Weak amorphous

As manufactured, PET is a relatively weak, amorphous (non-crystalline) polymer which has to be crystallised and orientated by stretching to give it its textile properties. Orientation is carried out during the spinning operation. Equally important nowadays is the use of PET as a replacement for glass in soft drink bottles. Although more expensive than the polyolefins or PVC, it has a distinctive appearance and can be readily separated from a waste stream. Its recovery for recycling will be discussed in Chapter 4. 

After preparation, polymeric gels typically consist of a weak amorphous solid structure containing an interconnected network of very fine pores filled with... 

Fumkawa et al. [140] reported that PHB and PHBHHx were immiscible in PLLA. However, PLA was more compatible with PHBHHx than with PHB. The Tg of PLA and PHBHHx did not change significantly. The of PLLA in the PHB/PLLA and PHBHHx/PLLA blends shifted, respectively, to lower and higher temperatures with an increase in the PHB or PHBHHx component. IR spectra of the blends were analyzed and weak amorphous bands of PLLA were observed in the spectra of the 80/20 PHBHHx/ PLLA blend. Amorphous bands of PHBHHx were not observed in the spectra of the 20/80 PHBHHx/PLLA blend. 

The term cracking at simultaneous action of stress and environment was introduced for polymers (mainly polyethylenes) being in stressed state at mobile polar liquids presence. It has been shown [17], that in the end the most weak amorphous part of semicrystalline polymer is responsible for materials strength at this fracture kind. This allows to connect occurring at cracking phenomena to polar liquid diffusion in amorphous regions. 

High temperature (>1000°C) properties of the HPSN s is controlled by the second phase [9-11]. In order to improve the high temperature properties (e.g. creep, subcritical crack growth, oxidation) of the HPSN materials, the effects of the weak amorphous second phase must be minimized. Research, done by others in order to improve the second phase effects, involved ... 

Extrusion Resins. Extmsion of VDC—VC copolymers is the main fabrication technique for filaments, films, rods, and tubing or pipe, and involves the same concerns for thermal degradation, streamlined flow, and noncatalytic materials of constmction as described for injection-molding resins (84,122). The plastic leaves the extmsion die in a completely amorphous condition and is maintained in this state by quenching in a water bath to about 10°C, thereby inhibiting recrystallization. In this state, the plastic is soft, weak, and pHable. If it is allowed to remain at room temperature, it hardens gradually and recrystallizes partially at a slow rate with a random crystal arrangement. Heat treatment can be used to recrystallize at controlled rates. 

The properties of elastomeric materials are also greatly iafluenced by the presence of strong interchain, ie, iatermolecular, forces which can result ia the formation of crystalline domains. Thus the elastomeric properties are those of an amorphous material having weak interchain iateractions and hence no crystallisation. At the other extreme of polymer properties are fiber-forming polymers, such as nylon, which when properly oriented lead to the formation of permanent, crystalline fibers. In between these two extremes is a whole range of polymers, from purely amorphous elastomers to partially crystalline plastics, such as polyethylene, polypropylene, polycarbonates, etc. 

If the weak bonding model is valid for high angle grain boundaries (>20°) it follows that diffusion in amorphous preparations of a given material should also show this measure of enhanced diffusion, when compared widr die crystalline material. 

Fig. 23.2. A schematic of o linear-amorphous polymer, showing the strong covalent bonds (full lines) and the weak secondary bonds (dotted lines). When the polymer is loaded below Tg, it is the secondary bonds which stretch.

Synthetic rubber (elastomers) are high molecular weight polymers with long flexible chains and weak intermolecular forces. They have low crystallinity (highly amorphous) in the unstressed state, segmental mobility, and high reversible elasticity. Elastomers are usually cross-linked to impart strength. 

According to Hosemann-Bonart s model8), an oriented polymeric material consists of plate-like more or less curved folded lamellae extended mostly in the direction normal to that of the sample orientation so that the chain orientation in these crystalline formations coincides with the stretching direction. These lamellae are connected with each other by some amount of tie chains, but most chains emerge from the crystal bend and return to the same crystal-forming folds. If this model adequately describes the structure of oriented systems, the mechanical properties in the longitudinal direction are expected to be mainly determined by the number and properties of tie chains in the amorphous regions that are the weak spots of the oriented system (as compared to the crystallite)9). 

Ethylnitrolic acid is an expl compd and forms numerous metallic salts, some of which are expls Potassium Salt. KC2H303N2, colorl amorph powder, si sol in methanol a weak expl Silver Salt. AgC2H303N2) white amorph powder, insol in w and dil ale. Sensitive to light,... 

Fig. 28 Raman spectra of polymeric sulfur (S ) prepared by various methods [109,173], of large disordered rings (S ) [182], and of photo-induced amorphous sulfur (a-S) [119], respectively. The spectrum of a-S has been smoothed for clarity. The position of the stretching vibration of a-S is pressure-shifted to higher wavenumbers. The very weak signals in the spectra of Sj, at ca. 150 and 220 cm are probably caused by the presence of Sg. In addition, the weak shoulder at ca. 470 cm observed in spectra of Sj, may originate from Sg, too...

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