GB2158112A - Treatment process for utilization of rubber wood - Google Patents

Abstract

A method for the stabilisation of rubber wood comprises treating the same at a temperature of between 120 DEG C to 150 DEG C and at a pressure of 2 Kg/cm to 15 Kg/cm to denature the latex contained therein and render the same biologically stable. By adjusting the temperature pressure and treatment time it is possible to also achieve a selected wood colour in the range of light yellow to dark brown.

Description

SPECIFICATION Treatment process for utilization of rubber wood The present invention relates to a treatment process for rubber wood. The rubber tree (rubber tree after rubber solution (latex) is derived) is usually artificially planted in farm land in various countries such as Malaysia, Thailand and Indonesia, and this wood can be easily obtained and is recognized by many experts as having excellent qualities.

The rubber tree belongs to Euphorbiaceae, and its scientific name is Hevea brasiliensis Muell-Arg.

Generally, it is called a rubber tree or a Para rubber tree, and the collection of rubber latex is normally stopped 20-25 years after planting, and in many cases the trees are then burnt after felling.

At present, a very small quantity of rubber wood is used as raw material for fish boxes, chip board or for making charcoal, but generally it is not sufficiently utilized. The reasons for this are as follows: (1) The rubber wood has low resistance to discolouring and putrefying bacteria and is subject to violent destruction in short time. This is because the rubbery substances are contained in the molecular structure of vessels or the intersices of the rubber wood and the rubber wood include starches, saccharides and aromatics and hence discolouring and putrefying bacteria utilize them as a substrate.

(2) The latex fills the entire structure of the rubber wood, and hence it permeates naturally onto the upper surfaces even after lumbering or fabrication is complete.

(3) When the rubber wood is infested with egg-laying wood borers, the wood is destroyed. In case of the rubber wood, complete control of such insects by ordinary insecticide treatment is difficult.

(4) Defects such as bending, torsion, warping and splitting occur frequently on the rubber tree, and yield after fabrication is extremely low.

Thus, the rubber tree has extremely low resistance to discolouring and putrefying bacteria and is greatly destroyed by insects and the latex remained in the wood permeates and, therefore, the rubber wood is most difficult to utilize effectively worldwide.

However, since the rubber tree has the following features, when the problems mentioned in the foregoing are solved, inversely, it will be recognized a kind of tree having extremely high value of utilization.

(1) Since the rubber trees are densely planted on flat farm land according to a plan, felling and transportation are easy, and hence the rubber wood can be obtained at extremely low cost as compared with other kinds of wood.

(2) Countries like Thailand and Malaysia are strongly desirous of planned felling of rubber trees and their utilization, and no permit for cutting down is required and indeed felling is encouraged by subsidy.

(3) Every year, rubber trees are planted according to a plan and with such a magnitude of growth and a huge quantity of stock pile in addition to the trees already available future quantitative demand can be readily met. Also, the colour of the wood is a graceful white, and since wood work of high precision is possible, it is suitable for high class demands such as furniture, household furnishings and the like.

According to the present invention there is provided a method for the stabilization of rubber wood which comprises treating the same at a temperature between 120"C and 150"C and at a pressure of 2 Kg/cm to 15 Kg/cm to denature the latex and render the same biologically stable.

This invention also relates to the improvement of the wood to resemble high class oak wood, cry wood, teak wood which is produced by adjusting the temperature pressure and treatment time to achieve a wood colour in the colour range of light yellow, reddish brown to dark brown.

The primary reason for the rubber wood to have an extremely weak resistance to the insects, discolouring and putrefying bacteria is the presence of the rubber solution in the composition which is the feature of the rubber wood, namely the latex.

The latex is composed of plant rubber, starches (polysaccharide deglucose polymer), refined oil, oil and fat, oleic acid, linolic acid and the like, and has the preferable composition against the destruction by the insects or bacteria.

Also, the unique aromatic property included in the latex improves the inducing actions of the insects.

The latex permeates from the portion of the formed layer to the inside of the rubber wood at the time of forming the intermediate zone in which the rubber wood produces the cell division and shifts to the core wood, and there is an adhesion uniformly to the cellulose at the time of forming the cell film, and at the same time, is adhered to the major portions of the wood such as hemicellulose, lignin, and is accumulated in the vessels and otherintersices of the rubber wood.

