Isothermal of Polymers

Figure 2.8 Adsorption isotherms of polymer fraction of SNF on different cement brands (polymer adsorption is refered to 1 g of cement).

Pressure-area isotherms of polymers or proteins often show no defined phases. Even at very low film pressures the behavior is not ideal. The behavior depends strongly on the specific structure of the polymer and the subphase, and isotherms are often irreversible. In general, the... 

Figure 1. Hysteresis isotherm of polymer 3S on a water/air interface. The compression and decompression rate is 50 Mm/min.

Figures 15.1 and 15.2 show how the general shapes of the sorption isotherms of polymers are affected by the Tg and thermal history of the polymer, the measurement temperature, and whether polymer-penetrant interactions are strong enough for sorption to cause plasticization.

Adsorption isotherms of polymers on surfaces usually exhibit a high affinity character. That is, at low polymer concentration virtually all the polymer is adsorbed, with very little left in solution (often immeasurable quantities). It is also common to find that the adsorption process is very slow and that adsorbed polymer cannot be readily removed by washing with the same solvent used for adsorption. Explain these observations using logical physical reasoning at the molecular level and, where possible, thermodynamic arguments as support. 

Adsorption Isotherms. Because of the strong tendency of polymer chains to adsorb at attractive surfaces, the surface gets saturated at very small bulk concentrations. Adsorption isotherms of this nature are known as high affinity isotherms. The adsorption isotherm of polymer chains adsorbing on solid substrates depends on the polymer molecular weight, solvent quality, and polymer-surface interactions. Figure 3 a illustrates the adsorption isotherms for polymer chains in a good solvent as a function of concentration. The surface excess... 

Vega, L.F. Panagiotopoulos, A.Z., and Gubbins, K.E., Chemical potentials and adsorption isotherms of polymers confined between parallel plates, Chem. Eng. Sci., 49( 17), 2921-2930 (1994). 

ISOTHERMS OF POLYMER ADSORPHON FROM DILUTE SOLUTIONS... 

A more perfect form of the adsorption isotherm was derived by Silberberg, based on concepts of conformation of adsorbed chains and the structure of the adsorption layer formed by the sequences of bound segments and loops extending into the solution. According to Silberberg, the shape of the chain is determined by the adsorption energy and surface structure, i.e., by the character of the arrangements of active centers in it. Real isotherms of polymer... 

The majority of polymer flow processes involve significant heat dissipation and should be regarded as nou-isothermal regimes. Therefore in the finite element modelling of polymeric flow, in conjunction with the equations of continuity... 

Wynne-Jones and Marshfound somewhat similar results with a number of carbons made by pyrolysis of eight organic polymers at a series of temperatures. The isotherms of Nj at 77 K and of COj at 195 K were measured, and the apparent surface area calculated by the usual BET procedure. (Owing to the microporous nature of the solids, these figures for area will be roughly proportional to the uptake at saturation and therefore... 

Fig. 4.22 Apparent specific surface A(app) of carbons obtained from the decomposition of polymers, plotted against the carbonization temperature, (a) Polyfurfuryl carbons (b) dibenzanthrone carbons (c) polyvinylchloride carbons. O, A(app) estimated from CO2 isotherm at 195 K (a fCOj) = 17-0 A ) A. /f(app) estimated from N2 isotherm at 77 K = 16-2 A ). (Courtesy Marsh and Wynne Jones.)...

In describing the various mechanical properties of polymers in the last chapter, we took the attitude that we could make measurements on any time scale we chose, however long or short, and that such measurements were made in isothermal experiments. Most of the experimental results presented in Chap. 3 are representations of this sort. In that chapter we remarked several times that these figures were actually the result of reductions of data collected at different temperatures. Now let us discuss this technique our perspective, however, will be from the opposite direction taking an isothermal plot apart. 

Thermodynamic Properties. The thermodynamic melting point for pure crystalline isotactic polypropylene obtained by the extrapolation of melting data for isothermally crystallized polymer is 185°C (35). Under normal thermal analysis conditions, commercial homopolymers have melting points in the range of 160—165°C. The heat of fusion of isotactic polypropylene has been reported as 88 J/g (21 cal/g) (36). The value of 165 18 J/g has been reported for a 100% crystalline sample (37). Heats of crystallization have been determined to be in the range of 87—92 J/g (38). 

Fig. 3. Water sorption isotherms of poIy(trans-3,4-dihydroxytetrahydiopyran-6,2-diyloxy-methylene) 24 and its related polymers at 20 °C.

Polymers have inherently high hydrocarbon ratios, making liquefaction of waste plastics into liquid fuel feedstocks a potentially viable commercial process. The objective is to characterise the thermal degradation of polymers during hydrogenation. LDPE is studied due to its simple strueture. Isothermal and non-isothermal TGA were used to obtain degradation kinetics. Systems of homopolymer, polymer mixtures, and solvent-swollen polymer are studied. The significant variables for... 

Figure 2. Influence of the ionic strength and the polymer concentration on the binding isotherms of Pb2+ by sugar-beet pectins in water (empty symbols) and in 0.1 M NaNOs (full symbols) at 25°C ( ) 2 mequiv. COO. l-, ( ) 8 mequiv. COO-.l-i (—) total binding of added Pbz+.

Fig. 111.—Experimental values of the interaction parameter %i plotted against the volume fraction of polymer. Data for polydi-methylsiloxane M =3850) in benzene, A (New-ingi6). polystyrene in methyl ethyl ketone, (Bawn et aV ) and polystyrene in toluene, O (Bawn et alP) are based on vapor pressure measurements. Those for rubber in benzene, T (Gee and Orr ) were obtained using vapor pressure measurements at higher concentrations and isothermal distillation equilibration with solutions of known activities in the dilute range.

Isothermal Kinetics of Polymers Oxidation and Its Relation to the Concentration of Oxygen in Surrounding Atmosphere 487... 

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