The present invention relates to linseed oil which has been processed for the purpose of improving the properties of the oil in connection with the use in for example impregnation of products based on cellulose, such as wood. The invention also relates to a process for the manufacture of such linseed oil.
Even if the present invention is applicable in relation to other cellulose-based products than wood the invention will in the following be described in connection with wood in the form of different types of lumber. Decomposition of wood when used outdoors is almost exclusively caused by fungi and bacteria. The requirement for growth of such micro-organisms is the presence of water. Furthermore, a suitable temperature and access to nutrition and oxygen are required. Prevention of decomposition can be based on the elimination of one or more of these conditions necessary for the growth of the micro-organisms. As an example there can be mentioned that if the moisture content is brought down to a value lower than about 20% biological decomposition is substantially prevented.
A number of different impregnation processes for the protection of wood are known, and these methods can in principle be divided up into techniques based on the supply of a substance poisonous to the growth of the micro-organisms, and techniques whereby the wood is given hydrofobic properties, for example by impregnation with some kind or oil. In the latter case an impregnation agent is crude linseed which can be of hot- or cold-pressed type, both of which by suitable heat treatment are concerted into boiled linseed oils. The use of such linseed oils is, however, associated with certain drawbacks for example a viscosity which is unfavourably high for ease of handling, a contents of components constituting substrate for the relevant micro-organisms, unfavourable drying properties, etc. One method used for lowering the viscosity is dilution with a solvent something which, however, is environmentally unacceptable. The use of chemical poisons is presently frequently used but should for the future be mainly prohibited for environmental reasons. Also impregnation with a combination of hydrofobation and toxic treatment is used, for example treatment with creosote.
The present invention has for an object to provide a processed linseed oil with properties which are substantially improved, mainly in connection with the use of the linseed oil for the impregnation of wood and wood products.
Another object of the invention is to provide a process for the manufacture of such linseed oil of improved properties.
Yet an object of the invention is to provide a process, whereby the uptake of the oil by the wood or the wood product in connection with impregnation is substantially increased and can even reach a near 100 percent level of uptake.
In connection with extensive research and experimental work it has in accordance with the invention been found that a treatment of linseed oil resulting a situation that its content of free tocoferol will be less than about 100 ppm, results in substantially improved properties of the linseed oil, particularly in connection with its use as an impregnating agent for wood or lumber.
These and other objects of the invention which will be clear from the following description are obtained by a processed linseed oil essentially consisting of linolenic, linolic and oleic acids, mainly in the form of triglycerides, the linseed oil being characterized in that its contents of free tocoferol is less than about 100 ppm.
It is particularly preferred that the processed linseed oil contains free tocoferol in a concentration less than about 75 ppm and particularly less than about 50 ppm.
Even if the processed linseed oil according to the present invention can be based on cold pressed as well as hot pressed linseed oil it is preferred to use cold-pressed linseed oil as a starting material for the linseed oil according to the invention.
The new process according to the invention for the manufacture of a linseed oil of the above type is characterized by the following steps:
a) heating crude linseed oil to an increased temperature lower than the boiling point of water,
b) adding a heated inorganic acid to the oil and mixing the oil,
c) separation of precipitated materials, for example by sedimentation and discharge and removal of bottom deposit formed,
d) adding a heated aqueous solution of alkali to the oil and mixing the oil,
e) discharge of the soap formed, and
f) rinsing the oil with hot water until a clear rinsing water is obtained.
The heating in step a) above suitably takes place at a temperature lying within the range about 80 to about 99xc2x0 C. while avoiding that the boiling point of water will be reached.
The inorganic acid is preferably added in an amount of about 0.5 to 30% by weight based on the weight of the oil. Among suitable inorganic acids there may be mentioned phosphoric acid, sulphuric acid and hydrochloric acid. It is preferred to use as an inorganic acid phosphoric acid, for example thermal phosphoric acid, at a concentration of for example 80% and in a quantity of about 0.5 to about 2% by weight, particulary from about 1 to about 1.5% by weight.
The mixing in step b) suitably lasts until the reaction has come to a stop, which corresponds to a period of about 10 to about 30 minutes.
As alkali any suitable alkaline compound can be used, for example hydroxides of alkali or earth alkali metals, particularly sodium hydroxide or potassium hydroxide. Particularly preferred is sodium hydroxide, also called caustic soda. The alkaline compound is suitably added in a quantity equivalent to about 2 to 5% by dry weight based on the weight of the oil. Alkali is suitably added in the form of an aqueous solution in a quantity of about 7 to 15% by weight water also this based on the weight of the oil.
For the purpose of avoiding thickening of the oil during heating the oil may in a further step be heated while adding a suitable agent, such as manganese tetraborate. A suitable temperature range for the heating of the oil in this further step is from about 120 to about 140xc2x0 C. In order to improve the trying properties of the processed oil a suitable catalyst can be added, for example example manganese tetraborate. The agent used as a catalyst can be the same as the agent used to avoid thickening of the oil during heating.
The invention will in the following be further described with reference to non-limiting examples, wherein quantities and percentages relate to weight if not otherwise stated. In the examples abbreviations concerning the fatty acid present in the linseed oil are furthermore used. Accordingly, for example oleic acid is abbreviated C18:1, linolic acid C18:2 and linolenic acid C18:3. The number following the colon thus indicates the degree of unsaturation.