CN104194695A - Grafted nano ambary fiber crystal whisker modified urea formaldehyde resin adhesive and preparation method thereof - Google Patents

Abstract

The invention discloses a grafted nano kenaf fiber whisker modified urea-formaldehyde resin adhesive and a preparation method thereof, which is prepared from formaldehyde, urea, polyvinyl alcohol and a reaction enhancer, wherein the molar ratio of formaldehyde to urea is 1.1- 0.95:1, the addition of polyvinyl alcohol accounts for 0.1-0.8% of the total weight; the addition of the reaction enhancer accounts for 0.1-3.0% of the total weight; the preparation method includes adding the reaction enhancer and then adding the first batch of urea, the molar ratio It is 2.0-2.2: 1, add the second batch of urea, the molar ratio is 1.4-1.2:1, finally add the third batch of urea, the molar ratio is 0.95-1.1:1; the advantage of the present invention is: adopt the formaldehyde of low molar ratio and Urea is used as a raw material, and self-made acrylic acid grafted nano-kenaf fiber whiskers are added to increase the branching degree of resin molecules and the molecular weight of resin, so that the prepared low molar ratio urea-formaldehyde resin has low formaldehyde content, high bonding strength and low cost.

Description

A grafted nano-kenaf fiber whisker modified urea-formaldehyde resin adhesive and preparation method thereof

technical field

The invention relates to an adhesive, in particular to a grafted nano-kenaf fiber whisker-modified urea-formaldehyde resin adhesive and a preparation method thereof, belonging to the field of adhesives. the

Background technique

With the improvement of people's living standards and the continuous and stable development of construction, decoration, packaging and other industries, the output of wood-based panels in my country has grown rapidly. The total output of wood-based panels, plywood, furniture, and wood flooring has ranked first in the world for many years in a row. In 2013, the total output of wood-based panels in China was 272 million m ³ , accounting for about 50% of the world's total output. Based on the average production of 9m ³ wood-based panels per ton of adhesive, the consumption of wood adhesives in China in 2013 was about 30 million tons (solid content 50%), of which urea-formaldehyde resin and its modified products accounted for more than 80% of the total output of adhesives, occupying a dominant position . The reason why urea-formaldehyde resin adhesives can be widely used in the wood industry is that it has advantages that other resins cannot match, such as sufficient raw materials, low price, good water solubility, and light color of the adhesive layer. However, urea-formaldehyde resin also has some obvious disadvantages. In addition to poor aging resistance and water resistance, it cannot be used to prepare wood-based panels for outdoor use. Its fatal disadvantage is the release of formaldehyde from glued wood-based panels. With the improvement of people's quality of life and the enhancement of health and environmental awareness, people have increasingly noticed that urea-formaldehyde resin adhesives will release formaldehyde during preparation and use, and its glued wood-based panels will also continuously release formaldehyde during use, polluting Habitat environment, damage people's health.

At present, there are mainly four methods to reduce the release of formaldehyde from wood-based panels: 1) Using low molar ratio modified urea-formaldehyde resin adhesive; 2) Adding formaldehyde scavenger to the modified urea-formaldehyde resin adhesive; 3) Post-treatment of wood-based panels ; 4) Use other environmentally friendly adhesives. But all there are many defectives in these technical methods. For example: 1) Although the use of low molar ratio modified urea-formaldehyde resin adhesives can effectively reduce the formaldehyde emission of wood-based panel products, the bonding strength of the products is often reduced, which cannot meet the requirements of use; and it can lead to prolonged curing time and reduced production efficiency; 2) Adding formaldehyde scavenger to urea-formaldehyde resin adhesives for wood-based panels can effectively reduce the release of free formaldehyde from wood-based panels, but it often reduces the bonding strength of wood-based panels at the same time; at the same time, the price of general formaldehyde scavenger is often much higher than that of urea-formaldehyde resin adhesives. Adding improves product cost and reduces product competitiveness; 3) Carry out post-processing to wood-based panels, as the invention patent application with publication number CN1526528 discloses a method for preparing E1/EO grade environment-friendly wood-based panels using ammonia vacuum method. Manufacturing process; the utility model patent with publication number CN2394770 discloses a treatment device for reducing formaldehyde emission from wood-based panels. These post-processing methods not only make the manufacturing process of wood-based panels complicated, but also require huge investment in post-processing equipment and significantly increase production costs. ; 4) The use of other environmentally friendly adhesives, such as isocyanate adhesives, has led to a substantial increase in the production cost of wood-based panels and increased difficulty in the production process, which is difficult for enterprises and users to accept; the use of ordinary protein adhesives to prepare wood-based panels has low bonding strength and poor water resistance , Easy to mold, poor sizing performance, and easy to open glue for wood-based panels. To sum up, although the above measures can effectively reduce the release of free formaldehyde from wood-based panels, they cannot completely solve the problem of formaldehyde release, or cannot be popularized due to reasons such as high production costs. the

