Brabender torque

Techniques for evaluating processing stabiHty and mechanochemical effects include using a Brabender torque rheometer (29,30), injection mol ding (26,28), capillary rheometry (26,28), and measuring melt index as a function of residence time (26). 

The use of Brabender torque rheometer enabled us to evaluate the behavior of melt viscosity vs. time at low shear stresses the usual operating conditions were adopted—i.e., granules (28 grams) were introduced in the bowl, the temperature was fixed at 187 °C, and each run was started after 5 minutes of conditioning. 

The apparatus used for the first tests included a 3/4-inch diameter, 20 1 L/D laboratory extruder. The second series of evaluations was run on a Brabender torque rheometer equipped with mixing head. The third tests utilized large scale processing equipment including a two-roll,... 

Figure 2. Processing stability of polypropylene in a Brabender torque...

Figure 10.21. Variation of torque with temperature of plasticized PVC in a Brabender torque rheometer. [Adapted, by permission, from Ramos-de Valle L, Gilbert M,J. Vmyl Technol, 12, 4, 1990, p.222-5.]...

Figure 7.24. Morphology changes as function of Brabender torque ratio and composition. The numbers show the mean domain diameter in jxm and the length-to-diameter ratio (in parentheses). V, E3/HV2 E2/HV3 0, E4/HV1 O, E1/HV4 , E1/MV2 O, E2/HV1 A,...

Viscosity is affected by the discussed additives in different ways. Figure 10.36 shows a marginal decrease in viscosity with concentration. Addition of ultrahigh molecular weight silicone additive, which is used as a mold release, decreases viscosity of polyethylene melt and thus lowers energy input in extrusion (Figure 10.37). Addition of 0.2 wt% of silicone additive reduced Brabender torque by 40%, elongational viscosity by a factor of four, and increased spiral mold flow by 30%. ... 

Figure 12-3. Brabender torque rheometer. (Courtesy of C. W. Brabender Instruments, Inc.)...

ASTM D3795 - Thermal Flow and Cure Properties by Brabender Torque Rheometer - This test give a simulation of what will happen during injeetion or transfer molding. 

The rigid PVC formulation was prepared using a high intensity mixer. Hyperdispersants were added to the calcium carbonate filled and un-filled dry blends. The dry blends were then analyzed using a Brabender torque rheometer and a 16 mm twin screw extfuder. The torque rheometer studies were performed at 188°C, 10 min, 65 grams and 75 rpm. The 16 mm twin screw exu-uder was set at temperatures 160, 165, 170, 180°C and the output was measured at 30,40 and 50 rpm. 

If the torque as measured in a Brabender is plotted in an Arrhenius plot against 1/T characteristic linear dependencies are observed (Fig. A). While powder flow is observed up to the softening point of PVC a distinct linear relationship between shear rate and reciprocal temperature exists between 150 - 180°C indicating one mechanism of flow. The deviation above ca. 180°C indicates a change in flow mechanism. 

The addition of an intermolecular plasticizer, i.e., a monomer of the first class, allows the graft reaction. Table 18 summarizes these results. The Brabender curves (torque or consistency versus time) generally go through a maximum, or so-called peak , before leveling out. These are the peak values given in Table 18. 

Treatment of PVC, suspended in chlorobenzene, with Et2AlCl followed by the addition of methanol greatly improved the thermal stability (6). This will be the subject of a separate publication. However, the nature of the improvement was different—i.e., film pressed in air at 200°C was yellow not colorless, but processing stability as determined by the torque rheometer test in the Brabender Plasticorder at 195°C was far superior and was measured in hours rather than minutes. The removal of labile chlorine atoms by Et2AlCl undoubtedly contributed to heat resistance. However, in the absence of a further reaction, such dehalo-genation probably became dehydrohalogenation, contributing to color development. 

High Density Polyethylene - [Both regular and high molecular weight (HMW)]. The time to increase in torque at 220°C. by the Brabender Plasticorder was determined as a measure of crosslinking. Yellowness Index after the Brabender test at 220°C. and after the first extrusion at 260°C. were also performed. 

Checks on raw material sometimes are made by using a small single-screw extruder as a rheometer, or a test machine designed for the purpose—such as a Brabender Plastograph (a device for measuring torque, which may be attached for the purpose to a small extruder). 

Brabender Processing. In another series of tests, two commercial (stabilized) resins, unstabilized polypropylene, and the latter with 0.4% DLTDP + 0.1% PPP were masticated for five minutes at 50 r.p.m. and 180 °C. in the Brabender apparatus, then mixed for 25 minutes at 150 r.p.m. and 200°-215°C. Meter-gram torque readings were plotted over the mixing cycle along with temperature, and intrinsic viscosity was measured for each formulation before and after processing. 

Torque Rheometer. The Brabender plastograph was also used to study the relative processing stabilities of the polymers. The conditions were those recommended by P. G. O Leary (24). The melt viscosity-time curves are shown in Figure 10. Resins D, I, and E are the least stable, and A, H, G, and B are the most stable. 

Since this was the case, all data from Brabender measurements were measured as quickly as possible. When a constant reading could not be achieved, the slowly changing torque was extrapolated to zero time. The correction was normally less than 10%. The data for Solprene 414C are shown in a double logarithmic plot of shear stress against shear rate on Figure 3. 

Two properties were recorded as a result of processing each sample in the Brabender Plasticoder (1) time in minutes to reach a rapid increase in torque and (2) the color of each test sample as determined by yellowness index (ASTM D1925-70). 

High Density Polyethylene (HDPE). The preferred method of evaluating HDPE was found to be the time to cross link at 220 0 using the Brabender apparatus, as is made evident by the rapid increase in torque. Determining melt viscosity by multiple extrusion showed only small differences compared to the base polymer. 

Utilizing A Torque Rheometer (Brabender Plasti-corder) At Constant Mixer Temperature, The Society of The Plastics Industry, Vinyl Dispersions Division, New York, 1968. 

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