Soft elasticity

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

In the massive form poly(vinyl chloride) is a colourless rigid material with limited heat stability and with a tendency to adhere to metallic surfaces when heated. For these, and other, reasons it is necessary to compound the polymer with other ingredients to make useful plastics materials. By such means it is possible to produce a wide range of products, including rigid piping and soft elastic cellular materials. 

It has been also shown that when a thin polymer film is directly coated onto a substrate with a low modulus ( < 10 MPa), if the contact radius to layer thickness ratio is large (afh> 20), the surface layer will make a negligible contribution to the stiffness of the system and the layered solid system acts as a homogeneous half-space of substrate material while the surface and interfacial properties are governed by those of the layer [32,33]. The extension of the JKR theory to such layered bodies has two important implications. Firstly, hard and opaque materials can be coated on soft and clear substrates which deform more readily by small surface forces. Secondly, viscoelastic materials can be coated on soft elastic substrates, thereby reducing their time-dependent effects. 

In the JKR experiments, a macroscopic spherical cap of a soft, elastic material is in contact with a planar surface. In these experiments, the contact radius is measured as a function of the applied load (a versus P) using an optical microscope, and the interfacial adhesion (W) is determined using Eqs. 11 and 16. In their original work, Johnson et al. [6] measured a versus P between a rubber-rubber interface, and the interface between crosslinked silicone rubber sphere and poly(methyl methacrylate) flat. The apparatus used for these measurements was fairly simple. The contact radius was measured using a simple optical microscope. This type of measurement is particularly suitable for soft elastic materials. 

Pa, would deform appreciably under the action of loads comparable to the pull-off force given by Eq. 16. It is for this reason that the JKR type measurements are usually done on soft elastic materials such as crosslinked PI rubber [45,46] or crosslinked PDMS [42-44,47-50]. However glassy polymers such as polystyrene (PS) and PMMA are relatively hard, with bulk moduli of the order of 10 Pa. It can be seen from Eq. 11 that a varies as Thus, increasing K a factor of... 

With natural rubber and c/5-polyisoprene the normal cross linking agent used is sulphur. When mixed with natural rubber and heated, the sulphur reacts with the alpha methylenic carbon atoms of adjacent molecules, predominantly by S, and Sj cross links. If a low percentage of sulphur is added, normally about 2% by weight on the rubber, the end product is a soft elastic material. 

One of the important aspects of the development of P-plastomers was the expectation that these materials were amenable to plastics processing such as fiber and film formation and yet would yield soft elastic fabrication. This combination was hitherto unknown [24]. The formation of nonwoven fabrics including spun-bond and melt-blown nonwoven fabrics as well as their laminated forms has been documented. Similarly, cast film operation to form elastic monolithic films or composite structures which are not only amenable to these processes, but also to a variety of postfabrication processes have been described. 

WR Ebert. Soft elastic gelatin capsules a unique dosage form. Pharm Tech 1(10) 44—50, 1977. 

S Vemuri. Measurement of soft elastic gelatin capsule firmness with a universal testing machine. Drug Dev Ind Pharm 10 409 424, 1984. 

The mechanical properties also depend on the relative block lengths. For instance, Fluoro-PSB-II is a soft, elastic material. Differential scanning calorimetry (DSC) measurements and wide-angle X-ray scattering (WAXS)... 

PVA must be cross-linked in order to be useful for a wide variety of applications. A hydrogel can be described as a hydrophilic, cross-linked polymer, which can sorbe a great amount of water by swelling, without being soluble in water. Other specific features of hydrogels are their soft elastic properties, and their good mechanical stability, independent of the shape (rods, membranes, microspheres, etc.). 

Of these three PP isomers (called that because they all have the same formula, just different stereoconfigurations), isotactic makes the best plastic. Atactic polypropylene is soft, elastic, and rubbery but not as good as rubber, natural, or synthetic. It is usually separated from the isotactic propylene and discarded as waste, which adds considerable cost to the remaining isotactic. The iso tactic form has a high degree of crystallinity with the chains packed... 

The mechanics of surface wrinkling necessitate that there be a reasonable modulus difference between the film of interest and the soft substrate (Es 2MPa for PDMS). In order to probe softer materials, the wrinkling metrology can be inverted, such that a sensor film of known modulus is adhered to a soft substrate of unknown modulus. Rearrangement of (1) leads to the following expression for the modulus of the soft, elastic substrate ... 

The average of the soft elastic force with respect to variations... 

Valproic acid is a carboxylic acid designated as 2-propyl-pentanoic acid. It is also known as dipropylacetic acid. Capsules and syrup are antiepileptics for oral administration. Each soft elastic capsule contains 250 mg valproic acid. 

There are striking differences in physical properties between the atactic and isotactic forms. The atactic material is soft, elastic, somewhat sticky, and rather soluble in solvents such as 1,1,2,2-tetrachloroethane. Isotactic polypropene is a hard, clear, strong crystalline polymer that melts at 175°. It is practically insoluble in all organic solvents at room temperature, but will dissolve to the extent of a few percent in hot 1,1,2,2-tetrachloroethane. That the difference between the atactic and isotactic polymers arises from differences in the configurations of the methyl groups on the chains is shown in a... 

Good bread should have a pleasant odour and a crust which is brownish, shining, uniform and adherent to the crumb. The latter should be more or less white (according to the extent to which the offals are separated), soft, elastic, porous, homogeneous, free from spots, and of pleasant, non-add taste. 

Ebert W.R. 1977. Soft elastic gelatin capsules A unique dosage Rtim/naceutical Technology, 1(10) 44. 

Vemuri S. 1984. Measurement of soft elastic gelatin capsinteness with a universal testing machiBeug Development and Industrial Pharmacy, 10 409-423. 

Groenewold J (2001) Wrinkling of plates coupled with soft elastic media. Physica A 298 32—45... 

R. A. Kenley, S. Chandry, and G. A. Visor, Multidimensional column-switching liquid chromatographic method for dissolution testing of enprostil soft elastic gelatin capsules, J. Pharm. Sci., 75 999 (1986). 

A three-column ion-exchange and reversed-phase system has been developed for the assay of enprostil in soft elastic gelatin capsules [336]. A two-column approach has also been used to resolve D,L-amino acids in complex matrices [337]. Erythromycin A and its known impurities were resolved using two C18 columns [338]. 

Rubber materials are soft, elastic solids, made of mobile, flexible polymer chains (with a glass transition temperature (Tg) typically lower than 0 °C) which are linked together to form a three-dimensional network. They are characterised by a low, frequency independent elastic modulus (of the order 105 to 106 Pa) and usually by a large maximum reversible deformation (up to a few hundred per cent). Rubber elasticity is based on the properties of crosslinked polymer chains at large spatial scales, the presence of crosslinks ensures the reversibility of the deformation, while at short scales, mobile polymer chains behave as molecular, entropic springs. 

Vicunas are smaller than llamas, and adults weigh only about 100 pounds. Hairs from this animal are the finest or thinnest known, about 1/2000 inches in diameter. Like other camel relatives, the vicuna has a layered coat. The innermost hairs are extremely soft, elastic, and have a strongly cohesive outer surface. This last property makes these fibers resistant to dyes, stains, and water. As these animals are small, and their hair so fine, it takes fleece from about forty vicuna to make one coat. 

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