Polycarbonate barrier properties

Certain polymers have come to be considered standard building blocks of the polyblends. For example, impact strength may be improved by using polycarbonate, ABS and polyurethanes. Heat resistance is improved by using polyphenylene oxide, polysulphone, PVC, polyester (PET and PBT) and acrylic. Barrier properties are improved by using plastics such as ethylene vinyl alchol (EVA). Some modem plastic alloys and their main characteristics are given in Table 1.2. 

The chapters devoted to structure-permeability properties of the more commercially advanced amorphous nylons (Chapter 5 (50)) and experimental polycarbonates (Chapter 7 (51)) illustrate many of the general principles needed for optimizing the barrier properties of essentially any polymer family. These chapters consider the importance of intersegmental packing and intrasegmental mobility on... 

Oriented LCP layers can be coextruded with other thermoplastics, such as polyethylene terephthalate, nylon, polycarbonate, and high-density polyethylene. The primary benefit of the LCP layer is to improve the barrier properties of the container. For example, using an LCP layer comprising 5% of the wall thickness of a container along with PET and tie layer in the other 95% will increase the oxygen barrier by more than 20 times compared with a pure PET... 

The following TPs are the main thermoforming materials processed high-impact and high-heat PS, HDPE, PP, PVC, ABS, CPET, PET, and PMMA. Other plastics of lesser usage are transparent styrene-butadiene block copolymers, acrylics, polycarbonates, cellulosics, thermoplastic elastomers (TPE), and ethylene-propylene thermoplastic vulcanizates. Coextruded structures of up to seven layers include barriers of EVAL, Saran, or nylon, with polyolefins, and/or styreneics for functional properties and decorative aesthetics at reasonable costs.239-241... 

Weld lines (also known as knit lines) are a potential source of weakness in molded and extruded plastic products. These occur when separate polymer melt flows meet and weld more or less into each other. Knit lines arise from flows around barriers, as in double or multigating and use of inserts in injection molding. The primary source of weld lines in extrusion is flow around spiders (multiarmed devices that hold the extrusion die). The melt temperature and melt elasticity (which is mentioned in the next section of this chapter) have major influences on the mechanical properties of weld lines. The tensile and impact strength of plastics that fail without appreciable yielding may be reduced considerably by in doublegated moldings, compared to that of samples without weld lines. Polystryrene and SAN copolymers are typical of such materials. The effects of weld lines is relatively minor with ductile amorphous plastics like ABS and polycarbonate and with semicrystalline polymers such as polyoxymethylene. Tliis is because these materials can reduce stress concentrations by yielding [22]. 

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