Polymer impregnated bamboo

Abstract

An engineering or constructional member comprising at least two strips bonded with an adhesive; each of the strips comprises bamboo impregnated or treated with a polymer derived from one or more furfuryl alcohol resin precursors.

Claims

1. An engineering or constructional member comprising at least two strips bonded together with an adhesive; wherein each of the strips comprises bamboo impregnated with a polymer derived from one or more furfuryl alcohol resin precursors, dried and cured at a temperature between 50 and 180 degrees Celsius which provides protection against degradation by microorganisms, splintering and delamination; and wherein the bonded bamboo impregnated with the polymer are not carbonized or pyrolysed and are of a dark brown bamboo color.

2. An engineering or constructional member as claimed in claim 1 wherein the furfuryl alcohol resin precursors are selected from polymerisable monomers or oligomers selected from the group consisting of furfuryl alcohol (FA), bishydroxymethyl furan (BHMF), trihydroxymethyl furan (THMF), oligomers of FA, BHMF and THMF condensation products of these compounds and mixtures thereof.

3. An engineering or constructional member as claimed in claim 1 wherein the furfuryl alcohol resin precursors are selected from the group consisting of: furfuryl alcohol, bishydroxymethyl furan and oligomers and condensation products thereof.

4. An engineering or constructional member as claimed in claim 1 bonded with an adhesive selected from the group consisting of: epoxy resins, urea-formaldehyde resins, melamine-formaldehyde resins, methylene diphenyl isocyanate or polyurethane resins or other moisture resistant adhesives.

5. An engineering or constructional member as claimed in claim 4 comprising a panel, board, decking, cladding, marine component, marine article, flooring, floor tile, constructional component, furniture or sporting equipment.

6. An engineering or constructional member as claimed in claim 1 which is more resistant to attack by an insect, termite or other pest than a component made from untreated bamboo.

7. An engineering or constructional member as claimed in claim 1, wherein the bamboo and impregnated polymer have been subjected to a maximum temperature of 180 degrees Celsius.

8. A method of manufacture of polymer impregnated bamboo as claimed in claim 1 comprising the steps of impregnating the bamboo with a polymerisable composition comprising: (i) one or more furan resin polymerisable monomers, or oligomers; (ii) a catalyst; (iii) a solvent selected from the group consisting of: water, acetone, C.sub.1-C.sub.4 alcohols and mixtures thereof; wherein the one or more wood compatible polymerises or monomers or oligomers has a boiling point not less than 50 C. higher than the boiling point of the solvent and atmospheric pressure; and (iv) optionally one or more stabilisers or other ingredients; to produce impregnated bamboo; subjecting the impregnated bamboo or bamboo article to a water removal process; and maintaining the bamboo at a higher temperature to form the polymeric material to produce polymer treated bamboo.

9. An apparatus for manufacture of an engineering or constructional member as claimed in claim 1 by polymer impregnation of bamboo comprising: a container adapted to receive pieces of bamboo or one or more bamboo articles to be treated, the container having a pump for applying reduced pressure to the container; a steam generator adapted to supply superheated steam to the chamber; and sensors adapted to monitor parameters selected from pressure, temperature, humidity and concentration of volatile organic compounds within the container.

10. An apparatus as claimed in claim 9, further comprising a carrier moveable into and out of the container, in use the carrier comprising a cage arranged to receive and retain pieces of bamboo, and a carriage on which the cage is mounted.

11. An apparatus as claimed in claim 9, wherein an inlet for superheated steam is provided.

12. An apparatus as claimed in claim 9, wherein a heat exchanger within the vessel is provided for direct heating.

Description

(1) The invention is further described by means of example but not in any limitative sense with reference to the accompanying drawings of which:

(2) FIG. 1 is a schematic flow chart showing the steps in manufacture of a composite article in accordance with the invention; and

(3) FIG. 2 is a cross sectional view of an engineering component in accordance with the invention.

(4) The first stage of manufacture of the composite article is harvesting of the bamboo cones (1) followed by optional storage to allow drainage of sap (2) before the cones are cut into pieces (3) with a desired length suitable for impregnation. The cut pieces are crushed or further cut to form pieces with a desired size (4).

(5) A supply of bamboo pieces or bamboo articles, for example split culms, is organised into a separated stack on a trolley or other carrier (5) using spacers so that each culm is separated from adjacent culms. The pieces may be placed in a cage to prevent movement or floating during impregnation. The stack is then moved on the carrier into an impregnation autoclave or tank (6).

(6) The autoclave is filled with an impregnating solution from buffer tanks supplied from storage tanks via a mixing and measuring tank. The pieces are allowed to become impregnated with the solution (7).

