Wash Chemistry

Detergent Chemistry for Industrial Laundry: Surfactants, Builders, and Bleach Systems

Most industrial laundry plants run whatever chemical package their current supplier bottles, changing brands only when price rises or a sales rep visits. The formulation behind that package, which surfactant class, how much alkalinity, and which bleach chemistry, determines wash quality and fabric life far more than the name printed on the drum.

Published July 6, 2026 — Stalwart Engineering Technical Notes

Surfactant classes and where each fits

Industrial detergent formulations combine two or three surfactant classes rather than relying on one. Anionic surfactants, typically linear alkylbenzene sulfonate (LAS), are the workhorse cleaning agents: cheap, effective on particulate and oily soil, but they foam heavily and lose efficiency in hard water because calcium and magnesium ions bind to the sulfonate group. Nonionic surfactants, mainly alcohol ethoxylates, are far less sensitive to water hardness and produce low foam, which is why they dominate formulations for tunnel washers and high-extract front-load machines where foam carryover into the extraction stage causes drainage and residue problems. Amphoteric surfactants appear in smaller proportions, mainly to improve soil suspension and prevent redeposition on synthetic fabrics.

The ratio between these classes should track the machine type in use. A plant running open-pocket washer-extractors with generous liquor ratios can tolerate a higher LAS content because foam has room to dissipate. A plant running tunnel washers with countercurrent water reuse needs a low-foam nonionic-dominant formula, since foam carried forward through the wash zones interferes with mechanical action and fouls water reuse piping.

Builders and alkalinity sources

Alkalinity does the heavy lifting against protein and oily soil by saponifying fats and breaking down proteinaceous stains at elevated pH. Sodium carbonate (soda ash) is the standard low-cost alkalinity builder; sodium metasilicate provides stronger alkalinity plus some corrosion protection for machine metal parts, at higher cost. Sodium tripolyphosphate, once the dominant builder worldwide for its sequestering and buffering properties, has been phased out of most commercial formulations in India in response to discharge-quality concerns over phosphate loading in receiving water bodies; zeolite-based builders and polycarboxylate co-builders have largely replaced it.

Target wash liquor pH varies by fabric and soil type: 9.5 to 10.5 for general institutional linen, up to 11.5 for heavily soiled workwear and kitchen linen, and closer to neutral for delicate synthetics and garments carrying reactive dyes that hydrolyse under strong alkali. Running every load at maximum alkalinity regardless of soil level is a common and costly mistake — it accelerates cotton fibre degradation over repeated wash cycles and increases the neutralizing acid dose needed in the sour step.

Bleach: chlorine-based versus oxygen-based systems

Sodium hypochlorite remains the cheapest and fastest-acting bleach for white cotton and polycotton institutional linen, and it provides genuine disinfection value in healthcare laundry. Its drawbacks are well known to any plant that has run it too long or too hot: yellowing of optical-brightened whites from over-chlorination, accelerated fibre tendering, and total incompatibility with colored or blended synthetic fabric, which it will strip or damage on contact.

Oxygen-based systems built on sodium percarbonate or hydrogen peroxide, activated with tetraacetylethylenediamine (TAED) to generate peracetic acid at wash temperature, give gentler bleaching suitable for colored workwear and blended fabrics, at a higher chemical cost per kilogram of linen processed. Plants running mixed white and colored production lines typically stock both systems and dose according to a program selected at the machine controller, rather than trying to find a single compromise chemistry that damages one category to accommodate the other.

Water hardness and sequestering agents

Calcium and magnesium in the supply water react with anionic surfactants and with soap-forming fatty soils to leave insoluble scum on fabric and machine surfaces, and they inactivate a portion of the detergent dose before it ever reaches the soil. EDTA and phosphonate-based sequestrants tie up these ions in solution so surfactant activity is not lost. Plants supplied by borewell water with hardness above roughly 150 to 200 mg/L as CaCO3 should budget for either a higher sequestrant dose or upstream softening; dosing more surfactant to compensate for hardness losses is more expensive over a year than installing a softener.

Matching chemistry to dosing hardware

None of this chemistry delivers consistent results without accurate, load-proportional dosing. A chemical dosing system calibrated to actual batch weight, rather than assumed rated capacity, prevents both the under-dosing that leaves soil behind and the over-dosing that wastes chemical and leaves surfactant residue in the rinse. Formulation changes and dosing pump calibration should always be reviewed together; a new chemistry with a different specific gravity or viscosity will throw off a peristaltic pump's volumetric dose even if the mass dose target is unchanged.

A practical framework for evaluating a chemical switch

Run a controlled trial batch against the current chemistry on identical soil-classified linen, and compare whiteness/rewash rate, not just sales literature claims.
Check the safety data sheet for pH, corrosivity, and compatibility with existing dosing pump seal materials before committing to a full changeover.
Model the cost per kilogram of processed linen, not cost per litre of concentrate; a cheaper-looking product dosed at twice the rate is not a saving.
Consider downstream effluent load. Chemical oxygen demand contribution varies substantially between builder systems and affects loading on the plant's effluent treatment plant.