ADDITIVES | POLYAMIDES
Nylostab S-EED form hydrogen bonds with the polyamide matrix. It is easy to disperse in the compound, but does not migrate from the end-prod- uct, says Emilie Meddah, Technical Business Devel- opment Manager at Additives Plastics, Clariant. In addition to acting as a light stabiliser to
Figure 1: Chart showing the effect of Byk-Max CT 4275 nanoclay additive in place of kaolin on tensile strength and tensile modulus in a glass fibre reinforced PA6 compound Image: Byk
care is required to achieve optimum exfoliation and dispersion of this product. Byk says it is beneficial to use the longest possible twin screw processing unit (> 40 L/D) and a screw design configured for high dispersion. To avoid compaction, the additive is best introduced using a side feeder. The com- pany says care should also be taken not to “over- shear” the material as this can cause agglomeration and reduction of aspect ratio.
Multifunctional option
Nylostab S-EED is a multifunctional stabiliser developed by Clariant for use in PA compounds across a range of applications, including packaging, electrical and electronics and transportation. As a HALS-type light stabiliser, the amide groups of
prevent degradation during aging in-use (including outdoor exposure), the Nylostab S-EED additive enhances heat stabilisation and acts as a process- ing stabiliser during multiple recycling loops. It can also improve surface aesthetics, creating a smoother surface in pigmented, glass-fibre rein- forced parts, says Meddah. She points to the example of a black pigmented, 33% glass-rein- forced PA66 injection moulded automotive part. With a 0.3% addition of Nylostab S-EED, a lower moulding temperature could be used and the part displayed a smoother and glossier surface. She says this is due to the glass fibres aligning at the surface, producing a resin-rich surface that enhances surface quality, while the fibres remain randomly dispersed in the core to preserve mechanical properties. Heat stabilisers are used to prevent degradation and colour change during use or storage of PA. When employed in combination with copper halide stabilisers, Nylostab S-EED boosts long-term stability and inhibits the colour change that can be induced by copper halide stabilisers. “While this colour shift is not a problem for black or dark shades, it can be noticeable in lighter colours,” says Meddah. “Injection moulded PA6 plaques contain- ing 0.25% S-EED in combination with a copper- halide had the same initial and aged colour as an unstabilised plaque, and had more than 33% increase in time to break after ageing at 135°C.”
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