Elastomers analysis techniques

Characterisation of Elastomers Using (Multi) Hyphenated Thermogravimetric Analysis Techniques... 

The thermal characterisation of elastomers has recently been reviewed by Sircar [28] from which it appears that DSC followed by TG/DTG are the most popular thermal analysis techniques for elastomer applications. The TG/differential thermal gravimetry (DTG) method remains the method of choice for compositional analysis of uncured and cured elastomer compounds. Sircar s comprehensive review [28] was based on single thermal methods (TG, DSC, differential thermal analysis (DTA), thermomechanical analysis (TMA), DMA) and excluded combined (TG-DSC, TG-DTA) and simultaneous (TG-fourier transform infrared (TG-FTIR), TG-mass spectroscopy (TG-MS)) techniques. In this chapter the emphasis is on those multiple and hyphenated thermogravimetric analysis techniques which have had an impact on the characterisation of elastomers. The review is based mainly on Chemical Abstracts records corresponding to the keywords elastomers, thermogravimetry, differential scanning calorimetry, differential thermal analysis, infrared and mass spectrometry over the period 1979-1999. Table 1.1 contains the references to the various combined techniques. 

Table 1.5 Comparison of hyphenated thermogravimetric techniques for elastomer analysis ...

DMA is an analysis technique used to determine the dynamic properties of the elastomers [13, 14]. Dynamic properties of the elastomeric materials are important because they influence the performance of certain parts such as wheels and tyres. This method determines the storage modulus G (elastic behaviour), loss modulus G (energy dissipation), tan 8, loss compliance ]" and glass transition temperature (Tg) values. The Tg of the soft segment can determine the low temperature behaviour of polyurethane elastomers. This is not only influenced by the nature of the soft... 

Dynamic mechanical analysis techniques permit measurement of the ability of materials to store and dissipate mechanical energy during deformation. DMA is used to determine the modulus, glass transition, mechanical damping and impact resistance, etc., of thermoplastics, thermosets, elastomers and other polymer materials. Information regarding the phase separation of polymers is also available by DMA [2]. In DMA, viscoelastic materials are deformed in a sinusoidal, low strain displacement and their responses are measured. Elastic modulus and energy dissipation are the measured properties. 

Sircar and co-workers [8] compared experimental and data from the literature for the Tg of some common elastomers determined by different thermal analysis techniques, including DSC, TMTA, DMTA, dielectric analysis and thermally stimulated current methods. Elastomers examined include natural rubber, styrene-butadiene rubber, polyisoprene, polybutadiene, polychloroprene, nitrile rubber, ethylene-propylene diene terpolymer and butyl rubber. Tg values obtained by DSC, TMA and DMTA were compared. Experimental variables and sample details, which should be included along with Tg data were described, and the use of Tg as an indication of low temperature properties was discussed. 

Sircar, A. K., Galaska, M. L., Rodrigues, S., and Chartoff, R. P., Glass Transition of Elastomers Using Thermal Analysis Techniques, Rubber Division Meeting, ACS Lonisville, KY (Oct. 1996)... 

In an NMR analysis of the effects of /-irradiation induced degradation on a specific polyurethane (PU) elastomer system, Maxwell and co-workers [87] used a combination of both H and 13C NMR techniques, and correlated these with mechanical properties derived from dynamic mechanical analysis (DMA). 1H NMR was used to determine spin-echo decay curves for three samples, which consisted of a control and two samples exposed to different levels of /-irradiation in air. These results were deconvoluted into three T2 components that represented T2 values which could be attributed to an interfacial domain between hard and soft segments of the PU, the PU soft segment, and the sol... 

Sircar [138] has reviewed the analysis of elastomer vulcanisate composition by TG/DTG techniques. The classical ASTM method, D297-93 [139], is too lengthy to be of much practical use on a routine basis, often requires preliminary identification of the polymer and is costly. TG has gained itself wide acceptance as a method for quantitative compositional analysis of vulcanisates ASTM El 131 [140], is basically designed for the analysis of rubber compounds [141]. Thermogravimetric analysis can be used to determine ... 

Valuable reviews and books of structural analysis of elastomers have been published by several authors [1-6]. Some of these reviews provide excellent explanation on the basic theory of sequence distribution of copolymer and NMR techniques applicable to elastomers. Typical high-resolution 3H- and 13C-NMR spectra of various vulcanisates and raw rubbers are depicted in a book written by Kelm [6]. The assignments and references shown for each rubber are very useful for structural studies of elastomers. In view of recent progress in the hardware and software of NMR, this chapter describes some of the more recent applications of high-resolution NMR to the structural characterisation of elastomers, after a brief description on the fundamental structural features of elastomers. 

Mixing and extrusion techniques are usually applied to elastomers for processing and improvement of physical properties. These mechanical processes normally lead to the occurrence of radical reactions such as chain scission, chain coupling, and crosslinking. The 13C-NMR analysis of EP showed that the shearing of polymer resulted in hydrogen abstraction. This was followed by disproportionation reaction to form olefins [75]. 

A powerful technique for the study of orientation and dynamics in viscoelastic media is line shape analysis in deuteron NMR spectroscopy [1]. For example, the average orientation of chain segments in elastomer networks upon macroscopic strain can be determined by this technique [22-31]. For a non-deformed rubber, a single resonance line in the deuterium NMR spectrum is observed [26] while the spectrum splits into a well-defined doublet structure under uniaxial deformation. It was shown that the usual network constraint on the end-to-end vector determines the deuterium line shape under deformation, while the interchain (excluded volume) interactions lead to splitting [26-31]. Deuterium NMR is thus able to monitor the average segmental orientation due to the crosslinks and mean field separately [31]. 

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