Biomass hot melt adhesive and preparation method thereof

Abstract

This invention discloses a biomass hot melt adhesive and its preparation method, belonging to the field of environmentally friendly adhesive technology. Addressing the industry pain points of existing biomass hot melt adhesives, such as difficulties in melt processing and the inability to simultaneously achieve both bonding performance and environmental friendliness, this invention uses a modified lignin graft copolymer prepared by a ring-opening grafting reaction of lignin sulfonate with L-lactide and ε-caprolactone as the matrix, compounded with nano-cellulose whiskers, cashew phenol-based plasticizers, composite crosslinking agents, and bio-based antioxidants to construct a fully biomass formulation system. The product is obtained through a solvent-free melt reaction blending process. The product of this invention is completely biodegradable, possesses excellent hot melt processability, bonding strength, water resistance, and storage stability, and the preparation process is green and environmentally friendly, suitable for large-scale industrial production, and can replace traditional petroleum-based hot melt adhesives.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly adhesive technology, specifically relating to a biomass hot melt adhesive and its preparation method. Background Technology

[0002] Hot melt adhesives are solvent-free, solid at room temperature, and possess adhesive properties after melting upon heating. They are widely used in food packaging, wood processing, bookbinding, textile lamination, automotive interiors, and many other fields due to their advantages such as fast curing speed, wide bonding range, convenient storage and transportation, and no volatile organic compound (VOC) emissions. Currently, commercially available hot melt adhesives use petroleum-based polymers as their core matrix, such as ethylene-vinyl acetate copolymer (EVA), polyolefin (APAO), and petroleum-based polyesters. Their raw materials rely entirely on non-renewable petroleum resources, and they are difficult to degrade in the natural environment after disposal. This not only exacerbates the supply and demand imbalance of petroleum resources but also causes serious white pollution and ecological damage.

[0003] With the continued advancement of the global "dual-carbon" strategy and increasingly stringent environmental regulations, the development of renewable and fully biodegradable biomass-based hot melt adhesives has become a core research direction and industrial development trend in the adhesive industry. Lignin is the second most abundant natural biomass polymer material after cellulose. Globally, the paper and pulp industry alone produces over 50 million tons of industrial lignin byproducts annually, but less than 5% of lignin is utilized for high-value purposes. The vast majority is directly burned as fuel or discharged with wastewater, causing not only a huge waste of biomass resources but also serious environmental pollution problems. Lignin's molecular structure contains a rigid aromatic ring skeleton and numerous phenolic and alcoholic hydroxyl active sites, possessing excellent structural stability, cohesive strength, and adhesive potential, making it an ideal biomass raw material to replace petroleum-based resins in the preparation of environmentally friendly hot melt adhesives.

[0004] However, pure lignin has insurmountable application defects that limit its large-scale application in the field of hot melt adhesives: First, lignin molecules have extremely strong hydrogen bonding and π-π stacking interactions, resulting in a high glass transition temperature. It is a brittle solid at room temperature and easily decomposes at high temperatures without a clear melting and flow range, failing to meet the melt processing requirements of hot melt adhesives. Second, pure lignin has poor film-forming properties, resulting in a brittle adhesive layer with insufficient flexibility. Interface cracking easily occurs during bonding, leading to a significant decrease in bond strength. Third, lignin molecules contain a large number of hydrophilic hydroxyl groups, resulting in adhesives with extremely poor water resistance. In humid environments or under boiling conditions, the adhesive layer easily absorbs water, swells, and falls off, with a bond strength retention rate of less than 40%, failing to meet the weather resistance requirements of practical applications. Fourth, lignin has poor compatibility with other biomass components, and physical blending easily leads to phase separation, resulting in poor storage stability and rapid performance degradation of the adhesive.

[0005] Furthermore, existing biomass hot melt adhesives generally suffer from the industry pain point of "performance incompatibility": to improve melt flowability, a large amount of petroleum-based plasticizers must be added, sacrificing the product's bio-based content and environmental friendliness; to ensure a fully biomass formulation, it is impossible to balance bond strength, water resistance, thermal stability, and processing flowability, resulting in product performance far lower than traditional petroleum-based hot melt adhesives. Meanwhile, existing technologies for modifying lignin mostly involve simple physical blending or conventional cross-linking modification, failing to address the fundamental problems of lignin's difficult melt processing, high brittleness, and poor water resistance at the molecular structure level, and also failing to achieve synergistic effects between various biomass components, thus failing to break through the performance bottleneck of existing biomass hot melt adhesives.

