The invention further relates to a preservative composition kit and different methods of preservative treatment, as well as different uses of the chitosan preservative composition and the preservative composition kit respectively. Finally the invention relates to different products having been treated with the chitosan-containing preservative composition.

Background There has for a long time been a need for an impregnation agent (hereafter for simplicity denoted preservative) which is environmentally friendly and not contains toxic compounds.

This relates to preservatives for marine uses as well as land-based uses. Liquid preservatives used today e. g. for fish farming nets contains toxic copper compounds and other toxicants, while preservatives for land based wood contains arsenic oxide, toxic phenols and other toxic compounds. These toxicants are not desirable in preservatives, but are used in lack of alternatives of more environmentally friendly agents.

There is also a need for a more effective and non-toxic fire retardant for wood. The existing fire retardants comprise e. g. ammonium borate and other types of ammonium compounds that are more or less toxic. The problem with ammonium compounds is that they are easily washed out of materials and the aging process is rapid and lifetime correspondingly short.

Therefore a continuous maintenance and surveillance is required. Acetic anhydride is also used for pressure impregnated wood to obtain a fire retardant effect. None of these substances give an adequate fire retarding effect, and many of them cannot be used indoors, as they may release toxic gases under influence of strong heat.

Chitosan is a modified form of chitin and the modification can take place by different deacetylation processes. Deacetylation takes place by separating the acetyl group from the (rest of the) chitin molecule.

Chitin is found in shellfish, insects, octopus etc. and in some plants, but are mainly extracted from shellfish like shrimps, crab etc. It is assumed that these animals have had the same structure of the chitin for protection against e. g. parasites for more than 600 million years, and chitin is one of the oldest polymers on earth together with cellulose. It can thus be said that nature itself has these two types of saccharides are ideal and therefore the two organic materials produced most widely in the nature. The natural production of

chitin from living organisms is estimated to 100-200 x 109 tons per year. The utilization of this worldwide is less than 1%, where the chitin mainly is regarded as a waste problem.

The availability of chitin as a raw material is thus very good.

Chitosan and other types of polysaccharides and polymers have been tried in several ways as a preservative against fungus and rot in wood. Chitosan alone has shown a good protective effect, but with the present technology a high concentration of chitosan in required. In addition it is easily washed out, so its use as a commercial preservative is therefore limited.

US patent No. 5,549,739 describes a wood modifier composition comprising chitosan. The composition described concerns chitosan in a form soluble in water and with a molecular weight between 320 and 48,000, which composition also includes colloidal silica.

According to the patent the chitosan can be enzymatically depolymerized. Industrial scale treatment with the modifier according to this patent will be expensive and complex.

A common feature for all these agents and especially the fire retardants is that the aging process is rapid so they lose their ability to protect the wood. This is due to the fact that a lot of the compounds are washed out or disappear in other ways. The aging process, which mainly takes place due to external influences, may lead to a complete loss of the protective effect after some time.

Many fire retardants do not provide a deep penetration of the wood. The fire retarding effect is thus limited to the outer part of the wood and the protective effect may be lost completely if the wood is subjected to a further preparation.

Objective The object of the present invention is therefore to provide a preservative that is environmentally friendly, i. e. which is not toxic, and which can cover substantially all application areas of the traditional, toxic preservatives.

It is furthermore an object to provide such a preservative which may be used for wood as well as for textiles, hereunder fabrics used for fishing nets and other marine applications, as well as a preservative for use in concrete, paint or varnish, to stop growth of fungus and algae.

It is furthermore an object to provide such a preservative that is endurable, which means that it only to a low extent will be washed out of the substrate to which it is applied.

It is still another object to provide a preservative as described above, which through

addition of environmentally friendly additives will constitute a fire retardant.

It is also an object to provide a preservative that may be applied by conventional techniques, as with mechanical applicators as well as with use of vacuum/pressure impregnation.

The invention The invention relates to a preservative composition as defined by the characterizing part of claim 1 and claim 25. Preferred embodiments of the preservative composition are disclosed by the claims 2-20. The invention also relates to a composition kit as defined by claim 21, preferred embodiments of which are disclosed by claims 22-24.

The invention further relates to a method for the manufacture of the preservative as defined by the characterizing part of claim 26. Preferred embodiments of the method are disclosed by claims 27-30.

The invention still further relates to methods for treatment of substrates with said method as defined by claims 31-42. The invention still further relates to different uses of the preservative as defined by the claims 43-47. Finally the invention relates to different products as treated with preservative as defined by claims 48-51.

