Latex chemical reactions

This term was originally limited to the chemical reaction of rubber with sulphur to bring about the following effects (a) reduced thermoplasticity, (b) increased tensile strength and resistance to abrasion, and (c) reduced solubility in organic solvents. Since many other substances can bring about the above changes the term has now been widened to include any treatment which will introduce crosslinks in the rubber matrix. Vulcanised Latex... 

The engineering analysis and design of these operations addresses questions which are different than those addressed in connection with the shaping operations. This is illustrated in Fig. 1 which is a flow sheet, cited by Nichols and Kheradi (1982), for the continuous conversion of latex in the manufacture of acrylonitrile-butadiene-styrene (ABS). In this process three of the nonshaping operations are shown (1) a chemical reaction (coagulation) (2) a liquid-liquid extraction operation which involves a molten polymer and water and (3) a vapor-liquid stripping operation which involves the removal of a volatile component from the molten polymer. The analysis and design around the devolatilization section, for example, would deal with such questions as how the exit concentration of... 

As compressed carbon dioxide is a nonpolar molecule with weak van der Waals forces (low polarizability per volume), it is a relatively weak solvent [1], Thus, many interesting separations and chemical reactions involving insoluble substances in CO2 can be expected to take place in heterogeneous systems, for example, microemulsions, emulsions, latexes and suspensions. Microemulsion droplets 2-10 nm in diameter are optically transparent and thermodynamically stable, whereas kinetically stable emulsions and latexes in the range from 200 nm to 10 pm are opaque and thermodynamically unstable. 

Natural rubber-based adhesives constitute many nsefnl types of adhesives. They have been made from the latex that is collected from the sap of rubber trees grown in Malaysia and other countries of Sonth East Asia. Rnbber of this type was first collected from the Hevea brasiliensis tree - seeds from the tree were first taken from the Amazon forests in Brazil, propagated in Kew in London, and then supplied, over a century ago, to Malaya and adjacent counuies, where there are now many millions of rubber trees, yielding cis-polyisoprene-based natnral rnbber. This has similar properties to the principal SBR synthetic rubber, derived from styrene and butadiene, both of which are obtained by the cracking process from crnde oil, with subsequent chemical reactions. Natural rubber is obtained from the uee by tapping the bark, when the latex flows out spontaneously as the tree is wounded. This latex is about 33% solids - most natural rubber latex is concentrated to 60% and preserved with ammonia for transport and storage. 

The major goals of our catalysis research are to determine the range of catalytic processes that may be performed in colloidal environments and to understand the mechanisms of chemical reactions that take place at the surface and within colloidal particles. Despite the wide use of colloidal polymers (also known as latexes) in rubber, coatings, and adhesives, few chemical reactions have been carried out with them. The likely reasons are that their structures are not well understood, and they can be difficult to maintain in the colloidal state without coagulation. These problems require that we investigate not only chemical reactions, but also colloid stabilization and surface stmctures, for chemical reactions using active colloidal catalysts proceed at the particle surface. 

Today s environmental concerns demand clean reaction processes that do not use harmful organic solvents.Water is without doubt the most environmentally friendly solvent. NR latex is exuded from the Hevea tree as an aqueous emulsion therefore, it would be desirable to modify the NR latex. Many chemical reactions, such as hydrogenation, epoxidation, chlorination,graft copolymerization and oxidative degradation have been performed on the reactive double bonds of the isoprene structure along the molecular chain. 

R, R and R are respectively the polymerization, initiator decomposition, and latex particle generation rates functions, and U is the heat transfer coefficient between the emulsion and the jacket fluid, according to standard expressions [2, 42], Uj is the heat transfer coefficient associated to the heat lost to the surroimdings. Q is the heat generation rate by chemical reaction, and H is the emulsion-jacket fluid heat exchange rate. C is the heat capacity of the emulsion, and Cj is the heat capacity of the jacket system made by the reactor (R), jacket (J) and insulator (I) walls as well as by the jacket fluid (F). Thus,... 

The concept of free radical capture efficiency was incorporated into the work of Hansen and Ugelstad [26,27], Based on the mechanism of mass transfer with simultaneous chemical reactions, the net rate of absorption of free radicals by a single latex particle (pJNp) can be written as... 

Asua et al. [56-58] also derived a mechanistic model for predicting the desorption rate coefficient, which considers several possible chemical reactions for the desorbed free radicals in the continuous aqueous phase and the competitive free radical desorption and bimolecular termination reaction in the latex particles containing more than one free radical. Some other representative publications related to the free radical desorption process can be found in references 59-61. 

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