Chitosan

Nearly every natural polymer carries its charge the same way: negative. Chitosan is the large-volume exception. Along its backbone sit free primary amines, and in mildly acidic water those amines pick up protons until the entire chain behaves as a cationic polyelectrolyte. That single flipped sign is why chitosan can do jobs no other natural polymer can: it neutralises the surface charge that keeps fine solids suspended, it chelates dissolved metal ions through the same amine nitrogens, and it clings to negatively charged surfaces from cellulose fibres to seed coats to bacterial membranes.

We supply that polymer as flake and powder across the full working range — degrees of deacetylation from the high 70s to above 95%, viscosities from free-pouring 20 mPa·s solutions up to 2,000 mPa·s gels, and molecular weights from short-chain low-viscosity grades to long-chain polymers whose bridging builds film and floc strength. Every grade is reported against the same fixed test conditions, so the number on the certificate is the number in your tank.

Two Dials Decide Everything: Deacetylation and Chain Length

Chitosan is not one product with a catalogue number; it is a coordinate system. Degree of deacetylation sets how much positive charge each gram carries and how readily the chain dissolves. Molecular weight — read most conveniently as solution viscosity — sets how strongly the chain bridges particles and how tough the dried film is. Our standard coordinate grid looks like this:

One caution travels with every viscosity figure in this market: a viscosity quoted without its concentration, its acid and its temperature is close to decorative. Ours are all read at 1% polymer in 1% acetic acid at 20°C on a rotational instrument — and we can supply the same lot characterised by SEC/GPC with a polydispersity index when your method needs the distribution, not just an average.

Cone-and-plate rheology on a chitosan acetate solution — a viscosity number is only useful if the test conditions travel with it.

Getting a Clear Solution, Every Time

The polymer that arrives as powder only becomes the cationic workhorse once it is dissolved, and most failed first attempts trace back to the same two mistakes. Dispersion before acidification, and patience with the water you use:

• Suspend the powder in the water first, then add the dilute acetic, lactic or hydrochloric acid. Pour acid onto dry powder and each particle's outer skin gels while its core stays dry — you will spend the afternoon filtering lumps.
• Warm water helps but is not magic; 40–50°C shortens dissolution times noticeably without stressing the chain.
• Residual ash and protein are silent saboteurs — a low-ash grade dissolves visibly faster and throws a clearer solution than a crude one at identical deacetylation, which is why our impurity limits sit on the certificate next to the viscosity, not buried behind it.
• Above roughly pH 6.5 the amines deprotonate and the polymer comes back out of solution. If your process must run near neutral, ask about our carboxymethylated and quaternised water-soluble grades instead of forcing the base polymer past its limits.

Water: Where the Positive Charge Pays Rent

Most of what makes water hard to treat is negatively charged: colloidal clay and silt, anionic dyes, dissolved metal complexes, emulsified oils. Add chitosan and the cationic chain adsorbs onto those surfaces, collapses their charge, and bridges particle after particle into settleable flocs. Reviews of chitosan-based treatment report 80–95% colour removal for reactive and acid dye streams under optimised pH and dose, high adsorption capacities for Pb(II), Cd(II), Cu(II) and Cr(VI) on chitosan beads and composites with repeated regeneration cycles, and meaningful turbidity and COD reductions in municipal and mixed industrial effluent at low doses. For metal capture the working sweet spot is around pH 5–7 — enough charge for the amine sites to function, few enough competing protons to block them.

A jar-test row mid-run: charge neutralisation at work, flocs forming and the water clearing from the top down.

Films and Coatings: The Chain That Dries Into a Barrier

Dissolved chitosan casts into clear, coherent films with a genuinely useful permeability profile — the amine-rich structure is a fair barrier to oxygen while allowing the water-vapour transmission many applications need, and the surface it leaves is naturally antimicrobial against a broad range of bacteria and fungi. Cast thickness is set by the coating step, and film behaviour is finished chemistry: crosslink with ionic or covalent agents to tune swelling, blend with other biopolymers to adjust flexibility, or plasticise for handling strength.