In the typical rubber wood treatment process of this invention, the rubber wood is placed into an autoclave where the pressure of abov 2 Kg/cm2 can be applied, and the door is closed, and hot water is introduced into a separately prepared autoclave, and while feeding the steam into the autoclave, the pressure is gradually increased, and the temperature is raised, and the heating process using the hot water can be carried out. In case the preparation of the hot water is difficult, the water can be introduced into the autoclave, and it can be made the hot water by using the steam.

When the heating temperature exceeds 130"C, the latex contained in the rubber wood starts the thermal decomposition, and the component alteration starts. Furthermore, when the heating and pressure are collectively used, and the temperature reaches 140"C and the pressure exceeds 4 Kg/cm2, all the latexes remaining uniformly in the structure of the rubber wood are completely melted, and the component alteration occurs whereby the colouration occurs. The colouration is almost proportional to the heating temperature and heating time, and changes from light yellow to reddish brown to dark brown and from light colour to dark colour, and the operation like a dyeing process can be carried out as if using a desired dye.

As the heat source of the heating, the steam is used instead of the hot water and the pressure and heating are applied to raise the temperature while gushing the steam to the rubber wood in the autoclave, the component alteration of the latex that is the component of the rubber wood occurs by the thermal decomposition, and it is possible to alterate and dye the entire rubber wood in light yellow, reddish brown or dark brown.

Also, in a separate process of this invention, the rubber wood is placed into a sealed drying chamber, and the heated air is blown into the drying chamber under pressure, and the temperature is raised while continuing the application of the pressure. When the heating temperature exceeds 130"C, the thermal decomposition of of the latex starts, and the melting and component alteration proceed.

Furthermore, when the heating and the pressure are applied and the heating temperature exceeds 140"C, all the latexes remaining uniformly in the structure of the rubber wood are completely melted, and the component alteration of the latexes occurs and the latexes are adhered.

According to this invention, the latex contained in the rubber wood is subjected to the heating and pressure process using the autoclave or the sealed drying chamber, and the component alteration is caused by the thermal decomposition to produce the appearance like the high class oak wood, cherry wood, teak wood, and at the same time, the wood component detesting the insects or bacteria is produced, and as a result, the rubber wood can be treated to become the rubber wood having a strong antiseptic property.

The insecticiding process of the rubber wood at present is generally carried out by using -BHe, DDT, dieldrin, phoxime, chlordane, arsenic compounds, fluorine compounds, methylbromide and the like which have a strong poisonous character, and for the antiseptic process, zinc compounds, copper compounds, chromium compounds, chlorine compounds, fluorine compounds, arsenic compounds, nitro compounds are generally used. Most of these chemicals are designated as violent poisons by law, and are dangerous chemicals to human beings, and are becoming a pollution problem worldwide at present.

In this invention, the chemicals are not used at all, and the rubber wood is subjected to the heating and pressure process only to prevent the destruction by insects or bacteria, and this invention can be said as an epoch making invention in view of the economy, safety, pollution free character.

Moreover, according to this invention, the colour of the rubber wood can be made as the colour of the light yellow to dark brown extremely resembling the oak wood, cherry wood, teak wood which are the woods suitable for high class furnitures.

The distindt dyeing mentioned above utilizes the dyeing character produced by the component alteration caused by the heating decomposition of the latex in the rubber wood, and the dyeing phenomenon of the rubber wood becomes a light colour in case of relatively low temperature or high temperature for short hours, and becomes a dark colour in case of high temperature for long hours.

The rubber wood that has been evaluated as relatively low class wood by the colouration by this treatment process comes to be evaluated as the high class wood, and such evaluation can explore an extremely valuable path for the effective utilization of the rubber wood.

The dyeing of the wood component of the rubber wood by the component alteration of the latex by the heating treatment process mentioned in the foregoing is characteristic accompanied by an extremely unique phenomenon.

This phenomenon is due to the quantity of accumulation of the latex remaining in the wood structure of the rubber wood, and as a result, much of the latex are contained in the portion so called a ribbon grain in which the periphery of the annual ring pattern and the wood structure are ciosely intersected more than the other portions, the colouration of this portion is colour developed in the dark colour, and is expressed as if the natural wood grain.

The external appearance produced by weaving the dark colour dyed portion like wood grain and the tension wood portion that is white wood produces a high class feeling that cannot be anticipated in the untreated wood, and improves greatly the added value of the rubber wood along with the appropriate colouration of oak colour, cherry colour or teak colour which is the overall wood colour change.

