The immediate future could see the manufacture of polymethyl methacrylate (PMMA) -- better known as acrylic glass -- from natural raw materials such as sugars, alcohols or fatty acids. Acrylic plastic refers to a family of synthetic, or man-made, plastic materials containing one or more derivatives of acrylic acid. The most common acrylic plastic is polymethyl methacrylate (PMMA). PMMA is a tough, highly transparent material with excellent resistance to ultraviolet radiation and weathering. It can be colored, molded, cut, drilled, and formed. These properties make it ideal for many applications including airplane windshields, skylights, automobile taillights, and outdoor signs. One notable application is the ceiling of the Houston Astrodome which is composed of hundreds of double-insulating panels of PMMA acrylic plastic.
Conventionally, PMMA is manufactured by polymerising methyl methacrylate (MMA). In a bacterial strain, scientists at the University of Duisburg-Essen and the Helmholtz Centre for Environmental Research (UFZ) have found an enzyme which could be used for the biotechnological production of a precursor of MMA. Compared with the previous chemical production process, Dr Rohwerder’s biotechnological process is far more environmentally friendly.
The enzyme newly discovered by Dr. Thore Rohwerder und Dr. Roland H. Müller, called 2-hydroxyisobutyryl-CoA mutase, makes it possible to turn a linear C4 carbon structure into a branched one. Compounds of this type are precursors of MMA. Parent compounds may of course include intermediate products from the petrochemical industry. The revolutionary aspect, however, is that this enzyme, integrated into metabolically appropriate microorganisms, can also transform sugars and other natural compounds into the products desired.
Until now, the only way to produce this precursor -- 2-hydroxyisobutyrate (2-HIBA) -- was a purely chemical process based on petrochemical raw materials. The chemicals industry worldwide is searching for suitable biological processes, so that in future, renewable raw materials can also be used as a basis for MMA synthesis. The mutase presented here provides the solution: an enzyme which shifts a functional group from one position to another within a molecule. The duo discovered the enzyme in a newly isolated bacterial strain they found while searching for bacteria to break down the pollutant MTBE (methyl tertiary butyl ether).
In the medium to long term, up to ten percent of today's demand for MMA could feasibly be produced by biotechnological means. The world market is over 3 mln tons valued at €4 billion. It will take about four years to establish the bacterial system in a functioning technological process (pilot plant). In about 10 years, a technological process is then conceivable, with an annual turnover of 150 to 400 million euro.
Conventionally, acrylic plastic polymers are formed by reacting a monomer, such as methyl methacrylate with a catalyst. The catalyst, typically an organic peroxide, starts the reaction and enters into it to keep it going, but does not become part of the resulting polymer. Acrylic plastics are available in three forms: flat sheets, elongated shapes (rods and tubes), and molding powder. Molding powders are sometimes made by a process known as suspension polymerization in which the reaction takes place between tiny droplets of the monomer suspended in a solution of water and catalyst. This results in grains of polymer with tightly controlled molecular weight suitable for molding or extrusion.