[0006] Therefore, developing a biomass hot melt adhesive that is entirely biomass-based, contains no petroleum-based components, is completely biodegradable, and simultaneously possesses excellent melt processing fluidity, high bonding strength, excellent water resistance and thermal stability, good storage stability, simple preparation process, and is suitable for large-scale industrial production has significant environmental protection value, resource utilization value, and market application prospects. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a biomass hot melt adhesive and its preparation method. By designing the molecular structure, the invention achieves efficient toughening modification of lignin and constructs a synergistic formulation system of all biomass. While ensuring the bio-based content and complete degradability, it solves the core pain points of existing biomass hot melt adhesives, such as difficult melting and processing, low bonding strength, poor water resistance and thermal stability, and inability to be scaled up industrially. The invention provides an environmentally friendly biomass hot melt adhesive product whose performance can completely replace traditional petroleum-based EVA hot melt adhesives.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] A biomass hot melt adhesive, by weight, comprises the following core components: 60-85 parts of modified lignin graft copolymer, 5-15 parts of nanocellulose whiskers, 10-25 parts of cashew phenolic plasticizer, 0.5-3 parts of composite crosslinking agent, and 0.1-1 parts of antioxidant.

[0010] The modified lignin graft copolymer is prepared by a ring-opening grafting reaction of lignin sulfonate with L-lactide and ε-caprolactone, with a grafting rate of 15%-30%. The lignin sulfonate is one or a combination of sodium lignin sulfonate and calcium lignin sulfonate, with a number average molecular weight of 5000-12000 and a degree of sulfonation of 0.8-1.8 mmol / g. During the grafting reaction, the mass ratio of lignin sulfonate, L-lactide, and ε-caprolactone is 100:120-180:40-80.

[0011] Furthermore, the nanocellulose whiskers are prepared from cotton pulp or wood pulp by sulfuric acid hydrolysis, with a diameter of 5-20 nm, a length of 100-500 nm, a crystallinity of ≥80%, and a surface hydroxyl content of ≥3.5 mmol / g.

[0012] Furthermore, the cashew phenol-based plasticizer is an epoxy-based cashew phenol plasticizer, which is prepared by epoxidation reaction of cashew phenol extracted from natural cashew shell oil and epichlorohydrin. Its epoxy value is 2.5-3.5 mmol / g, with no solvent residue and 100% bio-based content.

[0013] Furthermore, the composite crosslinking agent is a complex of triglycidyl citrate and hexamethylene diisocyanate trimer, with a mass ratio of 2:1 to 5:1; wherein triglycidyl citrate is a bio-based crosslinking agent, prepared by reacting citric acid with epichlorohydrin, and can undergo crosslinking reaction with hydroxyl groups in the system, taking into account both environmental friendliness and crosslinking efficiency.

[0014] Furthermore, the antioxidant is a food-grade bio-based antioxidant, specifically one or more combinations of tea polyphenols, vitamin E, and phytic acid, which can effectively inhibit thermal oxidative degradation during the processing and use of hot melt adhesives, and improve the thermal stability and storage stability of the product.

[0015] As a preferred embodiment, the biomass hot melt adhesive comprises the following components by weight: 70-80 parts of modified lignin graft copolymer, 6-12 parts of nanocellulose whiskers, 12-20 parts of cashew phenolic plasticizer, 1-2 parts of composite crosslinking agent, and 0.3-0.8 parts of antioxidant.

[0016] This invention also provides a method for preparing the above-mentioned biomass hot melt adhesive, comprising the following steps:

[0017] Preparation of S1 modified lignin graft copolymer: 100 parts by mass of lignin sulfonate, 120-180 parts by mass of L-lactide, and 40-80 parts by mass of ε-caprolactone were added to a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor three times. Under nitrogen protection, the temperature was raised to 105-115℃, and the mixture was stirred at 50-70 r / min until the material was completely melted. 0.3-0.6 parts by mass of stannous octoate catalyst were added, and the temperature was further raised to 125-135℃. The mixture was kept at this temperature and stirred for 5-7 h. After the reaction, the product was naturally cooled to room temperature, washed three times with anhydrous ethanol, and dried in a vacuum drying oven at 60℃ until constant weight was obtained to obtain the modified lignin graft copolymer. The grafting rate was controlled within the range of 15%-30% by nuclear magnetic resonance hydrogen spectroscopy.