Contents of the invention

In order to solve the above problems, the present invention designs a grafted nano-kenaf fiber whisker-modified urea-formaldehyde resin adhesive and a preparation method thereof, adopting low molar ratio formaldehyde and urea as raw materials, and grafting nano-kenaf fibers by adding self-made acrylic acid Whiskers can increase the branching degree of resin molecules and increase the molecular weight of synthetic resins, which can make the resin molecules align in the curing process and increase the crystallinity of resin molecules, so that the prepared low molar ratio urea-formaldehyde resin not only has low formaldehyde content and high bonding strength, And the cost is low. the

Technical scheme of the present invention is:

A grafted nano-kenaf fiber whisker modified urea-formaldehyde resin adhesive, prepared from formaldehyde, urea, polyvinyl alcohol and a reaction enhancer, wherein the molar ratio of formaldehyde to urea is 1.1-0.95: 1, the The added amount of the polyvinyl alcohol accounts for 0.1-0.8% of the total weight; the added amount of the reaction enhancer accounts for 0.1-3.0% of the total weight.

Preferably, the molar ratio of formaldehyde to urea is 1.08-0.98:1, the amount of polyvinyl alcohol added accounts for 0.3-0.5% of the total weight, and the amount of reaction enhancer added accounts for 0.5-2.0% of the total weight. the

Wherein, the reaction enhancer is the crosslinking enhancer is acrylic acid grafted nano kenaf fiber whiskers;

The solid content of the reaction enhancer is 100%.

A preparation method of the above-mentioned grafted nano kenaf fiber whisker modified urea-formaldehyde resin adhesive, comprising the following steps:

1) Put formaldehyde into the reaction kettle, adjust the pH value to 7.0 with alkali, add reaction enhancer, add polyvinyl alcohol solution at 50°C, and keep warm for 20 minutes; then add the first batch of urea, so that the molar ratio of formaldehyde to urea is 2.0-2.2︰1, keep warm at 60°C for 20 minutes; then raise the temperature to 90°C within 40 minutes, keep warm for 1 hour, and keep the pH value at 6.0-7.0;

2) Control the pH value to 3.4-4.2, react at 95°C to viscosity: 25°C, apply -4 cups for 22-24 seconds, add the second batch of urea, make the molar ratio of formaldehyde to urea 1.4-1.2:1, and adjust the pH The value is 4.2-4.5, react to viscosity: 25°C, apply -4 cups for 24-27 seconds, adjust the pH value to 7.0-7.5;

3) Finally, add the third batch of urea, so that the molar ratio of formaldehyde to urea is 0.95-1.1:1, react for 30 minutes, cool down to 35°C and discharge.

Wherein, the formaldehyde concentration is 36.5-37.5%; the alkali is selected from one or more mixtures of sodium hydroxide, sodium carbonate, and triethanolamine; the acid is selected from formic acid, acetic acid, ammonium chloride, citric acid One or more of them are mixed. the

Among them, 1 mol nano-kenaf cellulose suspension is placed in a four-necked flask, kept at a constant temperature to 80 ° C, and 3.5 mol/L potassium persulfate is used as an initiator to initiate it; then 1.8 mol of acrylic acid monomer is added to obtain a mixture and then extract the polymerization reaction mixture with ethyl acetate at room temperature to remove the acrylic acid polymer; finally use a rotary evaporator to extract at 50°C to obtain the cross-linking enhancer used in the present invention. the

