Preparation method for uniformly mixing and stirring biomass adhesive

Abstract

The invention discloses a preparation method for uniformly mixing and stirring a biomass adhesive, which realizes molecular-level uniform mixing of biomass components by constructing a synergistic action mechanism of a three-way gradient shear force field and an intelligent temperature control system and combining a nano material directional dispersion technology. Compared with the prior art, the adhesive strength of the product is improved by 80% or above, the emission of volatile organic compounds is reduced by 82%, and the adhesive is particularly suitable for the fields of high-end wood products and environment-friendly packaging materials and is excellent in mixing uniformity, water resistance and environment-friendly performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass material processing, and particularly relates to a method for uniformly stirring and preparing a biomass adhesive based on the synergistic action of multi-stage dynamic temperature control and gradient shear force, and is particularly applicable to the fields of wood processing, packaging materials, and formaldehyde-free wood-based panels. Background Art

[0002] The traditional biomass adhesives have the following technical bottlenecks:

[0003] 1. Component stratification problem: Phase separation occurs between lignin and polysaccharide substances due to molecular weight differences. For example, in patent CN103421466A, protein and starch are compounded, but the problem of uniform dispersion is not solved.

[0004] 2. Insufficient thermal stability: High-temperature stirring easily causes uneven gelatinization of starch. For example, in patent CN105885773A, a soybean flour-based adhesive is used, and its water resistance only meets the lowest national standard requirements.

[0005] 3. Low mixing efficiency: Most of the existing technologies use single-axis stirring (such as patent CN101831256B), and the mixing efficiency is lower than 75%.

[0006] 4. Poor environmental performance: Traditional adhesives have high VOC emissions (such as in patent CN202210950134.4, VOC control is not mentioned).

[0007] Existing improved technologies such as the protein and starch compounding process in CN103421466A are not optimized, and the mixing uniformity is only 80%; CN105885773A relies on inorganic bases to enhance water resistance, resulting in a high pH value of the colloid and limited applications; CN101831256B uses potassium persulfate as an oxidant, which is costly and has residual harmful substances. Therefore, there is an urgent need to develop a stirring process with good mixing uniformity, water resistance, and environmental performance. Summary of the Invention

[0008] 1. Technical Problems

[0009] 1. The problem of molecular-level uniform dispersion of biomass components (such as lignin, starch, protein);

[0010] 2. The collaborative optimization of dynamic viscosity regulation and temperature field during the mixing process;

[0011] 3. The directional dispersion of nano-enhancers (such as SiO2) and the strengthening of interfacial bonding.

[0012] 2. Technical Solutions

[0013] 1. Three-dimensional gradient shear system

[0014] Structural design: Coaxial three-way stirring device (inner-layer propeller, middle-layer toothed paddle, outer-layer frame paddle), speed ratio (2.5 - 3.5):(5 - 6):1.

[0015] Mechanism of action:

[0016] The inner-layer propeller (200 - 300 rpm) realizes axial material transportation;

[0017] The middle-layer toothed paddle (500 - 600 rpm) generates high-frequency shear force to break up agglomerated particles;

[0018] The outer-layer frame paddle (80 - 120 rpm) forms a global circulating flow field to eliminate dead corners.

[0019] 2. Temperature-viscosity coupling control algorithm

[0020] Real-time feedback mechanism: Through the linkage of an on-line viscosity sensor and a PID temperature control system, dynamically adjust the process parameters:

[0021] Process stage Temperature control range (°C) Viscosity threshold (mPa·s) Functional objective Premixing 45±2 ≤500 Reduce the initial viscosity and promote flow Activation 65±1 800-1200 Trigger crosslinking reaction Curing 50±1 1500-1800 Stabilize the colloid structure

[0022] 3. Nano-enhancer directional dispersion technology

[0023] Aerosol spraying process: Spray SiO2 nanoparticles (20 - 50 nm) three times with a carrier gas pressure of 0.3 - 0.5 MPa, with an interval of 5 minutes, and the dispersion uniformity ≥ 98.5%.

[0024] Interface modification: Pretreat the nanoparticles with a silane coupling agent (KH-550) to enhance the interfacial bonding force with the biomass matrix.

[0025] 3. Technical effects

[0026] Performance improvement: The mixing uniformity reaches 93.7% - 95.2% (traditional process ≤ 75%); the wet-state bonding strength is 3.1 - 3.4 MPa (national standard ≥ 1.5 MPa); the VOC emission ≤ 95 μg / g (traditional adhesives ≥ 520 μg / g).

