Plastics liquid foods

Three different approaches have been presented for estimating the partitioning of solutes between plastics and liquids. In the context of evaluating the output from these different approaches it is also useful to define the expected experimental ranges and limits for partition coefficients based on the solutes, plastic and contacting liquid phases involved. Table 4-9 shows approximate upper and lower limits for partition coefficients one may normally encounter in plastic/food systems based on the polarities of the solutes, plastics and foods. The table also gives approximate ranges of partition coefficient values for various solutes between typical food contact plastics and liquid phases. 

Plastic monolayer in contact with liquid food... 

One of the most important migration problems occurs if a liquid food or food simulant F with the volume Vp and density pp comes in contact with a plastic layer P of thickness dp and density pp. The mass transfer takes place across an interface with area A between two different media with different characteristics, e.g., with different diffusion coefficients Dp and Z>p of the migrant. If the value of a quantity is desired, for example, the concentration of the substance transported across the interface in one of the two media, then a mass balance must be considered that takes into account the ratio of the contact surface area and the volume of the corresponding medium. The model describing this process is based on the following assumptions ... 

Polyethylene (PE) is a member of the polyolefin family, which also includes PP and various plastics with different molecular linearily, densities, polymerization processes, and substitution types. PE densities are relatively low with values ranging from 0.940 to 0.970 g/cm for HOPE and from 0.916 to 0.940 g/cm for LLDPE. Typically, these PEs not only have good processability (e.g., can be converted into bags, films, and bottles) but also exhibit an excellent water vapor barrier property, which is required for many water-sensitive food products such as dried and liquid foods. However, this type of plastic is not appropriate for easily oxidized food products due to its low oxygen barrier property. The properties of polyolefins can be significantly affected by environmental conditions and physical factors, such as the density, crystallinity, presence of free volume, polarity, humidity, and temperature [44]. 

An alternative to release of antimicrobial agents could be the use of a surface that is inherently antimicrobial. Such a system could be applicable to liquid foods (especially if agitated) and those with intimate contact with the package surface. One such system is available in Japan (Louis, 1990 Hirata, 1992) and consists of a plastic film impregnated with silver-bonded zeolite particles. As the microorganisms contact the zeolite, they take up the silver, which kills them. A 1% silver zeolite in polyethylene has been evaluated in a model system by Hirata (1992) who found that the microbial count on the surface could be reduced from up to 10 cells/ml to less than 10 cells/ml in 24 hours. This system appears to have considerable promise. 

Non-Newtonian Flow Behavior. All liquids showing deviations from the behavior above are non-Newtonian. Many liquids encountered in industrial practice, such as paints, emulsions, most mineral slurries, latex, paper pulp, plastic melts, liquid foods, polymeric liquids, and concentrated wastewater sludge, are non-Newtonian. 

The problem of permeability exists whenever a plastic material is exposed to vapor, moisture, or liquids. Typical cases are electrical batteries, instruments, components installed underground, encapsulated electrical components, food packaging, and various fluid-material containers. In these cases, a plastic material is called upon to form a barrier either to minimize loss of vapor or fluid or to prevent the entrance of vapor or fluid into a product. From the designers viewpoint, the tolerable amount of permeation established by test under conditions of usage with a prototype product of correct shape and material is the only direct answer. 

Rheology is the study of flow and deformation of materials under the influence of external forces. It involves the viscosity characteristics of powders, liquids, and semisolids. Rheological studies are also important in the industrial manufacture and applications of plastic materials, lubricating materials, coatings, inks, adhesives, and food products. Flow properties of pharmaceutical disperse systems can be of particular importance, especially for topical products. Such systems often exhibit rather complex rheological properties, and pharmaceutical scientists have conducted fundamental investigations in this area [58-64],... 

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