What is the Kauri–Butanol or KB value?
Written by Moises Kleinberg, MSc.
Technical matters Director of the Mexican Institute for Dry cleaning and Laundry
Mr. Klienberg is a long time friend and collegue of Everett Childers and a valuable source of information relating tot he textile cleaning industry.
The Kauri Tree (Agathis Australis), belongs to the Araucarian family and it is one of the biggest trees in the world. The only place on earth where it grows is in the northern part of New Zealand. It produces a protection resin, similar to Amber, so common in the central and South American jungles. When the Kauri Tree suffers from any rupture or wound, it secrets large quantities of a protection resin. Some of which falls to the earth and fossilizes, absorbing all kinds of impurities
The first English settlers in that part of New Zealand found that the native Maoris would make artesian sculptures out of that resin to create all kinds of ornaments. Soon, they discovered that the Kauri resin had excellent varnish properties. While exploiting the kauri gum industry as a raw material for the manufacturing of varnishes and linoleum, the settlers turned into real miners in the search of kauri “nuggets”. Just like all those industries, which depended on the exploitation of natural resources without renewing them, very soon the demand overwhelmed the diminishing fossil gum supply.
At the same time, the chemists could profoundly analyze all the kauri solution properties, to find the best possible solvent that could serve as a vehicle for the kauri gum varnish application.
Soon enough, they found that the gum could not be dissolved in petroleum distillates. It was easily diluted however, in alcohols and ketones, but especially in butyl alcohol, also known as n-butanol.
The kauri gum yields crystal clear solutions when dissolved in n-butanol and when the solvent is vaporized, after a varnish application, a highly pure gum coat remains on the treated surface. When the kauri gum is dissolved in pure n–butanol and then applied as a varnish, the remaining resin tends to be highly brittle and it shows a poor resistance towards the weather conditions. The task was then to find a mixture of solvents that would completely dissolve the gum in the first place, but at the same time, they would vaporize in such a manner that the remaining coat would have good elastic, water and sun proof properties.
During the varnish industry’s peak, a wide range of solvents and their different mixtures where analyzed as vehicles for the kauri application. It was found that when small amounts of other solvents were poured into a kauri solution in pure butanol, the mixture could keep its transparency up to a certain amount. When that quantity was exceeded, the kauri gum started precipitating and a certain degree of turbidity was observed. The limit at which the kauri–butanol solution would remain clear before getting turbid, depended on the specific solvent that was incorporated. That is to say, that each solvent had its own maximum amount at which the kauri would start precipitating. This phenomenon lead the chemists to think that they could grade each solvent, according to the amount that a standard kauri–butanol solution could bear.
At that time, by the beginning of the 20th century, a method that could evaluate the properties of each solvent had to be developed. For some reason, hidden in the huge load of technical information, specially regarding to the painting industry, the Kauri–Butanol value was proposed as a measure of solvent “power”. Without a consistent theoretical background, that would relate this value with the particular characteristics of each solvent, the meaning of that measurement was empirically established. It was stated that the higher the KB value, the “stronger” a solvent was, without defining exactly the meaning of a stronger solvent.
The Kauri–Butanol value definition is, according to the ASTM (method D 1133), the volume given in milliliters of any solvent with which at 25 °C (77 °F), a standard kauri–butanol solution is titrated and a certain amount of turbidity is detected. The accepted KB value range goes from 20 or 25, to 120 or 130.
Up to these days, many people still misinterpret the KB value’s meaning. They relate the KB value with the titrating solvent “power”. As a matter of fact, there is not such a thing as “solvent power”. In further briefings, the solvent theory shall be discussed. Each solvent has its own capacity to dissolve a certain type of substances more or less effectively than others, depending on it’s own physico-chemical properties, as well as those of the substance that has to be dissolved. In the beginning, the KB value was only used to evaluate the behavior of petroleum fractions. They would yield KB values of up to 30 or 35. Since these method was arbitrarily taken as a measure of the “solvent’s power”, very soon it was adopted to measure other type of solvents. For instance, chlorinated hydrocarbons, such as perchloroethylene, may be the most representative solvent in our industry. It yields a KB value of about 90.
