CN111205794A - Starch adhesive for thermosetting artificial board and preparation method thereof - Google Patents
Starch adhesive for thermosetting artificial board and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
- C09J151/00—Adhesives based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Adhesives based on derivatives of such polymers
- C09J151/02—Adhesives based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Adhesives based on derivatives of such polymers grafted on to polysaccharides
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
- C08F2/12—Polymerisation in non-solvents
- C08F2/16—Aqueous medium
- C08F2/22—Emulsion polymerisation
- C08F2/24—Emulsion polymerisation with the aid of emulsifying agents
- C08F2/26—Emulsion polymerisation with the aid of emulsifying agents anionic
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F251/00—Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof
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Abstract
The invention discloses a thermosetting artificial board starch adhesive and a preparation method thereof, belonging to the technical field of adhesive preparation. The invention takes starch as a main raw material, and adopts a semi-continuous seed emulsion polymerization method for preparation after acidolysis. By accurately controlling the pregelatinization temperature, the addition time of the initiator, the addition amount of the crosslinking monomer, the dropping speed of the crosslinking monomer and the concentration of the crosslinking monomer dispersion liquid, the reaction degree of the crosslinking monomer is reasonably controlled, and the step of dropping the comonomer is omitted. Meanwhile, the reaction time is greatly shortened, the consumption of petroleum monomers is reduced, the complex reaction steps are simplified, the proportion of starch in the total solid content is increased from 40% to over 75%, and the cost of the starch adhesive is reduced. The adhesive has good water resistance and strong cohesion, and the properties of the manufactured artificial board exceed the standards of II artificial boards, so the adhesive is suitable for mass production and is widely used for bonding hot-pressing wood decoration, artificial boards and plywood.
Description
Technical Field
The invention relates to a thermosetting artificial board starch adhesive and a preparation method thereof, belonging to the technical field of adhesive preparation.
Background
Along with the development of building and decoration, the demand of the consumer market in China on wood products is greatly increased. But China occupies less area of the forest, so the artificial board prepared by taking other non-wood plants as raw materials becomes an excellent way for solving the problem of wood shortage. Most of artificial boards on the market are produced by adopting a hot pressing process, and the production efficiency is higher by using a three-aldehyde series adhesive with thermosetting property, but the raw material of the adhesive is not renewable, and harmful gases such as formaldehyde and the like are released to have adverse effect on the environment.
The starch is a biological macromolecule with abundant natural content, has wide source, low price, environmental protection, regeneration, good bonding and film-forming properties, and simple operation for preparing the adhesive. Therefore, starch-based wood-based adhesives are a major trend today. Although the hot-pressing artificial board can greatly improve the production efficiency of the artificial board, the bonded adhesive is also used for having better thermosetting property. In addition, the market requirements on artificial boards are more and more strict, and the water resistance of the adhesive is also high. Aiming at the performance requirements of the adhesive, the research team previously prepared the thermosetting starch adhesive, which has achieved ideal effects in the aspects of storage stability, dry strength and the like, but the process flow of the thermosetting starch adhesive involves the simultaneous dropwise addition of a graft comonomer and a crosslinking monomer, the reaction control requirement is high, the reaction time is long, and the monomer dosage and the proportion of starch still have room for further improvement. Therefore, the starch adhesive is further improved, the reaction time is shortened, the starch proportion is increased, the monomer consumption is reduced, and the wider application of the starch adhesive is promoted.
Disclosure of Invention
In order to make the preparation process of the starch adhesive simpler, more convenient and faster and the process stable, the invention makes a great deal of research on the mechanism of graft copolymerization, and the control of five key steps of pre-gelatinization temperature, initiator adding time, addition amount of crosslinking monomer, crosslinking monomer dropping speed and crosslinking monomer dispersion liquid concentration, prepares the artificial board starch adhesive with water resistance meeting the II-type plywood, and compared with the previous research, improves the proportion of starch in the total solid content from 40% to over 75%, and greatly reduces the cost.
The invention takes starch as raw material, adopts crosslinking monomer which is double bond with polymerization property and hydroxymethyl with condensation property, adds the crosslinking monomer after grafting reaction, leads the system to be in starvation state by controlling the adding speed of the initiator and the crosslinking monomer, improves the copolymerization rate of the monomer and reduces the homopolymerization rate. Meanwhile, because the crosslinking monomer adopted by the invention has very high-temperature crosslinking curing speed, in order to prevent excessive crosslinking from causing excessive viscosity or gelation of a system, a grafting monomer is firstly added into the pre-emulsion, and the grafting monomer can generate steric hindrance after being copolymerized with starch, thereby greatly reducing the reaction rate of the starch and the crosslinking monomer. However, the more the grafting monomer is, the better, the moderate graft copolymerization reaction can effectively increase the steric hindrance of the starch, thereby saving the original reaction time of dripping the grafting monomer and reducing the cost.
