Water soluble polymer-based barrier properties

This type of material, based on hydrocolloids is generally not very resistant to water and their moisture barriers properties are poor. In some cases, water solubility or sensitivity to water is a functional advantage, e.g. for die formulation of soluble sachets to carry chemicals such as fertilisers or pesticides. For die majority of uses, the improvement of water resistance and water barrier properties is of first importance. Chemical modification of biopolymers and development of specific additives (cross linking agents or plasticisers) adapted to the polymer structure are then proposed. Regarding these developments, protein rich materials which have a non monotonous complex structure with very large potential fimctional properties are promising (Cuq et al, 1998). 

This book covers both fundamental and applied research associated with polymer-based nanocomposites, and presents possible directions for further development of high performanee nanocomposites. It has two main parts. Part I has 12 chapters which are entirely dedicated to those polymer nanocomposites containing layered silicates (clay) as an additive. Many thermoplastics, thermosets, and elastomers are included, such as polyamide (Chapter 1), polypropylene (Chapter 4), polystyrene (Chapter 5), poly(butylene terephthalate) (Chapter 9), poly(ethyl acrylate) (Chapter 6), epoxy resin (Chapter 2), biodegradable polymers (Chapter 3), water soluble polymers (Chapter 8), acrylate photopolymers (Chapter 7) and rubbers (Chapter 12). In addition to synthesis and structural characterisation of polymer/clay nanocomposites, their unique physical properties like flame retardancy (Chapter 10) and gas/liquid barrier (Chapter 11) properties are also discussed. Furthermore, the crystallisation behaviour of polymer/clay nanocomposites and the significance of chemical compatibility between a polymer and clay in affecting clay dispersion are also considered. 

PNC have been prepared with virtually all polymers, from water-soluble macromolecules to polyolefins and high-temperature specialty resins such as polyimide (PI). Elastomer-based PNCs with large clay platelets have been commercialized for improved barrier properties in automotive tires or sport balls. Elastomeric epoxy resins with clays demonstrate substantial improvement in mechanical properties (e.g., tensile modulus and strength) [Varghese and Karger-Kocsis, 2005 Utracki, 2008]. In this chapter we focus primarily on clay-containing PNCs, the CPNCs. 

Other biopolymers useful for synthesis of nanocomposites include (i) gelatin—a water-soluble protein obtained by extracting collagen liom animal skin and bones and thermal denaturation. (ii) PHB—a natural product of biosynthesis performed by bacteria in nature, (iii) Chitosan—a natural polymer widely found in exoskeletons of crustaceans and insects, as well as in the cell walls of microorganisms (Maiti et al. 2003 Zheng et al. 2002 Takegawa et al. 2010). Moreover, the mechanical and water vapor barrier properties of chitosan-based nanocomposites with cellulose nanofibers could be enhanced. 

The properties of PLA are significantly influenced by the stereochemistry of its monomers. When PLA has high stereochemical purity, it tends to form a highly crystalline structure. Copolymerization of different lactide isomers can yield a variety characteristics of PLA. The effect of isomerization in PLA can be detected by IR and NMR spectroscopic methods. Many studies have proven that PLA has a low solubility in a wide range of solvents/liquids, such as water, alcohol and paraffin. This indicates that PLA can be safely employed as a food packaging material without causing adverse health effects. In addition, PLA also possesses barrier properties that are just as effective as LDPE and PS. The green aspect of PLA means that it represents a viable environmentally friendly substitute for petrochemical-based polymers. 

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