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 degrees C range were determined for 14 polymers. Conditions for accelerated migration tests are proposed based on worst-case activation energy in the 40-60 degrees 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.

Comparison of isopropanol and isooctane as food simulants in plasticizer migration tests.

In the last 25 years, plastics have faced a massive demand in packaging technology due to their desirable properties, such as flexibility, light weight, etc. Moreover, their packaging applications have spread in the area of food and pharmaceutical products. Much concern has arisen from that fact as most of these plastics contain high amounts of additives which tend to migrate when they come into contact with liquid or solid surrounding media. Plasticized PVC is one of the most popular polymers in packaging technology and at the same time is subject to criticism for the high concentration levels of plasticizer in most of its applications. In an attempt to carry out simple and realistic migration tests, many investigators used simple organic substances which simulate as much as possible the behaviour of foods towards plasticizer migration. Much of our previous work intended to examine migration of dioctyl phthalate (DOP) from PVC sheets into some simple surrounding media, such as methanol, white spirit, paraffin oil, etc. The present work is focused on the examination of the plasticizer migration into two promising food simulants, namely isopropanol and isooctane. Radioactivity measurements were employed in order to detect quantitatively the plasticizer which had migrated into the surrounding liquid. In contrast to similar studies, the phenomenon of migration was studied until equilibrium was reached.

Surface treated polyethylene fibres as reinforcement for acrylic resins.

The use of poly(methyl methacrylate) as a bone and dental cement material over several decades has provided us with experience related to processing and performance. A recognized disadvantage of such cements is their mechanical behaviour, expressed by low crack propagation resistance, impact strength, fatigue resistance and reduced fracture toughness. Many attempts have been made to resolve these problems either by modifying the poly(methyl methacrylate) chemical structure via copolymerization or incorporating reinforcing additives. The latter is of great importance, because it can lead to the preparation of composite materials with considerably improved performance. Besides reinforcement, the incorporation of additives, such as fibres, results in better processing characteristics, e.g. lowers polymerization exotherm. In this work, poly(methyl methacrylate) reinforced with Tekmilon ultra high modulus polyethylene fibres was studied, focussing on the interfacial bonding between matrix and reinforcement. Some finishing agents were used to treat the fibres and their efficiency was mainly evaluated through the effect on the mechanical properties of the composite material prepared.