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Open Access Article
1 - Shape memory polymers: Structure, mechanism, functionality, and applications
Hamidreza Haydari Marziyeh HosseiniIn the last three decades, many researches have been conducted in the field of shape memory polymers, and in the past few years, the interest in research in this field has received a lot of attention. In this study, a comprehensive and complete review of the structure, MoreIn the last three decades, many researches have been conducted in the field of shape memory polymers, and in the past few years, the interest in research in this field has received a lot of attention. In this study, a comprehensive and complete review of the structure, mechanism, model and applications of this category of polymers has been done. In general, the mechanisms of shape memory polymers are divided into three groups: direct thermal induction, indirect thermal induction, and optical induction, and each has its own switch unit that controls the shape structure. These switches have amorphous and semi-crystalline phase, which are defined in two phase and molecular levels. Also, increasing the mechanical properties, including the strength and toughness of shape memory polymers, is of great importance, which can increase their efficiency. Shape memory polymers can be used in medical, aerospace, textile and other industries. In the textile industry, the electrospinning process is used as a simple and efficient method for the preparation of shape memory polymer fibers and the development of their structure, and the mechanism and method of preparation of these fibers will be investigated. In the last three decades, many researches have been conducted in the field of shape memory polymers, and in the past few years, the interest in research in this field has received a lot of attention. In this study, a comprehensive and complete review of the structure, mechanism, model and applications of this category of polymers has been done. Manuscript profile -
Open Access Article
2 - Crystallinity of polymers determined by differential scanning calorimetry (II)
Mina AlizadehaghdamDifferential scanning calorimetry (DSC) is widely used to determine the crystallinity of semicrystalline polymers. In the two-phase model, the measured heat of fusion is compared to the melting enthalpy of a completely crystalline polymer to get the crystallinity degree MoreDifferential scanning calorimetry (DSC) is widely used to determine the crystallinity of semicrystalline polymers. In the two-phase model, the measured heat of fusion is compared to the melting enthalpy of a completely crystalline polymer to get the crystallinity degree. Fusion heat of a polymeric sample is identified by area under the melting endotherm and a baseline. A correct baseline is heat capacity of the semicrystalline sample. It varies with both temperature and crystallinity and is difficult to evaluate. Enthalpy of a process is a state-function quantity and is independent of the process path. In polymer melting, temperature increase and fusion process occur simultaneously. This makes evaluation of the fusion heat challenging. Herein, alternative paths are supposed in which temperature increase and fusion process occur separately and sequentially. This leads to a convenient enthalpy evaluation. Two alternative paths can be defined: first, polymer melts at a constant temperature which is followed by temperature increase of the melt; second, polymer temperature increases without any change in crystallinity degree which is followed by polymer melting at a constant temperature. Lastly, an enthalpy deficiency due to the amorphous-crystalline interface and an excess enthalpy due to the defects present in crystalline regions are investigated how to affect the crystallinity. Manuscript profile
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