1. An aldehyde-free adhesive synthesized from papermaking black liquor is characterized by comprising the following components: black liquor of paper making, polyvinyl alcohol, oxidized starch, an initiator, a film forming substance and a preservative.

2. The aldehyde-free adhesive of claim 1, wherein the aldehyde-free adhesive comprises the following components in parts by weight: 55-80 parts of papermaking black liquor, 5-10 parts of polyvinyl alcohol, 1-5 parts of oxidized starch, 1-20 parts of initiator, 1-5 parts of film forming substance and 0.1-0.5 part of preservative.

3. The aldehyde-free adhesive according to claim 1 or 2, wherein the papermaking black liquor is derived from waste liquor produced in wood papermaking, bagasse papermaking, bamboo papermaking, reed papermaking, straw papermaking and mushroom grass papermaking.

4. The aldehyde-free adhesive according to claim 3, wherein the papermaking black liquor is distilled and concentrated in advance to remove 40-50% of water by mass, and then is used as a raw material for preparing the aldehyde-free adhesive, and the solid content of the concentrated papermaking black liquor is 20-45%.

5. The aldehyde-free adhesive of claim 1 or 2, wherein the initiator is selected from at least one of a persulfate, a sulfite, a sulfate, a phenolic compound, and an aldehyde;

and/or the persulfate is selected from at least one of potassium persulfate, ammonium persulfate and sodium persulfate, the sulfite is selected from at least one of sodium sulfite, potassium sulfite and calcium sulfite, and the sulfate is sodium dodecyl sulfate;

and/or the phenolic compound is selected from at least one of resorcinol, phenol and bisphenol A;

and/or the aldehyde is formaldehyde.

6. The aldehyde-free adhesive of claim 1 or 2, wherein the film forming material is at least one selected from the group consisting of polyvinyl acetate emulsion, vinyl acetate-acrylic emulsion, styrene-acrylic emulsion, and acrylic emulsion.

7. The aldehyde-free adhesive of claim 1 or 2, wherein the preservative is selected from at least one of borax, pentachlorophenol, and zinc oxide.

8. The aldehyde-free adhesive of claim 1 or 2, wherein the aldehyde-free adhesive comprises the following components in parts by weight: 5-8 parts of polyvinyl alcohol, 5-8 parts of oxidized starch, 0.01-0.05 part of persulfate, 5-8 parts of styrene-acrylic emulsion, 0.008-0.015 part of sulfite, 0.01-0.025 part of borax, 0-0.3 part of zinc oxide, 55-80 parts of papermaking black liquor, 1-5 parts of formaldehyde and 0-0.03 part of sodium dodecyl sulfate.

9. The method for preparing the aldehyde-free adhesive according to any one of claims 1 to 8, wherein the method comprises the steps of adding the components into the papermaking black liquor, uniformly stirring, raising the temperature to 70-95 ℃, reacting for 1-3 hours, cooling to 30-60 ℃, discharging and packaging.

10. Use of the aldehyde-free adhesive of any one of claims 1 to 8 in the preparation of artificial boards, including plywood, particle board and fiber board.

Background

Most of the artificial board production in China is applied to furniture manufacturing and interior decoration, and adhesives used for manufacturing various indoor artificial boards are mainly urea-formaldehyde resin adhesives, so that the problem of high free formaldehyde emission is generally solved. The formaldehyde is released continuously from the products made using the urea formaldehyde resin adhesive. Formaldehyde is a toxic gas with strong irritation, which not only pollutes the environment, but also has strong irritation to the eyes, nose, throat and other organs of people, causing the abnormality of lung function, liver function and immune function.

The formaldehyde in the environment polluted by high-concentration formaldehyde can cause various diseases such as throat inflammation, respiratory tract damage and serious carcinogenesis after long-term life. Recent authoritative investigation shows that in cities of China, after the pollutants of a coal smoke type and a photochemical smog type, modern people are trapped in a third-party pollution period of indoor air pollution, and the most serious indoor air pollution is caused by the adhesives, the artificial boards and the coatings in turn. Therefore, the development of environment-friendly adhesives has become a necessary trend and becomes a new hotspot in the field of adhesive research.

