Multiphase Systems Inhomogeneous Products

Inhomogeneities in a material can be clearly seen from the rheological behaviour. Some negative effects of inhomogeneities include processing problems, such as surface distortion and even melt fracture, as well as a significant deterioration of the mechanical and optical performance of products. 

Reproduced with permission from M. Gahleitner, Progress in Polymer Science, 2001, 26, S95. 

An important practical aspect is the fact that inhomogeneity can be the cause of the appearance of so-called gels in both PE and PP films. These gels can result from the polymer itself, from decomposition products, and from non-polymeric impurities, for example, additive agglomerates or dirt particles from the production environment, such as cellulose fibres from bags. 

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The production of species i (number of moles per unit volume and time) is the velocity of reaction,. In the same sense, one understands the molar flux, jh of particles / per unit cross section and unit time. In a linear theory, the rate and the deviation from equilibrium are proportional to each other. The factors of proportionality are called reaction rate constants and transport coefficients respectively. They are state properties and thus depend only on the (local) thermodynamic state variables and not on their derivatives. They can be rationalized by crystal dynamics and atomic kinetics with the help of statistical theories. Irreversible thermodynamics is the theory of the rates of chemical processes in both spatially homogeneous systems (homogeneous reactions) and inhomogeneous systems (transport processes). If transport processes occur in multiphase systems, one is dealing with heterogeneous reactions. Heterogeneous systems stop reacting once one or more of the reactants are consumed and the systems became nonvariant. 

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