(7) After impregnation, the impregnated bamboo or bamboo articles are transferred to a drying chamber (8). The drying chamber is provided with a heat exchanger, or inlet for superheated steam and a condenser connected to an outlet for recycling condensate collected from the condenser to the storage tank. Gases from the condenser are routed through an air purifier.

(8) The bamboo pieces may be impregnated (7) by any conventional technique including: application of pressure up to 15 atmospheres; vacuum followed by pressure; or by application of atmospheric or low pressure followed by higher pressure and a final vacuum step.

(9) The impregnating solution may comprise one or more furan resin prepolymers including for example monomers selected from furfuryl alcohol, bis hydroxymethyl furan, tris hydroxymethyl furan or oligomers of these compounds.

(10) Mixtures of monomers or of monomers and oligomers may be used, provided that they are sufficiently fluid to penetrate and impregnate the bamboo.

(11) A general method which may be used includes the steps of securing the bamboo pieces in a cage so that they will not float; closing the autoclave and applying a partial vacuum; filling the autoclave with the treating mixture while maintaining the vacuum to submerge the bamboo; pressurising the autoclave to a pressure in the range of 5-14 atmospheres dependent on the dimensions of the bamboo or bamboo articles and desired rate of impregnation; reducing the pressure to 2 or 3 atmospheres and expelling the liquid using the remaining pressure within the autoclave. Finally, the pressure is released and the treated bamboo is removed.

(12) A typical treatment solution may comprise:

(13) TABLE-US-00001 furfuryl alcohol 22.5% maleic anhydride 0.5% citric acid 1.0% ethanol 71.0% water 5.0%.

(14) A liquid uptake of up to 70 or 80% in relation to dry bamboo mass may be achieved. This was surprising in view of the difficulty of impregnation of bamboo.

(15) Alternative impregnating solutions are disclosed in WO2004/011216 and WO2004/011214 the disclosures of which are incorporated into this specification by reference for all purposes.

(16) When the impregnated bamboo pieces have been placed (9) within the drying chamber, a pre-vacuum is applied for a short period to remove any air from the chamber in order to prevent a risk of fire or explosion. The pressure during the pre-vacuum period may be up to 0.3 bar due to evaporation of water from the impregnated bamboo.

(17) The container is then heated to a temperature of about 70 C. over a period of 3-6 hours. During this heating up period the pressure may rise from the pre-vacuum pressure of less than 0.2 bar to between about 0.2 and about 0.4 bar, preferably about 0.3 bar.

(18) The relative humidity may be about 90%.

(19) The conditions within the container are maintained by control of pressure, injection of superheated steam and external heating.

(20) The moisture content of the bamboo is determined by measurement of the amount of water collected from the container. The drying stage may be complete when the moisture content of the bamboo is about 15% or lower.

(21) After the drying stage is complete the pressure is allowed to rise (10) to about 1 bar and the temperature is increased to from about 100 to about 140 C. preferably, about 100 C. with the relative humidity increasing from about 60 to about 80% by addition of superheated steam to the container, in order to prevent cracking or deformation of the bamboo.

(22) The curing conditions may be maintained for about 10 hours dependent on the nature of the polymer composition and the thickness of the bamboo or bamboo articles.

(23) When the curing is complete the polymer impregnated bamboo pieces or bamboo articles are removed from the container (11).

(24) The pieces of impregnated bamboo are bonded together using adhesives to form composite structures, for example, decking or flooring.

(25) The pieces are placed in a mold (12) and uncured adhesive composition is added. A vacuum may be used to assist penetration by the adhesive between the pieces. The adhesive is then cured (13) using heat and pressure as required to form a cured composite article. The article is then removed from the mold (14) and finished by cutting to size and machining as necessary.

(26) FIG. 2 shows a cross-sectional view of an engineering component comprising a polymer impregnated bamboo in accordance with this invention. The engineering component may comprise a floorboard, wall panel or other constructional component, for example used for making buildings. An array of strips of polymer impregnated bamboo (20) are arranged side by side and are bonded together by layers of curable adhesive (21) to form a solid laminate structure. A layer of adhesive (22) extends beyond the ends of the impregnated strips (20) to form an upper surface (25) of the component. The upper surface (25) may be provided with a non-slip or wear-resistant coating, for example by bonding aggregate particles into the upper surface. Alternatively, the surface (25) may be polished to provide a decorative appearance. At the sides of the component (27) the impregnated bamboo pieces (24) are cut with cured adhesive (23) provided to form perpendicular edges so that the component may be fitted to an adjacent similar component. Lower surface (26) may be coated with bitumen or other heat softenable adhesive to facilitate application to floor or other underlying surfaces.

(27) Polymer treated bamboo manufactured in accordance with this invention was tested for decay resistance.