The prior art CN110885668A discloses an aldehyde-free adhesive and a preparation method thereof. The formaldehyde-free adhesive comprises the following components in parts by weight: 10-40 parts of soybean derivative, 0.1-1.5 parts of developing agent, 80-160 parts of water, 0.1-0.8 part of chemical modifier and 0.5-2.5 parts of cross-linking agent. The components are easy to obtain, the cost is low, formaldehyde is not contained, and the bonding strength of the formaldehyde-free adhesive is excellent. However, the protein macromolecular structure of the soybean protein needs to be utilized to perform various chemical reactions with the cross-linking agent, and the soybean protein has high cost, so that the popularization and the application of the type of aldehyde-free adhesive are prevented.

The prior art CN 112694582A discloses a method for synthesizing a lignin-based phenolic resin adhesive by directly replacing phenol with lignin, which comprises the following steps: (1) crushing, sieving, washing and drying the raw materials to obtain raw material powder; (2) adding 50g of raw material powder into 500ml of acidified tetrahydrofurfuryl alcohol, controlling the reaction temperature at 135 ℃ and the reaction time at 90min to obtain a pretreatment material; (3) carrying out non-woven fabric suction filtration on the pretreated material to obtain filtrate, slowly dripping the filtrate into 2000ml of distilled water, and carrying out sedimentation, centrifugation and drying to obtain lignin; (4) mixing lignin and phenol to obtain a mixed solution, adding 40ml of sodium hydroxide solution and formaldehyde into the mixed solution, and carrying out two-step reaction to obtain a target product. However, in the method, the acidified tetrahydrofurfuryl alcohol is used for extracting lignin from the raw material, and the obtained high-activity lignin is mixed with phenol to synthesize the lignin-based phenolic resin. Without being able to directly utilize the lignin.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The first purpose of the invention is to provide an aldehyde-free adhesive synthesized by papermaking black liquor.

The second purpose of the invention is to provide a preparation method of the aldehyde-free adhesive.

The third purpose of the invention is to provide the application of the aldehyde-free adhesive in the preparation of artificial boards.

In order to achieve the purpose, the technical scheme of the invention is as follows:

the invention relates to an aldehyde-free adhesive synthesized by papermaking black liquor, which comprises the following components: black liquor of paper making, polyvinyl alcohol, oxidized starch, an initiator, a film forming substance and a preservative.

Preferably, the aldehyde-free adhesive comprises the following components in parts by weight: 55-80 parts of papermaking black liquor, 5-10 parts of polyvinyl alcohol, 5-10 parts of oxidized starch, 1-20 parts of initiator, 5-10 parts of film forming substance and 0.01-0.5 part of preservative.

Preferably, the papermaking black liquor is derived from waste liquor generated in wood papermaking, bagasse papermaking, bamboo papermaking, reed papermaking, straw papermaking and fungus grass papermaking.

Preferably, the papermaking black liquor is distilled and concentrated, water with the mass content of 40-50% is removed, then the papermaking black liquor is used as a raw material for preparing the aldehyde-free adhesive, and the solid content of the concentrated papermaking black liquor is 20-45%.

Preferably, the initiator is selected from at least one of persulfates, sulfites, sulfates, phenolic compounds, and aldehydes.

Preferably, the persulfate is at least one selected from potassium persulfate, ammonium persulfate and sodium persulfate, the sulfite is at least one selected from sodium sulfite, potassium sulfite and calcium sulfite, and the sulfate is sodium dodecyl sulfate.

Preferably, the phenolic compound is selected from at least one of resorcinol, phenol, bisphenol a; the aldehyde is formaldehyde.

