Modeling the Migration of Monomers from Methacrylate Polymers for Estimation of Exposure Potential
Methacrylate-based polymers are made of monomers and other starting substances which are chemically reacted to a macromolecular structure, the polymer, which forms the main structural component of the plastics. To the polymer additives are added to achieve defined technological effects. The polymer as such is an inert high molecular weight structure. As substances with a molecular weight above 1 000 Da usually cannot be absorbed in the body the potential health risk from the polymer itself is minimal. Potential health risk may occur from exposure to non- or incompletely reacted monomers or other starting substances, or from low molecular weight additives, which are released from the final polymer materials and articles by a process called migration. Therefore monomers, other starting substances and additives should be assessed for their risk to health.
In recent decades International and National food contact regulations, including FDA standards, the European Framework Regulation1 and related directives, amendments and guidelines, as well as regulations/guidelines at national level have been developed to ensure the safety of food contact materials. These regulations have established standardized methods for the determination of migration that include test conditions including time, temperature and test medium (food simulant) representing worst foreseeable conditions of use of the plastic material or article. These methods can be used for the safety assessment of polymers under other conditions of use if the test medium is replaced with a suitable simulant representing the bodily fluids that are likely to be contacted, e.g. sweat, saliva etc.
The properties of various acrylic and methacrylic polymers were investigated to determine if data could be provided to do reliable modeling of migration. For this purpose, 11 representative acrylic polymers2 containing five different acrylic monomers3 were studied using the standard migration method used for the assessment of food safety. These studies used contact of the polymers with five different contact media (simulants) at three different temperatures (20°C, 40°C, 60°C). The simulants were selected to represent likely exposure conditions during typical use. For example, for food contact applications, water (aqueous foods), a neutral oil (fatty food) and an adsorbent resin (dry foods) were selected as representative simulants. To represent sucking rigid plastic articles, such as toys, artificial saliva was selected, to represent handling acrylic articles coming where contact with human skin is likely, a sweat simulant was selected. For each combination of contact media (simulant) and temperature the diffusion coefficients (D) of the monomers in the polymer and the partition coefficients between polymer and contact media were derived.
The studies showed that migration of monomers from acrylic polymers can be conservatively described by migration modelling. This is based on the observation that, under the experimental conditions used, the mass transport processes of monomers from acrylic polymers primarily follow Fick's 2nd law of diffusion. Thus, at a constant dose, the surface concentration will decrease in a predictable manner with time. There were some exceptions noted. Deviations from this ideal situation were observed in cases where interactions between the simulant and the polymer occurred. These included effects such as strong partitioning between the acrylic polymer and the simulant, or, swelling of the polymer by the simulant which caused time dependent accelerated diffusion.
Overall, the study showed that it is possible to assess exposure potential using the experimental results obtained. Application of the migration data showed:
- Migration of monomers from acrylic polymers is diffusion controlled.
- The diffusion rates of monomers (and other substances) from acrylic polymers are extremely low.
When the calculated migration amounts of the monomers were compared to the tolerable daily intake (TDI) values listed in European food packaging legislation, the potential exposures were calculated to be roughly 100 times below the specified group TDI values. This illustrates that there is very low potential for exposure of consumers to monomers migrating from acrylic polymers during normal use of these materials.
1COMMISSION REGULATION (EU) No 10/2011 on plastic materials and articles intended to come into contact with food
2Polymer descriptions: MMA homopolymer (High density polymer); 2 MMA/MA copolymers and 2 MMA/EA copolymers (Medium density range); MMA based rubber-modified BA copolymer, MMA based rubber-modified EA copolymer (Low density polymers); MMA homopolymer (High density resin); EMA/MMA copolymer (Intermediate density resin); MMA/nBMA copolymer (Very low density resin); iBMA homopolymer (Very low-density resin)
3methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, and n-butylmethacrylate