The reaction mechanism of the invention is as follows: the added grafting monomer forms a linear polymer to increase the steric hindrance of the starch and the crosslinking monomer, in order to reduce the problems of reaction efficiency reduction and monomer and starch implosion caused by homopolymerization reaction of the crosslinking monomer, the crosslinking monomer is added after preliminary grafting to further form the linear polymer into a macromolecular polymer, and the linear polymer can be further crosslinked to form a macromolecular reticular structure under a hot pressing process, so that the water resistance and the bonding strength of the starch adhesive are greatly improved. The grafting process is completed while adding the pre-emulsion, not only for improving the uniformity of the reaction and reducing the reaction viscosity, but also for the most important purpose, the free radical reaction is generated through the initiator, so that the reaction with the starch is changed into a linear polymer, the side chain group is enlarged by the reaction with the hydroxyl at the C6 position, the structure is more complex, the steric hindrance of the reaction between the side chain group and the crosslinking monomer is increased, the reaction rate of the crosslinking monomer and the starch is reduced, the occurrence of the gelation phenomenon is avoided, the crosslinking monomer can slowly react with the starch polymer, and the possibility that the crosslinking monomer is rapidly copolymerized on the active hydroxyl of the starch to cause the gelation due to overlarge local viscosity is avoided.
In the aspect of key control points, the invention carries out accurate control aiming at the following control points:
① and the pre-gelatinization temperature is not more than 85 ℃, if the pre-gelatinization temperature is too high, the starch is exposed to too many reaction sites, so that the grafting monomer in the pre-emulsion can not effectively increase the steric hindrance of the starch molecules, and the starch is easy to gel when the crosslinking monomer is dripped.
② the time remaining after the addition of the pre-emulsion is controlled to within 15min the initiator is acting as a free radical reaction which, if added too long after the addition of the pre-emulsion, results in the pre-emulsion having homopolymerized the graft monomer and not being able to prevent implosion by copolymerization with starch to form steric hindrance.
③ the addition amount of the cross-linking monomer is not more than 6% of the dosage of the starch, excessive addition can excessively cross-link with the starch, increase the length of a starch side chain and increase the local viscosity, and the starch and the cross-linking monomer are polymerized to form gel, and the addition amount of the cross-linking monomer is too small, so that the viscosity strength of the starch glue is reduced.
④ the dripping time of the cross-linking monomer is controlled at 2.5-3 h, when the cross-linking monomer is dripped, the speed is too high, the cross-linking monomer and local starch are reacted too much to form a large molecule or homopolymerization is carried out, so that the local viscosity is too high and gel is caused, the dripping speed is too low, although the starch and the cross-linking monomer form a better copolymer, the steric hindrance of the starch copolymer is increased because a part of the cross-linking monomer reacts with the starch at a slow speed, so that the subsequently added cross-linking monomer is subjected to the repulsion force of the steric hindrance, a homopolymer is more easily formed, the probability of the reaction with the starch is reduced, and the product performance can not meet the application requirements.
⑤ the concentration of the cross-linking monomer dispersion should not be too high, otherwise it is easy to form gel, and the mass fraction is controlled to be 5% -10%.
The invention aims to provide a thermosetting artificial board starch adhesive, and the formula of the artificial board starch adhesive comprises the following components: (in parts by mass)
The second purpose of the invention is to provide a preparation method of the thermosetting artificial board starch adhesive, which comprises the following steps:
taking starch milk prepared from starch as a main raw material, carrying out acidolysis treatment on the starch milk, adjusting the pH value, and carrying out pre-gelatinization; mixing and stirring part of the grafting monomer, the emulsifier and the initiator uniformly to prepare a seed emulsion, adding the seed emulsion into the pregelatinized starch emulsion, adding the rest of the initiator after the grafting reaction is determined, gradually dropwise adding the crosslinking monomer for reaction, raising the temperature after the reaction is finished, keeping the temperature for a period of time to remove the residual grafting monomer, finally cooling, stirring uniformly and discharging to obtain the starch adhesive.