[0018] S2 Premixing Treatment: According to the formula weight parts, add the modified lignin graft copolymer, nanocellulose whiskers, cashew phenolic plasticizer, composite crosslinking agent, and antioxidant into a high-speed mixer, and mix at high speed for 10-20 minutes at 75-85℃ and 1000-1300r / min to fully disperse and uniformly disperse each component, thus obtaining the premixed material.

[0019] S3 Melt Reaction Blending: The premixed material is added to a parallel twin-screw extruder for melt reaction blending. The temperatures of each zone of the twin-screw extruder are set as follows: Zone 1 105-115℃, Zone 2 120-130℃, Zone 3 135-145℃, Zone 4 140-150℃, Zone 5 135-145℃, and the die head 130-140℃. The screw speed is set to 180-220 r / min, and the residence time of the material in the extruder is controlled to be 2.5-3.5 min. In-situ crosslinking reaction is completed simultaneously with melt blending to build a stable crosslinked network structure.

[0020] S4 Granulation: The molten material extruded from the twin-screw extruder is cooled to room temperature in a water cooling tank and then fed into a pelletizer to obtain biomass hot melt adhesive granules with uniform particle size. The finished product has been tested and found to be 100% bio-based and has no VOC emissions. It can be directly used in hot melt adhesive coating, bonding and other application scenarios.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention prepares modified lignin graft copolymers by covalently grafting polylactic acid-polycaprolactone flexible copolymer segments onto lignin molecular chains via a ring-opening grafting reaction. On the one hand, the rigid aromatic ring skeleton of lignin itself is retained, ensuring the cohesive strength and thermal stability of the adhesive matrix; on the other hand, the grafted flexible segments significantly weaken the hydrogen bonding and π-π stacking interactions between lignin molecules, significantly reducing the glass transition temperature of lignin, giving it excellent melt flowability and film-forming properties, and solving the core defects of pure lignin, such as lack of melt flow range, easy decomposition at high temperatures, and inability to be hot-melted. At the same time, the grafted segments are covalently bonded to lignin, avoiding the phase separation problem caused by physical blending, and greatly improving the storage stability of the adhesive, breaking through the bottleneck of lignin application in the field of hot melt adhesives from the root of molecular structure.

[0023] (2) The present invention adopts a 100% biomass-based formula system, without any petroleum-based resin, plasticizer, or additives. After the product is discarded, it can be completely biodegraded in the natural environment. The controlled composting biodegradation rate is ≥90% in 28 days, completely eliminating the dependence on petroleum resources, eliminating the risk of white pollution, and fully complying with environmental protection requirements and the dual-carbon policy orientation. Meanwhile, the synergistic effect of each component achieves a comprehensive performance improvement: Nanocellulose whiskers, as biomass reinforcing fillers, with their ultra-high strength and crystallinity, form a dense hydrogen-bonded cross-linking network with the modified lignin matrix, which not only significantly improves the cohesive strength, bonding strength, and heat distortion temperature of the adhesive, but also forms a hydrophobic barrier structure inside the adhesive layer, significantly improving water resistance; Cashew phenol-based plasticizer has excellent compatibility with the matrix resin, which not only effectively reduces the melt viscosity of the system and improves the processing fluidity, but also improves the flexibility and low-temperature performance of the adhesive layer through long alkyl chains. The epoxy groups it contains can also participate in the cross-linking reaction, avoiding the defects of traditional plasticizers that are easy to migrate and precipitate; The composite cross-linking agent achieves moderate cross-linking of the system, further balancing the bonding strength, flexibility, and water resistance of the adhesive, and solving the performance contradiction of existing biomass hot melt adhesives that are "strong but brittle, tough but weak".

