Hydrophilic packaging polymers

Table III. FLAVOR ADSORPTION OF HYDROPHILIC PACKAGING POLYMERS...

C. Lopez-de-Dicastillo, Development and Characterization of Hydrophilic Active Polym.s for Food Packaging, PhD Thesis, Universidad Politecnica de Valencia, Valencia, 2011. 

Poly(ethylene-i (9-vinyl alcohol) is made by saponification of ethylene—vinyl acetate copolymers. The properties of these materials depend on the amount of vinyl alcohol present in the copolymer. High vinyl alcohol content results in more hydrophilic materials possessing higher densities, stiffness, and moduh. They are used commercially as barrier resins for packaging. Important producers include Du Pont and EVALCA (74) (see Barrier polymers). 

For most applications for food packaging, sorption of water in most hydrophilic polymers can be fit to a saturation isotherm, such as Equation 3. A simplified form would be ... 

Poly(3-hydroxybutyrate- o-3-hydroxyvalerate) (PHBV) is a soft, malleable and thermosoftening biodegradable polymer material. It can be easily converted into films, which are applicable for packaging, carry bags, disposable bottles and so on. The hydrophilic backbone chain of the polymer, which contains atoms of oxygen in the polymer chain, accelerates the degradation of bacteria and pathogens. 

Static charges on polymer surfaces can be controlled by the presence of antistatic agents that make the surface more conductive or less resistive. For example, water within a hydrophilic polymer can act as an antistatic agent and prevent static buildup. The amount of water is important for example, water in a polyamide in equilibrium with air at 65% RH acts as an antistatic agent, but at iow RH values, water is not effective. Since most polymers used in packaging are not hydrophilic, antistatic additives may be used to control static. Generally, these agents are cationic, anionic, or nonionic surfactants. 

Cellulose fibres are crystalline and very strong materials when they are dry. However, they are hydrophilic and in the presence of moisture they absorb water, becoming permeable by microorganisms. For this reason paper became much less important as a food packaging material when the cheap hydrophobic synthetic polymers emerged in the second half of the 20th century. 

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