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CN-121991603-A - Cross-linking modification process of degradable starch-based adhesive

CN121991603ACN 121991603 ACN121991603 ACN 121991603ACN-121991603-A

Abstract

The invention discloses a crosslinking modification process of a degradable starch-based adhesive, and belongs to the technical field of adhesive preparation. The process comprises the steps of firstly compounding corn starch and tapioca starch, pre-gelatinizing to obtain uniform starch paste, regulating pH by using dilute hydrochloric acid and a buffer solution step by step, sequentially adding citric acid, boric acid and epichlorohydrin for crosslinking reaction, adding small molecular polyol subjected to dehydration pretreatment for intercalation modification, matching trehalose for locking moisture, adding modified carboxymethylated chitosan and natural lecithin to form a dense interface film and improving system compatibility, finally adding modified carboxylated polyvinyl alcohol for toughening, and carrying out vacuum degassing, corrosion prevention, filtration and low-temperature aging to obtain the finished product. The invention solves the problems of poor water resistance, insufficient toughness and low structure and storage stability of the existing starch-based adhesive, and the prepared adhesive has high bonding strength, excellent wet retention rate and toughness, good system compatibility, uniform performance and biodegradability.

Inventors

  • PU DEXING
  • ZHONG YOUZHENG

Assignees

  • 长沙市汇华胶粘剂科技有限公司

Dates

Publication Date
20260508
Application Date
20260409

Claims (10)