[0024] (3) This invention employs a solvent-free melt reaction blending process, which does not use any toxic or harmful organic solvents throughout the entire process, resulting in no waste emissions and meeting the requirements of green chemical production. The preparation process is continuous, the reaction conditions are mild, and there are no special requirements for production equipment. Conventional twin-screw extrusion equipment can be used to achieve large-scale production, resulting in high production efficiency and low cost. This solves the shortcomings of existing lignin modification processes, such as large solvent consumption, complex processes, serious pollution, and inability to be scaled up industrially. At the same time, this invention uses lignin, a by-product of the papermaking industry, cashew nut shell oil, a by-product of agricultural product processing, and natural cellulose as core raw materials, realizing the high-value utilization of biomass waste, significantly reducing production costs, and possessing significant economic and social benefits. Detailed Implementation

[0025] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0026] Example 1

[0027] This embodiment provides a biomass hot melt adhesive, which, by weight, comprises the following components: 75 parts of modified lignin graft copolymer, 8 parts of nanocellulose whiskers, 15 parts of cashew phenol-based plasticizer, 1.5 parts of composite crosslinking agent, and 0.5 parts of antioxidant tea polyphenol.

[0028] The modified lignin graft copolymer has a grafting rate of 22.4%, the sodium lignin sulfonate used in its preparation has a number-average molecular weight of 8000 and a sulfonation degree of 1.2 mmol / g; the nanocellulose whiskers have a diameter of 10-15 nm, a length of 200-300 nm, and a crystallinity of 85%; the cashew phenolic plasticizer has an epoxy value of 3.2 mmol / g; and the composite crosslinking agent is a mixture of triglycidyl citrate and hexamethylene diisocyanate trimer in a mass ratio of 3:1.

[0029] The preparation method of the biomass hot melt adhesive in this embodiment specifically includes the following steps:

[0030] Preparation of S1 modified lignin graft copolymer: 100 parts by weight of sodium lignin sulfonate, 150 parts by weight of L-lactide, and 50 parts by weight of ε-caprolactone were added to a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor three times. Under nitrogen protection, the temperature was raised to 110℃ and stirred at 60 r / min until the material was completely melted. 0.5 parts by weight of stannous octoate catalyst were added, and the temperature was further raised to 130℃. The reaction was maintained at this temperature and stirred for 6 h. After the reaction was completed, the product was naturally cooled to room temperature, washed three times with anhydrous ethanol, and dried in a vacuum drying oven at 60℃ to constant weight to obtain the modified lignin graft copolymer. The grafting rate was 22.4% as determined by 1H NMR spectroscopy.

[0031] S2 Premixing Treatment: According to the above formula by weight, the modified lignin graft copolymer, nanocellulose whiskers, cashew phenolic plasticizer, composite crosslinking agent, and antioxidant tea polyphenols are added to a high-speed mixer and mixed at 80℃ and 1200r / min for 15min to ensure that the components are fully dispersed and uniform, thus obtaining the premixed material.

[0032] S3 Melt Reaction Blending: The premixed material is added to a parallel twin-screw extruder for melt reaction blending. The temperatures of each zone of the twin-screw extruder are set as follows: Zone 1 110℃, Zone 2 125℃, Zone 3 140℃, Zone 4 145℃, Zone 5 140℃, and Die Head 135℃. The screw speed is set to 200 r / min, and the residence time of the material in the extruder is controlled to 3 min. The in-situ crosslinking reaction is completed simultaneously with the melt blending.

[0033] S4 Granulation: The molten material extruded from the twin-screw extruder is cooled to room temperature in a water cooling tank and then fed into a pelletizer to be pelletized, resulting in biomass hot melt adhesive granules with uniform particle size.

[0034] Example 2

[0035] This embodiment provides a biomass hot melt adhesive, which, by weight, comprises the following components: 65 parts of modified lignin graft copolymer, 12 parts of nanocellulose whiskers, 20 parts of cashew phenolic plasticizer, 2 parts of composite crosslinking agent, and 0.8 parts of antioxidant vitamin E.

[0036] The modified lignin graft copolymer has a grafting rate of 26.8%, the calcium lignin sulfonate used in its preparation has a number-average molecular weight of 6000 and a sulfonation degree of 1.5 mmol / g; the nanocellulose whiskers have a diameter of 5-10 nm, a length of 300-400 nm, and a crystallinity of 88%; the cashew phenolic plasticizer has an epoxy value of 3.5 mmol / g; and the composite crosslinking agent is a mixture of triglycidyl citrate and hexamethylene diisocyanate trimer in a mass ratio of 4:1.

