Microstructure design in mixed biopolymer composites

Abstract

This paper is an overview of recent work on some particular aspects of the behaviour of biopolymer solution and gel mixtures, the focus being on aspects that are of particular relevance to the materials found in food systems. As such, the following areas are considered. (1) The phase behaviour of such mixtures in terms of the microstructures formed, the ideas of phase volume, phase continuity, surface tension and the use of the Flory–Huggins theory to model the behaviour. (2) The kinetics of phase separation in terms of the evidence for spinodal decomposition, ripening processes and the interplay between the kinetics of phase separation, gelation and molecular ordering. (3) The effects of shear on the composite microstructure in terms of particle size and shape, and how shear can be used to cause phase inversion of the system. (4) The material properties of the composites, including the fracture behaviour, the effect of particle size, and the role of the interface between the phases. It is clear that over the past few years a considerable literature has been built up on mixtures of biopolymers. Despite this growing understanding it remains a fact that we are not capable, as yet, of designing the microstructure of mixed biopolymer composites, although it is clear that there is a considerable technological advantage in being able to do so.