Melt flow temperature

Another interesting development in membrane fabrication has been the use of porous base films [71]. The grafting of a monomer and subsequent sulfonation still leads to porosity in the membrane bulk. However, this membrane may be densified by impregnating it to substantially fill the porosity, or the porosity may be collapsed by the appHcation of pressure and heat. The heating may be carried out to at least a melt flow temperature of the film but at a lower melting temperature (Tm) than grafted side chains. 

Diol chain extender Tensile strength (MPa) Elongation at break (%) 300% modulus (MPa) Permanent set (%) Melt flow temperature rc ... 

Cellulose esters are easy materials to extrude and injection mould [47], Some of the innate properties inelude a relatively narrow window between the melt flow temperature and the deeomposition temperature. Therefore, in most commercial apphcations, plasticizers are used in conjunetion with cellnlose esters. Triethyl citrate is usually used for eellulose acetate (CA) and dioctyl adipate for cellullose aeetate propionate (CAP). 

A bifunctional fluorocompound [e.g., C10F19 OC6H4SO2N (CH2CH20H)2l reacted with a polyanhydride [e.g., pyromellitic dianhydridel and pH adjusted with NH3 to 8-9 Urethane adduct nof containing fluorine + urethane adduct of a fluorocompound (e.g., N-ethylperfluorooctanesulfonamidoethanol) both adducts are water insoluble and have major transition temperature >45°C and melt flow temperature 200°C Component A >1 phase of a water-insoluble polymer (e.g., 3 7 90 itaconic acid-methyl acrylate-vinylidene chloride polymer) Component B =1 phase of a fluoropolymer [e.g., 90 10 C8Fi7S02N(CH3)CH2CH202 C—CH==CH2-butyl acrylate copolymer]... 

Melt flow rate Melt-formed ceramics Melt fracture Melting temperature... 

Modification of BPA-PC for adaptation to the conditions of production of CD and CD-ROM disks, and of substrate disks for WORM and EOD was necessary. BPA-PC standard quaHties for extmsion and injection mol ding have, depending on molecular weight, melt flow indexes (MEI), (according to ISO 1130/ASTM 1238 in g/10 min at 300°C/1.2 kg, between less than 3 g/10 min (viscous types) up to 17 g/10 min. For CDs and optical data storage disks, however, MEI values exceeding 30 g/10 min, and for exceptionally short cycle times (5—7 s) even >60 g/lOmin are demanded at an injection mass temperature of 300°C (see Table 5). 

Melt Index or Melt Viscosity. Melt index describes the flow behavior of a polymer at a specific temperature under specific pressure. If the melt index is low, its melt viscosity or melt flow resistance is high the latter is a term that denotes the resistance of molten polymer to flow when making film, pipe, or containers. ASTM D1238 is the designated method for this test. 

Fig. 9. Melt flow index as a function of temperature for varying molecular weights of poly(ethylene oxide). WSR = Polyox water-soluble resins.

PPS is well-recognized for its exceptional chemical resistance. There are no known solvents for PPS below 200°C. A comprehensive survey of solvents for PPS has been published (115). Extreme conditions are required to dissolve PPS in both common and exotic solvents. Solution viscosity measurements are made difficult by this high temperature requirement. Inherent viscosity measurements are performed in 1-chloronaphthalene at 206°C at a concentration of 0.4 g of polymer per deciliter of solution. The inherent viscosity of PPS solutions shows a usefiil response to increa sing molecular weight. Table 2 shows a correlation of inherent viscosity measurements with melt flow measurements. 

Amorphous nylons are transparent. Heat-deflection temperatures are lower than those of filled crystalline nylon resins, and melt flow is stiffer hence, they are more difficult to process. Mold shrinkage is lower and they absorb less water. Warpage is reduced and dimensional stabiUty less of a problem than with crystalline products. Chemical and hydrolytic stabiUty are excellent. Amorphous nylons can be made by using monomer combinations that result in highly asymmetric stmctures which crystalline with difficulty or by adding crystallization inhibitors to crystalline resins such as nylon-6 (61). 

Processing PC resins by extmsion or injection-molding methods requires melt temperatures of 290—320°C. High melt viscosity at low shear rates prevents mold flash and drool. At injection shear rates, apparent viscosities decrease, and easy melt flow allows manufacture of large, complex parts. 

PPS resins are chiefly used for injection mol ding. The melt flow of the glass-fiUed resins is very stiff, and high injection pressures are required. Mold surface wear is heavier than for most other engineering plastics. Mol ding melt temperatures are near 330°C for optimum surface gloss and impact strength, mold temperatures of 130°C should be used. The resins are brown to brown-black. 

Vitreous ceramics are made waterproof and strengthened by glazing. A slurry of powdered glass is applied to the surface by spraying or dipping, and the part is refired at a lower temperature (typically 800°C). The glass melts, flows over the surface, and is drawn by capillary action into pores and microcracks, sealing them. 

As the temperature is decreased, free-volume is lost. If the molecular shape or cross-linking prevent crystallisation, then the liquid structure is retained, and free-volume is not all lost immediately (Fig. 22.8c). As with the melt, flow can still occur, though naturally it is more difficult, so the viscosity increases. As the polymer is cooled further, more free volume is lost. There comes a point at which the volume, though sufficient to contain the molecules, is too small to allow them to move and rearrange. All the free volume is gone, and the curve of specific volume flattens out (Fig. 22.8c). This is the glass transition temperature, T . Below this temperature the polymer is a glass. 

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