Processing/shear techniques

Figure 9.6 is a schematic of the various dispersion mechanisms operative in producing nanoplatelets of very high aspect ratio. The nominal size of a dry nanoclay particle is about 8-20 pm. Comprisingthe partide are approximately 1-3 million clay platelets, consisting of bundles of platelets called tactoids. Through a combination of chemistry and processing/shear techniques, the partide is separated into tactoids and the platelets are peeled from the tactoid to become fidly dispersed or exfoliated. 

Recently, focus has been placed on small amplitude oscillatory shear technique to measure the dynamic moduli during the gelation process to identify the gel point. By this method, the continuous evolution of the viscoelastic properties throughout the... 

Molding Technique Advantages Disadvantages Typical Process Shear Rate (sec )... 

Speckle shearing interferometry, or shearography, is a full field optical inspection teclmique that may be used for the nondestructive detection of surface and, sometimes, subsurface defects. Whilst being more sensitive in the detection of surface defects, it may also be considered for pipe inspection and the monitoring of internal conoslon. In contrast, laser ultrasound and other forms of ultrasound, are point by point measurement techniques, so that scanning facilities and significant data processing is required before information on local defects is extracted from any examination of extensive areas [1 - 3]. 

A sliding plate rheometer (simple shear) can be used to study the response of polymeric Hquids to extension-like deformations involving larger strains and strain rates than can be employed in most uniaxial extensional measurements (56,200—204). The technique requires knowledge of both shear stress and the first normal stress difference, N- (7), but has considerable potential for characteri2ing extensional behavior under conditions closely related to those in industrial processes. 

The production of the hard polymer/elastomer combinations is more simple. The two components are mixed together under conditions of intensive shear. In some cases, grafting may occur. In a variation of this technique, the elastomer can be cross-linked while the mixing is taking place, a process described as dynamic vulcanization (32). 

Shear strength is measured via a simple single overlap shear specimen of standard dimensions (Fig. 9). In contrast to its simple appearance, the forces in a thin-adherend shear specimen can be quite complex due to the inherent offset loading of the specimen and subsequent bending in the substrates. The single overlap shear test is anything but a pure shear test, but the configuration is easy to manufacture, simple to test and is firmly entrenched in the industry as a primary examination technique for materials qualifications, inspection and process control. 

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