CN111647112A - Viscosity-adjustable thermosetting artificial board starch adhesive and preparation method thereof - Google Patents
Viscosity-adjustable thermosetting artificial board starch adhesive and preparation method thereof Download PDFInfo
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- CN111647112A CN111647112A CN202010592401.6A CN202010592401A CN111647112A CN 111647112 A CN111647112 A CN 111647112A CN 202010592401 A CN202010592401 A CN 202010592401A CN 111647112 A CN111647112 A CN 111647112A
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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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27D—WORKING VENEER OR PLYWOOD
- B27D1/00—Joining wood veneer with any material; Forming articles thereby; Preparatory processing of surfaces to be joined, e.g. scoring
- B27D1/04—Joining wood veneer with any material; Forming articles thereby; Preparatory processing of surfaces to be joined, e.g. scoring to produce plywood or articles made therefrom; Plywood sheets
- B27D1/08—Manufacture of shaped articles; Presses specially designed therefor
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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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Abstract
The invention discloses a viscosity-adjustable thermosetting artificial board starch adhesive and a preparation method thereof, belonging to the technical field of adhesive preparation. According to the invention, starch is used as a main raw material, after acidolysis, the viscosity of the adhesive is reasonably controlled by accurately controlling the pre-gelatinization temperature, the pre-gelatinization duration and the dropping speed of the crosslinking monomer and by dropping the crosslinking monomer and the initiator in sections, so that the control requirement of industrial production on the reaction accuracy is reduced, and the method can be widely applied to application fields with different requirements on the viscosity of the adhesive. The adhesive product prepared by the invention has no formaldehyde release and has the advantage of environmental protection. Meanwhile, 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 viscosity-adjustable thermosetting artificial board starch adhesive and a preparation method thereof, belonging to the technical field of adhesive preparation.
Background
With the rapid development of the home decoration industry, the demand for wood boards is also increasing year by year. However, the area occupied by all people in China is small, and the area occupied by people in China is reduced year by year, so that the use of artificial boards to replace wood is a poor choice for solving the problem. At present, most of artificial boards on the market are produced by adopting a hot pressing process, and the adhesive of a 'trialdehyde' series with thermosetting property is used, but the adhesive has poor water resistance, the raw materials are not renewable, and harmful gases such as formaldehyde and the like release adverse effects on the environment.
Starch is a biological macromolecule with abundant natural content, has wide sources, low price, environmental protection, regeneration, good bonding and film-forming properties and simple operation for preparing the adhesive, so that the starch-based adhesive is widely concerned by researchers. However, the traditional starch-based adhesives still have many problems, such as poor water resistance, and in addition, the proportion of starch in most of the starch-based adhesives is less than 50 percent of the total solid content, so that the starch-based adhesives depend on non-renewable resources to a great extent, and have high cost and poor environmental protection; the research and development team successfully prepares the starch-based adhesive with high starch content, wherein the starch solid content of the starch-based adhesive can reach 75%, but the viscosity of the adhesive is too high when the starch solid content of the starch-based adhesive is too high, the adhesive is difficult to apply to narrow places, and the problems of uneven reaction, unstable reaction system and the like exist. Therefore, it is necessary to find a high starch content adhesive with adjustable viscosity.
Disclosure of Invention
[ problem ] to
At present, the proportion of starch in most starch-based adhesives is less than 50 percent of the total solid content, the starch-based adhesives greatly depend on non-renewable resources, and the starch-based adhesives have higher cost and poorer environmental protection property; however, when the starch content in the starch-based adhesive is too high (more than 75%), the viscosity of the adhesive is too high, the adhesive is difficult to apply to narrow places, and the problems of non-uniform reaction, unstable reaction system and the like exist.
[ solution ]
In order to expand the fault tolerance and application range in the preparation process of the adhesive, the invention provides the thermosetting artificial board starch adhesive with adjustable viscosity and the preparation method thereof.
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. According to the invention, by regulating and controlling the pre-gelatinization temperature and the pre-gelatinization time, the finally prepared adhesive with adjustable viscosity is changed, the fault tolerance rate is increased, and different requirements of different fields can be met. Meanwhile, the crosslinking efficiency is improved by adopting a step-by-step dripping method, and the thermosetting property is improved to a certain extent.
