Semi-crystalline character

PET fibers in final form are semi-crystalline polymeric objects of an axial orientation of structural elements, characterized by the rotational symmetry of their location in relation to the geometrical axis of the fiber. The semi-crystalline character manifests itself in the occurrence of three qualitatively different polymeric phases crystalline phase, intermediate phase (the so-called mes-ophase), and amorphous phase. When considering the fine structure, attention should be paid to its three fundamental aspects morphological structure, in other words, super- or suprastructure microstructure and preferred orientation. 

XRD and TA analysis have both shown the semi-crystalline character of the in this chapter described PK terpolymer system. The main properties of the crystalline phase measured on non-stabilised, powdery reactor samples, are ... 

Due to its high crystallinity, polyacetal is more rigid and stronger than other thermoplastics especially at elevated T (50-120°C). Because of its semi-crystalline character, POM requires a greater heat input for melting than amorphous resins. It has a fairly high heat of fusion (160-200 kJ/kg) but because of lower melt temperature (210°C), it requires considerably lower total heat energy than other crystalline polymers (viz., POM = 435-475, HDPE = 720, PA-66 = 756-786 kJ/kg). 

As a consequence of their semi-crystalline character, the mechanical properties of TPSs are characteristic of partially crystalline polymers [81] with B-type crystallinity being the major factor influencing the mechanical behaviour of glycerol-PLS [100]. This recrystallization can also be a problem because after long-tom storage TPSs can become rigid and brittle. 

When the structural features of crystalline polymers are examined beyond the level of the unit cell, it is very important that their semi-crystalline character... 

PBT s thermal endurance is determined by its semi-crystalline character. The high degree of crystallization is the reason why parts molded from PBT without external mechanical load can be heated temporary almost to melt temperature without significant damage or deformation. Thus their practical service temperature under... 

The semi-crystalline character of polybutylene terephthalate and polyethylene terephthalate is the reason for their good resistance to chemicals. Organic solvents, such as aliphatic hydrocarbons, fuels, alcohols, ethers, long-chain esters, fats, oils, perchlorinated hydrocarbons, and the fiuorinated hydrocarbons used in aerosol technology do not attack thermoplastic polyesters at room temperature. These plastics are also resistant to weak acids, weak bases, water, and to aqueous solutions of neutral and acid salts at room temperature. However, they are non-resistant to strong acids, oxidizing acids, strong bases, ketones, and phenols. 

The discrepancy in values for the small particle sample (quartz A) as opposed to the large particle sample (quartz B) has been reported (14, 16). This behavior has been explained in terms of the semi-amorphous character of the smallest quartz particles obtained in crushing and grinding operations. While larger particles are believed to be representative of increasing ideality in surface crystalline order, there is, at present, no confirmation for the supposition that the larger (20- to 40-micron) quartz B particles approach the ideal crystal structure. Thermal analysis shows that, relative to the large particles, as much as 48% of the less than 5-micron material may be noncrystalline with respect to the a — j quartz transition (16). 

The sorption of a fluid into a polymer is dependent on the crystallinity of the polymer. The diffusion of a supercritical fluid and therewith the diffusion of small molecules dissolved in this fluid into an amorphous polymer is much more pronounced than it is into a crystalline polymer because of better swelling of the amorphous polymer. As a consequence, the sorption by the PA-6 granules is not expected to be large, since PA-6 is a semi-crystalline polymer. Also, the fact that PA-6 has a polar character, due to the amide bonds in the polymer chain, does not have a positive effect on the amount of CO2 absorbed by the polymer. 

Poly(3-hydroxya]kanoate)s (PHAs) are natural polyesters, which many organisms in the environment accumulate in the form of intracellular granules to store carbon and energy when they are subjected to stress conditions [1-3]. PHAs are produced by a fermentation process in the bacteria by means of enzymatic polymerization (PHA synthase). The type of biosynthesized polymers is determined by the substrate specificities of the PHAs synthases and depends on the carbon source. PHAs are semi-crystalline, isotactic (only the enantiomer of absolute configuration R is present in these polymers) with a hydrophobic character. Although the most well-studied PHA is poly(3-hydroxybutyrate) (PHB), over 140 constitutive monomer units [4] have been investigated. 

In semi-crystalline materials, the heterogeneous character of oxidation can be described by preferential oxidation of the amorphous regions with subsequent oxidative degradation of the crystalline regions. 

Injection molding operation is the most widely employed processing methods in the plastics industry. During the injection molding process of semi-crystalline polymers, the processing conditions and the positiorrs in the cavity influence crystal structures of the articles, which are the important parameters of describing crystallized polymer mecharrical characters. 

In the present paper, we first review briefly the rigid rod models for liquid crystalline phase transitions. In these models, emphasis is placed on the anisotropic form and on the orientation dependent intermolecular interactions between rigid particles. Conformational studies on isolated chains have shown that liquid crystalline polymers are rather semi-rigid in character although only a narrow range of deformations is possible due to intrachain interactions. The effect of chain flexibility on the formation of liquid crystalline phases has been pointed out both experimentally and the-oretically J. 

Poly(l,4-benzamide), abbreviated here as PpBA, was the first nonpeptide, synthetic condensation polymer reported to form liquid crystalline phases [11, 39,42,48-50]. Technologically important is poly(l,4-phenylene terephthalamide), abbreviated here as PpPTA. In both polymers the non-flexibility or semi-rigid chain structure is caused by the paralinked benzene rings and the partial double bond character of the carbon-nitrogen bond in the predominantly trans amide linkages. 

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