Extruder expander

Foamed polystyrene, too, dates from the thirties. The method of adding blowing agents to polystyrene in an extruder so that the extrudate expands was developed by Dow (L5). It is still used today on a large scale. 

Orlando, FI., 7th-llth May, 2000, paper 703 EFFECT OF CHEMICAL BLOWING AGENT DOSAGE ON THE PROPERTIES OF EXTRUDED EXPANDED POLYPROPYLENE Dixon D Martin P J Harkin-Jones E Belfast,Queen s University (SPE)... 

Cross-linked polyethylene foams are produced by eilher radiation or chemical cross-linking of an extruded expandable sheet containing a chemical blowing agent. These products have finer texture and a softer, more resilient feel than extruded low density polyethylene foams and are used in comfort cushioning and cushion packaging applicutinns. 

Wheat starch has been formulated in a variety of snack foods, whether they are extruded, expanded, microwaved or in the form of a stick or half products.570-574 In the case of yogurt or custard-type milk desserts, modified wheat starches were used for their thickening or gelling properties.575,576... 

Inward expansion (Celuka process) where the extrudate is fed on to the calibrator walls via a die mandrel, the torpedo creating a space into which the extrudate expands. The die and calibrator are... 

Extruded structural foams are produced with conventional extruders and a specially designed die with an inner, fixed torpedo located at the center of its opening. The extrudate from this die is hollow. The outer layer of the extrudate cools and solidifies to form solid skin the remaining extrudate expands toward the interior of the profile. The Celuka process, developed by Ugine-Kuhlmann [93], is widely used commercially. 

Fig. 12. Activation spectrum for change in yellowness index of extruded, expanded, polystyrene foam on exposure to a filtered xenon source (189 h exposure at 50 Q determin by the cut-on filter technique [122]...

The die is bolted to the end of the extruder. Usualfy, a breaker plate or screen (see Figure 7.19) is placed between the die and the screw tip this increases direct flow along the axis by inhibiting rotation, and filters the pofymer liquid. The die shapes the product but, because of viscoelastic swell, the cross-section of the extrudate expands as it leaves the die. It is then necessary to bring it to the correct size pulling, as indicated schematically in Figure 7.22. In order to achieve predsely the correct diameter, the extrudate is shaped as it cools, all the while under a tension from the haul-ofi. 

Prasad et al. [106] reported a linear relationship between A7/d (0-425 J/g) and azodicarbonamide content (0-36%). DSC thus allows detection of the level of undecomposed CBAs present in processed foam products and establishes the onset temperature for the decomposition. Advantages of DSC over EGA techniques are ease of operation, shorter analysis time, and detection of azodicarbonamide concentrations as low as 1%. Dixon etal. [107] have correlated thermal analysis data (DSC, TGA) of a variety of CBAs with cell morphology of extruded, expanded PP rod samples. CBAs with a higher temperature and rate of gas evolution lead to foams displaying a finer cell size structure and higher cell density. 

In 2000, Patterson reported properties of extruded expanded rigid vinyl composites with 40 percent 80-mesh hardwood fiber (American Wood Fibers), dried to 0.5 -1.0 percent moismre surface treatment was unstated. Samples containing either sodium bicarbonate or azodicarbonamide at unspecified levels were extruded and expanded to two densities, 0.60 and 1.01 g/cm, based on an unexpanded density of 1.31 g/cm. At the lower density, the product was comparable in mechanical properties to pressure-treated pine, with anticipated improved durability and eventual cost advantage with rising lumber prices. Formulations of this type appearing in commercial literature are typically as follows ... 

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