The reaction mechanism of the invention is as follows: the viscosity of the adhesive is changed by adjusting the gelatinization temperature and the gelatinization time, the crosslinking efficiency is improved by adopting a step-by-step dripping method, and the thermosetting property is improved to a certain extent. In the preparation process, pre-crosslinking is carried out firstly, and a macromolecular reticular structure can be formed by further crosslinking 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 an initiator, so that the reaction with the starch is changed into a linear polymer, the side chain group is enlarged due to the reaction with hydroxyl at the position of C6, the structure is more complex, the steric hindrance of the reaction between the cross-linking monomer and the cross-linking monomer is increased, the reaction rate of the cross-linking monomer and the starch is reduced, the cross-linking rate of the cross-linking monomer and the starch is reduced through the added grafting monomer, the gelation phenomenon is avoided, the cross-linking monomer can slowly react with the starch polymer, and the possibility that the cross-linking monomer is rapidly copolymerized on the active hydroxyl of the starch to cause the gel due to overla.
In the aspect of key control points, the invention carries out accurate control aiming at the following control points:
the pre-gelatinization temperature and the pre-gelatinization time are not more than 85 ℃. The viscosity is controlled to be 2000-7000 mPas when the pre-gelatinization temperature is controlled to be 75-80 ℃, and the viscosity is controlled to be 7000-13000 mPas when the pre-gelatinization temperature is controlled to be 80-85 ℃. 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 cannot effectively increase the steric hindrance of starch molecules, and the starch is easy to gel when the crosslinking monomer is dripped.
Secondly, adding a crosslinking monomer and an initiator in a sectional dripping mode, and controlling the dripping time of the crosslinking monomer within 2.5-3 h. The specific operation is as follows: after the grafting reaction is carried out for 20-40 min, firstly dropwise adding a crosslinking monomer solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed, dropwise adding at a constant speed within 30-40 min, then adding 10g of an initiator solution with the mass concentration of 1%, preserving heat for 10-20 min, repeating the step of dropwise adding the crosslinking monomers for 2 times, wherein the total dropwise adding time is controlled within 3h, and the sectional dropwise adding of the monomers and the initiator increases the crosslinking reaction efficiency of the crosslinking monomers and starch, so that the thermosetting property of the adhesive is improved, and the reaction efficiency is greatly improved.
The invention provides a method for preparing a viscosity-adjustable thermosetting artificial board starch adhesive, which comprises the following steps:
the formula of the artificial board starch adhesive comprises: (in parts by mass)
Taking starch milk prepared from starch as a main raw material, carrying out acidolysis treatment on the starch milk, adjusting the pH value of the starch milk, and carrying out pre-gelatinization at the temperature of 75-85 ℃ for 20-50 min; mixing and stirring part of grafting monomers, an emulsifier and an initiator uniformly to prepare a seed emulsion, adding the seed emulsion into the pregelatinized starch emulsion, adding the initiator after primary grafting is finished for further grafting, dropwise adding a crosslinking monomer solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed within 30-40 min after grafting reaction is carried out for 20-40 min, adding a reconfigured initiator solution after dropwise adding is finished, preserving heat for 10-20 min for reaction, repeating the step of dropwise adding the crosslinking monomers for 2 times, and controlling the total dropwise adding time within 3 h; after the reaction is finished, heating and preserving heat to remove residual grafting monomers, finally cooling, uniformly stirring 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 be 60-75 ℃, adding hydrochloric acid diluted to be 0.5mol/L for acidolysis for 1.5-3 h, and then adding a sodium hydroxide solution to adjust the pH of the starch milk to be 4-6;
(3) adjusting the gelatinization temperature of the acidolyzed starch milk according to the required viscosity range, wherein the pre-gelatinization temperature is 75-85 ℃, and the pre-gelatinization time is 20-50 min;
(4) adding water into an initiator accounting for 50-70% of the total mass of the initiator to prepare an initiator solution with the mass concentration of 1-2%, taking 15-20% of the initiator solution by mass, grafting a monomer and an emulsifier to prepare a seed emulsion, and dropping the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed to react;
(5) and (3) immediately adding the rest initiator solution obtained in the step (4) for further grafting after 5-10 min of preliminary grafting is finished, after the grafting reaction is carried out for 20-40 min, firstly dropwise adding a crosslinking monomer solution accounting for 1/3 of the total mass of the crosslinking monomer at a constant speed, dropwise adding at a constant speed within 30-40 min, and adding a reconfigured initiator solution after dropwise adding is finished, wherein the initiator solution is: adding water into the rest initiator accounting for 30-50% of the total mass of the initiator to prepare initiator solution with the mass concentration of 1-2%, and dividing into 3 parts, wherein the part is one of the initiator solution; keeping the temperature for 10-20 min for reaction, repeating the step of dripping the crosslinking monomer for 2 times, and controlling the total dripping time within 3 h;
(6) and (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) to 80-90 ℃, preserving 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, when the pre-gelatinization temperature in the step (3) is 75-80 ℃ and the pre-gelatinization time is 20min, the viscosity range of the prepared starch adhesive is 2000-5000 mPa & s; in the step (3), when the pre-gelatinization temperature is 80-85 ℃ and the pre-gelatinization time is 20min, the viscosity range of the prepared starch adhesive is 3000-10000 mPa & s; in the step (3), when the pre-gelatinization temperature is 80 ℃ and the pre-gelatinization time is 20-30 min, the viscosity range of the prepared starch adhesive is 3000-11000 mPa & s; and (3) when the pre-gelatinization temperature is 80 ℃ and the pre-gelatinization time is 30-50 min, the viscosity range of the prepared starch adhesive is 9000-16000 mPa & s.
