Grades hydrogen

During the last 15 years several companies have developed hydrogenated grades of nitrile rubber to both improve its thermal stability and solvent resistance. Although the hydrogenation of a poly diene backbone was done as early as the 1920s, real commercial products with acrylonitrile were not introduced until the mid-1980s.59... 

Table 1. Hydrogen Grades Available. (Units in ppm (mole/mole) unless otherwise stated)... 

Three such polymer modifications designed to improve the service characteristics of NBR are now commercially available. These are the saturated (or hydrogenated) grades, the antioxidant bound types and the carboxylated grades. 

In contrast to nitrile rubber, fully hydrogenated NBR is not attacked by ozone. Even under extreme conditions (e.g., 2 ppm ozone, 40 °C, 50% rel. humidity, 60% strain, 168 h) no cracks appear. Even under cyclic load these rubbers exhibit excellent ozone crack resistance. Elastomer parts based on HNBR are highly ozone-resistant without the addition of antiozonants. Partially-hydrogenated grades behave differently, depending on the vulcanization system. Ozone resistance quickly decreases with increasing double bond content. However, peroxide vulcanized rubbers behave more favorably than sulfur vulcanized rubbers [697]. 

Dimer-S cycloaliphatic resins tend to be somewhat unstable, but there are hydrogenated grades which are sufficiently stable to have commercial acceptance. 

Rosins - These are abietie aeid resins obtained from wood sourees. There are several different types wood rosins obtained from the naptha extraetion of pine stumps, gum rosins obtained from the destruetive distillation of turpentine, and tall oil rosins obtained by the destruetive steam distillation of tall oil from the manufacture of paper. Rosins are widely used in the adhesive and sealant industry. In hot melts they oxidize and diseolor easily at high temperatures due to the imsaturation in the resin. Hydrogenated grades are available which have much better thermal stability. 

The cmde product from any hydrogen peroxide process can be used as such, but commercial grades are further purified, concentrated, and stabili2ed. 

Table 8. 1993 Technical-Grade Hydrogen Peroxide Price Schedule ...

Aqueous hydrogen peroxide is sold in grades ranging from 3 to 86 wt %, most often containing 35, 50, and 70 wt % H2O2. In the United States, the only use for 86% H2O2 (ca 1994) is for attitude (flight path behavior) control of space craft, etc. This minor amount is imported. 

The 30% reagent-grade hydrogen peroxide is purer than the industrial grades, is covered by ACS reagent specification, and is used as a laboratory reagent and in some specialty uses (see Fine chemicals). Several grades are also marketed for electronics use and thus have exceptionally low impurity levels. Some of these latter contain very Httie or no stabilizers (see Electronic materials). 

The ethynylation reaction takes place at 10—40°C and 2 MPa (20 atm) and hquid ammonia is the solvent. The methylbutynol is converted into methylbutenol by selective hydrogenation and then is dehydrated over alumina at 250—300°C. Polymerization-grade isoprene is obtained. 

Acetophenone can react with formaldehyde to yield light-resistant resins which are used as additives in nitrocellulose paints. It is also used as a photoinitiator, and in the pharmaceuticals, perfumery, and pesticide industries (344). It can be hydrogenated to 1-phenylethanol which is used for the production of aromatic ester fragrances (345). Technical-grade acetophenone is available at 2.29/kg perfume-grade acetophenone was 6.50/kg in October 1994. 

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