Chitin & Chitosan

Chitin is the second most abundant biopolymer on earth, and the only one that arrives with nitrogen on every repeat unit. Its backbone is a chain of β-(1→4)-linked N-acetyl-D-glucosamine — close to cellulose in shape, except that where cellulose carries a hydroxyl group, chitin carries an acetamido group. Remove most of those acetyl groups and the same chain becomes chitosan, now decorated with free primary amines that pick up a proton in dilute acid and turn the molecule into a cationic polyelectrolyte. Nearly everything these two materials are bought for — flocculation, film formation, ion chelation, crosslinkability — comes back to that single functional group.

We supply the whole ladder rather than one rung of it. Shell-grade chitin and chitosan powders in a range of deacetylation and viscosity bands; water-soluble chitooligosaccharides down to defined dimer and hexamer standards; the amino sugars that sit underneath them; acid salts that dissolve without anyone handling mineral acid; chemically modified derivatives that push the polymer into neutral pH or under a light source; and nanoscale formats from individualised nanocrystals to nanofibre hydrogels. Every grade is described by the parameters that actually govern behaviour rather than by a product name alone, and every one of them can be adjusted toward your process.

Where the polymer comes from

Chitin is not harvested for its own sake. It is recovered from streams that already exist — the shells left behind when shrimp and crab are peeled, the pens that squid processors discard, the mycelium left over from fungal fermentation. Which of those streams a batch starts from decides the polymorph you get, the impurities you have to work around, and, in the end, how easily the polymer will dissolve or fibrillate.

Those streams are then taken through four steps. Dilute hydrochloric acid strips calcium carbonate out of the shell; dilute sodium hydroxide at elevated temperature takes the protein out; a peroxide or permanganate–oxalate stage removes residual pigment; and concentrated alkali at high temperature finally removes acetyl groups. Each step is a dial rather than a switch. Stop the deacetylation early and you still have chitin; carry it further and you get a chitosan with a stated degree of deacetylation, a different solubility threshold and a lower molecular weight, because hot alkali shortens the chain as well as deacetylating it.

Shell from seafood peeling lines is the highest-volume chitin feedstock, and the load of mineral and protein it carries is what the first two process steps exist to remove.

Chitin: the polymer that refuses to dissolve

Native chitin is held together by a dense network of hydrogen bonds, which is precisely why it is useful as a structural filler and precisely why it is awkward as a raw material. It does not dissolve in water, in alcohols, in ketones or in dilute acid or alkali. Getting it into solution takes a solvent system that can compete with those hydrogen bonds — lithium chloride in dimethylacetamide, fluorinated alcohols such as hexafluoroisopropanol, certain imidazolium ionic liquids, or the cold alkali–urea aqueous systems described in the literature. Most industrial users therefore handle chitin as a solid: a powder, a flake, or a precursor that is deacetylated one step further to chitosan.

Crystalline chitin is stiff: axial moduli reported for α-chitin from X-ray diffraction sit in the 40–60 GPa range, and values quoted for β-chitin run considerably higher, though the numbers move depending on whether they come from diffraction, atomic force microscopy or simulation. That stiffness, plus the fact that chitin is a food-chain by-product rather than a crop, is why it turns up as a reinforcing phase in composites and as the starting point for every nanoscale format described further down this page.

Milled chitin presents as an ivory, faintly fibrous powder; the crystalline texture survives drying and is what limits how quickly the powder wets out.

Polymorphs: why α, β and γ do not behave alike

The same repeat unit can pack in three different ways, and the packing decides the processing route. In α-chitin the chains run antiparallel, which gives the tightest hydrogen-bonding network and the most stable crystal; it is what crustacean shell, insect cuticle and most fungal walls are built from. In β-chitin the chains run parallel, the network is looser, and the material swells in water. In γ-chitin the two arrangements coexist along the same fibril. The practical consequence is visible at the fibril level: native α-chitin fibrils measure roughly 5–10 nm across, β-chitin fibrils closer to 3–4 nm.

Because β-chitin holds itself together less tightly, it can be taken down to individual nanofibres with nothing more aggressive than mechanical treatment in water at pH 3–4 — the surface amine groups become cationic under those conditions and push the fibrils apart electrostatically, so no TEMPO oxidation or other chemical modification is required. α-chitin from shell needs more help: either an oxidation step to carboxylate the fibril surface, or a partial deacetylation followed by mechanical disintegration. If your process depends on a stable aqueous dispersion rather than a solvent-borne one, the polymorph you start from is the first decision to make.

Squid pens are a translucent, low-crystallinity β-chitin source; their fibrils separate in mildly acidic water without any chemical modification.

