Which PEI Grade for Water Treatment, Paper & Adhesives? MW Selection Guide

CAS 9002-98-6 · Branched PEI 600–70,000 MW · Alfa Chemical, Zhengzhou, China

Polyethyleneimine CAS 9002-98-6 is not a single product. It is a family of cationic polymers that share one CAS number but behave very differently depending on molecular weight. A 600 MW grade and a 70,000 MW grade arrive in the same packaging category, carry the same SDS hazard classification, and still do completely different jobs in a formulation.

That is the part most grade-selection guides skip. They list molecular weights, show a table, and leave the reader to guess which number fits the application. This article takes a different approach: it explains what each grade physically does in an industrial system, then maps the grades to water treatment, paper, adhesives, and inks.

Alfa Chemical manufactures branched PEI in Zhengzhou, China, across four commercial molecular weights. For grade-specific datasheets, see the PEI CAS 9002-98-6 product page.

Why PEI Grade Selection Is Not a One-Size Decision

Branched PEI is produced by the cationic ring-opening polymerization of aziridine. The result is a highly branched structure with primary, secondary, and tertiary amine groups in roughly a 25/50/25 ratio. Each type of amine reacts differently with substrates, and the ratio changes as molecular weight increases.

Low molecular weight grades have short chains. They penetrate porous substrates easily, have low viscosity, and react quickly with epoxy, isocyanate, and aldehyde groups. High molecular weight grades have long chains. They bridge between particles, form larger flocs, and produce stronger adhesion to surfaces - but they also bring higher viscosity and slower diffusion.

The practical consequence: choosing the wrong grade does not just reduce performance. It can reverse it. A flocculant grade used as a crosslinker will not penetrate. A crosslinker grade used as a flocculant will not bridge. For other cationic polymers used alongside PEI, browse our organic chemistry intermediates.

The Four Commercial Grades and What They Do

PEI 600 MW - The Reactive Crosslinker

At 600 MW, the polymer chain is short and the amine density relative to chain length is high. Viscosity is low, typically in the 1,000–4,000 mPa·s range at 25°C. This grade penetrates porous substrates quickly and reacts fast with epoxy, isocyanate, and aldehyde groups.

Where it works best: epoxy curing accelerators, surface primers for metals and glass, and paper wet strength. Where it falls short: flocculation. Short chains cannot bridge between particles, so sedimentation and drainage applications underperform.

PEI 1,800 MW - The Balanced Grade

PEI 1,800 sits between the reactive grades and the flocculant grades. Viscosity is still workable in water-based systems, but chain length is sufficient for some bridging. This grade often performs best in paper and packaging, especially recycled fiber systems where fiber bonding has been weakened by repeated processing.

It is also a solid choice for pigment dispersants and ink adhesion promoters. It does not form the large, stable flocs required for high-turbidity industrial effluent, so it is not a replacement for higher molecular weight grades in water treatment.

PEI 10,000 MW - The Retention and Drainage Aid

At 10,000 MW, the polymer chain is long enough to bridge between fibers and fillers. This makes it effective in paper machine wet-end applications where retention and drainage rates directly affect production speed. It also works as a coagulant aid in water treatment and as an adhesion promoter in coatings.

For high-turbidity wastewater, PEI 70,000 outperforms it in bridging efficiency. Grade selection here depends on the particle size distribution of the suspended solids. Full specifications for CAS 9002-98-6 are listed on the CAS 9002-98-6 product page.

PEI 70,000 MW - The High-Performance Flocculant

PEI 70,000 is the workhorse for water treatment and industrial separation. Extended polymer chains form effective molecular bridges between particles, producing larger and more stable flocs than lower grades. Viscosity is high (10,000–20,000 mPa·s at 25°C), and the product is typically supplied as a 50% aqueous solution.

Applications include industrial and municipal wastewater treatment, paper and pulp retention, mineral processing, and demanding adhesion promotion. It is less suitable for reactive crosslinking or surface priming where penetration matters. If you need batch documentation before ordering, you can request COA & SDS directly.

