TOFA 185 is the main feedstock for dimer acid production thanks to the high unsaturation represented by its min. iodine value of 150: two unsaturated C18 fatty acid molecules join catalytically through their double bonds (dimerize) to form a C36 dicarboxylic acid, i.e. dimer acid. Dimer acid is then polycondensed with a diamine to make polyamide resins and hot-melt adhesives; the low rosin acid and low unsaponifiable content of TOFA 185 yield a lighter-colored, more consistent dimer acid.

What is dimer acid?

Dimer acid is a long-chain acid formed by joining two fatty acid molecules and carrying two carboxyl groups (dicarboxylic) in its molecule. Because it is typically made from C18 fatty acids (oleic, linoleic), the main component of the product is C36 dimer acid; the reaction also produces monomer (unreacted fatty acid) and trimer (a C54 acid where three molecules joined) as by-products.

The value of dimer acid comes from its two carboxyl groups and long, branched, flexible hydrocarbon backbone. Its difunctional structure makes it usable as a monomer in polycondensation reactions (polyamide, polyester, polyurethane), while its long non-polar chain gives the final polymer flexibility, water resistance and adhesion.

Iodine value and the role of dimerization

The dimerization reaction proceeds through the carbon–carbon double bonds (unsaturation) in the fatty acid molecule. The iodine value is a measure of the density of these double bonds: the higher the number, the more double bonds in the molecule and therefore the more reactive sites for dimerization. The min. iodine value of 150 of TOFA 185 guarantees the reactive unsaturation needed for dimerization.

  • Unsaturated C18 fatty acids (oleic, linoleic) bond to each other through their double bonds.
  • The reaction is usually run under heat with a clay (montmorillonite)-type catalyst.
  • The product is separated into dimer/monomer/trimer fractions by distillation.
  • High iodine value = higher potential dimerization conversion.
BİO BAZLI ÜRÜNLERTall Oil Fatty Acids 185 (TOFA)For dimer acid production, TOFA 185 gives a lighter-colored, consistent dimer through high unsaturation (min. iodine value 150) and low impurity.

From dimer acid to polyamide resin

The largest use of dimer acid is in polyamide resins. Dimer acid is put through a polycondensation reaction with a diamine (e.g. ethylenediamine) to produce dimer-based polyamides. Unlike classic nylons, these polyamides are low-melting, flexible and solvent-soluble; these properties make them valuable as adhesive and ink resins.

Key applications of dimer-based polyamides:

  • Hot-melt adhesives — bookbinding, packaging and footwear industries.
  • Printing ink resins — binders especially in flexo and gravure inks.
  • Reactive polyamide hardeners (curing agents) for epoxy resins.
  • Corrosion inhibitors and metalworking additives.

Effect of purity on the final polyamide

The color and consistency of dimer acid, and therefore of the polyamide, depend directly on the purity of the starting fatty acid. The max. 2% rosin acid and max. 4% unsaponifiable content of TOFA 185 yield fewer by-products in the dimerization reaction, a lighter-colored dimer acid and therefore a clearer/lighter-colored polyamide resin. Since rosin acids do not take part in dimerization and remain a source of color, low rosin content is especially important for color-sensitive adhesive and ink resins.

Safe handling and storage

TOFA 185 and the dimerization process run at high temperature; there is a risk of hot fatty acid vapor/fumes and splashing. Use heat- and chemical-resistant gloves, face/eye protection and good ventilation, apply safe temperature control on heated reactors and transfer lines, and follow the product's current Safety Data Sheet (SDS).
  • Store TOFA 185 at 20–40 °C in closed containers, protected from moisture.
  • As an unsaturated fatty acid, prolonged air exposure can cause oxidation/color darkening; keep containers tightly closed.
  • Bulk shipment is in carbon steel or stainless steel tanks; ISO tank 20–22 MT net.
  • Shelf life is typically 12 months and can be extended to 24 months with controlled monitoring.
How is dimer acid produced?

It is produced by joining two unsaturated fatty acid molecules (typically oleic and linoleic acid) through their double bonds (dimerization) under heat with a clay-type catalyst. The product is separated into dimer, monomer and trimer fractions by distillation.

Why is TOFA 185 suitable for dimer acid production?

The high unsaturation represented by its min. iodine value of 150 provides the reactive double bonds needed for dimerization, while its max. 2% rosin acid and max. 4% unsaponifiable content yield a lighter-colored, more consistent dimer acid.

What is dimer acid used for?

Its biggest use is in polyamide resins, which go into hot-melt adhesives, printing ink resins and epoxy hardeners. It is also used as a corrosion inhibitor and metalworking additive.

How does iodine value relate to dimerization?

The iodine value measures the density of double bonds (unsaturation) in the fatty acid. Since dimerization proceeds through these double bonds, a high iodine value means more reactive sites and higher potential dimerization conversion.

How do dimer-based polyamides differ from classic nylon?

Thanks to the long, flexible chain of dimer acid, dimer-based polyamides are lower-melting, more flexible and solvent-soluble, which makes them suitable as adhesive and ink resins.