Cross-linking composite materials based

Gas barrier properties were evaluated to access the potential of isotropic all-cellulosic based composites for packaging applications. The mechanical properties, fiexibility and biocompatibility of these materials can be useful, in particular, for food packaging. Due to the nature of the envisaged application insoluble materials are required. This requisite is only fulfilled by cross-linked composites and, therefore, we have decided to subject only cross-Unked films for gas permeation measurements. 

Figure 18 shows the temperature dependence of the proton conductivity of Nafion and one variety of a sulfonated poly(arylene ether ketone) (unpublished data from the laboratory of one of the authors). The transport properties of the two materials are typical for these classes of membrane materials, based on perfluorinated and hydrocarbon polymers. This is clear from a compilation of Do, Ch 20, and q data for a variety of membrane materials, including Dow membranes of different equivalent weights, Nafion/Si02 composites ° ° (including unpublished data from the laboratory of one of the authors), cross-linked poly ary lenes, and sulfonated poly-(phenoxyphosphazenes) (Figure 19). The data points all center around the curves for Nafion and S—PEK, indicating essentially universal transport behavior for the two classes of membrane materials (only for S—POP are the transport coefficients somewhat lower, suggesting a more reduced percolation in this particular material). This correlation is also true for the electro-osmotic drag coefficients 7 20 and Amcoh...

Equation (56) states that the effect of a thermal gradient on the material transport bears a reciprocal relationship to the effect of a composition gradient upon the thermal transport. Examples of Land L are the coefficient of thermal diffusion (S19) and the coefficient of the Dufour effect (D6). The Onsager reciprocity relationships (Dl, 01, 02) are based upon certain linear approximations that have a firm physical foundation only when close to equilibrium. For this reason it is possible that under circumstances in which unusually high potential gradients are encountered the coupling between mutually related effects may be somewhat more complicated than that indicated by Eq. (56). Hirschfelder (BIO, HI) discussed many aspects of these cross linkings of transport phenomena. 

In the case of PSSZ a more extensive study was carried out. In particular, it was shown that the nitrogen content of the ceramic is in good correlation with the value of x when x < 0.75. For X > 0.5 Si-Si-Si sequences were hardly detected. A PSSZ prepared with equimolar amounts of Me2SiCl2 and (ClHMeSi)2NH was converted into PCSZ upon thermolysis (temperature of the bath 425 °C, 8h), cross-linked by y-irradiation, then pyrolyzed to afford SiCN-based material containing a very small amount of oxygen [4a]. In a preliminary study carried out at the Laboratoire des Composites Thermostructuraux, F-33600 Pessac, France (Prof R. Naslain), SiCN fibers were obtained (tensile strength 2 400 MPa Young s modulus 235 GPa). 

NMR is not, of course, the only analytical technique used to establish the composition and microstructure of polymeric materials. Others include >66 ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy, and infrared (IR) spectroscopy. IR and Raman spectroscopy are particularly useful, when by virtue of cross-linking (see. e.g. Chapter 9), or the presence of rigid aromatic units (see Chapter 4). the material neither melts nor dissolves in any solvent suitable for NMR. The development of microscopy based on these spectroscopic methods now makes such analysis relatively simple (see below). Space precludes a detailed account of these and many other techniques familiar to the organic chemist. Instead we focus for the remainder of the chapter on some of the techniques used to characterize the physical properties of polymeric materials. 

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