Furthermore, in this invention, the quality of the wood of the tension wood portion is highly improved by the filling and shifting with the permeation of the molten latex into the wood structure of rough construction of the tension wood that has small quantity of lignin in the wood structure of the rubber wood by the heating treatment process mentioned in the foregoing.

In case of the untreated tension wood, when it it subjected to shaving by a plane, grinding by a sander, rough surface, inverted grain, irregular grain occur frequently, and also, when the coating process is applied, uneven quality occurs due to a quantity of suction of excessive paint and the process and coating becomes extremely difficult, but the treated wood becomes the process finish and the coat finish entirely similar to the healthy wood portion, and the permeation filling effect of the molten latex to the tension wood is expressed remarkably.

By the way, not only the tension wood portion, but also, the wood structure of the rubber wood after treatment including the healthy portion produces the hardness and luster as if the synthetic resin is permeated into the wood structure by the uniform adhesion of the molten latex into the wood structure, and the sense of high quality of wood structure and the beautiful appearance are expressed.

In this invention, as a result of life-size tests discovers that a relationship illustrated in the following table is produced between a thickness of the rubber wood and the heating and pressure applying condition by hot water.

Also, as a result of test of the sample of the life-size tests, if the heating treatment at which the colour of the wood changes sufficiently to light yellow is carried out, it has been discovered that the effects of insecticide property and antiseptic property can be fully demonstrated, and the workability of plane shaving, sander grinding, coating can be greatly improved.

Furthermore, with respect to the physical strength of the treated rubber wood, as a result of the fabrication tests, in the bending work, boring work, dovetail work, and dowel joint work, it has been confirmed that there is no change in comparison with the untreated wood.

TABLE Wood quality improving tests by heating and pressure treatment process of rubber wood thick- hot applied treat- degree of antiseptic insecticid- plane sander coating ness of water pressure ing colouration effect ing effect shaving fabrica- fabricatreated temper- time in core wood property tion tion wood ature portionn property property (m/m) ( C) (Kg/cm) (hour) 125 2.5 3 none ineffective ineffective poor poor poor 130 3.0 3 light yellow effective good good good 30 135 3.5 3 light yellow effective effective good good good 140 4.0 3 reddish brown effective effective good good good 150 5.0 3 dark brown effective effective good good good 125 2.5 6 none ineffective ineffective poor poor poor 130 3.0 6 reddish brown effective effective good good good 30 135 3.5 6 reddish brown good effective effective good good good 140 4.0 6 dark brown effective effective good good good 150 5.0 6 dark brown effective effective good good good 125 2.5 3 none ineffective ineffective poor poor poor 130 3.0 3 none ineffective ineffective poor poor poor 40 135 3.5 3 light yellow effective effective good good good 140 4.0 3 light yellow effective effective good good good 150 5.0 3 reddish brown effective effective good good good 125 2.5 6 none ineffective ineffective poor poor poor 130 3.0 6 light yellow effective effective good good good 40 135 3.5 6 reddish brown effective effective good good good 140 4.0 6 dark brown effective effective good good good 150 5.0 6 dark brown effective effective good good good 125 2.5 4 none ineffective ineffective poor poor poor 50 135 3.5 4 light yellow effective effective good good good 140 4.0 4 light yellow effective effective good good good 150 5.0 4 reddish brown effective effective good good good 125 2.5 8 none ineffective ineffective poor poor poor 50 135 3.5 8 reddish brown effective effective good good good 140 4.0 8 dark brown effective effective good good good 150 5.0 8 dark brown effective effective good good good (Note) (1) Heating and pressure treatment process using hot water (2) Used autoclave is a dia. of 1.5 m and a length of 9 m, heating pressure boiling tank.

(3) Width of test wood is 100 mlm. length 1,000 m/m.

(4) Antiseptic test is based on a result of 2 months of comparison of accumulation outdoor tree shade with untreated rubber wood.

(5) Insecticiding test is carried out in a box in which Scolytidae and Platypodidae are breeding.

(6) Plane shaving property, sander fabrication property and coating property are based on a result of fabrication test conducted by furniture maker.