[0037] The preparation method of the biomass hot melt adhesive in this embodiment specifically includes the following steps:

[0038] Preparation of S1 modified lignin graft copolymer: 100 parts by weight of calcium lignin sulfonate, 120 parts by weight of L-lactide, and 80 parts by weight of ε-caprolactone were added to a high-pressure reactor. The air inside the reactor was replaced three times with high-purity nitrogen. Under nitrogen protection, the temperature was raised to 110℃ and stirred at 60 r / min until the material was completely melted. 0.6 parts by weight of stannous octoate catalyst were added, and the temperature was further raised to 135℃. The reaction was maintained at this temperature and stirred for 5 h. After the reaction was completed, the product was naturally cooled to room temperature, washed three times with anhydrous ethanol, and dried in a vacuum drying oven at 60℃ until constant weight was obtained to obtain the modified lignin graft copolymer. The grafting rate was 26.8% as determined by 1H NMR spectroscopy.

[0039] S2 Premixing Treatment: According to the above formula by weight, the modified lignin graft copolymer, nanocellulose whiskers, cashew phenolic plasticizer, composite crosslinking agent, and antioxidant vitamin E are added to a high-speed mixer and mixed at 85℃ and 1300r / min for 12 minutes to ensure that the components are fully dispersed and uniform, thus obtaining the premixed material.

[0040] S3 Melt Reaction Blending: The premixed material is added to a parallel twin-screw extruder for melt reaction blending. The temperatures of each zone of the twin-screw extruder are set as follows: Zone 1 105℃, Zone 2 120℃, Zone 3 135℃, Zone 4 140℃, Zone 5 135℃, and Die Head 130℃. The screw speed is set to 220 r / min, and the residence time of the material in the extruder is controlled to 3.5 min. The in-situ crosslinking reaction is completed simultaneously with the melt blending.

[0041] S4 Granulation: The molten material extruded from the twin-screw extruder is cooled to room temperature in a water cooling tank and then fed into a pelletizer to be pelletized, resulting in biomass hot melt adhesive granules with uniform particle size.

[0042] Example 3

[0043] This embodiment provides a biomass hot melt adhesive, which, by weight, comprises the following components: 80 parts of modified lignin graft copolymer, 6 parts of nanocellulose whiskers, 12 parts of cashew phenolic plasticizer, 1 part of composite crosslinking agent, and 0.3 parts of antioxidant phytic acid.

[0044] The modified lignin graft copolymer has a grafting rate of 18.7%, the sodium lignin sulfonate used in its preparation has a number-average molecular weight of 10,000 and a sulfonation degree of 1.0 mmol / g; the nanocellulose whiskers have a diameter of 15-20 nm, a length of 100-200 nm, and a crystallinity of 82%; the cashew phenolic plasticizer has an epoxy value of 2.8 mmol / g; and the composite crosslinking agent is a mixture of triglycidyl citrate and hexamethylene diisocyanate trimer in a mass ratio of 2:1.

[0045] The preparation method of the biomass hot melt adhesive in this embodiment specifically includes the following steps:

[0046] Preparation of S1 modified lignin graft copolymer: 100 parts by weight of sodium lignin sulfonate, 180 parts by weight of L-lactide, and 40 parts by weight of ε-caprolactone were added to a high-pressure reactor. The air inside the reactor was replaced three times with high-purity nitrogen. Under nitrogen protection, the temperature was raised to 110℃ and stirred at 60 r / min until the material was completely melted. 0.4 parts by weight of stannous octoate catalyst were added, and the temperature was raised to 125℃. The reaction was maintained at this temperature and stirred for 7 h. After the reaction was completed, the product was naturally cooled to room temperature, washed three times with anhydrous ethanol, and dried in a vacuum drying oven at 60℃ to constant weight to obtain the modified lignin graft copolymer. The grafting rate was 18.7% as determined by 1H NMR spectroscopy.

[0047] S2 Premixing Treatment: According to the above formula by weight, the modified lignin graft copolymer, nanocellulose whiskers, cashew phenolic plasticizer, composite crosslinking agent, and antioxidant phytic acid are added to a high-speed mixer and mixed at 75℃ and 1100r / min for 18min to ensure that the components are fully dispersed and uniform, thus obtaining the premixed material.

