Almost nobody buys a preservative by reading its mechanism of action. It is bought on price per kilogram and on two words in the data sheet: broad spectrum. Then, three weeks into summer storage, a batch of liquid detergent separates, a wipe solution grows a biofilm, or a customer reports an off-odour in a skin cream — and the preservative carries the blame, even though in most cases the chemistry was simply incompatible with the base it was dosed into.
A water-based product has to be preserved against pH, temperature, electrolyte, surfactant charge and legislation at the same time. A system that satisfies four of those five will still fail. This guide works through the 19 blends in our preservative range segment by segment and states the operating windows that decide whether a preservative works or merely costs money.
The five constraints that decide everything
Before comparing actives, settle these five numbers for the base you are preserving. Nearly every preservative complaint traces back to one of them.
| Constraint | Why it decides the outcome | What to state in the brief |
|---|---|---|
| pH window | Efficacy and chemical stability both fall away outside the window. Iodopropynyl butylcarbamate (IPBC, CAS 55406-53-6) works best from mildly acidic to neutral — around pH 4-9 — and is reported to decompose above pH 9, releasing iodine and volatile propargyl alcohol. | The pH of the finished product across its whole shelf life, not the pH of the concentrate. |
| Addition temperature | IPBC begins to degrade from about 70 °C upward. Thermogravimetric analysis puts the onset of decomposition at 91 °C, and isothermal work shows 81.2% retention after 24 hours at 80 °C, falling to 49.4% at 90 °C. | The actual temperature in the vessel when the preservative is dosed, and whether the process has a cool-down phase at all. |
| Electrolyte load | Salt is a rheology tool, not a neutral filler. Its thickening effect follows a bell-shaped curve: past the maximum, more electrolyte thins the product, causes haze, worsens low-temperature flow and can destabilise the phase. | Whether the base is salt-thickened, how far it sits from the viscosity maximum, and whether the preservative must be salt-free. |
| Surfactant charge | Anionic surfactants associate with cationic actives and can pull them out of solution, which is why some wipe and personal care systems explicitly require an anionic-free environment. | The surfactant system and its charge, plus whether the preservative must be anionic-free. |
| Market legislation | The same molecule can be legal in a household cleaner and prohibited in a cosmetic. Methylisothiazolinone (MIT, CAS 2682-20-4) is limited to 0.01% in rinse-off cosmetics in the EU and is not permitted in leave-on products; sodium pyrithione (CAS 3811-73-2) appears in EU cosmetics Annex II as a prohibited substance. | The destination market and the product classification — cosmetic, biocide, or treated article. |
Liquid detergents, hard-surface cleaners and dishwash
Liquid detergents are water-rich and stored at ambient temperature for a year or more, so they support microbial growth even when the pH and surfactant level look hostile. The complication is that the base is usually also the rheology system: in sulphate and LAS systems salt is the cheapest thickener available, and it only works near the top of a narrow curve.
Two consequences govern preservative choice here:
- Salt-free is not a marketing word. A preservative that carries electrolyte moves the formulation along the salt curve — sometimes past the maximum, where viscosity falls, the product hazes and low-temperature flow deteriorates. It matters even more in acrylic-thickened systems, where the polymer network is sensitive to ionic strength and to cationic species.
- Addition has to happen late. A detergent process can run hot. Dosing an IPBC or isothiazolinone system into a warm batch destroys part of the active before the product is even filled.
| Grade | Positioning | Addition | Typical level |
|---|---|---|---|
| YS-812 | Salt-free, water-clear blend with synergistic action, for general detergent, wool and silk detergent, fabric softener, hand and machine dishwash, hand wash, bathroom, toilet-bowl, glass and speciality cleaners | Dilute and add below 50 °C | 0.05–0.2% |
| YS-806 | Salt-free, heat-resistant grade for the same detergent family, with low irritation | Best added below 80 °C — the option when the process has no cool-down step | 0.05–0.2% |
| YS-808 | Economical, long-lasting bacteriostatic blend engineered for hand and machine dishwash, also suitable for other liquid detergents | Standard cool-down addition | 0.05–0.2% |
Both salt-free detergent grades carry the same process warning: keep them away from organic amines, mercaptans, sulfites and strong reducing agents. The reason is mechanistic. Actives of this family work by oxidising or alkylating microbial thiol groups and enzymes, so a reducing agent in the same vessel simply consumes the active before it ever reaches a microorganism.