Example 1 50 sheets of rubber wood plank having a thickness of 25 mm, a width of 100 mm and a length of 1000 mm were accumulated by means of a stainless steel mesh, and the planks were fixed by a wire rope, and were mounted on a cart and were placed into an autoclave having a diameter of 1,500 mm and a length of 9,000 mm, and its door was closed, and then, hot water of 85"C stored in an auxiliary tank was introduced into the autoclave, and the heated steam was gushed into the hot water in the autoclave immediately to raise the temperature, and the pressure and the heating were applied until the hot water temperature in the autoclave reached 1 30 C by collectively using application of the pressure.

When the hot water temperature was recorded at 130"C, application of the pressure was carried out for 3 hours while keeping the pressure condition of 3 Kg/cm2.

The pressure was released in 3 hours, and the hot water was returned to the auxiliary tank, and the door was open, and the heat treated rubber wood was drawn outside while being mounted on the cart, and the colouration condition of the planks by the heating alteration was checked, whereby it was discovered that all the planks showed the reddish brown colour on their outside, but when the planks were cut, the core portions had slightly light yellow when compared with the outside. (This test plank was made as No. 1.) 50 sheets of the rubber wood planks of identical dimension in identical condition were let out for 3 hours, and the same planks were left out in the condition of a maximum temperature of 140"C and pressure of 4.0 Kg/cm2 in the same pressure and heating condition for 3 hours, and then they were drawn outside of the autoclave, and were checked, whereby all the 50 sheets of the test wood planks were altered and coloured by heating to the same reddish brown with respect to both the outside and the core portion. (This test plank was made as No. 2.) Each 10 sheets were arbitrarily drawn out from two test wood planks of No. 1 and No. 2 having undergone the pressure and heating tests, and those planks were stacked in crosspiece mode in a rubber forest having a height of 4m together with 10 sheets of the resultant untreated rubber wood planks of the same dimension to conduct the adhesion test of the discolouring and putrefying bacteria.

In one week, the resultant untreated rubber wood planks were completely adhered and fixed and propagated with the discolouring and putrefying bacteria completely on the surface and both sides and the reverse surface while the treated test rubber wood planks of No. 1 and No. 2 were adhered with mold, but there were no adhesion and propogation action of the discolouring and putrefying bacteria at all on the surfaces thereof. In 2 months, when each 10 sheets of the No. 1 and No. 2 of the test wood planks were cut and checked, there were no trace of the discolouring and putrefying bacteria at all on the cut surfaces.

From this result, it was confirmed that the treated wood planks whose outside were heated and coloured in the reddish brown were altered to the wood planks having a strong resistance to the discolouring and putrefying bacteria.

Next, each 5 sheets of the insect damage test wood planks were drawn out from the two test wood planks of the No. 1 and No. 2, and the planks were put together with 5 sheets of the untreated wood planks of the same dimension, and the planks were cut to the planks having a length of 100 mm, and the wood planks were divisionally placed into three pieces of insect boxes of a 50 cm square and a height of 50 cm containing 200 wood borers, and the insect damage tests were carried out.

As a result, the untreated wood planks were bored with several insect holes in merely 15 minutes after the start of the test, and numerous holes were bored in 12 hours. On the other hand, the treated wood planks of the No. 1 and No. 2 were confirmed of absence of any insect hole until all the insects were dead.

From the foregoing result, in the rubber wood plank having a thickness of 25 mm, where the wood plank was treated in the condition of the pressure of 4.0 I < g/cm2, heating of 140"C and treating time of longer than 3 hours, it was discovered that complete insecticiding and putrefying properties were obtained.

Example 2 100 sheets of the rubber wood single plates having a thickness of 1.5 mm and a width of 450 mm and a length of 1 m and stainless steel meshes having a thickness of 1 mm were interposed between the wood single plates and were stacked, and they were fixed by a wire rope, and were mounted on the cart to be placed into an autoclave having a diameter of 1.5 mm and a length of 9m, and the pressure and heating were applied in the same method identical with the Example 1, and they were left out in the condition of 135"C and 3.5 Kg/cm2 for 30 minutes, and then they were drawn outside from the autoclave, and were checked, whereby all the plates were altered and coloured in dark brown by the heating decomposition of the latex.

This coloured single plate was subjected to the putrefying and insecticiding test identical with the Example 1, and as a result, it was confirmed that the putrefying and insecticiding properties were complete.

Example 3 A square rubber bar having a thickness and width of 60 mm and a length of 400 mm was dried to have a less than the percentage of moisture content of 8%, and was cut and fabricated for parts of furniture, and then, was charged into the autoclave.

