Multi-layer materials

It is becoming common practice to have the cross-section of a plastic moulding made up of several different materials. This may be done to provide a permeation barrier whilst retaining attractive economics by having a less expensive material making up the bulk of the cross-section. To perform stress analysis in such cases, it is often convenient to convert the cross-section into an equivalent section consisting of only one material. This new section will behave in exactly the same way as the multi-layer material when the loads are applied. A very common example of this type of situation is where a solid skin and a foamed core are moulded to provide a very efficient stiffness/weight ratio. This type of situation may be analysed as follows ... 

The next most important aspect is the issue of the oxygen depletion in the chamber. The atmosphere inside the closed compartment often becomes oxygen-deficient before the test ends. Thus, after the oxygen level gets below 14% burning often ceases. This means that, when testing thick samples (typically multi-layered materials or composites) one of the components may not get to burn at all. 

From these equations, the thermal stress profile through the thickness of the multi-layered material with a compositional profile can be calculated. If E and aA T vary continuously with z, o is continuous too. Because, the effective properties change as functions of the position in an FGM material, it is necessary to estimate the local composite properties as functions of... 

The Ilford polymer layer coating comprises a polyethylene coated paper support which is coated onto the front side of the said support, the ink receiving layer being a mixture of gelatin and rice starch. Ilford products use multi-layer materials, containing polymer dry layers as well as microporous layers, a top coat which optimizes... 

Multi-layer packaging which includes materials other than plastics, e.g., metals and paper, even if the food contact layer or part of the food contact layer consists of plastic, is currently not covered by any specific legislation. These multi-layer materials are regulated either by national legislation or by Article 3 of the Framework Regulation (EC 2004). Article 3 states that... 

Rapra Technology Ltd has undertaken a detailed investigation into the migration of species from different types of adhesives used with laminated multi-layer materials (Barber et al, 2003). Migration of aromatic amines, BADGE, bisphenol A and polyols were examined. A description of the samples used and a brief summary of some of the results obtained from this analytical work are given below. 

Microwave susceptors are used for crisping and browning food in a microwave oven. The susceptor is a multi-layer material usually made of a paper layer, a thin aluminium layer and finally a polyethylene terephthalate layer which is in contact with the food. The susceptor absorbs the energy of the microwaves and this heat is transferred to the food resulting in a crispy surface at the part in contact with the food. 

Multi-layer materials are used for special reasons, e.g. where an already shrink wrapped material has to undergo a further (secondary) shrink wrapping operation. This means that a different material is essential to prevent sticking, e.g. coextruded LDPE/EVA/PP where the PP inner layer will not stick to LDPE. Usage of multi-layer materials is limited. 

Moreover, energy recovery is probably the best solution for very contaminated and dispersed plastics (for example, the yoghurt pot which is a multi-layered material, with low mass and whose residual content after consumption can be significant). It is tme that the high calorific value of plastics helps regulate the incineration of honsehold waste, improve the quahty of effluents (fewer micropollutants and unbumed compounds in slag) and conserve oil used in the production of heat and electricity. Most European cities are equipped with urban heating networks, which could become possible due to the incineration of urban waste. 

Such sensors can be provided as tube sensors or as flat tape sensors. Tape sensors allow its integration into composites or into the interface zone of multi-layer materials. Several sensors can be interrogated by multiplexing. 

The process by which layers of a multi-layered material are separated from one another is called exfoliation. 

MTA is now being used commercially to visualise the spatial distribution of phases, components and contaminants in polymers, foods biological materials and electronic materials. Pollock and Hammiche [4] review various applications that have been described in the literature to date, ranging from multi-layer materials and interphase regions in composites, to the use of the regions technique as a means of surface treatment in this paper. 

---