Fusion-melt process

At the end of the first stage, the melt is cooled to 150°C, maleic anhydride is added, and the temperature is raised to 180°C to re-start the process of condensation. The progress of the reaction is monitored by the measurement of carboxylic functionality and viscosity. As the reaction proceeds rapidly, the temperature only needs to be elevated to 210°C to drive the reaction. The stabihty of isophthalic acid esters at higher temperatures allows the development of polymers with higher molecular weight. (In contrast, high-molecular weight phthalic resins cannot be produced by the fusion melt process, since phthalic anhydride sublimes above 200°C.)... 

Polyamides. Coating powders based on polyamide resins have been used in fusion-coating processes for along time (1). Nylon-11 [25587-80-8] h.2LS been used almost exclusively however, more recently, coating powders also have been sold based on nylon-12 [24937-16-4]. The properties of these two resins are quite similar. Nylon-6 [25038-54-4] and nylon-6,6 [32131 -17-2] are not used because the melt viscosities are too high. 

Schmelz-verfahren, n. melting process, fusion process smelting process, -warme, /. heat of fusion, -wasser, n. water from melting ice or snow, -werk, n. smeltery foundry enameled work. 

The terms enthalpy of fusion, enthalpy of vaporization, enthalpy of combustion, and many more cause some students to believe that there are many different kinds of enthalpies. There are not. These names merely identify the processes with which the enthalpy term is associated. Thus, there are processes called fusion (melting), vaporization, sublimation, combustion, and so forth. The corresponding enthalpy changes are called by names that include these descriptions. 

According to Hoffman s crystallization theory, a drop in the heat of fusion corresponds to an exponential decrease in nucleation and crystal growth rates [63]. Implicitly, the rate of crystallization is severely retarded by the presence of 3HV comonomer [64, 69, 72]. These low crystallization rates can hamper the melt processing of these copolymers since they necessitate longer processing cycle times. 

Although the disorientation process might be looked upon as a melting process, eq. (9.54) does not give a good estimate of the entropy of fusion of polymers. A more reasonable approach is to introduce the mean square displacement length of the actual chain in its unperturbed state [7], The number of such units would then replace r in eq. (9.54), but one still needs to determine the coordination number z in an independent manner. 

Preparation. The ores are converted to an acid-soluble form by fusion chemical processes to obtain beryllium hydroxide or oxide and then beryllium chloride or fluoride are then applied, followed by electrolysis in the melt. 

The most common applications of DSC are to the melting process which, in principle, contains information on both the quality (temperature) and the quantity (peak area) of crystallinity in a polymer [3]. The property changes at Tm are often far more dramatic than those at Tg, particularly if the polymer is highly crystalline. These changes are characteristic of a thermodynamic first-order transition and include a heat of fusion and discontinuous changes in heat capacity, volume or density, refractive index, birefringence, and transparency [3,8], All of these may be used to determine Tm [8],... 

The melting process can be characterized by the entropy change on fusion8. Thermal analysis of fusion is illustrated in Fig. 1. We can break the overall entropy of fusion ASf into the three approximate parts positional, orientational, and conformational entropy of fusion... 

The melting point of a compound is the temperature at which the solid and liquid phases are in equilibrium at one atmosphere pressure is specified because the melting process involves a change in volume and is therefore pressure dependent. Since the melting point can be determined easily experimentally, it is the most commonly reported physical property for organic compounds. However, in the absence of a rigorous theory of fusion, it is one of the most difficult to predict. 

Fusion — A process in which a continuous him or a solid body is formed by melting and flowing (coalescence) of polymer particles. 

Van den Mooter et al. prepared solid dispersions of tamazepam in PEG 6000 and polyvinylpyrrolidone K30 (PVP K30) by the fusion (melting) and cooling process. In contrast to the very slow dissolution rate of pure temazepam, the dispersion of the drug in the polymers enhanced the dissolution rate considerably. This can be attributed to improved wettability and dispersibility and a decrease of the crystalline fraction of the drug. 

The process of fusion uses heat to melt all or some of the components of the ointment the mixture is then allowed to cool with constant stirring until congealed. Additional components of the ointment preparation that were not subject to the initial melting process are added to the congealing mixture as it is being cooled and stirred. Heat-labile substances are added to the preparation after careful observation that the... 

PHASE TRANSITIONS Another type of constant-temperature process is a phase transition such as the melting of a solid at constant pressure. This occurs reversibly at the fusion temperature, Tf, because an infinitesimal change in external conditions, such as reducing the temperature, can reverse the melting process. The reversible heat when 1 mol of substance melts is = AHfus, so... 

Melting takes place at a constant temperature. The molar heat of fusion tells us that every mole of Na, 23 grams, absorbs 2.6 kj of heat at 97.5°C during the melting process. We want to know the amount of heat that 5.0 grams would absorb. We use the appropriate unit factors, constructed from the atomic weight and to find the amount of heat absorbed. 

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