By the present invention the modified chitosan is immobilized in the substrate at low concentrations in a way that it will not be washed out, dissolve or disappear in any other way, while providing a protective effect. The chitosan is first dissolved in an acid, like formic acid or another organic acid or a combination of such acids. Mineral acids can also be used with the exception of sulphuric acid, which is not able to dissolve the chitosan.

When dissolved, the chitosan is if necessary depolymerized, e. g. to a viscosity of 10 cP or lower, by means of an oxidizing agent like hydrogen peroxide, sodium hypochlorite or the like. The depolymerization step has the function of reducing the viscosity of the preservative. For use as an impregnation fluid for wood, the depolymerization is typically carried out until the viscosity is less than 10 cP.

When the chitosan is dissolved to a concentration typically between 0.1 and 10% by weight and depolymerized to an aqueous solution, an anion able to form a relatively water- insoluble complex with chitosan is added. The normal way to add the anion will be as a salt where the counter ion is an environmentally friendly or acceptable cation. In the following the addition of the anion may some times be referred to as the addition of the salt.

Due to the increased stability that the anion provides to the chitosan, the anion (and/or the

salt) according to the invention is sometimes referred to as a stabilizer in the following text.

Alternatively the salt including the anion of the invention is added to the water together with non-dissolved chitosan, whereafter the acid is added, causing the chitosan to dissolve in the solution.

The salt is preferably chosen from a group including sulphites, phosphites, benzoates, phenolates, anhydrides and sulphamines. The salt is preferably added in a concentration low enough to avoid precipitation of chitosan, typically in the range 0.1-10% by weigth.

The chitosan solution is then applied to a material (substrate) e. g. by mechanical applicators or by means of pressure, alternatively a combination of vacuum and pressure. For pressure impregnation, equipment conventional therefor may be utilized.

In most or all of the groups of salts mentioned there may be found both toxic and non-toxic compounds. It will be understood from the objective of the application that a non-toxic salt will always be preferred over a toxic salt.

By dissolving the chitosan in acid, the chitosan will react will the acid. The pH should not, however, be reduced to a value lower than 4. If the pH accidentally is reduced too much, adding carbonates, e. g. ammonium hydrogen carbonate to the desired level prior to adding the salt, may raise it.

In the following, we will give a more detailed description of different aspects of the invention using sulphite as an example of the preferred salt.

After the chitosan solution has been applied and dried, the oxygen in the air will oxidize the sulphite to sulphate. As part of the invention, the inventors have discovered that while the chitosan complexes according to the invention have a limited water-solubility in the free, powder form, and they become practically water-insoluble when impregnated into a substrate and thereby immobilized within the internal structure of the substrate.

The impregnated material will comprise chitosan, sulphite/sulphate and salts of the organic acid utilized, e. g. chitosan forminate. Both the chitosan and many of the salts of the organic acids, like fonninate, have a preservative effect and will protect the material against attack from fungus and rot. Used alone these substances, however, have the significant disadvantage that they will easily be washed out of the substrate, which the complex according to the present invention does not.

Ammonium is known to have a fire retardant effect. When a fire retarding effect is desired, ammonium sulphite could be used as a stabilizer in the chitosan solution. A binding

between the chitosan and the ammonium will be formed during drying with the formation of ammonium sulphamine glucose (ammonium chitosan sulphite), ammonium sulphamine, chitosan sulphate and e. g. ammonium terminate or other ammonium salts of the acid used to dissolve the chitosan. Ammonium may also be used as the counterion in other salts within the frame of the invention, like phosphite, benzoate, anhydride, sulphamine and the like.

An advantage with the use of ammonium sulphite is that it forms chitosan sulphate and ammonium sulphamine glucose (ammonium chitosan sulphite) with the chitosan.

Ammonium sulphamine, also known as AMS, is used as a weed-killer and a fire retardant.

These substances alone can not be used in a marine environment as they very easily dissolve in water and rapidly will be washed out. When the ammonium compound is bound to chitosan, however, neither the chitosan nor the ammonium compound will be easily dissolved, and they will therefore keep and enhance their protective effect for a substantial period of time.

The preservative according to the invention may also be used in liquid or dehydrated form as a soil improver and herbicide. Used in the form of a dry powder not impregnated into a substrate, the solubility is higher than for the corresponding complex in a substrate. It may also be applied as a soil improver in the form of wood chips from sawing and working of impregnated wood, in which case it will remain in the soil for a longer period of time, as it will not easily decompose. Wood chips of this kind may also be used in fire retardant chipboards or the like.

