additives feature | Coupling agents
where scrap is reintroduced as a structural layer. The grade links the normally immiscible major (up to 90% PE) and minor (PA or EVOH) components to improve dispersion, along with elongation, toughness and other mechanical properties in containers. Meanwhile, compounders use Fusabond’s compati- bilizing and dispersion properties to reduce the cost of commodity products such as PP containers, while maintaining mechanical properties. Calcium carbonate (CaCO3
) is used in these containers for rigidity. Accord-
ing to Torradas, a “small amount of Fusabond” increases CaCO3
DuPont’s Fusabond polymer modifi ers are used as coupling agents in fl exible pipe and other end-uses
7% is typical), the materials raise or help maintain select properties of commodity and engineering thermoplastics, and also compatibilize streams of mixed recyclate. Fusabond A560, for example, improves adhesion
between glass reinforcements and polyamide (PA) 6 and 66 resins, owing to its maleic anhydride group, which reacts with PA and ethylene-vinyl alcohol (EVOH). DuPont says this can increase the notched Izod impact strength of glass-reinforced PA by 30 to 50%. A560 also contributes to reduced melt viscosity in highly fi lled compounds and to retention of tensile strength, modulus and heat-deformation temperature. In addition, Fusabond grades reportedly work well as
This blow moulded polyolefi n
agrochemical
bottle for Brazil uses a DuPont Fusabond
coupling agent
coupling agents in highly fi lled polyolefi ns. One important area is formulations with fl ame-retardant mineral fi llers. Here the use of Fusabond as an additive enhances fi ller dispersion, improving compound homogeneity, elevating fl ame-retardant loadings and maintaining tensile strength and elongation-at-break properties. One Fusabond grade, M603, is touted as a compatibilizer for PE-based recycling streams and production of polymer lumber. In the latter, M603 strengthens the composite and reduces moisture absorption by cellulose fi bres in the compound. Torradas says that the grade can also be used with polymer lumber materials that are not fully dried, saving compounders time and money. In another reclaim application,
Torradas says M603 can improve the in-house recycling of PA or EVOH during the injection moulding or blow moulding of PE-based barrier containers,
14 COMPOUNDING WORLD | January 2013 loading, reducing PP use and saving
the compounder money, without affecting properties. Elvaloy grades are for neat and glass-reinforced
polyesters — polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). The PTW grade is a soft E-nBA-GMA (ethylene/n-butyl acrylate/glycidal methacrylate) terpolymer that bonds to and disperses consistently throughout polyester. It is especially compatible with glass and so toughens reinforced PBT. Elvaloy AC has similar properties in glass-reinforced
polyesters, but as a copolymer it increases melt fl ow over terpolymer versions, thereby improving process- ability. DuPont tweaks the chemistries of these resin
modifi ers to meet the coupling agent needs of evolving and emerging applications, and to create enhanced formulations with otherwise incompatible polymers and fi llers. “There are fewer new polymers and more interest in blending what’s available,” Torradas says in explaining this trend. Another company using resin chemistry as the basis for coupling agents is Chemtura. John Yun, technology manager at the company, says Polybond coupling agents are comprised of polyolefi ns and their deriva- tives, which are grafted with reactive
functional chemical groups such as maleic anhydride and acrylic acid. The additives are primarily for blending non-polar polymers like PP, PE and their deriva- tives with polar fi llers, such as glass fi bres, CaCO3, talc, mica, natural fi bres and others.
The coupling agents achieve this, Yun adds, by carrying polar functional groups along the non-polar polymer backbone. “This nature of bipolarity in Polybond coupling agents gives rise to affi nity at the interface of polymers and fi llers,” he explains. “The
functional groups form covalent bonds or secondary bonds while the polymer part imparts physical entanglement
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