Extrusion temperature

Recommended extrusion temperatures for some common packaging plastics are 

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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. 

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). 

TABLE 5.4 Properties of whey protein isolate as function of extrusion temperature (Onwulata et ai, 2003a)... 

Nylon blends, dyeing, 9 204 Nylon block copolymer, 19 762 Nylon carpet fibers, stain-resistant, 19 764 Nylon-clay nanocomposites, 11 313-314 Nylon extrusion, temperatures for, 19 789t Nylon feed yarns, spin-oriented, 19 752 Nylon fiber(s), 24 61 production of, 19 740 world production of, 19 7654 Nylon fiber surfaces, grafting of polymers on, 19 763-764... 

A number of thermal stability tests arc available, some of which have developed into national (DIN) or international industrial standards (ISO). Pigments in thermoplastic systems, for instance, are studied under heat extrusion conditions [110]. The colorant to be tested, possibly together with titanium dioxide, is dispersed in the thermoplastic, using a mixer and a granulating extruder (Sec. 1.8.3). The pigmented test pellets are then fed into a screw extruder which ejects a standardized test specimen with defined dimensions [111]. Starting at the lowest possible temperature level, the extrusion temperature is increased by intervals of 10 or 20°C between samples. 

Materials Minimum Section Thickness, (in.) Extrusion Temperature (°F) Extrusion Pressure (ksi) Extrusion Exit Speed (fpm) Extrusion Ratio InlAo/A,)"... 

Figure 15. Exterior morphologies of soy extrudates produced at different temperatures. Note that the diameter and surface smoothness increased when the extrusion temperature increased. (Mag.

Is substantially unreactive with the polymer at the extrusion temperature,... 

The extrusion temperatures of the polymer far below the melting point of the drug. Upon cooling of the extruded fibers, dissolved drugs may either recrystallize or remain soluble, which results in a supersaturated state. The amount of the dissolved drug can be correlated to the release properties. The state in which the drugs are left after extrusion determine their properties of permeation. 

Generally speaking, the appearance of the pipes and profiles was fairly good it was still noted that the extrudate appearance improves considerably, extrusion temperatures being the same, by operating with screw rotation speeds shifted toward high values. 

Fig. 2 Effect of extrusion temperature on melt stability of PP processed with 300 ppm tocopherol and on its level of retention in the polymer (Reproduced with kind permission of Polym Degrad Stab, 1999, 64 145)...

The overall effect of the initial tocopherol concentration on the product distribution in PE was somewhat similar to that observed in PP, in that increasing the tocopherol concentration resulted in the lowering of the concentrations of the trimers, aldehydes, and in only little change in the concentration of tocoquinone. The main difference found in the case of PP was the absence of the spirodimer, under all extrusion conditions examined (see e.g. Fig. 9) [34]. This difference is attributed to the greater oxidisability of PP at the higher extrusion temperatures used for this polymer (compared to PE). This is supported by the observation that the SPD, when used as an authentic (synthesised) sample in extruded PP, was much less thermally stable under PP processing conditions than the other tocopherol products such as the TRI and DHD [33]. 

Cooling of Extruded PE Wire5 Consider a copper conductor, 0.16 in in diameter, coated by extrusion to a 0.62-in insulated wire (first transatlantic cable core wire). The conductor is preheated to the extrusion temperature 412°F, and... 

Starch can readily be modified by concurrent heat, application of moisture, and pressure. Such modifications may be conducted in extruders. Low moisture content favors formation of water-soluble starch with increased water-binding capacity, 65a 65e The solubility, water binding-capacity, and viscosity of gels prepared from extruded starch do not show linear relationships against either the moisture content in starch or the extrusion temperature.65c-65f Such extruder variables as the type of screw (either single or twin), pattern of the barrel and die heating, screw velocity, and geometry of the screw thread are also essential factors.65 ... 

Pyrazines are the most widespread Maillard reaction products found in processed foods. The quantity of each pyrazine identified is greater in the samples extruded at 165°C than in those at 120°C. Extrusion conditions have been noted to favor the production of pyrazines at high temperatures (12), but as extrusion temperatures continue to increase, the rate of volatilization may become greater than the rate of production. 

ETFE resins have a good thermal stability however, for high-temperature applications thermal stabilizers are often added67 A wide variety of compounds, mostly metal salts, such as copper oxides and halides, aluminum oxide, and calcium salts, will act as sacrificial sites for oxidation. Addition of certain salts can alter the decomposition from oligomer formation to dehydrofluorination. Iron and other transition metal salts accelerate the dehydrofluorination. Hydrofluoric acid itself destabilizes ETFE at elevated temperatures and the degradation becomes self-accelerating. For that reason, extrusion temperatures higher than 380°C (716°F) should be avoided.68... 

Bastioli et al.172 claimed expanded articles from extruded compositions of starch, mixtures of EAA and EVOH copolymers, and an inorganic carbonate. Typically, the synthetic copolymers comprised 20-40% of the composition. Preferred extrusion temperatures were in the range 180°C to 210°C. Extrusion of a typical blend in a single-screw extruder at a temperature of 180°C produced a closed cell foam with a density of approximately 1.2 lb/ft3 (19kg/m3). 

Tomboulian et al. (2002) has reported that butylated hydroxytoluene (BHT) can impart a "burnt plastic" odor and is an additive in HDPE pipes. Quinone may be derived from BHT due to interactions with residual chlorine in pipes (Anselme et al., 1985). Yam et al. (1996) reported that antioxidants, such as vitamin E, Irganox 1010, and BHT, contributed to off-flavors in water. Vitamin E yielded less off-flavor, possibly due to lower aldehyde and ketone concentrations. Extrusion temperatures over 280 °C and exposure time for melt contributed to more oxidation of LDPE films and higher intensities of off-flavors in water in contact with LDPE with different antioxidants (Andersson et al., 2005). 

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