• Film-forming solutions from 1–2% w/v are the usual casting range; higher solids give tougher films at the cost of viscosity you have to pump.
• Surface energy is adjustable in post-treatment — contact-angle work on cast films shows how wettability, printability and release can be moved by acylation or surfactant rinses.
• As a dip or spray coating at 1–2% w/v, chitosan forms a semi-permeable layer that slows respiration and moisture loss — nano-chitosan coating trials on tomatoes recorded 30–40% less weight loss and 7–10 days of delayed ripening at 20°C.

Film casting on a glass belt — the doctor blade gap, not the recipe, is what sets finished film thickness.

A sessile drop on a cast chitosan film — contact angle tells you how the finished surface will wet, coat and print.

Down to Nanofibres

Chitosan solutions carry enough chain entanglement to electrospin, and the resulting mats put the polymer's surface chemistry on a very large interfacial area. In practice chitosan is usually spun as a blend — with PEO or PVA for spinnability, or with synthetic carriers where mechanical strength matters — and the mats go into filtration media, sorbent layers, wound-dressing research, enzyme immobilisation supports and controlled-release encapsulation. Fibre diameter follows the solution: viscosity, conductivity and feed rate move the jet, which is why we can supply grades matched to the window your spinning rig was tuned around rather than a single one-size polymer.

Electrospinning onto a rotating drum collector — the fibre jet leaves the needle thousands of times thinner than it is.

Agriculture: Seeds, Leaves and Soil

The same positive charge that clears water also holds onto soil and seed surfaces, which is why chitosan has become one of the most-studied natural materials in crop research. As a seed coating it is a film-former with grip: chickpea seed treated with chitosan nanoparticle formulations reached 90% germination against 75% for water-treated controls, and pepper seed coated with nano-chitosan germinated 4.9–5.3 days sooner on average. As a foliar or soil input it acts as an elicitor, switching on the plant's own defence and secondary-metabolite pathways — reported responses include elevated peroxidase and catalase activity, higher chlorophyll content under salinity stress, and reduced leaching of nitrate and phosphate from treated growing media because the cationic chain improves the medium's anion exchange capacity. Dose discipline matters: published work places the optimum for nano-formulations around 30 ppm, with adverse effects reported above roughly 90 ppm.

Seed coating in a pan coater — chitosan's film-forming grip is what keeps the actives on the seed and off the soil.

Every Lot, the Same Numbers

• Degree of deacetylation by ¹H NMR, FTIR band ratio and titration — reported on all three so the methods can be cross-checked against your own.
• Viscosity at 1% in 1% acetic acid, 20°C, rotational viscometer; SEC/GPC molecular weight and polydispersity on request.
• Moisture ≤10%, ash ≤1% (≤0.2% on purified grades), insoluble matter ≤1%, residual protein ≤0.5% by Kjeldahl nitrogen.
• pH of a 1% solution 4.0–6.0; appearance white to off-white free-flowing powder against a retained reference.
• Heavy metals by ICP: Pb ≤10 ppm, As ≤0.5 ppm — tighter windows quoted per application where the discharge consent or formulation demands it.
• Particle size 40–200 mesh to order, or milled below 0.5 mm for fast-wetting dispersion work.

Specified Your Way

Because chitosan is a coordinate system rather than a fixed product, most of what we ship is cut to order: a deacetylation window instead of a nominal value, a viscosity band matched to your dosing pump, a particle cut matched to your blender, salt forms — hydrochloride, lactate, glutamate — for acid-free handling, water-soluble carboxymethyl and quaternised derivatives for neutral-pH systems, and depolymerised fractions for applications that want the amine without the chain. Tell us the two dials your process actually depends on and we will return a sample lot with the full analytical pack behind it.

Send us your target deacetylation and viscosity window, and we will match the grade and document every number that matters.

For Research or Industrial Raw Materials, Not For Personal Medical Use!