  1. 1. The crosslinking modification process of the degradable starch-based adhesive is characterized by comprising the following steps of: (1) Starch pretreatment, namely mixing a starch raw material with a plasticizer, adding deionized water, uniformly stirring, and pre-gelatinizing to form uniform starch paste; (2) The cross-linking reaction, namely, after the pH value of the starch paste is adjusted, three cross-linking agents are sequentially added for reaction to form a cross-linked product; (3) Adding pretreated micromolecular polyol into the crosslinked product, stirring and uniformly mixing the mixture to obtain a polyol intercalation modified crosslinked system; (4) Film forming and compatibility regulation, namely adding modified carboxymethylated chitosan and natural lecithin into a polyol intercalation modified crosslinking system, and stirring and dispersing to obtain a mixed system; (5) Toughening and post-treatment, namely adding modified carboxylated polyvinyl alcohol into the mixed system obtained in the step (4), heating and stirring, and carrying out corrosion prevention and filtration treatment to obtain the degradable starch-based adhesive.
  2. 2. The crosslinking modification process of the degradable starch-based adhesive according to claim 1, wherein in the step (1), the starch raw material is a mixture of corn starch and tapioca starch, the mass ratio of the corn starch to the tapioca starch is 7:3-8:2, the plasticizer is glycerol, the addition amount is 3% -5% of the total mass of the starch raw material, the pregelatinization treatment temperature is 65-75 ℃, the stirring speed is 150-200r/min, and the temperature is reduced to 40-50 ℃ after the treatment is completed.
  3. 3. The crosslinking modification process of the degradable starch-based adhesive according to claim 1 is characterized in that in the step (2), three crosslinking agents are citric acid, boric acid and epichlorohydrin in sequence, when in crosslinking reaction, the initial pH value of starch paste is regulated to 4.0-4.5 by dilute hydrochloric acid with the concentration of 0.1-0.5mol/L, citric acid accounting for 2% -4% of the total mass of starch raw materials is dripped, the dripping rate is 2.5-3.5mL/min, the pH value of a system is regulated to 5.0-6.0 by citric acid-borax buffer solution, boric acid accounting for 0.5% -1.5% of the total mass of starch raw materials is dripped, the dripping rate is 1.0-2.0mL/min, then the pH value is regulated to 7.0-7.5 by sodium hydroxide-borax composite weak base buffer solution, the dripping rate is 0.8-1.2mL/min, the total heat-insulating reaction time is 150-180min, and the pH value of the system is regulated to 6.5-7.5 after the whole reaction is finished.
  4. 4. The crosslinking modification process of the degradable starch-based adhesive according to claim 1, wherein in the step (3), the small molecular polyol is selected from glycerol or xylitol, the addition amount of the small molecular polyol is 2% -3% of the total mass of the starch raw material, the pretreatment condition of the small molecular polyol is 75-85 ℃ and the pretreatment condition of the small molecular polyol is vacuum dehydrated for 1.5-2.5h under the pressure of minus 0.08-0.10 MPa, and the water content after the treatment is less than or equal to 0.8%.
  5. 5. The process for crosslinking modification of a degradable starch-based adhesive according to claim 4, wherein the preparation steps of the modified carboxymethylated chitosan are as follows: 1a) Adding chitosan with deacetylation degree more than or equal to 90% into isopropanol, dispersing uniformly, adding sodium hydroxide aqueous solution with mass fraction of 25% -35%, and preserving heat and alkalizing for 1.5-2.5h at 40-50 ℃ to obtain an alkalizing system; 2a) Adding 2-3% of epoxypropyl trimethyl ammonium chloride by mass of chitosan into an alkalization system, stirring for reacting for 1-1.5h, dissolving chloroacetic acid into isopropanol, slowly dripping into the alkalization system, and carrying out heat preservation and etherification for 3.5-4.5h at 55-65 ℃ to obtain an intermediate system; 3a) Adjusting the pH of an intermediate system to 6.5-7.5 by using 8-12% by mass of dilute hydrochloric acid, filtering, collecting a solid product, washing the solid product by using absolute ethyl alcohol and deionized water in sequence, vacuum drying the solid product to constant weight at 55-65 ℃, and crushing the solid product to 70-90 meshes to obtain the modified carboxymethyl chitosan, wherein the substitution degree of carboxymethyl is 0.8-1.0, and the water solubility of a neutral system is more than or equal to 95%.
  6. 6. The process for crosslinking modification of a degradable starch-based adhesive of claim 5, wherein the preparation of the modified carboxylated polyvinyl alcohol comprises the steps of: 1b) Adding polyvinyl alcohol with the alcoholysis degree of 88% into deionized water, heating to 85-95 ℃, stirring until the polyvinyl alcohol is completely dissolved to form a polyvinyl alcohol aqueous solution with the mass fraction of 8-12%, and cooling to 45-55 ℃; 2b) Adding an iron chloride-copper chloride composite catalyst into a polyvinyl alcohol aqueous solution, wherein the mass ratio of the iron chloride to the copper chloride in the composite catalyst is 1:1, slowly dropwise adding 25-35% of hydrogen peroxide after stirring and dissolving, and carrying out heat preservation reaction for 2.5-3.5h at 45-55 ℃; 3b) Adding sodium sulfite into the system, stirring and mixing, vacuum drying to constant weight at 55-65 ℃, and crushing to 50-70 meshes to obtain the modified carboxylated polyvinyl alcohol, wherein the carboxyl content of the modified carboxylated polyvinyl alcohol is 1-2%.
  7. 7. The crosslinking modification process of the degradable starch-based adhesive according to claim 6, wherein in the step (3), dried modified carboxymethylated chitosan and modified carboxylated polyvinyl alcohol are mixed with micromolecular polyalcohol, and placed in a vacuum drying oven with the temperature of 80-90 ℃ and the pressure of minus 0.09-0.11 MPa for dehydration for 1.2-1.8 hours, the total moisture after the mixing is controlled to be less than or equal to 0.8 percent, and natural trehalose accounting for 0.3-0.5 percent of the total mass of starch raw materials is added after the dehydration, and the mixture is stirred and mixed.
  8. 8. The crosslinking modification process of the degradable starch-based adhesive according to claim 7, wherein in the step (4), the addition amount of the modified carboxymethyl chitosan is 0.2-0.4% of the total mass of the starch raw material, the addition amount of the natural lecithin is 0.8-1.2% of the total mass of the starch raw material, the modified carboxymethyl chitosan is added after being dissolved in absolute ethyl alcohol accounting for less than or equal to 3% of the total mass of the system, the stirring speed is 100-160r/min, and the stirring time is 20-30min.
  9. 9. The crosslinking modification process of the degradable starch-based adhesive according to claim 7, wherein in the step (5), the addition amount of the modified carboxylated polyvinyl alcohol is 8% -10% of the total mass of the starch raw material, the stirring time is 30-40min, the vacuum degassing treatment is introduced in the stirring process, and the vacuum degree is-0.07 to-0.09 MPa.
  10. 10. The crosslinking modification process of the degradable starch-based adhesive according to claim 9, wherein in the step (5), the preservative is sodium dehydroacetate or epsilon-polylysine, the addition amount is 0.2% -0.3% of the total mass of the system, a multi-stage filtration mode of 70-90 mesh rough filtration and 190-210 mesh fine filtration is adopted for filtration, and the adhesive is aged for 20-28 hours at a low temperature under the condition of 23-27 ℃ after filtration; In the step (5), the temperature is raised and stirred to 58-62 ℃.

