ADDITIVES | FUNCTIONAL FILLERS
Schematic showing different POSS structures. The example on the left has POSS cages bearing all phenyl groups. In the right-hand structure, the phenyl POSS cages also
contain silanols
Image: Hybrid Plastics
powders and are typically added directly at the extruder throat using a standard powder feeder at effective loading levels of 0.5 - 3 wt%. In PEEK, the addition of heptaphenyl trisilanol POSS results in viscosity reductions ranging from 7% in high sheer regions, to 60% in low sheer regions, he says. Lichtenhan points out that many technical aspects of phenyl and phenyl trisilanol POSS in PEEK and related aromatic polymers have been investigated by Professor Sarah Morgan at the University of Southern Mississippi as well as the United States Air Force Laboratory. Morgan says: “High temperature flow and dispersion are com- mon problems that POSS seems to solve. POSS is becoming known in the thermoplastics market- place for these types of niche but critical process- ing challenges.”
POSS in practice
One company using POSS in its compounds is The Resin Enterprise. Its Temppeclear grades are based on polyphenylene ether (PPE). CEO Linda Marlin says the additive can improve the resin’s processing parameters, physical properties, and colour. Temppeclear grades, which are available with and
Right: Microscale image of glass microspheres from Potters Engineered Glass Materials
without reinforcement, impact modifier, and flame retardant, are being offered as an alternative to polysulphone (PSU) and polyetherimide (PEI). “PPE by itself has notable physical properties, such as high heat distortion temperatures and stiffness,” Marlin says. “However, unalloyed PPE has in the past processed with extreme difficulty and the base polymer has provided only opaque colour opportunities.” She says PPE is, as a consequence, frequently blended with polymers such as polysty- rene and polyamide in commercial products from other leading suppliers. “With the addition of the proprietary additive we
are now able to provide a translucent or clear, amber tint PPE product that processes well. The new colour is similar to a polysulphone or PEI. Not only is the colour alike but the physical properties of the new compound are also comparable to these two high heat materials,” Marlin says. Temppeclear is also said to be much less dense than PSU or PEI – and less costly. The only problem the company faces at present
is getting hold of PPE. “Unfortunately, PPE went on short supply about the same time we came out with this product,” says Marlin. “I think it can be a very successful project, but PPE obviously has to be readily available.”
Glass microspheres Solid and hollow engineered glass microspheres can produce advantageous processing and product characteristics in a wide range of thermo- plastic applications, says Douglas Rudnick who works in Technical Service at Potters Engineered Glass Materials. “Injection moulded parts with very tight tolerances in shape can see compounding benefits with solid microspheres achieving high levels of warpage control,” he says. “Due to glass microspheres’ unique property of having an aspect
60 COMPOUNDING WORLD | August 2018
www.compoundingworld.com
PHOTO: POTTERS
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