Chitosan: deacetylation is the real design lever

Deacetylation converts a rigid structural polymer into a soluble cationic one, and the degree to which it is carried out does most of the work in defining the grade. Both the European and United States pharmacopoeias bracket chitosan at 70–95% deacetylation, which is wide enough to cover materials that behave quite differently in a beaker. Free amine content sets the charge density and the pH at which the polymer stays in solution; molecular weight, set separately by the processing conditions, sets the viscosity of the solution and the strength of the film left behind when it dries.

Getting it into solution, and keeping it there

Chitosan needs its amines protonated before it will dissolve, and the amine pKa sits near 6.5, so plain water will not do it. Dissolve the powder in dilute acetic, lactic, formic or hydrochloric acid and the polymer goes into solution; above roughly pH 6 the charge fades, the chain coils and the material comes back out. What the acid leaves behind matters more than most people expect, because the counterion stays in the dried film: acetate gives a different surface charge and a different residual acidity from chloride. Where acid handling is undesirable, the salt grades described later dissolve directly in water with no acid addition at all.

Two practical points decide whether a batch dissolves cleanly. Disperse the powder in water first and add the acid afterwards, otherwise the outer layer of each particle protonates and gels while the inside stays dry, and you end up filtering out lumps. And remember that residual ash and protein work against you — a low-ash, low-protein grade dissolves noticeably faster than a crude one at the same deacetylation, which is why the impurity columns of the specification deserve as much attention as the viscosity figure.

The same chitosan in two states: an undissolved milky suspension on the left, a clear working solution after acid addition on the right.

Reading a specification that survives scale-up

Polysaccharide specifications are only comparable when the test conditions travel with the number. A viscosity quoted as “200 mPa·s” without saying at what concentration, in which acid and at what temperature is close to meaningless, because doubling the concentration can multiply the reading several times over. The table below lists the parameters we report as standard and the conditions we hold them under.

Because molecular weight can be measured in several ways, two suppliers can quote honest numbers for the same material and still disagree by a factor of two. Ask which method produced the figure, and compare like with like. The polydispersity index is the other number worth insisting on: it tells you whether you are buying a narrow, reproducible polymer or a broad blend that will behave differently from batch to batch.

Chitooligosaccharides: cutting the chain until it dissolves

Hydrolyse chitosan far enough and the rules change. Once the chain is short — a degree of polymerisation of roughly 2–20, with the bulk of the mass below 1 kDa — the material dissolves in plain water with no acid at all, because a short chain no longer needs every amine protonated to stay in solution. That single property is what makes oligosaccharides attractive: they can be dosed into a neutral formulation, and they move through a process stream that would precipitate the parent polymer on contact.

How the chain is cut determines what you receive. Enzymatic hydrolysis is the controlled route: chitosanase gives predominantly dimers and trimers, hemicellulase yields a spread from dimer to hexamer, and proteases and lipases cut to wider and less uniform distributions. Acid hydrolysis is cheaper but less selective, and it leaves the acetylation pattern less predictable. The distinction matters because behaviour is strongly length-dependent: the size effects reported in the literature tend to appear from five units upward, chitohexaose binds certain lectins around forty times more strongly than chitopentaose, and an assay run with a heterogeneous mixture will often hide effects that a defined single-length oligomer reveals.

For mechanistic work, the mixed powder is the wrong starting point. A defined oligomer fixes the two variables that a bulk hydrolysate leaves open — chain length and the pattern of acetyl groups — and enzyme kinetics are notoriously sensitive to both. Where a project needs a whole series, we can supply a ladder of single-length fractions together with the matching bulk material from the same hydrolysis run.

Marine amino sugars as reference materials

Underneath the polymer sit the monomers, and they are bought for a different reason: as standards rather than as bulk. Glucosamine and its acetylated form are the two units that alternate along the chitin chain, and their ratio is what every deacetylation measurement is trying to determine. The wider family of amino sugars turns up in marine glycoconjugates and in the enzymatic digests used to characterise them, which makes calibrated reference materials a routine requirement rather than a nicety.

We supply these as characterised powders with the purity method stated, so they can be dropped straight into a calibration set. Where a project needs the labelled or sulfated analogues, say so at the enquiry stage and we will confirm what is available before you build the method around it.

Chitosan Salts: dissolution without the acid bottle

Converting the amine to an acid salt solves the handling problem at the outset. The powder goes into water and dissolves — no dilute acid to prepare, no dosing line corroded by it, no pH adjustment step before the material is added. The trade-off is that the counterion comes along for the ride, and it changes measurable properties: solution pH, surface charge, hygroscopicity, and how the dried film behaves.

Glutamate, acetate, formate, ascorbate and sulfate forms are also produced, and the choice is usually dictated by what the rest of the formulation can tolerate rather than by the polymer itself. Tell us which acid the downstream chemistry expects and we will prepare the salt against it instead of forcing a standard grade into the gap.

