Grades of stearic acid

A wide range of different grades of stearic acid are commercially available that have varying chemical compositions and hence different physical and chemical properties see Table III. A specification for stearic acid is contained in the Food Chemicals Codex (FCC). 

As mentioned earlier, this is the most widely used fatty acid for filler treatment. However, the reader must bear in mind that most commercial grades of stearic acid, as used in pre-coating fillers, are actually complex blends containing both saturated and... 

Rubber grades of stearic acid are defined in ASTM D4817. This standard defines five different grades of stearic acid (which are actually grades based on blends of stearic, palmitic, and oleic acids in different proportions). 

Stearic anhydride. Mix 1000 g of stearic acid (a commercial grade of stearic acid is suitable, provided that it has a good heat stability, an iodine value below 4 and crystallises well) and 550 g of acetic anhydride and boil under a reflux condenser for eight hours. Remove the excess of acetic anhydride and the acetic acid formed during the reaction, under vacuum, taking care that the temperature does not rise above 135 . 

Stearic acid (C18H36O2) and palmitic acid (C16H32O2) are common fatty acids. Commercial grades of stearic acid usually contain palmitic acid as well. A 1.115 g sample of a commercial-grade stearic acid is dissolved in 50.00 mL benzene d = 0.879 g/mL). The freezing point of the solution is found to be 5.072 °C. The freezing point of pure benzene is 5.533 °C, and Kf for benzene is 5.12 °C kg mol . What is the mass percent of palmitic acid in the stearic acid sample ... 

Table I compares the specifications for the 40-55% grades. Glyceryl monostearate PhEur and mono- and di-glycerides USPNF. PhEur divides glyceryl monostearate 40-55 into three types according to the proportion of stearic acid ester in the mixture, and those specifications are presented in Table II. Table III presents the specifications for glyceryl monostearate USPNF (90% monoglycerides). Since the JP specifications are broad enough to encompass both grades, JP is included in both Table I and Table III.

Several grades of oleic acid are commercially available ranging in color from pale yellow to reddish brown. Different grades become turbid at varying temperatures depending upon the amount of saturated acid present. Usually, oleic acid contains 7-12% saturated acids, such as stearic and palmitic acid, together with other unsaturated acids, such as linoleic acid. A specification for oleic acid is contained in the Food Chemicals Codex (FCC). The EINECS number for oleic acid is 204-007-1. 

Several grades of the acid are available in commerce, varying in color from pale yellow to red-brown and, depending nn the amount of saturated acid present, becoming turbid at 8-16, The acid of commerce usually contains 7-12% satura ted acids, e g., stearic, palmitic also some linoleic. etc., unsaturated acids. 

Materials. Two different lots of stearic acid were used in the experiments reported here, one purified sample being used for the stearic acid experiments, the other for making lithium stearate. The initial source for both was Eastman Kodak White Label grade, further purified by recrystallization according to the method of Brown and Kolb (6) from freshly distilled reagent grade acetone at — 20°C. 

Rubber-grade "stearic acid is usually a mixture of stearic acid (a Cl8 saturated fatty acid) and palmitic acid (a Cl6 saturated fatty acid) usually with a very small amount of oleic acid (a Cl8 fatty acid with one unsaturated site per molecule). Just as zinc oxide is ubiquitous in rubber recipes, so is rubber-grade stearic acid. Stearic acid and zinc oxide are almost always used together in rubber compounding. After these two ingredients are mixed in the rubber stock, they react with each other to solubilize the zinc (ion) into the rubber so that it will initiate the vulcanization process. 

Rubber grade zinc oxide can be surface modified, usually by the deposition of 0.2 to 0.4% of stearic acid, propionic acid, or light oil to facilitate mixing (see Section 7.2). 

FIGURE 1.7 Effect of zinc oxide and magnesium oxide levels on compound and vulcanizate properties of CR. (Notes (a) All vulcanizates were cured 30 min at 150°C. (b) Formulation CR (medium fast crystallization grade) 100, stearic acid 0.5, PBNA 2, SRF N762 30, ETU 0.5. (c) Excerpt from technical information bulletin Baypren 2.2.1, Bayer AG.)... 

Cure Characteristics. Methods of natural rubber production and raw material properties vary from factory to factory and area to area. Consequentiy, the cure characteristics of natural mbber can vary, even within a particular grade. Factors such as maturation, method and pH of coagulation, preservatives, dry mbber content and viscosity-stabilizing agents, eg, hydroxylamine-neutral sulfate, influence the cure characteristics of natural mbber. Therefore the consistency of cure for different grades of mbber is determined from compounds mixed to the ACSl formulation (27). The ACSl formulation is as follows natural mbber, 100 stearic acid, 0.5 zinc oxide, 6.0 sulfur, 3.5 and 2-mercaptobenzothiazole (MBT), 0.5. 

Castor oil [CO Structure (4.3)] is a triglyceride of ricinoleic (12-hydroxyoleic) acid about 90% of the fatty acid portion of the molecule consists of ricinoleic acid and 10% in the form of non-hydroxy acids consisting largely of oleic and linoleic acids. Small amounts of stearic and dihydroxystearic acids are also found in some industrial grades. 

Calcium carbonate is the most commonly used extender. It is widely available and low in cost, and it provides for improvements in certain performance properties. The material is a mineral that is mined throughout the world. Common forms of calcium carbonate include limestone, marble, calcite, chalk, and dolomite. It is manufactured by precipitation processes and is commercially available from a number of sources. Calcium carbonate is available in many different particle sizes and in various grades. To improve dispersion in certain resins, the filler is often coated with calcium stearate or stearic acid. 

The water used had a conductivity of ca. 1 X 10-6 ohm-1 cm.-1 All chemical reagents were analytical grade and were used without further purification. The temperature was kept at 25° 0.5° C. for the paraffin work. The stearic acid used was a specimen 99% pure. 

The unsaturation, as determined by the iodine value (IV), decreases from an IV of 10.0 for a single press to an IV of 1.0 for a triple press stearic acid grade. 

Identification Transfer about 100 mg of sample into a small, conical flask fitted with a suitable reflux condenser. Transfer 50 mg each of USP Palmitic Acid Reference Standard and USP Stearic Acid Reference Standard into a similar flask to serve as the Standard Solution. Treat the contents of each flask as follows Add 5.0 mL of a solution prepared by dissolving 14 g of boron trifluoride in methanol to make 100 mL [commercial reagent, 14% w/v, may be used (Applied Science, or equivalent)]. Swirl to mix, andrefluxfor 15 min. Cool, transfer the reaction mixture with the aid of 10 mL of chromatographic-grade hexane to a 60-mL separator, and add 10 mL of water and 10 mL of saturated sodium chloride solution. Shake, allow the mixture to separate, then drain and discard the lower, aqueous layer. Pass the hexane layer through 6 g of anhydrous sodium sulfate into a suitable flask. 

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