Acid value measures free acid density, iodine value measures unsaturation, rosin acid content measures the rosin carried into the fatty acid fraction, and unsaponifiables measure residue that never reacts. The first sets stoichiometry, the second predicts drying and dimerisation behaviour, and the last two govern colour and yield loss.
What does acid value measure and what does it set in your recipe?
Acid value expresses the amount of potassium hydroxide needed to neutralise the free acid in one gram of sample (mg KOH/g) and is measured on TOFA by ASTM D1980. Its meaning for a formulation is direct: if you are running esterification, saponification or neutralisation, this number sets how much of the counter-reactant (polyol, alkali, amine) you dose.
Acid value is therefore a calculation input, not a quality badge. The min 185 limit of TOFA 185 is preferred not because it is inherently "better" than the min 180 of TOFA 180, but because it holds free acid density in a narrower band. If acid value drifts between lots, so does the counter-reactant ratio in the recipe, and the batch lands above or below the intended conversion.
The same line also reveals product identity across the rest of the family. Hardwood CTO is defined at acid value min 96 (ASTM D465 / ASTM D664): as a crude mixture its free acid density is naturally lower. Ecophalt (Tall Oil Pitch) sits at 40-70 (ASTM D664 / ISO 6619). TOFA Rich Distillate is reported with a single value of 178.5. The same-named line tells three different stories on three different products.
What does iodine value mean? Unsaturation, drying and dimerisation
Iodine value expresses the amount of iodine that adds to the unsaturated bonds of a sample (g I2/100 g) and is measured on TOFA by ASTM D5768. In short, it is the measure of double-bond density in the chains, and unsaturation is the precondition for interaction with oxygen, for cross-linking and for dimerisation.
That shows up in three places in a formulation. In systems that form a film by oxidative drying, double-bond density governs the drying behaviour. In dimer acid production the structure that reacts is precisely those double bonds. In the warehouse, the same unsaturation means oxidation risk under uncontrolled conditions, which is why TOFA is kept in closed containers, protected from sunlight and moisture.
In TOFA 180 and TOFA 185 the iodine value limit is identical: min 150 in both grades. The choice between the two grades is therefore not made on unsaturation; the distinction sits on colour, rosin acid and unsaponifiables. This also prevents a common misreading: the grade with the higher acid value is not automatically the more reactive grade.
BİO BAZLI ÜRÜNLERTall Oil Fatty Acids 185 (TOFA)TOFA 185: acid value min 185 (ASTM D1980), iodine value min 150 (ASTM D5768). Request a sample and a per-lot CoA to verify stoichiometry in your own recipe.Why is rosin acid content written as a separate line?
Rosin acids are the abietic-type components of tall oil and have a different skeleton from a fatty acid: they are ring structures that carry a carboxyl group but do not behave like a long straight-chain fatty acid. Because distillation cannot remove all of them, some remain in the fatty acid fraction, where they are measured by ASTM D1240.
For a formulator that carry-over affects two things: colour development and viscosity behaviour. Ring-structured rosin acids tend to darken the system and raise viscosity. That is why lines where colour stability is critical call for the max 2% limit of TOFA 185, while the max 3% limit of TOFA 180 is sufficient where tolerance is wider.
Rosin acid is not always an unwanted component. In the DTO grades it is deliberately kept high: max 40% in the industrial grade and max 30% in the mid-high and premium grades. The same component is an impurity limit in one product and the definition of the product in another.
What do unsaponifiables measure and why are they a yield problem?
Unsaponifiables (ASTM D1065) are the share of components that do not enter the saponification reaction when treated with alkali: sterols, hydrocarbons and other neutral matter. Because they carry no carboxyl group they do not enter esterification either.
The practical consequence is a yield and purity problem. That share of every kilogram you weigh in never joins the reaction, stays in the product and can surface as a colour, odour or compatibility issue in the finished article. The limits differ markedly between grades: max 4% in TOFA 185 and max 6% in TOFA 180. On the DTO side the premium grade carries max 6% and the other two grades max 7%, while the value reported for TOFA Rich Distillate is 5.2%.
