Rheological Properties and Viscosity

Colombini and co-workers [42] used DMTA and DETA (Chapter 12) to explore the relaxation processes occurring in amorphous and semi-crystalline polyethylene naphthalene-2,6,-dicarboxylate. The two secondary relaxations P and P, the main a-relaxation and the p-relaxation processes were revealed by both mechanical and electro viscoelastic responses of the polymer. The DMTA results clearly identified the T(a) loss factor peak. 

Habas and co-workers [43] carried out an investigation into the viscoelastic properties of aqueous solutions of a four-branched polyethylene oxide - polypropylene oxide - polyethylene oxide triblock copolymer in the unimer range using TMA, DMTA and small-angle neutron scattering. The aqueous solutions were characterised in the crystalline phase and a modified version of Eyring s theory was used to describe the stress-time dependence of ordered solutions. 

Kontou and Spathis [44] carried out an investigation into the relationship between long-term viscoelasticity and viscoplastic responses of two types of ethylene-vinyl acetate metallocene-catalysed linear low-density polyethylene using DSC, DMTA and tensile testing. A relaxation modulus function with respect to time was obtained from values of relaxation spectra and treated as a material property. This relaxation modulus function was used to describe the corresponding tensile data and a constitutive analysis, which accounts for the viscoelastic path at small strains and the viscoplastic path at high strains, was employed to predict the tensile behaviour of the ethylene polymers (see also [45 9]). 

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Xylanases Highly functional enzymes used to improve bread systems because of their capacity to hydrolyze the xylan backbone of arabinoxylans present in cell walls. They are widely used to improve bread properties via the modification of dough rheological properties and viscosity. Most commercial xylanases are obtained from microorganisms. 

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