ABS ( Acrylonitrile butadiene styrene )

 

Acrylonitrile butadiene styrene
 
Monomers in ABS polymerAcrylonitrile butadiene styrene, or ABS, (chemical formula (C8H8 C4H6C3H3N)x) is a common thermoplastic used to make light, rigid, molded products such as pipes, golf club heads (used for its good shock absorbance), automotive body parts, wheel covers, enclosures, protective head gear, and toys including LEGO bricks. It is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15% to 35% acrylonitrile, 5% to 30% butadiene and 40% to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly(styrene-co-acrylonitrile). The nitrile groups from neighbouring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures. ABS can be used between −25 C and 60 C.

Production of 1 kg of ABS requires the equivalent of about 2 kg of oil for raw materials and energy. It can also be recycled.

Synthesis
Acrylonitrile butadiene styrene can be found as a graft copolymer, in which styrene-acrylonitrile polymer is formed in a polymerization system in the presence of polybutadiene rubber latex; the final product is a complex mixture consisting of styrene-acrylonitrile copolymer, a graft polymer of styrene-acrylonitrile and polybutadiene and some unchanged polybutadiene rubber. There are, therefore, many variables to the process besides the different positions of the starting materials, so this technique is capable of producing polymers with a much wider range of properties.ABS can be made by blending, the technique involved mechanical blending by mixing a butadiene-acrylonitrile rubber with styrene-acrylonitrile resins, the process is being carried out under such conditions that the two polymers underwent some grafting. This technique is rather limited and has been largely suppressed by chemical process.

Properties
ABS is derived from acrylonitrile, butadiene, and styrene. Where acrylonitrile are synthetic monomers produced from propylene and ammonia; butadiene is a petroleum hydrocarbon obtained from butane; and styrene monomers, derived from coal, are commercially obtained from benzene and ethylene from coal. The advantage of ABS is that this material combines the strength and rigidity of the acrylonitrile and styrene polymers with the toughness of the polybutadiene rubber. The most amazing mechanical properties of ABS are resistance and toughness. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance. The impact resistance can be amplified by increasing the proportions of polybutadiene in relation to styrene and acrylonitrile although this causes changes in other properties. Impact resistance does not fall off rapidly at lower temperatures. Stability under load is excellent with limited loads.

Even though ABS plastics are used largely for mechanical purposes, they also have good electrical properties that are fairly constant over a wide range of frequencies. These properties are little affected by temperature and atmospheric humidity in the acceptable operating range of temperatures. The final properties will be influenced to some extent by the conditions under which the material is processed to the final product; for example, molding at a high temperature improves the gloss and heat resistance of the product whereas the highest impact resistance and strength are obtained by molding at low temperature.

ABS polymers are resistant to aqueous acids, alkalis, concentrated hydrochloric and phosphoric acids, alcohols and animal, vegetable and mineral oils, but they are swollen by glacial acetic acid, carbon tetrachloride and aromatic hydrocarbons and are attacked by concentrated sulfuric and nitric acids. They are soluble in esters, ketones and ethylene dichloride.

The aging characteristics of the polymers are largely influenced by the polybutadiene content, and it is normal to include antioxidants in the composition. On the other hand, the cost of producing ABS is roughly twice the cost of producing polystyrene, ABS is considered superior for its hardness, gloss, toughness, and electrical insulation properties. However, it will be degraded when exposed to acetone.