The chitosan solution may further be used in painting and cement or as a primer for plastic materials like polyester or the like.

The preservative according to the invention also relates to pressure impregnation of timber logs of freshly cut spruce, which is known not to receive impregnation any deeper than 3 mm into the wood, due to the fact that the cell structure will close during the process.

Burning under sufficiently high temperature may destroy material impregnated according to the invention. The material will then be carbonized without burning with a flame, and the exhaust gases will not be any more toxic than gases from untreated material.

Impregnated wood is preferably ground to chips for use in chipboards or the like, but not for soil improvement if it is not known in what kind of environment it has been used.

As earlier indicated the step of depolymerizing the chitosan has the function of reducing its

viscosity, which may be required for some areas of application, like impregnation of wood.

For other application areas, like impregnation of textiles or fish farming nets, this step may be omitted or carried out to a lesser degree. The inventors have found that impregnating ropes, fish farming nets etc. with the preservative according to the invention, as a secondary effect, enhances the strength of the substrate and delays its aging. These effects also vary with the degree of depolymerization of the chitosan. Generally it can be said that the optimal viscosity and hence the required degree of depolymerization could be developed by trial and error for each relevant use. Chitosan with varying chain lengths, belonging to poly-, oligo-and monosaccharides respectively, may also be used in combination.

While the combination of sulphite and chitosan is slowly oxidized under formation of the desired insoluble complex, the formation of complexes may occur much more rapid for other combinations according the invention. When the formation of complexes is quite rapid, the preservative may not be kept as a stable solution in the presence of air. In such cases it is preferred that the different components of the preservative are added separately to the substrate to be impregnated. The process may then be conducted as a two or three step reaction. The first step typically involves applying a chitosan solution alone, preferably followed by a drying period. Thereafter a solution of the salt is applied, leading to n situ formation of the insoluble preservative (complex) within the substrate.

Fields of use As indicated, protection against growth of fungus and rot in wood and fabric materials, as well as providing said materials with a fire retarding effect, are considered to constitute the main fields of use for the preservative according to present invention. In the following a further elaboration of some of the secondary fields of use is given Soil improvement Chitosan in solid form, for example impregnated into chips of wood may be used directly or be ground to a fine powder that is worked into the soil, or spread on top of it. It can also be applied in the form of pellets or the like. It will work as a fertilizer for the plants and at the same time as a herbicide. When the decay (release) process starts due to the enzyme in the plant roots, the chitosan will enhance the plant's ability to resist attack from fungus and bacteria, while the ammonium sulphate will contribute as a nitrogen source. This decay process is slower than for traditional nitrogen-containing fertilizers and will therefore hold up for a longer time in the soil and not represent the same danger for contamination as traditional fertilizers, where the nitrogen is washed out more rapidly.

In liquid form the solution should have a pH of 5-6 when applied to the soil.

Utility plant protective agent A chitosan solution with a pH in the range 5.5-6.5 is sprayed on utility plants to avoid attack from fungus, rot and insects. The chitosan will lie as a breathing film over the plants and protect them against attack, while the plants simultaneously exploit the chitosan, this way improving the resistance against disease attacks. The plants need repetitive treatments of the chitosan solution as they consume it over time. The chitosan solution may also be spread on the ground as a dry powder, not immobilized within a substrate, and will also in this condition prevent growth of fungus and weed.

Additive to paints/primers etc.

A chitosan solution may be worked into the paint base or used alone. When the chitosan is added to the paint, it could first be neutralized and/or have sulphate/sulphite added prior to its addition to the paint. The chitosan will this way receive increased ability to bind to the paint, while it simultaneously prohibits attack from fungus and rot to the surface treated.

When the chitosan is used alone, it is firstly applied as a solution with low viscosity that is allowed to absorb into the wood as a primer and subsequently a high viscosity solution is applied as an outer coating.

Additive to concrete and cement constructions etc Chitosan with high viscosity is dissolved in acid to which ammonium sulphite is added.

Thereafter the solution is neutralized and the"jelly"dried. The resulting powder is mixed with the cement in an amount of 2.5 vol-%. The chitosan fibers act as an extra bonding agent for the cement, while simultaneously protecting against fungus and algae. The chitosan present also acts as a buffer against acidic influence on the concrete, thereby reducing the corrosive effect of acidic rain.

