Rheological measurement procedure

Rheological Measurement of Polymer Melts Using Dynamic Mechanical Procedures... 

Rheological Measurements Three types of rheological measurements have been carried out. In the first type, transient (creep) measurements were performed on a 20% w/w dispersion of latex A, as a function of coverage by PVA. These experiments were carried out using a "Deer" rheometer (PDR 81, Integrated Petronic Systems, London) fitted with a stainless steel concentric cylinder. The procedures used have been described in detail before (21,22). 

ASTM D 4440-95a, Standard Practice for Rheological Measurement of Polymer Melts Using Dynamic Mechanical Procedures, ASTM, West Conshohocken, PA, 1997. 

The dependence of the experimentally observed ODT on the ordering temperature (final quenching temperature) was shown recently by rheology measurements on SI3 and SI low molecular weight samples [91]. This dependence resembles the dependence of the melting temperature in semicrystalline homopolymers on the crystallization temperature. The existence of an equilibrium transition temperature (Todt°) was demonstrated and a procedure, analogous to the known Hofmann-Weeks plot for crystalline polymers, was proposed as a means to calculate Todt°. The phenomenon was attributed to the fact that grains when produced at different temperatures have different sizes. 

Rheological measurements Two instruments were used to investigate the rheology of the suspensions. The first was a Haake Rotovisko model RV2(MSE Scientific Instruments, Crawley, Sussex, England) fitted with an MK50 measuring head. This instrument was used to obtain steady state shear stress-shear rate curves. From these curves information can be obtained on the viscosity as a function of shear rate. The yield value may be obtained by extrapolation of the linear portion of the shear stress-shear rate curve to zero shear rate. The procedure has been described before (3). 

The capillary rheometer is a valuable tool for predicting the processability of thermoplastic resins. This is done by measuring melt viscosities at shear rates and temperatures commonly encountered in extrusion and injection molding. This procedure is difficult and time consuming due to the complex nature of rheological measurements and analyses. An automated system for acquisition and analyses of capillary rheometer data has been developed to speed up and simplify this important analytical technique. 

Evaluation of the stability/instability of suspensions without any dilution (which can cause significant changes in the stracture of the system) requires carefully designed techniques that should cause as little disturbance to the structure. The most powerful techniques that can be applied in any industrial laboratory are rheological measurements [1-7]. These provide accurate information on the state of the system, such as sedimentation and flocculation, and may also be applied to predict the long-term physical stability of the suspension. The various rheological techniques that can be applied and the measurement procedures are listed below. 

ASTM D4440-95a, Rheological measurements of polymer melts using dynamic mechanical procedures. 

ASTM D4440-01 (ISO 6721-10), Rheological Measurements of Polymer Melt Using Djmamic Mechanical Procedures ... 

The method of ultrasound Doppler velocimetry (UDV) [9] was proposed to measure the viscosity of non-Newtonian fluids over a wide range of shear rates and in a short period of time. This is a noninvasive, nondisturbing, quick, and accurate procedure. The distribution of shear-stress can be found by pressure drop. At a radial position, the ratio of shear-stress to shear rate, by definition, yields the viscosity at that point. Thus, for the shear rate range in the flow, viscosity values can be obtained by means of only one online experiment. This is a method known in the literature as pointwise rheological measurement [10,11]. 

Figures 6.5.3-6.6.S show data collected in our lab over two days during our Rheological Measurements summer short course. No special efforts other than standard calibration procedures were made. Hie agreement illustrates what one can expect from normal operation of modem rheological instruments with stable, polymeric samples. Such an exercise is reassuring to the new liieologisL...

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