Degradation reaction

The glycogen phosphorylase reaction degrades glycogen to produce limit dextrins, which are further degraded by debranching enzyme, as already described. 

A number of important physical changes in a polymer may be measured by DSC. These include the glass transition temperature (Tg), the crystallization temperature (Tc), the melt temperature (Tm), and the degradation or decomposition temperature (TD). Chemical changes due to polymerization reactions, degradation reactions, and other reactions affecting the sample can be determined (Table 16.1). A typical DSC trace showing these transitions is shown in Fig. 16.1. 

Very recently, attempts have been made to develop PP/EOC TP Vs. In order to make TPVs based on PP/EOC blend systems, phenolic resin is ineffective because the latter needs the presence of a double bond to form a crosslinked network structure. Peroxides can crosslink both saturated and unsaturated polymers without any reversion characteristics. The formation of strong C-C bonds provides substantial heat resistance and good compression set properties without any discoloration. However, the activity of peroxide depends on the type of polymer and the presence of other ingredients in the system. It has been well established that PP exhibits a (3-chain scission reaction (degradation) with the addition of peroxide. Hence, the use of peroxide only is limited to the preparation of PP-based TPVs. Lai et al. [45] and Li et al. [46] studied the fracture and failure mechanism of a PP-metallocene based EOC based TPV prepared by a peroxide crosslinking system. Rajesh et al. 

Radiation-induced chlorination of polyisobutene in carbon tetrachloride was studied at various temperatures. The process is a chain reaction with a G value of about 10 to 105, depending on the reaction conditions. At very low dose rates (0.1 to 0.2 rad I sec), the chlorination rate is directly proportional to the dose rate. At higher dose rates, the rate approaches a square-root dependence on the dose rate. The termination reaction and the influence of oxygen are discussed. The reaction is first order with respect to chlorine concentration. An activitation energy of about 4 kcal/mole was obtained. In connection with the chlorination reaction, degradation of the polyisobutene takes place. This degradation was followed by osmometric measurements. The structure of the chlorinated product was briefly investigated by IR spectroscopy. 

Degradation reactions Degradation of polypropylene by shear-heating, degradation of PET with ethylene glycol... 

Most PET is prepared by catalysed ester-interchange between DMT and glycol, followed by catalysed polycondensation. In the case of PET prepared directly from TA, catalysts are customarily used only in the polycondensation stage. The choice of the best catalyst or catalysts is obviously of extreme importance in the commercial preparation of PET. Rates of reaction must be as fast as can practically be achieved, and colour-forming side reactions, degradations, or reactions that lead to the copolymerization of excessive amounts of diethylene glycol must be minimized. 

Although this book is intended to address the chemorheology and reactive processing of polymers, the chemical reactions in the melt phase (e.g. branching reactions, degradation) may affect the subsequent solid-state and performance properties of the polymer. Furthermore, the end product of the reactive processing is the solid polymer and the transformation process from the liquid to the solid state of a polymer is fundamental to the success of the processing operation. It is therefore important to examine the way the polymer achieves its solid-state properties, and one of the most important properties... 

The major causes of instability of cellulose nitrate are due to the products of hydrolytic, thermal and photochemical reactions. Degradation of the polymer is autocatalytic, that is, the products of breakdown tend to catalyse a faster and more extensive degradation reaction than the primary processes, if allowed to remain in contact with degraded cellulose nitrate. 

The photolytic degradation of urea herbicides also proceeds in several steps. In addition to hydrolysis reactions, degradation products hydroxylated in the ring are formed in photonucleophilic reactions. In the case of monuron and linuron, hydrolysis is even preceded by the exchange of the chlorine at< ms of the ring for hydroxyl groups (Rosen et al., 1969 Crosby and Tang, 1969). 

When amino acids are metabolized, the excess nitrogen is concentrated into uric acid, a compound with five amide bonds. A series of enzyme-catalyzed reactions degrades uric acid to ammonium ion. The extent to which uric acid is de-... 

The Primary Redox-Reactions Degradation of Organic Matter... 

The residence time distribution depends on the screw configuration, throughput (or the degree of fill) and the screw speed. All three factors need to be optimized considering the rate of reaction, degradability of materials and productivity. 

During grafting in PP and PE, there occur opposing side reactions (degradation and crosslinking of the chains). It can be assumed, therefore, that certain quantities of... 

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