Functionalized Chitosan Derivatives: new chemistry on an old backbone

Chitosan offers two convenient handles — the C2 amine and the C6 hydroxyl — and grafting chemistry onto either one changes where the polymer can work. Carboxymethylation makes it zwitterionic and water-soluble at neutral pH, which removes the acid step and the acid residue together. Quaternisation installs a permanent positive charge that no longer depends on pH. Methacrylation adds groups that polymerise under light, turning the polymer into a photocurable hydrogel precursor. Each of these keeps the backbone and changes the behaviour, and each is specified by the extent of the reaction rather than by the name alone.

Chitin & Chitosan Nanomaterials: fibrils, crystals and particles

Chitin is already a nanomaterial in its native state. Around eighteen to twenty polymer chains assemble into an elementary fibril roughly 7 nm across, and those fibrils bundle into the fibres that give a crab shell or a squid pen its stiffness. What the nano grades do is separate those fibrils from one another, and the method of separation determines the shape and the surface chemistry you end up with.

Three routes cover most of what is asked for. Oxidation of α-chitin under TEMPO conditions converts the C6 hydroxyls to carboxylates on the fibril surface, and a mild mechanical step then releases individualised nanocrystals, reported at roughly 340 nm long by 8 nm wide. Partial deacetylation followed by disintegration produces a mixture of whiskers and longer nanofibres. And β-chitin from squid pen fibrillates with nothing but shear in acidic water. Separately, chitosan itself assembles into nanoparticles when its cationic chains meet a polyanion such as tripolyphosphate; diameters reported in the literature span roughly 90 nm to a few hundred nanometres on the usual preparation routes, with surface charges between about +15 and +60 mV, and every one of those figures is a function of molecular weight, ratio, pH, ionic strength and mixing regime rather than a property of the polymer alone.

Two properties make these formats worth the extra cost. Chitin nano films break down thermally near 200°C, which is high enough for most polymer processing, and their oxygen permeability sits roughly two orders of magnitude below that of polylactic acid — around 1 against 184 mL·µm·m⁻²·day⁻¹·kPa⁻¹. In practice that means a thin chitin layer can replace a much thicker barrier coating.

Light passing through a dilute nanoparticle suspension leaves a visible scattering path — a quick bench check that the colloid is still dispersed rather than aggregated.

Nanofibre hydrogels and free-standing films

At low solids content, individualised chitin fibrils entangle instead of settling, and the dispersion turns into a translucent hydrogel that holds a large amount of water and thins under shear. Dry it down and the same network collapses into a transparent film. The aspect ratio of the fibrils decides which of those behaviours dominates: short stiff whiskers pack tightly and give harder, more brittle films, while the long β-chitin fibres from squid pen show the strongest shear-thinning and hold gel-like flow across the whole shear-rate range.

Handling is a matter of protecting the surface charge. Dilute the dispersion rather than concentrating it by evaporation, keep the pH on the acidic side where the fibril surfaces stay charged, and add salt only when you intend to trigger aggregation — because that is exactly what it will do. Where a project needs a set solids content for a coating or a casting line, we can supply the dispersion concentrated to that figure rather than leaving you to evaporate it down.

Individualised chitin nanofibres form a translucent hydrogel at low solids, with a fibrillar network visible through the wet gel.

Where these materials are put to work

The pattern across all of these applications is the same: a positively charged polymer meeting something negatively charged, or a chelating amine group meeting a metal ion. Which format is right depends less on the field than on the phase you have to work in — solution, dispersion or solid.

Storage, handling and what shortens the chain

• Chitosan is hygroscopic. Keep containers sealed, store them cool, dry and out of direct light, and expect the powder to pick up moisture if a drum is left open in a humid room.
• Loss on drying is quoted at 10% or below for standard grades and 5% or below for tighter ones. Re-check the moisture after long storage rather than assuming the figure on the original certificate still holds.
• Strong acid, elevated temperature, high shear and irradiation all shorten the chain. If you mill, homogenise or autoclave the material as part of your own process, expect the viscosity to fall — plan the specification around the viscosity you need after your step, not before it.
• Defined oligomers and amino sugar standards are best held frozen and dry. Once in solution, aliquot and use within about a month, because repeated freeze-thaw cycles degrade short chains quickly.
• Disperse powder into water before adding acid, or use a salt grade. Adding powder to acid directly produces gelled lumps that will not dissolve afterwards.
• Endotoxin-controlled grades lose their value if handled alongside ordinary material. Store and weigh them separately, with dedicated equipment.

Grades built around your process

Most enquiries we receive are not for a catalogue number. They are for a behaviour that has to be hit inside an existing process, and the fastest way there is usually to adjust a grade that already exists rather than to invent a new material.

Send us the constraint rather than the specification — a pH the material has to survive, a viscosity it has to stay under, a molecular weight it has to sit below — along with a description of what the material has to do in your process, and we will come back with the grade, the test conditions and a sample that demonstrates the answer.

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