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additives | Coupling agents Right: Addivant’s


Polybond 3249 and 3349


MAH-grafted LLDPEs are targeted at HFFR cable applications


methyl acrylate (MA) as comonomers. They can be used in a range of polyesters, including PET and PBT.


Filler compatibility Coupling agents are often used to improve properties in compounds with high loadings of halogen-free flame retardant (HFFR) minerals, such as magnesium dihydroxide [MDH or Mg(OH)2


] or aluminum trihydrate


(ATH). The modifier acts to create a chemical coupling between the mineral and the polymer, which results in better mechanical properties and improved flame retardancy. At K2016, Addivant highlighted two MAH-grafted LLDPE-based coupling agents for polyethylene HFFR wire and cable, targeted at applica- tions that require higher elongation and reduced gel formation – Polybond 3249 and 3349. The new additions are targeted at improving


post-aging property retention. Polybond 3249 is slightly better for elongation retention after aging while Polybond 3349 is slightly better for tensile retention, says the company. The additives are said to be drop-in replacements for existing coupling agents being used in HFFR formulations. Another new grade is Polybond 7200, which is a higher graft-level PP-based grade for filled PP compounds. Kenrich Petrochemicals produces Ken-React


titanate, zirconate, and aluminate coupling agents, which can be used with fillers that do not react with silane coupling agents, such as calcium carbonate, carbon black, carbon fibres, carbon nanotube’s, graphene, boron nitride, barium sulphate, and non- hydroxyl bearing fillers and fibres. Titanates, added at low levels (typically 0.2 to 0.6


phr), lower the viscosity of the filled polymer and improve flow and mechanical properties. Titanate coupling agents, which are an organometallic chemis- try, behave differently from silanes and other additives, says Sal Monte, President of Kenrich. “[Titanates are]


Figure 1: Effect of Orevac MAH-grafted PP on fibre adhesion in a 30% glass reinforced PP compound


proton (H+) reactive… while the silane function may be termed hydroxyl (OH-) reactive via a silanol-siloxane mechanism requiring water of condensation. Since almost all three-dimensional particulates and species have surface protons, titanates are more universally reactive than silanes,” Monte explains. Titanates form a 1.5-2.0 nanometer monolayer on the


surface of the filler, which allows complete adhesion between the filler and the matrix polymer. They are not sensitive to pH variation and, unlike silanes which are not reactive above 100°C, titanates can have an in situ catalytic reaction during thermoplastic melt compound- ing of unfilled as well as filled compositions, resulting in beneficial changes in the morphology and mechanical properties of the polymer. “In addition to substrate adhesion via coordination coupling and polymer catalysis, the pendant heteroatom organofunctional groups can have phosphorous, carboxyl, amino, mercapto, and polar and non-polar ligands that help to compatibilise and promote further adhesion,” says Monte.


Source: Arkema Glass fibers without Orevac CA100 48 COMPOUNDING WORLD | November 2016


Glass fibers with 2% Orevac CA100 www.compoundingworld.com


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