Temperature effects extrusion

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

Polyacrylamide gel electrophoresis results suggest that p-LG undergoes a greater conformational loss as a fimction of extrusion temperature than a-LA, presumably due to intermolecular disulfide bond formation. Atomic force microscopy indicates that texturization results in a loss of secondary structure of aroimd 15%, total loss of globular structure at 78 °C, and conversion to a random coil at 100 °C (Qi and Onwulata, 2011). Moisture has a small effect on whey protein texturization, whereas temperature has the largest effect. Extrusion at or above 75 °C leads to a uniform densely packed polymeric product with no secondary structural elements (mostly a-helix) remaining (Qi and Onwulata, 2011). 

Little previous work has focused directly on the impact of water content on the formation of pyrazines. Koehler and Odell (19) specifically chose a solvent system of lower water content for their stutfy Maga and Sizer (2Q) investigated the effects of initial moisture content and temperature of extrusion on the formation of pyrazines in potato flakes. 

Heat generated by the dry extrusion method does not adversely effect fat quality. Temperatures of the magnitude of 350-400°F are needed to produce off-odor development, whereas temperature for extrusion is generally in the 250-300°F range. 

Figure 9.12. Effects of dispersion and temperature in extrusion of 70/30 blends of Marlex polypropylene and ionomer (a) and (b), sections perpendicular and parallel, respectively, to flow direction, extrusion at 190 C (c) and (d), sections perpendicular and parallel, respectively, to flow direction, extrusion at 225 C. (VanOene, 1972.)...

PA-6 (50-45) or PA-66 or PA-11 or PA-612 or PA-610 or PA-1212 or PA-6-66 copolymer/ABS (45-50)/imidized acrylate copolymer (56% methyl glutarimide, 40% MMA, 2% MAA, 1% glutarlc anhydride) (0-10) SSE at 240°C or two different types of TSE/torque rheometry/TEM/DSC/ mechanical properties vs. extrusion conditions and morphology/ductile-brittle transition temperatures/effects of PA amine end-group concentration Majumdar et al. 1994a... 

Absolute thermal similarity is difficult to achieve in extrusion processes. This similarity indicates equal temperatures in corresponding locations (Fig. 12.2). A distinction has to be made between processes with small heat effects like low reaction enthalpy or small viscous dissipation and those with high-temperature effects. For... 

Cost may limit process control to either crucial or most effective parameters, eg, pressure and temperature in extrusion (189). Process simulation for optimization of parameters (190) prior to process implementation is also a cost-effective tool (see Processing, Modeling). 

Amorphous Polymers. As compared to semicrystalline polymers, the SSE exerts a lower effect on tensile modulus and tensile strength of linear amorphous pol3uners. It has been shown (23) that the room-temperature hydrostatic extrusion of PMMA gives an increase in the above parameters only by dozens of percent. A similar result has been attained during the three-point bending tests of the extruded PC (23). 

Wet spinning represents a somewhat different case from melt or dry spinning. For example, temperature effects and heat transfer play a much smaller role than in the other two principal spinning types. On the other hand, pre-extrusion effects may be more important for wet spinning than for dry spinning. Unfortunately, data related to such effects are even sparser for wet spinning than for melt spinning. 

Karaman, L Robertson, J. Im, J.T. Mathaudhu, S.N. Luo, Z.P. Hartwig, K.T. (2004). The effect of temperature and extrusion speed on the consolidation of zirconium-based metallic glass powder using equal-channel angular extrusion. Metallurgical and Materials Transactions A, Vol. 35A, No. 1, (January 2004), pp. 247-256, ISSN 1073-5623... 

Beta III Effect of billet temperature on extrusion properties... 

Reactive blending or extrusion in the presence of a free-radical initiator or reactive monomer have a better chance. Combining shear-temperature effect in the... 

Fig. 8 The effect of process parameters on scaffolds pore size (a) liquefier temperature, (b) extrusion pressure and (c) deposition speed...

The temperature of the store is liable to vary from that of the work area. To overcome any temperature effects the material should be placed in the work area for typically 24 h prior to use, to allow temperatures to equalise and to minimise the effect when the new supply is fitted to the pumps. Small temperature differences will affect extrusion rates and it will take an operator several assemblies to adjust to the new conditions. In an automated system even a small change is unacceptable. 

Another example of static SIMS used in a more quantitative role is in the analysis of extmded polymer blends. The morphology of blended polymers processed by extrusion or molding can be affected by the melt temperature, and pressure, etc. The surface morphology can have an effect on the properties of the molded polymer. Adhesion, mechanical properties, and physical appearance are just a few properties affected by processing conditions. 

The venting works because at a typical extrusion temperature of 250°C the water in the plastic exists as a vapour at a pressure of about 4 MN/m. At this pressure it will easily pass out of the melt and through the exit orifice. Note that since atmospheric pressure is about 0.1 MN/m the application of a vacuum to the exit orifice will have little effect on the removal of volatiles. 

Kalyan et al. [56] have also studied the effect of alpha-olefin comonomers on the rheological properties and processing of LLDPE. The characteristics of the resins are shown in Table 2. It is found that 1-octene-based LLDPE has the lowest shear viscosity as compared to 1-butene- and 1-hexene-based polymers (Fig. 9). Decrease in power consumption, pressure before the die, temperature in the die, and increase in output has also been found according to shear viscosities of the polymers during tubular film extrusion. 

Preliminary tests were made on melt mixed blends of PP and LCP to study the effect of processing temperature on the shape and size of the dispersed LCP phase. Extrusion experiments were made below as well as above the melting temperature of the LCP. Two different polypropylenes were tested to determine the effect of the viscosity of the matrix on the final morphology. 

TPEs are materials that possess, at normal temperatures, the characteristic resilience and recovery from the extension of crosslinked elastomers and exhibit plastic flow at elevated temperatures. They can be fabricated by the usual techniques such as blow molding, extrusion, injection molding, etc. This effect is associated with certain interchain secondary valence forces of attraction, which have the effect of typical conventional covalent crosslinks, but at elevated temperatures, the secondary... 

Distortion Another problem with extrusions is caused by distortion of the section by the effect of heat and other environmental conditions such as exposure to water or chemical agents that tend to soften the plastic. These distortions are generally reversals of the profile back to the shape that it had exiting in the die. This action indicates that the post die forming operations were done at a lower than desirable temperature which results in a molded-in stress. When the stress is relieved the product distorts. In some instances these stresses cannot be eliminated by process changes so that the product is inherently deficient in performance. 

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