additives | Clarifiers and nucleators
barrier performance in polyethylene. “The use of nucleating agents for passive barrier enhancement is a relatively new area in which the particles themselves do not affect permeation,” Dotson says. The argument is that the directional crystalline orientation of nucleated PE lamellae in the polymer film creates a passive “tortuous path” for permeants during their travel through the article. Milliken introduced the first commercial nucleating
agent for polyethylene, Hyperform HPN-20E, in 2006; it can also be used as a high-performance nucleating agent for polypropylene. “Its primary performance enhancements are improved clarity of LLDPE blown film, reduced water vapour transmission rates in LLDPE and HDPE films, and improved cycle times in injection moulding in the presence of pigments,” Dotson says. More recently (2014), Milliken launched a second-
generation PE nucleating agent, Hyperform HPN 210 M. Its primary value set consists of improved flexural modulus and dimensional stability in injection mould- ings. Both additives work by inducing particular crystalline morphologies, some of which involve providing passive tortuosity of PE lamellae. Polyethylene typically consists of three-dimensional spherulitic crystals that are made up of lamellae that grow radially from a centre point. These strand-like lamellae are “stitched” together with amorphous tie-chains (Figure 1). Gas molecules have no trouble migrating between the lamellae through the amorphous tie-chain layers of the spherulite. From any direction, a permeant would have the same path through this unoriented matrix; the only resistance to migration would be flat in the MD/TD plane of the article. Nucleating agents not only induce crystallisation at
higher temperatures and at higher rates, but specific interactions of the growing polymer crystal with the surface topology of the nucleating agent will direct
BruggolenTP-P1401 nucleating agent produces smooth surfaces in injection mouldings. Photos show the surface of parts in 50% reinforced PA6 using a conventional nucleating agent (left) and with 1.5 % of TP-P1401 (right) Source: Brüggemann Chemical
preferred crystalline growth in a specific direction. Dotson says that nucleating agents like Hyperform HPN-20E and 210 M cause PE lamellae to grown only in the MD/TD plane of the film or moulding. This forces water vapour, for example, to travel 20% slower around and between lamellar plates to exit through the normal direction. By increasing the crystalline density only in the plane of the film, and not in the normal direction, permeants such as CO2
and water vapour can migrate up to 60%
more slowly through some HDPE films (although barrier improvements of 30-50% are more common).
PA nucleation Nucleating agents are not only used for polyolefins. Brüggemann Chemical launched a nucleating agent for polyamides, Bruggolen TP-P1401, last year at K 2016. The company says the new product is non-volatile and stable even at high processing temperatures. It enables shorter cycle times, thus increasing productivity, and also optimises dimensional stability and mechanical proper- ties. It disperses very easily in the polyamide matrix, which makes it ideal for compounding and also for direct application in injection moulding, the supplier claims. “With 1.5 % Bruggolen TP-P1401 in unfilled polyam-
ide 6, for example, cycle times can be reduced by up to 60 %,” says Klaus Bergmann, Business Unit Manager for Polymer Additives. He also claims that surface qualities of reinforced polyamide materials are better than with conventional nucleating agents.
Comparison of the effect of different nucleating agents on gloss of 50% glass reinforced PA6 Source: Brüggemann Chemical
56 COMPOUNDING WORLD | May 2017
Click on the links for more information: ❙
www.milliken.com ❙
www.njceurope.com ❙
www.emeraldmaterials.com ❙
www.brueggemann.com
www.compoundingworld.com
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