[0048] S3 Melt Reaction Blending: The premixed material is added to a parallel twin-screw extruder for melt reaction blending. The temperatures of each zone of the twin-screw extruder are set as follows: Zone 1 115℃, Zone 2 130℃, Zone 3 145℃, Zone 4 150℃, Zone 5 145℃, and Die Head 140℃. The screw speed is set to 180 r / min, and the residence time of the material in the extruder is controlled to 2.5 min. In-situ crosslinking reaction is completed simultaneously with melt blending.

[0049] S4 Granulation: The molten material extruded from the twin-screw extruder is cooled to room temperature in a water cooling tank and then fed into a pelletizer to be pelletized, resulting in biomass hot melt adhesive granules with uniform particle size.

[0050] Comparative Example 1

[0051] Unmodified lignin-substituted lignin graft copolymer

[0052] Formula: By weight, it includes 75 parts unmodified sodium lignosulfonate, 8 parts nanocellulose whiskers, 15 parts cashew phenolic plasticizer, 1.5 parts composite crosslinking agent, and 0.5 parts antioxidant tea polyphenols.

[0053] Preparation process: The S1 modification step was omitted, and unmodified sodium lignosulfonate was directly used for subsequent premixing, melt blending, and granulation steps. The remaining process parameters were completely consistent with those in Example 1.

[0054] Single variable: Replace the modified lignin graft copolymer with an equal mass of unmodified sodium lignin sulfonate, while keeping all other conditions unchanged.

[0055] Comparative Example 2

[0056] Removal of nanocellulose whisker components

[0057] Formula: By weight, it includes 75 parts modified lignin graft copolymer, 15 parts cashew phenolic plasticizer, 1.5 parts composite crosslinking agent, and 0.5 parts antioxidant tea polyphenol.

[0058] Preparation process: No nanocellulose whiskers were added in the premixing step, and all other formulations and process parameters were completely consistent with those in Example 1.

[0059] Single variable: Remove the nanocellulose whisker component, and keep all other conditions unchanged.

[0060] Comparative Example 3

[0061] Petroleum-based plasticizers as alternatives to cashew phenol-based plasticizers

[0062] Formula: By weight, it includes 75 parts modified lignin graft copolymer, 8 parts nanocellulose whiskers, 15 parts dioctyl phthalate (DOP), 1.5 parts composite crosslinking agent, and 0.5 parts antioxidant tea polyphenols.

[0063] Preparation process: The cashew phenol-based plasticizer was replaced with an equal mass of petroleum-based DOP plasticizer, and all other formulations and process parameters were completely consistent with those in Example 1.

[0064] Single variable: Replace the biomass cashew phenolic plasticizer with an equal mass of petroleum-based DOP plasticizer, keeping all other conditions unchanged.

[0065] Comparative Example 4

[0066] Corn starch-modified lignin graft copolymer

[0067] Formula: By weight, it includes 75 parts food-grade corn starch, 8 parts nanocellulose whiskers, 15 parts cashew phenolic plasticizer, 1.5 parts composite crosslinking agent, and 0.5 parts antioxidant tea polyphenols.

[0068] Preparation process: The S1 modification step was omitted, and corn starch was directly used for subsequent premixing, melt blending and granulation steps. The remaining process parameters were completely consistent with those in Example 1.

[0069] Single variable: The modified lignin graft copolymer was replaced with an equal mass of corn starch, while all other conditions remained unchanged.

[0070] Comparative Example 5

[0071] The amount of modified lignin graft copolymer used is less than the lower limit of the claims.

[0072] Formula: By weight, it includes 50 parts modified lignin graft copolymer, 8 parts nanocellulose whiskers, 15 parts cashew phenolic plasticizer, 1.5 parts composite crosslinking agent, and 0.5 parts antioxidant tea polyphenol.

[0073] Preparation process: All process parameters are completely consistent with those in Example 1.

[0074] Single variable: The amount of modified lignin graft copolymer is 50 parts, which is lower than the lower limit of 60 parts in claim 1, and the proportions and processes of the other components are exactly the same.

[0075] Comparative Example 6

[0076] The amount of modified lignin graft copolymer exceeds the upper limit of the claims.

[0077] Formula: By weight, it includes 90 parts modified lignin graft copolymer, 8 parts nanocellulose whiskers, 15 parts cashew phenolic plasticizer, 1.5 parts composite crosslinking agent, and 0.5 parts antioxidant tea polyphenol.

