Method of preparing environmentally-friendly water-resistant tannin-based wood adhesive

Abstract

An environmentally-friendly epoxy tannin resin based polyurea adhesive and its preparation method are provided. The method includes preparing the environmentally-friendly water-resistant tannin-based wood adhesive by graft copolymerization of epoxy tannin, which is obtained by epoxidation of tannin using epoxy chloropropane, with triethylene tetramine and subsequent deamination reaction of them with urea.

Claims

1. A method of preparing a water-resistant tannin-based wood adhesive, comprising the steps of: (a) adding tannin to epoxy chloropropane aqueous solution; (b) heating the epoxy chloropropane aqueous solution to 80° C.; (c) after a predetermined period of time of reaction, adding 20 wt % NaOH aqueous solution to the epoxy chloropropane aqueous solution; (d) maintaining the epoxy chloropropane aqueous solution at 80° C. for three hours; (e) cooling the epoxy chloropropane aqueous solution to 20° C.; (f) using absolute ethyl alcohol and acetone to dilute, suction filter, and rotary evaporate the epoxy chloropropane aqueous solution for 3 to 5 times to obtain epoxy tannin; (g) using triethylene tetramine to graft copolymerize the epoxy tannin; and (h) deaminating the graft copolymerized epoxy tannin with urea to obtain the water-resistant tannin-based wood adhesive.

2. The method of claim 1, wherein a quantity ratio of the epoxy tannin, the triethylene tetramine, and the urea is n.sub.epoxy tannin:n.sub.triethylene tetramine:n.sub.Urea=1:1:(2-3).

3. The method of claim 1, wherein epoxide equivalent of the epoxy tannin is 100-300 g/mol.

4. The method of claim 1, wherein step (f) further comprises the sub-steps of: (f1) adding the epoxy tannin and the triethylene tetramine in a proportion [n.sub.epoxy tannin:n.sub.triethylene tetramine=1:1] to a single-necked flask; (f2) maintaining the single-necked flask at 60° C. for four hours; (f3) transferring the single-necked flask to an oil bath pan; (f4) heating the oil bath pan to 120° C.; (f5) adding urea to the oil bath pan; (f6) maintaining the oil bath pan at 120° C. for 12 hours to obtain epoxy tannin based polyurea prepolymer; and (f7) adding water to the epoxy tannin based polyurea prepolymer until a 55-65 wt % aqueous solution is obtained wherein the 55-65 wt % aqueous solution is the water-resistant tannin-based wood adhesive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a flow chart of a method of preparing environmentally-friendly water-resistant tannin-based wood adhesive according to the invention; and

[0022] FIG. 2 is a table of bonding strength of plywood.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Referring to FIG. 1, it illustrates a method of preparing environmentally-friendly water-resistant tannin-based wood adhesive of the invention. The method comprises the steps of: adding tannin to epoxy chloropropane aqueous solution; heating the epoxy chloropropane aqueous solution to 80° C.; after a predetermined period of time (e.g., 3 hours) of reaction, adding 20 wt % NaOH aqueous solution to the epoxy chloropropane aqueous solution; maintaining the epoxy chloropropane aqueous solution at 80° C. for three hours; cooling the epoxy chloropropane aqueous solution to 20° C.; using absolute ethyl alcohol and acetone to dilute, suction filter, and rotary evaporate the epoxy chloropropane aqueous solution for 3 to 5 times to obtain epoxy tannin; using triethylene tetramine to graft copolymerize the epoxy tannin; and deaminating the graft copolymerized epoxy tannin with urea to obtain the water-resistant tannin-based wood adhesive.

[0024] The following embodiments enables those skilled in the art to gain a more comprehensive understanding of the invention, but do not limit the invention in any way. Unless otherwise specified, % in the following embodiments refers to mass percent.

Embodiment 1: n.SUB.ET.:n.SUB.TETA.:n.SUB.U.=1:1:2

[0025] Add 150 g epoxy chloropropane and 100 g distilled water to a three-necked flask equipped with a mechanical stirrer and a reflux condenser; after 30 min mechanical stirring at room temperature, weigh 30 g mimosa tannin, add it to the system, and heat up the system to 80° C.; weigh 45 g 20% sodium hydroxide solution in proportion [m(tannin):m(sodium hydroxide)=1:1.5], add it to the system slowly using a constant pressure dropping funnel; after adding sodium hydroxide solution, perform 80° C. thermal reaction for 3 h; after end of reaction, cool the obtained mixture to room temperature, dilute it to 1,000 mL using absolute ethyl alcohol, conduct suction filtration using a suction filter unit equipped with a 1 μm glass fiber filter membrane, then conduct rotary evaporation of the obtained filtrate by filtration (repeat this step twice), and repeat this step using acetone to obtain ET, and measure the epoxide equivalent of ET:EE=216 g/mol. Weigh 5 g ET and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 2.78 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