The nano kenaf cellulose has a diameter of 9-46nm and an aspect ratio of 6-150. the

The advantages of the present invention are:

1) The present invention uses self-made acrylic acid grafted nano-kenaf fiber whiskers to modify urea-formaldehyde resin, which is added in the first step of resin preparation, which improves the molecular branching degree of the initial reaction of urea-formaldehyde resin, increases the molecular weight of the resin under the same viscosity, and reduces Increase the viscosity of the resin, prolong the storage period of the resin, so that the urea-formaldehyde resin produced has a high bonding strength when the molar ratio of formaldehyde to urea is 0.95-1.1:1, which can make the glued wood-based panel products glued together The strength reaches the national standard;

2) Self-made acrylic acid grafted nano-kenaf fiber whisker modified urea-formaldehyde resin can increase the content of crystalline regions in the synthetic resin, make the resin form a large number of crystalline regions during the curing process, and reduce the formaldehyde emission of its glued products;

3) The self-made acrylic-grafted nano-kenaf fiber whiskers used in the present invention are derived from the natural plant kenaf, which is a renewable resource and helps to solve the problem of depletion of synthetic fossil raw materials used in conventional wood-based panel adhesives. Principles of environmental protection and sustainable development;

4) In the method of the present invention, the basic "alkali-acid-alkali" synthesis process of urea-formaldehyde resin is not changed, and only a reaction enhancer needs to be added when starting feeding, the process is simple, and there is no need to modify existing equipment.

The present invention will be further described below in conjunction with implementation. the

Detailed ways

Preferred embodiments of the present invention are described below, and it should be understood that the preferred embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention. the

Unless otherwise stated, the percentages used in the present invention are all percentages by weight. the

Example 1

A grafted nano kenaf fiber whisker modified urea-formaldehyde resin adhesive, prepared from formaldehyde, urea, polyvinyl alcohol and a reaction enhancer, wherein the molar ratio of formaldehyde to urea is 1.07: 1, each raw material See Table 1 below:

Table 1 The molar ratio of formaldehyde to urea is 1.07︰1 Raw material ratio of urea-formaldehyde resin

Wherein, the reaction enhancer (i.e. cross-linking enhancer) is acrylic acid grafted nano kenaf fiber whiskers;

The solid content of the reaction enhancer is 100%.

A preparation method of the above-mentioned grafted nano kenaf fiber whisker modified urea-formaldehyde resin adhesive, comprising the following steps:

1) Put 591.2 parts by weight of 37% industrial formaldehyde into the reaction kettle, adjust the pH value to 7.0 with lye, add 5 parts by weight of reaction enhancer, heat up to 50°C, add 30 parts by weight of polyvinyl alcohol solution, and keep warm for 20 minutes ; Add 208.3 parts by weight of the first batch of urea, and keep it warm at 60°C for 20 minutes; within 40 minutes, raise the temperature to 90°C, keep it warm for 1 hour, and keep the pH value at 6.0-7.0;

2) Use acid solution to control the pH value of 3.4-4.2, react at 95°C to viscosity: 25°C, apply -4 cups for 22-24 seconds, add the second batch of urea 128.2 parts by weight, and use acid solution to adjust the pH value to 4.2- 4.5, react to viscosity: 25°C, apply -4 cups for 24-27 seconds, adjust the pH value to 7.0-7.5 with lye;

3) Add 72.3 parts by weight of the third batch of urea, react for 30 minutes, lower the temperature to 35°C, adjust the pH value to 7.0-8.0 with lye, and discharge.

Result: Resin Quality Index

solid content 54-59%

pH value 7.2-7.5 Viscosity(20℃) 60-180mPa*s curing speed 60-90s Free formaldehyde content ≤0.1% Applicable period ≥6 hours Storage period 30-60 days

Wherein, the cross-linking enhancer is acrylic acid grafted nano kenaf fiber whiskers, and the synthesis process is as follows: 1 mol nano kenaf cellulose suspension is placed in a four-necked flask, and the temperature is kept at 80°C, and 3.5 mol/L Potassium persulfate is used as initiator to initiate it, and the initiation time is 15 minutes; Then add the acrylic acid monomer reaction of 1.8mol for 8 hours, obtain the mixture that grafting rate is about 21%; Extract at room temperature for 24 hours to remove the acrylic acid polymer; finally use a rotary evaporator to extract at 50°C for 40 minutes to obtain the crosslinking enhancer for the present invention. the

