Physical aging viscoelastic properties

In this article on physical aging, the phenomena associated with structural recovery and physical aging are described, starting with discussion of volume recovery, enthalpy recovery, viscoelastic properties, and failure. There are more in-depth reviews of the phenomena and models associated with the glass transition... 

OrwoU RA (2007) Densities, coefficients of thermal e q>ansion, and compressibilities of amorphous polymers. In Mark JE (ed) Physical properties of polymers handbook. Springer, New York Shaw MT, MacKnight WJ (2005) Introduction to polymer viscoelasticity, 3rd edn. Wiley, Hoboken Struik LCE (1978) Physical aging in amorphous polymers and other materials. Elsevier Scientific, Amsterdam van Krevelen DW (1997) Physical properties of polymers their correlation with chemical structure their numerical estimation and prediction from additive group contributions, 3rd edn. Elsevier, Amsterdam... 

The nonlinear viscoelasticity modulus E t, e) is a function of time, t and strain, e. The compound behaviour is nonlinear even at very small deformation [9]. As described in Chapter 6, the presentation of modulus data requires t and e axes. The plot is a curved surface. When we consider the property changes resulting from physical ageing and from various deformational history [14], the separability of time and strain does not hold and linearisation of nonlinear data will not work. 

During aging, there are changes in most textural and physical properties of the gel. Inorganic gels are viscoelastic materials responding to a load with an instantaneous elastic strain and a continuous viscous deformation. Because the condensation reaction creates additional bridging bonds, the stiffness of the gel network increases, as does the elastic modulus, the viscosity, and the modulus of rupture. 

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