Basic Compounding Formulation

The basic compounding formulation specifies the minimum requirement of fillers, vulcanizing agents, and other substances that must be added to the rubber compound to achieve the desired properties. After the rubber, cure system and reinforcing filers have been selected it will be necessary to make several adjustments before all requirements are satisfied. It is generally sensible to start with the simplest mix formula for meeting the requirements. The recipe or the formula is usually written on the basis of hundred parts of rubber. For example if 5 parts of zinc oxide is to be added it is denoted as 5 phr (five parts per hundred rubber). Elementary compounding 

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The procedure used in the preceding sections for cyclopropane serves equally well in the analytic determination of the numbers of structure and stereoisomeric compounds which obtain when essentially different radicals of valence one or alkyl radicals are substituted in the basic compound. We have to assume, however, that there is enough information on the basic compound to determine the three groups discussed in Sec. 56. This is certainly the case for the most important basic compounds, benzene and naphthalene. I omit the formulation of rules which are obvious in the preceding example. 

This assay is altogether more difficult since three active ingredients are involved and several excipients interfere in the analysis, including one major excipient (methylparaben), which is not removed in the extraction process. In addition the active ingredients are bases which have a tendency to interact with any uncapped silanol groups in the stationary phase and it is essential to use a column which is deactivated with respect to the analysis of basic compounds. The three active ingredients are all at different concentrations in the formulation so that attention has to be paid to selection of a detection wavelength at which each component can be detected. In this particular assay a DAD would be useful. 

Macrolide and lincosamide antibiotics are weakly basic compounds slightly soluble in water but readily soluble in common organic solvents. They are most composed of several closely related components that may vary in proportion depending upon the source of the formulation. Macrolides other than oleandomycin are stated to be unstable at both acidic and basic aqueous solutions. 

The principles of compounding were reviewed earlier in this text and cover the fundamental characteristics of polymers, filler systems, and the basics of vulcanization in the context of compound development for tire applications. A compound formulation consists of four basic components the polymer network, the filler or particulate reinforcing system, the stabilizer system, and the vulcanization system (Figure 14.21). In addition a series of secondary materials such as resins, processing oils, and short fiber reinforcements may be included in a formula (Duddey, 2004 Rodgers and Waddell, 2004 Long, 1985). Elastomers used in radial tires are basically of four types ... 

The action of accelerators is improved by the presence of activators in practice, a combination of zinc oxide and a fatty acid is nearly always used. Specifically, the activator increases the efficiency of the vulcanizing system so that, typically, only about 5 sulphur atoms are combined for each cross-link formed. As a consequence, the vulcanizate shows improved physical properties, aging characteristics and appearance (less sulphur bloom). The use of accelerator-activator systems is standard practice in rubber compounding and a typical basic tread formulation might be as follows ... 

Although acceptable cure characteristics are obtained with a conventional system based on 2 5 phr sulphur and 0 5 phr sulphenamide, this formulation is not recommended for ENR as the vulcanizates have poor ageing characteristics compared with unmodified NR. The cause of this is discussed in Section 6.9. Semi-EV or EV-type cure systems have been found to be the most satisfactory for ENR. Examples of such systems are recorded in Table 1. The need to compound ENR with a base affects the vulcanization characteristics, and one of the factors to be considered in the choice of base is the processing safety of the mix. " Stronger bases can markedly reduce scorch delay by base catalysis of the vulcanizing system and should only be employed at low levels, whereas the less basic compounds can be employed at higher concentrations (Fig. 9). 

In order to improve the internal stress performance even further or to provide toughness for potting and adhesive applications it is advantageous to introduce reactive additives to the basic epoxide compound formulation. One of the most popular additives that has found considerable use in this type of application is a rubber-like liquid copolymer known as carboxyl terminated butadiene/acrylonitrile (CTBN). The generalised molecular structure of this material is ... 

The key consideration in the analysis of any sustained release dosage form as previously discussed (see Sections II.A, II.B, II.C.l, and II.C.2rg) is to determine what solvent or solvent system will be most appropriate to assure the dissolution of the drug and its excipients to make it amenable to HPLC analysis. Aqueous solubility of weak acids and bases is governed by the pfCa of the compound and the pFI of the medium. In an acidic or low pFI medium, weak acids will be unionized and will be more soluble in organic solvents. The reverse is the case for basic compounds as previously discussed in Section II.B. Because the formulation of sustained release dosage forms tend to rely on the use of insoluble plastics (i.e., methyl acrylate-methyl methacrylate, polyvinyl chloride, and polyethylene), hydrophilic polymers (i.e., methylcellulose, hydroxypropyl-methylcellulose, sodium carboxymethyl cellulose, and carbopol 934), and fatty compounds (i.e., waxes such carnauba wax and glyceryl tristearate), similar hydro-organic solvents and sample preparation steps that have been discussed for tablets and capsules can also used for their analysis by HPLC (see Sections II.A, II.B, II.C.l, and II.C.2). 

Inorganic additives such as glass fibers, pigments, heat stabihzers, UV stabihzers, and flame retardants are commonly incorporated into basic polymer formulations to impart special behavior. In most cases, these additives are compounded into the base polymer after the reaction and presented for processing after a separate operation is performed. 

Plastic compounders are companies that purchase bulk material from the resin producers, and then formulate custom compounds through the mixing and blending of base polymers with various additives. While some resin producers do some basic compounding, it is typically on a limited scale for a few specific resins (usually only standard materials are produced in high volume). Most compounders offer a wide variety of resins in a number of different versions—in high-volume or low-volume production—and are also capable of formulating specialized compounds on demand. 

The basic metal salts and soaps tend to be less cosdy than the alkyl tin stabilizers for example, in the United States, the market price in 1993 for calcium stearate was about 1.30— 1.60, zinc stearate was 1.70— 2.00, and barium stearate was 2.40— 2.80/kg. Not all of the coadditives are necessary in every PVC compound. Typically, commercial mixed metal stabilizers contain most of the necessary coadditives and usually an epoxy compound and a phosphite are the only additional products that may be added by the processor. The requited costabilizers, however, significantly add to the stabilization costs. Typical phosphites, used in most flexible PVC formulations, are sold for 4.00— 7.50/kg. Typical antioxidants are bisphenol A, selling at 2.00/kg Nnonylphenol at 1.25/kg and BHT at 3.50/kg, respectively. Pricing for ESO is about 2.00— 2.50/kg. Polyols, such as pentaerythritol, used with the barium—cadmium systems, sells at 2.00, whereas the derivative dipentaerythritol costs over three times as much. The P-diketones and specialized dihydropyridines, which are powerful costabilizers for calcium—zinc and barium—zinc systems, are very cosdy. These additives are 10.00 and 20.00/kg, respectively, contributing significantly to the overall stabilizer costs. Hydrotalcites are sold for about 5.00— 7.00/kg. 

The future for amino resins and plastics seems secure because they can provide quaHties that are not easily obtained in other ways. New developments will probably be in the areas of more highly specialized materials for treating textiles, paper, etc, and for use with other resins in the formulation of surface coatings, where a small amount of an amino resin can significantly increase the value of a more basic material. Additionally, since amino resins contain a large proportion of nitrogen, a widely abundant element, they may be in a better position to compete with other plastics as raw materials based on carbon compounds become more costly. 

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