Vacuum drying preparation method of environment-friendly biomass adhesive

Abstract

The invention discloses a vacuum drying preparation method of an environment-friendly biomass adhesive, and belongs to the technical field of adhesives. According to the method, forestry and agricultural residues and vegetable protein are used as raw materials, and the biomass adhesive which is free of formaldehyde, high in bonding strength and excellent in water resistance is prepared through the steps of mechanochemical pretreatment, multi-component composite reaction, vacuum drying and the like. The method is characterized by comprising the following steps: (1) carrying out micro-nano treatment on raw materials by adopting a mechanochemical method to improve the reaction activity of lignin; (2) introducing a plant protein and starch composite system, and combining a cross-linking agent to optimize colloid performance; and (3) residual moisture and volatile substances are removed through a vacuum drying process, so that the storage stability and the curing efficiency of the adhesive are remarkably improved. Experiments show that the dry strength of the product is larger than or equal to 8 MPa, the wet strength is larger than or equal to 2.5 MPa, the curing time is shortened to be within 15 minutes, and the product is suitable for the fields of plywood, fiberboards and the like and has remarkable environment-friendly and economic values.

Description

Technical Field

[0001] The present invention relates to the technology for preparing biomass adhesives, and particularly to an environmentally friendly adhesive based on agricultural and forestry waste and plant protein and its vacuum drying process, which is applicable to the fields of wood-based panels (such as plywood, fiberboard, particleboard), packaging materials (such as cartons, wooden pallets), and building decoration materials. The present invention solves the technical problems of low bonding strength, poor water resistance, and long curing time of traditional biomass adhesives through multi-component synergistic modification and vacuum drying process. Background Art

[0002] Traditional adhesives (such as urea-formaldehyde resin, phenolic resin) mainly rely on petrochemical raw materials, and volatile organic compounds (VOCs) such as formaldehyde released during their production cause serious harm to human health and the environment. According to the statistics of the "China Adhesive Industry Report", the market share of traditional adhesives reached 65% in 2023, but the problem of excessive formaldehyde release limits their application.

[0003] In recent years, biomass adhesives have become a research hotspot, but the existing technologies still have the following defects:

[0004] 1. Insufficient bonding strength: The dry strength of single-protein or starch adhesives is generally lower than 6 MPa, and the wet strength is less than 1 MPa (see document CN103421466A);

[0005] 2. Poor water resistance: Biomass components (such as starch, protein) contain a large number of hydrophilic groups such as hydroxyl and amino groups, which are easy to absorb moisture and cause bonding failure (document CN115678112A);

[0006] 3. Poor storage stability: Residual moisture (>5%) will cause microbial growth or colloid stratification (document CN117432101A);

[0007] 4. Low curing efficiency: The existing process requires a curing time of more than 30 minutes, which is difficult to meet the requirements of continuous production.

[0008] Existing improvement schemes such as CN118085815A use mechanochemical method to activate lignin, but do not optimize the drying process, resulting in a relatively high water content (6%-8%) of the product; CN120987654A improves water resistance by adding a cross-linking agent, but excessive cross-linking agent dosage (>3%) will reduce the fluidity of the colloid. The present invention combines vacuum drying with multi-component cross-linking to significantly improve the comprehensive performance of the product while ensuring environmental protection. Summary of the Invention

[0009] Technical Problems

[0010] Aiming at the deficiencies of the existing technology, the present invention needs to solve the following problems:

[0011] 1. How to improve the dry / wet strength of the biomass adhesive to industrial application standards;

[0012] 2. How to reduce the water content (≤5%) and improve the storage stability through process optimization;

[0013] 3. How to shorten the curing time to within 15 minutes to meet the production line efficiency requirements.

[0014] Technical solution

[0015] 1. Raw material selection and pretreatment

[0016] Main materials: Agricultural and forestry waste (peanut shells, straw, bark) are crushed to a particle size of ≤100 μm, with a lignin content of ≥35% and a cellulose content of ≥40%. They are mixed with plant proteins (soybean protein, cottonseed protein) in a ratio of 3:1 - 5:1 to form an adhesive matrix;

[0017] Auxiliary materials:

[0018] Starch glue: Oxidized corn starch or tapioca starch (degree of substitution 0.02 - 0.05) is used to enhance the initial viscosity;

[0019] Crosslinking agent: A silane coupling agent (KH550 or KH560) is compounded with furfuryl urea resin to form a three-dimensional network structure;

[0020] Water resistance aid: Nano-silica (particle size 20 - 50 nm) and magnesium oxide act synergistically to fill the pores of the colloid and form a hydrophobic barrier.

[0021] 2. Mechanochemical activation

[0022] Mechanism: The ball mill generates mechanical shear force at 300 - 500 rpm, destroying the crystalline region (002 crystal plane) of lignin and increasing the specific surface area to 15 - 20 m 2 / g;

[0023] Alkali treatment: A 0.5 - 1.5 mol / L NaOH solution promotes the cleavage of the β-O-4 bond of lignin, generating phenolic hydroxyl groups and carboxyl groups, which react with the amino groups of plant proteins to form Schiff bases.

[0024] 3. Vacuum drying process

[0025] The first stage (20 - 30 kPa, 50 °C): Remove free water to avoid film formation on the surface of the colloid;

[0026] The second stage (≤10 kPa, 60 °C): Deeply remove bound water and low molecular weight volatiles, and reduce the porosity of the colloid to below 5%.

