Amorphous deformation

Jakeways et al. [69] addressed only the crystalline chain deformation to explain PTT s elastic recovery. The macroscopic deformation must also simultaneously involve the partially irreversible amorphous chain deformation. The higher the applied strain, then the more dominant was the irreversible amorphous deformation with deviation from affine deformation. 

K. Kong and S.J. Eichhom, Crystalline and amorphous deformation of process-controlled cellulose-II fibres. Polymer, 46, 6380-6390 (2005). 

The Young equation is a well-known special case of Eq. (5.75) valid for the contact of an amorphous, deformable phase (1) with a rigid phase (s) and a gas phase (g)... 

The melt temperature of a polyurethane is important for processibiUty. Melting should occur well below the decomposition temperature. Below the glass-transition temperature the molecular motion is frozen, and the material is only able to undergo small-scale elastic deformations. For amorphous polyurethane elastomers, the T of the soft segment is ca —50 to —60 " C, whereas for the amorphous hard segment, T is in the 20—100°C range. The T and T of the mote common macrodiols used in the manufacture of TPU are Hsted in Table 2. 

Linear-amorphous polymers (like PMMA or PS) show five regimes of deformation in each of which the modulus has certain characteristics, illustrated by Fig. 23.1. They are ... 

The Phillips Corporation have recently introduced interesting copolymers related to PPS. In addition to the use of p-dichlorobenzene and Na2S, a second aromatic dichloro compound is used. For the marketed material PAS-2 this is 4,4 -dichlorodiphenylsulphone whilst for the developmental products PAS-1 and PAS-B the compounds are 4,4 -dichlorodiphenyl and 4,4 -dichlorodiphenyl-ketone. Each of these copolymers is amorphous, so that a high heat deformation resistance requires a high value for. ... 

It was ironic that a few years later, Rosenhain began to insist that the material inside the slip bands (i.e., between the layers of unaffected crystal) had become amorphous and that this accounted for the progressive hardening of metals as they were increasingly deformed there was no instrument to test this hypothesis and so it was unfruitful, but none the less hotly defended ... 

Typically, a semicrystalline polymer has an amorphous component which is in the elastomeric (rubbery) temperature range - see Section 8.5.1 - and thus behaves elastically, and a crystalline component which deforms plastically when stressed. Typically, again, the crystalline component strain-hardens intensely this is how some polymer fibres (Section 8.4.5) acquire their extreme strength on drawing. 

The mode of action of plasticizers can be explained using the Gel theory [35 ]. According to this theory, the deformation resistance of amorphous polymers can be ascribed to the cross-links between active centres which are continuously formed and destroyed. The cross-links are constituted by micro-aggregates or crystallites of small size. When a plasticizer is added, its molecules also participate in the breaking down and re-forming of these cross-links. As a consequence, a proportion of the active centres of the polymer are solvated and do not become available for polymer-to-polymer links, the polymer structure being correspondingly loosened. 

In one of the most significant observations, small amounts of recrystallized material were observed in rutile at shock pressure of 16 GPa and 500 °C. Earlier studies in which shock-modified rutile were annealed showed that recovery was preferred to recrystallization. Such recrystallization is characteristic of heavily deformed ceramics. There has been speculation that, as the dislocation density increases, amorphous materials would be produced by shock deformation. Apparently, the behavior actually observed is that of recrystallization there is no evidence in any of the work for the formation of amorphous materials due to shock modification. Similar recrystallization behavior has also been observed in shock-modified zirconia. 

In the studies carried out by one of the authors [52], the values of Ea and E were determined for PET fibers of the microfibrillar and of the lamellar substructure. The results have been presented in Tables 8 and 9. The results obtained show that for both types of substructure the resistance to deformation, that is, the value of E, depends on the degree of molecular orientation of the amorphous material of the fiber fa) and the density of this amorphous phase of the fiber da)- However, this dependence assumes a different form for the microfibrillar and for the lamellar substructure. In the first case, it has the form ... 

Stress-corrosion cracking based on active-path corrosion of amorphous alloys has so far only been found when alloys of very low corrosion resistance are corroded under very high applied stresses . However, when the corrosion resistance is sufficiently high, plastic deformation does not affect the passive current density or the pitting potential , and hence amorphous alloys are immune from stress-corrosion cracking. 

There is greater similarity in the behavior of stretched melts and solid samples prepared by, e.g. pressure molding, probably, for the reason of parallelism in structure formation and destruction caused by deformation in melts and the amorphous regions of solid matrices. It is also possible to use identical equations for longitudinal viscosity and strength which present them as functions of the filler concentration [34]. 

Crazing. This develops in such amorphous plastics as acrylics, PVCs, PS, and PCs as creep deformation enters the rupture phase. Crazes start sooner under high stress levels. Crazing occurs in crystalline plastics, but in those its onset is not readily visible. It also occurs in most fiber-reinforced plastics, at the time-dependent knee in the stress-strain curve. 

Glassy state In amorphous plastics, below the Tg, cooperative molecular chain motions are frozen , so that only limited local motions are possible. Material behaves mainly elastically since stress causes only limited bond angle deformations and stretching. Thus, it is hard, rigid, and often brittle. 

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