Molecular weight reduction

Radiation Effects. The primary effect of radiation is the degradation of large molecules to small molecules. Molecular weight reduction can be... 

Lubricants. Lubricants are used to improve the melt flow, screw feeding, and mold release of nylons. Long-chain acids, esters, and amides are used together with metal salts, eg, metal stearates. Improved melt flow is mainly a function of molecular weight reduction during mol ding. Mold release is improved by waxes of limited compatibiHty with nylon, which migrate to and lubricate the mold surface. 

Coal Hquefaction iavolves raising the atomic hydrogen-to-carbon ratio from approximately 0.8/1.0 for a typical bituminous coal, to 2/1 for Hquid transportation fuels or 4/1 for methane (4). In this process, molecular weight reduction and removal of mineral matter and heteroatoms such as sulfur, oxygen, and nitrogen may need to be effected. 

The solid fuel composition is, therefore, concerned with the pursuit of higher I p involving both flame temperature elevation and molecular weight reduction. Concomitantly, it is desirable to have high heat of combustion, which also dictates the combustion chamber temperature. The actual composition is, therefore, set on the basis of the energy quantum inherent in the various constituents. 

Hawkins, G.W. "Molecular Weight Reduction and Physical Consequences of Chemical Degradation of Hydroxypropylguar in Aqueous Brine Solutions," Polvm. Mat. Sci. Eng.(1986) 55, 588-93. 

On the basis of the data at hand, we are currently considering two possible modes of molecular weight reduction. The first involves the generation of thermally weak bonds by the initial addition of hydrogen. We suggest that the addition of hydrogen to the structures below may be a key to the cleavage of critical bonds in coal. 

They may also act as reactive super plasticisers to increase rubber flow while increasing the mechanical properties of the rubber. Viscosity reduction or polymer solvation and higher filler loading can be accomplished with less plasticiser. Flow is achieved through molecular rearrangement and not average molecular weight reduction of the rubber. 

On the basis of the results described, there seem to be at least three processes which are responsible for the molecular weight reduction in substituted silane high polymers upon irradiation in solution (i) Chain abridgement by silylene extrusion which occurs only at short wavelengths (ii) chain scission by silicon-silicon bond homolysis and (iii) chain scission by 1,1-photochemical reductive elimination. 

Since chemical nucleating agents actively scission PET chains as part of their action, a drop in PET intrinsic viscosity can result. One strategy to offset this accompanying molecular weight reduction is to use both a nucleating agent and a chain extender in combination. 

Newer nucleators include pyrrole-based salts which seem to produce chemical nucleation with a minimal molecular weight reduction. 

Molecular weight reduction probably plays a role even in pretreatment processes that are not intended to cause this effect (19). The most common method of molecular weight reduction is the addition of dilute acid to hydrolyze the acetal groups (I). The acid may be generated in situ by the liberation of acetic acid from acetate groups by steam or hot water. 

Other methods of molecular weight reduction include pentosanase treatment or formation of low-molecular-weight acetals. Oxidative cleavage of hemicellulose also could lead to reduced molecular weight. 

Dispersal of lignin as a colloid is a close relative of true solution as a means of lignin removal. Dispersing agents include alkalis. Effective dispersion may involve molecular weight reduction as a necessary condition. 

The feed stream can be reactor polymer in powder form, which is then chemically modified (e.g., peroxide molecular weight reduction of polypropylene, known as... 

PTFE is attacked by irradiation by y-rays, high-energy electron beams, or X rays. The degradation of the polymer in air or oxygen occurs due to scission of the chain and is fairly rapid. Such scission results in molecular weight reduction.20 When irradiated by an electron beam, the molecular weight is reduced up to six orders of magnitude to produce micropowders.21... 

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