The nano kenaf cellulose has a diameter of 9-46nm and an aspect ratio of 6-150. the

Comparative example 1

The raw material formula is shown in the following table 2:

Table 2 The molar ratio of formaldehyde to urea is 1.07:1 Raw material ratio of urea-formaldehyde resin:

Be 1.07 to prepare raw materials by formaldehyde and urea mol ratio, and reaction step comprises:

1) Put 591.2 parts by weight of 37% industrial formaldehyde into the reactor, add 3 parts by weight of polyvinyl alcohol solution, adjust the pH value to 7.0 with lye, add 208.3 parts by weight of the first batch of urea, and heat up to 90°C within 1 hour , keep warm for 1 hour, and keep the pH value at 6.0-7.0;

2) Use acid solution to control the pH value to 3.4-4.2, react at 95°C to viscosity: 25°C, apply -4 cups for 24-27 seconds, add the second batch of urea 128.2 parts by weight, keep warm for 30 minutes, and adjust the pH with lye The value is 7.0-7.5;

3) Add 72.3 parts by weight of the third batch of urea, react for 30 minutes, lower the temperature to 35° C., adjust the pH value to 7.0-8.0 with lye, and discharge. the

Results: Resin Quality Indicators solid content 54-59% pH value 7.2-7.5 Viscosity (20°C) 100-250 mPa*s curing speed 80-110s Free formaldehyde content ≤0.3% Applicable period ≥6 hours Storage period 20-40 days

Example 2

A grafted nano kenaf fiber whisker modified urea-formaldehyde resin adhesive is prepared from formaldehyde, urea, polyvinyl alcohol and a reaction enhancer, wherein the mol ratio of the formaldehyde to urea is 1:0.98, each raw material See Table 3 below:

Table 3 The molar ratio of formaldehyde to urea is 1:0.98 Raw material ratio of urea-formaldehyde resin raw material moles content,% weight fraction Remark formaldehyde 7.12 37 569.8 response enhancer 100 10 polyvinyl alcohol 10 50 urea 7.04 99.8 430.2 U1=210.8 copies U2=140.5 parts U3=78.9 copies Acid solution (formic acid + ammonium chloride) 30 Appropriate amount 50% each Lye (sodium hydroxide + triethanolamine) 30 Appropriate amount 50% each

It is 1:0.98 to prepare raw materials by formaldehyde and urea molar ratio, and reaction step comprises:

1) Put 569.8 parts by weight of 37% industrial formaldehyde into the reaction kettle, adjust the pH value to 7.0 with lye, add 10 parts by weight of reaction enhancer, heat up to 50°C, add 50 parts by weight of polyvinyl alcohol solution, and keep warm for 20 minutes ; Add 210.8 parts by weight of the first batch of urea, keep the temperature at 60°C for 20 minutes; raise the temperature to 90°C within 40 minutes, keep the temperature for 1 hour, and keep the pH value at 6.0-7.0;

2) Use acid solution to control the pH value of 3.4-4.2, react at 95°C to viscosity: 25°C, apply -4 cups for 22-24 seconds, add the second batch of urea 140.5 parts by weight, and use acid solution to adjust the pH value to 4.2- 4.5, react to viscosity: 25°C, apply -4 cups for 24-27 seconds, adjust the pH value to 7.0-7.5 with lye;

3) Add 78.9 parts by weight of the third batch of urea, react for 30 minutes, lower the temperature to 35°C, adjust the pH value to 7.0-8.0 with lye, and discharge.

