Vinylidene chloride copolymers gases

Conversely, cling film (plasticised PVC/PVDC, (poly(vinyl chloride)/poly (vinylidene chloride), copolymer, which has very high gas-barrier properties) on peeling from a roll generates static electricity thus promoting adhesion to a surface, e.g., ceramics, but not metallic surfaces which conduct the static electricity away... 

However, replacement strategies are not straightforward with compromises on either performance and cost having to be addressed. An excellent example of this centres around the chlorine issue. Chlorine imparts a unique set of properties to addition polymers, such as the ability to crystallise on film formation. Vinylidene chloride copolymers have exeellent gas, odour and moisture barrier properties impossible to achieve from non-chlorinated waterborne film forming materials. In the barrier packaging area it has a unique position, with proposed replacements being unable to fully match its overall... 

On account of its low thermal stability, polyfvinylidene chloride) is seldom used in paints. Vinylidene chloride copolymers with vinyl chloride, acrylonitrile, or acrylates are mainly employed. These heat-sealable copolymers are efficient gas barriers and have an outstanding resistance to chemicals. They are marketed as solid resins and dispersions. Vinylidene chloride copolymers are mainly used for coating foodpackaging foils. They are also important in paint coatings where good chemical resistance is required. 

Polyvinyl chloride-vinylidene chloride copolymer is veiy strong and is used as thin films. It has very low gas and water vapor permeabilities, is heat shrinkable and heat sealable. However, it has a brown tint for which it is sometimes not liked for food applications. 

Wang and Smith [74] used pyrolysis - gas chromatography to elucidate the composition of, and carry out structural studies on, vinyl chloride-vinylidene chloride copolymers. 

Copolymers of acrylonitrile and vinylidene chloride have been used for many years to produce films of low gas permeability, often as a coating on another material. Styrene-acrylonitrile with styrene as the predominant free monomer (SAN polymers) has also been available for a long time. In the 1970s materials were produced which aimed to provide a compromise between the very low gas permeability of poly(vinylidene chloride) and poly(acrylonitrile) with the processability of polystyrene or SAN polymers (discussed more fully in Chapter 16). These became known as nitrile resins. 

In this paper we would like to describe a new design, based on gas chromatographic analysis of the monomer mixture, for production of constant composition copolymers and its application to emulsion copolymerization. This design was already shortly described and applied to solution copolymerization (3) of methylmethacrylate and vinylidene chloride. Since then, the apparatus was made more simple, more reliable and more accurate. It is actually monitored by an analogic computering system which keeps the ratio of the monomers constant by controlling the addition of one of them. The process based on it can be called corrected batch process because the initial value of this ratio is kept up to the end. 

Inverse gas chromatography, IGC, has been used to study water sorption of two poly (vinylidene chloride-vinyl chloride) and poly (vinylidene chloride-acrylonitrile) copolymers, at temperatures between 20 and 50°C and low water uptakes. It was found that the specific retention volume of water increases with decreasing amount of water injected, increases dramatically with decreasing temperature and strongly depends on the type of copolymer. Thermodynamic parameters of sorption namely free energy, entropy, enthalpy of sorption and activity coefficient were calculated. 

The compositional analysis of a copolymer can be achieved by several methods other than NMR spectroscopy, such as elemental analysis, infrared and ultraviolet spectroscopies, and pyrolysis-gas chromatography. However, NMR spectroscopy has several advantages it does not need calibration if the operation conditions are properly set, and it can distinguish impurities easily. Quantitative aspects of compositional analysis by H and 13C NMR have been discussed for styrene-MMA copolymer12 and vinylidene chloride-acrylonitrile copolymer,13 respectively. 

With the growing demand for coextruded products, barrier plastics have shown significant growth in the last several years. Historically, the high barrier resins market has been dominated by three leading materials — vinylidene chloride (VDC) copolymers, ethylene vinyl alcohol (EVOH) copolymers, and nitrile resins. Since 1985, however, there has been a lot of interest worldwide in the development of moderate to intermediate barrier resins, as apparent from the introduction of a number of such resins, notably, aromatic nylon MXD-6 from Mitsubishi Gas Chemical Company, amorphous nylons SELAR PA by Du Pont and NovamidX21 by Mitsubishi Chemical Industries, polyacrylic-imide copolymer EXL (introduced earlier as XHTA) by Rohm and Haas and copolyester B010 by Mitsui/Owens-Illinois. 

Materials The competitive oxygen barrier resins investigated include Dow Chemical Company s vinylidene chloride/vinyl chloride (VDC) copolymer (experimental grade XU 32009.02), Mitsubishi Gas Chemical Company s aromatic nylon MXD-6, Du Pont s amorphous nylon SELAR PA 3426, Rohm Haas s polyacrylic-imide XHTA-50A and two EVOH resins — Kuraray s EVAL EP-E105 (44 mole% ethylene content) and Nippon Gohsei s SOARNOL D (29 mole% ethylene content). ... 

General Description Polyvinylidene Chloride (PVDC) resin is a copolymer of vinylidene chloride (VDC) with vinyl chloride or other monomers Dow Plastics vinyl chloride and vinylidene chloride, Saran, is usually supplied as a white, free-flowing powder. Dow Saran polymers are known worldwide for their gas-moisture, and chemical-barrier properties, and for their ignition-resistant properties. 

Poly(vinylidene chloride) (PVDC). The homopolymer is intractable in the conventional plastics processing techniques. For this reason, copolymers of vinylydene chloride with vinyl chloride or terpolymers with vinyl chloride and acrylonitrile are used. Due to its exceptionally low vapour, gas, and aroma permeability, PVDC films are used for packaging and for the barrier layer in composite films. Paper varnished by PVDC is a widespread packaging material. Trade names Diofan (FRG), Ixan (B), Saran (USA). 

Copolymers of acrylonitrile with other monomers are widely used. Copolymers of vinylidene chloride and acrylonitrile hnd application as low-gas-permeability films. Styrene-acrylonitrile (SAN polymers) copolymers have also been used in packaging applications. A number of acrylonitrile copolymers were developed for beverage containers, but the requirement of very low levels of residual acrylonitrile monomer in this application led to many of these products being removed from the market. One copolymer currently available is Barex (BP Chemicals). Acrylonitrile is also used with butadiene and styrene to form ABS polymers. Unlike the homopolymer, copolymers of acrylonitrile can be processed by many methods including extra-sion, blow molding, and injection molding. BP Chemicals is a major supplier of these copolymers. 

The main application of the vinylidene chloride — vinyl chloride copolymers is for filaments, which are made by melt extrusion and drawing. The filaments are used for such applications as car upholstery, garden chair fabrics and filter cloths where toughness, durability and chemical resistance are required. These copolymers are also used for packaging film, which is made by extrusion and biaxial stretching. The film has very good clarity, toughness and moisture and gas impermeability. 

The main use of the vinylidene chloride — acrylonitrile copolymers is as coatings for materials such as cellophane, paper and polyethylene. The coatings confer moisture and gas impermeability and they are heat-sealable. 

A considerable number of other chlorinated polymers find commercial use as a means to impart fire retardancy into a product. Poly(vinylidene chloride) (PVDC) and its copolymers are described here, particularly because of their gas and vapour barrier properties. 

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