Multi-layer packaging adhesives

O2 barrier, selective CO2/O2 barrier, aroma barrier (simple or multi-layer packaging) Medical goods (bone fixation, suture threads, films, non-woven tissues, etc.) Super-absorbent materials (material for plant planting in desert, nappies, etc.) Adhesives (glue) ... 

Coextrusion produces multilayer laminates in a single process step. Two or more extruders feed different molten polymers into a multi-manifold die which layers them directly, or into a modular feedblock which layers them before feeding them into the die. This is used primarily in the packaging field, to sandwich an impermeable barrier layer between two commodity outer-film layers, and often includes adhesive tie layers to bond the barrier layer to the outer layers. 

In general, when two or more different types of polymer are mixed, they show immiscibility (separation of phases), and exhibit a dispersion of the minor phase (the dispersed phase) in the major phase (the matrix). The cohesion between these different phases is low in most cases, and so the mechanical performances of the blends produced by simple blending are generally low, and need improvement. This is of prime importance in the preparation of mnlti-layered prodncts (packaging films, bottles, and so on) or multi-material parts, as well as where plastics are reinforced by fillers or by fibres. In such cases, interfacial cohesion between different phases can be improved by the use of special additives, called adhesion promoters or compatibilisers, that act at inter-phases. 

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