Elastic films

Resins vary from soft, elastic, film-forming materials to hard plastics. 

Tamarind kernel powder is insoluble in cold water, but upon heating forms thick viscous coUoidal dispersions at relatively low concentrations (2—3%). Upon drying, elastic films are formed. Tamarind seed polysaccharide is used as a low cost textile sizing agent in India. 

Oilseed proteins are used as food ingredients at concentrations of 1—2% to nearly 100%. At low concentrations, the proteins are added primarily for their functional properties, eg, emulsification, fat absorption, water absorption, texture, dough formation, adhesion, cohesion, elasticity, film formation, and aeration (86) (see Food processing). Because of high protein contents, textured flours and concentrates are used as the principal ingredients of some meat substitutes. 

Anionic polymerization of pivalolactone with the polystyrene anion produced only homopolymer mixtures, but the polystyrene carboxylate anion was able to give a block copolymer336. The block efficiency depends on catalyst ratio and conversion because the initiation step is slow compared with propagation337. Tough and elastic films were obtained by graft copolymerization or block copolymerization of pivalolactone onto elastomers containing tetrabutylammonium carboxylate groups338,339. ... 

Lower-density E-plastomers have found alternate use in cast film processes to make elastic film laminates with good breathability which contain laminates of liquid impermeable extensible polymeric films with extensible-thermoplastic-polymer-fiber nonwovens and nonwoven webs of polyethylene-elastomer fibers as the intermediate layers. The development relates to a breathable film including an E-plastomer and filler that contributes to pore formation after fabrication and distension of the film. The method and extent of distension is designed to produce a breathable film by stretching the film to form micropores by separation of the film of the E-plastomer from the particulate solids. This film is useful for manufacture of absorbent personal-care articles, such as disposable diapers and sanitary napkins and medical garments. In detail, these constructions comprise a liquid impermeable extensible film comprising polyolefins. The outer layer contains extensible-thermoplastic-polymer-fiber nonwovens, and an elastic intermediate layer contains nonwoven webs of fiber E-plastomers. The intermediate layer is bonded to the film layer and the outer... 

When there is a high percentage of proteins, such as in gelatin—which will form an elastic film in conjunction with corn sirup and other sugar products—stability is not too much of a problem. In freshly whipped egg or vegetable protein foams, frappes, or mazettas, in which the foam product is incorporated as part of a complete food batch, the foam is assimilated before its stability becomes a factor and further processing tends to stabilize the foam. 

Another observation should be made with respect to the term elastic in describing interfacial capacitors. It was originally introduced by Crowley [1] for membranes and reflects the compressibility of lipid layers which behave in some respects like an elastic film. Its relation to electrochemical interfaces is less obvious. Consider an interface between a metal electrode and an electrolyte. As we will see in Section III, the effective gap of the interfacial capacitor is the distance between the centers of mass of the electronic, e, and ionic, i, charge density distributions... 

There are now many synthetic polymeric materials available for film coating, many of which meet all the requirements of a good film former. These include lack of toxicity and a suitable solubility profile for film application and upon ingestion, together with the ability to produce a tough, yet elastic film even in the presence of powdered additives such as pigments. The film must, of course, be stable to heat, light, and moisture and be free from undesirable taste or odor. 

In addition to electric charge between particles other factors are in some cases operative in preventing actual contact, thus the medium may be strongly adsorbed by the surface, and the thin film may not readily be displaced on collision of the two neutral particles, in other cases a tough elastic film may be formed, possessing definite mechanical strength and necessitating a violent impact to ensure rupture. 

THE SURFACE OF LIQUID WATER BEHAVES LIKE AN ELASTIC FILM... 

The possibility for the existence of mesophase in a rubbery state 36,46), typical only for macromolecular compounds with their natural ability to display big reversible deformations, reveals interesting prospects from the viewpoint of creation of new types of liquid-crystalline materials in the form of elastic films, as well as for development of the theory of viscoelastic behaviour of such unusual elastomers. 

