Peptization


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peptization

[‚pep·tə‚zā·shən]
(chemistry)
Aggregation in which a hydrophobic colloidal sol is stabilized by the addition of electrolytes (peptizing agents) which are adsorbed on the particle surfaces.
Liquefaction of a substance by trace amounts of another substance.

Peptization

 

the spontaneous breakup of aggregates— lumps, flocs, or clots that have formed by the accumulation of cohered colloidal particles—into smaller aggregates or individual primary particles. A particularly graphic example is the peptization of gelatinous precipitates (coagels), which are formed by the coagulation of sols and highly dispersed suspensions. Peptization involves the “colloidal dissolution” of the precipitate; that is, the coagulate becomes a sol once again. The term “peptization” is derived from the apparent similarity between this phenomenon and the breakdown of proteins by the enzyme pepsin.

Peptization may be observed upon elevation of temperature or upon removal of the coagulating reagents by rinsing the precipitate. The most typical form of peptization occurs upon introducing peptizing agents—substances that promote disaggregation, that is, the separation of cohered particles—into a dispersion medium. The peptizing agents may be electrolytes or surfactants, which cause particle surfaces of the disperse phase to become lyophilic. For example, the peptization of ferric hydroxide gel in an aqueous medium is made possible by the addition of small quantities of ferric chloride, whereas kaolin is peptized by humic acids.

Agitation usually accelerates peptization. Recrystallization and coalescence, which often occur in colloidal precipitates upon aging, hinder peptization, since they promote the consolidation of particles. The coagulation of sols by polyvalent ions and polyelectrolytes yields precipitates that also resist peptization.

Peptization is used to obtain liquid disperse systems from powders or pastes in chemical and food-processing technology. It plays an important role in the group of processes determining the cleansing action, formation, and destruction of various disperse structures. Sometimes peptization may be harmful, for example, if it occurs during the process for the purification of water or the clarification of wine.

L. A. SHITS

References in periodicals archive ?
in 2-3 micron size###hydrolyzing + acid peptization at 80 AdegC
###Ti(OBu)4 +HNO3 peptization, room###MO###mainly I>>I>> = 365 nm,
Anderson, Peptization Process in the Sol-Gel Preparation of Porous Anatase (TiO2), Chem.
Ferreira, Hydrothermal Synthesis of Nanosized Titania Powders: Influence of Peptization and Peptizing Agents on the Crystalline Phases and Phase Transitions, Synthesis (Stuttg)., 68, 1361 (2000).
The vulcanizate offers the best abrasion resistance with a moderate reduction in molecular weight (peptization), and in a tighter network (without oil), in line with what was observed for the 5% initial modulus.
26) and since with only the rubber present the mixer is relatively underloaded for peptization within the batch, relatively larger amounts of chemical peptizer (0.25 --> 0.5 phr) are necessary to give a useful reduction in viscosity (refs.
Blends of fatty acid soaps with chemical peptizers are intended to achieve peptization by lubrication of the molecular chain (also acting as dispersant and processing aids) and by chain scission (ref.
Peptization was done as a part of the first-stage internal mixer mixing cycle.
Silica-filled vulcanizates prepared from raw rubber subjected to peptization show some effects attributable to peptization (table 7).
In summary, for a silica filled compound, processing and wear are improved while tear properties and fatigue block tearing resistance fall when compound viscosity is decreased by lowering (premastication and/or peptization) the viscosity of raw natural rubber.
Peptization - In order to decrease the third-stage viscosity, we combined peptization during the first-stage sequence and the optimized three-stage mixing procedure (mixing sequence n degrees 11).