Crutosan impregnated materials receding secondary treatment with acetic anhydnde Materials like finished woodwork, textiles and marine constructions of tree as well as seine, may be impregnated with a pure chitosan liquid or chitosan liquid with sulphites and thereafter given a secondary treatment with acetic anhydride (C2H3OO) 2O, which leads to a conversion of the chitosan to the insoluble chitin. The impregnated material is allowed to lay in acetic anhydride for three hours in a closed tank, and is thereafter washed clean of acetic anhydride.

Examples The examples comprises tests of some general properties of the preservative and some properties that are related to the interaction between the preservative and the substrate material that it is intended to protect.

Solubilitytests Solubility tests were performed on chitosan dissolved in fonnic acid with ammonium sulphite as a stabilizer, on chitosan dissolved in formic acid with ammonium phosphite as stabilizer, chitosan dissolved in formic acid without stabilizer and chitosan dissolved in acetic acid without stabilizer. a) Formic acid with stabilizer: 10 1 water was added to 500g chitosan and stirred to form a suspension before the formic acid was added. The formic acid was added to an extent where all the chitosan was dissolved, and the resulting pH was 5. Subsequently 50g of sulfamic acid was added under constant agitation, followed by the addition of 20g of ammonium sulphite under vigorous agitation. Thereafter the solution was allowed to rest under continued agitation for additional 15 minutes. Thereafter all. sample of the solution was evaporated at 40 °C under agitation until only solid particles remained. b) The process of a) was repeated with acetic acid replacing the formic acid. c) Formic acid without stabilizer: 101 water was added to 500g chitosan and stirred to form a suspension before the formic acid was added. The formic acid was added to an extent where all the chitosan was dissolved, and the resulting pH was 5. The solution was allowed to rest under continued agitation for additional 15 minutes. Thereafter all. sample of the solution was evaporated at 40 °C under agitation until only solid particles remained. d) The process of c) was repeated with acetic acid replacing the formic acid The tests were conducted under normal and under extreme conditions.

1.0 to 2.0 g of the compounds chitosan + ammonium sulphite, chitosan + ammonium phosphite, chitosan formiate and chitosan acetate respectively, were added to 1000 ml of the solutions described above. The solutions were stirred with a magnetic stirrer for a period from 1 hour to 24 hours. All solutions were thereafter filtered with a 1.2, m filter.

The filters for the compounds chitosan + ammonium sulphite and chitosan + ammonium phosphite were flushed with ion exchanged water subsequent to the filtering. The filters were placed on aluminum foil and dried for 24 hours at 55 °C before weighing. The results in % by weight are shown in tTable 1.

Table 1: Solubility of chitosan salts (in %) with and without stabilizer Chitosanforminate + Chitosan forminate + Chitosan Chitosan forminate acetate ammoniumsulphite ammonium phosphite Ion exchanged 10.6 4. 3 100 > 80 water,20 °C Ion exchanged 11.3 22.7 100 100 water,60 °C Acidic, acetic acid, 7.6 5.3 100 >80 H=1. 1, 20°C Acidic, acetic acid, 7.1 7.0 100 >80 H = 1.1, 60 °C Alkaline, NaOH, 18.4 22.3 <5 <1 (p. i.) pH= 13-14,20 °C Alkaline, NaOH, 26.1 27.0 <5 <1 (p. i.) pH =13-14,60 °C Synthetic seawater, 5.4 11.9 < 5 < 1 (p. i.) NORSOK-quality, 0°C Synthetic seawater, 7.2 16.9 < 5 < 1 (p. i.) NORSOK-quality, 30°C (p. i. = practically insoluble) Tests were also conducted on samples of the solution immobilized within porous materials (white cotton sheets) with and without stabilizer. The cotton sheets were immersed in the respective solution and dried. The sheets were cut into pieces of approximately 10.0 g or 50 cm2 each, and each sheet was exposed to one of the four solutions, 50 ml liquid for 1 day. The sheets were wrung out but not rinsed after exposure.

The results are shown in table 2.

