Investigation on the gelation behavior of biodegradable poly(butylene succinate) during isothermal crystallization process |
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Authors: | Fa-liang Luo Xiu-qin Zhang Wei Ning Du-jin Wang |
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Institution: | (a**) a Beijing National Laboratory for Molecular Sciences,CAS Key Laboratory of Engineering Plastics,Institute of Chemistry, Chinese Academy of Sciences,Beijing 100190,China b Key Laboratory of Energy Resource & Chemical Engineering in Ningxia,Ningxia University,Yinchuan 750021,China c Graduate School of Chinese Academy of Sciences,Beijing 100190,China |
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Abstract: | The early stage of polymer crystallization may be viewed as physical gelation process, i.e., the phase transition of polymer from liquid to solid. Determination of the gel point is of significance in polymer processing.
In this work, the gelation behavior of poly(butylene succinate) (PBS) at different temperatures has been investigated by rheological
method. It was found that during the isothermal crystallization process of PBS, both the storage modulus (G′) and the loss modulus (G″) increase with time, and the rheological response of the system varies from viscous-dominated (G′ < G″) to elastic-dominated (G′ > G″), meaning the phase transition from liquid to solid. The physical gel point was determined by the intersection point of loss
tangent curves measured under different frequencies. The gel time (t
c) for PBS was found to increase with increasing crystallization temperature. The relative crystallinity of PBS at the gel
point is very low (2.5%–8.5%) and increases with increasing the crystallization temperature. The low crystallinity of PBS
at the gel point suggests that only a few junctions are necessary to form a spanning network, indicating that the network
is “loosely” connected, in another word, the critical gel is soft. Due to the elevated crystallinity at gel point under higher
crystallization temperature, the gel strength S
g increases, while the relaxation exponent n decreases with increasing the crystallization temperature. These experimental results suggest that rheological method is
an effective tool for verifying the gel point of biodegradable semi-crystalline polymers. |
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Keywords: | Poly(butylene succinate) Gelation process Rheological analysis |
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