Plasticizers migration

Migration is defined as the diffusion of an additive from a plastic to other contacting materials. A variety of restrictions and assumptions have been used to establish a theoretical understanding of migration. These include  

total amount of plasticizer desorhed after infinite time of extraction 

In an experiment to evaluate plasticizer migration from a plasticized film into an unplasticized PVC film no boundary effect was identified. There was no accumulation of plasticizer between the films. Also data indicated that the interface did not influence 

SM specific migration of individual components (here, plasticizer and epoxidized soya bean oil). 

Each migrating component behaved differently with each food simulant. DEHP was extracted at a similar rate by all three simulants. TEHTM was extracted at the fastest rate by isooctane followed by sunflower oil whereas ESBO was extracted most rapidly by ethanol followed by isooctane. The extraction rate of the plasticizer affects the ESBO extraction rate. This study indicates that additives in combination may react differently to extracting media than would a single additive. 

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Vinyl-coated fabrics exhibit high density, extremely low water vapor and air permeabiUty, cold touch, poor flex endurance, and plasticizer migration. However, they have good scratch resistance and colorabiUty and are inexpensive. 

In some cases, plasticization of a PSA may be detrimental to its performance. A well-known example is the deterioration of the performance of an adhesive applied to plasticized PVC. Migration of the plasticizer from the flexible vinyl into the PSA often softens the adhesive to the point where it fails cohesively from the vinyl, leaving sticky residue behind during removal of the adhesive-coated article from the substrate. One way to address this detrimental effect of plasticizer migration is to formulate an already plasticized PSA, perhaps because a better balance exists between the plasticizer in the PVC substrate and the PSA in contact with it [101]. 

Kozyrod, R.P. Ziaziaris, J. (1989) A survey of plasticizer migration into foods. J Food Protect., 52, 578-580... 

Mercer, A., Castle, L., Comyn, J. Gilbert, J. (1990) Evaluation of a predictive mathematical model of di-(2-ethylhexyl) adipate plasticizer migration from PVC film into foods. Food Add. Contam., 7, 497-507... 

Example 7-4. Ten 4 cm diameter circular 2(X) gm thick plastic film pieces are mounted on a stainless steel wire and placed in a glass vial containing 100 ml solvent. What percentage of the additives initially contained in the plastic migrate into the liquid over the 24 hour period (Dp = 2.10E-10 cm2/s) Note that the plastic additives are readily soluble in the solvent, the solvent has low viscosity and the solvent does not swell the plastic. 

Till, D.E., Reid, R.C., Schwartz, P.S., Sidman, K.R., Valentine, J.H., and Whelan R.H. 1982, Plasticizer Migration from Polyvinyl Chloride Film to Solvents and Food. Food Cosmet. Tox. 20,153-175. 

The plastic surface, at the time of bonding, may be well suited to the adhesive process. However, after aging, undesirable surface conditions may present themselves at the interface, displace the adhesive, and result in bond failure. These weak boundary layers could come from the environment or from within the plastic substrate itself. Plasticizer migration and degradation of the interface through uv radiation are common examples of weak boundary layers that can develop with time at the interface. 

Plasticizer migration from the vinyl part into the adhesive bond line can degrade the strength of the joint. Adhesives must be tested for their ability to resist the plasticizer. PVC can be made with a variety of plasticizers. An adhesive suitable for a certain flexible PVC formulation may not be compatible with a PVC from another supplier. Nitrile rubber adhesives have been found to be very resistant to plasticizers and are often the preferred adhesive for flexible PVC films. However, certain epoxy adhesive formulations have also been found to provide excellent adhesion to flexible PVC substrates. Several such starting formulations are presented in Table 16.7. A comparison of the performance of several classes of adhesive when bonding PVC to itself and to various other materials is given in Table 16.15. 

Polymer Science Series B 44, Nos. 1-2, Jan./Feb.2002, p.45-9 IR SPECTROSCOPY STUDY OF PLASTICIZER MIGRATION FROM POLY(VINYL CHLORIDE)-BASED COMPOSITIONS... 

Polyvinyl Chloride (PVC) With PVC plasticizer migration to the adhesive bond line can cause difficulties, especially in the softer, highly plasticized materials. Adhesives must be tested for their ability to resist the plasticizer. Nitrile-rubber adhesives are resistant to plasticizers. Polyurethanes and neoprenes are also used. Even rigid PVC contains up to 5% plasticizer. Most vinyl materials are fairly easy to... 

Polyacrylates and polyacrylate copolymers (suitable for mechanically and thermally resistant adhesive bonds, no plasticizer migration)... 

Acrylate dispersions are among the best performing aqueous adhesives, since they require no plasticizers to render them flexible and allow no plasticizer migration from the plastic materials (impermeable boundary). These dispersions are therefore always used in products in which hazards to humans must be excluded, for example in wound bandages. 

The promising results by Huber et al. [37] and Choi and Kwak [38] with a reduction in the migration of highly branched polyesters to hexane and polymer substrates suggested that the introduction of branches in the plasticizer structure could be an effective way to prevent the release of plasticizer also in aqueous environments. Volatihty, extractabihty, and exudation tests for PVC/hyperbranched polycaprolactone showed that there was no plasticizer migration even at very harsh conditions, while 7-78% of additives in PVC/DEHP migrated out of the samples [91]. 

Plasticizer Organic compounds with low molecular weight physically integrated in the polymer structure, that is, not by a chemical reaction, thus contributing to higher deformability and/or plastification of the polymer. Under adequate conditions (higher temperatures) they can diffuse out of the polymer structure (plasticizer migration). 

It is critical that the plasticizers that are compatible in the liquid compound remain so when the compound cures to a rubber. Many adhesion failures have been the result of plasticizer migration that destroys the adhesive bond. 

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