Syntans

Syntans, short for synthetic tannins, are a class of chemical tanning agents used in leather processing. They are synthetic or semi-synthetic compounds designed to mimic some properties of natural tannins and are applied during retannage or post-tanning to modify the leather's appearance and performance.

Chemistry and types: Most syntans are water-soluble polyphenolic condensates or sulfonated aromatic compounds. Common examples include sulfonated naphthalene- and phenol-formaldehyde condensates. They are formulated to bind effectively to collagen, operate at typical tanning bath pH, and be compatible with chrome-tanned or vegetable-tanned leathers. Formulations range from lighter to deeper color and can be designed to be formaldehyde-free.

Application and effects: In the retannage bath, syntans improve fullness and tightness, enhance dye uptake and uniformity, and increase wet and dry rub resistance. They can help stabilize shade, reduce undesirable graining, and tailor the leather’s handle. Syntans are used to achieve specific end-use properties and can reduce the amount of mineral tanning chemicals required.

Environmental and processing considerations: Syntans enable regulated performance with a wider range of tannages and can be formulated to meet environmental constraints. Their effects depend on bath charge, pH, temperature, and interaction with other tanning or retanning agents, so process control is important.