The phenomenon of insolubilization of rubber by carbon black has been known for at least twenty-seven years. There have been many attempts during this time to establish a relationship between insolubilization, or bound rubber formation, and reinforcement of rubber by carbon black. It was postulated, as far back as 1925, that there was a parallelism between particle size and insolubilization. This in spite of the fact that the methods available for determining particle size of very fine powders at that time were relatively crude. It was postulated at that time that there was a close relationship between the phenomena of vulcanization and reinforcement. This concept has had recurrent periods of popularity since that time. The insolubilization of rubber by carbon black, or other pigments, has been estimated by various techniques by the early investigators in the field. In more recent work, the trend has been toward a very straightforward experimental approach. Bound rubber in an uncured rubber-filler compound is usually determined by static extraction using the same apparatus and techniques used in determining the gel content of unfilled polymers. It follows that, using this method, polymer insoluble because of crosslinking, or gel, cannot be distinguished from polymer insolubilized by incorporation of fine fillers. In investigating the formation of bound rubber, therefore, the presence of gel in the polymer being used, or formation of polymer gel during processing must be taken into account.
1. Tensile strength is apparently a function of the particle size of the pigment and how well it is dispersed in a polymer. 2. Modulus and abrasion resistance are apparently functions of the interaction of the pigment and the polymer. This cannot be attributed entirely to bound-rubber formation, since bound rubber may occur without reinforcement, as shown by the results with silica pigment. 3. Results of processing studies show that Philblack O has a stabilizing effect on the polymer during processing and more consistent and better properties are obtained if processing is performed with carbon black present at temperatures below those for gel formation. This effect is more pronounced for less stable polymers such as polybutadiene. 4. Philblack O slows down gel formation. 5. It is possible that silica may have a destabilizing effect on polybutadiene unless it is buffered with agents such as resins, stearic acids, and diethylene glycol.
Pre-esterify tall oil with polyol before adding maleic to eliminate seeds .A.LTHOUGH much has been written about maleic-treated drying oils and rosin esters, little has been published about maleic-treated tall oils which are significant commercially. One earlier article (3) from this laboratory reported the effect of varying the amount of excess polyol. This article deals with work done over several years on reaction of maleic acid with tall oil.The amount of maleic anhydride used with tall oil varies from as little as 0.5%, when only a slight boost in viscosity or bodying rate is required, to 10% or more when maximum viscosity is sought for a blending vehicle. A problem associated with the latter type of vehicle initiated the experiments described. Major goals were to relate maleic reactivity with tall oil composition and eliminate formation of insoluble material.
Effects of Tall Oil Composition on Maleic ReactivityAlthough abietic acid is the principal rosin acid in tall oil, its percentage will vary somewhat with the source of the crude oil and method of refining. As maleic is generally assumed to react
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