In one embodiment of the invention, the starch is any one of corn starch, waxy corn starch, tapioca starch, wheat starch, cross-linked starch, or a combination thereof.
In one embodiment of the invention, the concentrated hydrochloric acid is 12mol/L concentrated hydrochloric acid.
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 an embodiment of the invention, the crosslinking monomer is one or a mixture of several of N-hydroxyacrylamide derivatives having copolymerization and condensation functional groups, such as N- (isobutoxymethyl) -acrylamide, N-dimethylacrylamide, N-isopropoxymethacrylamide, N-butoxymethylacrylamide and the like, so that the water resistance of the adhesive can be improved through two-step crosslinking, and no free formaldehyde exists in the adhesive.
In one embodiment of the present invention, the dropwise addition of the crosslinking monomer solution in the step (5) is an aqueous solution of a crosslinking monomer with a dropwise concentration of 10 to 20% by mass.
The invention provides a thermosetting artificial board starch adhesive with adjustable viscosity prepared by the method.
The invention provides the application of the viscosity-adjustable thermosetting artificial board starch adhesive in the hot-pressing bonding of artificial boards, plywood and wood blocks and the decoration of wood.
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 ℃.
[ advantageous effects ]:
(1) according to the invention, the viscosity of the adhesive is changed by regulating and controlling the pre-gelatinization temperature and time, so that the starch adhesive with very low viscosity in the range of 2000-5000 mPa & s can be prepared, the starch adhesive with very high viscosity in the range of 12000-16000 mPa & s can also be prepared, the starch adhesives with different viscosities can be applied to different occasions, for example, in cracks of a ship body board, glue can not be applied, and the adhesive with low viscosity can be dripped by using fluidity and then re-hot-pressed. The range is 12000-16000 mPas, and the adhesive is suitable for objects which are not water-resistant or applied to the condition that the adhesive with low viscosity easily flows in a vertical state. Meanwhile, in the final temperature rise and preservation stage, the viscosity is measured by sampling every 5-10 min, and the temperature and time of temperature rise and preservation are adjusted in time, so that the viscosity of the starch adhesive meets the actual requirements, the fault tolerance rate is increased, and the market application field is greatly expanded.
(2) The invention provides a novel addition mode of a crosslinking monomer and an initiator. After 20-40 min, firstly dripping 1/3 crosslinking monomer solution at a constant speed within 30-40 min, then adding 10g of 1% initiator solution, preserving heat for 10-20 min, and repeating the steps, wherein the total dripping time is controlled within 3h, so that the crosslinking reaction efficiency of crosslinking monomers and starch is increased, the thermosetting property is improved, and the reaction efficiency is greatly improved by dripping the monomers and the initiator in sections. The artificial board prepared by the starch adhesive has the property exceeding the requirement of GBT 9846-.
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 viscosity measurement method comprises the following steps:
the viscosity of the prepared starch adhesive is measured by an NDJ-8S digital viscometer, a No. 4 rotor is used in the measuring process, the rotating speed is 30r/min, the measurement is carried out at the temperature of 20-30 ℃, and the average viscosity within 1min is recorded.
