Polyamine is one of those water treatment chemicals that is easy to buy and hard to buy well. Two suppliers can both quote “polyamine, 50% solids” and deliver materials that behave completely differently in a plant – because the property that actually matters is not the solid content but the charge density, and charge density moves inversely with viscosity.
This guide covers the chemistry and the practical selection logic for polyamine (CAS 42751-79-1): what the molecule does, why we supply seven grades from 50 to 6000 mPa.s, how to match a grade to water treatment, papermaking or oil-water separation, how dosing order decides whether the programme works, and how polyamine compares with polyDADMAC and polyacrylamide.
What Is Polyamine?
In water treatment, “polyamine” refers to a family of cationic polyelectrolytes – water-soluble polymers carrying a high density of positive charges along the chain. The commercial product is an aqueous solution, typically 40-50% solids, with a light yellow colour and a viscosity that ranges from water-thin to syrupy depending on the degree of polymerisation.
Because it is a polymer rather than a single molecule, it has no meaningful molecular formula or melting point. It is bought and sold on three numbers: solid content, pH of a 1% solution, and viscosity. Those three numbers are the whole datasheet, and the viscosity is the one that predicts performance.
Chemical Identity and Specification
| Item | Detail |
|---|---|
| Common name | Polyamine; cationic polyamine coagulant |
| CAS number | 42751-79-1 |
| Chemical class | Cationic polymer (polyelectrolyte), aqueous solution |
| Appearance | Light yellow viscous liquid |
| Solid content | 50 +/- 1% (grades A-E); 40 +/- 1% (grades F-G) |
| pH (1% solution) | 4 – 8 |
| Viscosity at 25 deg C | 50 – 6000 mPa.s (3# spindle, 60 rpm), by grade |
| Ionic character | Cationic, high charge density |
Three specification notes that matter more than they look:
- Viscosity is measured at fixed spindle and speed (3# spindle, 60 rpm). Comparing viscosities from different spindles is meaningless – a supplier quoting “3000 mPa.s” without the measurement conditions is telling you nothing.
- pH 4-8 is a wide window, and that is deliberate: the products are acidic to neutral and the plant may adjust. But a batch at pH 4 and a batch at pH 8 will behave differently in a buffered system; the figure is worth checking per lot.
- Solid content does not equal active charge. A 50% product with low charge density can underperform a 40% product with high charge density. This is the single most common purchasing mistake.
How Polyamine Works
Cationic polyamines work by two mechanisms, and the grade determines which one dominates:
| Mechanism | What happens | Favoured by |
|---|---|---|
| Charge neutralisation | Positive charges on the polymer neutralise the negative surface charge of colloids and particles, collapsing the electrostatic barrier so they can approach and aggregate | Low molecular weight, high charge density (grades A-B) |
| Bridging flocculation | A long polymer chain adsorbs on two or more particles and links them into a floc | High molecular weight (grade E, and PAM) |
This is why one product family spans such a wide viscosity range: at low viscosity you are selling charge, at high viscosity you are selling bridges. Choosing the wrong end of the ladder is the most common cause of “the polyamine did not work”.
The Seven Grades: A to G
| Grade | Solids (%) | Viscosity (mPa.s) | Charge density | Best at |
|---|---|---|---|---|
| A | 50 +/- 1 | 50 – 200 | Highest | Charge neutralisation, anionic trash, colour removal |
| B | 50 +/- 1 | 200 – 500 | Very high | Potable and industrial water clarification |
| C | 50 +/- 1 | 600 – 1000 | High | General-purpose coagulation with some bridging |
| D | 50 +/- 1 | 1000 – 3000 | Medium | Wastewater and process water with mixed load |
| E | 50 +/- 1 | 3000 – 6000 | Medium-low | Bridging flocculation, faster settling, larger flocs |
| F | 40 +/- 1 | 600 – 1000 | High | Same duty as C at lower active content – easier dilution and lower freight weight |
| G | 40 +/- 1 | 1000 – 3000 | Medium | Same duty as D at lower active content |
Grades F and G exist for a practical reason: some plants dilute to a working strength themselves and would rather not pay to ship water, while others need the lower active content to keep dosing pumps in range. The chemistry is the same; the logistics differ.
Application 1: Water and Wastewater Treatment
Polyamine is used as a primary coagulant or as a coagulant aid ahead of a conventional clarifier. Its advantages over inorganic coagulants are that it adds no aluminium or iron, barely changes pH, and produces less sludge per unit of turbidity removed.
| Duty | Typical grade | Notes |
|---|---|---|
| Potable water, low turbidity, colour | B | High charge density for dissolved colour and fine colloids |
| Municipal wastewater, primary clarifier | C or D | Balance charge and floc size |
| Industrial effluent with mixed load | D or E | Bridging matters when the suspension is coarse |
| Coagulant aid with PAC or alum | A or B | Charge neutralisation lets you cut the inorganic dose |
Dosing order is not optional. Polyamine must go in first, under rapid mixing, before any high-molecular-weight flocculant. Reverse the order and the anionic flocculant coats the particles first, leaving nowhere for the polyamine to work – and both chemicals are wasted.