Why is there no saponification number on a TOFA sheet?
The saponification number (ASTM D94) measures the potassium hydroxide needed to saponify both the free acids and the ester-bound acids in a sample. Acid value sees only the free acid, while saponification number sees the total acid potential. The gap between the two indicates the ester-bound structure in the product.
That line does not appear in the TOFA specification, because the product is already the free fatty acid fraction separated by distillation. In the DTO grades it is reported explicitly: min 170 in the industrial grade and min 175 in the mid-high and premium grades, against acid numbers of min 165, min 170 and min 170 respectively. TOFA Rich Distillate likewise carries acid number 178.5 and saponification number 184 together. If you see both lines side by side on a sheet, what you are holding is something other than a pure fatty acid fraction.
When do the colour and moisture lines come into play?
On the TOFA specification, colour appears as an appearance description rather than a numeric line: TOFA 180 is an amber to dark amber liquid and TOFA 185 a light yellow to amber liquid. On another item in the family colour is quantified: the DTO industrial grade reports colour (iodine) as max 80 by ASTM D1348.
Moisture is likewise a line that varies by product. In the DTO grades it is measured by ASTM E203 and defined as max 1.0% in the industrial grade, trace in the mid-high grade and trace amounts in the premium grade. Because water content affects both the acid value measurement and the esterification balance, ask for this line on the document if your formulation is water sensitive.
In what order should a formulator use these lines?
- Identify the reaction type: if you are running esterification, saponification or neutralisation, start with acid value.
- If you expect behaviour that depends on unsaturation (oxidative drying, cross-linking, dimerisation), check the iodine value: min 150 in both grades.
- If colour is critical in your finished product, read rosin acid content and the appearance line together.
- If you are calculating yield, put the unsaponifiables limit into the calculation: the gap between max 4% and max 6% shows up in the recipe.
- If the sheet also carries a saponification number, note that the product is not a pure fatty acid fraction and contains ester-bound structure.
- Confirm the decision with a sample: measure it in your own laboratory with the same methods and compare against the per-lot CoA.
What is acid value and why does it matter?
It is the amount of potassium hydroxide needed to neutralise the free acid in one gram of sample (mg KOH/g), measured on TOFA by ASTM D1980. It sets the dosing of the counter-reactant in esterification, saponification and neutralisation. Min 180 in TOFA 180 and min 185 in TOFA 185.
What does iodine value mean?
It measures unsaturation, that is double-bond density in the chains (g I2/100 g), by ASTM D5768, and predicts oxidative drying, cross-linking and dimerisation behaviour. The limit is identical in TOFA 180 and TOFA 185: min 150.
Does a higher acid value mean a more reactive product?
No. Acid value shows free acid density, not unsaturation. Reactivity tied to unsaturation is measured by iodine value, and that limit is the same in both TOFA grades (min 150). The real difference between the grades sits on colour, rosin acid and unsaponifiables.
Why are unsaponifiables a yield problem?
They are neutral components that enter neither saponification nor esterification (ASTM D1065), so that share of the mass you weigh in stays in the product without reacting. The limit is max 4% in TOFA 185 and max 6% in TOFA 180.
What is the difference between saponification number and acid value?
Acid value measures only free acid, while saponification number (ASTM D94) measures both free and ester-bound acid; the gap indicates ester-bound structure. A TOFA sheet has no saponification number, while the DTO grades report min 170 to min 175.
Is rosin acid content always an impurity?
No. In TOFA it is carry-over into the fatty acid fraction and is limited (max 2% in TOFA 185, max 3% in TOFA 180). In the DTO grades it is deliberately kept high: max 40% in the industrial grade and max 30% in the mid-high and premium grades. The same component can be an impurity or the definition of the product.