OT 70 PG is listed as a powerful defoamer for acidic medium in paper and fertiliser duty. It is not a drop-in for alkaline black liquor.
Acid medium is a different foam
Alum, rosin size, and acid pH change how foam films drain. A surfactant that works in black liquor can underperform, or leave deposits, on an acid machine. The buying question is pH and furnish, not a generic “paper antifoam.”
Esteem lists OT 70 PG specifically for acidic medium. EO/PO copolymers remain the kraft and pulp-washing family. Non-silicone defoamers cover mills that cannot accept silicone in the sheet.
Specification that avoids a wrong sample
Send pH, temperature, addition point, and a silicone yes/no. If the complaint is felt filling, that is a felt-cleaning brief. If the complaint is ink flotation, that is deinking. Defoamer selection starts only after the duty is named.
Dose on a machine trial, not only a shake test. Acid foam can look controlled in a cylinder and still crater a coating.
| Grade family on the table | Published duty | Wrong brief |
|---|---|---|
| OT 70 PG | Acidic medium, paper and fertiliser | Alkaline black liquor |
| Product 21 P / 5100 / 5500 | EO/PO pulp and washer antifoam | Acid sizing crater control |
| Product 209 / SDS | Non-silicone defoamer | A silicone-required knock-down |
| Felt-cleaning surfactants | Clothing detergency | Sheet foam only |
Acid foam is a different film
On an acid machine the stabilisers are often rosin soaps that have been set with alum, plus fines and starch fragments. The surface is less like a high-pH fatty-acid soap and more like a weakly charged, sometimes tacky dispersion. A molecule designed to enter alkaline black-liquor films can sit in the water phase and do very little, or it can deposit because its cloud point and solubility were set for a different pH.
OT 70 PG is published for acidic medium, including paper and fertiliser duty. That sentence is a pH boundary. It does not mean the grade is a universal paper antifoam, and it does not mean an EO/PO washer antifoam becomes acceptable if the dose is raised.
Silicone, non-silicone, and spots
Silicone antifoams spread extremely fast and collapse films at low dose. They also leave spots if the droplet is not emulsified for the furnish, and those spots show up in sizing, coating, and converting. Product 209 and Product SDS are listed as non-silicone defoamers for mills that cannot accept that risk.
The choice is therefore three-way, not two-way. Acid pH points at an acid-medium defoamer. Hot alkaline washing points at EO/PO. A silicone ban points at the non-silicone pair even when the pH would otherwise allow a different knockdown chemistry. Name the constraint that is actually binding.
Where the dose should land
Stock, white water, and the coater are different dilution and shear environments. A grade that controls vat foam can still leave microfoam that becomes a crater when the coating is metered. Felt filling is a detergency problem for the clothing, not a reason to raise antifoam until the felt looks clean.
Run the trial at the addition point you will use in production, at the machine pH, and with the furnish that carries the foam. A cylinder test in tap water will not reproduce alum, fines, or the shear of a coater.
How to Specify with Esteem
- State machine pH and whether the foam is acid sizing, alum-rich, or alkaline kraft.
- Name temperature and the point of addition: stock, white water, or coater.
- Say if silicone spots are rejected by the converting customer.
- Record current defoamer and the defect: craters, foam spots, or drainage loss.
- Trial one acid-medium grade and one EO/PO grade only if pH actually crosses both regimes.
Compare grades on paper defoamers. Non-silicone Product 209 and Product SDS sit beside the EO/PO and acid-medium lines.