Safety of re-cycled plastics for food contact materials: Testing to define a functional barrier

Re-cycled polymers can be used for food packaging with a layer of virgin polymer as a functional barrier protecting the food from contamination by material from the re-cycled layer. A mathematical treatment of the diffusion of the contaminant (initially at a uniform concentration in the re-cycled plastic) is made by considering the diffusion through the two layers with a constant diffusivity. In order to better define the role of the functional barrier, the case without transfer of contaminant through the external surfaces is considered. Dimensionless numbers are used so as to draw master curves either for the kinetics of contaminant transfer or for the profiles of concentration of contaminant in the material. The efficiency of the functional barrier can be defined by the lag time for the start of migration.     

Esr study of the migration of paramagnetic additives from rigid PVC to pure or mixed fatty esters used as food simulators

The ESR study presented here provides an insight into the behaviour of paramagnetic additives in rigid PVC before, during and after contact with methyl fatty esters and their migration from the plastic material. Before contact, diffusion processes took place in rigid PVC. The mobility of the NO group of the paramagnetic additives is directly linked to the displacement of the whole molecule. Methyl fatty esters plasticize the PVC matrix, increase the mobility of the additive in the material and enhance their migration. The increased lability is due to methyl ester penetration into the polymeric network. Penetration was greatest with short chain esters and probe migration was greater when more penetrating simulators were used. If a fast migration test is required, methyl oleate could be an interesting approach. Results describing the behaviour of binary mixtures as simulators are very complex, probably because they depend to a large extent on the type of paramagnetic additive.     

Effects of clinical counseling on college achievement.

To investigate the effects of clinical counseling on the academic achievement of college students, each of 132 counseled students was compared to a "hypothetical twin" which represented the average of 5 noncounseled students closely matched to the counseled students on each of 5 control dimensions: age, sex, high school average, number of college credits, and cumulative index. No significant differences in achievement were found between counseled students and their controls. However, when counseled students were grouped according to the counselor they had seen, significant differences emerged. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Safety assessment of polymeric additives for food packaging: Hydrolysis of polymeric plasticizers by digestive fluids

The in vitro hydrolysis of poly(1,2‐propylene adipate) by digestive fluid liquids was studied to assess the safety of polymeric plasticizers that could migrate into food. A high extent of hydrolysis was obtained with freshly prepared intestinal fluid solutions. High performance size exclusion chromatography analysis indicated that the bulk plasticizer completely disappeared and that low molecular weight oligomers were formed within 4 h. Hydrolysis did not result in a significant conversion to the free monomers, like adipic acid, as was shown by gas‐phase chromatography. Measurements by NMR indicated that the cleavage selectively occurred at primary ester linkages. Fractionation of the hydrolysis products on silica gel gave six oligomeric fractions, which were recovered and analyzed. The absolute molecular weight of the plasticizers and the average molecular weight of the hydrolysis products were evaluated using proton NMR. Hydrolysis did not take place (<2%) under simulated gastric and saliva conditions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 956–966, 2002     

The power of adaptiveness and additional queries in random-self-reductions

We study random-self-reductions from a structural complexity-theoretic point of view. Specifically, we look at relationships between adaptive and nonadaptive random-self-reductions. We also look at what happens to random-self-reductions if we restrict the number of queries they are allowed to make. We show the following results:

Evaluation of migration models that might be used in support of regulations for food-contact plastics

Materials and articles intended to come into contact with food must be shown to be safe because they might interact with food during processing, storage and the transportation of foodstuffs. Framework Directive 89/109/EEC and its related specific Directives provide this safety basis for the protection of the consumer against inadmissible chemical contamination from food-contact materials. Recently, the European Commission charged an international group of experts to demonstrate that migration modelling can be regarded as a valid and reliable tool to calculate 'reasonable worst-case' migration rates from the most important food-contact plastics into the European Union official food simulants. The paper summarizes the main steps followed to build up and validate a migration estimation model that can be used, for a series of plastic food-contact materials and migrants, for regulatory purposes. Analytical solutions of the diffusion equation in conjunction with an 'upper limit' equation for the migrant diffusion coefficient, D_P, and the use of 'worst case' partitioning coefficients K_P,F were used in the migration model. The results obtained were then validated, at a confidence level of 95%, by comparison with the available experimental evidence. The successful accomplishment of the goals of this project is reflected by the fact that in Directive 2002/72/EC, the European Commission included the mathematical modelling as an alternative tool to determine migration rates for compliance purposes.     