Surfactants form semiflexible elastic films at interfaces. In general, the Gibbs free energy of a surfactant film depends on its curvature. Here we are not talking about the indirect effect of the Laplace pressure but a real mechanical effect. In fact, the interfacial tension of most microemulsions is very small so that the Laplace pressure is low. Since the curvature plays such an important role, it is useful to introduce two parameters, the principal curvatures... 

Huang R (2005) Kinetic wrinkling of an elastic film on a viscoelastic substrate. J Mech Phys Solids 53 63-89... 

Low internal phase emulsions typically result when high shear conditions are used for emulsification, while low shear mixing can lead to high internal phase, or concentrated, emulsions [435]. There are several conditions needed to form a concentrated emulsion. Low shear mixing is required while the internal phase is slowly added to the continuous phase, and the surfactants used to create the emulsion need to be able to form elastic films [435—438]. The formation of concentrated emulsions has also been linked to surfactant-oil phase interactions [436] and therefore the oil-water interfacial tension and the potential for surfactant-surfactant interactions [439]. 

Air-water interface Surface tension Film elasticity Film viscosity Foam generation... 

Fig. 15 A/S)C vs./s for a roughly purely elastic film (upper) and a nearly perfectly viscous film (lower) are represented by the shaded area, where the conditions are the same as those of Fig. 4...

Films are either coextruded [12] or printed on the back of a very transparent material. The binder of these screen inks or gravure inks has to have a high melting point or crosslinking to form an elastic film to avoid being replaced by the hot injected polymer. It is also possible to coat the backside of the film with an adhesion promoter, which prevents direct contact between the printed area and the polymer. This coating can also improve the adhesion between the film and the injection-molded part [13]. 

We have described a semiquantitative method for the measurement of the intrinsic bond strength between elastic substrates and elastic films that fail by brittle fracture. The essential features of the analysis, adapted from AR, were verified by measurements on the PET-Ni couple. The precision of the technique was 6%, in this case. The interfacial shear strength of Ni on PET doubled after ion etching, reaching about 10 kg/mm. ... 

Equating real and imaginary parts of Equation 3.58 yields velocity and attenuation changes resulting from the SAW/film interaction. With elastic films, the intrinsic elastic moduli are real, resulting in real 0 and imaginary liy/ko, so that Aa/ko = 0. Substituting the ( > expressions written in terms of the Lame constants (A, fi) from Table 3.3 into Equation 3.58 yields the Tiersten formula [52]... 

Modified polyurethanes as shown in Fig. 4.6 are used for valuable hand variations and as additives for cellulose crosslinkers. Their flexible and elastic films on the fibre surface improve elastic resilience, which is, for example, important for pile fabrics. The principle of their elasticity is, as in elastan fibres, the molecular combination of so-called weak and hard segments. The large weak... 

The chemical structures of the lipid studied are shown in the Fig. 1. There are two different types of behavior for monolayers from those lipid mixtures (i) solid film formation with relatively low pressure of a collapse (cholesterol rich monolayers) and (ii) viscous elastic film formation, when the concentration of CHL is less 30% in the monolayer. The character of the behavior of a monolayer is quite similar upon replacing of CHL by Q3P, though the LB film morphology is essentially different. 

The preparation of the first starch acetate, as well as the first cellulose acetate, was announced by SchUtzenberger in 1865. These acetates were prepared by heating the carbohydrates in acetic anhydride to about 140-160 . Further examination of this reaction has been made by Traquair who found that on heating starch to 90° with acetic anhydride a derivative of low acetyl content (1-4%) is obtained which is capable of forming clear, somewhat elastic films. This starch acetate, termed Feculose, was produced commercially for a time, being sold for use as a thickening agent and as a size for textiles and paper. 

Usually creep test results are expressed in terms of the compliance J° = Axlt)/Ay ylt). For an ideally elastic interface J° =1/G°. However, for visco elastic films J°(t) l/G lt). General relations exist by which J°(t) can be converted into G (t) and vice versa, but for an accurate conversion J°(t) has to be known over quite a long range of time. In dilation, creep tests are hard to perform except for elastic interfaces, because in such a test a constant Ay should be applied to the interface and this is experimentally very difficult. 

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