High melt processing temperatures

Can vitamin E withstand the high melt processing temperatures of polymers, e.g. polyolefins, and, if it does, how efficient would it be compared to the commercial norms such as Irganox 1010 (III) and Irganox 1076 (IV) ... 

To address the question of whether the biological antioxidant would withstand the high melt processing temperatures, dl-a-tocopherol (synthetic vitamin E) was extruded at different concentrations in PE and PP under different processing temperatures ranging from 210 °C to 285 °C. Similar experi-... 

Note that due to their high melt-processing temperature, PEI resins are not compatible with many standard polymer additives. Often additives that work well in other, lower-temperature polymers wiU decompose or volatilize in the hot PEI melt. In general, like most amorphous polymers, PEI resins should be processed at least 150°C (270°F) above the polymer s Tg [340 to 400°C (664 to 752°F) for most polyetherimides]. Selection of appropriate additives to blend with PEI is hest handled by the resin manufacturer or those with significant experience in the selection of suitable blending materials. 

High melt processing temperatures require more thermal stability in the FR systems and this usually means the more expensive bromine compounds. Remember, the FR system must be stable at processing conditions and decompose to extinguish the fire at temperatures slightly above the highest processing temperature. When the thermal properties of the polymer allows, chlorine-based compounds are used with antimony oxide, because they usually decompose at lower temperatures and they are usually less expensive than their bromine counter parts. 

PTT exhibits melt rheological behavior similar to that of PET. At low shear rates the melt is nearly Newtonian. It shear-thins when the shear rate is >1000s 1 (Figure 11.10) [68], At the melt processing temperatures of PET, 290°C, and of PTT, 260°C, both polymers have similar viscosities of about 200Pas. However, PTT has a lower non-Newtonian index than PET at high shear rates. The flow behavior can be modeled by the Bueche equation, as follows ... 

Polyarylsulfone (PAS) thermoplastics have relatively low melt-processing temperatures, considering their high mechanical properties. For one thing, they are hydrolytically stable. They have a heat-distortion temperature at least 204°C (400 F) at 1,820 kPa (264 psi), tensile strengths to 124 MPa (18,000 psi) or better, and a flexural modulus up to 1.17 X 10 psi. Under stress they are highly resistant to mineral acids and alkali and salt solutions. Their applications are in electrical and electronic items, frozen-food packaging, and aircraft interiors. 

One of the main limitations of intrinsically conductive polymers (ICP s) towards their wide application as conductive additives for thermoplastics is their poor thermal-oxidative stability at typical melt processing temperatures (i.e., above 200 °C). On the other hand, the use of high surface area carbon blacks (CB) as conductive additives is limited due to the increased melt viscosity of their blends with thermoplastics. Eeonomers are a new class of thermally stable, chemically neutral, and electrically conductive composites made via in-situ deposition of conductive polyaniline (PANI) or polypyrrole (PPY) on CB substrates. Eeonomer composites are more stable (up to 300 °C) than pure ICP s and more easily processible with thermoplastics than CB. Use of Eeonomers as conductive additives for plastics lead to compounds with improved electrical, mechanical, and processing properties. By varying Ae conductive polymer to CB ratio, it is possible to fine tune the polarity of Eeonomer composites and achieve very low percolation thresholds. This control is possible because of preferred Monomer localization at the 2D phase boundary of the immiscible polymer blends. 

The major difficulties involved in making electrically conductive thermoplastic blends using polyaniline, polypyrrole, or their composites, are two-fold. The first is the thermal instability of doped polyaniline and polypyrrole at melt processing temperatures (1-3), The second is the chemical incompatibility of acidic conductive polyaniline with acid sensitive polymers such as the nylons. Conductive polyaniline is quite acidic and the adjustment of its acidity to neutral pH values eliminates its high conductivity (4,5). The authors present here thermal aging studies of conductivity and thermal gravimetric analysis - mass spectroscopy (TGA-MS) of Eeonomers which show pH independence of conductivity in acidic to neutral environments. The tunable surface properties of Eeonomer composites allows one to optimize the processibility as well as the electrical and mechanical properties of their blends with various thermoplastics. 

The viscosity for high molecular weight SPS homopolymer as a function of apparent shear rate is shown in Rgure 14.3 for typical melt processing temperatures [3]. 

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