Copolymers shrinkage

Fitzer, Frohs and Heine (1986) [209] used TMA and DSC to study the optimum heating rate for a 6% MA/1% ITA PAN copolymer. Shrinkage measurements indicated the start and end of the stabilization reaction. The optimum heating rate was 5°Cmin reducing to l°Cmin when the reaction started, in order to avoid overheating by the exothermic reaction and stopping at 270°C to avoid over-oxidation. 

Some cast (unoriented) polypropylene film is produced. Its clarity and heat sealabiUty make it ideal for textile packaging and overwrap. The use of copolymers with ethylene improves low temperature impact, which is the primary problem with unoriented PP film. Orientation improves the clarity and stiffness of polypropylene film, and dramatically increases low temperature impact strength. BOPP film, however, is not readily heat-sealed and so is coextmded or coated with resins with lower melting points than the polypropylene shrinkage temperature. These layers may also provide improved barrier properties. 

Acrylic Resins. The first synthetic polymer denture material, used throughout much of the 20th century, was based on the discovery of vulcanised mbber in 1839. Other polymers explored for denture and other dental uses have included ceUuloid, phenolformaldehyde resins, and vinyl chloride copolymers. Polystyrene, polycarbonates, polyurethanes, and acryHc resins have also been used for dental polymers. Because of the unique combination of properties, eg, aesthetics and ease of fabrication, acryHc resins based on methyl methacrylate and its polymer and/or copolymers have received the most attention since their introduction in 1937. However, deficiencies include excessive polymerization shrinkage and poor abrasion resistance. Polymers used in dental appHcation should have minimal dimensional changes during and subsequent to polymerization exceUent chemical, physical, and color stabiHty processabiHty and biocompatibiHty and the abiHty to blend with contiguous tissues. 

Another amorphous terephthalate has also been introduced commercially. This is a copolymer based on 1,4-cyclohexylene glycol with a combination of terephthalic acid and isophthalic acid. The copolymer is claimed to have excellent optical properties, have low moulding shrinkage and be relatively easy to vaccum form. As with other terephthalates it is considered in more detail in Chapter 25. 

Block copolymer micelles containing PB cores were cross-linked either by UV or fast electron irradiation [79-81]. This was accompanied by a shrinkage of the micelles. 

The modification of PET with low levels of naphthalate comonomer increases the Tg and enables optimally oriented articles (films, fibers, containers, etc.) to resist higher temperatures without shrinkage. Heat setting under tension may be applied to further extend thermal stability. In addition, when retention of optical transparency is required, such copolymers crystallize less readily than PET, and may readily be quenched from the melt to the transparent, amorphous state. Thus,... 

ISO 14236 2000 Plastics pipes and fittings - Mechanical-joint compression fittings for use with polyethylene pressure pipes in water supply systems ISO 14616 1997 Plastics - Heatshrinkable films of polyethylene, ethylene copolymers and their mixtures - Determination of shrinkage stress and contraction stress ISO 14632 1998 Extruded sheets of polyethylene (PE-HD) - Requirements and test methods... 

Lam P.K. and Piggott M.R. (1989b). The durability of controlled matrix shrinkage composites Part 2, Properties of carbon fiber-epoxy copolymer pultrusion, J. Mater. Sci. 24, 4427-4431,... 

Hot blown plastic films usually do not possess sufficient orientation to be heat shrinkable at temperatures below 100°C. For certain shrink packaging applications low temperature shrinkage is essential and can be obtained by biaxial orientation below the melting point. Radiation crosslinking was found to facilitate orientation of these copolymers greatly because of the much greater bubble stability which results from crosslinking. 

Copolymers of ethylene and norbomene exhibit excellent transparency, high moisture barrier, high strength and stiffness, and low shrinkage. In comparison to poly(ethylene) (PE) and polypropylene) (PP), they show a very low gas permeability. They are used for blister packaging in pharmacy applications and for flexible films for food packaging. Multilayer films consisting of PP outer layers and a cyclic olefin copolymer are in use. 

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