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additives feature | Coupling agents

DuPont’s Fusabond Grade M603 is used to compatibilize PE-based recycling streams in Brazil

of polymer chains driven by the thermodynamics during the mixing process.” As a result, PP, PE and polyolefin derivatives achieve

enhancements in such mechanical properties as tensile, flexural, impact and adhesion strength in applications like multilayer film and coatings. According to Yun, Chemtura is supplying these

coupling agents for five major applications: PP with short and long glass fibres; PP and PE filled with natural fibres such as wood flours, cellulose, starch and others; PP filled with mineral fillers like CaCO3

, talc and

colour pigments; adhesive layers between printing ink and PP in flexible packaging; and PP/PA blends. Yun identifies evolving applications for which

Polyblend additives have a fit. One is dispersion of colour pigments in automotive and home appliances. Another is flexible packaging for heavy-duty goods com- prising a woven PP layer and an ink-print layer. Here the Polybond coupling agents improve adhesion between the ink layer and woven PP. The third is wire and cable compounds with more than a 70% loading of halogen-free flame retardants. To regain the compro- mised mechanical properties such a formulation creates, Polybond compatibilizes the flame retardant with the polymer, in the process restoring elongation and tensile strength. Yun notes that recycling is another important

application, especially in lines where PA can mix with and contaminate PP scrap. “A small addition of Polybond coupling agents makes [both materials] compatible and maintains PP integrity,” he says. Other materials getting a closer look by some

compounders are titanates (Ti) and zirconates (Zr), both organometallics. Kenrich Petrochemicals, which sells liquid Ti grades under KR or LICA brand names, and liquid Zr additives as NZ and KZ brands, has promoted

16 COMPOUNDING WORLD | January 2013

, carbon black, carbon fibre and graphene. Ti and Zr are also thermally stable catalysts, says Kenrich president Salvatore Monte. This means they can repolymerize a macromolecule in an extruder’s polymer melt to rebuild molecular weight — a process Monte likens to reactor-based metallocene catalysis. Among the advantages of Ti and Zr when added to thermosets, is a curative function that provides methacrylic, acrylic, amino and mercapto moieties that react with UV light, free radicals, peroxides, sulphur and other curing agents to increase cross-linking and other functions, Monte says. In compounding, loadings of 0.2 to 0.4% by weight

the materials for years, claiming they offer advantages that coupling agents such as silanes do not. Ti and Zr reportedly compatibilize polar and non-polar polymers, and react with all organic and inorganic materials. Conventional silanes, in contrast, work with many reinforcements and mineral fillers, but according to Kenrich they have less effect on materials such as CaCO3

are typical for unfilled polymers when Ti and Zr are used as adhesion promoters, catalysts or process aids. Loadings range from 0.35 to 0.7% by weight when they are used with mineral fillers, pigments and fibres. Monte says that information about applications is

restricted by non-disclosure agreements. Recently developed grades, however, show the types of benefits Kenrich provides with its organometallic chemistry. One grade for unsaturated polyester converts the MEKP (methyl ethyl ketone peroxide) curing reaction to endothermic from exothermic to eliminate micro-bub- ble formation in parts. New coupling agents for advanced composites are formulated for carbon and aramid materials. The additives even have use in recycling. “Because

the titanates are in situ catalysts in the melt, they regenerate scissored molecular chains and rebuild mechanical properties,” Monte explains. “They will also copolymerize, so whereas not more than 5% PP can be blended with high-density PE without having delamina- tion and compatibility issues, [Kenrich] coupling agents will allow a 50/50 PP/HDPE blend that in effect acts as a new polymer.” This of course means recycling has to be a melt

process, which Monte acknowledges adds cost. But as he notes, these coupling agents “will become more viable when the use of recycled commodity plastics become part of a sustainability culture in large markets such as automotive.” Silane formulations are also being tweaked for new

and evolving needs. The dual functionality of silanes, evident in their ability to achieve molecular bonds between organic resins and inorganic substrates, gives

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