Peptizers, chemical

Peptizers such as pentachlorothiophenol are generally used at levels between 0.1 and 0.25 phr. This enables significant improvement in compound processability, reduction in energy consumption during mixing, and improvement in compound uniformity. High levels can, however, adversely 

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Neoprene AH (1975). It is a methylacrylate-modified elastomer which is non-crystallizing and is chemically peptizable in aliphatic solvents. However, it is generally prepared as a dispersion in hexane, and has balanced properties between conventional solvent-borne adhesives and aqueous systems. 

Table 15.5 shows the results of Mochel [22] for the effect of conversion upon the gel content of polychloroprene rubbers prepared by emulsion polymerization at 40 °C. In section (a) of this table are shown results for polymers produced in the absence of added sulfur section (b) shows results for polymers produced with the addition of 0.6 parts of sulfur per 100 parts by mass of chloroprene, before chemical peptization of the polymer. In both types of reaction system, polymer gel begins to form quite early in the reaction. However, these results indicate that sulfur has a slight tendency to act as a modifier during the polymerization, in that the onset of gel-formation is delayed when sulfur is present. Also delayed is the pdnt at which the polymer is virtually entirely gel. Mochel et al. [23] have reported results for the molar mass distribution of a thiuiam-modified polychloroprene rubber produced by emulsion polymerization at 40 °C,... 

Mixing Chemical peptizer 2,2 -Dibenzami didiphenyl-disulfide Pentachlorothiophenol Reduces polymer viscosity by chain scission reduces molecular weight... 

Styrene butadiene rubber is generally marketed at lower viscosity grades than NR and this permits its use in rubber compounding without premastication. Mechanical or chemical peptizing (or dispersing as a colloid, or suspension) is not required in SBR rubber. While most properties of SBR are comparable with NR, in some respects, such as heat build up, tack and gum tensile strength, SBR is inferior but addition of resins and reinforcing fillers improves these properties acceptably. 

Mastication of ENR can be carried out on an open mill or in an internal mixer, and chemical peptizers may be employed to increase the rate of breakdown (Fig. 7). 

The most common chemical peptizers in general use are based on a number of chemical classes. These are aromatic mercaptans, arylam-iiles, sulphonic acids and derivatives, pentachlorothiophenol and... 

The processing of natural rubber with chemical peptizers both in single-stage, full-chamber mastication and as part of a mixing cycle (called in batch peptization) was investigated for efficiency of breakdown and possible effects of chemical peptizers on subsequent vulcanizate properties. 

Alternative peptizers , or viscosity reducers as they may more properly be called, are based upon fatty-acid soaps. These are known to be less potent than true chemical peptizers and as they are used at substantially greater concentrations, they may be more evenly and quickly distributed. Two types of material are available in this category (a) fatty-acid soaps and (b) blends of such soaps with chemical peptizers. For convenience these are dealt with separately. 

Fatty-acid soaps have some inherent characteristics which make them more acceptable as a means of reducing compound viscosity than do chemical peptizers. Because of their fatty-acid soap base they could eliminate or reduce the need for added fatty acid activators, and considerably reduce the stickiness of low-viscosity natural rubber masterbatches. They can be used in a number of applications where conventional chemical peptizers could cause contamination problems, e.g. in the food industry. They must, however, be used in considerably higher dosages than chemical peptizers. 

Internal lubrication. Unlike chemical peptizers these materials do not catalyse the breakdown of the backbone of the polymer chain during mechanical shearing, but appear to act as internal... 

Blends of Fatty-Acid Soaps with Chemical Peptizers... 

These materials were introduced to the market in order to achieve the type of breakdown desired but not achieved by chemical peptizers or fatty-acid soaps alone. The blend should ensure rapid, even distribution of the chemical peptizer, eliminating the localized peptization often encountered with poorly dispersed material and resulting in a more homogeneous and less tacky peptized material. Better dispersion arises because of higher bulk of the blend, and lubrication of surface of the peptizer by the fatty-acid soap facilitates dispersion. 

Fig. 15. Effect of fatty-acid soap/chemical peptizer blends on viscosity. Conditions K2A Intermix, 50 rpm, 100 psi, start 100°C.

Crowther, B. G., Peptization of natural rubber in an internal mixer, Pt II. Fatty add soaps and blends with chemical peptizers, Nat Rubber TechnoL, 14(1), 1983, 1. 

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