additives feature | Foaming agents
Mecaplast studied the effect of different blowing agents – the first gave an average cell diameter of 75 microns (left) compared to 156 microns for the second additive (right)
researchers was controlling the bubble size. The researchers found that some mechanical properties are not affected by bubble size while some others, such as impact behaviour, are highly affected. The type of blowing agent and the percentage of talc (used as a filler) had a significant influence on bubble size.
Researchers at the University of Bayreuth are developing high-perfor- mance particle foams
Nucleating news Various nucleating agents, including minerals and nanomaterials, can be used to nucleate cell growth in polymer foams. DMH Performance Additives recently launched Equicell, an organic particle nucleator in a concentrate form, for extruded polymer foams. The additive has been used on a limited basis in PS foams for several years, and the company is now extending its use to other polymers. “Equicell has been successfully tested in PS, PE, and PLA, and we believe it is useful in a wide range of polymers,” says Dan McWilliams, principal at DMH Performance Additives. He notes that Equicell is a drop-in alternative to talc that feeds reliably with no die build-up or wear. It is also an alternative to chemical nucleators, which are used to provide higher percent- ages of closed cells to create a strong sheet, thus lowering part weight and cost. “Equicell achieves these
benefits at a lower cost compared to chemical nuclea- tors,” claims McWilliams. The additive provides uniform cell-size distribution, which increases impact strength and reduces brittleness.
Particle progress Much development is being done in particle foams, such as expanded polypropylene (EPP), expanded polystyrene (EPS), expanded thermoplastic polyurethane (ETPU) and others, which are formed by fusing together foamed beads. Particle foams use physical blowing agents, although CFAs and other additives can be used as nucleants. Particle foams offer complex shapes; low, tuneable densities; and a uniform microstructure, noted researchers from the University of Bayreuth at AMI’s Polymer Foam 2014 conference. Work conducted at the department of Polymer Engineering at the University of Bayreuth produced expanded polybutylene terephtha- late (PBT) bead foams, which are recyclable and exhibit thermal resistance. “Foaming semicrystalline polyesters (such as PBT) is
generally difficult due to their weak melt properties and their narrow processing windows,” explains Amir Fathi, group leader of Polymer Foams at the University of Bayreuth. “Here we have managed to create PBT particle foams with rather low densities and very homogenous cell morphology. This material has much higher thermal stability comparing to conventional particle foams such as EPP and EPS and could be therefore used in newer applications. This development is currently under further modifications at our group and we are aiming to incorporate newer functionalities such as flame retardant behaviour.” The researchers have also worked on newer
generations of bead foams based on technical polymers such as polyethylene terephthalate (PET) and polyamide (PA) through foam extrusion processes coupled with underwater pelletization. “Finding the optimum processing conditions to foam these materials is rather challenging due to their very narrow processing
58 COMPOUNDING WORLD | January 2015
www.compoundingworld.com
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