Extrusion moisture content

Qi, P. X. and Onwulata, C. 1. (2011). Physical properties, molecular structures and protein quality of texturized whey protein isolate (WPl) Effect of extrusion moisture content. /. Dairy Sci. (Accepted for publication). doi 10.3168/jds.2010-3942. 

The harder grades of PP/EPDM blends (Santo-prene ) can be blow molded. The resins are characterized by a co-continuous morphology and high viscosity. The recommended parameters for blow molding are similar to profile extrusion. Moisture content is critical and should be kept below 0.1%. 

The harder grades are usually used in this process. Parameters of process are similar to profile extrusion. Moisture content in this application should always be kept low (below 0.1%). Compression or transfer molding... 

Another event which may occur is hydrolysis. This is a chemical reaction between the plastic and water. It occurs extremely slowly at room temperature but can be significant at moulding temperatures. Hydrolysis causes degradation, reduction in properties (such as impact strength) and it is irreversible. Table 4.3 indicates the sensitivity of plastics to moisture. Note that generally extrusion requires a lower moisture content than injection moulding to produce good quality products. 

Required maximum moisture content for extrusion/injection moulding (%)... 

Besides the main depolymerization reactions, side reactions should also be considered in the kinetic description of a PET recycling process. This is emphasized by the results obtained from a PET extrusion model [85] shown in Figures 2.19-2.23. The complete set of reactions summarized below in Table 2.10 have been used, but shear effects have not been taken into account. Chain degradation, accompanied by a significant reduction of intrinsic viscosity, occurs even within residence times of a few minutes. Carboxyl end groups, vinyl end groups and acetaldehyde are formed in amounts depending on residence time, temperature and initial moisture content of the PET flakes. 

The attributes of the extrudate, such as density, thickness, and moisture content, are controlled by variables due to the formulation, extrusion process, and equipment design. The properties of the wet feed material and its ability... 

Among the formulation variables that control extrudability of a product, several studies (25,26,33-35) point to the fluid or moisture content of the wet feed material being more critical than others. The force or torque of extrusion and power consumption are often inversely proportional to moisture content of the extrudate as seen from Figures 11 and 12 (26,36-38), while the particle size of pellets increases linearly with water content when extruded with gravity feed basket and roll extruders (33). Using instrumented gravity feed and radial screw extruders, a three- to fourfold decrease in the force has been noted, with a 10% increase in water content of feed material (37). 

Figure 11 Torque of extrusion as a function of moisture content of wet mass of MCC at varying screw speeds a-19 rpm, -28 rpm, c-38 rpm, d-4S rpm. Source From Ref 26.

The formation of moisture gradients within the material during extrusion, resulting in migration of liquid from within the interparticulate spaces to surface of the extrudate, has been reported (40,25). At low initial moisture content, the friction within the chamber can result in higher temperatures leading to loss of moisture of up to 12% from the extrudate surface. This effect is more pronounced with A-A extruders. 

Iyer RM, Augsburger LL, Pope DG, Shah RD. Extrusion/Spheronization— Effect of moisture content and spheronization time on pellet characteristics. Pharm Dev Tech 1996 1(4) 325-331. 

A patent has been recently issued on extrusion encapsulation to Miller and Mutka ( ). This patent contains no new formulation or process innovations but rather a refinement of the existing art (1, 3), A flow chart of the overall process is presented in Figure 1 with a view of the extrusion process presented in Figure 2. The carbohydrate matrix consists of a high DE maltodextrin and sugar, e.g., 6025 g of 20 DE maltodextrin solution (70% solids) plus 4125 g sugar (Example 1 in patent). This carbohydrate matrix is heated to promote solubility and then cooked to 120 to 124 C to reduce moisture content. They found a... 

Fig. 7. Predicted topographic plot of xylan conversion (AX, %) with inoculum amount and moisture content. The ranges presented on the plot are ranges of xylan conversion predicted in each region. The diamond marks the conditions chosen for preparation of treated stems for the extrusion tests.

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 ... 

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. 

Pre-Extrusion Blending. Based on the moisture contents of the corn starch and various protein sources, blends of 0,5,15,30, and 50% (dry weight) of each protein source were made by first dry mixing for 10 minutes in a Paterson-Kelly Model LB-P-8 twin shell blender followed by the appropriate amount of 20°C tap water to obtain a total moisture content of either 15 or 25% (wet basis). The moistened mixtures were then blended for an additional 20 minutes followed by overnight equilibration at room temperature in air-tight bags. 

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