[0078] Preparation process: All process parameters are completely consistent with those in Example 1.

[0079] Single variable: The amount of modified lignin graft copolymer is 90 parts, which is higher than the upper limit of 85 parts in claim 1, and the proportions and processes of the other components are exactly the same.

[0080] Comparative Example 7

[0081] The amount of nanocellulose whiskers exceeds the upper limit of the claims.

[0082] Formula: By weight, it includes 75 parts modified lignin graft copolymer, 20 parts nanocellulose whiskers, 15 parts cashew phenolic plasticizer, 1.5 parts composite crosslinking agent, and 0.5 parts antioxidant tea polyphenol.

[0083] Preparation process: All process parameters are completely consistent with those in Example 1.

[0084] Single variable: The amount of nanocellulose whiskers is 20 parts, which is higher than the upper limit of 15 parts in claim 1, while the proportions and processes of the other components are exactly the same.

[0085] Comparative Example 8

[0086] The melt blending temperature exceeds the preferred range of the claims.

[0087] Formula: Completely identical to Example 1.

[0088] Preparation process: In the S3 melt reaction blending step, the temperature of each zone of the twin-screw extruder is set as follows: Zone 1 150℃, Zone 2 165℃, Zone 3 180℃, Zone 4 185℃, Zone 5 180℃, and Die head 175℃. All other steps and parameters are completely consistent with those in Example 1.

[0089] Single variable: The melt blending temperature is significantly outside the preferred range defined in the claims, while all other conditions remain unchanged.

[0090] Comparative Example 9

[0091] Eliminate the melt reaction blending step and perform only physical mixing.

[0092] Formula: Completely identical to Example 1.

[0093] Preparation process: Add all components to a high-speed mixer and mix at 80°C and 1200 rpm for 30 minutes to directly obtain a powdered hot melt adhesive product without the twin-screw melt reaction blending and granulation steps.

[0094] Single variable: The melt reaction blending and in-situ crosslinking steps are eliminated, and only simple physical mixing is performed. The rest of the formulation is exactly the same.

[0095] Comparative Example 10

[0096] Existing conventional EVA-based biomass hot melt adhesive (control sample)

[0097] Formula: By weight, it includes 60 parts of EVA resin (VA content 28%), 20 parts of unmodified lignin, 15 parts of rosin resin, 3 parts of paraffin wax, and 0.5 parts of antioxidant 1010.

[0098] Preparation process: Following the conventional hot melt adhesive preparation process of existing technology, all components were added to a twin-screw extruder, melt-blended at 120-150℃, extruded and granulated to obtain a control hot melt adhesive sample.

[0099] Single variable: Existing conventional EVA-based biomass hot melt adhesive formulations and processes were used as performance controls.

[0100] Performance testing

[0101] All examples and comparative samples underwent performance testing in accordance with current national standards. The testing items and corresponding standards are as follows:

[0102] 1. Softening point: Tested according to GB / T 15332-1994 "Determination of softening point of hot melt adhesives - Ring and Ball method" (°C);

[0103] 2. Melt viscosity: Tested at 180℃ (mPa·s) according to GB / T 2794-2013 "Determination of viscosity of adhesives - Rotational viscometer method";

[0104] 3.180° Peel Strength: According to GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes", the peel strength of PE film and birch veneer were tested respectively. The sample width was 25 mm and the tensile speed was 300 mm / min (PE film, N / 25 mm).

[0105] 4. Tensile shear strength: According to GB / T 7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)", the tensile shear strength of birch-birch was tested at a tensile speed of 5 mm / min (birch, N / 25 mm).

[0106] 5. Water resistance: The bonded birch-birch sample was boiled in 100℃ boiling water for 30 minutes. After being removed and dried, the shear strength was tested immediately, and the strength retention rate was calculated (shear strength after boiling / shear strength before boiling × 100%) (MPa).

[0107] 6. Heat distortion temperature: Tested according to GB / T 1634.2-2019 "Determination of heat distortion temperature of plastics under load - Part 2: Plastics and hard rubber", with a load of 0.45 MPa (°C);

[0108] 7. Biodegradation rate: The biodegradation rate (%) after 28 days was tested in accordance with GB / T 19277.1-2011 "Determination of final aerobic biodegradation capacity of materials under controlled composting conditions by means of determination of carbon dioxide released - Part 1: General method".

