Thermal and Rheological Behavior

For example, preheating coal at ca. 200°C (ca. 390°F) tends to have an adverse effect on the caking properties but may also increase ease of, say, gasification (insofar as caking coals can be difficult to gasify efficiently) (Chapters 20 and 21) and may also increase the ease of dissolution by organic solvents during liquefaction processes (Chapters 18 and 19). 

Nevertheless, in the temperature range 350°C-500°C (660°F-930°F), coals (depending on rank) soften, become plastic, and then coalesce to form the solid residue (coke). Two important physicochemical aspects of the change ensue and can be identified as follows (1) the coal becomes plastic, and (2) at the higher temperatures of this range, the solid material contracts. 

FIGURE 13.5 Relationship of volatile matter yield to softening points and decomposition points of various coals. (From Gibson, J., Coal and Modern Coal Processing An Introduction. G.J. Pitt and G.R. Millward (Eds.), Academic Press, New York, 1979.) 

FIGURE 13.6 Possible reactions for the functional groups during coal pyrolysis. 

Such coke has a relatively low resistance to abrasion and thus it is apparent that the inherent strength and abrasion resistance are predetermined by the behavior of the original coal in the plastic range. 

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Assessments were made on a variety of polyetherimides and it was found that the thermal and rheological behavior were quite similar for this entire polymer family. 

Salome Machado, A. A., Martins, V. C. A., and Pl-epis, A. M. G. (2002). Thermal and rheological behavior of collagen chitosan blends. Journal of Thermal Analysis and Calorimetry 67, 491-498. 

The previous sections have described the structural units and molecular weights of high molecular weight polymer chains. We have not, however, discussed the thermal and rheological behavior of polymers. Many polymers crystallize into well-ordered structures. Others do not crystallize and, at low temperatures, form high modulus disordered glasses. 

Li XH, Meng YZ, Chen GQ, Li RKY (2004) Thermal properties and rheological behavior of biodegradable aliphatic polycarbonate derived from carbon dioxide and propylene oxide. J Appl Polym Sci 94 711-716... 

A lot of solid properties are easily determined so large amounts of data are available about mechanical, rheological, thermal and ageing behaviors of poly-nadimides [35-37]. These will be presented in Sects 5 and 6. It is worth mention-... 

Adhesives have very broad range of performance requirements. The performance spectrum ranges from pressure sensitive products where almost minimal adhesion is required, to extremely high performance adhesives with strength equivalent to that of metals. But the scope of the adhesive s performance goes well beyond adhesive strength. Flowability, force to adhere and mechanical, thermal, electrical, barrier, and optical properties as well as chemical and weather resistance and rheological behavior all must be considered in adhesive formulations. These essential parameters are discussed below from the point of view of the influence of fillers. 

Fang et al. (2005) studied the thermal and rheological properties of two types of m-LLDPEs, two LDPEs, and their blends. The C2+6 m-LLDPE-1 was immiscible, whereas the C2+8 m-LLDPE-2 was miscible with the LDPEs, indicating that increasing the length of SCB in m-LLDPEs promoted miscibility with LDPE. The Palieme (1990, 1991) emulsion model provided good predictions of the linear viscoelastic behavior for both miscible and immiscible blends. The low-frequency data showed an influence of the interfacial tension on the elastic modulus of the blends for the immiscible blends. 

Although considerable progress has been made in understanding heat transfer in polymeric systems, much still remains to be done. There are a number of reasons why this is so, including lack of good physical data such as (thermal conductivities, specific heats, and rheological behavior), and failure to cope with such complexities of polymer behavior as elastic effects, compressibility, and viscous dissipation. 

In this chapter we aim to demonstrate the relationship of the structure of polymers with their thermal, solution, and rheological behavior. Besides providing a general review of such behavior, we will emphasize some of the recent developments in these areas. 

Lard viscoelastic behavior was different from that of PO (Fig. 47). The G values of all lard blends increased as a result of CIE and also displayed a nonlinear response with blend SFC. Cornily and Le Meste (1985) studied the flow behavior of lard and of its fractions at 15°C and attempted to establish relationships between thermal, compositional, and rheological behavior. 

The processability, properties, and performance of conventional polymers can be suitably modified by the addition of both low and high molar weight liquid crystal compounds, making possible the development of new materials for advanced technological applications. In many cases the rheological, thermal, and mechanical behavior of commercial polymers have been reported to be improved by blending with liquid crystal polymers... 

PP is probably the most thoroughly investigated system in the nanocomposite field next to nylon [127-132]. In most of the cases isotactic/syndiotactic-PP-based nanocomposites have been prepared with various clays using maleic anhydride as the compatibilizer. Sometimes maleic anhydride-grafted PP has also been used [127]. Nanocomposites have shown dramatic improvement over the pristine polymer in mechanical, rheological, thermal, and barrier properties [132-138]. Crystallization [139,140], thermodynamic behavior, and kinetic study [141] have also been done. 

An important difference between the PS-gas systems (Kwag et al., 1999) and the PDMS-C02 system (Gerhardt et al., 1997) is that the viscosity measurements of the PS-gas systems are conducted at temperatures within 75 °C of T of PS, whereas the PDMS-C02 measurements were performed nearly 200 °C above Tg of PDMS. The difference between these two thermal regimes leads to several differences in the observed rheological behavior. The viscosity reductions relative to the pure polymer are much greater for PS-gas systems than for PDMS-C02 systems at similar dissolved gas compositions, and the dependence of ac on temperature is much more pronounced for the PS-gas systems. These trends are consistent with the observations of Gerhardt et al. (1997, 1998) that the effect of dissolved gas on polymer melt viscosity occurs primarily through a free-volume mechanism. 

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