Embodiment 2: n.SUB.ET.:n.SUB.TETA.:n.SUB.U.=1:1:2.5

[0026] Add 150 g epoxy chloropropane and 100 g distilled water to a three-necked flask equipped with a mechanical stirrer and a reflux condenser; after 30 min mechanical stirring at room temperature, weigh 30 g mimosa tannin, add it to the system, and heat up the system to 80° C.; weigh 45 g 20% sodium hydroxide solution in proportion [m(tannin):m(sodium hydroxide)=1:1.5], add it to the system slowly using a constant pressure dropping funnel; after adding sodium hydroxide solution, perform 80° C. thermal reaction for 3 h; after end of reaction, cool the obtained mixture to room temperature, dilute it to 1,000 mL using absolute ethyl alcohol, conduct suction filtration using a suction filter unit equipped with a 1 μm glass fiber filter membrane, then conduct rotary evaporation of the obtained filtrate by filtration (repeat this step twice), and repeat this step using acetone to obtain ET, and measure the epoxide equivalent of ET:EE=216 g/mol. Weigh 5 g ET and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 3.47 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

Embodiment 3: n.SUB.ET.:n.SUB.TETA.:n.SUB.U.=1:1:3

[0027] Add 150 g epoxy chloropropane and 100 g distilled water to a three-necked flask equipped with a mechanical stirrer and a reflux condenser; after 30 min mechanical stirring at room temperature, weigh 30 g bayberry tannin, add it to the system, and heat up the system to 80° C.; weigh 45 g 20% sodium hydroxide solution in proportion [m(tannin):m(sodium hydroxide)=1:1.5], add it to the system slowly using a constant pressure dropping funnel; after adding sodium hydroxide solution, perform 80° C. thermal reaction for 3 h; after end of reaction, cool the obtained mixture to room temperature, dilute it to 1,000 mL using absolute ethyl alcohol, conduct suction filtration using a suction filter unit equipped with a 1 μm glass fiber filter membrane, then conduct rotary evaporation of the obtained filtrate by filtration (repeat this step twice), and repeat this step using acetone to obtain ET, and measure the epoxide equivalent of ET:EE=216 g/mol. Weigh 5 g ET and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 4.17 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

[0028] Contrast 1: n.sub.ET:n.sub.TETA:n.sub.U=1:1:0.5

[0029] Add 150 g epoxy chloropropane and 100 g distilled water to a three-necked flask equipped with a mechanical stirrer and a reflux condenser; after 30 min mechanical stirring at room temperature, weigh 30 g mimosa tannin, add it to the system, and heat up the system to 80° C.; weigh 45 g 20% sodium hydroxide solution in proportion [m(tannin):m(sodium hydroxide)=1:1.5], add it to the system slowly using a constant pressure dropping funnel; after adding sodium hydroxide solution, perform 80° C. thermal reaction for 3 h; after end of reaction, cool the obtained mixture to room temperature, dilute it to 1,000 mL using absolute ethyl alcohol, conduct suction filtration using a suction filter unit equipped with a 1 μm glass fiber filter membrane, then conduct rotary evaporation of the obtained filtrate by filtration (repeat this step twice), and repeat this step using acetone to obtain ET, and measure the epoxide equivalent of ET:EE=216 g/mol. Weigh 5 g ET and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 0.69 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

[0030] Contrast 2: n.sub.ET:n.sub.TETA:n.sub.U=1:1:4

[0031] Add 150 g epoxy chloropropane and 100 g distilled water to a three-necked flask equipped with a mechanical stirrer and a reflux condenser; after 30 min mechanical stirring at room temperature, weigh 30 g mimosa tannin, add it to the system, and heat up the system to 80° C.; weigh 45 g 20% sodium hydroxide solution in proportion [m(tannin):m(sodium hydroxide)=1:1.5], add it to the system slowly using a constant pressure dropping funnel; after adding sodium hydroxide solution, perform 80° C. thermal reaction for 3 h; after end of reaction, cool the obtained mixture to room temperature, dilute it to 1,000 mL using absolute ethyl alcohol, conduct suction filtration using a suction filter unit equipped with a 1 μm glass fiber filter membrane, then conduct rotary evaporation of the obtained filtrate by filtration (repeat this step twice), and repeat this step using acetone to obtain ET, and measure the epoxide equivalent of ET:EE=216 g/mol. Weigh 5 g ET and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 5.56 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

