast, since the width for the PS/PVME blend is larger, the prime factor appears to be concentration fluctuations. In the PMMA/PEO blend, where, again, as increase in the spectral width is found, there may be contributions from both concentration fluctuations and a lower free volume.</p><p>Orthopositronium(o-Ps) lifetime and intensity values for the three blends and the constituent homopolymers, measured by PAL spectroscopy, are qualitatively consistent with the behavior of the stress relaxation spectra, using arguments based on free volume concepts.</p> 1993 English text Case Western Reserve University School of Graduate Studies / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=case1056644954 http://rave.ohiolink.edu/etdc/view?acc_num=case1056644954 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
| collection |
NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Physical aging mechanical properties miscible polymer blends |
| spellingShingle |
Physical aging mechanical properties miscible polymer blends Chang, Geng-Wen Physical aging in the mechanical properties of miscible polymer blends |
| author |
Chang, Geng-Wen |
| author_facet |
Chang, Geng-Wen |
| author_sort |
Chang, Geng-Wen |
| title |
Physical aging in the mechanical properties of miscible polymer blends |
| title_short |
Physical aging in the mechanical properties of miscible polymer blends |
| title_full |
Physical aging in the mechanical properties of miscible polymer blends |
| title_fullStr |
Physical aging in the mechanical properties of miscible polymer blends |
| title_full_unstemmed |
Physical aging in the mechanical properties of miscible polymer blends |
| title_sort |
physical aging in the mechanical properties of miscible polymer blends |
| publisher |
Case Western Reserve University School of Graduate Studies / OhioLINK |
| publishDate |
1993 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=case1056644954 |
| work_keys_str_mv |
AT changgengwen physicalaginginthemechanicalpropertiesofmisciblepolymerblends |
| _version_ |
1719421129326592000 |