期刊
APPLIED RHEOLOGY
卷 32, 期 1, 页码 56-68出版社
DE GRUYTER POLAND SP Z O O
DOI: 10.1515/arh-2022-0125
关键词
poly(3-hydroxybutyrate); tacticity; viscosity; free volume; thermal expansion
类别
资金
- Bavarian State Ministry of the Environment and Consumer Protection through the BayBiotech grant [TLK01U-69042]
By studying the viscosity of poly(3-hydroxybutyrate) (PHB), it was found that it is correlated with temperature, shearing rate, and tacticity. The results showed that the viscosities of PHB can be fitted using the Herschel-Bulkley-Cross-Doolittle model with single-point correction, and there is a discontinuous behavior in the viscosity as tacticity changes. Additionally, the values of vibrational and excess free volume were found to correlate with the structural and external properties of PHB.
The viscosities of poly(3-hydroxybutyrate) (PHB) with mixed tacticities were determined as functions of temperature and shearing rate via plate-plate viscosimetry, and fitted by a combined Herschel-Bulkley-Cross-Doolittle model while applying Carvalho et al.'s single-point correction. They were compared to values of slit viscosimetry, obtained during processing at a temperature of 428 K. In both cases, measured values and fitted model parameters as a function of tacticity exhibited a discontinuous behaviour at a fraction of meso diads of 0.7. To further investigate, we calculated values of vibrational and excess free volume. We found that these correlate with structural and external properties, some of which were reported in earlier works, namely the paracrystalline contents and specific volumes of the materials at room temperature, as well as their energies of fracture during tensile testing. These, in turn, correlate with the statistical averages of relative lengths of chain segments of similar a- or iso-tacticity. Hence, we found that expressing changing tacticities simply by a continuous progression of the fraction of meso diads is insufficient to trace associated discontinuities of the flow behaviour in mixed-tacticity PHB. We conclude that free volume is generated by polymer chain conformational disorder, which should be treated on the oligomeric chain segment level.
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