Description

Cross-linking modification process of degradable starch-based adhesive Technical Field The invention relates to the technical field of adhesive preparation, in particular to a crosslinking modification process of a degradable starch-based adhesive. Background The starch-based adhesive has the advantages of renewable raw materials, biodegradability, environmental friendliness and the like, becomes an important substitution direction of petroleum-based adhesives, and is widely applied to the fields of packaging, wood processing, paper bonding and the like. However, the natural starch has a large number of hydroxyl groups in molecular chains, and excessive hydrogen bonds are easy to form among molecules, so that the prepared adhesive has inherent defects. For example, a single crosslinking mode is difficult to build a stable network structure, the adhesive has poor structural stability, the adhesive strength in a dry state is not easy to crack, toughness is not kept up, impact is not carried out in practical use, the existing starch-based adhesive has poor water resistance, is easy to swell and debond when meeting water, has poor wet adhesive strength, limits the application scene to a dry environment, has poor compatibility among various modified components, is easy to agglomerate and delaminate, and has uneven performance at each part of the adhesive. In order to solve the problems, the prior art adopts a mode of modifying a single cross-linking agent and simply adding a toughening agent or a water-resistant agent, and can improve certain performance to a certain extent, but other performance attenuation is easy to cause, and multi-performance cooperative improvement is difficult to realize. Therefore, it is necessary to provide a crosslinking modification process for degradable starch-based adhesives to solve the above technical problems. Disclosure of Invention The invention aims to provide a crosslinking modification process of a degradable starch-based adhesive, which aims to solve the problems of poor structural stability, insufficient water resistance and low toughness of the existing starch-based adhesive. In order to achieve the aim, the invention provides the following technical scheme that the crosslinking modification process of the degradable starch-based adhesive comprises the following steps: (1) Starch pretreatment, namely mixing a starch raw material with a plasticizer, adding deionized water, uniformly stirring, and pre-gelatinizing to form uniform starch paste; (2) The cross-linking reaction, namely, after the pH value of the starch paste is adjusted, three cross-linking agents are sequentially added for reaction to form a cross-linked product; (3) Adding pretreated micromolecular polyol into the crosslinked product, stirring and uniformly mixing the mixture to obtain a polyol intercalation modified crosslinked system; (4) Film forming and compatibility regulation, namely adding modified carboxymethylated chitosan and natural lecithin into a polyol intercalation modified crosslinking system, and stirring and dispersing to obtain a mixed system; (5) Toughening and post-treatment, namely adding modified carboxylated polyvinyl alcohol into the mixed system obtained in the step (4), heating and stirring, and carrying out corrosion prevention and filtration treatment to obtain the degradable starch-based adhesive. Preferably, in the step (1), the starch raw material is a mixture of corn starch and tapioca starch, the mass ratio of the corn starch to the tapioca starch is 7:3-8:2, the plasticizer is glycerol, the addition amount of the plasticizer is 3% -5% of the total mass of the starch raw material, the pregelatinization treatment temperature is 65-75 ℃, the stirring speed is 150-200r/min, and the temperature is reduced to 40-50 ℃ after the treatment is completed. The method is characterized in that in the step (2), citric acid, boric acid and epichlorohydrin are adopted as the three crosslinking agents in sequence, when in crosslinking reaction, the initial pH value of the starch paste is regulated to 4.0-4.5 through dilute hydrochloric acid with the concentration of 0.1-0.5mol/L, citric acid accounting for 2% -4% of the total mass of the starch raw material is dripped, the dripping speed is 2.5-3.5mL/min, then the pH value of the system is regulated to 5.0-6.0 through citric acid-borax buffer solution, boric acid accounting for 0.5% -1.5% of the total mass of the starch raw material is dripped, the dripping speed is 1.0-2.0mL/min, then the pH value is regulated to 7.0-7.5 through sodium hydroxide-borax composite weak base buffer solution, epichlorohydrin accounting for 1% -3% of the total mass of the starch raw material is dripped, the total heat-preserving reaction time is 150-180min in the whole course, and the pH value of the system is regulated to 6.5-7.5 after the reaction is finished. Preferably, in the step (3), the small molecular polyol is selected from glycerol or xylitol, the addi