Wherein, the cross-linking enhancer is acrylic acid grafted nano kenaf fiber whiskers, and the synthesis process is as follows: 1 mol nano kenaf cellulose suspension is placed in a four-necked flask, and the temperature is kept at 80°C, and 3.5 mol/L Potassium persulfate initiates it as initiator, and the initiation time is 15 minutes; Add the acrylic acid monomer reaction of 1.8mol then for 8 hours, obtain the mixture that grafting ratio is about 21%; Polymerized reaction product is used ethyl acetate again Extract at room temperature for 24 hours to remove the acrylic acid polymer; finally use a rotary evaporator to extract at 50°C for 40 minutes to obtain the crosslinking enhancer for the present invention. the

The nano kenaf cellulose has a diameter of 9-46nm and an aspect ratio of 6-150. the

Results: Resin Quality Indicators solid content 58-62% pH value 7.2-7.5 Viscosity (20°C) 60-180 mPa*s curing speed 60-90s Free formaldehyde content ≤0.07% Applicable period ≥6 hours Storage period 30-60 days

Comparative example 2

Raw material formula sees the following table 4:

Table 4 The molar ratio of formaldehyde to urea is 1:0.98 Raw material ratio of urea-formaldehyde resin: raw material moles content,% weight fraction Remark formaldehyde 7.12 37 569.8 polyvinyl alcohol 100 5 urea 7.04 99.8 430.2 U1=210.8 copies U2=140.5 parts U3=78.9 parts Acid solution (formic acid + ammonium chloride) 30 Appropriate amount 50% each Lye (sodium hydroxide + triethanolamine) 30 Appropriate amount 50% each

It is 1:0.98 to prepare raw materials by formaldehyde and urea molar ratio, and reaction step comprises:

1) Put 569.8 parts by weight of 37% industrial formaldehyde into the reaction kettle, add 5 parts by weight of polyvinyl alcohol solution, adjust the pH value to 7.0 with lye, add 210.8 parts by weight of the first batch of urea, and heat up to 90°C within 1 hour , keep warm for 1 hour, and keep the pH value at 6.0-7.0;

2) Use acid solution to control the pH value of 3.4-4.2, react at 95°C to viscosity: 25°C, apply -4 cups for 24-27 seconds, add the second batch of urea 140.5 parts by weight, keep warm for 30 minutes, and adjust the pH with lye The value is 7.0-7.5;

3) Add 78.9 parts by weight of the third batch of urea, react for 30 minutes, lower the temperature to 35°C, adjust the pH value to 7.0-8.0 with lye, and discharge.

Results: Resin Quality Indicators solid content 54-59% pH value 7.0-7.5 Viscosity (20°C) 100-250 mPa*s curing speed 100-120s Free formaldehyde content ≤0.15% Applicable period ≥6 hours Storage period 20-40 days

Experimental example

Add 0.5% ammonium chloride and 0.3% citric acid to the urea-formaldehyde resins of Example 1-2 and Comparative Example 1-2 respectively, and then add 30% flour to make three-layer plywood of 400×400mm.

Poplar veneer: dry to 6-10% moisture content; thickness 1.5mm;

The veneer adhesive used the product of Example 1-2 of the present invention and the product of Comparative Example 1-2.

Plywood is prepared by the following normal process:

(1) Glue sizing: Glue is applied on both sides of the core board, and the amount of glue applied is 320-360g/m ² ;

(2) Aging method and time: closed aging, 20-30 minutes;

(3) Pre-compression pressure and time: pre-compression for 40 minutes, pressure 0.9MPa;

(4) Hot pressing pressure: 1.0MPa, hot pressing temperature is 120-130oC, hot pressing time is high pressure 90s/mm.

According to the test method of GB/T17657-1999 "Physical and Chemical Properties of Wood-Based Panels and Decorated Wood-based Panels", the performance test of the produced plywood products is carried out. The test results are shown in Table 5. the

Table 5 Formaldehyde emission and bonding strength of glued plywood

The experimental results show that the modified urea-formaldehyde resin prepared by the technology of the present invention can effectively reduce the formaldehyde emission of plywood, improve the water-resistant bonding performance, and reach the standard of class II plywood in the national standard (poplar wood ≥ 0.70MPa).

cost analysis

The modified urea-formaldehyde resin adhesive of the present invention is easy to use, does not need to modify the existing wood-based panel production equipment and process, and therefore does not need to increase equipment investment.