The autoclave was equipped with two pieces of pipes for gushing the steam which had a diameter of 50 mm and a length of 3.5m at the upper and lower portions of the inside of the autoclave having a diameter of 1 sum and a length of 4m, and the positions of the pipes were located at right and left of the upper and lower portions of the autoclave, and the upper pipes were bored with 200 pieces of holes having a diameter of 3 mm per one pipe on the side and the upper surface so that the steam was gushed at an angle of 1800.

The square rubber bars charged into the autoclave were stacked by means of the stainless steel meshes having a wire diameter of 1 mm, and the steam was gushed to the square rubber bars with the gushed pressure of 5 Kg/cm2, and the temperature in the autoclave was gradually raised while applying the pressure, and when it reached 1 40 C, the application of pressure was suspended, and the heating and pressure were applied for 3 hours while performing the steam gushing necessary for holding the temperature of 140 C.

After the heating and pressure were over, the gushing of the steam into the autoclave was suspended, and the pressure was eliminated, and the temperature in the autoclave was lowered below 80QC and then the square rubber bars were drawn outside of the autoclave.

The square rubber bar having undergone the treatment process of this invention was such that: (A) The alteration colouration of dark brown by heating decomposition was observed in a depth of about 80 mm from two surfaces of an end and of about 10 mm from four surfaces other than an end surface.

(B) The alteration colouration of light brown by heating decomposition was observed in a depth of about 120 mm at both surface sides of an end in the direction of a center portion and about 12 mm at four surfaces otherthan surface of an end.

(C) The component alteration colouration of light yellow was observed uniformly in the remaining center portion.

When the test was conducted on the treated square rubber bars of the portions that could be clearly sectioned with respect to the degree of the component alteration colouration of the A, B, C, whereby the following result was obtained.

(1) When the rubber wood planks of A, B, C were compared with the core portion material for cut fabrication before the treatment, the portions of the tension wood of the untreated rubber wood that had not been pressure treated became easily fabricated with were considered to be difficult for cutting and grinding (sander), and generation of uneven surface and reverse grain was not observed at all.

(2) When the rubber wood planks of A, B, C were compared with the cutting fabricating material before the treatment, the remarkable improvement in the coating property was observed. Particularly, the portion of the tension wood before the treatment caused an excessive absorption of paint and coating irregularity while the treated rubber wood showed the great improvement of quality as it was finished in the coating condition entirely identical with the healthy rubber wood.

(3) In case of the A and B rubber wood, the excessive latex remaining portion and the tension wood portion of white wood produced a difference of shade of slight brown colour from the alteration colouration due to heating decomposition of other healthy portions, and this difference in the colour expresed the unique colour of the material and wood dovetail pattern which expressed a natural feeling such as teak wood, oak wood and cherry wood.

(4) In case of the A, B, C rubber wood planks, it was discovered that there was no abnormality at all in the natural generation of the discolouring and putrefying bacteria in the wood shade of outdoor, and also in the growth test for 2 months in rainy season (average temperature 28"C and humidity 70%) in Thailand and they were materials having strong resistance to discolouration property and antiseptic property.

(5) When the A, B, C rubber wood planks were placed into the insect breeding box for 2 months to carry out the insect damage test, it had been confirmed that there was no insect damage at all on the A, B, C rubber wood planks until the insects were dead, and they became complete insecticiding rubber wood planks.

By the way, the untreated rubber wood having undergone the insect damage test in the same condition was destroyed by numerous insects already in 7 minutes after it was placed into the insect breeding box, and generation of damage by the insects was observed in 3 days to a degree where the shape of the test rubber wood was not recognized.

Claims (7)

1. A method for the stabilisation of rubber wood which comprises treating the same at a temperature between 120 C and 150"C and at a pressure of 2Kg/cm to 15 Kg/cm to denature the latex and renderthe same biologically stable.

2. A method according to Claim 1 wherein the temperature, pressure and treatment time are adjusted to achieve a wood colour in the colour range light yellow to dark brown.

3. A method according to either of claims 1 or 2 wherein treatment is effected by steam and pressure in a closed vessel.

4. A method according to either of Claims 1 or 2 wherein the treatment is effected by hot air in a sealed drying chamber.

5. A method according to any preceding claim wherein the temperature is about 140"C and the pressure exceeds 4Kg/cm.

6. A method substantially as hereinbefore set forth with reference to the foregoing examples.

7. Stabilized rubber wood when produced by a method according to any one of Claims 1 to 6.