Mix and match brings out the best from polyolefins

Tom Shelley reports on new PE and PP developments that enable solutions that save users a pile of money By mixing and matching polyolefins, particularly different types of polyethylene and polypropylene, it is possible to produce polymers with very superior properties, in some cases matching those of competing materials costing up to four times as much. One of the world's major practitioners of the approach has just announced a second generation version of the technology and also a research and development agreement to take it and other developments on further. Polyethylene was originally discovered in 1933 and is the largest volume produced polymer in the world, not least because it is relatively inexpensive compared with other products. Borealis has recently announced its 'Borstar PE 2G' technology which Wim Roels, vice president polyolefins research and development said gives PE pipes made with it a tenfold better resistance to stress cracking as well as improved resistance to crack propagation. When we asked how it worked, Mr Roels declined to give details but did tell us that the materials were, "Not homogeneous" and made up of "Different fractions." He also said that it was the company's intention to apply the technology to polypropylene in, "The next two years." The company press release describes the technology as a "New catalyst system in combination with process improvements." Using mixtures of chemically similar but physically different polymers seems to be a Borealis speciality and is applied to many of the company's products. These may be supplied in mixed form, or as in the case of automotive parts, mixed in the moulding machine. The example cited was Nepol 6B600HP-9502, which consists of typically 10mm long granules, chopped out of continuous glass fibre reinforced polypropylene containing up to 60 per cent glass, diluted in the machine with BJ100HP that contains no glass. The purpose is to produce mouldings reinforced with fibres longer than is possible with conventional chopped fibre and with easier flow characteristics. In the medical field, we were told of bottles made of LE6609PH polyethylene bottles that could be steam sterilised at 114 deg C, use of bi-modal PE to reduce the weight of plastic bottles by 7 to 15 per cent and a dialyser filter where replacement of PC by PP cut the cost of the material used by 75 per cent. In other fields, low loss 3G antenna cable insulation is made of a foam derived from a mixture of high density (HD) and low density (LD) PE. According to Gustaf Akermark, VP business unit wire and cable, The HD is there to give the mechanical strength and the LD, the melt strength for blowing. Blown foam made from a mixture of two grades of polypropylene is key to thermal insulation on pipes to be used in the BP Thunder Horse development in the Gulf of Mexico, according to Lorenzo de Lorenzi, vice president unit pipe utilities water and gas. The specifications require enduring oil temperatures of up to 132 degC in water depths of up to 2200m. The blown foam sits between an outer layer of syntactic foam containing glass spheres and an inner layer of epoxy. The development has been undertaken in conjunction with Thermotite, a division of Bredero Shaw, and is known as the 'Thermotite 7 layer system'. PE films for packaging and other purposes are also able to benefit from the company's multi-modal technologies. The new technology agreement will allow Novolen's metallocene single site polypropylene catalyst technology rights to be made available to Borealis. Borealis Pointers * Borealis has further advanced its technologies to produce PE grades made up of mixtures of different types of material. Advantages include greater resistance to stress cracking and stress propagation and improvements in strength to unit weight * There are instances where PP can be used to replace PC with materials cost savings of up to 75% * PP is also available in multi modal forms although the newest manufacturing advances will not be applied to be these materials until two years from now * Blown foams for electrical and thermal insulation also benefit from being made from mixtures of different kinds of PE and PP