Personal care: shampoo, conditioner, masks and creams
Personal care is the segment where preservative choice is decided by the base rather than by the budget. A sulphate-free shampoo, a cationic conditioner and a low-pH exfoliant are three different chemical environments, and the range is built around that: five blends covering pH 2-9, pH 4-9 and pH 3-10, one of which tolerates addition at 60 °C for processes that cannot cool further.
| Grade | Working pH | Addition temperature | Typical level | Notes |
|---|---|---|---|---|
| YS-801 | 2-9 | below 50 °C | 0.06–0.2% | Broad-spectrum daily-care system; the widest pH span of the range |
| YS-802 | 4-9 | below 50 °C | 0.06–0.2% | For neutral to mildly acidic creams and lotions |
| YS-803 | 2-9 | below 50 °C | 0.06–0.2% | Acid-side work: toners, peel products, low-pH cleansers |
| YS-804 | 3-10 | below 50 °C | 0.06–0.2% | Extends into the alkaline range for soap-based and near-neutral gels |
| YS-805 | 3-10 | below 60 °C | 0.06–0.2% | The heat-tolerant option where a batch cannot be cooled below 50 °C |
Two regulatory facts decide whether a given personal care brief can use an isothiazolinone or IPBC-containing system at all, and both are regularly discovered too late:
- MIT is a rinse-off-only preservative in the EU, with a maximum of 0.01% in the ready-to-use preparation. The CMIT/MIT 3:1 mixture is capped at 0.0015% (15 ppm), also rinse-off only, and the two entries are mutually exclusive — a formula cannot contain both the mixture and MIT alone.
- IPBC has three tiers, not one: 0.02% in rinse-off products, 0.01% in leave-on products, and 0.0075% in deodorants and antiperspirants. It is not permitted in oral hygiene or lip products, nor in body lotion or body cream at any concentration.
Both ceilings sit far below the 0.06–0.2% use levels typical of a blended system, which is precisely why blended products exist: the secondary actives carry the load, and the restricted molecule is present only in the small amount the legislation allows.
Wet wipes and nonwoven wiping products
A wipe is the hardest preservation problem in the consumer range. The liquid is dilute, spread over an enormous surface area, packed warm, opened repeatedly and often stored in a bathroom; the nonwoven itself can adsorb part of the active; and the surfactant system has to wet the substrate properly or the wipe will not release its lotion evenly. Dosage therefore runs higher than in a cream — 0.1–0.3% across the range.
| Grade | Target wipe | Formulation constraint | Level |
|---|---|---|---|
| YS-201 | General, baby, personal care, feminine and kitchen wipes | Colourless, odourless, water-soluble; can be dosed at any stage of production | 0.1–0.3% |
| YS-202 | Hotel and catering wipes, shoe-shine, leather-care and automotive wipes | Economical, synergistically boosted; dilute and add below 50 °C | 0.1–0.3% |
| YS-203 | Beauty wipes, baby wipes and sheet masks | Needs about 0.1% anionic or non-ionic surfactant in the wipe solution for proper wetting, mixed in under stirring | 0.1–0.3% |
| YS-204 | Feminine care and disinfecting wipes | Fast-acting and low-irritation; the wipe solution must be free of anionic surfactants | 0.1–0.3% |
| YS-T10 | General wipes, baby disinfecting wipes, care and feminine wipes, kitchen wipes, plus cotton towel, detergent and skin-cream uses | IPBC and MIT system (CAS 55406-53-6; 2682-20-4), easily dispersed in wipe solution — IPBC is poorly water-soluble while MIT is highly soluble | 0.1–0.3% |
Those two constraint notes are not boilerplate. YS-203 and YS-204 sit on opposite sides of the same compatibility rule: one needs a surfactant present in order to wet out, the other needs the anionic surfactant absent so that the active stays available. Pick the grade against the wipe solution you already have, not the other way round.