Functional barriers: Properties and evaluation

Functional barriers are multilayer structures deemed to prevent migration of some chemicals released by food-contact materials into food. In the area of plastics packaging, different migration behaviours of mono- and multilayer structures are assessed in terms of lag time and of their influence of the solubility of the migrants in food simulants. Whereas barriers to oxygen or to aromas must prevent the diffusion of these compounds under conditions of use, a functional barrier must also be efficient under processing conditions, to prevent diffusion of substances when the polymer layers are in contact at high (processing) temperatures. Diffusion in melted polymers at high temperatures is much slower for glassy polymers, than in polymers that are rubbery at ambient temperature. To evaluate the behaviour of functional barriers under conditions of use, a set of reference diffusion coefficients in the 40-60°C range were determined for 14 polymers. Conditions for accelerated migration tests are proposed based on worst-case activation energy in the 40-60°C range. For simulation of migration, numerical models are available. The rules derived from the models can be used both by industry (to optimize a material in terms of migration) or by risk assessors. Differences in migration behaviour between mono- and multilayer materials are discussed.     

Convexity of Yield Surface with Directional Distortional Hardening Rules

The present paper examines the convexity of the yield surface in the directional distortional hardening models by Feigenbaum and Dafalias. In these models anisotropy develops through kinematic and directional distortional hardening, supplemented by the classical isotropic hardening, and the associative flow rule is used. However, the issue of convexity, which naturally arises due to the distortion of the yield surface, was not fully addressed. The present paper derives the necessary and sufficient conditions to ensure convexity of the yield surface for the simpler Feigenbaum and Dafalias models, but it is not as straightforward to derive corresponding conditions for convexity of the Feigenbaum and Dafalias model version which contains an evolving fourth-order tensor. In this case convexity will be addressed first in general and then at the limit state for which simple restrictions on the material constants to ensure convexity are derived. Numerical examples will show that some of the yield surfaces simulated in the original Feigenbaum and Dafalias publication will not stay convex if loaded beyond what was done in these publications. Therefore the material constants for these cases are recalibrated based on the derived relations for satisfaction of the convexity requirement, and the fitting of the yield surfaces is repeated with the new set of constants and compared with the previous case.     

Comparison of digital with videotape echocardiography in patients with chest pain in the emergency department

Sterol carrier protein 2 (SCP2) has been implicated in adrenal steroidogenesis by in vitro studies. In order to clarify the clinical significance of SCP2 in human steroidogenesis, we investigated the expression of SCP2 mRNA in various types of adrenocortical tissue and one testis and examined the correlation between the amounts of SCP2 and other values such as the free cholesterol content and the cholesterol side-chain cleavage (SCC) activity in the tissue mitochondria. The types of adrenocortical tissue examined included adrenocortical carcinomas (N = 3), adrenocortical adenomas from patients with Conn's syndrome (N = 3) and from patients with Cushing's syndrome (N = 3), non-functioning adrenocortical adenomas (N = 2) and normal adrenal glands (N = 2). Northern blot hybridization predominantly revealed a 1.8-kb SCP2 mRNA in all tissue specimens examined. The mRNA concentrations of SCP2 in two out of three adrenocortical carcinomas were relatively lower than those in other types of tissue. No other special tendency was observed regarding the mRNA expression levels in various tissue specimens. The mRNA concentrations of SCP2 correlated significantly with mitochondrial contents of free cholesterol (r = 0.67, p < 0.01), but was not correlated with the SCC activities in mitochondria measured by an in vitro enzyme assay. The mitochondrial SCC activities, however, were correlated significantly with the protein levels of mitochondrial P-450 scc determined by a Western blot analysis (r = 0.79, p < 0.01). The significant positive correlation between mRNA concentrations of SCP2 and the mitochondrial content of free cholesterol suggests that the central role of SCP2 in human steroidogenic tissues may be in part a translocation of cytoplasmic free cholesterol to the mitochondria, as demonstrated previously by in vitro studies.