Torque rheometer test

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. 

The high level of unsaturation in the cw-1,4-polybutadiene per se and after dehydrochlorination as well as the unsaturation generated in the PVC has its drawbacks in the potential susceptibility to crosslinking. This may be responsible for the unexpectedly small improvement in the processibility of the cw-l,4-polybutadiene PVC graft copolymer, as indicated by the torque rheometer test. 

ASTM D3795, Test Methodfor Thermal Flow/ Cure Properties of Thermosetting Plastics by Torque Rheometer, Vol. 8.02, ASTM, Philadelphia, Pa., 1993. 

Torque rheometers are multipurpose instruments well suited for formulating multicomponent polymer systems, studying flow behavior, thermal sensitivity, shear sensitivity, batch compounding, and so on. The instrument is applicable to thermoplastics, rubber (compounding, cure, scorch tests), thermoset materials, and liquid materials. 

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,... 

Some of the test methods being used to measure the processing stability of polypropylene include melt flow drift measurements at elevated temperatures using an extrusion plastometer (melt indexer), melt viscosity retention measurements using a torque rheometer, retention of melt flow after repeated extrusions, and injection molded spiral test measured by the flow in inches at various temperatures and the retention of melt flow of the injected spirals. The nine commercial resins were evaluated by these methods. 

Measurements of bulk density and friction as described in Sections 3.4.1 and 3.4.2 have some relevance, as do the melt properties described in Section 3.6. However, apart from measurements of PVC gelation rates described in Section 3.7 using a torque rheometer. melting rate as a processability test appears to be quite unusual. 

Powder and friction properties are covered in section 3.4. In ASTM D2395 [50] a test is described that measures the ability of PVC polymer to absorb plasticizer whilst remaining a free-flowing powder. The PVC polymer powder is mixed with liquid plasticizer in cither a sigma blade mixer or a planetary mixer heated at 88 C and the torque is continuously recorded by a torque rheometer. The mix passes through a sticky state before becoming dry as the plasticizer is absorbed. The change in motor drive torque with time is used to measure the time taken for this absorbtion. 

An alternative to the torque rheometer for dynamic heat stability testing of plastieized PVC is a two-roll mill. Measuring the time taken for the onset of sticking to the mill surface avoids serious chlorine evolution and can be used for any color, but it relies much on operator judgment. 

The Brabender plasti-corder flow test is used with screw injection molding of TS resins to graphically and accurately measure the flow as it relates to IM. Concern about whether a compound would have a sufficient flow life during its residence time in the barrel led to the use of this test. It is basically a torque rheometer designed to measure and record torque (in meter-grams) vs. the mixing time. It produces a flow curve that is a measure of the compound s processability. 

A torque rheometer is used to determine fusion characteristics of PVC compounds. Components of formulation are first mixed in a beaker in an intensive mixer or ribbon blender. The rheometer is equipped with roller head and the premixed sample is added to a chamber having preselected temperature (typical temperatures used are 140 for flexible compounds, 180 for semirigid compounds, and 197°C for rigid compounds). The amount of the sample added is selected such that it occupies 65% of mixer bowl. Mixing is continued until torque peak is reached. Mixing time and maximum torque are two important results of testing. 

In the study of hlling modihcation, a torque rheometer is a common piece of small test equipment. Because it is equipped with a corresponding internal mixer chamber, the material shows an opposite reaction on rotors in the process of mixing. The opposite reaction is measured by a force transducer and converted into torque value, and the torque value reflects... 

The test requires the use of a torque rheometer equipped with a sigma-style mixer measuring head, as shown in Figure 12-4. The mixer is heated either electrically or by circulating heat-transfer oil through the jacket. To obtain consistency, a standard formulation is established as follows ... 

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. 

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