Application 2: Papermaking
In papermaking, the same chemistry solves a different problem: anionic trash. Recycled fibre and mechanical pulp carry dissolved and colloidal anionic substances that consume cationic additives (retention aids, sizing agents, strength resins) before they reach the fibre. A low-viscosity polyamine – grade A or B – neutralises that trash ahead of the wet end, so the expensive additives do their job.
The same grades also act as retention and drainage aids and support alkaline sizing. The distinction from polyDADMAC is worth noting: both are cationic, but polyDADMAC has a lower charge density and higher cost per charge, while polyamine delivers more charge per kilogram at a lower price – which is why polyamine is often the first-choice trash catcher in recycled-fibre mills.
Application 3: Oil-Water Separation
Produced water, refinery desalting effluent and oily wastewater are stabilised by negatively charged droplets and solids. Cationic polyamine neutralises those charges, allowing the droplets to coalesce and separate. Medium-viscosity grades are typical here, often combined with a demulsifier or a reverse-demulsifier programme.
The practical constraints are different from water treatment: salinity is high, temperature may be elevated, and the water often contains residual treatment chemicals from upstream. Jar tests must be run at the actual brine composition and temperature, not on synthetic tap water.
Polyamine Versus PolyDADMAC and PAM
| Property | Polyamine | PolyDADMAC | PAM (cationic) |
|---|---|---|---|
| Charge density | High | Medium | Low to medium |
| Molecular weight | Low to medium | Medium | High |
| Dominant mechanism | Charge neutralisation | Charge neutralisation plus some bridging | Bridging flocculation |
| Cost per unit charge | Low | Higher | Low per mass, low charge |
| Typical use | Coagulation, trash capture, demulsification | Coagulation, sludge conditioning, paper | Flocculation, settling, dewatering |
The usual programme is a sequence, not a choice: inorganic coagulant or polyamine for charge, then PAM for floc size. Which cationic you pick depends on the charge demand of the water – and the grade of polyamine depends on how much bridging you also need. The full comparison is in Polyamine vs PAM vs PolyDADMAC, and the charge-based decision chart is in Flocculant selection chart.
Jar Testing: How to Select a Grade Properly
- Measure the charge demand of the water first (colloid titration or streaming current). Without that number you are guessing.
- Screen three grades – one low, one medium, one high viscosity – across a dose series. Do not screen seven grades; you will exhaust patience before you find the answer.
- Hold mixing constant. Rapid mix time and intensity change floc size more than the polymer choice does.
- Judge on settled turbidity plus floc size and settling rate, not on clarity alone. A fast-settling dense floc can beat a clearer but slow-settling one.
- Confirm overdosing behaviour. Cationic polymers restabilise colloids when overdosed – the water gets worse, not better. Find that point deliberately so your plant operators know where it is.
Handling, Storage and Safety
| Issue | Practice |
|---|---|
| Dilution | Dilute to 0.1-1% before dosing; use soft or demineralised water where available, since high-hardness dilution water can cloud the solution |
| Storage | 5-35 deg C, sealed, out of direct sunlight; do not freeze – freezing can separate the polymer irreversibly |
| Viscosity drift | Long storage at elevated temperature changes viscosity; re-check before use in critical dosing systems |
| Spills | The solution is extremely slippery – contain and clean with absorbent, do not hose into drains |
| Incompatibility | Do not mix with anionic polymers or anionic surfactants in the same tank; they precipitate each other |
| Personal protection | Gloves and eye protection; avoid prolonged skin contact |
Packaging and Supply
| Item | Detail |
|---|---|
| Standard pack | 200 kg polyethylene drum |
| Bulk pack | 1000 kg IBC on request |
| Documents | COA per batch (appearance, solids, pH, viscosity), SDS in English, shipping documents |
| Samples | Available for jar tests – tell us the application and we will suggest two or three grades to screen |
Frequently Asked Questions
Is polyamine the same as polyDADMAC? No. Both are cationic polymers used as coagulants, but polyamine has a higher charge density and lower molecular weight for the same mass, and usually costs less per unit of charge.
Why does the datasheet give a viscosity range rather than a number? Because it is a polymer: viscosity tracks molecular weight, which varies within a controlled band. A supplier quoting a single figure without measurement conditions is not giving you a usable specification.
Can I dose polyamine and PAM together? In the same tank, no – they neutralise each other. In sequence, yes: polyamine first at rapid mix, PAM later at slow mix.
Does polyamine add aluminium or change pH? No aluminium, and the pH effect is small compared with alum or PAC. That is one of its main advantages in pH-sensitive systems.
Which grade should I start with? Grade B for most potable and industrial clarification duties; grade A when the problem is dissolved colour or anionic trash; grade D or E when the suspension is coarse and settling rate matters.
Contact PolyBlueChem for grade selection, jar-test samples and quotations.
Related reading
- Choosing a polyamine grade: solid content and viscosity
- Polyamine in papermaking: anionic trash capture and retention
- Polyamine in oil-water separation and refinery desalting
- Polyamine vs PAM vs PolyDADMAC
- Flocculant selection chart by charge and application
- Polyamine product page and full grade table