In one embodiment of the present invention, the preparation method specifically comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20-45% by mass ratio based on dry basis of starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50-65 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5-2.5 h, and then adjusting the pH to 4-6;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80-85 ℃, and pre-gelatinizing for 20-40 min;
(4) preparing a seed emulsion from an initiator, a grafting monomer and an emulsifier which account for 10-20% of the total addition amount, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, immediately adding the rest of the initiator for further grafting after 5-10 min of preliminary grafting is finished, dropwise adding a crosslinking monomer solution with the mass concentration of 5-15% within 2.5-3 h at a constant speed after 20-40 min, and adding the initiator with the mass concentration of 1% within 1.5-2 h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80-90 ℃, keeping the temperature for 0.2-1 h to remove residual monomers, and cooling to 30-50 ℃ to obtain the starch adhesive.
In one embodiment of the invention, the starch is any one of corn starch, waxy corn starch, tapioca starch, wheat starch, potato starch, cross-linked starch, or a combination thereof.
In one embodiment of the invention, the concentrated hydrochloric acid is laboratory concentrated hydrochloric acid (36-38% concentration) or industrial hydrochloric acid (30-32% concentration).
In one embodiment of the present invention, the sodium hydroxide is a sodium hydroxide solution having a concentration of 10 mol/L.
In one embodiment of the invention, the initiator is a persulfate.
In one embodiment of the present invention, the grafting monomer is one or a mixture of vinyl acetate, acrylic acid and propylene.
In one embodiment of the invention, the emulsifier is any one or combination of sodium dodecyl sulfate, sodium dodecyl sulfonate, cetyl trimethyl ammonium bromide, octyl phenol polyoxyethylene ether-10 (OP-10) and phosphate ester emulsifier.
In one embodiment of the present invention, the crosslinking monomer is one or more of N-hydroxy acrylamide derivatives having copolymerization and condensation functional groups, such as N-methylol acrylamide, N-methoxy methacrylamide, N-isopropoxy methacrylamide and N-butoxy methacrylamide.
The third purpose of the invention is to provide that the thermosetting artificial board starch adhesive prepared by the method is applied to the bonding of hot-pressing artificial boards, and can also be used for the decoration of wood, and the hot-pressing bonding of artificial boards, plywood and wood blocks.
In one embodiment of the invention, the bonding method of the hot-pressing artificial board is to uniformly coat the adhesive on the thin board and then place the thin board at normal temperature for 5-15min, wherein the hot-pressing pressure is 0.3-0.6MPa, and the temperature is controlled at 90-130 ℃.
The invention has the beneficial effects that:
(1) the invention solves the problems of unstable preparation process and high cost of the starch adhesive, reasonably controls the reaction degree of the crosslinking monomer and omits the step of dripping the comonomer by accurately controlling the pregelatinization temperature, the addition time of the initiator, the addition amount of the crosslinking monomer, the dripping speed of the crosslinking monomer and the concentration of the crosslinking monomer dispersion liquid. Meanwhile, the reaction time (5h) is greatly shortened, the petroleum monomer consumption is reduced, the complex reaction steps are simplified, most importantly, the proportion of starch in the total solid content is increased from 40% to over 75%, and the cost of the starch adhesive is reduced.
(2) The artificial board prepared by the starch adhesive has the property exceeding the requirement of GBT 9846-.
(3) The preparation method of the starch adhesive disclosed by the invention is simple to operate, low in cost, green and environment-friendly, simple and time-saving in process and suitable for industrial production.
Detailed Description
The present invention is further described below in conjunction with embodiments, it being understood that these examples are for illustrative purposes only and do not limit the scope of the present invention.
The effect of pregelatinization temperature control on the properties of the adhesive is reflected by examples 1, 2:
example 1
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The obtained product has milky appearance, luster and low initial viscosity, and is hot pressed at 100 ℃ and 0.4MPa to prepare the three-layer plywood, wherein the dry strength of the prepared three-layer plywood is 1.87MPa, and the wet strength of the prepared three-layer plywood is 1.54 MPa. (the wet strength is measured after soaking for 3h, if the glue is broken within 3h, the wet strength is measured by 0, the relative wet strength is represented by the glue breaking time, and the longer the glue breaking time is, the better the water resistance is), which are all greater than the national standard of 0.7 MPa.
Example 2
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the mass ratio of 20 percent based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 90 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); the temperature is reduced to 70 ℃, after 5min of preliminary grafting is finished, the rest initiator is immediately added for further grafting, and after 20min, a crosslinking monomer solution with the mass concentration of 5% is uniformly dripped within 3h, and the result shows that in the experimental process, the crosslinking monomer is dripped for about 1h, namely, gel.
