A method for the modification of wood materials to improve mechanical properties, water resistance and flame retardancy by utilizing a combination of mineralization with infusion and polymerization of biopolymers, comprising:
- (i) preparing and pre-treating wood materials comprising:
- (a) sawing wood materials into wood boards with a maximum thickness of 6 cm, in which the wood materials include softwood and sapwood;
- wherein the softwood materials include pine, American pine, yellow pine, white pine, yellow poplar, tamarind, acacia, cajuput, cinnamon, rubber, eucalyptus, ash, oak, red oak, black walnut, teak, American cherry, cedar, bread tree, sapele, and neem;
- (b) soaking the wood boards in 0.5%-1.5% Ca(OH)2 solution at a ratio of 1:2 (w/v) for 12-72 hours;
- and
- (c) washing the wood boards from step (b) with water, and drying to a moisture content below 20% to obtain treated wood boards;
- (ii) hardening the pre-treated wood boards via the creation and deposition of mineral crystal or metal oxide inside the wood fiber, including steps:
- (a1) adding the pre-treated wood boards into an immersion equipment, setting a negative pressure of −0.5 to −1 bar maintained for 30-90 minutes, then adding a first salt solution into the equipment at a ratio of 1:2 (w/v) for immersing the pretreated wood boards with pH 2-4, at 40° C.-50° C. for 30-45 minutes, then reducing temperature to 25° C.-30° C. for 0.5-3 hours;
- wherein the first salt solution has a concentration of 10%-20%;
- the first salt solution includes a sodium carboxymethyl cellulose (NaCMC) component or a carboxymethyl cellulose (CMC) component, a first salt mixture, and the rest is water;
- in which a ratio between the sodium carboxymethyl cellulose (NaCMC) component or the carboxymethyl cellulose (CMC) component and the first salt is 1:(25-75);
- the first salt mixture includes a monovalent or multivalent anionic moiety creating mineral crystal, and a monovalent cation moiety;
- the monovalent cation is selected from the group consisting of Na+, NH4+, and combinations thereof;
- the monovalent or multivalent anionic moiety creating the mineral crystal is selected from the group consisting of HCO3−, CO32−;
- PO43−, HPO42−, H2PO4−, SiO32−, SO42−, B4O72−, and combinations thereof;
- (a2) adding the wood boards from step (a1) to another immersion equipment, setting a negative pressure of −0.5 to −1.0 bar maintained for 60-120 minutes, then adding a second salt solution into the equipment at a ratio of 1:2 (w/v) for immersing the wood boards for 1-3 hours;
- wherein the second salt solution has a concentration of 10%-20%;
- the second salt solution includes a second salt mixture, and the rest is water, in which the second salt solution is obtained by homogeneously dissolving the second salt mixture with a molar mass of 5-10 mol with 5 liters of water;
- the second salt mixture includes a divalent metal cation moiety creating mineral crystal, and a monovalent or multivalent anionic moiety;
- the divalent metal cation moiety creating mineral crystal is selected from the group consisting of Mg2+, Ca2+, Cu2+, and combinations thereof;
- the monovalent or multivalent anionic moiety is selected from the group consisting of Cl−, NO3−, an anion of formic acid (HCOO−), and anion of acetic acid (CH3COO−), and anion of citric acid (C3H5O(COO)33−), and combinations thereof;
- and
- (iii) washing the wood boards from step (ii) with water, and drying to a moisture content below 20%;
- (iv) treating the wood for flame resistance by adding the treated wood boards from step (iii) into another immersion equipment, setting a negative pressure of −0.5 to −1.0 bar maintained for 90-150 minutes, then adding a third salt solution into the equipment at a ratio of 1:2 (w/v) for immersing the wood boards for 1-3 hours;
- wherein the third salt solution has a concentration of 20%-40%;
- the third salt solution includes a third salt mixture, and the rest is water;
- the third salt mixture includes a monovalent or multivalent anionic moiety, and a monovalent cation moiety;
- the monovalent cation moiety is selected from the group consisting of Na+, NH4+, and combinations thereof;
- and
- the monovalent or multivalent anionic moiety is selected from the group consisting of PO43−, HPO42−, H2PO4−, SiO3−, SO42−, B4O72−, and combinations thereof;
- (v) treating the wood for water resistance by immersing the wood boards from step (iv) in a colloidal system at a ratio of 1:2 (v/v) at 70° C. for 1-3 hours;
- wherein the colloidal system has a concentration of 0.2%-2%;
- the colloidal system is selected from the group consisting of pectin, chitosan, lignin, and combinations thereof;
- in which the combination of colloidal system is chitosan and lignin;
- (vi) adding the wood boards from step (v) into another immersion equipment, setting the negative pressure of −0.5 to −1.0 bar maintained for 120-180 minutes, then adding a fourth salt solution into the equipment at a ratio of 1:2 (w/v) for immersing the wood boards at 70° C.-90° C. for 30-60 minutes, then reducing temperature to 30° C.-35° C. for 3-4 hours;
- wherein the fourth salt solution has a concentration of 10%-20%, in which the fourth salt solution includes a sodium carboxymethyl cellulose (NaCMC) component or a carboxymethyl cellulose (CMC) component, the second salt mixture, and the rest is water;
- in which a ratio between the sodium carboxymethyl cellulose (NaCMC) component or the carboxymethyl cellulose (CMC) component and the second salt mixture by mass is 1:(25-75);
- the second salt mixture includes the divalent metal cation moiety creating mineral crystal, and the monovalent or multivalent anionic moiety;
- the divalent metal cation moiety creating mineral crystal is selected from the group consisting of Mg2+, Ca2+, Cu2+, and combinations thereof;
- the monovalent or multivalent anionic moiety is selected from the group consisting of Cl−, NO3−, an anion of formic acid (HCOO−), an anion of acetic acid (CH3COO−), an anion of citric acid (C3H5O(COO)33−), and combinations thereof;
- and
- (vii) drying the wood boards from step (vi) to a moisture content of 10%±2% to obtain a modified wood.