Gas barrier property

PEN has excellent gas-bairier properties. The gas-permeation coefficients of unoriented cast film and biaxially oriented films for PEN and PET are given in Table 10.4. 

PEN has lower gas permeation coefficients than PET for carbon dioxide, oxygen and moisture for botli film types. Although the gas-banier properties of PEN are similar to Arose of poly(vinyl dichloride), it is not affected by moisture in tire environment. Botlr oriented and unoriented PEN films restrict gas diffusion more 

7 Barrier Properties and Chemical Resistance 7.1 Gas Barrier Properties 

Results for drawn polyethylene give a value of e/k = 124 K which agrees well with the value of 118 K calculated by Michaels and Bixler from the second virial coefficient. 

The changes in the diffusion coefficient with draw ratio are more complex than those for the solubility, because the former depends both on the size of the diffusant molecule and on the structure of the polymer. The results for helium are shown in Fig. 55. It can be seen that there is no change in the diffusion coefficient up to draw ratio 9 followed by a rapid drop between draw ratios 10 and 12 and then a more gradual fall at higher draw ratios. No differences can be detected between either homopolymers of different molecular weight or between these and the hexene-1 copolymers. 

Measurements of helium diffusion coefficients over the temperature range 25-55 °C showed no significant changes in activation energies throughout the drawing range. 

It was therefore concluded that the changes in diffusion which occur on drawing result from shorter jumps between activation sites as a result of greater blockage of available paths. 

About a 25% reduction in the oxygen permeability has been observed in PDMS/hexadecyltrimethylammonium ions-modified fluorohectorite (8 wt%) nanocomposite [139]. Jia etal. [187] observed a 31% reduction in the nitrogen gas permeability in silicone rubber containing 30 phr [CHjfCHj), ] N(CH3) -modified MMT compared to neatsihcone rubber. They also noted that the extent of intercalation and the dispersion of the modified MMT are further improved when fumed silica (20 phr) is initially mixed up with the silicone rubber. As a result, the corresponding ternary nanocomposite exhibits a 40% reduction in the permeability compared to the neat silicone rubber 

Transport of gases and vapours in polymers is an important subject both from the technological and scientific point of view. Applications include protective coatings, packing materials for food, pharmaceuticals and cosmetics and selective barriers for 

Photoacoustic spectroscopy and related photothermal procedures [2] are well established spectroscopic techniques. The photoacoustic technique, apart from providing direct optical absorption spectra, can also be used to perform depth 

The room temperature characterisation of an LDPE sample s thermal properties was based upon the measurements of the thermal diffusivity, a, and of the heat capacity, pcp, where p is the material density and Cp is the specific heat at constant pressure (heat capacity per unit volume) [43]. To complete the determination of the sample thermal properties, knowing a and pc the sample thermal conductivity, K, is readily obtained from Equation 8.1  

The contribution to the photoacoustic signal from the thermoelastic bending is the dominant mechanism. This effect is essentially due to the temperature gradient created inside the sample along an axis perpendicular to the surface exposed to the incident radiation [43]. 

Permeation studies of CO2 and O2 were performed using a sample holder which had its sides sealed off one from another. The permeate gas being studied was introduced on one side and kept at a constant pressure of 0.10 MPa. On the other side the concentration of the gas was measured using a photoacoustic gas analyser as it was 

PET films are widely used as packaging material for food, pharmaceuticals, electronics and medical products because of its good mechanical properties. PET is known for its low gases and solvents permeability. However, in order to enhance its barrier properties, many approaches were developed crystallization, orientation, coating, metallization, copolymerization, incorporation of nanodispersed clay (2). 

Classical values of PET film permeability are given below (9). 

Oxygen permeability is influenced by the crystallinity of polymer because the diffusion of oxygen is affected by more tortuous path through polymer due to increased crystallinity, so that stretching causes the decrease of oxygen permeability. Incorporation of 

Amorphous PET Semi-crystalline PET PET loaded with 30 % glass fibers 

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Oriented polypropylene film has exceUent water-vapor barrier but poor gas barrier properties exceUent clarity, or opacity in newer forms and good heat-seal properties in packagiag appHcations. 

