Poly shrinkage

Poly(methyl methacrylate) and poly(vinyl acetate) precipitate from the resin solution as it cures. This mechanism offsets the contraction in volume as the polyester resin cross-links, resulting in a nonshrinking thermoset. Other polymer additives such as poly(butylene adipate) provide similar shrinkage... 

Depending on the type of filter device, additional requirements may be made of the cloth. For example, in a plate-and-frame press, the sealing properties of cloths are very important. In this case, synthetic cloths are more applicable staple cloths, followed by poly filament and monofilament cloths. In leaf filters operating under vacuum and pressure, the cloth is pulled up onto rigid frames. Since the size of a cloth changes when in contact with the suspension, it should be pretreated to minimize shrinkage. 

The other severe problem in the application of PET regarding food containers or bottles is that these products cannot be hot-filled. This limitation is caused by the low Tg of PET, which causes shrinkage during hot-filling. Alternatively, multilayer containers can overcome the problems, but, however, at higher manufacturing costs. PET in combination with an intermediate layer of poly(ethylene-co-vinyl alcohol) (PEVOH) or polybutylene has been used in such... 

Low-profile additives are generally materials such as poly (vinyl acetate), polystyrene, polyethylene or polycarbonate. During the unsaturated polyester cure cycle, the low-profile additives separate into a second phase, which expand to counteract the shrinkage of the curing unsaturated polyester resin. Material development and the science of low-profile additives have helped create substantial markets for unsaturated polyesters. Their use in automotive markets, where Class A show room quality surfaces is a requirement, is an example of this. 

As one might expect the rate of p-nitrophenyl heptanoate hydrolysis increased at low ethanol concentrations as a result of apolar binding. The rate of p-nitrophenyl acetate hydrolysis also increased markedly at low ethanol concentration. This finding was explained by a conformational effect on the polymer, that is, lower ethanol concentration brings about a shrinkage of the polymer, which increases concerted interactions of the imidazole residues. The hydrolysis of 3-nitro-4-dodecanoyloxybenzoate was found to be 1700 times faster in the presence of poly[4(5)-vinylimidazole] compared to free imidazole (77). A double-displacement mechanism was demonstrated for this system (75). 

Dilatometry utilizes the volume change that occurs on polymerization. It is an accurate method for some chain polymerizations because there is often a high-volume shrinkage when monomer is converted to polymer. For example, the density of poly(methyl methacrylate) is 20.6% lower than that of its monomer. Polymerization is carried out in a calibrated reaction vessel and the volume recorded as a function of reaction time. Dilatometry is not useful for the usual step polymerization where there is a small molecule by-product that results in no significant volume change on polymerization. 

Since solvent evaporation and imidization in themselves are not destructive processes, the most crucial temperature regime lies between 150 °C and 250 °C. Here solvent removal and maximum imidization occurs simultaneously causing tremendous shrinkage and the creation of maximum stress in the polymer film. At this point it is not unusual to observe cracking problems in the polymer film, depending on the inherent mechanical properties of the partially cured poly-... 

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. 

Poly (vinyl chloride) fibers (PVC) [96, pp. 642-645], are characterized by their flame retardance. They are dyed preferably with disperse dyes [50, p. 404], [6, pp. 611], As with modacrylic fibers, high temperatures must not be used because of shrinkage of the PVC fiber. Hence, some fibers are dyed at 60-65 °C with dyeing accelerants. Other PVC fibers can be dyed at 100°C without a carrier and a few even at 110°C. Dyes must be selected with regard to the lightfastness desired. 

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