The effect of pregelatinization temperature control on the properties of the adhesive is reflected by examples 1, 2, 3:
[ example 1 ]
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 30% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 60 ℃ at the speed of 2 ℃/min, diluting 8.6g of 12mol/L concentrated hydrochloric acid solution to 0.5mol/L, adding the diluted solution into the starch milk for acidolysis, carrying out acidolysis for 1.5h, and then adding 10mol/L sodium hydroxide solution to adjust the pH value to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 75 ℃ at the rate of 1 ℃/min, and pre-gelatinizing for 20 min;
(4) dissolving 0.51g of initiator in 40g of water to prepare an initiator solution, mixing the initiator solution accounting for 15 percent of the total mass of the initiator solution with an emulsifier and a grafting monomer to prepare a seed emulsion, cooling the system in the step (3) to 70 ℃, and then dripping the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed within 10 min;
(5) and (3) immediately adding the rest initiator solution obtained in the step (4) for further grafting after 5min of preliminary grafting is finished, after 20min of grafting reaction is carried out, dropwise adding a crosslinking monomer aqueous solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed, wherein the mass concentration of the crosslinking monomer aqueous solution is 20%, the dropwise adding speed is constant speed within 30min, adding 10g of a reconfigured initiator solution with the mass concentration of 1% after the dropwise adding is finished, preserving heat for 10min for reaction, repeating the step of dropwise adding the crosslinking monomers for 2 times, and preferably controlling the total dropwise adding time within 3 h.
(6) And (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The obtained product is milky in appearance, glossy and extremely low in initial viscosity, the viscosity is measured by referring to the viscosity measurement method, the viscosity range of the starch adhesive prepared by the embodiment is 2000-4000 mPas, and the starch adhesive is suitable for glue supplement of finished products, for example, glue can not be applied to cracks of ship boards, and the adhesive with low viscosity can be dripped into the crack by using fluidity and then is subjected to hot pressing.
Hot pressing at 100 deg.C and 0.4Mpa to obtain three-layer plywood with dry strength of 1.77Mpa and wet strength of 1.54 Mpa. (the wet strength is measured after soaking for 3h, if the glue is broken within 3h, the wet strength is calculated as 0, the relative wet strength is represented by the glue breaking time, the longer the glue breaking 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 2 ]
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 30% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 60 ℃, diluting 8.6g of 12mol/L concentrated hydrochloric acid solution to 0.5mol/L, adding the diluted solution into the starch milk for acidolysis for 1.5h, and then adding 10mol/L sodium hydroxide solution to adjust the pH value to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 85 ℃ at the rate of 1 ℃/min, and pre-gelatinizing for 20 min;
(4) dissolving 0.51g of initiator in 40g of water to prepare an initiator solution, mixing the initiator solution accounting for 10 percent of the total mass of the initiator solution with an emulsifier and a grafting monomer to prepare a seed emulsion, and adding the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed within 10min when the temperature of the system in the step (3) is reduced to 70 ℃;
(5) and (3) immediately adding the rest initiator solution obtained in the step (4) for further grafting after 5min of preliminary grafting is finished, after 20min of grafting reaction is carried out, dropwise adding a crosslinking monomer aqueous solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed, wherein the mass concentration of the crosslinking monomer aqueous solution is 20%, the dropwise adding speed is constant speed within 30min, adding 10g of a reconfigured initiator solution with the mass concentration of 1% after the dropwise adding is finished, preserving heat for 10min for reaction, repeating the step of dropwise adding the crosslinking monomers for 2 times, and preferably controlling the total dropwise adding time within 3 h.
(6) And (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The obtained product is milky white and glossy, has high initial viscosity, and the viscosity is measured by referring to the viscosity measuring method, so that the viscosity range of the starch adhesive prepared by the embodiment is 8000-10000 mPas, the starch adhesive is suitable for the condition of normal sizing, and the spreadability is good.
Hot pressing at 100 deg.C and 0.4Mpa to obtain three-layer plywood with dry strength of 1.87Mpa and wet strength of 1.68 Mpa. (the wet strength is measured after soaking for 3h, if the glue is broken within 3h, the wet strength is calculated as 0, the relative wet strength is represented by the glue breaking time, the longer the glue breaking 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 3 ]
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 30% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 60 ℃ at the speed of 2 ℃/min, diluting 8.6g of 12mol/L concentrated hydrochloric acid solution to 0.5mol/L, adding the diluted solution into the starch milk for acidolysis, carrying out acidolysis for 1.5h, and then adding 10mol/L sodium hydroxide solution to adjust the pH value to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 90 ℃ at the rate of 1 ℃/min, and pre-gelatinizing for 20 min;
(4) dissolving 0.51g of initiator in 40g of water to prepare an initiator solution, mixing the initiator solution accounting for 15 percent of the total mass of the initiator solution with an emulsifier and a grafting monomer to prepare a seed emulsion, cooling the system in the step (3) to 70 ℃, and then dripping the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed within 10 min;
(5) and (3) immediately adding the rest initiator solution obtained in the step (4) for further grafting after 5min of preliminary grafting is finished, after 20min of grafting reaction is carried out, dropwise adding a crosslinking monomer aqueous solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed, wherein the mass concentration of the crosslinking monomer aqueous solution is 20%, the dropwise adding speed is constant speed within 30min, adding 10g of a reconfigured initiator solution with the mass concentration of 1% after the dropwise adding is finished, preserving heat for 10min for reaction, repeating the step of dropwise adding the crosslinking monomers for 2 times, and preferably controlling the total dropwise adding time within 3 h.