Grade Comparison at a Glance

How to Match Grade to Application

Paper and Packaging

For wet strength, PEI 600 and 1,800 are the standard choices. Lower molecular weight grades react more completely with crosslinkers and distribute more evenly through the fiber matrix. For retention and drainage, PEI 10,000 is the workhorse - it bridges fines and fillers onto fibers without slowing the machine.

A practical starting point: if your paper machine runs recycled fiber and you are seeing strength loss, trial PEI 1,800 at 0.5–1.5% on dry fiber weight, crosslinked with a glycidyl silane. Adjust from there based on wet tensile results.

Water and Wastewater Treatment

PEI 70,000 is the default for industrial effluent. It works across a wide pH range and is particularly effective when suspended solids carry a negative surface charge. Typical dosage ranges from 5–50 ppm depending on turbidity and competing anionic species.

For municipal treatment, PEI 70,000 is often used as a coagulant aid downstream of inorganic coagulants like PAC or ferric chloride. The combination produces denser flocs and reduces sludge volume. Jar tests with PEI require rapid mixing (1–2 minutes at 200–300 rpm) followed by slow mixing (15–20 minutes at 30–50 rpm). Skipping the rapid mix phase is a common reason formulators see poor flocculation.

Adhesives and Coatings

PEI 600 is the adhesion promoter of choice for epoxy and polyurethane systems. Application rates are low, typically 50–150 mg/m² for primer applications. For ink and coating adhesion, PEI 10,000 or 70,000 provides better bridging to pigment particles and substrate surfaces. For water-based adhesives, PEI 1,800 offers a balance of reactivity and formulation compatibility.

Inks, Dyes, and Pigment Dispersants

PEI 1,800 and 10,000 are the workhorse grades here. The amine groups adsorb onto pigment surfaces, providing electrostatic stabilization. For high-solids dispersions, PEI 10,000 gives better viscosity control. For dye fixation, PEI 70,000 provides stronger ionic bonding to anionic dyes.

What About Linear PEI 25,000?

Linear PEI 25,000 is a different product category. It is a transfection reagent used in molecular biology research, not an industrial flocculant or adhesion promoter. It is supplied as a solid, dissolves in hot water and low-pH cold water, and is used in mammalian cell expression systems.

If your application is industrial - water treatment, paper, adhesives, coatings - linear PEI 25,000 is not the right specification. The cost is significantly higher and the performance characteristics are optimized for biological research, not industrial processing.

R&D use only. Not for human or veterinary use. Not for diagnostic, therapeutic, or drug use.

Supplier Selection: What to Verify

PEI is manufactured by a limited number of producers globally. When evaluating a supplier, the technical questions that matter are:

Compliance Notes for International Buyers

PEI (CAS 9002-98-6) is not listed on common dual-use export control lists. It is classified under HTS 3901.90.25 for polymer dispersions. However, the linear 25,000 MW transfection-grade material may attract additional scrutiny in some jurisdictions because of its use in biological research.

For industrial-grade branched PEI, standard export documentation - COA, SDS, and commercial invoice - is sufficient for most destinations. Buyers in regulated industries should confirm their internal compliance requirements before ordering.

Handling and Storage

PEI is an irritant. Handle with gloves and eye protection in a ventilated area. The 50% aqueous solutions are alkaline (pH 10–12) and should not be mixed with strong acids without proper neutralization controls. Store at 2–8°C for long-term stability, though room-temperature storage is acceptable for short periods. Keep containers closed to prevent moisture absorption.

Where Alfa Chemical Fits

Alfa Chemical supplies branched PEI from Zhengzhou, China, in four molecular weight grades: 600, 1,800, 10,000, and 70,000. Each batch ships with a GPC-verified COA and SDS. Packaging ranges from 1 kg research samples to 200 kg drums.

If you are evaluating PEI for a specific application - paper wet strength, wastewater flocculation, or epoxy adhesion - the grade selection depends on your system chemistry, not on a generic specification sheet. Send us your application details and we will recommend the grade that fits. Visit the contact page to request grade selection support, or browse the full PEI product page for specifications, COA, and packaging options.

All products are supplied for research and development use only. Not for human or veterinary use. Not for diagnostic, therapeutic, or drug use. COA and SDS are available with every shipment.