Preferably, the film-forming material is at least one selected from polyvinyl acetate emulsion, vinyl acetate-acrylic emulsion, styrene-acrylic emulsion and acrylic emulsion.

Preferably, the preservative is selected from at least one of borax, pentachlorophenol and zinc oxide.

Preferably, the aldehyde-free adhesive comprises the following components in parts by weight: 5-8 parts of polyvinyl alcohol, 5-8 parts of oxidized starch, 0.01-0.05 part of persulfate, 5-8 parts of styrene-acrylic emulsion, 0.008-0.015 part of sulfite, 0.01-0.025 part of borax, 0-0.3 part of zinc oxide, 55-80 parts of papermaking black liquor, 1-5 parts of formaldehyde and 0-0.03 part of sodium dodecyl sulfate.

The invention also relates to a preparation method of the aldehyde-free adhesive, which comprises the steps of adding the components into the papermaking black liquor, uniformly stirring to fully mix the components, and then immediately using or storing in a sealed manner.

The invention also relates to application of the aldehyde-free adhesive in preparing artificial boards, wherein the artificial boards comprise plywood, shaving boards and fiber boards.

The invention has the beneficial effects that:

the invention provides an aldehyde-free adhesive synthesized from papermaking black liquor, which comprises the raw materials of papermaking black liquor, polyvinyl alcohol, oxidized starch, an initiator, a film forming substance and a preservative. The invention utilizes the lignosulfonate contained in the papermaking black liquor, and can be used as a raw material of the aldehyde-free adhesive, thereby avoiding environmental pollution and human body injury caused by formaldehyde in the adhesive. The aldehyde-free adhesive is used for manufacturing artificial boards, and has the characteristics of high adhesive strength, good water resistance, no aldehyde and environmental protection.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.

The embodiment of the invention relates to an aldehyde-free adhesive synthesized by papermaking black liquor, which comprises the following components: black liquor of paper making, polyvinyl alcohol, oxidized starch, an initiator, a film forming substance and a preservative.

In one embodiment of the invention, the aldehyde-free adhesive comprises the following components in parts by weight: 55-80 parts of papermaking black liquor, 5-10 parts of polyvinyl alcohol, 5-10 parts of oxidized starch, 1-20 parts of initiator, 5-10 parts of film forming substance and 0.01-0.5 part of preservative.

Wherein the papermaking black liquor is derived from waste liquor generated in wood papermaking, bagasse papermaking, bamboo papermaking, reed papermaking, straw papermaking and fungus grass papermaking. The waste liquor produced by the alkaline pulping process of the paper industry is dark brown, so the waste liquor is called black liquor. The black liquor contains a large amount of suspended solids, organic pollutants and toxic substances, and the direct discharge of the black liquor into a water body can cause serious pollution. However, the black liquor also contains a large amount of lignosulfonate, which can be used as a raw material for the aldehyde-free binder.

Because the paper-making black liquor raw pulp has high water content, the invention preferably carries out distillation concentration in advance, namely, water with the mass content of 40-50% is removed, and then the obtained product is used as a raw material for preparing the aldehyde-free adhesive. The solid content of the concentrated papermaking black liquor is 20-45%.

The oxidized starch is a modified starch obtained by oxidizing starch in acid, alkali and neutral media under the action of an oxidizing agent. The oxidized starch reduces the gelatinization temperature of the starch, reduces the viscosity of hot paste and increases the thermal stability, and the oxidized starch is a thickening agent with low viscosity and high concentration and is used for replacing soybean protein.

Because the lignosulfonate contains hydroxymethyl, the lignosulfonate can perform a crosslinking reaction with carboxyl on oxidized starch to form a crosslinked network structure, so that the water-resistant adhesive bonding performance of the aldehyde-free adhesive is enhanced. If lignin is directly used as a raw material, the lignin needs to be degraded at high temperature and high pressure so as to generate a hydroxymethylation reaction, and the content of hydroxymethyl in the lignin is increased.

