Additives used to improve the polymer performance are active products that interfere with the compound. Their effects depend on their distribution, dispersion, wetting and actual compatibility with the matrix at macro and micro scales.
All these issues can be solved using wetting, dispersing and coupling agents or using modified additives or polymers. Really, the roles are not so clear-cut and most additives have a main effect and one or several collateral actions. Using usual classification, one can discern:
-Wetting agents such as Natural waxes, Synthetic waxes, Polyolefin waxes, Fatty acids and derivatives: generally the cheapest but the less efficient
-Oligomeric derivatives: Polyacrylates, Polyether structures, Polyester condensation products
-Silanes, the most efficient in terms of performance/price ratio. The organic part of organosilanes plays a prominent role in the adaptation to the additive/matrix couple. For example, for a same level of hard clay in the same polymer, two grades treated with silanes enhance tensile modulus of 60 and 110%.
-Titanates and zirconates, more universal than silanes but more expensive.
-Grafting of polymers with chemical functions compatible with the used additive ease wetting and coupling. Anhydride maleic or methacrylate grafted polymers are commonly used.
-Chemically modified additives: for example organo-modified nanoclays.
Research and development efforts lead to innovative dispersing-coupling additives such as POSS, Hyperbranched additives, Fluorosurfactants. It must be noticed that the action of additives can be made more acute using unusual mixing methods, for instance chaotic mixing, layer multipliers, Solid-State Shear Pulverization (SSSP).