[0027] Process optimization: The curing time is shortened to 12 - 15 minutes (traditional ≥ 30 minutes); the energy consumption is reduced by 40% (comparative patent CN103421466A). Specific implementation methods

[0028] Example 1: Special type for wood processing

[0029] This example aims at the requirements of the wood processing industry for high-strength and fast-curing adhesives, and the specific implementation steps are as follows:

[0030] Raw material selection and pretreatment:

[0031] 1. Enzymatic lignin: Prepared by co-hydrolysis of agricultural and forestry waste (wheat straw, corn cob) with cellulase-xylanase. The enzymatic hydrolysis conditions are pH 4.8, temperature 50 °C, and reaction time 48 hours. The molecular weight of the obtained lignin is controlled at 5000-8000 Da, and the ash content is ≤1.2%;

[0032] 2. Modified starch: Cassava starch is selected as the raw material, alkali-treated with 0.5 mol / L NaOH solution at 60 °C for 2 hours, and then cross-linked and modified with 3% epichlorohydrin, with a degree of substitution of more than 0.25;

[0033] 3. Nano-SiO2: Hydrophobic nanoparticles synthesized by the gas phase method, with a specific surface area of 200 ± 10 m 2 / g. Before use, it is surface-modified with the silane coupling agent KH-550, and the addition amount of the modifier is 3% of the mass of SiO2;

[0034] 4. Cross-linking agent: Branched polyethyleneimine (PEI, molecular weight 1800) is used, dissolved in deionized water to prepare a 30% concentration solution for standby.

[0035] Mixing process parameters:

[0036] 1. Premixing stage:

[0037] Put 35 kg of enzymatic lignin and 25 kg of modified starch into a three-layer stirring reaction kettle with a volume of 500 L. The kettle body is made of 316L stainless steel;

[0038] Turn on the jacket circulating water system, set the initial temperature at 45 °C, and the heating rate is precisely controlled by the PLC system; Start the three-way stirring device: The inner layer propeller rotates at 250 rpm, the blade diameter is 120 mm, and the pitch ratio is 1:1.2, responsible for axial material transportation; The middle layer toothed blade rotates at 550 rpm, the blade diameter is 200 mm, the tooth height is 10 mm, and the tooth spacing is 5 mm, generating high-frequency shear force to break agglomerated particles; The outer layer frame blade rotates at 100 rpm, and the gap between the blade and the kettle wall is ≤3 mm, forming a global circulation flow field;

[0039] Continuously mix for 15 minutes, and monitor the D90 value of the particles ≤50 μm through an online laser particle size analyzer.

[0040] 2. Activation stage:

[0041] Heat up to 65 °C at a gradient of 2 °C / min, and at this time, add 3 kg of PEI cross-linking agent solution;

[0042] Increase the rotation speed of the middle layer toothed blade to 600 rpm, strengthen the shear rate to 1200 s-1, and trigger the starch-lignin cross-linking reaction;

[0043] The apparent viscosity was monitored in real time by an online viscometer (Brookfield DV3T). When the viscosity reached 1000 mPa·s, timing was started and maintained for 20 minutes.

[0044] The vacuum degassing system was turned on simultaneously. The vacuum degree was -0.08 MPa to remove the water vapor and trace volatiles generated by the reaction.

[0045] 3. Aging stage:

[0046] The temperature was decreased to 50 °C at a gradient of 1 °C / min. During this process, 1.5 kg of nano-SiO₂ was injected in three times: The first injection: the carrier gas pressure was 0.4 MPa, the injection time was 30 seconds, and the nozzle diameter was 0.5 mm; The second injection: after an interval of 5 minutes, the carrier gas pressure was 0.45 MPa, and the injection time was 45 seconds; The third injection: after an interval of 5 minutes, the carrier gas pressure was 0.35 MPa, and the injection time was 60 seconds.

[0047] The rotation speed of the outer frame paddle was adjusted to 120 rpm to strengthen the overall mixing, and shearing was continued for 30 minutes until the viscosity was stabilized at 1650 ± 50 mPa·s.

[0048] The final colloid was discharged after being filtered through a 200-mesh filter screen and stored in a sealed container.

[0049] Example 2: Special type for packaging materials

[0050] In view of the special requirements of food-grade packaging materials for environmental protection and flexibility, the specific implementation steps are as follows:

[0051] Raw material selection and pretreatment:

[0052] 1. Chitosan: A food-grade raw material with a deacetylation degree of ≥90% was selected and dissolved in a 2% acetic acid solution to prepare a 25% concentration colloidal solution. Ultrasonic treatment (40 kHz, 30 minutes) was used to remove undissolved particles.

