Production of ABS materials

The term ABS was originally used as a general term to describe various biends and copolymers containing acrylonitrile, butadiene and styrene. Prominent among the earliest materials were physical blends of acrylonitrile-styrene copolymers (SAN) (which are glassy) and acrylonitrile-butadiene copolymers (which are rubbery). Such materials are now obsolete but are referred to briefly below, as IVpe 1 materials, since they do illustrate some basic principles. Today the term ABS usually refers to a product consisting of discrete cross-linked polybutadiene rubber particles that are grafted with SAN and embedded in a SAN matrix. 

By altering theses variables, blends may be produced to give products varying in processability, toughness, low-temperature toughness and heat resistance. 

Although the nitrile rubbers employed normally contain about 35% acrylonitrile the inclusion of nitrile rubber with a higher butadiene content will increase the toughness at low temperatures. For example, whereas the typical blend cited above has an impact strength of only 0.9ftlbfin- notch at 0°F, a blend of 70 parts styrene-acrylonitrile, 30 parts of nitrile rubber (35% acrylonitrile) and 10 parts nitrile rubber (26% acrylonitrile) will have an impact value of 4.5 ftlbf in notch at that temperature.  

To produce the Type 2 polymers, styrene and acrylonitrile are added to polybutadiene latex and the mixture warmed to about 50°C to allow absorption of the monomers. A water-soluble initiator such as potassium persulphate is then added to polymerise the styrene and acrylonitrile. The resultant materials will be a mixture of poly butadiene, polybutadiene grafted with acrylonitrile and styrene, and styrene-acrylonitrile copolymer. The presence of graft polymer is essential since straightforward mixtures of polybutadiene and styrene-acrylonitrile copolymers are weak. In addition to emulsion processes such as those described above, mass and mass/suspension processes are also of importance. 

In recent years there has been an increased demand for a variety of special ABS grades, for example products with improved flcune retardancy. 

---

LiBH4, NaBH4 and the ammonium salts all possess low solubility in the organic solvents in question, ivith slow dissolution kinetics. The slow dissolution of the reactants is the rate-limiting step and prohibits, together with the production of large amounts of by-products, the economic production of AB materials. 

The polymers described above have been chemically pure, although physically helerodisperse. It is oflen possible lo combine two or more of these monomers in the same molecule to form a copolymer. This process produces still further modification of molecular properties and, in turn, modification of the physical properties of file product. Many commercial polymers are copolymers because of the blending of properties achieved in this way. For example, one of the important new polymers of the past ten years has been the family of copolymers of acrylonitrile, butadiene and styrene, commonly called ABS resins. The production of these materials has grown rapidly in a short period of time because of their combination of dimensional stability and high impact resistance. These properties are related to the impact resistance of acrylonitrile-butadiene rubber and the dimensional stability of polystyrene, which are joined in the same molecule. 

From the presence of monomeric amino borane in the gas phase, one can postulate that it may be the precursor for the formation of polymeric amino borane as well as for borazine, since it is known to be unstable at room temperature [79]. Another process not fully understood is the formation of cyclic products. A strong influence of the reaction environment is observed. The decomposition of AB material in the solid form almost exclusively results in solid polymeric BNH -products. Cyclic products such as borazine or cycloaminoborane (BH2NH2)3) are then only formed in minute amounts, whereas in solution cyclic products are preferred. The exact parameters that control this selection process have not yet been determined. 

The application of AB materials as hydrogen source materials requires a cost effective production or at least an economical regeneration procedure for spent material. As pointed out, the type of spent material depends very much on the dehydrogenation procedure. Decomposition of AB in the solid state and in inert solvents leads, depending on the conditions, to products of various B N H rations, divers degree of polymerization, and of very different reactivity. 

