Klucel® G (500 g)

Klucel® G (500 g) — the cellulose ether that also works without water

Klucel® G is hydroxypropyl cellulose — abbreviated HPC —: a non-ionic cellulose ether manufactured by Ashland (formerly Hercules) and distributed by CTS, with CAS number — the international register that identifies every chemical substance — 9004-64-2. It dissolves in cold water and in most polar organic solvents — ethanol, methanol, 95 % isopropanol, dimethyl sulfoxide, propylene glycol —, and that dual solubility is its whole point: it allows consolidating and adhering on works where introducing water is not an option. Two traits set it apart from what resembles it: on heating in water it does not gel, it precipitates — exactly the opposite of methylcellulose —, and in an organic solvent heat speeds up dissolution instead of spoiling it.

What is it used for?

• Adhering and repairing works on paper without introducing water, dissolved in ethanol at 1-2 %, when wetting the support is ruled out.
• Local consolidation of leather with red rot — the degradation of vegetable-tanned leather that turns it into a reddish powder —, applied in alcohol: it reduces surface powdering. That leather darkens irreversibly the moment it meets water, and there lies the reason for the alcohol route.
• Fixing powdering layers and pastel, in a thin layer and at low concentration.
• Paper and parchment with sensitive inks and corrosion — iron gall ink and copper corrosion, where treating with non-aqueous polymers is standard practice.
• Thickening polar solvents, acids and bases for controlled cleaning: alcohols, amines, dimethyl sulfoxide. It does not thicken non-polar ones: aliphatic and aromatic hydrocarbons and petroleum distillates are not solvents for it.

Why choose Klucel® G?

• It is the grade the field uses. In the Getty Conservation Institute survey of 155 conservators from the Book and Paper Group of the American Institute for Conservation (AIC), grade G was the hydroxypropyl cellulose used almost exclusively.
• The viscosity of the solution does not vary between pH 2 and 11 — manufacturer's data —, which allows thickening the acids and bases in common use in the field. The solution is prepared for immediate use; if stored, it keeps best between pH 6 and 8.
• It forms no peroxides (0.00 milliequivalents per gram at every time point of the Getty test) and its photochemical stability against visible light and near ultraviolet is excellent. On ageing it does not become insoluble: it keeps redissolving in its own solvent. What it is not — and this is told in full below — is the most thermally stable of the cellulose ethers.
• Flexible film without plasticisers. The manufacturer states it: Klucel films are flexible in themselves, do not turn tacky at high humidity and act as a barrier against oils and greases.
• Viscosity maximum in a hydroalcoholic mixture: 7 parts water and 3 parts alcohol by weight give 500 mPa·s at 2 %, against 270 in water alone and 210 in ethanol. With the same product, almost twice the body.

The limits, stated

• It is not the most thermally stable cellulose ether. The Getty classified it in 1990 as thermally unstable, and in chain scission grade G came behind carboxymethyl cellulose and methylcellulose. The condition that defuses this is set by the very source that classified it: applied at 1 or 2 % and in a thin layer, which is how it is used, discolouration, if it occurs at all, is barely perceptible. In full, in the frequently asked questions.
• Medium adhesive strength. That is how the distributor describes it, and the conservators surveyed by the Getty agree: it is not a strong adhesive. It bonds paper and board and consolidates; it does not solve a joint under mechanical load.
• Insoluble in water above 45 °C, and it precipitates — it does not gel. Heating the water to speed up dissolution achieves the opposite. Precipitation is completely reversible: cooling below 40 °C with stirring redissolves it and restores the original viscosity.
• On leather with red rot, it consolidates at the surface. It reduces powdering, but it does not give strength back to the leather matrix and it neither reverses nor halts the deterioration. It can leave tidelines, gives a matt finish, and the film breaks with repeated flexing.
• As a fixative, take care with organic pigments. A higher moisture content in vehicles such as this one can accelerate the fading of organic pigments — carmine lake is named explicitly —. The support should be kept close to pH 7 before and after treatment.
• Mixed with resins that react with its free hydroxyl groups, the film may become insoluble, and high temperature and low pH accelerate that curing. That is the real limit of its reversibility.
• Drying an aqueous application with heat can cause blushing and spoil the film.

Pack size and storage

• Pack size: 500 g container.
• Store between 5 and 35 °C, in a dry, well-ventilated place, with the container tightly closed and upright.
• Shelf life: the manufacturer declares no expiry date. What it does publish is a storage figure: low and medium viscosity types — grade G is one — retain on average 97 % of their original viscosity after three years at room temperature and with frequent exposure to air. It is worth dating the container on the day it is opened.
• Identification: off-white odourless powder · viscosity 150-400 mPa·s at 2 % in water at 25 °C · pH 5.0-8.5 at 2 % · molecular weight 370,000 (manufacturer's data) · CAS no. 9004-64-2.
• Not classified as hazardous under Regulation (EC) 1272/2008. Like any fine organic powder, it is combustible in suspension: handle without raising a dust cloud, away from ignition sources and with the container tightly closed. Clear up spills — the wetted product makes the floor slippery.

Klucel® is a trademark of Ashland (formerly Hercules), the manufacturer of the polymer. This 500 g container is distributed by C.T.S.

Also in the catalogue: citric acid 99.5 % (1 kg) is one of the cleaning acids that this thickener holds at constant viscosity within its pH range. The criterion for Klucel® G is the solvent and the type of work: it is chosen when the treatment has to be done without introducing water, when an alcohol or an acid has to be thickened, and to consolidate or adhere without asking it to bear mechanical load. The catalogue holds other conservation adhesives and consolidants with their own pages, among them Aquazol® 200 (1 kg). If you are unsure between them for a particular case, write to us and we will look at it together.

Frequently asked questions

Any questions? Write to us on WhatsApp, visit innovart.art or email us at info@innovart.art and we will advise you.