(6) And (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) to 80 ℃, keeping the temperature for 0.2h to remove residual monomers, and cooling to 30 ℃ to obtain the starch adhesive.
The product obtained was milky white in appearance, matt, free-flowing and formed a 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 viscosity is in direct proportion to the pre-gelatinization temperature, and when the pre-gelatinization temperature is low, the formed adhesive has the mobility similar to that of water, so that the adhesive has a certain application range in the fields with requirements on the mobility of the adhesive.
The influence of the pregelatinization time control on the performance of the adhesives is demonstrated by examples 4, 5 and 6
[ example 4 ]
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 30% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 60 ℃ at the speed of 2 ℃/min, diluting 8.6g of 12mol/L concentrated hydrochloric acid solution to 0.5mol/L, adding the diluted solution into the starch milk for acidolysis, carrying out acidolysis for 1.5h, and then adding 10mol/L sodium hydroxide solution to adjust the pH value to 4;
(3) the temperature of the starch milk after acidolysis is up to 80 ℃ at the speed of 1 ℃/min, and the starch milk is pre-gelatinized for 20 min;
(4) dissolving 0.51g of initiator in 40g of water to prepare an initiator solution, mixing the initiator solution accounting for 15 percent of the total mass of the initiator solution with an emulsifier and a grafting monomer to prepare a seed emulsion, cooling the system in the step (3) to 70 ℃, and then dripping the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed within 10 min;
(5) and (3) immediately adding the rest initiator solution obtained in the step (4) for further grafting after 5min of preliminary grafting is finished, after 20min of grafting reaction is carried out, dropwise adding a crosslinking monomer aqueous solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed, wherein the mass concentration of the crosslinking monomer aqueous solution is 20%, the dropwise adding speed is constant speed within 30min, adding 10g of a reconfigured initiator solution with the mass concentration of 1% after the dropwise adding is finished, preserving heat for 10min for reaction, repeating the step of dropwise adding the crosslinking monomers for 2 times, and preferably controlling the total dropwise adding time within 3 h.
(6) And (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) 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 the embodiment is milky white and glossy, has low initial viscosity, and the viscosity is measured by the viscosity measuring method, and the viscosity range of the starch adhesive prepared in the embodiment is 3000-5000 mPas.
And (3) carrying out hot pressing at 100 ℃ under the condition of 0.4Mpa to obtain the three-layer plywood with the dry strength of 1.7MPa and the wet strength of 1.5MPa (the wet strength is measured after soaking for 3h, if the plywood is cracked within 3h, the wet strength is calculated as 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 0.7MPa of the national standard.
[ example 5 ]
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 30% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 60 ℃ at the speed of 2 ℃/min, diluting 8.6g of 12mol/L concentrated hydrochloric acid solution to 0.5mol/L, adding the diluted solution into the starch milk for acidolysis, carrying out acidolysis for 1.5h, and then adding 10mol/L sodium hydroxide solution to adjust the pH value to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃ at the rate of 1 ℃/min, and pre-gelatinizing for 30 min;
(4) dissolving 0.51g of initiator in 40g of water to prepare an initiator solution, mixing the initiator solution accounting for 15 percent of the total mass of the initiator solution with an emulsifier and a grafting monomer to prepare a seed emulsion, cooling the system in the step (3) to 70 ℃, and then dripping the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed within 10 min;
(5) and (3) immediately adding the rest initiator solution obtained in the step (4) for further grafting after 5min of preliminary grafting is finished, after 20min of grafting reaction is carried out, dropwise adding a crosslinking monomer aqueous solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed, wherein the mass concentration of the crosslinking monomer aqueous solution is 20%, the dropwise adding speed is constant speed within 30min, adding 10g of a reconfigured initiator solution with the mass concentration of 1% after the dropwise adding is finished, preserving heat for 10min for reaction, repeating the step of dropwise adding the crosslinking monomers for 2 times, and preferably controlling the total dropwise adding time within 3 h.
