Amorphous part

Highest thermal performance with PPS compounds requires that parts be molded under conditions leading to a high level of crystallinity. Glass-filled PPS compounds can be molded so that crystalline or amorphous parts are obtained. Mold temperature influences the crystallinity of PPS parts. Mold temperatures below approximately 93°C produce parts with low crystallinity and those above approximately 135°C produce highly crystalline parts. Mold temperatures between 93 and 135°C yield parts with an intermediate level of crystallinity. Part thickness may also influence the level of crystallinity. Thinner parts are more responsive to mold temperature. Thicker parts may have skin-core effects. When thick parts are molded in a cold mold the skin may not develop much crystallinity. The interior of the part, which remains hot for a longer period of time, may develop higher levels of crystallinity. 

Polycarbonates. Polycarbonates (qv) are pardy crystalline thermoplastics with some disorder in the crystalline part and considerable order in the amorphous part. This disorder conveys high impact strength which, combined with its good transparency and outdoor exposure resistance, makes polycarbonates usefiil for vandal-resistant glazing and outdoor lighting. It is easily processed by extmsion and injection mol ding. Various uv and dame-retardant agents are often added. 

Figure 8.10. A sample of rubber treated to make it half crystalline, half amorphous. On stretching, measurable extension is restricted to the amorphous part (after Treloar 1970).

The volume inside the semicrystalline polymers can be divided between the crystallized and amorphous parts of the polymer. The crystalline part usually forms a complicated network in the matrix of the amorphous polymer. A visualization of a single-polymer crystallite done [111] by the Atomic Force Microscopy (AFM) is shown in Fig. 9. The most common morphology observable in the semicrystalline polymer is that of a spherulitic microstructure [112], where the crystalline lamellae grows more or less radially from the central nucleus in all directions. The different crystal lamellae can nucleate separately... 

Although it has been found that the separated amylose component can be readily orientated to yield fiber patterns, amylopectin usually gives poor or amorphous patterns. In the granule, however, amylopectin does exhibit crystallinity, since waxy maize starch gives a diffraction pattern and other waxy starches behave similarly.193 -195 (This suggests that the branch points in the amylopectin molecule may be in the amorphous part of the granule.)... 

It is generally believed that the physical state of the amylose component is amorphous and therefore it is found in the amorphous parts of the granules. It is, however, not separated from the amylopectin component. By chemically cross-linking the polymers, it was shown that amylose... 

Sometimes, the effect of adding an inactive to an active metal was surprisingly small usually it was with metals on carrier. We suspect that in these cases a small (X-ray diffraction-) amorphous part of the active metal was present unalloyed. Another point is that an inactive metal might be actually active, at least moderately, in particular in cooperation with an active Group VIII metal. This is probably the case with some Cu alloys (168). 

For the PVN-PEO polyblends, volume changes at melting temperature (Figure 6) as well as x-ray data at room temperature (2) show that the 25% (PEO) blend is completely amorphous, and that the 50 and 75% blends contain significant amounts of amorphous PEO. Calculations based on specific volume data indicate that the crystalline part of both the 50 and 75% blends consists of PEO, whereas the amorphous part contains 46% PEO and 54% PVN. Another important result is that the unusual phenomenon of a well in the modulus temperature curves (Figure 1) was observed only for the blends which exhibit crystallinity. Based on these observations, the behavior of blends could be interpreted by postulating that the amorphous PEO forms a complex phase with PVN in the ratio of 3 to 1 monomer units (i.e., 46 wt. % PEO to 54 wt. % PVN), respectively. 

With A U = 2 kcal/gmol we find 2°g = 200 K for x - 1 (complete state of disorder) and 400 K for x = 0.5. In the case of partially crystalline material, the glass transition temperature exists only for the amorphous part. 

Three questions concerning ultrastabilization remain outstanding. They regard the precise mechanism of A1 removal, the nature of the intermediate defect structure (both are depicted schematically in Fig. 38), and the origin of the silicon needed for framework reconstruction. Gas sorption studies (172) indicate that materials prepared in a manner similar to that for sample 4 in ref. 163 (see above) contain a secondary mesopore system with pore radii in the range IS-19 A, suggesting that tetrahedral sites are reconstituted with silicon that, contrary to earlier speculations, does not come only from the surface or from amorphous parts of the sample, but also from its bulk, which may involve the elimination of the entire sodalite cages. 

MacGillavry, C. H. Anisotropy in the so-called amorphous part of polyvinyl alcohol. Rec. trav. chim. 69, 509—514 (1950). 

The equilibrium ratio polymer/monomer is the same in the base catalysed polymerization as in the hydrolytic process (43, 94) and so is the equilibrium content of cyclic oligomers in both processes (43). Using the extremely fast basic polymerization it was made possible to follow the equilibrium in the range of very low temperatures, where it was hardly possible before. It was found that in polymers which were prepared below their melting point, the monomer content is essentially lower than would be expected from the extrapolation of the temperature depend-ence of the equilibrium monomer content obtained at higher temperatures (94) (fig. 5). This indicates that the crystaline fraction of the polymer does not participate in the equilibrium. It is possible to establish the concentration of the amorphous part independently, e. g. 

In literature opinions differ on the mineral compostition. This composition is determined with the help of X-ray diffraction, but this cannot be used for the amorphous part and there lies the origin of... 

Recent advances in the methods used for evaluating fibre diffraction patterns place importance on matching the whole pattern (16). The methods used for calculating the scattering for the models described above could be extended to model the amorphous part of the pattern prior to subtraction or matching the calculated structure. 

It is believed that chain scission occurs through simple hydrolysis, but the kinetics of this hydrolysis are influenced by anions, cations, and enzymes [190]. The process is autocatalytic and the products of hydrolysis such as carboxylic groups participate in the transition state. Water preferentially enters the amorphous parts but crystalline domains are also affected [125]. The degradation of aliphatic polyesters is believed to be dominated by a hydrolytic mechanism but it is also promoted by enzymatic activities [4,7,191-193]. 

Sometimes crystallization is possible in the solid state polymers are, however, never totally crystalline, but are still partly amorphous. The amorphous part may be above or below Tg, i.e. in the rubbery or in the glassy condition. 

A partially crystalline polymer could follow curve c at Tm the amorphous part passes into a rubber, the crystalline part is unaffected. The actual curve resembles more curve d, i.a. as a result of a broad melting region. 

After what has been said about the T-t equivalence, it is not surprising that the time dependency of E resembles the T-de pendency, which we have considered in detail before. In (log t) we see, indeed, the same phases and transitions as in E(T) (Figure 6.17). It should be remarked that this time-temperature equivalence only holds for amorphous polymers or for the amorphous part in semi-crystalline polymers. 

Crystallite sizes are of order 102-103A. The amorphous parts of the material are in a fluid state at T > Tg and in a glassy state at T < Tg. 

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