[0109] 8. Storage stability: Place the adhesive sample in a constant temperature and humidity chamber at 40℃ and 60% relative humidity for 30 days, and test the change rate (%) of melt viscosity before and after storage. At the same time, observe whether there is plasticizer precipitation or clumping.

[0110] Test Results and Data Analysis

[0111] The performance test results for all embodiments and comparative examples are shown in the table below:

[0112] Table 1 Performance test results of the examples and comparative examples

[0113]

[0114]

[0115]

[0116] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A biomass hot melt adhesive, characterized in that, The product comprises, by weight, the following components: 60-85 parts of modified lignin graft copolymer, 5-15 parts of nanocellulose whiskers, 10-25 parts of cashew phenolic plasticizer, 0.5-3 parts of composite crosslinking agent, and 0.1-1 parts of antioxidant; wherein the modified lignin graft copolymer is prepared by a ring-opening grafting reaction of lignin sulfonate with L-lactide and ε-caprolactone, and its grafting rate is 15%-30%.

2. The biomass hot melt adhesive according to claim 1, characterized in that, The lignin sulfonate is one or a combination of sodium lignin sulfonate and calcium lignin sulfonate, with a number-average molecular weight of 5000-12000 and a degree of sulfonation of 0.8-1.8 mmol / g.

3. The biomass hot melt adhesive according to claim 1, characterized in that, In the preparation of the modified lignin graft copolymer, the mass ratio of lignin sulfonate, L-lactide, and ε-caprolactone is 100:120-180:40-80.

4. The biomass hot melt adhesive according to claim 1, characterized in that, The cellulose nanofiber whiskers have a diameter of 5-20 nm, a length of 100-500 nm, and a crystallinity of ≥80%.

5. The biomass hot melt adhesive according to claim 1, characterized in that, The cashew phenol-based plasticizer is an epoxy-based cashew phenol plasticizer, which is prepared by epoxidation reaction of cashew phenol and epichlorohydrin, and has an epoxy value of 2.5-3.5 mmol / g.

6. The biomass hot melt adhesive according to claim 1, characterized in that, The composite crosslinking agent is a complex of triglycidyl citrate and hexamethylene diisocyanate trimer, with a mass ratio of 2:1 to 5:

1.

7. The biomass hot melt adhesive according to claim 1, characterized in that, The antioxidant is a bio-based antioxidant, specifically one or more of tea polyphenols, vitamin E, and phytic acid.

8. The biomass hot melt adhesive according to claim 1, characterized in that, By weight, it includes the following components: 70-80 parts modified lignin graft copolymer, 6-12 parts nanocellulose whiskers, 12-20 parts cashew phenolic plasticizer, 1-2 parts composite crosslinking agent, and 0.3-0.8 parts antioxidant.

9. The biomass hot melt adhesive according to claim 1, characterized in that, The biomass hot melt adhesive has a bio-based content of 100% and a controlled composting biodegradation rate of ≥90% in 28 days.

10. A method for preparing a biomass hot melt adhesive as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. By mass, 100 parts of lignin sulfonate, 120-180 parts of L-lactide, and 40-80 parts of ε-caprolactone are added to a reactor. Under nitrogen protection, the temperature is raised to 105-115℃ and stirred until the material is completely melted. Then, 0.3-0.6 parts of stannous octoate catalyst are added, and the temperature is raised to 125-135℃. The reaction is maintained at this temperature for 5-7 hours. After the reaction is completed, the product is washed and vacuum dried to obtain the modified lignin graft copolymer. S2. According to the formula, add the modified lignin graft copolymer, nanocellulose whiskers, cashew phenolic plasticizer, composite crosslinking agent and antioxidant into a high-speed mixer and mix for 10-20 minutes at 75-85℃ and 1000-1300r / min to obtain the premixed material. S3. Add the premixed material to the twin-screw extruder for melt reaction blending. The temperature settings for each zone of the twin-screw extruder are as follows: Zone 1 105-115℃, Zone 2 120-130℃, Zone 3 135-145℃, Zone 4 140-150℃, Zone 5 135-145℃, and Die head 130-140℃. The screw speed is 180-220 r / min, and the material residence time is 2.5-3.5 min. S4. The extruded material is cooled with water and pelletized to obtain the finished biomass hot melt adhesive.

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