Polycarbonate processing conditions

Schmidt, L. B., et al., Injection Molding of Polycarbonate Compact Disks Relationship between Process Conditions, Birefringence, Block Error Rate, SPE-ANTEC, 1992. 

BPA polycarbonate becomes plastic at temperatures around 220°C, The viscosity decreases as the temperature increases, exhibiting Newtonian behavior, with the melt viscosity essentially independent of the shear rate, At the normal injection molding temperature of 270-3l5°C, the melt viscosity drops from 1.100 to 360 Pa j s (11.000 to 3,600 poise). Because the viscosity of polycarbonate can only be reduced by increasing the temperature, the ultimate limit on molecular weight is controlled by the processing conditions and the thermal stability of the polymer. 

Pyrolysis and reforming of several types of common plastics (polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polyurethane, and polycarbonate) were studied qualitatively, using a micro-reactor interfaced with a MBMS. Each type of plastic pyrolyzed at 550-750°C. This was followed by steam reforming of vapors in a fixed bed of C-11 NK catalyst at 750-800°C. The composition of the product gas (mass spectrum) was observed for different values of the steam-to-carbon mtio and space velocity that changed depending on the size of plastic samples. Preliminary tests showed that at process conditions similar to those used for reforming natural gas, polymers were almost completely converted to hydrogen and carbon oxides. 

Brief reviews covering redistribution reactions in polyester and in polycarbonate binary blends have been prepared by Porter et al. [1989] and Porter and Wang [1992]. Selected references for redistribution processes in PEST/PEST blends are listed in Table 5.7. Early studies of these processes focused on measuring the extent of redistribution under specific processing conditions rather than on producing compatibilized polymer blends with an attractive balance of properties. A number of more recent studies have reported the limits of miscibility for certain melt-mixed polyester pairs in the absence of transesterification — see for example the NMR study of PC/PET blends [Abis et al., 1994]. 

Since there are multiple reactive sites on the epoxide-containing polymers, some crosslinked copolymer may result if the acid-containing polymer is functionalized at both ends. The proportion of crosslinked copolymer formed also depends upon blend composition and processing conditions. An example is also included in this section where a compatibilizing copolymer is postulated to form by reaction between acidic phenolic end-groups on polycarbonate and epoxide groups grafted to PP [Zhihui et al., 1997]. 

The conductivity of the composite strongly depends on the synthesis conditions stirring speed, initial pyrrole/matrix ratio, polycarbonate concentration. For composites containing less than 15% of pyrrole, it ranges from 10 -2 S/cm. Microwave properties are also strongly dependent on the processing conditions (method, temperature). 

An important factor with thermoforming is that the polymer should show a pronounced rubbery region on the temperature scale. For this reason, amorphous polymers such as PVC, PS, poly(methyl methacrylate) (PMMA), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), etc. are well suited for thermo forming. With semicrystalline polymers, the rubbery region is largely masked by the crystallinity (Fig. 23.19). With PE and polypropylene (PP), thermoforming is, therefore, a critical operation, in which the processing conditions should be very carefully controlled. 

KAV 96] Kavano Y., Keskkula H., Paul D.R., Effect of polycarbonate molecular weight and processing conditions on mechanical behaviour of blends with a core-shell impact modifier , Po/ywer, vol. 37, no. 20, pp. 4505 518,1996. 

Kgure 5.17. Spatially resolved fluorescence emission spectra of soUd bisphenol-A polycarbonate in a melt-polymerization microreactor before (A) and after (B) optimization of processing conditions. Inset) Microreactor cross section and locations of spectral measurements. From ret 73. 

Fig. 4.183c Time to fracture as a function of applied load for polycarbonate using the constant tensile stress method (c) for different processing conditions at 23 °C [07Ram],...

The choice of the membrane depends on several factors chemical and thermal resistance to the process conditions, sharp separation, wettability of the membrane, tendency to adsorb hydrophobic materials and resistance to cleaning. The most common polymeric materials are PTFE, PVDF, PP, PS, CA/CN, CTA, PE, polycarbonate, polyester, poly ether imide and nylon 6. Of these, only PTFE, PVDF and PP have excellent to good chemical stabiHty. Even though hydrophilic CA/CN and CTA membranes have limited chemical stabiHty, they are best suited for treating high fouling feeds using tubular membranes. 

Kasaliwal G, GOldel A and Potschke P (2009) Influence of processing conditions in small-scale melt mixing and compression molding on the resistivity and morphology of polycarbonate-MWNT composites, J Appl Polym Sci 112 3494-3509. 

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