The experiments show that excessive pregelatinization temperature can cause excessive reaction sites to be exposed by starch, so that the steric hindrance of starch molecules cannot be effectively increased by the grafting monomers in the pre-emulsion, and the local viscosity is too high and the starch is gelled due to sudden polymerization when the crosslinking monomers are dripped.
The effect of monomer graft copolymerization time control on adhesive performance is demonstrated by examples 3, 4, 5
Example 3
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The appearance of the product obtained in the embodiment is milky white, glossy and low in initial viscosity, hot pressing is carried out at 100 ℃ and under the condition of 0.4MPa, the dry strength of the manufactured three-layer plywood is 1.7MPa, the wet strength is 1.5MPa (the wet strength is measured after soaking for 3h, if the plywood is cracked within 3h, the wet strength is measured by 0, the relative wet strength is represented by the cracking time, the longer the cracking time is, the better the water resistance is, and the dry strength and the wet strength are both greater than the national standard of 0.7 MPa.
Example 4
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, after 5min of preliminary grafting is finished, adding the rest initiator for further grafting after 15min, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h at a constant speed after 20min, and adding 20g of initiator with the mass concentration of 1% 1.5h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The product obtained in this example was milky white, matt, pasty and in the form of a gel.
Example 5
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, after 5min of preliminary grafting is finished, adding the rest initiator for further grafting after 1h, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h at a constant speed after 20min, and adding 20g of the initiator with the mass concentration of 1% 1h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The product obtained in this example was milky white, matt, pasty and in the form of a gel.
The effect of the length of the graft copolymerization on the performance of the adhesive is demonstrated by examples 3, 4 and 5, the properties of the products obtained in the examples according to the formulation method are shown in table 1:
TABLE 1 Properties of the products obtained in the examples at different graft copolymerization times
| Examples of the invention | 3 | 4 | 5 |
| Difference between Pre-emulsion and initiator addition time | 0min | 15min | 1h |
| Product(s) | Adhesive with good property | Gel | Gel |
As can be seen from table 1, adding the initiator at different times has a great influence on the graft copolymerization and the properties of the adhesive, the efficiency of the graft reaction without the initiator is low due to the monomer racing effect, and the initiator can initiate a radical reaction to copolymerize the starch with the graft monomer more efficiently, so that in example 3, adding the initiator 5min after adding the pre-emulsion (condensation reflux) can maximize the reaction of the graft monomer with the starch, thereby increasing the steric hindrance of the starch copolymer, so that the starch copolymer exists not as a homopolymer but as an oligomer. In example 4, the initiator is not added in time, so that the grafting reaction between the grafting monomer and the starch does not occur successfully, the steric hindrance of the starch molecule surface is not increased, and the grafting monomer and the crosslinking monomer are polymerized to form undesired gel in a crosslinking stage, so that the optimal initiator adding time is 5-15 min.
The influence of the control of the amount of crosslinking monomer on the properties of the adhesive was investigated by examples 6, 7, 8:
example 6
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The appearance of the product obtained in the embodiment is milky white, glossy and low in initial viscosity, hot pressing is carried out at 100 ℃ and 0.4Mpa, the dry strength of the manufactured three-layer plywood is 1.3Mpa, the wet strength is 0.8Mpa (soaking for 3h for measuring the wet strength, if the glue is broken within 3h, the wet strength is 0, the relative wet strength is represented by the glue breaking time, and the longer the glue breaking time is, the better the water resistance is relatively), and the dry strength and the wet strength are all more than 0.7Mpa of the national standard.
Example 7
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1h, and then adjusting the pH to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The appearance of the product obtained in the embodiment is milky white, glossy and low in initial viscosity, the three-layer plywood prepared by hot pressing at 100 ℃ and 0.4MPa has the dry strength of 1.7MPa and the wet strength of 1.1MPa (the wet strength is measured after soaking for 3h, if the plywood is cracked within 3h, the wet strength is 0, the relative wet strength is represented by the cracking time, and the longer the cracking time is, the better the water resistance is), and the better the three-layer plywood is higher than the national standard of 0.7 MPa.
Example 8
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the mass ratio of 20 percent based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10 percent of the total addition amount into seed emulsion, and adding the seed emulsion into a reaction system; cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (3) heating the grafted and cross-linked modified emulsion to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The product obtained in this example was milky white, glossy, very viscous and gel-free.
