Polystyrene food containers, styrene

Analysis and Levels of Styrene Dimers and Trimers in Polystyrene Food Containers... 

STYRENE DIMERS AND TRIMERS IN POLYSTYRENE FOOD CONTAINERS 729... 

Eoamed polystyrene sheet has exceUent strength, thermal resistance, formabUity, and shock resistance, as weU as low density. It is widely known for its use in beverage cups, food containers, building insulation panels, and shock absorbent packaging. Polystyrene products can be recycled if suitable coUection methods are estabUshed. Eoamed polystyrene sheet can also be easily therm oformed (see Styrene plastics). 

Tawfik, M.S. and Huyghebaert, A. (1998). Polystyrene cups and containers styrene migration, Food Addit Contam., 15, 5, 592-599. 

High impact polystyrene (HIPS) is synthesized by emulsion polymerization of styrene in styrene-butadiene latex. The higher impact characteristics of HIPS make it suitable for use in the manufacture of sheets, food containers, window frames, household goods, etc. 

Styrene is a major industrial chemical, primarily because of its use in making polystyrene. Polystyrene is a clear, hard, colorless solid at room temperature that can be molded easily at 250°C. More than 6 million tons of polystyrene are produced in the United States each year to make food containers, toys, electrical parts, insulating panels, appliance and fm-niture components, and many other items. The variation in properties shown by polystyrene products is typical of synthetic polymers. For example, a clear polystyrene drinking glass that is britde and breaks into sharp pieces somewhat like glass is much different from a polystyrene coffee cup that is soft and pliable. 

Polystyrene (10.8) A thermoplastic polymer made from styrene monomer used in plastic model kits and plastic cutlery. Can be aerated to produce a foam (Styrofoam ) and made into coffee cups or insulated food containers. 

The most important use of polystyrene is in packaging. Molded polystyrene is used in items such as automobile interior parts, furniture, and home appliances. Packaging uses plus specialized food uses such as containers for carryout food are growth areas. Expanded polystyrene foams, which are produced by polymerizing styrene with a volatile solvent such as pentane, have low densities. They are used extensively in insulation and flotation (lifejackets). 

Styrene is a commercially important monomer that is used extensively in the manufacture of polystyrene resins and in co-polymers with acrylonitrile and 1,3-butadiene (reinforced plastics). Exposure to styrene occurs due to intake of food that has been in contact with styrene-containing polymers. lARC has determined that styrene is possibly carcinogenic to humans. There is no restriction on using styrene within the European Union (i.e., there is no SML). 

High-impact polystyrene (HIPS) is produced by polymerizing styrene in the presence of a rubber, usually poly(l,3-butadiene). HIPS has improved impact resistance compared to polystyrene and competes with ABS products at low-cost end applications such as fast-food cups, lids, takeout containers, toys, kitchen appliances, and personal-care product containers. HIPS as well as ABS and SMA are used in physical blends with other polymers, such as polycarbonates, polyesters, and polyamides, to improve impact resistance (Sec. 2-13c-3). 

Content of residual styrene monomer in polystyrene containing food contact materials... 

The results of a recent survey by the Inspection Health Protection/Food Inspection Department, Utrecht, Netherlands (van Lierop, Wildervanck 1996), shown in Table 14-lb, found an average residual styrene monomer content of 224 mg/kg in 31 different polystyrene containing food contact articles and packaging. The two highest contents found were 888 and 1459 mg/kg and in 14 articles less than 150 mg/kg was found. A comparison of the results of the two studies from 1988 and 1996 supports the stated industry objective of reducing styrene monomer contents and shows an overall downward trend. 

In addition to styrene migration from the primary package, polystyrene containing toys, surprises and other items packed inside a package together with product can also be a source of styrene monomer off-flavor. The polystyrene used may or may not be food grade and the overwrap for the item is usually not a barrier to the transmission of styrene into the food. 

A guide for estimating the general behavior of partition coefficients is like dissolves like . Thus styrene, a relatively nonpolar hydrocarbon, will tend to remain in a nonpolar polystyrene polymer if the package contains a polar aqueous food (Chapter 9). 

About two-thirds of all the styrene produced in the United States is used in the manufacture of polystyrene. Polystyrene is a clear, colorless, hard plastic that is easily molded and made into a foam known as styrofoam. It is used in the insulation of electrical wires and devices, in containers for hot and cold foods and drinks, and for the insulation of buildings. 

Date K, Ohno K, Azuma Y, Hirano S, Kobayashi K, Sakurai T, Nobuhara Y, Yamada T. Endocrine-disrupting effects of styrene oligomers that migrated from polystyrene containers into food. Food Chem Toxicol 2002 40 65-75. 

Indeed, simple monomers, snch as styrene, ethylene, propylene, hexene, vinyl chloride, acrylonitrile and caprolactam, nsnally do occur in the corresponding polymers. In addition to unreacted monomer, any non-polymerisable impnrities in the original monomer feed to the polymerisation conld occur in the final prodnct. Thns, styrene monomers can contain low concentrations of numerous saturated and nnsatnrated hydrocarbons, ethyl benzene being particnlarly prevelent and these, particnlarly the saturated compounds which do not polymerise, will occur in the finished polymer and have implications in the nse of the polymer food packaging. It is not nnknown for compounds as toxic as benzene to occnr at very low concentrations, nsnally less than 10 parts per million in styrene monomer, and this could, therefore, also occur in the polymer. For foodgrades of polystyrene, the monomer content is nsnally nowadays limited to 0.2% maximum. Acrylonitrile monomer may be fonnd in amonnts up to 0.1 % in finished polymer, whilst negligible amounts of monomer are fonnd in polyamide and polymethyl-1-pentene. With thermosets, phenol and formaldelyde are likely to be found even in the most carefully manufactured grades. 

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