Migration of additives

Additive molecules, in almost all cases, are much smaller in size than the associated polymer molecules and are mostly organic, hence, they can usually evaporate and go 

There are on-going studies into bonding the additive to the polymer backbone to block and hence control any migration of the additive. 

The migration of any additive within the polymer matrix is found to be affected by factors that include  

In (c), for example, it is known that filled systems permit less migration (and thus, noncarbon-black filled rubbers have the highest values of migration). 

The low-density of plastics is an advantage for their use in general, but, at the same time, the relatively loose packing of their molecular system allows the easy permeation of gases and liquids through them. This can be important in many applications, particularly in 

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Weak boundary layer. WBL theory proposes that a cohesively weak region is present at the adhesive-substrate interface, which leads to poor adhesion. This layer can prevent the formation of adhesive bonds, or the adhesive can preferentially form bonds with the boundary layer rather that the surface it was intended for. Typically, the locus of failure is interfacial or in close proximity to the silicone-substrate interface. One of the most common causes of a WBL being formed is the presence of contaminants on the surface of the substrate. The formation of a WBL can also result from migration of additives from the bulk of the substrate, to the silicone-substrate interface. Alternatively, molecular... 

Migration of additives such as plasticizers, internal mould release agents... Painting defects can appear a long time after painting. 

The process of migration of additives or contaminants from polymeric food packaging to food may be separated into three stages diffusion within the polymer, solvation at the polymer food interface, and dispersion into bulk food. 

The control of migration of additives, monomers or oligomers, from packaging materials, for example, into food (important for the enforcement of a high level of food quality and safety) or other consumer products ... 

Figge, K. 1972, Migration of Additives form Plastics Films into Edible Oils and Fat Simulants. Food Cosmetic Toxicology, 10, 815-828. 

O Brien A., Cooper I., (2002), Practical experience in the use of additive models to predict migration of additives from food contact polymers. Food Additives and Contaminants, 19, pp 56-62. 

Diffusion and migration of additives from the polymer matrix into a surface may have both accelerating or stabilizing effects. 

Long-term properties of polymers are severely affected and the service-life is reduced due to the migration of additives. There is also the possibility that some of the additives accumulate in the environment and affect our health and the environment. SPME has been applied for the extraction of several common polymer additives. Since additives often have rather low volatility, a significant advantage with SPME and HS-SPME compared to HS-GC-MS is the ability to extract even semi-volatile compounds [9,13]. 

For solid products the risk of migration is low and therefore interaction studies are not required over and above the normal stability test results. For semi-solid products it is necessary to look particularly at the migration of additives, vapour permeation and the effects of the product on the physical parameters of the pack. For liquid products the migration potential for the specific formulation is required, and the determination of active ingredient content under simulated use, along with extractives data is required for parenteral and ophthalmic products. Moisture permeation is important, particularly for solid products packaged in blister packs. 

Substances that are not natural to a food, xenobiotics, may become a part of the food by several routes. They may be deliberately added as food or color additives they may result indirectly from migration of additives from wrappings into the food they may also result from the incorporation of environmental pollutants into the food while that food is growing or maturing. 

Identification of polymers is a complex process. Additives change the physical properties of polymers and their presence may confuse the results of tests to examine flexibility, hardness and density. Degradation of polymers changes their physical and chemical properties compared with new materials. Degraded polymers are often stiffer and darker than new materials, which is likely to confuse identification based on appearance. Their surfaces may become tacky due to migration of additives or disrupted by the formation of cracks. 

Migration of additives of different types was studied in polyolefins. Figure 8.3 shows that the minimum hole size required for the displacement of additives, B, correlates well with specific volume of additives, Vg ao> extrapolated from measured values to OK. Figure... 

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