[0032] Contrast 3: n.sub.ET:n.sub.TETA:n.sub.U=1:1:0

[0033] Add 150 g epoxy chloropropane and 100 g distilled water to a three-necked flask equipped with a mechanical stirrer and a reflux condenser; after 30 min mechanical stirring at room temperature, weigh 30 g mimosa tannin, add it to the system, and heat up the system to 80° C.; weigh 45 g 20% sodium hydroxide solution in proportion [m(tannin):m(sodium hydroxide)=1:1.5], add it to the system slowly using a constant pressure dropping funnel; after adding sodium hydroxide solution, perform 80° C. thermal reaction for 3 h; after end of reaction, cool the obtained mixture to room temperature, dilute it to 1,000 mL using absolute ethyl alcohol, conduct suction filtration using a suction filter unit equipped with a 1 μm glass fiber filter membrane, then conduct rotary evaporation of the obtained filtrate by filtration (repeat this step twice), and repeat this step using acetone to obtain ET, and measure the epoxide equivalent of ET:EE=216 g/mol. Weigh 5 g ET and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

[0034] Contrast 4: n.sub.ET:n.sub.TETA:n.sub.U=1:0:2.5

[0035] Add 150 g epoxy chloropropane and 100 g distilled water to a three-necked flask equipped with a mechanical stirrer and a reflux condenser; after 30 min mechanical stirring at room temperature, weigh 30 g mimosa tannin, add it to the system, and heat up the system to 80° C.; weigh 45 g 20% sodium hydroxide solution in proportion [m(tannin):m(sodium hydroxide)=1:1.5], add it to the system slowly using a constant pressure dropping funnel; after adding sodium hydroxide solution, perform 80° C. thermal reaction for 3 h; after end of reaction, cool the obtained mixture to room temperature, dilute it to 1,000 mL using absolute ethyl alcohol, conduct suction filtration using a suction filter unit equipped with a 1 μm glass fiber filter membrane, then conduct rotary evaporation of the obtained filtrate by filtration (repeat this step twice), and repeat this step using acetone to obtain ET, and measure the epoxide equivalent of ET:EE=216 g/mol. Weigh 5 g ET in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 3.47 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

[0036] Contrast 5: n.sub.T:n.sub.TETA:n.sub.U=1:1:2.5

[0037] Add 30 g mimosa tannin and 100 g distilled water to a three-necked flask equipped with a mechanical stirrer and a reflux condenser; after stirring them evenly, heat up to 80° C. while stirring; weigh 45 g 20% sodium hydroxide solution in proportion [m(tannin):m(sodium hydroxide)=1:1.5], add it to the system slowly using a constant pressure dropping funnel; after adding sodium hydroxide solution, perform 80° C. thermal reaction for 3 h; after end of reaction, cool the obtained mixture to room temperature. Weigh 5 g tannin (T) and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 3.47 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

[0038] Contrast 6: n.sub.ET:n.sub.TETA:n.sub.U=1:1:2.5

[0039] The specific implementation method is shown in Embodiment 2; however, the difference is that the epoxide equivalent of ET in this contrast is 90 g/mol. Weigh 5 g ET and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 3.47 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

[0040] Contrast 7: n.sub.ET:n.sub.TETA:n.sub.U=1:1:2.5

[0041] The specific implementation method is shown in Embodiment 2; however, the difference is that the epoxide equivalent of ET in this contrast is 320 g/mol. Weigh 5 g ET and 4.84 g TETA in proportion, add them to a single-necked flask equipped with a magnetic rotor, and heat up to 60° C. for 4 h thermal reaction. Transfer the flask to an oil bath pan, heat up to 120° C., add 3.47 g urea, and after 12 h thermal reaction, prepare the obtained resin into 60% aqueous solution, which is adhesive.

[0042] The adhesives prepared using the above technology are used for preparation of three-layer poplar plywood; the double spread of lateral ply is 280 g/m.sup.2; hot-pressing technology: pressure 1 MPa, time 1 min/mm, temperature 220° C. After placing the pressed plywood for 1 week, perform a bonding strength test; the test conditions are: 24 h immersion in cold water, 3 h immersion in 63° C. warm water, and 3 h immersion in boiling water.

[0043] Referring to FIG. 2, the specific test results are shown. The environmentally-friendly water-resistant tannin-based wood adhesive prepared using the method provided by the invention has excellent water resistance, which is an obvious advantage compared with contrasts.

[0044] While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.