Molten-state Subject

Liquid crystal polymers (LCP) are a recent arrival on the plastics materials scene. They have outstanding dimensional stability, high strength, stiffness, toughness and chemical resistance all combined with ease of processing. LCPs are based on thermoplastic aromatic polyesters and they have a highly ordered structure even in the molten state. When these materials are subjected to stress the molecular chains slide over one another but the ordered structure is retained. It is the retention of the highly crystalline structure which imparts the exceptional properties to LCPs. 

The question as to the best formulation of structures and species in some binary fluoride systems was the subject of extensive experimental investigations, involving infrared and Raman spectroscopy in the molten state and in solutions as well as NMR spectroscopy and conductometric and cryoscopic measurements. Some crystal structure studies have also been published. The systems of SeF4 with BF3, SbF5, AsF5, NbF5, and TaFs have been studied recently. 

According to Lenz and Feichtinger 60), copolymers of these types containing p-oxybenzoyl or 3-mono- or 3,5-di-substituted p-oxybenzoyl units tend to reorganise to form block copolymers when held in the molten state, and sufficient sequences of the rigid-rod units are built up for the polymers to become semi-crystalline, infusible and insoluble. Such behaviour can clearly create problems of irreproducible processing behaviour in samples subjected to prolonged periods in the molten state. 

In polymer crystallization the challenge is to identify and clarify the transformations by which chain molecules pass from a disordered, molten state to the ordered supra-molecular organization known as the semi-crystalline state. The subject is highly relevant in terms of both basic science and technology it is indeed clear that many modern applications require complete control of the structure and the morphology of polymers from macroscopic dimensions down to below the nanoscale. As a simple example, making the crystallites in a polymer liber equally oriented and reducing the number of chain folds (or hairpins) therein, usually turn out to be very favorable requisites for mechanical performance. 

Perfluoralkoxy will be attacked by certain halogenated complexes containing fluorine. This includes chlorine trifluoride, bromine trifluoride, iodine pentafluoride, and fluorine. It is also subject to attack by such metals as sodium or potassium, particularly in their molten states. Refer to Table 2.24 for the compatibility of PFA with selected corrodents. Reference [1] provides a more detained listing. PFA has excellent weatherability and is not subject to UV degradation. 

In metallurgy it may be desirable to prolong the molten state of a metal before and after pouring. Contamination may be tolerable if the additives float as a slag on top of the metal. This type of pyrochemical heating is the subject of a British patent that claims mixtures of aluminum and silicon with salt-type oxidizers and sand. These are molded into slabs and put into packages to be laid on the surface of the molten metal. 

Alloys are manufactured by combining the component elements in the molten state followed by cooling. If the melt is quenched (cooled rapidly), the distribution of the two types of metal atoms in the solid solution will be random the element in excess is termed the solvent, and the minor component is the solute. Slow cooling may result in a more ordered distribution of the solute atoms. The subject of alloys is not simple, and we shall introduce it only by considering the classes of substitutional and interstitial alloys, and intermetallic compounds. 

Aromatic hydrocarbons which melt below 150 C can be subjected to color analysis in the liquid (molten) state using a visual comparison with platinum-cobalt standards. Standards are prepared Irom a stock solution of K2PtCl2 to form a scale varying in color intensity. Similar procedure was developed to evaluate color of halogenated organic solvents and their admixtures. ... 

Some transitions that are only known for macromolecules, however, will not be mentioned at all since they are covered elsewhere in this Encyclopedia (see, eg. Gel Point). Also we shall not be concerned here with the transformations from the molten state to the solid state of polymeric materials, since this is the subject of separate treatments (see Crystallization Kinetics Glass Transition Viscoelasticity). Unlike other materials, polymers in the solid state rarely reach full thermal equilibrium. Of course, all amorphous materials can be considered as frozen fluids (see Glass Transition) Rather perfect crystals exist for metals, oxides, semiconductors etc, whereas polymers typically are semicrystalline, where amorphous regions alternate with crystalline lamellae, and the detailed structure and properties are history-dependent (see Semicrystalline Polymers). Such out-of-equilibrium aspects are out of the scope of the present article, which rather emphasizes general facts of the statistical thermodynamics (qv) of phase transitions and their applications to polymers in fluid phases. 

Lundin and Yamamoto (1967) used the Knudsen effusion technique to determine the thermodynamic activities in the Gd-Y alloy system. The vapor pressures of both Gd and Y in the solid state are well below the measuring ability of this technique hence it was necessary to employ the molten state. Before analyses of the alloys, the vapor pressures of the pure components were measured. Vapors effused from nine liquid Gd-Y alloys at 1600°C were collected and subjected to X-ray spectrometer analysis. Activities of both components were determined from the ratio of the... 

A relatively new class of polymers, the liquid-crystalline polymers, exhibits orientational order, i.e. alignment of molecules along a common director in the molten state. Liquid-crystalline polymers are used, after solidification, as strong and stiff engineering plastics and fibres. Functional liquid-crystalline polymers with unique electrical and optical properties are currently under development. The fundamental physical and rheological aspects of liquid-crystalline polymers are the third subject of this chapter (section 6.5). 

Hot-melt extrusion has been approved as a solvent-free manufacturing process for ODFs. In this process, the API and other ingredients are mixed in a dry state, which is then subjected to a heating process and extruded out in a molten state. The blend of API, polymers... 

This section treats the flow behavior of SPS and particularly focuses on the temperature and molecular weight dependencies. The subject of this section is limited to the flow behavior of SPS in the molten state above its melting point. The effects of the tacticity on the rheological behavior in the amorphous state are discussed by comparing SPS with atactic polystyrene (APS) and isotactic polystyrene (IPS). 

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