Table 2: Solubility of chitosan salts fixated in cotton with and without stabilizer

Chitosan forminate + Chitosan forminate + Chitosan Chitosan acetate forminate ammonium sulphite ammonium phosphite Ion exchanged < 1 < 1 100 100 water, 20 °C (p. i.) (p. i. Ion exchanged < 1 < 1 100 100 water, 60 °C (p. i.) (p. i.) Acidic, acetic acid, < 1 < 1 100 100 pH = 1.1, 20 °C (p. i.) (p. i. Acidic, acetic acid, <1 <1 100 100 pH = 1.1, 60 °C (p. i.) (p. i.) Alkaline, NaOH, < 1 < 1 < 1 < 1 pH = 13-14, 20 °C (p. i.) (p. i.) (p. i.) (p. i.) Alkaline, NaOH, < 1 < 1 < 1 < 1 pH = 13-14, 60 °C (p. i.) (p. i.) (p. i.) (p. i.) Synthetic seawater, < 1 < 1 < 1 NORSOK-quality, (p. i.) (p. i.) (p. i.) (p. i.) O °C Synthetic seawater, < 1 < 1 < 1 < 1 NORSOK-quality, (p. i.) (p. i.) (p. i.) (p. i.) 30 °C (p. i. = practically insoluble) The results show that both chitosan acetate and chitosan terminate are 100 % soluble in ion exchanged water and acidic water.

Fish farming nets, textiles etc.

Untreated seine is impregnated with a chitosan solution of a 100 cP viscosity. 5% chitosan was first dissolved in formic acid and 0,5% ammonium sulphite was added as the salt. This yielded a solution with a pH of 5. Then the chitosan was impregnated into the substrate for 30 minutes at a pressure of 8 bar, whereafter the substrate was allowed to dry until the chitosan solution had been fixed in the fibres. After drying the substrate was treated with a 12% ammonium sulphate solution to accelerate the process of curing the chitosan. After the impregnation process was completed and the substrate dried, the chitosan solution was insolubly immobilized in the fibres.

Secondary treatment (impregnation) of the net may be performed by immersing/washing in chitosan solutions at certain intervals and according to the observed need for the relevant application/use.

Strengthtest The strength of a seine impregnated with the preservative according to example 1 was measured and compared with the strength of untreated seine and a seine impregnated with a copper solution. Two kinds of seines (knitted and woven) were used and the strength test repeated three times. Tests were performed on dry seines and on seines that had been immersed in seawater for 2 weeks. The following equipment was used for the test: Rupture test machine: Alvetron 10 TCT Cell : 2000N Tension velocity : 100mm/min.

Humidity : 48% Temperature : 23 °C Clamping of the samples: 4x5"holes"were made for attachment to the clamping chuck, with a distance of 20 mm between adjacent ones of these. The seines had 5 x 2 threads between the clamping chucks.

The average results are shown in table 3 below.

Table 3: Rupture strength (N)

Seine D/W Untreated Copper Chitosan Average value (N) 902 1070 1093 Woven Dry seine Std. deviation 83 10 25 Average value (N) 812 830 1000 Wet Std. deviation 77 97 30 Average value (N) 924 835 984 Tied seine Dry Std. deviation 75 35 17 Average value (N) 889 696 976 Wet Std.deviation 60 104 64 Test of aging W tests were performed in order to investigate whether chitosan treatment deteriorates or improves the seines'ability to resist aging inflicted by sunlight.

The samples was exposed for W light in a weatherometer, using the following equipment and conditions: Apparatus Atlas Xenon Weather-Ometer, type Ci 4000 Test method : ISO 4892-2: 1994 method A with cycle: 102 min."sun"and 18 min."sun and rain" Conditions: Big-standard thermometer (65 +/-3) C Air temperature : (40 +/-5) C Air humidity (50 +/-5) % RH Radiation level : 0. 5 W/m2 (between 290 and 800 nm) Average radiation intensisty : 550 W/m2 (between 290 and 800nm) Rupture tests were performed with the equipment described in relation to strength test above.

Table 4 Rupture strength subsequent to aging test

Seine trreatment time Rupture strength (N) Untreated Copper Chitosan tied t = 0 h 924 835 1137 t = 707 h 814 808 1010 woven t = 0 h 902 1070 1120 t= 493 h 663 1005 1200 The results show that chitosan treated seines are stronger than untreated seines and at least as strong as copper impregnated seines for the test period of approximately 1 year's use.

Tests of accelerated growth (fouling) Tests of accelerated growth were conducted with respect to weight increase of the seines.

These tests were performed under controlled conditions where water movement, oxygen content and pH are not related to real-life situations. The tests still conveniently serve the purpose of direct comparison.

