Optical spectroscopy crosslinking

Crosslinking of EPDM and Polydiene Rubbers Studied by Optical Spectroscopy... 

The aim of this chapter is to review optical spectroscopy studies on sulfur and peroxide crosslinking of polydiene rubbers, such as NR and BR (Sections 6.2.1 and 6.3.1, respectively), and to discuss in detail recent FT-Raman and FT-IR spectroscopy studies into the sulfur and peroxide crosslinking of EPDM (Sections 6.2.2 and 6.3.2, respectively). The results of optical spectroscopy studies will also be discussed in the light of results obtained with other techniques. Finally, the elucidation of the chemical structures of the crosslinks formed will allow enhanced understanding of the mechanisms of crosslinking and some preliminary insight into the structure/property relationships of crosslinked rubber. 

In more recent studies from Gonzalez and co-workers [88-90] it was concluded from dynamic mechanical analysis of peroxide-cured NR that a non-uniform crosslinked network results if a large amount of peroxide is used. This result seems to be in line with the optical spectroscopy studies discussed. 

Optical spectroscopy (IR/NMR/Raman) has been extremely useful in the study of the sulfur and peroxide crosslinking chemistry of elastomers, especially that of EPDM. The... 

The ultimate aim of optical spectroscopy or similar studies is to elucidate the chemistry of elastomer crosslinking with respect to both the structures formed and the reaction kinetics in order to provide a sound basis for structure/property relationships. As a result, it will be possible in the future to develop rubber products with less trial and error [18, 19, 55, 56, 125]. 

Analysis of chemical conversion and cure chemistry is another way of studying network structures. Several techniques are used for this purpose, e.g., optical spectroscopy [12], high-resolution NMR spectroscopy and titration of non-reacted functional groups. The spectroscopic methods can be used for quantitative analysis of crosslinks [13-15]. Chemical conversion is usually closely related to the network density. However, no exact quantitative information on the network structure can be obtained because reacted groups can form... 

Processing of rubbery materials The effect of milling on the heterogeneity of rubbery materials and changes in their chemical and physical structures is determined by means of optical spectroscopy, NMR relaxation experiments and NMR imaging (Chapters 3, 7 and 10). Welding of crosslinked polyethylenes is discussed in Chapter 5. 

In this context rheo-optical FTIR spectroscopy has proved a valuable technique to study the phenomenon of strain-induced crystallization on-line to the deformation process of the elastomer under investigation. Whith the aid of an appropriate absorption band which is characteristic of the threedimensional order in the crystalline phase the onset and progress of strain-induced crystallization during elongation and its disappearance upon recovery can be unambigously monitored simultaneously to the mechanical measurements. Representative for several rubber-like materials which have been investigated by this technique in our laboratory the results obtained with sulfur-crosslinked (1.8 % S) natural rubber (100% 1,4-ds-polyisoprene) and a radiation-crosslinked synthetic polyisoprene (93% 1,4-ds-isomer) lall be discussed in some detail here. 

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