[0053] 2. Cellulose nanocrystals: Prepared by sulfuric acid hydrolysis of cotton linter, with a length of 150 - 200 nm, a diameter of 20 - 30 nm, and a Zeta potential of -35 mV. Cationic modification was carried out with 0.1% cetyltrimethylammonium bromide (CTAB) before use.

[0054] 3. Tannic acid: An extract from Chinese gallnuts was selected with a purity of ≥98% and dissolved in deionized water at 50 °C to prepare a 10% solution.

[0055] 4. Glycerol: Food-grade purity, directly added without pretreatment.

[0056] Mixing process parameters:

[0057] 1. Predispersion stage:

[0058] Add 28 kg of chitosan solution and 15 kg of cellulose nanocrystals to a 300-L double-layer kettle, and set the initial temperature to 45 °C.

[0059] Start the middle-layer toothed paddle (rotation speed 550 rpm) for preliminary mixing. At the same time, inject nano-SiO2 in three times through the top aerosol injection system: First injection: carrier gas pressure 0.3 MPa, injection time 20 s, SiO2 addition amount 0.5 kg; Second injection: after a 5-minute interval, carrier gas pressure 0.35 MPa, injection time 25 s, SiO2 addition amount 0.5 kg; Third injection: after a 5-minute interval, carrier gas pressure 0.3 MPa, injection time 30 s, SiO2 addition amount 0.5 kg.

[0060] After each injection, start the high-frequency pulse mode (10 Hz, lasting for 1 minute) to promote the dispersion of nanoparticles by using instantaneous shear force.

[0061] 2. Coupled stirring stage:

[0062] Add 5 kg of tannic acid solution and 4 kg of glycerol, and switch to the variable-frequency stirring mode: the rotation speed of the inner-layer screw paddle changes periodically between 200 - 300 rpm (change period 2 minutes); the amplitude of the middle-layer toothed paddle is adjusted to 5 - 10 mm to generate alternating shear and extrusion effects.

[0063] Synchronously heat up to 65 °C, and dynamically adjust the stirring parameters according to the on-line viscosity detection value during the heating process: when the viscosity < 800 mPa·s, increase the rotation speed of the middle-layer paddle to 600 rpm; when the viscosity > 1200 mPa·s, reduce the rotation speed of the outer-layer frame paddle to 80 rpm and turn on the auxiliary wall scraping device.

[0064] 3. Aging control stage:

[0065] Cool down to 50 °C in a gradient manner, and link the cooling rate with the viscosity change rate: initial cooling rate 1.5 °C / min (when the viscosity increase rate > 50 mPa·s / min); later, adjust the cooling rate to 0.5 °C / min (when the viscosity increase rate < 20 mPa·s / min).

[0066] Maintain the outer-layer frame paddle at 100 rpm for full-range circulation for 30 minutes. Finally, the light transmittance of the colloid (wavelength 660 nm) ≥ 95%, and the pH value is stable at 6.8 - 7.2.

[0067] The finished product is made into a 0.2-mm-thick glue film through a casting film machine, sliced and packaged, and stored in the dark.

[0068] Combine experimental data with industry standards for comprehensive comparison:

[0069]

Claims

1. A preparation method for uniformly stirring a biomass adhesive, characterized in that It involves the synergistic effects of a three-way gradient shearing system, a temperature-viscosity coupling control algorithm, and a nano-enhancer directional dispersion technique.

2. According to the method described in claim 1, the three-way gradient shearing system includes an inner-layer propeller, a middle-layer toothed paddle, and an outer-layer frame paddle arranged coaxially, and the rotation speed ratio ranges from (2.5 - 3.5):(5 - 6):

1.

3. According to the method described in claim 1, the temperature control includes three stages: a premixing stage at 45 ± 2°C, an activation stage at 65 ± 1°C, and a curing stage at 50 ± 1°C, and the viscosity thresholds for each stage are ≤500 mPa·s, 800 - 1200 mPa·s, and 1500 - 1800 mPa·s respectively.

4. According to the method described in claim 1, the nano-enhancer is SiO2 nanoparticles with a particle size of 20 - 50 nm, and the dispersion method is aerosol spraying with a carrier gas pressure of 0.3 - 0.5 MPa.

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