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In partially crystalline polymers

Addition of a plasticizer decreases the Tg of the polymer and, in partially crystalline polymers, also influences both crystallization and melting. The amount of plasticizer affects its effectiveness. Thus, while the Tg of the polymer is strongly depressed by small plasticizer additions, the increase in the plasticizer content leads to lower decrease in To and in several systems two T values can be found [36J. Therefore, the increase in the plasticizer content in polymers does not show a monotonic decrease in Tg. [Pg.627]

Determination of the proportions of crystalline and amorphous material in partially crystalline polymers. Knowledge of the unit cell dimensions in high polymer crystals leads to a knowledge of the density of the crystalline regions. If the density of amorphous regions is also known, either by measurement of the density of an entirely amorphous specimen (if this can be obtained) or by extrapolation of the liquid density/temperature curve, it is possible to calculate, from the measured density of any partially crystalline specimen, the proportions of crystalline and amorphous material. Since the physical properties of polymer specimens are profoundly influenced by the degree of crystallinity, X-ray determinations of crystallinity are much used in such studies (see Bunn, 1957). [Pg.200]

Fig. la-c. Schematic representation of typical morphology in partially crystalline polymers (a) stack of crystalline lamellae of thickness lc and amorphous regions of thickness la (L = long period) (b) spherulites formed by a radial symmetric arrangement of stacked lamellae, during main crystallization (c) spherulites after the end of main crystallization... [Pg.115]

The control of biodegradation rate is of critical importance for many applications of degradable polymers. Amorphous polyesters absorb water and hydrolyse much more rapidly than crystalline materials. Consequently, in partially crystalline polymers, hydrolysis occurs initially in the amorphous phase and continues more slowly in the crystalline phase. This selective degradation leads to an increase in crystallinity by chemicrystallisation. A very similar selective abiotic oxidation process occurs in the semi-crystalline polyolefins which fragment rapidly due to failure at the crystallite boundaries. [Pg.106]

The chemical nature of the cross-link points is quite unimportant to typical cross-linked network properties such as elasticity and swelling in solvents. Most chemical cross-linking occurs via covalent bonds, but cross-linking can also be achieved with coordinate or electron-deficient bonds. Cross-link-like effects can also be caused by purely physical phenomena, for example, by crystallite regions in partially crystalline polymers, amorphous domains in block polymers, or molecular entanglements in amorphous polymers and polymer melts. [Pg.57]

Differing states of order give rise to differing specific heats in crystalline and amorphous polymers. Presupposing a two-phase model, a degree of crystallinity can be calculated in partially crystalline polymers by means of the enthalpy, analogous to Equation (5-3) ... [Pg.161]

Oriented thermoplastics can show large anisotropy in creep behaviour, expecially in partially crystalline polymers. Significantly different patterns of behaviour occur in different materials. Not only is there anisotropy of isochronous stiffness, but also of creep rate and non-linearity. If stiffoess is regarded as a function of time, direction and stress or strain, the behaviour is such that the variables are not normally separable. [Pg.363]

In partially crystalline polymers the creep behaviour of the oriented material varies systematically with structure. Anisotropic creep studies on oriented materuds, whilst considerably more complicated, can more readily lead to understanding of deformation mechanisms than do creep studies in isotropic materials. [Pg.363]

High-impact-strength thermoplastics always consist of a hard and a pliable component. The two components may be chemically or physically different. In partially crystalline polymers, the hard component is the crystalline component and the pliable component is the amorphous component. On the other hand, the hard component may be a material with a higher glass-transition temperature and the pliable component may be a rubber [for example, poly(styrene)-poly(butadiene)]. The two incompatible... [Pg.455]

Glass Transition—The reversible change in an amorphous polymer or in amorphous regions in partially crystalline polymer from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one. [Pg.8]

Horas, J.A. and Rizzotto, M.G. (1996) Gas diffusion in partially crystalline polymers. Part 1 concentration dependence. /. Polymer Sci., Polymer Phys., 34, 1541. [Pg.276]

Fig. 10. Schematic representation of segregation of amorphous components in partially crystalline polymer blends depicting the location of residual crystallisable polymer and non-crystallisable polymer in the interlamellar and interfibrillar regions within spherulites and interspherulitic locations. Solid lines represent the crystallisable component and dotted lines the non-crystallisable component taken from [60]... Fig. 10. Schematic representation of segregation of amorphous components in partially crystalline polymer blends depicting the location of residual crystallisable polymer and non-crystallisable polymer in the interlamellar and interfibrillar regions within spherulites and interspherulitic locations. Solid lines represent the crystallisable component and dotted lines the non-crystallisable component taken from [60]...
Even if one solves the indexing problem and then proceeds with the analysis by an evaluation of measured reflection intensities, one cannot expect to achieve an accuracy in the crystal structure data which would be comparable to those of low molar mass compounds. This is not only a result of the lack of single crystals, but represents also a principal property In small crystallites, as they are found in partially crystalline polymers, lattice constants can be affected by their size. In many cases crystallites are not only limited in chain direction by the finite thickness of the crystalline lamellae but also laterally since polymer crystallites are often composed of mosaic blocks. Existence of these blocks is indicated in electron microscopic investigations on... [Pg.156]

Figure 6.15 SAXS patterns related to typical morphological textures in partially crystalline polymers. Adapted with permission from Ref. [36] 2005, Springer. Figure 6.15 SAXS patterns related to typical morphological textures in partially crystalline polymers. Adapted with permission from Ref. [36] 2005, Springer.
As has been demonstrated by Bodor [65], the number distribution of the crystalline particle size in partially crystalline polymers can be determined by a method related to line broadening of X-ray scattering peaks. Figure 6.17 shows the particle size distribution of a linear PE sample that was cooled down from the melt atl60°Ctol25°C. [Pg.341]

In addition to the crystalline (a ) relaxation, other (broader) relaxations are observed in partially crystalline polymers arising from the amorphous regions of the material. These relaxations are related to similar broad absorptions found in amorphous polymers except they are perturbed due to the proximity of amorphous and crystalline regions (see ref. 10 for the example of crystalline poly(ethylene terephthalate) and further discussion below). [Pg.613]


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