Extrusion conditions

This is an expression for the pressure necessary at the extruder exit and therefore enables the appropriate extrusion conditions to be set. 

Extrusion conditions = 1.25 mil film blown at 2 and 1 blow up ratio using 63.5 mm, 20D smooth bore extruder, die gap 80 mil, melt temperature 193°C. 

The main design criteria of most TPE dies are to ensure that changes in flow channel diameter from the extruder barrel bore to the die exit are equal. Most of the viscoelastic materials exhibit a die swell on exit from a die. TPEs tend to show die swell significantly lower than that of typical thermoplastics. This swell must be taken into consideration in designing dies and adjusting extrusion condition to achieve a perfect profile. The die swell normally increases with increasing hardness and shear rate and decreasing temperature. 

Texturized or denatured WPl retained its native protein value, functionality, and digestibility when extruded below 50 °C changes in functionality occur at 65 °C and above. Through careful selection of extrusion conditions of temperature and moisture, TWPs with unique functionality can be produced. The degree of texturization increased with increasing temperature, but temperatures higher than 100 °C may be needed to form fibrous structures with WPl. 

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. 

The appearance of air bubbles in the polymer melt may occur under certain circumstances during processing. This phenomenon is rarely related to obvious faults in the polymer, but sometimes gas bubbles can be observed in cases of decreased thermal stability. Gas bubbles appear due to a certain amount of dispersed gas in the polymer matrix. Insufficient removal of gas from the extruder, particularly from the compression zone, can also cause the problem of air bubbles in the melt. An influence of the extruder screw could be established, because gas bubbles can be removed to some extent by using special screws or changing the extrusion conditions, along with the application of a vacuum. 

After a long development time, we started manufacture of the compound by carrying out a mull extrusion. The conditions for mull extrusion are especially important to produce good quality compound. The film processing is only possible when the selection of extrusion conditions is appropriate. The properties of the manufactured film are also affected by these conditions. The conditions of blown film processing for this starch compound are shown in Table 4. 

Extrusion parameters, such as basket temperature, extrusion rate, and die design, can be adjusted to suit a particular formulation and granule size. This is an empirical process based on experience. Extrusion characteristics represent an intimate interplay between press parameters and dough properties, the latter predominating. What is wanted is maximum production rate of a smooth, dense, homogeneous strand of these qualities, smoothness is perhaps most sensitive to extrusion conditions. 

Finally, we developed testing procedures that included Brabender studies and the use of high temperature Mooney machines, and our program began to move. We were able to correlate with production sheet extrusion conditions which enabled us to make our numerous product development changes rapidly on a small scale. 

Ma- Ar- Table XIII Tem- pera- tures, °C . Extrusion Conditions and Results Stock Ex- Spe- Content- Screw tru- cific sist- ... 

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]. 

When extrusion conditions are considered (Table IV), the most severe conditions (HTLM) resulted in the loss or decreased level of certain peaks however, the remaining components were at relatively high levels. The least severe conditions (LTHM) retained the highest number of volatiles. ... 

This initial study clearly demonstrated that protein type and amount as well as extrusion conditions can result in a vast array of both sensory and volatile compound differences. Further research, including compound identification, is required to more fully understand the complex interactions observed. 

Table III. Gas Chromatographic Volatile Comparison, Extrusion Conditions HTLM...

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. 

X-ray diffraction measurements were used to determine the orientation of talc and lead carboxylate fillers in plasticised PVC extrudates. Correlations between the extrusion conditions (draw ratio and temperature), the development of filler particle orientation and the tensile properties of the plasticised PVC were studied. The presence of fillers enhanced Young s modulus and this was predicted well by the model developed by Halpin and Tsai. The extrudates were stretched above and below the gel-liquid transition temperature of PVC (about 205C). Above this temperature, the PVC could be stretched more and the tensile results indicated that the crystallites which were surrounded by more flexible chains were more oriented. 24 refs. 

Journal of Vinyl and Additive Technology 3, No.3, Sept. 1997, p.210-5 EFFECT OF EXTRUSION CONDITIONS ON RIGID PVC FOAM... 

Results are presented of an investigation of the effect of extrusion conditions, such as melt temp., screw speed and draw-down, on process morphology of rigid PVC foams and the properties of the extruded profile, including density, cell structure and surface appearance. The optimum conditions for the best quality profile found in this study were 190 to 196C melt temp, and no greater than 20 rpm screw speed on a 63.5 mm single screw. 15 refs. 

Extruded compounded pellets were converted into strips (1 in. X 0.05 in.) using a % in. Brabender laboratory extruder. ASTM-D 638 Type I 0.05 0.005 in. tensile specimens were tensile cut from the extruded strips. Extrusion conditions used were typical for this class of materials. Extrusion take-off rates were controlled to minimize orientation in the extruded strips. Annealing experiments showed shrinkage to be approximately 2% in the longitudinal direction. 

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