Thermoreversible Networks: Viscoelastic Properties and by Klaas te Nijenhuis

By Klaas te Nijenhuis

This evaluation exhibits that the dimension of viscoelastic homes is a robust software within the learn of thermoreversible gels. even supposing many conclusions will be drawn approximately community improvement and its constitution, it's also proven that using extra concepts (e.g. small perspective S-ray and neutron scattering strategies and optical rotation) and the combo with thermodynamics and community types, widens the perception within the crosslinking technique and the gel constitution temendously. A common creation is through 8 Chapters touching on artificial polymers (PVC, PVAL, PMMA, playstation , PAN, PE, ABA blockcopolymers and LCP's) and 4 Chapters relating biopolymers (gelatin, agarose, carrageenans and gellan gum).

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Ohta et al. [85] studied the isothermal crystallization behaviour of commercial poly(vinyl chloride) and concluded that the exponent n in the Avrami equation has values between I and 2. They explain this behaviour as heterogeneous lineal (n = 1) or homogeneous lineal (n = 2) growth of the crystals. Their main conclusions are: a) gelation is caused by crystallites; this was already proven by Alfrey et al. [64-66] and by Hendus (see [59] and [67]) with the aid of X-ray diffraction and confirmed by Dorrestijn et al.

9 Time Temperature Superposition In order to increase the frequency window of the dynamic moduli, normally use is made of the time-temperature superposition principle. However, this principle can only be applied to systems in which the structure does not depend on temperature and, consequently, not to ageing (gelating) systems. Te Nijenhuis et al. [10-12], however, were able, by making use of an extrapolation procedure, to extend the procedure to ageing systems in the following way. After having aged the system for a certain time at a fixed temperature Ta, the moduli were measured over a frequency range as large as possible.

00 10001Tm(K"~) poly(vinyl chloride) used can be calculated from Ahu as given by Anagnostopoulos et al. 75 kJ/mol, respectively. g. [71,1). Extrapolation to c = 100% yields a melting temperature of the PVC used of 223 °C. 4 Solvent Dependence A systematic study of the gelation properties of various solvents and plasticizers has been reported by Walter [110], Juijn et al. [82, 841, Teplov et al. [120,1 and Te Nijenhuis et al. [10, 11, 13, 31]. As an example, results are shown in Fig. 9 wt% solution of Solvic 239 in three different plasticizers [11,1, namely D O P , dibutyl phthatate (DBP) and Reomol ATM (the trimetlitic acid ester of alphanol 79, a mixture of branched alcohols).

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