Rubber systems, mechanisms

ZnO nanoparticles possess greater surface/volume ratio. When used in carboxylated nitrile rubber as curative, ZnO nanoparticles show excellent mechanical and dynamic mechanical properties [41]. The ultimate tensile strength increases from 6.8 MPa in ordinary rabber grade ZnO-carboxylated nitrile rubber system to 14.9 MPa in nanosized ZnO-carboxylated nitrile mbber without sacrificing the elongation at failure values. Table 4.1 compares these mechanical properties of ordinary and nano-ZnO-carboxylated nitrile rubbers, where the latter system is superior due to more rubber-ZnO interaction at the nanolevel. 

Comparative Mechanical Properties Data on Ordinary ZnO and Nano-ZnO-Filled Carboxylated Nitrile Rubber Systems... 

Until 1920, the only flexible foam available was the natural sponge, but chemically foamed rubber and mechanically foamed rubber latex were introduced before World War II. These foams may consist of discrete unit cells (unicellular, closed cell), or they may be composed of interconnecting cells (multicellular, open cells) depending on the viscosity of the system at the time the blowing agent is introduced. Over 1.5 million tons of foamed plastic is produced annually in the United States. 

Schonherr [43] has described the combination of decomposition in a thermogravimetry oven and FTIR spectroscopy for the identification of base polymers in elastomers, as exemplified for nitrile rubber, and has presented infrared spectra for decomposition products of various rubbers. The same author [36] studied use of the integrated TG-FTIR system for the identification of sixteen vulcanised rubbers in mechanical goods reporting the characteristic infrared spectra of the degradation products at temperatures ranging from 334 °C to 635 °C. 

In rubber systems containing carbon black, flocculation may cause substantial changes in mechanical properties. Flocculation in these systems counteracts filler dispersion. Carbon black flocculation occurs in filled rubber stock during storage or during vulcanization in the absence of shear. " Temperature is the important kinetic factor which affects the flocculation rate (Figure 5.19). In addition to temperature and time, flocculation depends on the type of carbon black and its concentration. 

When bonding compounded rubber to fabric, for the manufacture of fabric reinforced expansion joints in the chemical plant piping systems, mechanical anchoring between cotton/Nylon/fibre and compounded rubber should be sufficient to ensure good adhesion. Synthetic fibres require treatment with chemical coatings to secure maximum adhesion and bond [8, 9]. 

Polypropylene (PP) is often blended with ethylene/propylene (BP) rubbers to improve the impact resistance. This so-called toughened PP (TPP) can be a mechanically blended PP/C2C3 rubber system or an in-situ polymerised PP/C2C3 rubber system. A number of rubber parameters (like concentration, particle size, particle size distribution, crystallinity, molecular weight etc.) determine the ultimate effect of the rubber addition on the impact resistance. DMA is one of the analytical techniques often used to investigate blends of polymers with an impact improver. The determination of the relation between the area of the rubber relaxation maximum as measured by DMA and the rubber concentration is usually a first step in such an investigation. The method to determine this area and the results measured on a series of PP/C2C3 rubber blends are reported below. 

Fig. 16.11 compares the payback time for the installation of sponge rubber ball mechanical cleaning of heat exchangers [EPRI 1987]. Although these data were again published in 1987 and will therefore include historical costs, they do indicate economic advantage in respect of the system. 

Scheme 1. Reaction mechanism of condensation-curing RTV-2 silicone rubber systems.

The fourth and fifth papers have to do with properties of pressure-sensitive adhesives. In particular, the matter of how the materials composing pressure-sensitive adhesives (rubbers and resins) interact and phase separate to produce the phenomenon of tack or pressure-sensitivity is addressed. Both studies use dynamic mechanical measurements to uncover phasing - one in a silicone and the other in natural and styrene-butadiene rubber systems tackified with various resins. 

Natural rubber (NR) is a classic elastomer with good processability and excellent mechanical properties. It is widely used in various applications such as automobiles, gloves, tyres and seals. With the increasing demand for NR composite materials for applications at high temperatures with high performance, for example in the automobile industry, there has long been increasing interest in NR-based composites blended with other rubber systems. ... 

Abstract Rubber materials are viscoelastic systems whose properties, broadly speaking, are complex functions of time, strain, strain rate, temperature (and composition if they are inhomogeneous). Material functions are mathematical relationships that intend to describe the behavior of a material, either a solid or a liquid, when submitted to a range of strains or strain rates, with obviously temperature effects. For viscoelastic materials, such as rubber gum and compounds, these functions obviously encompass both the linear and the nonlinear domains. Providing material functions are considered in their full complexity, in other terms with respect to a multiparametric approach, they provide information about the processing behavior and the mechanical properties of rubber systems. 

Roginovskaia, G. E, Mechanism of formation of phase structure in epoxide-rubber systems, Vysokomol. Soedin., A 25, 1979, 1983 (Russian). 

Dynamic mechanical analysis (DMA) has been used to study the flow behavior of hot-melt adhesives.Drummer and co-workers used DMA to study the viscoelastic behavior of adhesives. They found that dynamic mechanical measurements in adhesives provided insight in the macromolecular mobility of the polymer or rubber system studied. The viscoelastic behavior at various temperatures can be correlated with standard measurements such as adhesive force, shear strength, and tack. The authors concluded that three-dimensional DMA plots from frequency-temperature sweeps provide a complete overview of the frequency and temperature dependence ofthe adhesive. Foster, etal., characterized the hot-tack differences in hot-melt adhesives using DMTA. 

F. Yatsuyagagi, H. Kaidou, N. Suzuki, and M. Ito, Relationship between secondary structure of fillers and the mechanical properties of silica filled rubber systems , ACS Rubber Division Meeting, Providence, RI, April (2001)... 

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