Nylon. Nylon is the designation for a family of thermoplastic polyamide materials which in film form are moderate-oxygen barriers. The gas-barrier properties are equal to odor and flavor barrier properties important in food appHcations. Nylon films are usually tough and thermoform able, but are only fain moisture barriers (see Polyamides). 

Ethylene vinyl acetate copolymer (EVA) forms a soft, tacky film with good water-vapor barrier but very poor gas-barrier properties. It is widely used as a low temperature initiation and broad-range, heat-sealing medium. The film also serves for lamination to other substrates for heat-sealing purposes. 

To enhance water-vapor- or gas-barrier properties, layers of different plastics may be injected together or sequentially. Multilayer injection-molded pieces may be prepared as packaging or for blowing into bottle or jar shapes. 

Gas-Barrier Properties. The oxygen-barrier properties of PVA at low humidity ate the best of any synthetic resin. However, barrier performance deteriorates above 60% th (Fig. 9). No additives or chemical modifiers are known that can effectively reduce moisture sensitivity. The gas-barrier performance is affected by the degree of hydrolysis and rapidly diminishes as the hydrolysis is decreased below 98%. 

Oil Repellent. Fluorochemicals are the only class of material that can provide oil repeUency without altering the porosity of the paper or paperboard. Physical barriers to oil penetration are used primarily for their moisture- or gas-barrier properties, with retarded oil penetration as a secondary benefit. The most common od-repeUent additives are long-chain perfluoroalkyl phosphate salts of ammonia or diethanol amine. Commercial sources include Scotchban (3M), Zonyl (DuPont), and Lodyne (Ciba Specialties). There are also a fluorochemical carboxylate salt, Lodyne (Ciba Specialties), and fluorochemical copolymers, eg, Scotchban (3M). The widest range of oily fluid holdout is provided by the fluorochemical copolymers. 

Certain copolymers of this type have been found to have excellent gas barrier properties, with the dry polymer having an oxygen permeability only about 1/lOth that of polyvinylidene chloride. Unsurprisingly, the copolymer has a high moisture absorption and a high moisture vapour transmission rate. Where the material is swollen by water, gas permeability is also higher. 

Because of the excellent gas barrier properties, EVOH is of interest as a packaging material. However, because of its high water absorption it is usually used as an internal layer in a co-extruded film, sheet, bottle or tube. For example, the system HDPE-EVOH-EVA may be used as a barrier film for packaging cereals, and the system polystyrene-EVOH-polystyrene for packaging coffee and cream, whilst the system polystyrene-EVOH-polyethylene has the additional advantage of heat scalability. 

It is likely that excellent gas barrier properties exhibited by nanocomposite polymer systems will result in their substantial use as packaging materials in fumre years. 

This stretching, similar to the drawing of fibres, which promotes orientation and crystallite formation, is called biaxial orientation. It gives the film added strength and gas-barrier properties. In some processes, monoaxial (uniaxial) drawing is employed, e.g., polypropylene, which is then slit into thin strips and fabricated into heavy duty sacks, carpet backing, etc. The stenter process is used to make biaxial oriented poly(vinylidene dichloride) ("ding" film), polyester, polyamide and polypropylene films. 

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... 

The two most important properties induced by surface fluorination of plastics, ie., permeation and adhesion, were patented by Joffre3 in 1957. His results proved that surface fluorination created excellent liquid as well as gas barrier properties. 

Apart from the benefits of excellent barrier properties with regard to the permeation of nonpolar liquids and good adhesion, little is known about the influence of surface fluorination on gas barrier properties. The permeability of only a few inorganic gases through surface-fluorinated plastics such as PE,19 PP, and PET20 have been evaluated to some extent. 

Table 7.1 Effect of cw-isomer content on the gas-barrier properties of PCT...

One impediment of universally applying PET in the area of packaging is its gas-barrier properties. These can be slightly improved by measures to increase the density (crystallinity) during blow molding, for example, by treatment with ultrasound. Ultrasonic treatment during injection reduces the gas permeability to a certain extent [34],... 

H. Wu, L. T. Drzal, Graphene nanoplatelet paper as a light-weight composite with excellent electrical and thermal conductivity and good gas barrier properties., Carbon, vol. 50,... 

PCTFE is appreciated for good chemical resistance exceptional low-temperature behaviour down to -240/250°C gas barrier properties excellent resistance to light, UV and... 

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