Crystallinity ultimate degree

If PCT is modified with relatively high levels of comonomer, substantially amorphous materials result (see the following sections on PETG, PCTG and PCTA). However, it is possible to maintain crystallinity at lower levels of modification. For example, replacing up to about 10mol% of the terephthalate units with isophthalate results in a polymer with reasonable crystallization rates and ultimate degrees of crystallinity. 

From the IR measurements we have obtained the crystallization halftimes of each component in the blends at the different temperatures they are plotted in Figures 13, 14, 15, 16, and 17. They can be transformed into the crystallization rate vs. temperature of crystallization for the different blends, which are plotted in Figures 18, 19, 20, and 21. From the density—IR correlation we obtained the ultimate degrees of crystallinity of each component in the blends, and their change with blend composition is plotted in Figures 22 and 23. Since the crystallization behavior varies with temperature of crystallization, we will approach its interpretation looking at the behavior at each crystallization temperature separately. 

The interpretation of the effect of the difference between Tc and Tg on the ultimate degree of crystallinity depends on the approach taken to explain the nature of the Tg. In terms of a free-volume theory, one expects always to obtain the same ultimate degree of crystallinity regardless of the annealing temperature the only difference will be that the crystallization will proceed at a higher rate at high annealing temperatures. 

Figure 26. PET ultimate degree of crystallinity vs. PET percent in samples crystallized from glass (X) or melt (0) at 110°C...

It is expected that if trans esterification occurs, the intrinsic viscosity of the samples will decrease and the rates of crystallization and ultimate degrees of crystallinity will also decrease. Therefore a series of studies on the 50/50 blend which was kept in the melt for 2, 3, 5, 7, and 10 minutes were performed. The crystallization was followed by DSC and IR. Simultaneous measurements of the intrinsic viscosity were made on a 40 60 mixture of 1,1,2,2,-tetrachloroethane phenol. The results are plotted in Figures 28, 29, and 30. 

Xr Degree of crystallinity at time = t Ultimate degree of crys- ... 

The effects of isothermal crystallization at various temperatures on the ultimate degree of crystallinity and crystallization rate of high density polyethylene are illustrated in Figures 28 and 29. 

The properties of PHAs are dependent on their monomer composition and therefore it is of great interest that recent research has revealed that, in addition to PHB, a large variety of PHAs can be synthesized microbially. The monomer composition of PHAs depends on the nature of the carbon source and microorganism used. PHB is a typical highly crystalline thermoplastic whereas medium chain length PHAs are elastomers with low melting points and a relatively lower degree of crystallinity. By (chemical) modification of the PHAs, the ultimate properties of the materials can be adjusted even further, when necessary. 

It is probable that varying degrees of ordering of chains exist in a cellulosic material and that a sharp differentiation of crystalline and non-crystalline celluloses may not be feasible or even possible. Theoretically, the lateral surfaces of crystallites are amorphous but may have far less importance in determining such properties as strength, flexibility and extensibility than the non-crystalline cellulose which supplies continuity of structure in the direction of crystallite orientation. Yet properties like moisture absorption and swelling may be more dependent upon the amount of cellulose which exceeds a certain degree of disorder (permeability) than upon location. The definition of crystallinity may, therefore, be made ultimately in terms of practical objectives. 

Crystallinity and disorder are important structural parameters for understanding relationships between structure and physical properties. Flaws and distortions are the main features that limit the ultimate properties of textile fibers. Some of these crazes, cracks and voids are revealed under the electron microscope, either on the surface or in cross sections stained with heavy metals (J, 2). However, these staining techniques (that reveal the main morphological features) make it much more difficult to determine the degree of distortion of the crystalline fraction. Theoretically, line profile studies permit separation of effects due to crystalline size from those due to structural distortions. However, the lack of peaks in semicrystalline fiber x-ray patterns hinders that approach. 

POM has high values in yield strength and modulus and a low value in ultimate elongation owing to the high degree of crystallinity... 

The increase in both yield strength and modulus, and the decrease of ultimate elongation suggest that the degree of crystallinity of Nylon 66 has been increased during the treatments at both conditions. No significant difference has been found between two treatment conditions in terms of these three mechanical properties. 

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