(6) And (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) 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 the embodiment is milky white, glossy and appropriate in initial viscosity, the viscosity is measured by referring to the viscosity measuring method, and the range of the starch adhesive prepared in the embodiment is 9000-11000 mPas, and is similar to that of white latex.
And (3) carrying out hot pressing at 100 ℃ and 0.4Mpa to obtain the three-layer plywood with the dry strength of 1.58MPa and the wet strength of 1.34MPa (the wet strength is measured after soaking for 3h, if the glue is broken within 3h, the wet strength is calculated as 0, the relative wet strength is represented by the glue breaking time, the longer the glue breaking time is, the better the water resistance is, and the dry strength and the wet strength are both greater than 0.7MPa of the national standard.
[ example 6 ]
Formula (mass/g):
the process flow comprises the following steps:
(1) preparing starch and water into starch milk with the concentration of 30% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 60 ℃ at the speed of 2 ℃/min, diluting 8.6g of 12mol/L concentrated hydrochloric acid solution to 0.5mol/L, adding the diluted solution into the starch milk for acidolysis, carrying out acidolysis for 1.5h, and then adding 10mol/L sodium hydroxide solution to adjust the pH value to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃ at the rate of 1 ℃/min, and pre-gelatinizing for 50 min;
(4) dissolving 0.51g of initiator in 40g of water to prepare an initiator solution, mixing the initiator solution accounting for 15 percent of the total mass of the initiator solution with an emulsifier and a grafting monomer to prepare a seed emulsion, cooling the system in the step (3) to 70 ℃, and then dripping the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed within 10 min;
(5) and (3) immediately adding the rest initiator solution obtained in the step (4) for further grafting after 5min of preliminary grafting is finished, after 20min of grafting reaction is carried out, dropwise adding a crosslinking monomer aqueous solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed, wherein the mass concentration of the crosslinking monomer aqueous solution is 20%, the dropwise adding speed is constant speed within 30min, adding 10g of a reconfigured initiator solution with the mass concentration of 1% after the dropwise adding is finished, preserving heat for 10min for reaction, repeating the step of dropwise adding the crosslinking monomers for 2 times, and preferably controlling the total dropwise adding time within 3 h.
(6) And (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) 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, spreadable, but without flow.
The product obtained in the embodiment is milky white and glossy, has extremely high initial viscosity, and the viscosity is measured by referring to the viscosity measurement method, so that the range of the starch adhesive prepared in the embodiment is 12000-16000 mPas, and the starch adhesive is suitable for objects which are not water-resistant or applied to the condition that the adhesive with low viscosity easily flows in a vertical state.
And (3) carrying out hot pressing at 100 ℃ and 0.4MPa to obtain the three-layer plywood with the dry strength of 1.76MPa and the wet strength of 1.53MPa (the wet strength is measured after soaking for 3h, if the plywood is cracked within 3h, the wet strength is calculated as 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 0.7MPa of the national standard.
As proved by examples 4, 5 and 6, the influence of the graft copolymerization time on the performance of the adhesive is known, the pregelatinization time is short, the starch granules are not fully swelled and enough reaction sites are exposed, so that the subsequent graft copolymerization efficiency is greatly reduced, and most of the graft monomers and the crosslinking monomers exist in a homopolymerized state. Too long a pregelatinization time can expose the starch to too many reactive hydroxyl groups, which can lead to too vigorous a gel formation or too high a viscosity.
Comparative example 1
(1) Preparing starch and water into starch milk with the concentration of 30% by mass ratio based on the dry basis of the starch, and uniformly stirring;
(2) adjusting the temperature of the starch milk to 60 ℃ at the speed of 2 ℃/min, diluting 8.6g of 12mol/L concentrated hydrochloric acid solution to 0.5mol/L, adding the diluted solution into the starch milk for acidolysis, carrying out acidolysis for 1.5h, and then adding 10mol/L sodium hydroxide solution to adjust the pH value to 4;
(3) adjusting the temperature of the starch milk subjected to acidolysis to 80 ℃ at the rate of 1 ℃/min, and pre-gelatinizing for 30 min;
(4) dissolving 0.51g of initiator in 40g of water to prepare an initiator solution, mixing the initiator solution accounting for 15 percent of the total mass of the initiator solution with an emulsifier and a grafting monomer to prepare a seed emulsion, cooling the system in the step (3) to 70 ℃, and then dripping the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed within 10 min;
(5) and (3) immediately adding the rest initiator in the step (4) for further grafting after 5min of preliminary grafting is finished, and after 20min of grafting reaction is carried out, dropwise adding a crosslinking monomer solution at a constant speed within 3h for crosslinking reaction, wherein the mass concentration of the crosslinking monomer is 10%.
