A brown-stock antifoam is judged on drainage and soda loss, not on a beaker knock-down that ignores liquor solids and temperature.
Where washer foam actually costs money
Kraft brown-stock washers and deckers lose capacity when foam holds liquor in the mat. Soda leaves with the pulp, evaporation load rises, and later bleaching sees more carryover. The surfactant is not a “paper coating additive.” It is an antifoam for a hot, alkaline, high-solids liquor.
Esteem’s paper-defoamer table lists EO/PO copolymers for this duty, including grades described for brown-stock washing and black-liquor recovery, plus an alkyl-capped EO/PO used as a pulp-process antifoam. Those notes are the buying language. A tissue debonding surfactant or a coating wetting agent will not drain a washer.
How to choose the antifoam family
Match the polymer to temperature and solids. Uncapped EO/PO grades are the first screen for general washer foam. Alkyl-capped grades are the screen when persistence in hot liquor matters more than a fast surface flash. Acidic-medium defoamers such as OT 70 PG belong on acid papermaking or fertiliser-type duties, not as a default kraft washer dose.
Silicone-free is the usual mill request because silicone spots show up in sizing, coating, and converting. Confirm that constraint before the sample ships.
| Duty | Look first at | Do not treat it as |
|---|---|---|
| Brown-stock washer | EO/PO antifoam for pulp washing | A deinking flotation collector |
| Black liquor foam | Alkyl-capped or standard EO/PO antifoam | A felt-cleaning detergent |
| Acid paper machine | Acid-medium defoamer such as OT 70 PG | A kraft washer package |
| Tissue Yankee | Release / creping package | A brown-stock antifoam |
What is stabilising the washer foam
Black liquor is not a detergent bath. It is an alkaline solution of lignin, sodium salts of wood extractives, and residual pulping chemicals. The natural soaps are anionic. They adsorb at the air–liquor surface, slow film drainage, and let foam survive the drop from the wash shower into the vat. Temperature often sits well above the cloud point of a conventional alcohol ethoxylate, which is why a high-foam laundry nonionic is the wrong model.
Entrained air also changes drainage on the wire and the mat. A washer that looks “foamy” may be losing washing efficiency because liquor is held in bubbles instead of displacing the mat. The antifoam brief is therefore a washing brief, not only a housekeeping brief about foam over the handrail.
Why EO/PO copolymers fit this liquor
An EO/PO block puts a hydrophobic polyoxypropylene segment next to a hydrophilic polyoxyethylene segment. In hot alkaline liquor the PO-rich part prefers the air interface and disrupts the soap film. The EO-rich part keeps the molecule from simply oiling out as a neat defoamer slick. Alkyl-capped grades go further: the cap removes the terminal hydroxyl, so the molecule is less reactive and often more persistent in hot liquor.
Persistence is not the same as knockdown. A fast surface flash can collapse a beaker and still be gone before the next washer stage. A persistent grade stays through temperature and dilution. Say which one the mill is missing. Acid-medium grades such as OT 70 PG belong on acid machines, not as a substitute for this alkaline soap foam.
How to read a failed trial
If foam collapses and then returns within one stage, the dose is being stripped into the fibre mat or the grade has no residual activity after the cloud-point region. If the mat blinds or the sheet shows spots, the antifoam is too hydrophobic or too rich in silicone for that furnish. If washing efficiency falls while the vat looks calm, air has been replaced by a film that still blocks liquor flow.
Record pH, temperature at the addition point, washer stage, and whether the liquor is weak or strong. Those four numbers decide between an uncapped EO/PO, an alkyl-capped grade, and a non-silicone defoamer. They also stop a felt-cleaning detergent from being trialled as if it were an antifoam.
How to Specify with Esteem
- Name the washer line: brown stock, decker, or black-liquor evaporator feed.
- Give liquor solids, temperature, pH, and whether the furnish is hardwood, softwood, or mixed.
- State the failure: carryover, soda loss, washer blinding, or evaporator foam.
- Say if silicone is restricted and whether an alkyl-capped EO/PO is acceptable.
- Request a named grade from the paper defoamer table rather than “mill antifoam.”
Start from the paper defoamers table and the paper chemicals hub. Acidic-medium grades such as OT 70 PG are a different duty — see the companion acid-mill note.