Content of residual styrene monomer in polystyrene containing food contact materials

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

The level of unpolymerised residual styrene monomer in commercial grades of polystyrene material has been reduced over the years from 1000 mg/kg (0.1 % w/w) to a target level of 500 mg/kg (0.05 % w/w) by more complete devolatilization after the polymerization step (Brighton 1982). The legal limits for styrene monomer in materials can be much higher (e.g. Australia 2500 mg/kg, AS 2070.3-1992). Hempel and Riidt (1988) carried out a survey of residual volatiles found in polystyrene and polystyrene copolymers whose results are summarized in Table 14-la. 

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. 

Low monomer content PS materials are commercially available with specified styrene monomer levels of 150 ppm (mg/kg) that have actual contents of 100 ppm (ex. BASF O suffix materials 168 NO, 143 IO). These materials can be used for injection molding or extrusion and are priced above normal styrene monomer content materials (those where styrene 500 mg/kg). High impact polystyrene copolymer materials (HIPS) use normal monomer level polystyrene since there has been no commercial market for such materials. 

Type of Polymer Number of Samples Styrene monomer level (mg/kg) range and average Potential off-flavor substance frequency measured, range and levels in material (mg/kg) 

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