(6) And (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) 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, the product has luster and appropriate initial viscosity, the viscosity is measured by referring to the viscosity measurement method, the range of the starch adhesive prepared in the comparative example is 9000-11000 mPa & s, the starch adhesive is similar to white latex, hot pressing is carried out under the conditions of 100 ℃ and 0.4MPa, the dry strength of the prepared three-layer plywood is 1.43MPa, the wet strength is 1.27MPa (the wet strength is measured after soaking for 3h, if the adhesive is broken within 3h, the wet strength is 0, the relative wet strength is represented by the adhesive breaking time, the longer the adhesive breaking time is, the better the water resistance is, and the dry strength and the wet strength are both greater than 0.7MPa of the national standard.
Compared with the example 4, the sectional dropping of the crosslinking monomer can obviously improve the thermosetting property of the adhesive.
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. A method for preparing a thermosetting artificial board starch adhesive with adjustable viscosity is characterized by comprising the following steps:
firstly, the formula of the artificial board starch adhesive comprises: (in parts by mass)
Taking starch milk prepared from starch as a main raw material, carrying out acidolysis treatment on the starch milk, adjusting the pH value of the starch milk, and carrying out pre-gelatinization at the temperature of 75-85 ℃ for 20-50 min; mixing and stirring part of grafting monomers, an emulsifier and an initiator uniformly to prepare a seed emulsion, adding the seed emulsion into the pregelatinized starch emulsion, adding the initiator after primary grafting is finished for further grafting, dropwise adding a crosslinking monomer solution accounting for 1/3 of the total mass of the crosslinking monomers at a constant speed within 30-40 min after grafting reaction is carried out for 20-40 min, adding a reconfigured initiator solution after dropwise adding is finished, preserving heat for 10-20 min for reaction, repeating the step of dropwise adding the crosslinking monomers for 2 times, and controlling the total dropwise adding time within 3 h; after the reaction is finished, heating and preserving heat to remove residual grafting monomers, finally cooling, uniformly stirring and discharging to obtain the starch adhesive.
2. The method according to claim 1, characterized in that it comprises in particular 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 be 60-75 ℃, adding hydrochloric acid diluted to be 0.5mol/L for acidolysis for 1.5-3 h, and then adding a sodium hydroxide solution to adjust the pH of the starch milk to be 4-6;
(3) adjusting the gelatinization temperature of the acidolyzed starch milk according to the required viscosity range, wherein the pre-gelatinization temperature is 75-85 ℃, and the pre-gelatinization time is 20-50 min;
(4) adding water into an initiator accounting for 50-70% of the total mass of the initiator to prepare an initiator solution with the mass concentration of 1-2%, taking 15-20% of the initiator solution by mass, grafting a monomer and an emulsifier to prepare a seed emulsion, and dropping the seed emulsion into the reaction system pre-gelatinized in the step (3) at a constant speed to react;
(5) and (3) immediately adding the rest initiator solution obtained in the step (4) for further grafting after 5-10 min of preliminary grafting is finished, after the grafting reaction is carried out for 20-40 min, firstly dropwise adding a crosslinking monomer solution accounting for 1/3 of the total mass of the crosslinking monomer at a constant speed, dropwise adding at a constant speed within 30-40 min, and adding a reconfigured initiator solution after dropwise adding is finished, wherein the initiator solution is: adding water into the rest initiator accounting for 30-50% of the total mass of the initiator to prepare initiator solution with the mass concentration of 1-2%, and dividing into 3 parts, wherein the part is one of the initiator solution; keeping the temperature for 10-20 min for reaction, repeating the step of dripping the crosslinking monomer for 2 times, and controlling the total dripping time within 3 h;
(6) and (3) heating the emulsion subjected to grafting and crosslinking modification in the step (5) to 80-90 ℃, preserving the temperature for 0.2-1 h to remove residual monomers, and cooling to 30-50 ℃ to obtain the starch adhesive.
3. The method of claim 1 or 2, wherein the starch is any one of corn starch, waxy corn starch, tapioca starch, wheat starch, cross-linked starch, or a combination of more thereof.
