Antioxidant Migration Testing

Applications Radiotracer measurements, which combine high sensitivity and specificity with poor spatial resolution, have been used for migration testing. For example, studies have been made on HDPE, PP and HIPS to determine effects of manufacturing conditions on migration of AOs from plastic products into a test fat [443]. Labelled antioxidant was determined radio-analytically after 10 days at 40 °C. Acosta and Sas-tre [444] have used radioactive tracer methods for the determination of styrene ethyl acrylate in a styrene ethyl acrylate copolymer. 

It is well known from pipe pressure tests that immersion in water enhances antioxidant migration in comparison to air, as was observed in our experiments. Smith et al. attributed this to the influence of carbon black (Smith et al. 1992). Antioxidants are adsorbed at the earbon black surface, whereby the migration process is retarded considerably. During immersion in water some moisture is also present in the HDPE bulk material and this is preferentially adsorbed by the carbon black aggregates. The adsorption of water thereby supersedes that of the antioxidants and decreases the retardation coefficient and increases the apparent diffusion coefficient of the latter. In addition, it was suggested that the antioxidant forms loosely bonded clusters within the dry PE bulk material which may disperse slowly in contact with diffusing water thus enhancing the antioxidant diffusion coefficient (Le Poidevin 1977). 

PE is characterized by a very low water absorption, e.g. HDPE water absorption index = 0.04%. All antioxidants tested by us are insoluble in water, but they are distributed in PE melt perfectly (the classical feature required of any antioxidant [7]). Furthermore, according to the notion of diffusion, in cross-linked struetures such processes are hampered. That is why there is a low probability of the examined antioxidants migration from PEX-A - a conclusion, which is supported by the received experimental results. 

The migration/sorption behavior test for BHT and a-tocopherol in LDPE packaging materials in contact with fatty food simulants has indicated that the rate of migration of a-tocopherol into food simulants is lower than that for BHT. Since a-tocopherol was transferred from the film to the simulant to a lesser extent, it is considered a more stable antioxidant than BHT (Wessling et ah, 1998). BHT has also been found to migrate more rapidly than Irganox 1010 into dry food stored in LDPE wraps (Schwope et ah, 1987a). 

Plasticizers, antioxidants, and colorants are all potential contaminants of foods that are contained in plastics made with these chemicals. Control of potential migration of plastic components requires testing the containers with food simulants selected to yield information relevant to the intended type of food to be packaged (DeKruyf et al. 1983 Bieber etal. 1984). 

Volatility and Migration Rate. A study of the half-lives (T ) of the antioxidants in the polymer (see Table 1) at the same temperature suggests a reason for the lack of correlation between the two sets of results. In an oxygen absorption test, volatilization cannot occur, and the result is a true measure of the intrinsic activity of the antioxidant molecule. In an air oven test, on the other hand, physical loss of the antioxidant by migration and volatilization from the surface must dominantly influence the test results. Billingham and his coworkers ( 2) have shown that these two physical parameters determine the rate of loss of antioxidants from polymers. Increase in molecular mass generally decreases molecular mobility as well as volatility, and which factor dominates depends on the thickness of the sample ( 2). 

PLA composites containing flax fibres rich in poly(hydro3ybulyrate) (PHB) as reinforcement were prepared by compression moulding and further analyzed. Biochemical analysis of fibres revealed the presence of several antioxidant compounds, including cannabidiol and lutein. The prepared composites seem to have bacteriostatic, platelet anti-aggregated and non-cytotoxic effect. No tests on compound migration were reported. 

Figure 4.3 Migration of antioxidant lonox 330 from high-density polyethylene into different contact liqnids as a function of time. Tests were carried out at 20 °C...

In general, the test conditions of 10 days at 40 °C were found to be the most severe, giving higher migration results than 2 hours or 6 hours at 70 °C. The exception to this was for migration of the antioxidant, octadecyl-3-(3,5-di- er -butyl-4-hydroxy-phenyl)... 

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