Available Grades

In addition to the high-impact (toughened) polystyrenes dealt with later in this chapter, polystyrene is available in a number of grades. These may conveniently be grouped as follows  

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Modifications of Processes Based on Air Oxidation ofp-Xylene. Since the mid-1970s, starting in Japan, several companies have developed oxidation processes to yield relatively pure forms of terephthaUc acid without a separate purification. These products, normally called medium purity terephthahc acids, contain 200—300 ppm 4-formylbenzoic acid and trace amounts of acetic acid and thus do not meet normal specifications for the highest purity grades available (80,81). 

Additives and Modifications. For plastics uses, nylon is only rarely employed as the pure polymer, and is almost always modified to some extent even if only with the addition of a small amount of lubricant. There has been a dramatic increase in the range and number of combinations of additives used to modify nylons, resulting in a huge expansion in the number of commercial grades available and the uses to which they can be put. It is not unusual to find formulations that contain less than 50% nylon and half a do2en or more additives. 

The particle size distribution of Rhovanil Extra Pure vanillin shows a less narrow profile than other standard mesh grades available on the market. The product shows an improved mixabiUty in blending operations, allowing shorter blending time of compounds or food mixes, and better homogeneity of vanillin content, especially in low content vanillin blends. 

A.C7ylonitnk Content. Standard grades available ia the market contain between 15 to 50% acrylonitrile. The acrylonitrile content of nitrile mbber has a significant effect on two properties chemical resistance and low temperature performance. As the acrylonitrile content of the polymer is iacreased, the chemical resistance is improved whereas the low temperature properties are diminished. 

The commercial grades available in the 1970s used either zinc or sodium as the cross-linking ion and ranged in melt flow index from 0.4 to 14. The main application of the ionomer resins has been for packaging film. The polymer is particularly useful in composite structures to provide an outer layer with good heat sealability. The puncture resistance of film based on ionomer film has the puncture resistance of a LDPE film of twice the gauge. 

When this stage has been reached, the materials on the shortlist can be investigated further, checking suppliers, grades available, prices, processability and further details of the material properties, such as, for example, surface finish and scuff resistance, which do not normally feature in property tables. 

Transparent grades available, non-hygroscopic, low ash content, solvent resistant... 

Commercial grades Available in technical (95%) and polymer (99.9%) grades. Transported as a gas in pipelines, as a liquid in pressurized tank cars and steel cylinders. Difficult to store. 

Commercial grades Available in three grades refinery (50-70%), chemical (90-92%), and polymer (99%) grade. The remaining percentage in each case is mainly propane. It is shipped as a liquid in pipelines, tank cars, tank trucks, and steel cylinders. Storage is as a liquid at pressures of about 200 psi. 

Commercial grades Available in three grades refined-535, refined-485 (nitration grade), and industrial. The numbers following the grade refer to the freezing point specification times 100. It is shipped in steel drums, tank trucks, and tank cars under heavily regulated conditions. 

The proprietary surface treatment done on SLC1015 and other SLC grades available from Superior Graphite reduces dramatically the specific surface area of this group of carbon products. 

Most laboratory chemicals are available in a number of grades, usually according to the concentration of impurities that are present. Generally, the purer the chemical, the more expensive it will be. A supplier s catalogue will indicate the different grades available for a particular chemical, together with the related purity specifications. You should bear in mind that the specification may not identify all of the impurities that are present. The nature of the impurities may or may not be important, depending on how the chemical is to be used. 

This premium price is now seen as independent of the cyclical market pricing of caustic soda. So how long could you expect the differential to last The current view is that the more rayon grade, and the less diaphragm grade available, then the more the... 

All other chemicals employed were of the highest grade available. 5-Nitro-l,10-phenanthroline, 5-amino-l,10-phenanthroline [6] and benzo[15-crown-5], 15-nitrobenzo[15-crown-5], 15-aminobenzo[15-crown-5] were prepared according to the published methods [7, 8],... 

The benzoyl peroxide is recrystallized from chloroform and methanol at room temperature. The checkers used the 96% purity commercial grade available from the Lucidol Division of Wallace and Tiernan without further purification. 

Both sulfonyl chloride and isothiocyanate will hydrolyze in aqueous conditions therefore, the solutions should be made freshly for each labeling reaction. Absolute ethanol or dimethyl formamide (best grade available, stored in the presence of molecular sieve to remove water) should be used to dissolve the reagent. The hydrolysis reaction is more pronounced in dilute protein solution and can be minimized by using a more concentrated protein solution. Caution DMSO should not be used with sulfonyl chlorides, because it reacts with them. 

N,N-Dimethylformamide is distilled from calcium hydride at 71° (32 mm.) and stored under argon. The checkers used a freshly opened bottle of the product (white label grade) available from Eastman Organic Chemicals. 

Methylnaphthalene, 2-methylnaphthalene and methanol were purchased from Merck or Fluka in the highest purity grade available and used without further purification. 

The submitter used Magnesol, industrial grade, available from Reagent Chemical Research, Inc., Pilot Engineering Division. The checkers used Florisil TLC, available from E. Merck, Darmstadt, No. 12519. 

Diethyl maleate, practical grade, available from Eastman Organic Chemicals, was used without further purification. 

PBG, purest grade available (Frontier Scientific, Logan, UT, USA). 

Sodium and potassium were distilled into ampoules and stored in the dry box. Lithium and the alkaline earth metals were the best grade available commercially and were used without further purification. Reagent grade sodium iodide was dried at 300°C. in vacuo, recrystallized from anhydrous liquid ammonia, and heated to 200°C. in vacuo prior to use. The recrystallization procedure eliminated the rapid fading of dilute sodium-ammonia solutions containing sodium iodide which had been dried in the conventional manner. 

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