4. The method according to claim 1 or 2, characterized in that the initiator is a persulfate.
5. The method according to claim 1 or 2, wherein the graft monomer is one or a mixture of two or more of vinyl acetate, acrylic acid, and propylene.
6. The method according to claim 1 or 2, wherein the emulsifier is one or a mixture of two or more of sodium dodecyl sulfate, sodium dodecyl sulfonate, cetyl trimethyl ammonium bromide, octyl phenol polyoxyethylene ether-10 (OP-10), and phosphate ester emulsifier.
7. The method according to claim 1 or 2, wherein the crosslinking monomer is one or a mixture of two or more of N- (isobutoxymethyl) -acrylamide, N-dimethylacrylamide, N-isopropoxymethacrylamide, and N-butoxymethacrylamide.
8. The method according to claim 1 or 2, wherein the viscosity of the prepared starch adhesive is 2000-5000 mPa.s when the pre-gelatinization temperature is 75-80 ℃ and the pre-gelatinization time is 20 min; the pre-gelatinization temperature is 80-85 ℃, and the viscosity range of the prepared starch adhesive is 3000-10000 mPa & s when the pre-gelatinization time is 20 min; the viscosity range of the prepared starch adhesive is 3000-11000 mPa & s when the pre-gelatinization temperature is 80 ℃ and the pre-gelatinization time is 20-30 min; the viscosity range of the prepared starch adhesive is 9000-16000 mPa & s when the pre-gelatinization temperature is 80 ℃ and the pre-gelatinization time is 30-50 min.
9. The viscosity-adjustable thermosetting artificial board starch adhesive prepared by the method according to any one of claims 1-8.
10. The viscosity-adjustable thermosetting artificial board starch adhesive as claimed in claim 9, which is used for hot-press bonding of artificial boards, plywood and wood blocks, and decoration of wood.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114106749A (en) * | 2021-12-24 | 2022-03-01 | 江南大学 | Low-viscosity thermosetting particle board starch adhesive and preparation method thereof |
| CN114591707A (en) * | 2022-03-30 | 2022-06-07 | 江南大学 | High-temperature fast-curing starch-based shaving board adhesive and preparation method thereof |
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| JP2009263450A (en) * | 2008-04-23 | 2009-11-12 | Henkel Japan Ltd | Adhesive for label |
| CN109266265A (en) * | 2018-09-14 | 2019-01-25 | 江南大学 | A kind of thermosetting property wood-based plate starch adhesive and preparation method thereof |
| CN111205794A (en) * | 2020-02-26 | 2020-05-29 | 江南大学 | Starch adhesive for thermosetting artificial board and preparation method thereof |
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2020
- 2020-06-24 CN CN202010592401.6A patent/CN111647112A/en active Pending
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2009263450A (en) * | 2008-04-23 | 2009-11-12 | Henkel Japan Ltd | Adhesive for label |
| CN109266265A (en) * | 2018-09-14 | 2019-01-25 | 江南大学 | A kind of thermosetting property wood-based plate starch adhesive and preparation method thereof |
| CN111205794A (en) * | 2020-02-26 | 2020-05-29 | 江南大学 | Starch adhesive for thermosetting artificial board and preparation method thereof |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114106749A (en) * | 2021-12-24 | 2022-03-01 | 江南大学 | Low-viscosity thermosetting particle board starch adhesive and preparation method thereof |
| CN114106749B (en) * | 2021-12-24 | 2022-08-02 | 江南大学 | Low-viscosity thermosetting type shaving board starch adhesive and preparation method thereof |
| WO2023116055A1 (en) * | 2021-12-24 | 2023-06-29 | 江南大学 | Low-viscosity thermosetting particle board starch adhesive and preparation method therefor |
| US11879071B2 (en) | 2021-12-24 | 2024-01-23 | Jiangnan University | Low-viscosity thermosetting starch adhesive for particleboards, and preparation method therefore |
| CN114591707A (en) * | 2022-03-30 | 2022-06-07 | 江南大学 | High-temperature fast-curing starch-based shaving board adhesive and preparation method thereof |
| WO2023185048A1 (en) * | 2022-03-30 | 2023-10-05 | 江南大学 | Starch-based particle board adhesive capable of being quickly cured at high temperature, and preparation method therefor |
| US11981834B2 (en) | 2022-03-30 | 2024-05-14 | Jiangnan University | High-temperature fast-curing starch-based adhesive for particleboards and preparation method thereof |
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