One market point deserves stating plainly. In the EU, personal care wet wipes are classified as leave-on cosmetics, and MIT is restricted to rinse-off products. MIT-containing wipe systems therefore belong to markets where wipes are regulated differently, or to household, industrial and pet wipe categories — the active is not the issue, the classification is.
Textile dyeing, leather processing and industrial process water
Textile and leather preservation is a different problem from product preservation, because the thing being protected is not a finished good but a moving bath. Process water, size liquor, print paste and soaking pits all carry organic load at 30–60 °C for hours, which is ideal for bacteria and mould. The failure modes show up as slime on rollers and fabric, persistent odour, spotting, dye defects and, in leather, damage to the hide itself.
Two process realities drive grade selection:
- Temperature. High-temperature dyeing and drying lines cannot wait for a cool batch. YS-903 is the thermally stable, anti-fouling grade for those conditions, and YS-CG is the salt-free, heat-resistant blend that can be added below 80 °C — useful where the bath is also electrolyte-sensitive. YS-901 and YS-902 work in the pH 4-9 window and are added below 50 °C; YS-902 is the salt-free upgraded version with spatial protection and synergistic action.
- Reducing agents and sulfides. Dyeing baths use hydrosulfite and other reducing agents, and leather processing uses sulfide-containing liquors. As with liquid detergents, oxidative actives are consumed by these materials. Dose the preservative after the reducing stage, or choose a grade whose actives survive it.
Set process-water preservation levels against the water volume, not the substrate weight. A dyebath's organic load varies by an order of magnitude between a light shade and a heavy dark shade, and a level transposed from a product formulation will either be uneconomic or ineffective. Confirm the level on the actual bath.
Cat litter and other high-temperature, odour-critical applications
Cat litter is the application where preservation has to survive both heat and the biology of the end use. Tofu (soy) litter is extruded and dried; crystal and bentonite litters are blended and packed; and all of them are used in a warm, humid, ammonia-producing environment where bacterial and fungal growth, rather than product spoilage, is the visible problem. The two grades in the range are built on different active pairs:
- YS-T20 — IPBC with sodium pyrithione (CAS 55406-53-6; 3811-73-2): broad-spectrum antibacterial, antifungal and deodorising liquid blend for tofu, crystal and bentonite litter, sprayed and blended in for sterilisation, mould prevention and odour control.
- YS-T30 — IPBC with MIT (CAS 55406-53-6; 2682-20-4): heat-resistant system with fragrance retention, for the same substrates where the process runs hot or a fragrance has to be carried without being broken down.
Pyrithione chemistry brings properties worth knowing before it is specified. Sodium pyrithione works best in the pH 7-10 range, is unstable to light, oxidising agents and strong reducing agents, is deactivated to some degree by non-ionic surfactants, and chelates heavy metals — iron, manganese and zinc in particular. That last point interacts directly with the substrate: an iron-bearing clay, or process water carrying metal ions, will tie up part of the pyrithione and reduce measured efficacy, so dosing must be confirmed on the actual litter rather than on a clean laboratory blank.
Both grades are used at 0.1–0.2%, sprayed and blended during production. Sodium pyrithione is prohibited in EU cosmetic products (Annex II), so these systems are positioned for litter, household and industrial applications, where the biocide framework rather than the cosmetics regulation applies.