There are some solvents such as alcohols, ketones and glycol ethers that cannot be evaluated using the KB method, since they can readily dissolve the kauri gum, so they can hardly form any turbidity when titrated into a kauri–butanol standard solution.
In spite of the lack of a strong and consistent theoretical substance, in our cleaning industry the KB value has been accepted as a guide to determine the cleaning power of the solvents that are used in drycleaning machines.
Indeed, there is a certain relation between the KB value of a solvent and it’s capacity to clean the garments. Solvents with low KB values lesser than 35, tend to dissolve greases somewhat easily. Specially, the mineral ones. That is because the low KB value solvents can be relatively light fractions of petroleum or else, the new synthetic hydrocarbons that have similar physicochemical properties than those of the greases. These kinds of solvents tend to have some difficulties retiring lacquer and varnish stains from the garments.
On the other hand, this family of solvents normally doesn’t damage the fabrics or the ornaments of the garments that are treated with them.
It has been found in the literature regarding to the new carbon dioxide cleaning system, that the KB value attributed to the liquid CO2 is about 35, arguing then, a minimal damage to the washed garments. This article’s author has no information regarding the way that determination has been done, for the accepted ASTM method is performed at 25 °C (77 °F) and one atmosphere pressure. At room temperature, the liquid CO2, may exist only at 67 atmospheres pressure. Just as it is bottled in the medicinal tanks. The lowest pressure, at which the liquid CO2 may exist, is at 5.11 atmospheres. And yet the temperature has to be –57 °C (-70.6 °F) (fig. 5). Never the less, the advantages attributed to this liquid, are basically a good capability to dissolve most of the substances that compose the stains normally found in the garments and it’s low impact to health and to the environment.
The perchloroethylene has a KB value of about 90. Not that this solvent is “stronger” than the hydrocarbons. It has simply different properties that allow an easier dissolution of substances such as varnishes and lacquers. This solvent can still dissolve effectively some greases and oils, but it begins damaging some synthetic garments. It may also provoke a certain degree of color bleeding. Anyhow, perchloroethylene stays in a point where it can dissolve most of the stains found in the garments, while the potential damages that it can cause, are still controllable. That is why perc keeps being one of the leading solvents in the drycleaning industry.
There are some other types of solvents, such as 1,1,1, trichloroethylene, with a KB value of 124. This solvent, having good cleaning properties, it has been found to be too aggressive towards most of the synthetic garments. That is why it hasn’t been so successful in our industry.
As we can see, the Kauri–Butanol value, can be useful to evaluate the proper solvent to be used for a given cleaning task, taking on account the dissolutive capacity of the different solvents only. Today we have a wide variety of solvents from which to choose, for the available equipment that can be found in the world, works with perc, with a KB value of 90 and on hydrocarbons with KB values between 27 and 45. Anyway, those who have multisolvent equipment, can and have to choose the kind of solvent that best serves the particular cleaning needs of their plant. The KB value is one of the parameters that has to be taken on account for that purpose.
With the above explanation of how the kauri-butanol value of a solvent is determined it is apparent that a KBV number is only a wild estimate of how well a drycleaning solvent actually cleans fabrics. If the power of the solvent is too high for removing dyestuffs from a fabric there will be excess bleeding during cleaning. 1,1,1, trichloroethylene and perchloroethylene are two solvents that are known to bleed excess dyes from fabrics and are slightly better at removing oils and greases from fabrics. Hydro carbon solvents are much gentler on dyes and greases but will do an excellent job of overall cleaning normally soiled fabrics. GreenEarth® is also a gentle cleaner with adequate cleaning for normally soiled fabrics. Liquid Carbon Dioxide is also a gentle cleaner that has a lot of positive attributes.