Polymer melt spray

Results of a Study on High-Elastic Rating of a Polymer Melt Spray... 

Plasticisers are compatible and miscible with their host polymer causing them to swell and allowing them to be used for coating, moulding, spraying (when used as a suspension in a liquid solvent) or calendering, extrusion and injection moulding (when used as a polymer melt). 

Article 6 passes through inductor 7 of an HFC generator where it is heated above the polymer melting point and then passes through the spraying zone. Powder particles stick to the article or rebound from its surface, get to the rarefaction zone and are drawn into the channel of pipeline 1. The installation is loaded with the powder from bin 8. The ready coating is post-fused in the second inductor 9. 

In order to establish the way in which these various factors influence the performance of the extrusion head, studies were conducted on the flow characteristics of the polymer melts. The effects of the extrusion temperature and pressure were also studied together with the influence of the frequency of the ultrasound and construction of the channel the effectiveness of producing a high elasticity of the spray in the melt and the final properties of the solid produced. 

The limitations of the PGSS process are that the substances to be processed have to be in a liquid state. But most of the products used in the pharmaceutical and food industries will distort before reaching their melting point. Its use is mainly restricted to polymers since the dissolution of supercritical fluid reduces both viscosity and glass transition temperature. The polymer becomes spray able through a conventional nozzle. 

Drug substance properties should be carefully evaluated. These property will dictate the excipients, method, and process selection for ASD product. The properties to be considered are solubility in organic and aqueous solvents, miscibility with polymers, melting point, particle size, and thermal stability. These properties determine manufacturability, product performance, and long-term stability. For example, hot melt extrusion cannot be used for thermally labile drug molecules (Forster et al. 2001 Vasconcelos et al. 2007 Leuner and Dressman 2000). Qn the other hand, for spray drying process, drug solubility determines the selection of the solvent as well as inlet process temperature (Vasconcelos et al. 2007 Leuner and Dressman 2000). 

When spraying solutions of polymers, the spraying process is usually limited to viscosities less than 0.5 Pa s under spraying conditions. Higher viscosities give rise to the formation of fiber-particle mixtures and deformed spheres. Finally, at p. > 10 Pa s only fibers are formed (Lohner et al., 2005 Eggers and Villermaux, 2008). The same behavior can be observed when highly viscous melts are sprayed, see for example, Walz and Mayer (1966). 

There have been a number of studies of the breakup of viscoelastic filaments because of interfacial tension, all of which show that the viscoelastic response results in dynamics that differ markedly from the Rayleigh breakup of inelastic filaments, but the focus for interfacial tension-driven breakup has been on dilute polymer solutions of interest in aerial spraying and inkjet technology applications. The hterature is less extensive for breakup of polymer melts, and some of the issues relevant to dilute solutions are probably not of concern for melts because of the orders-of-magnitude difference in the ratio of interfacial to viscous (or elastic) stresses. 

Product from melt or suspension treatment is obtained directly as emmb or powder. Polymer recovered from solution treatment is obtained by precipitative cooling or spray drying. Polymer with now stable end groups may be washed and dried to remove impurities, especially acids or their precursors, prior to finishing operations. 

Methods for isolation of the product polycarbonate remain trade secrets. Feasible methods for polymer isolation include antisolvent precipitation, removal of solvent in boiling water, spray drying, and melt devolatization using a wiped film evaporator. Regardless of the technique, the polymer must be isolated dry, to avoid hydrolysis, and essentially be devoid of methylene chloride. Most polycarbonate is extmded, at which point stabiUzers and colors may be added, and sold as pellets. 

The key feature of ethylene glycol (EG) is the hydroxyl group, -OH, one on each of the two carbon atoms. The hydroxyls are responsible for its reactivity EG is a monomer used in the production of polyester polymers. The hydroxyls also give EG its most important physical property its solubility in water. That, linked with its low freeze point, makes EG suitable as an antifreeze and as a deicer. When EG is sprayed on ice, it combines with the water crystals and lowers the freeze point. This causes the mixture to melt and effectively keeps it in the liquid state. 

Many different processes are used to apply a thin layer of liquid-melted polymer, polymer solution or dispersion including rollers, spraying, calendering, and brushing. Here we will look at the industrial application of coatings onto film and sheetlike materials. Figure 18.16... 

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