Jul 25 2007
Polyolefins are very versatile polymers used in a wide variety of applications from packaging film to geomembranes and pipe. The polymer and the additives are varied to match the property requirements for each application.
There are food contact grades where only approved additives can be used and migration levels (SML) are strictly controlled by organisations such as the FDA in the United States and the European Union. Current research includes new additives from natural sources such as basil.
The REACH regulation governing the use of chemicals in all applications across Europe is due to be registered on 1st June 2008 and industry is working out how it will affect the supply of additives. Depending on the volume of use, the toxicology testing requirements can be very demanding. If a downstream user does not want to give away formulations, he may need to carry out Chemical Safety Testing himself.
Packaging film generally includes a wide variety of components: antislip agents to improve slide (e.g. oleamide and erucamide); antiblocking agents to roughen the film surface and prevent layers sticking to each other (as when film is in a roll, e.g. diatomaceous earth and talc); antioxidants protect against ageing particularly during heating (e.g. hindered phenolics); antistatic agents reduce the build up of charge on a film surface (which in turn can attract dust); anti-UV additives prevent light degradation; and antifogging agents stop the formation of droplets of condensation in packaging so that film remains transparent.
Some materials such as the new metallocene grades of polyolefin can be more difficult to work with. Processing aids such as fluoropolymers are used to overcome this problem and suppress gel formation. Lubricants such as fatty-esters are also used.
Nucleating agents are added to act as a centre for the formation of a highly ordered crystalline structure. This can add to material stiffness allowing for downgauging and a reduction in material costs.
For applications such as geomembranes used as reservoir covers, the material has to have high UV-resistance and potable water approval (migration levels must be low). Carbon black is a major component of many of these products, providing weatherability.
In pipe, the application determines the compound and properties. For example, potable water regulations govern drinking water pipes and outdoor pipes must withstand weathering. Additives containing lead are being phased out under voluntary agreements in Europe. Construction applications such as cable jacketing are now subject to stringent flame retardancy criteria to reduce the spread of fire and consumer electronics have similar standards. Polyolefins are flammable and burn easily, and moulding grades have a high Melt Flow Index leading to melting and dripping. To reach the UL 94 V-1 fire rating can be very difficult. Clay can help to improve flame retardancy, while other additives may interfere. To add to the problems, the more effective halogenated flame retardants are out of favour and substitutes are being sought.
Compound formulation is a complicated science as the compounder has to consider the desirable end properties and the interactions of all of the additives required to meet that target. Some additives will improve one aspect while reducing others.
AMI is organising an international conference, Polyolefin Additives 2008, to provide an opportunity to discuss the issues with the experts. It will be held at the Maritim Hotel in Cologne, Germany from 14-16 April 2008.