In one embodiment of the present invention, the initiator is selected from at least one of persulfates, sulfites, sulfates, phenolic compounds, and aldehydes.

Furthermore, the persulfate is selected from at least one of potassium persulfate, ammonium persulfate and sodium persulfate, the sulfite is selected from at least one of sodium sulfite, potassium sulfite and calcium sulfite, and the sulfate is sodium dodecyl sulfate. Because the single persulfate is not suitable for reaction initiation, and the persulfate and the sulfate are jointly used to form a redox system, free radicals are generated through redox reaction, and the whole process only involves the transfer of free electrons, the reaction activation energy is low, and the method is suitable for reaction at low temperature. On the basis, the sulfate is added, so that the starch molecules can be depolymerized, active groups in the molecules are exposed, the crosslinking reaction is facilitated, and meanwhile, the initiator is added, so that the temperature is slowly increased, a more compact crosslinking network is obtained, and the bonding strength of the adhesive is improved.

In one embodiment of the present invention, the phenolic compound is selected from at least one of resorcinol, phenol, bisphenol a; the aldehyde is formaldehyde. Because the addition amount of formaldehyde as an initiator is less, the formaldehyde is consumed after reaction and cannot be remained in the adhesive.

In one embodiment of the present invention, the film forming material is at least one selected from the group consisting of polyvinyl acetate emulsion, vinyl acetate-acrylic emulsion, styrene-acrylic emulsion, and acrylic emulsion. The film-forming material is capable of adhering to a material to form a film, mainly contains a polymer resin and water, and can be also called as an aqueous emulsion, wherein the solid content is 40-60 wt%.

In one embodiment of the invention, the preservative is selected from at least one of borax, pentachlorophenol, zinc oxide.

In one embodiment of the invention, the aldehyde-free adhesive comprises the following components in parts by weight: 5-8 parts of polyvinyl alcohol, 5-8 parts of oxidized starch, 0.01-0.05 part of persulfate, 5-8 parts of styrene-acrylic emulsion, 0.008-0.015 part of sulfite, 0.01-0.025 part of borax, 0-0.3 part of zinc oxide, 55-80 parts of papermaking black liquor, 1-5 parts of formaldehyde and 0-0.03 part of sodium dodecyl sulfate.

The embodiment of the invention also relates to a preparation method of the aldehyde-free adhesive, which comprises the steps of adding the components into the papermaking black liquor, uniformly stirring to fully mix the components, and then immediately using or hermetically storing. Specifically, the preparation method comprises the steps of adding the components except the papermaking black liquor into the papermaking black liquor, uniformly stirring, heating to 70-95 ℃, reacting for 1-3 hours, cooling to 30-60 ℃, discharging and packaging.

The embodiment of the invention also relates to application of the aldehyde-free adhesive in preparing the artificial board. The artificial board is a board or a molded product which is made by taking wood or other non-wood plants as raw materials, separating the raw materials into various unit materials through certain mechanical processing and then gluing the unit materials with or without adhesive and other additives. The preparation method comprises the steps of cutting and drying the veneers, the wood chips and the wood shavings, then gluing, forming and pressurizing to obtain the required board.

The artificial board comprises plywood, shaving board and fiberboard.

The plywood is a board which is made by rotary cutting steamed and softened log into large sheets, then bonding the large sheets by synthetic resin adhesive with good water resistance, pressurizing, drying, sawing edges and finishing the surface. The number of layers is odd, and is generally 3-13, which are called three-ply board, five-ply board, etc. The wood used for making plywood includes basswood, birch, water ash, beech, colored wood, eucalyptus, etc.

The fiberboard is a board prepared by crushing, soaking and grinding waste materials such as barks, wood shavings, branches and the like into wood pulp, and then carrying out pressure forming and drying treatment. The molding temperature and pressure are different, so that the molding can be divided into three types, namely hard, semi-hard and soft.