At present, the price of the environment-friendly melamine modified urea-formaldehyde resin adhesive with 50% solid content is 3000-4000 yuan/ton, and the price of phenolic resin adhesive is 5000-6000 yuan/ton. The modified urea-formaldehyde resin adhesive (55% solid content of the present invention ) The cost is about 2000 yuan/ton, far lower than phenolic resin adhesive and melamine modified urea-formaldehyde resin adhesive, and close to pure urea-formaldehyde resin adhesive, but the environmental protection and water-resistant bonding performance are greatly improved. the

In addition, the raw materials used in the present invention are commonly used raw materials in the production of this field, all of which can be obtained from the market, and will not affect the production results; the various equipment used in the present invention are all used in the production process of this field The conventional equipment, and the operation and parameters of each equipment are carried out according to the conventional operation, and there is nothing special about it. the

Claims (6)

1. the whisker modified urea-formaldehyde resin adhesive of engrafted nanometer kenaf, it is characterized in that: be prepared from by formaldehyde, urea, polyvinyl alcohol and increased response agent, wherein, described formaldehyde and the mol ratio of urea are 1.1-0.95 ︰ 1, and the add-on of described polyvinyl alcohol accounts for the 0.1-0.8% of gross weight; The add-on of described increased response agent accounts for the 0.1-3.0% of gross weight.

2. the whisker modified urea-formaldehyde resin adhesive of engrafted nanometer kenaf according to claim 1, it is characterized in that: described formaldehyde and the mol ratio of urea are 1.08-0.98 ︰ 1, the add-on of polyvinyl alcohol accounts for the 0.3-0.5% of gross weight, and the add-on of increased response agent accounts for the 0.5-2.0% of gross weight.

3. the whisker modified urea-formaldehyde resin adhesive of engrafted nanometer kenaf according to claim 1 and 2, is characterized in that: described crosslinking enhancer is acrylic acid-grafted nanometer kenaf whisker; The solids content of described increased response agent is 100%.

4. a preparation method for the whisker modified urea-formaldehyde resin adhesive of engrafted nanometer kenaf as described in claim 1-3 any one, is characterized in that, comprises the following steps:

1) formaldehyde is put into reactor, regulating pH value with alkali is 7.0, adds increased response agent, adds polyvinyl alcohol solution at 50 DEG C, is incubated 20 minutes; Add first urea, making formaldehyde and urea mol ratio was 2.0-2.2 ︰ 1 again, 60 DEG C of insulations 20 minutes; But in 40 minutes, be warming up to 90 DEG C, and be incubated 1 hour, keeping pH value is 6.0-7.0;

2) controlling pH value is 3.4-4.2, reacts to viscosity at 95 DEG C: 25 DEG C, be coated with-4 glasss of 22-24 seconds, add second batch urea, making formaldehyde and urea mol ratio is 1.4-1.2:1, and regulating pH value is 4.2-4.5, react to viscosity: 25 DEG C, be coated with-4 glasss of 24-27 seconds, regulating pH value is 7.0-7.5;

3) finally add the 3rd batch of urea, making formaldehyde and urea mol ratio is 0.95-1.1:1, reacts 30 minutes, the 35 DEG C of dischargings of lowering the temperature.

5. the preparation method of the whisker modified urea-formaldehyde resin adhesive of engrafted nanometer kenaf according to claim 4, is characterized in that: described concentration of formaldehyde is 36.5-37.5%; Described alkali is selected from one or more mixing in sodium hydroxide, sodium carbonate, trolamine; Described acid is selected from one or more mixing in formic acid, acetic acid, ammonium chloride, citric acid.

6. the preparation method of the whisker modified urea-formaldehyde resin adhesive of engrafted nanometer kenaf according to claim 4, it is characterized in that: described crosslinking enhancer is acrylic acid-grafted nanometer kenaf whisker, its synthesis technique is: 1mol nanometer kenaf element suspension is placed in to four-hole boiling flask, constant temperature to 80 DEG C, causes it as initiator with 3.5mol/L Potassium Persulphate; Then the Acrylic Acid Monomer that adds 1.8mol, obtains mixture; Again polymerization reaction mixture is at room temperature extracted and removes acrylate copolymer by ethyl acetate; Finally obtain the present invention's crosslinking enhancer with Rotary Evaporators 50 DEG C of extractings.