Chemical reactions depolymerization

The traditional pulp/paper composition metrics (e.g. specific lignin and cellulose contents) are based on chemical reaction (depolymerization) of the native biomass into fractions. Each separated fiaction is then independently pyrolysed, and the pyrolysis yields are fit to models, and the composite used to predict other woody species ... 

These techniques help in providing the following information specific heat, enthalpy changes, heat of transformation, crystallinity, melting behavior, evaporation, sublimation, glass transition, thermal decomposition, depolymerization, thermal stability, content analysis, chemical reactions/polymerization linear expansion, coefficient, and Young s modulus, etc. 

Most chemical reactions do not progress completely from reactants to products. Instead, the net reaction stops in the forward direction when equilibrium is established. Analysis of the contents of the reaction vessel would show a constant concentration of monomers and polymer once equilibrium is reached. This situation is actually a dynamic equilibrium, where the monomers are forming polymers at the same rate as the polymers depolymerize to monomer. Therefore, at equilibrium, the net concentrations of any one species remains constant. The amount of monomer converted into polymer will be defined by the equilibrium constant, K. This constant is the ratio of the concentration of the products to the reactants, with each concentration raised to the stoichiometric coefficients in the balanced equation. For Eq. 3.5 ... 

Chemical reactions Decomposition Depolymerization Carubrization Oxidation... 

Water is not just the solvent in which the chemical reactions of living cells occur it is very often a direct participant in those reactions. The formation of ATP from ADP and inorganic phosphate is an example of a condensation reaction in which the elements of water are eliminated (Fig. 2-22a). The reverse of this reaction— cleavage accompanied by the addition of the elements of water—is a hydrolysis reaction. Hydrolysis reactions are also responsible for the enzymatic depolymerization of proteins, carbohydrates, and nucleic acids. Hydrolysis reactions, catalyzed by enzymes called... 

The mechanism of formation of zeolites is very complex, stemming from the diversity of chemical reactions, including various polymerization and depolymerization equilibria, nucleation and crystal growth processes. The physical and chemical nature of the reactants, which typically involve a source of aluminum and silicon along with hydroxides and salts determine the formation of zeolites. Physical effects such as aging, stirring, and temperature also play an important role. These effects lead to the complexity of zeolite formation, but are also responsible for the large number of frameworks that can be synthesized and the rich chemistry associated with this area. Cl. 21... 

The need to drive the polymerizations to completion is common to all step-growth reactions that are carried out under conditions in which polymerization-depolymerization equilibria are significant (Section 5.4.2). This is accomplished in general by removal of a volatile product such as water or an alcohol. The rale of polymerization is often limited by the rate of transfer of such condensation products into the vapor state. A complete kinetic description of the process must then involve both the chemical reaction rate and the rate of mass transfer. The latter depends on the details of reactor design and stirring and therefore so does the rate of polymer production [1]. 

However, any of the multitude of chemical reactions that disrupt the intramolecular and intermolecular bonds within and among the wood components will have deleterious effects on wood properties. The obvious extreme would be the complete depolymerization and dissolution of the wood components with complete destruction of the wood. These processes of depolymerization or solubilization of the wood components do not have to go to completion to bring about marked changes in wood properties or degradation. 

Chemical reactions such as pyrolysis, depolymerization, and condensation could be clarified. Moreover, application of the technique seems to be promising in the mechanism of coal liquefaction as well as in that of mesophase formation. 

This process involves reversing chemical reaction where the organic polymer is converted back to more basic chemical building blocks. Among these processes, hydrolysis, glycolysis, methanolysis, and aminolysis are well known. This depolymerization process will also free the glass fiber reinforcement, which is an added value. 

Thus, decreases in the physical-mechanical characteristics of RubCon under the action of inorganic acids is caused by various speeds of chemical reactions such as corrosion, oxidation, sulfiding, chlorination, and so on. Processes of oxidation and depolymerization proceed with formation of low-molecular compounds containing hydroxyl and carboxyl groups. The process of oxidation has a branched-out character. 

Although the polyurethanes form useful adhesive bonds, particularly between metals and elastomers, their use in the aerospace industry for bonding purposes is limited. Because polyurethanes tend to depolymerize above 120 °C and are subject to hydrolysis, and because aromatic urethanes autoxidize when exposed to thermal or UV light (13). epoxies are the preferred bonding material. Recently they were studied as launch seals for both land and sea missile launch tubes and were found to be superior to seals based on neoprene rubber (14). The chemical reaction for this application is proposed to be that between isocyanates and amines (Reaction 3). 

The term reactive processing is used to describe a polymer processing that involves chemical reactions. In principle, any processing operation can be conducted as a reactive process, viz. reactive injection molding (RIM). However, most often the term refers to reactive extrusion, and in particular, to the reactive compatibilization of immiscible polymer blends, usually conducted in a TSE. During the last 50 years, the latter machines have been used as chemical reactors for the polymerization, depolymerization (chemical recycling), polymer modification and compatibilization [Brown, 1992, Xanthos, 1992 Utracki, 1989, 1991, 1994, 1997]. 

One area of Robert Simha s activity that is missing here is work on the kinetics and statistics of chemical reactions such as polymerization, copolymerization, depolymerization, degradation, and sequencing of biomacromolecules (e.g., proteins, polynucleotides, DNA). The decision to omit this topic was based, on the one hand, on its chemical character, and on the other, on the vastness of these topics, which would essentially require an additional volume. 

Oxidized products are normally prepared by treatment with an alkaline hypochlorite. This treatment results in two chemical reactions taking place simultaneously a partial depolymerization that lowers molecular weight, and the introduction of some carbonyl and carboxyl groups. 

In principle, the chemical reactions of macromolecules should be similar to those of low-molecular-weight substances. Experimentally, however, either degradation is found to occur at very much lower temperatures or, occasionally, there is degradation into different products. The decomposition of poly(ethylene), for example, begins at 200°C lower than that of hexadecane. At 450°C, poly(methyl methacrylate) will be almost completely depolymerized into monomer, methyl methacrylate (Table 23-2). At this temperature, on the other hand, low-molecular-weight primary esters decompose into olefins and acids. The nature of the product also depends on whether the experiment is carried out at atmospheric pressure under nitrogen or under high vacuum (Table 23-3). 

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