A comparison of the properties of the adhesives obtained with the above amounts of the three different crosslinking monomers is shown in Table 2:
TABLE 2 Properties of the Adhesives obtained with different amounts of crosslinking monomers
| Examples | 6 | 7 | 8 |
| Monomer content (g) | 4 | 5 | 6 |
| Dry strength/MPa | 1.3 | 1.7 | - |
| Wet strength/MPa | 0.8 | 1.1 | - |
"-" indicates that the glue was not applied normally.
As can be seen from table 2, N-methylolacrylamide (NMA) as a crosslinking monomer, whether viscosity or dry strength and wet strength increase with the amount of NMA, but not the more and better the crosslinking monomers, when there are too many, they will react further with the copolymer already formed with the starch to form too large molecules, allowing more hydroxyl groups on the starch to participate in the reaction or forming linear polymers on the starch molecules to increase viscosity and even to cause gel formation.
The effect of the dropping monomer speed on the performance of the adhesives was investigated by examples 9, 10, 11:
example 9
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature of the acidified starch milk to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 0.5h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30-50 ℃ to obtain the starch adhesive.
The adhesive obtained in this example has a very low viscosity and little utility value.
Example 10
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the mass ratio of 20 percent based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10 percent of the total addition amount into seed emulsion, and adding the seed emulsion into a reaction system; cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (3) heating the grafted and cross-linked modified emulsion to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The appearance of the product obtained in the embodiment is milky white, glossy, moderate in initial viscosity, 100 ℃, and hot-pressed at 0.4MPa, the dry strength of the prepared three-layer plywood is 1.85MPa, the wet strength is 1.17MPa (the wet strength is measured after soaking for 3h, if the plywood is cracked within 3h, the wet strength is 0, the relative wet strength is represented by the cracking time, the longer the cracking time is, the better the water resistance is, and the dry strength is greater than 0.7MPa of the national standard.
Example 11
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the mass ratio of 20 percent based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10 percent of the total addition amount into seed emulsion, and adding the seed emulsion into a reaction system; cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 4h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (3) heating the grafted and cross-linked modified emulsion to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The product obtained in this example was a gel, which was not spreadable.
TABLE 3 Properties of Adhesives made with different amounts of crosslinking monomer
| Examples | 9 | 10 | 11 |
| The dripping time per hour | 0.5～2 | 2.5～3 | 3～5 |
| Dry strength/MPa | - | 1.85 | - |
| Wet strength/MPa | - | 1.17 | - |
"-" indicates that the glue was not applied normally.
As can be seen from Table 3, the dropping speed of the crosslinking monomer has a great influence on the performance of the adhesive, the dropping time of the crosslinking monomer is preferably controlled to be 2.5-3 h, and the dropping speed of the crosslinking monomer is too high, so that the crosslinking monomer and local starch react too much to form a large molecule or homopolymerization due to the limitation of the stirring speed, and the local viscosity is too high to cause gel, so that the system is always in a starvation state. The dripping speed is too low, although the starch and the crosslinking monomer can form a better copolymer, the steric hindrance of the starch copolymer is increased because a part of the crosslinking monomer reacts with the starch at a slow speed, the subsequently added crosslinking monomer is subjected to the repulsion force of the steric hindrance, a homopolymer is more easily formed, the reaction with the starch is avoided, the viscosity is not up to the standard, and the reaction is more complicated due to the increase of the time cost. Therefore, the dripping time of the crosslinking monomer is determined to be 2.5 to 3 hours.
The effect of the concentration of the aqueous crosslinking monomer solution on the adhesive properties was investigated by examples 12, 13:
example 12
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 20% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10% of the total addition amount into seed emulsion, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 5% within 3h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The appearance of the product obtained in the embodiment is milky white, glossy and moderate in initial viscosity, hot pressing is carried out at 100 ℃ and 0.4MPa, the dry strength of the manufactured three-layer plywood is 1.91MPa, the wet strength is 1.64MPa (the wet strength is measured after soaking for 3h, if the plywood is cracked within 3h, the wet strength is 0, the relative wet strength is represented by the cracking time, and the longer the cracking time is, the better the water resistance is), and the dry strength and the wet strength are all more than 0.7MPa of the national standard.
Example 13
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the mass ratio of 20 percent based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature to 50 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5h, and then adjusting the pH to 4;
(3) adjusting the temperature to 80 ℃, and pre-gelatinizing for 20 min;
(4) preparing initiator, grafting monomer and emulsifier which account for 10 percent of the total addition amount into seed emulsion, and adding the seed emulsion into a reaction system; cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5min of preliminary grafting, dropwise adding a crosslinking monomer solution with the mass concentration of 20% within 3h after 20min, and adding 20g of the initiator with the mass concentration of 1% within 1.5h after dropwise adding the crosslinking monomer;
(5) and (3) heating the grafted and cross-linked modified emulsion to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The product obtained in this example was a gel.