Proving the system works instead of assuming it
A preservative that has been dosed correctly still has to be demonstrated. The reference method for water-based cosmetics is the preservative efficacy (challenge) test to ISO 11930: five organisms — Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Aspergillus brasiliensis — each inoculated at 10⁵–10⁶ CFU/g or mL, with counts at day 7, 14 and 28.
| Organism group | Criterion A | Criterion B |
|---|---|---|
| Bacteria | ≥ 3 log reduction by day 7, no increase to day 28 | ≥ 3 log reduction by day 14, no increase to day 28 |
| Yeast (C. albicans) | ≥ 1 log reduction by day 7, no increase to day 28 | ≥ 1 log reduction by day 14, no increase to day 28 |
| Mould (A. brasiliensis) | No increase from the initial count at day 14, ≥ 1 log by day 28 | No increase from the initial count through day 28 |
Three practical points decide whether that result means anything:
- Test at the end of the stability study, not only on day zero. A pass at T0 shows the system worked on the day of manufacture. Actives partition into the oil phase of an emulsion, adsorb onto a wipe substrate or a textile fibre, and drift with pH across shelf life — so the meaningful result is the one taken at the accelerated and long-term stability pull points.
- Validate neutralisation. If the neutraliser does not fully inactivate the preservative carried over into the counting plates, the outcome is a false pass that hides a failing formula.
- Build a dose ladder. Screen the candidate at 0.05%, 0.1%, 0.15% and 0.2% in the real base rather than at a single level, then take the lowest level that meets the criterion with margin. Over-preserving buys nothing: cost rises, sensory and colour risk rise, and for restricted actives the legal ceiling may sit below the level a formulator would otherwise have chosen.
Specification and procurement checklist
- Active content and carrier, given as a range with the analytical method — not "typical".
- Appearance and clarity for salt-free and water-clear grades, since haze is the same symptom as an electrolyte problem.
- Odour, and whether the grade is designed to be odour-neutral or to carry fragrance (YS-T30 is deliberately built to retain it).
- pH of the supplied product, so it can be checked against the base before blending.
- Registration status in the destination market — EU cosmetics Annex V for personal care and wipes, the biocidal products framework for detergents, process water and litter, and the corresponding local registration elsewhere. Ask for this before the sample, not after the purchase order.
- Freeze–thaw and low-temperature stability for winter shipping, plus storage guidance: keep containers below about 40 °C, ventilated and out of direct sunlight.
- Batch COA per lot, TDS and SDS in the customer's own language, and a sample for a trial in the customer's own base.
Selection quick answers
A salt-thickened liquid detergent that keeps drifting off its viscosity target? A salt-free grade — YS-812 or YS-806. A dishwash line competing on cost? YS-808. A process with no cool-down step? YS-806 below 80 °C for detergents, YS-805 below 60 °C for personal care, YS-CG below 80 °C for textile baths. An acid toner or a low-pH cleanser? YS-803 or YS-801. A soap-based or alkaline gel? YS-804 or YS-805. Baby wipes with a surfactant-rich solution? YS-203. Feminine or disinfecting wipes on an anionic-free solution? YS-204. Household and automotive wipes on a tight budget? YS-202. Slime and odour in a dyehouse bath? YS-903 for high-temperature lines, YS-902 where the bath is electrolyte-sensitive. Cat litter that is extruded and dried? YS-T30 for heat resistance and fragrance retention, YS-T20 where odour and mould control on a clay substrate matter most. The customer reports separation after adding the preservative? Check the salt curve and the pH window first — the grade is usually right and the dose point in the process is usually wrong.
Shanghai Better Chemical supplies the full preservative range — liquid detergent grades YS-806, YS-808 and YS-812; personal care grades YS-801, YS-802, YS-803, YS-804 and YS-805; wet wipes grades YS-201, YS-202, YS-203, YS-204 and YS-T10 (CAS 55406-53-6; 2682-20-4); textile and leather grades YS-901, YS-902, YS-903 and YS-CG; and cat litter grades YS-T20 (CAS 55406-53-6; 3811-73-2) and YS-T30 (CAS 55406-53-6; 2682-20-4) — together with the multifunctional boosters often used alongside them, 1,2-Hexanediol (CAS 6920-22-5) and Glyceryl Caprylate (CAS 26402-26-6). Every lot ships with a COA covering active content, appearance, odour, pH and specific gravity, with TDS/MSDS and samples for a challenge test in your own base. Tell us the product, its pH and process temperature, the surfactant system and the destination market, and we will match the grade, the dose point and the level — then confirm current pricing.