Other Impact-Modified Commercial Grafting-Based Polymers Typical HIPS and ABS polymers are opaque materials however, MABS (methyl methacrylate-acrylonitrile-butadiene-styrene) polymers, which are produced by processes similar to those used in the production of ABS, are transparent materials. This property is obtained by the addition of methyl methacrylate (MMA) to the recipe in order to impart transparency to the polymer by equalizing the refracting index of the rubber particles to that of the matrix. These materials find applications... 

There are two major producers of SAN for the merchant market in the United States, Bayer Corp. and the Dow Chemical Co., which market these materials under the names of Lustran and Tyril, respectively. Bayer became a U.S. producer when it purchased Monsanto s styrenics business in December 1995 (332). Some typical physical properties of these SAN resins have been shown in Table 11. These two companies also captively consume the SAN for the production of ABS as well as SAN-containing weatherable polymers. The other two U.S. SAN producers, either mainly consume the resin captively for ABS and ASA polymers (GE Plastics) or toll produce for a single client (Zeon Chemicals). BASF is expected to become a more aggressive SAN supplier in the United States since its Altamira, Mexico, stryenics plant came on-line in early 1999. Overall, U.S. SAN consumption has been relatively stable for the last few years, ranging from 43 x 10 to 44.5 x 10 t (95-98 million poimds) between 1994 and 1996. Most markets for SAN are growing at only GDP rates. Consumption growth for SAN in 1996-2001 is expected... 

The polybutadiene rubbers are mostly used in the production of impact-PS, and they are also recommended, as mentioned earlier, as a substitute, in total or in part, for some impact-PVC modifiers, mainly ABS. Contrary to this terpolymer, polybutadiene rubbers are not suitable for the production of transparent materials. 

Because they are similar, the aLkanolamines often can be used interchangeably. However, cost/perfomiance considerations generally dictate a best choice for specific appHcations. AMPD is manufactured in very low volumes for use as a reagent in certain medical diagnostic tests, although some is used in certain cosmetic products. 2-Ainino-1-butanol is used primarily as a taw material for the synthesis of ethambutol [74-55-5] an antituberculosis dmg. The first step in the synthesis of this dmg is the resolution of AB into its optical isomers because only (i)-2-amino-l-butanol, [5856-62-2] is utilized in this synthesis. 

Benzene is alkylated with ethylene to produce ethylbenzene, which is then dehydrogenated to styrene, the most important chemical iatermediate derived from benzene. Styrene is a raw material for the production of polystyrene and styrene copolymers such as ABS and SAN. Ethylbenzene accounted for nearly 52% of benzene consumption ia 1988. 

In addition to polystyrene and high-impact polystyrene there are other important styrene-based plastics. Most important of these is ABS, with a global capacity of about 5 X 10 t.p.a. and production of about 3 X 10 t.p.a. The styrenic PPO materials reviewed in Chapter 21 have capaeity and production figures about one-tenth those for ABS. Data for the more specialised styrene-acrylonitrile copolymers are difficult to obtain but consumption estimates for Western Europe in the early 1990s were a little over 60000 t.p.a. 

A final point needs to be made. Theory has indicated that AB cements should be amorphous. However, a degree of crystallization does sometimes occur, its extent varying from cement to cement, and this often misled early workers in the field who used X-ray diffraction as a principal method of study. Although this technique readily identifies crystalline phases, it cannot by its nature detect amorphous material, which may form the bulk of the matrix. Thus, in early work too much emphasis was given to crystalline structures and too little to amorphous ones. As we shall see, the formation of crystalUtes, far from being evidence of cement formation, is often the reverse, complete crystallinity being associated with a non-cementitious product of an acid-base reaction. 

The primary use of acrylonitrile is as the raw material for the manufacture of acrylic and modacrylic fibers. Other Major uses include the production of plastics (acrylonitrile-butadiene- styrene (ABS) and styrene-acrylonitrile (SAN), nitrile rubbers, nitrile barrier resins, adiponitrile and acrylamide (EPA 1984). 

---