Chemists at the University of PennsylvaniaPhiladelphiaUSAhave created a new process for free radical polymerisation. This is the chemical reaction responsible for creating an enormous array of everyday plastic productsfrom Styrofoam cups to PVC tubing to car parts.
Unlike the traditional method for polymerisationwhich has been around for more than 50 yearsthis method takes place at room temperatureuses less metal catalyst to drive the reaction and requires a very short reaction time.
“We have basically re-written the equation of how the polymerisation process can workwhich can have a direct impact on the cost of the reaction and the types of materials that we can create” said Virgil Perceca professor in Penn’s department of chemistry. He added: “Polymerisation is a billion-dollar-a-year industryand the applications for the technology are enormousranging from medicine to coatingsfrom mouldable forms of rubber to electronics and even complex organic synthesisall via these radical reactions.”
This new techniquecalled single electron transfer-living radical polymerisation
(SET-LRP)also offers chemists greater control over the molecular architecture of the polymers they create and allows them to use materials that did not work with the traditional process. The mechanism of the synthesis reaction works so well that there is very little worry about undesirable side reactionsand the resulting polymers do not need to be purified to remove the catalyst. Their findings are presented in the Journal of the American Chemical Societyavailable online.
“The SET-LRP mechanism can allow for a greater control over the three-dimensional structure of the polymers being created” Percec said. “The overall process is not only more efficientit also provides industrial chemists a new creative tool for building consumer and industrial products.”
Polymerisation links individual moleculesreferred to as monomerstogether to form synthetic products on a larger-scale. In the chemical reaction to create polymerschemists use catalysts to decrease the amount of energy it takes to create a shared bond between individual atoms of each monomer. The traditional methodreferred to as atom-transfer radical polymerisation or metal catalysed living radical polymerisationdemands high temperatures and a great amount of the metal catalystin part because the process depends on the energy it takes to transfer inner-sphere electrons – which are deep within the cloud of electrons surrounding an atom – in the act of bonding monomers together.
The new method created by Percec and his colleagues involves the transfer of outer-sphere electronswhich requires much lower activation energy andthereforea different catalytic cycle than atom-transfer radical addition. Both the traditional and SET-LRP processes use copper-based catalysts to drive the reactionbut the SET-LRP reaction uses a commonelemental form of copper – in the form of powder or wire – in the presence of environmentally friendly solventssuch as waterto move the reaction along. This prevents the build up of excess amounts of copper by-products and reduces the need to continually add more catalyst to keep the reaction going.
“While this might seem like a refinement of the traditional process –º the resulting polymersin factare structurally the same – this method involves an entirely different approach to the chemical reaction” Percec said.
Better ballistic protection
Meanwhilefor protection of military and civilian vehicles against today’s toughest threats – including improvised explosive devices (IEDs) and assault rifles – DSM Dyneema has announced the introduction of a new hard ballistic composite.
The company says that unsurpassed protection for shipsaircraft and land vehiclesincluding multi-hit capabilitiesflame retardance and heat resistancecan be obtained by using DyneemaHB26. As the new material is exceptionally lightweightit halves handling time and speeds up production.
Roshielda Danish manufacturer of composite protection solutionshas tested Dyneema HB26 in vehicle protection for the Danish armed forces. According md Peter Bertelsen“DyneemaHB26 is used in all solutions Roshield has provided to the Danish Army to be used in Iraq. The solution was tested with other materials and proved to be the best in terms of weight and performance. It was tested with real ammunition at the right protection level (classified) by the Danish Army. We believe the army is satisfied with the solutionwhich has already proven its capabilities in saving lives in armed conflicts. DyneemaHB26 has been an improvement to work with in production and we have been happy to test it for DSM Dyneema.”
DSM maintains that Dyneema superstrong polyethylene fibre is the lightest solution on the market and provides formidable protection against ballistic threats including assault rifles such as the AK47 and explosive devices such as IEDs.
“The HB26 product delivers a spall liner effect against real weaponsnot just in testing with small-calibre fragments as often seen in the market” said Steen Tanderupmarketing manager for vehicle protection DSM Dyneema. “It also shows very promising results for use in inserts and other personal protective gear.”
DyneemaHB26 is a unidirectional (UD) composite made of several layers of Dyneema fibreswith the direction of fibres in each layer placed perpendicular to those in the adjacent layers. This unidirectional configuration allows the energy transferred from the impact of a bullet or other threat to be distributed along the fibres much faster and more efficiently than in conventional woven fabrics.
In a related moveRoyal DSM has decided to construct two new manufacturing facilities at its Chemelot site in Geleenthe Netherlands.
DSM is making these investments in response to excellent market growth for two of the company's top specialty productsStanyl polyamide 46 and Stamylan UH ultra-high molecular weight polyethylenewhich is used among other things as a raw material for Dyneema high strength fibres (Fig.1). The new Stanyl plant and the new Stamylan facilitywhich will each double existing production capacityare scheduled to come on line in 2008. The total investment will be around E100million.
Stanyl is used in a variety of applicationssuch as automotivecell phonescomputers and personal electronics. In additionthere is rapid growth in newinnovative applications such as fine pitch connectors for LCDsreflector packages for LEDsand gears in all kind of applicationsfor example seat recliners and starter motors. Stamylan UH is used as a high strengthwear-resistant engineering plastic in industrialsports and other applicationsas well as in Dyneema fibres.
“Production of Stanyl base resin is supported by our ability to manufacture our own high-purity diaminobutane” commented Jos Goessenspresident of DSM Engineering Plastics. Diaminobutane is the key monomer in the production of Stanyl. DSM has also decided to start the basic engineering to debottleneck the diaminobutane plant in Geleento match the increased production capacity for Stanyl.
“With the second Stanyl facility and the capacity expansion for diaminobutanewe can secure the supply of Stanyl to support the excellent growth of our customers worldwide in the years ahead” concluded Goessens.
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