[0027] Beneficial effects

[0028] 1. Environmental friendliness: 100% of the raw materials are renewable, the VOCs emission is 0, and the formaldehyde release is not detected (GB / T 17657-2013 standard);

[0029] 2. High performance: Dry strength ≥ 8 MPa (GB / T 9846-2015), wet strength ≥ 2.5 MPa (tested after soaking in water for 24 h); The water resistance is improved by more than 200% (compared with CN103421466A);

[0030] 3. Efficient production: The curing time is shortened to 12 - 15 minutes (the traditional process takes 25 - 30 minutes), and the energy consumption is reduced by 30%;

[0031] 4. Storage stability: The water content ≤ 5%, and there is no stratification or mildew after storing at room temperature for 6 months. Specific implementation method

[0032] Example 1

[0033] Raw material ratio: Peanut shell powder (particle size 80 μm): 60%, soy protein powder: 15%, oxidized corn starch: 20%, silane coupling agent (KH550): 1%, nano-silica: 4%.

[0034] Preparation steps:

[0035] Pretreatment: Mix peanut shell powder and soy protein powder at a ratio of 4:1, and place them in a high-speed mixer for pre-dispersion for 10 minutes;

[0036] Mechanochemical activation: Add 1 mol / L NaOH solution (8% of the lignin mass), and react in a ball mill (400 rpm) for 3 hours at a temperature of 70°C;

[0037] Compound reaction: Add oxidized corn starch, silane coupling agent, and nano-silica in sequence, and stir at 60°C for 1.5 hours at a rotation speed of 200 rpm;

[0038] Vacuum drying:

[0039] First stage: Pressure 25 kPa, temperature 50°C, time 1 hour;

[0040] Second stage: Pressure 8 kPa, temperature 60°C, time 2 hours;

[0041] Finished product treatment: After cooling to room temperature, add 0.3% borax and seal for packaging.

[0042] Performance test: Dry strength: 8.7 MPa (GB / T 17657-2015), wet strength: 2.8 MPa (soaked in water for 24 h, 25°C), curing time: 12 minutes (hot pressing temperature 120°C, pressure 1.2 MPa), water content: 4.2% (GB / T 606-2003).

[0043] Example 2

[0044] Raw material ratio: straw powder (particle size 100μm): 55%, cottonseed protein powder: 18.3%, cassava starch: 22%, furfuryl urea resin: 1.5%, magnesium oxide: 3.2%.

[0045] Preparation steps:

[0046] Pretreatment: Mix the straw powder and cottonseed protein powder at a ratio of 3:1 and ultrasonically treat for 20 minutes (frequency 40kHz);

[0047] Mechanochemical activation: Add 0.8mol / L NaOH solution (6% of the lignin mass), and ball-mill for 4 hours (rotation speed 350rpm, temperature 60°C);

[0048] Compound reaction: Add cassava starch, furfuryl urea resin, and magnesium oxide, and stir at 50°C for 2 hours;

[0049] Vacuum drying:

[0050] First stage: Pressure 30kPa, temperature 45°C, time 1 hour;

[0051] Second stage: Pressure 10kPa, temperature 55°C, time 2.5 hours;

[0052] Final product treatment: Add 0.2% borax and encapsulate under nitrogen protection.

[0053] Performance test: Dry strength: 8.1MPa, wet strength: 2.5MPa, curing time: 14 minutes, water content: 4.8%.

[0054] Experimental data comparison

[0055] Index Example 1 of the present invention Example 2 Traditional urea-formaldehyde glue CN103421466A Dry strength (MPa) 8.7 8.1 9.0 6.5 Wet strength (MPa) 2.8 2.5 0.3 1.2 Formaldehyde release amount (mg / L) Not detected Not detected 0.5 Not detected Curing time (min) 12 14 20 25 Storage stability (months) ≥6 ≥6 ≥12 ≥3 Energy consumption (kWh / t) 85 90 120 110

Claims

1. A preparation method of an environment-friendly biomass adhesive, characterized in that It includes the following steps: (1) Pretreatment of raw materials: Grind agricultural and forestry waste to a particle size of ≤100 μm, and mix it with plant protein powder (soybean protein, cottonseed protein) at a mass ratio of 3:1 - 5:1; (2) Mechanochemical activation: Grind in a ball mill at 300 - 500 rpm for 30 - 60 minutes, add a sodium hydroxide solution with a mass of 5% - 10% of the lignin, and react at 60 - 80 °C for 2 - 4 hours; (3) Composite reaction: Add starch glue (corn starch, tapioca starch), crosslinking agent (0.5% - 1.5% silane coupling agent, 1% - 2% furfuryl urea resin), water - resistant auxiliary agent (3% - 8% nano - silica, 1% - 3% magnesium oxide), and stir - react at 50 - 70 °C for 1 - 2 hours; (4) Vacuum drying: Place the colloid in a vacuum drying oven, with a pressure of ≤10 kPa and a temperature of 40 - 60 °C, and dry until the water content is ≤5%; (5) Finished product packaging: After cooling, add a preservative (0.1% - 0.5% borax), and store it sealed.

2. The method according to claim 1, wherein The concentration of the sodium hydroxide solution described in step (2) is 0.5 - 1.5 mol / L.

3. The method according to claim 1, wherein The vacuum drying in step (4) is divided into two stages: the first stage has a pressure of 20 - 30 kPa and a temperature of 50 °C for 1 hour; the second stage has a pressure of ≤10 kPa and a temperature of 60 °C for 2 hours.