Pieces of seines of 100 cm2 were weighed dry and suspended in a 1 1 beaker filled with contaminated seawater. One beaker was used for each piece of seine. The beakers were placed at room temperature with night and day light for 5 weeks without change of water, assumed to correspond to 4 months in the sea.. At the end of the test the pieces were weighed and photographed. The pieces were allowed to dry over night and were weighed again.

Table 5: Tests of accelerated growth (fouling) Untreated seine Copper Chitosan impregnated seine impregnated seine Dry weight before test 2.57 4. 35 3.28 Dry weight after test 2.62 4. 46 3.19 % increase1. 92. 5-2. 7 The results show a reduction of weight for the chitosan sample compared to the other samples.

Leakage tests Six tests were performed to investigate the leakage of preservative from chitosan impregnated seines to seawater. 1 liter samples of the seawater in which the seines were tested, were evaporated down at 110 °C. The dry remains were weighed. Thereafter the remains were dried in an oven at 560 °C for 24 hours and weighed again. The weight difference is anticipated to constitute (total) organic carbon. Table 6 shows the highest and lowest values for these tests, measured as"total organic carbon" (TOC/1), as well as the mean value for the tests.

Table 6: Leakage tests of chitosan from seine Highest value (TOC/1 12.1 mg Lowest value (TOC/1) 4.8 mg Mean value (TOC/1) 7. 78 mg The test result shows that leakage is at an acceptably low level.

Example 2 Impregnation of wood.

Three different preservative liquids were prepared for the test.

A) Solution of chitosan in formic acid To 10 1 of water was added 500 g chitosan and the mixture was stirred to a suspension prior to the addition of formic acid, which was added to an amount where all the chitosan was

dissolved and the pH of the solution was 5. Then 50 g of sulfamic acid was added under continuous stirring. Thereafter 20g of ammonium sulphite was added under vigorous stirring. 1 liter of the solution was evaporated down at 40 °C under stirring until only solid particles remained.

B) Solution of chitosan in acetic acid.

A chitosan solution in acetic acid and with ionic stabilizer was prepared the same way as with formic acid.

C) The solutions A and B were mixed in 50/50 by volume ratio.

Wood bricks (surface pieces of pine) with dimensions 50x25x15 mm were climatized for four weeks. The bricks were weighed, the dimensions were measured and the year rings counted. They were dried in an oven for 18 hours at 103 +/-2 °C, cooled in a desiccator and weighed. 16 bricks were impregnated in each batch with three different chitosan solutions (A, B and C). The bricks were put in a beaker and glass spheres were put on top to prevent the bricks from floating. The beaker was placed in a pressure tank and exposed to vacuum for 30 minutes. The preservative liquid solution was added and the tank pressurized for two hours. The bricks were wiped off and weighed again. Thereafter they were conditioned for four weeks (20 °C and 65% humidity). Thereafter they were weighed again and vacuum packed. The bricks were then sterilized with gamma rays, weighed again and exposed to two different fungi: Glueoph Trabeum and Poria Placenta for 16 weeks.

Figures 1 and 2 show results after 12 of the 16 weeks, compared with non-treated bricks.

The wood material may be dried at once, or it may-in wet or dry condition-receive an additional treatment with a sulphite/sulphate-only solution or with another stabilizer according to the invention. A weak hydroxide solution may also be used in order to fix the chitosan rapidly to the wood structure. For wood to be used indoors, an hydroxide solution is preferred for environmental reasons.

The wood may thereafter be treated in ordinary ways, e. g. with paint. Wood material that is pressure impregnated with a chitosan solution according to the invention may also be covered with plastic substances like polyester or the like. The chitosan will improve the binding between the polyester and the wood, which in turn makes it possible to use impregnated panel as panel for bathrooms or the like.

Example 3 Timber logs of spruce Logs of spruce that recently were debarked were pressure impregnated. A vacuum of 0.7 bar was applied for 3 hours whereafter a 2.5 % by weight solution of the chitosan preservative was introduced and a pressure of 8 bar was supplied. It was found that this relatively low pressure, compared to the more usual 12-16 bar, is required in order to avoid that the cell structure closes due to low water content, which would render it practically impossible to have the preservative penetrate the logs. The low pressure was compensated by a longer treatment period of 8 hours. After completed treatment the excess chitosan solution was pumped back to the buffer tank, and the pressure tank depressurized.

Investigations of the logs showed that the solution had penetrated into their core. The treatment may be done in one or in two steps, as the second treatment step may be one with a sulphite-only or a sulphate-only solution.