Rheological behaviour types

The extent of LCB and its distribution depends mainly on the catalyst system and the conditions used in the polymerisation. Polymerisation conditions (monomer and comonomer concentration, type of catalyst, temperature and concentration of transfer agents) are important variables to be taken into account when one is looking at the rheological behaviour of the polymers. By decreasing the ethene concentration and increasing the polymerisation time in the reactor the LCB frequency can be enhanced [59, 81]. The polymers made with these catalysts have a complex branching structure composed of comb and tree structures of different lengths. 

Figure 6.15 Illustration oftime-dependent types of rheological behaviour.

The influence of plasticiser content and type, and different PVC K-values on the rheological behaviour of plastisol, used for coated fabrics, has been determined (266). 

FIG. 155. Types of rheological behaviour (a) Newtonian liquid (b) anomalous (pseudoplastic) liquid (c) Bingham body (d) real plastic body (e) thixotropic body (f) dilatant body. The viscosity is given by the tangent of the indicated angle. 

Rheological behaviour expressed by the dependence of the rate of deformation on stress is illustrated for various types of materials in Fig. 155. A Bingham body is described by the relationship... 

The yield point is lowered by gradual increase in water content in the raw material mix, until the range of liquid suspension is reached. If the system contains so much liquid that the particles of solids are mutualy separated by thick liquid layers, these suspensions behave like Newtonian liquids. Deviations from this simple rheological behaviour arise when the particles come into mutual contact. The yield point will arise or various types of non-linear dependence of deformation rate on stress will occur. 

Figure 8.3 Basic types of rheological behaviour (a) Newtonian, (b)—(c) non-Newtonian /(b) shear thickening, (c) shear thinning, A) pseudoplastic. (e) plastic (Bingham plow), in which o0 is the yield stress and On is the Bingham yield stress/.

Figure 1.9 Examples of flow curves OH linear co-ordinates of different types of rheological behaviour...

The second types of blends that can be produced are miscible blends where the blend may have a higher viscosity than PP and appears to be remarkably elastic. The chemical structure of the miscible block appears to be more important in governing the observed viscosity of the system where it has increased the viscosity of the system For instance. Song et. al has shown that the rheological behaviour of blend PP and POE (polyethylene-l-octene) is highly... 

The investigation of the rheological behaviour of chitosan solutions has been carried out by studying the influence of different parameters such as chemical con5)osition, concentration, ionic strength, pH and the effect of the type of acid [54, 80-85]. Furthermore, the role of hydrophobic association phenomena on the viscoelastic behaviour of chitosan solutions is an interesting feature [86] which requires further understanding. 

The DuPont 983 DMA is a versatile laboratory instrument for characterising the viscoelastic and rheological behaviour of materials. This system is designed to operate in any of four modes fixed frequency, resonant frequency, stress relaxation, or creep. It is discussed in detail next as an example of the type of equipment now available. 

For the NR based blends, therefore, the rheological behaviour must be considered case by case such as blending with thermoplastics and blending with other rubbers. In the case of the chemically modified NR based-blends, it was not only the type of polymer used to blend with NR, but also the variation of the chemical modification of NR would control the different rheological property of the blends. Special-property NR based blends obtained from the... 

The melt rheological behaviour in terms of Mooney viscosity, apparent shear stress, and apparent shear viscosity at 100 of two types of blends that included a blend between maleated STR 5L (MNR) and cassava starch and a... 

What three types of rheological behaviour are typical of attractive particle networks ... 

Another type of rheometer with parallel plates was designed and tested by Kuder et al. (2007) to evaluate the rheological behaviour of the fibre-reinforced cement matrices that are too stiff for testing with ordinary rheometers as shown in Figure 12.3. It appeared from the tests of fibre-reinforced mortars that at lower fibre amounts the properties of the mix were decided by the matrix and the fibres only reduced its yield stress and viscosity. At higher fibre contents, the mechanical interlocking and entangling of fibres determined the mix behaviour. Similar influence of the fibres may be expected for concrete mixes also. 

As with other physico-chemical properties of colloidal microgels the rheological behaviour of dispersions distinctly changes in response to environmental stimuli. At low temperatures the viscoelastic properties of poly(NIPAM) microgels change dramatically with temperature [89, 90]. At low temperatures poly(NIPAM) dispersions display elastic-type behaviour as... 

All surfactant systems containing interacting rodlike micelles show qualitatively a similar rheological behaviour (9). The viscosity increases sharply at the concentration c at which the rotational volumes of the rods start to overlap and a transient network is formed. This network can be an entanglement network, the micelles can also be fused together or they can hold together by adhesive contacts. It is conceivable that all of these types of networks can exist in surfactant solutions, and theoretical models have been derived for all of these situations. 

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