engleski

Additive group-contribution methods for predicting properties of polymer systems

Polymer materials are used in a wide range of technological applications nowadays. Reliable knowledge of thermophysical properties of pure polymers and their mixtures in the whole composition and a wide temperature and pressure range determines whether a given polymer is suitable for a specific application. At the other hand, the accurate knowledge of the thermodynamic properties of the systems is a vital prerequisite for the computer-aided syntheses, design, and optimization of industrial processes involving polymers. However, experimental data of polymer solubility are often scarce, and at this point, thermodynamics provides a powerful tool for modeling and extrapolating experimental data. At the beginning of the development of thermodynamic models, the main interest was directed to the development of predictive gE-models for VLE of subcritical compounds. Today, group-contribution methods are available which also can handle supercritical compounds, very asymmetric systems and even systems containing polymers. Different properties of pure polymer and polymer solutions can be predicted with use of group contributions. Examples of properties, that group-contribution methods can model, are the density, the solubility parameter, the melting and glass transition temperatures, as well as the surface tension. Phase equilibrium for polymer solutions and blends can also be estimated with group-contribution methods. Analogously as for mixtures with low-molar-mass components, two different approaches exist for predicting phase equilibrium in mixtures which contain polymers: activity-coefficient approach and equation-of-state approach. During the last decade, dramatic development took place in the applications of group-contribution activity-coefficient models for polymers1 in areas such as: estimation of the solubility limits in LLE and SLE, selective dissolution, gas solubilities, applications related to techniques for tailoring or modifying polymers with the desired physical properties, applications related to biotechnology, and many others. This overview presents group-contribution models for predicting properties of pure polymers, polymer/solvent and polymer/polymer mixtures. The state of art can be easily considered taking into account that polymer solutions and blends are complicated systems, with frequent occurrence of LLE in many forms (UCST, LCST, closed loop), significant effect of temperature and polymer molar mass in phase equilibrium, the free-volume effects, and other factors causing these difficulties. The choice of a suitable model depends on the actual problem and demands, especially on the following: type of mixture (solution or blend, binary or multicomponent), type of phase equilibrium (VLE, LLE, SLE), conditions (temperature, pressure, concentration), type of calculation (accuracy, speed, yes/no answer, or complete design). The performance of various models and their range of application will be discussed. References: 1. G. Bogdanić: Additive Group Contribution Methods for Predicting the Properties of Polymer Systems (Chapter 7, pp. 155-197), Polymeric Materials, Ed. A. Nastasijević, Transworld Research Signpost, Trivandrum, Kerala, India (2009).

group-contribution methods; properties; VLE; LLE; polymer systems; prediction; correlation

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