(28) The treated materials included in the test were supplied by Kebony ASA. a) Furfuryl alcohol resin treated bamboo 1) Solid Bamboo 2) Brittle samples where the fibres were falling apart b) Furfuryl alcohol resin thermally treated bamboo 1) Solid Bamboo 2) Brittle samples where the fibres were falling apart.
Test Fungi Postia placenta (Fr.) M. J. Larsen & Lombard, strain FPRL 280 Trametes versicolor (L.) Lloyd, strain CTB 863 A Gloeophyllum trabeum BAM Ebw. 109
Preparation of Test Specimens

(29) The samples were sawn into the size, 10525 mm (Bravery 1979). Control samples were prepared from untreated P. sylvestris sapwood.

(30) Accelerated Ageing (Water Leaching) According to EN 84

(31) The specimens were leached according to EN 84. Each material was leached separately. The specimens were vacuum-impregnated with de-ionised water and placed in water flasks. The water volume in relation to specimen volume was 5:1. Ten exchanges of water were made during a 14-day period. The specimens were oven-dried and weighed.

(32) Decay Testing According to the Miniblock Test (Bravery 1979)

(33) The test specimens were sterilized by autoclaving. Each sample was put on a plastic-net in a petri-dish together with one untreated P.Sylvestris control. For each treatment 6 replicates were used. There were 6 replicates3 fungi=18 samples per treatment. For 2 treatments, there were 36 treated samples and 36 untreated samples. There were 6 correction values per treatment and 6 virulence samples per fungi.

(34) Inoculation with Fungal Mycelium

(35) One inoculum overgrown with mycelium of respective test fungus was placed in each petri-dish. The petri-dishes were placed in a culture room (22 C, 85% RH).

(36) Test Duration and Termination

(37) The test was run for 9 weeks (1 week for the inoculum to start growing and 8 weeks for the test). The wood specimens were wiped clean from fungal mycelium, weighed, oven-dried (18 h at 103 C) and weighed again. Mass loss due to decay was calculated.

(38) Results

(39) Calculation of Correction Values (from Specimens in Non-Inoculated Petri-Dishes)

(40) The mass loss values were corrected for the leaching to agar. Therefore correction values were calculated (Table 1). These correction values for each group of samples are obtained by placing them in sterile petri-dishes under the same conditions and time as those who have been inoculated with fungal mycelium.

(41) TABLE-US-00002 TABLE 1 Correction values for the different treatments and untreated Correction values Treatment Mass loss (%) Furfuryl alcohol impregnated Bamboo 0.2 Untreated P. Sylvestris sapwood 0.3 Furfuryl alcohol impregnated treated Bamboo 0.2 Untreated P. Sylvestris sapwood 0.2
Test Fungus: Trametes versicolor
Virulence Samples for Trametes versicolor

(42) The mass loss for unmodified pinus sylvestris sapwood as virulence control and of the control lying next to each sample was after 8 weeks above 13.8% (See Table 2).

(43) Test samples for Trametes versicolor

(44) The treated bamboo had a mass loss of 2.4% and the Furfuryl alcohol polymer impregnated heat treated bamboo had a mass loss of 1.5% (see Table 2).

(45) TABLE-US-00003 TABLE 2 Mass loss for the different treatments and the untreated control. Corrected mass loss (%) Postia Tramets Gloeophyllum Treatment placenta versicolor trabeum Furfuryl alcohol impregnated 0.7 2.4 2.5 Bamboo Untreated P. Sylvestris sapwood 28.8 13.9 18.7 Furfuryl alcohol impregnated 0.4 1.5 1.7 heat treated bamboo Untreated P. Sylvestris 28.8 13.8 20.6 sapwood Virulens P. Sylvestris sapwood 21.9 15.8 20.6
Test Fungus: Gloeophyllum trabeum
Virulence Samples for Gloeophyllum trabeum

(46) Mass loss for unmodified pinus sylvestris controls sapwood as virulence control and of the control lying next to each sample was after 8 weeks over 18.7% (see Table 2).

(47) Test Samples for Gloeophyllum trabeum

(48) The furfuryl alcohol polymer treated bamboo had a mass loss of 2.5% and the furfuryl alcohol polymer heat treated bamboo had a mass loss of 1.7% (See Table 2).

(49) Test Fungus: Postia placenta

(50) Virulence Samples for Postia placenta

(51) Mass loss for unmodified Postia placenta controls sapwood as virulence control and of the control lying next to each sample was after 8 weeks over 20% (See Table 2).

(52) Test Samples for Postia placenta

(53) The furfuryl alcohol polymer treated bamboo had a mass loss of 0.7% and the furfuryl alcohol polymer heat treated bamboo had a mass loss of 0.4% (See Table 2).