From the above examples, it can be seen that the concentration of the crosslinking monomer cannot be too high, when the concentration of the crosslinking monomer is too high, the crosslinking monomer can rapidly crosslink with more starch molecules, the possibility of sudden polymerization is increased, and the monomer after copolymerization with the starch molecules can further react to increase the viscosity of the system, so as to cause gelation.
Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. The thermosetting artificial board starch adhesive is characterized by comprising the following components in percentage by weight: (in parts by mass)
2. The method for preparing the thermosetting artificial board starch adhesive in claim 1 is characterized by comprising the following steps:
taking starch milk prepared from starch as a main raw material, carrying out acidolysis treatment on the starch milk, adjusting the pH value, and carrying out pre-gelatinization; mixing and stirring part of the grafting monomer, the emulsifier and the initiator uniformly to prepare a seed emulsion, adding the seed emulsion into the pregelatinized starch emulsion, adding the rest of the initiator after the grafting reaction is determined, gradually dropwise adding the crosslinking monomer for reaction, raising the temperature after the reaction is finished, keeping the temperature for a period of time to remove the residual grafting monomer, finally cooling, stirring uniformly and discharging to obtain the starch adhesive.
3. The preparation method of claim 2, wherein the initiator, the grafting monomer and the emulsifier, which account for 10-20% of the total addition amount, are prepared into a seed emulsion and added into the pre-gelatinized reaction system; and (3) cooling to 70 ℃, immediately adding the rest initiator for further grafting after 5-10 min of preliminary grafting is finished, dropwise adding a crosslinking monomer solution with the mass concentration of 5-15% within 2.5-3 h at a constant speed after 20-40 min, and adding the initiator with the mass concentration of 1% within 1.5-2 h after dropwise adding the crosslinking monomer.
4. The method according to claim 2, wherein the method comprises the steps of:
(1) preparing starch and water into starch milk with the concentration of 20-45% by mass ratio based on dry basis of starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 50-65 ℃, adding 0.5mol/L hydrochloric acid, carrying out acidolysis for 1.5-2.5 h, and then adjusting the pH to 4-6;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80-85 ℃, and pre-gelatinizing for 20-40 min;
(4) preparing a seed emulsion from an initiator, a grafting monomer and an emulsifier which account for 10-20% of the total addition amount, and adding the seed emulsion into the reaction system after the pre-gelatinization in the step (3); cooling to 70 ℃, immediately adding the rest of the initiator for further grafting after 5-10 min of preliminary grafting is finished, dropwise adding a crosslinking monomer solution with the mass concentration of 5-15% within 2.5-3 h at a constant speed after 20-40 min, and adding the initiator with the mass concentration of 1% within 1.5-2 h after dropwise adding the crosslinking monomer;
(5) and (4) heating the emulsion subjected to grafting and crosslinking modification in the step (4) to 80-90 ℃, keeping the temperature for 0.2-1 h to remove residual monomers, and cooling to 30-50 ℃ to obtain the starch adhesive.
5. The method according to claim 2, wherein the initiator is a persulfate.
6. The preparation method according to claim 2, wherein the grafting monomer is one or more of vinyl acetate, acrylic acid and propylene.
7. The preparation method of claim 2, wherein the emulsifier is any one or more of sodium dodecyl sulfate, sodium dodecyl sulfonate, cetyl trimethyl ammonium bromide, octyl phenol polyoxyethylene ether-10 (OP-10), and phosphate ester emulsifier.
8. The method according to claim 2, wherein the crosslinking monomer is one or more selected from N-hydroxy acrylamide derivatives having copolymerization and condensation functional groups such as N-methylol acrylamide, N-methoxymethyl acrylamide, N-isopropoxy methacrylamide and N-butoxymethyl acrylamide.
9. The thermosetting artificial board starch adhesive of claim 1 is used for bonding hot-pressing artificial boards, decorating wood, and hot-pressing artificial boards, plywood, and wood blocks.
10. The application of claim 9, wherein the hot-press type artificial board is bonded by uniformly coating an adhesive on a thin board and then standing at room temperature for 5-15min, wherein the hot-press pressure is 0.3-0.6MPa and the temperature is controlled at 90-130 ℃.
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