Particle board is a board pressed from wood shavings or wood fiber stock with or without size applied. The shaving board has small density, uniform material, easy moisture absorption and low strength.

Example 1

An aldehyde-free adhesive synthesized from papermaking black liquor comprises the following components in parts by weight: 5 parts of polyvinyl alcohol, 5 parts of oxidized starch, 0.01 part of sodium persulfate, 5 parts of styrene-acrylic emulsion, 0.008 part of sodium sulfite, 0.01 part of borax, 55 parts of papermaking black liquor and 1 part of formaldehyde.

Adding the components into the papermaking black liquor, uniformly stirring, heating to 85 ℃, reacting for 1.5 hours, cooling to 30 ℃, discharging and packaging.

Example 2

An aldehyde-free adhesive synthesized from papermaking black liquor comprises the following components in parts by weight: 8 parts of polyvinyl alcohol, 8 parts of oxidized starch, 0.05 part of sodium persulfate, 8 parts of styrene-acrylic emulsion, 0.015 part of sodium sulfite, 0.025 part of borax, 0.3 part of zinc oxide, 80 parts of papermaking black liquor, 3 parts of formaldehyde and 0.03 part of sodium dodecyl sulfate.

The procedure was as in example 1.

Example 3

An aldehyde-free adhesive synthesized from papermaking black liquor comprises the following components in parts by weight: 6 parts of polyvinyl alcohol, 6 parts of oxidized starch, 0.03 part of sodium persulfate, 6 parts of styrene-acrylic emulsion, 0.010 part of sodium sulfite, 0.015 part of borax, 0.15 part of zinc oxide, 60 parts of papermaking black liquor, 5 parts of formaldehyde and 0.15 part of sodium dodecyl sulfate.

The procedure was as in example 1.

The black paper-making liquid in the above examples is from Yifuke county, Ming city, Fujian province, and the solid content after evaporation and concentration is 30-35%.

Based on example 3, the raw materials and the amounts used were changed to obtain comparative examples 1 to 5. The specific settings are shown in table 1.

TABLE 1

Examples	Altered originalMaterials and dosage
		Comparative example 1	Oxidized starch was replaced with soybean flour, and other raw materials and amounts were the same as in example 3
Comparative example 2	Sodium persulfate was replaced with sodium sulfite, and the other raw materials and amounts were the same as in example 3
		Comparative example 3	Sodium sulfite was replaced with sodium persulfate, and the other raw materials and amounts were the same as in example 3
Comparative example 4	Sodium dodecyl sulfate was not used, and other raw materials and amounts were the same as in example 3
		Comparative example 5	The black liquor is not concentrated, and other raw materials and the using amount are the same as those in example 3

Test example

The aldehyde-free adhesives prepared in the above examples and comparative examples were mixed with wood fibers at a mass ratio of 1:1, respectively, and then added to a mixing agitator to mix uniformly. Then placing the mixture into a hot-pressing mold frame, and paving the mixture uniformly and flatly. And cold pressing for 20s to form, then hot pressing for 8min at the temperature of 180-230 ℃ and under the pressure of 6MPa, and relieving pressure and cooling to obtain the medium-density fiberboard. The mechanical property and formaldehyde emission of the board are detected according to the method specified in the national standard GB/T11718-2009 Density fiberboard in a dry state. The mechanical properties include static bending strength, elastic modulus, internal bonding strength and water absorption thickness expansion rate.

The medium density fiberboard of example 3 has a density of 0.86g/cm³"Jingqu" (silent and quiet bent)The strength was 44.4MPa, the elastic modulus was 2965MPa, the internal bond strength was 1.66MPa, the water-absorbing thickness expansion rate was 11.5%, and the formaldehyde emission was 0mg/100 g.

The test results for examples 1 and 2 are similar to example 3. The test results of comparative examples 1 to 5 were all lower than those of examples.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.