Analysis of bound rubber

Although many interface models have been given so far, they are too qualitative and we can hardly connect them to the mechanics and mechanism of carbon black reinforcement of rubbers. On the other hand, many kinds of theories have also been proposed to explain the phenomena, but most of them deal only with a part of the phenomena and they could not totally answer the above four questions. The author has proposed a new interface model and theory to understand the mechanics and mechanism of carbon black reinforcement of rubbers based on the finite element method (FEM) stress analysis of the filled system, in journals and a book. In the new model and theory, the importance of carbon gel (bound rubber) in carbon black reinforcement of rubbers is emphasized repeatedly. Actually, it is not too much to say that the existence of bound rubber and its changeable and deformable characters depending on the magnitude of extension are the essence of carbon black reinforcement of rubbers. 

The new interface model and the concept for the carbon black reinforcement proposed by the author fundamentally combine the structure of the carbon gel (bound mbber) with the mechanical behavior of the filled system, based on the stress analysis (FEM). As shown in Figure 18.6, the new model has a double-layer stmcture of bound rubber, consisting of the inner polymer layer of the glassy state (glassy hard or GH layer) and the outer polymer layer (sticky hard or SH layer). Molecular motion is strictly constrained in the GH layer and considerably constrained in the SH layer compared with unfilled rubber vulcanizate. Figure 18.7 is the more detailed representation to show molecular packing in both layers according to their molecular mobility estimated from the pulsed-NMR measurement. 

Calculations have also shown that the fraction of bound rubber contains only a small part of the surface attachments in the vulcanizate. Analysis of the interrelationship of the number of attachments, the crosslink density, and the properties of the vulcanizate indicates that the reinforcement is connected with the concentration of links on, or close to, the surface of the particle. 

Several studies characterizing the reactions of alkenyl radicals with quinone dumines and quino-neimines were published in the late 1970s. Quinone dumines react with allylic radicals yielding both the reduced PPD and the alkylated product. In these experiments 2-methyl-2-pentene served as a model olefin (model for NR). Samples of the olefin and quinoneimines or quinone diimine were heated to 140°C. Isolation and analysis of products demonstrated that 40%-70% of the imine or diimine was reduced to the corresponding PPD, while 20%-50% was isolated as the alkylated product. This alkylation reaction (via an allylic radical) represents the pathway to the formation of rubber-bound antidegradant. ... 

It is of interest to examine the development of the analytical toolbox for rubber deformulation over the last two decades and the role of emerging technologies (Table 2.9). Bayer technology (1981) for the qualitative and quantitative analysis of rubbers and elastomers consisted of a multitechnique approach comprising extraction (Soxhlet, DIN 53 553), wet chemistry (colour reactions, photometry), electrochemistry (polarography, conductometry), various forms of chromatography (PC, GC, off-line PyGC, TLC), spectroscopy (UV, IR, off-line PylR), and microscopy (OM, SEM, TEM, fluorescence) [10]. Reported applications concerned the identification of plasticisers, fatty acids, stabilisers, antioxidants, vulcanisation accelerators, free/total/bound sulfur, minerals and CB. Monsanto (1983) used direct-probe MS for in situ quantitative analysis of additives and rubber and made use of 31P NMR [69]. 

Re-aggregation, filler cluster 76 Region of analysis 134 Reinforced rubber 76 Reinforcement, hydrodynamic 63-64 Relaxation time 118 Rubber, bound 47-50, 61 -, reinforced 33, 60, 63, 76... 

A rapid technique for determining bound MAH content in maleated EPDM rubbers was established. It is based on the application of diffuse reflectance FTIR which permits the analysis of such products directly without any sample preparation other than removing unreacted monomer and initiator. The spectrum obtained also allows the evaluation of the rubber s relative oxidation extent. Baseline and band choices as well as calculation methods required are discussed. 12 refs. 

In the scientific literature, nuclear magnetic resonance (NMR)," bound rubber measurements and glass transition (Tg) determination through calorimetric analysis are preferentially adopted for investigating the filler-rubber interaction, whereas microscopic analysis is in particular selected for assessing filler distribution and dispersion and for depicting the nature of the filler network. ... 

Since we are dealing with a niunber of different effects superimposed on each other, according to Kraus, it is natural to observe a lack of correlation between the bound rubber content and reinforcement. The nature of polymer-filler bonds and their role in the reinforcement of elastomers was considered by Rehner. On the basis of analysis of the deformation properties, it was estab-hshed that the strength of bonds present in vulcanizates is characterized by a very broad spectnim of forces. From the data on the swelling of filled systems, it is possible to determine the concentration of physical bonds (or attachments) of macromolecides to the surface, which restrict the degree of swelhng and the niunber of chemical crosshnks. 

Pliskin I and Tbkita N (1972) Bound rubber in elastomers analysis of elastomer-filler interaction and its effect on viscosity and modulus of composite systems, J Appl Polym Sci 16 473-492. 

The advantage of the Py-GC-MS method over other methods for measuring styrene content of SBR copolymer is its relatively easy use for analysis of clear polymers as well as polymers containing process oils, fillers, and carbon black, and even cured rubbers. Moreover, the percent bound styrene obtained by this technique is not affected by changes of copolymer microstructure. Results of this work clearly show that the percentage of styrene obtained by this technique correlates very well with the results obtained by other methods. 

Antioxidants have been shown to improve oxidative stability substantially (36,37). The use of rubber-bound stabilizers to permit concentration of the additive in the rubber phase has been reported (38—40). The partitioning behavior of various conventional stabilizers between the rubber and thermoplastic phases in model ABS systems has been described and shown to correlate with solubility parameter values (41). Pigments can adversely affect oxidative stability (32). Test methods for assessing thermal oxidative stability include oxygen absorption (31,32,42), thermal analysis (43,44), oven aging (34,45,46), and chemiluminescence (47,48). 

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