Degradable polylactic acid-based hot melt adhesive and preparation method thereof

Abstract

The invention discloses a degradable polylactic acid-based hot melt adhesive and a preparation method thereof, and belongs to the technical field of hot melt adhesives, the degradable polylactic acid-based hot melt adhesive is prepared by taking polylactic acid as a matrix material, has good degradability, and adsorbs and decomposes carbon-containing gas by plating a nickel film on the surface of glass fiber as a catalytic center, so that the carbon-containing gas can be degraded, and the degradation rate of the carbon-containing gas is improved. Growing a carbon nanotube on the surface of the substrate; a large number of pyrenyl groups contained in an end-capped polylactic acid matrix are combined with the carbon nanotubes under the pi-pi action, the surface properties of the carbon nanotubes can be changed, an interpenetrating network structure is formed through polyurethane and epoxy resin, a flame-retardant functional ligand is anchored in the composite material, migration of a flame retardant is avoided, and a porous zinc skeleton has a catalytic effect, so that the flame-retardant performance of the composite material is improved. The insertion of the porous zinc skeleton can synergistically play a role with the nickel film, so that the generation of a carbon layer is promoted, and the flame-retardant capability is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot melt adhesives, and particularly relates to a degradable polylactic acid-based hot melt adhesive and a preparation method thereof. Background Art

[0002] Polylactic acid is prepared from lactic acid obtained by fermenting polysaccharide substances such as corn and potato starch as basic raw materials through polycondensation or ring-opening polymerization of its dimer. It is worth noting that the characteristic that polylactic acid, under natural conditions, is biodegradable and finally only generates carbon dioxide and water meets the requirements of environmentally friendly materials, so it is one of the most concerned biodegradable materials nowadays. This material has been widely used in fields such as packaging materials, fibers, and biomedical materials.

[0003] Hot melt adhesive is a plastic solvent-free adhesive, which is solid at room temperature and becomes a liquid adhesive that can flow and has certain viscosity when heated to a certain temperature. Due to its non-toxic and pollution-free characteristics, it is widely used. Currently, the commonly used hot melt adhesives on the market are mainly divided into two types: EVA-based hot melt adhesive and polyurethane-based hot melt adhesive. However, the raw materials of these two types of hot melt adhesives all come from non-renewable resources, and they degrade slowly under natural conditions, which is easy to cause environmental pollution.

[0004] Chinese Patent Application CN113817434B discloses a halogen-containing flame-retardant polyurethane hot melt adhesive and a preparation method thereof. By introducing polyether polyol A with a benzene ring structure into the molecular structure of the polyurethane hot melt adhesive, the flame retardant performance of the hot melt adhesive can be significantly improved. Compared with the phosphorus-based flame retardant that forms a protective layer through chemical reactions to isolate oxygen to achieve the flame retardant function, the flame retardant efficiency is low, and the flame retardant effect is insufficient when used as an electronic component binder. Summary of the Invention

[0005] The purpose of the present invention is to provide a degradable polylactic acid-based hot melt adhesive and a preparation method thereof. By forming an interpenetrating network structure between polyurethane and epoxy resin, and through the entanglement between the networks, the flame retardant functional ligands are anchored in the composite material to avoid the migration of the flame retardant. Moreover, the interpenetrating network can disperse stress when subjected to external forces, improve the overall toughness of the material, and avoid the problem of large brittleness of polylactic acid; the porous zinc skeleton has a catalytic effect, and the penetration of the porous zinc skeleton can cooperate with the nickel film to promote the formation of a carbon layer and increase the flame retardant ability.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A degradable polylactic acid-based hot melt adhesive and a preparation method thereof, comprising the following steps:

[0008] The capped polylactic acid matrix, functionalized modified composite, interpenetrating toughening and flame retardant, and butylated hydroxyanisole are added to a reaction kettle according to a mass ratio of 60-70:5-8:18-22:1-2, stirred at 160-170 °C and 80-90 r / min for 2-3 h, and extruded and granulated using a twin-screw extruder to obtain a degradable polylactic acid-based hot melt adhesive.

[0009] Further, the capped polylactic acid matrix is prepared by the following steps:

[0010] Add the L-lactic acid solution to a reaction kettle, stir at 20-25 °C and 500-700 r / min for 15-20 min, under a nitrogen atmosphere, heat in an oil bath to 110-120 °C, vacuum dehydrate for 2-3 h, then add the catalysts methanesulfonic acid and stannous acetate, heat to 150-160 °C, and continue the reaction for 8-9 h. Then add chloroform, precipitate with absolute ethanol, filter by suction, wash the filter cake with deionized water 2-3 times, and vacuum dry at 60-80 °C for 1-2 h to obtain a polylactic acid prepolymer; add the polylactic acid prepolymer, 1,3-diaminopyrene, and hexafluoroisopropanol to a reaction kettle, under nitrogen protection, stir at 150-170 °C and 500-700 r / min for 15-20 min, add sodium dodecylbenzenesulfonate, and continue the reaction for 4-6 h. Filter, wash the filter cake with deionized water 2-3 times, and vacuum dry at 60-80 °C for 1-2 h to obtain the capped polylactic acid matrix.

[0011] Further, the dosage ratio of the L-lactic acid solution, methanesulfonic acid, stannous acetate, and chloroform is 40-50 mL:1-2 mL:1-2 g:500-600 mL.

[0012] Further, the dosage ratio of the polylactic acid prepolymer, 1,3-diaminopyrene, hexafluoroisopropanol, and sodium dodecylbenzenesulfonate is 10-12 g:14-16 g:300-400 mL:1-2 g.

[0013] Further, the functionalized modified composite is prepared by the following steps:

[0014] Pre-treated high-silica glass fibers, polyethylene glycol sulfate as a surfactant, nickel sulfate, citric acid as a complexing agent, and L-cysteine as a stabilizer are stirred at 40 - 50 °C and 400 - 500 r / min for 40 - 60 min, filtered, and the filter cake is washed with deionized water until the last washing liquid is neutral to obtain nickel-plated high-silica glass fibers with a surface nickel film thickness of 20 - 30 nm; the nickel-plated high-silica glass fibers are placed in PECVD, high-purity argon with a gas flow rate of 40 - 50 L / h and methane with a gas flow rate of 5 - 7 L / h as a carbon source are introduced for 10 - 12 min, the reactor temperature is 980 - 1020 °C, the treatment time is 2 - 3 h, then the treated powder is washed with deionized water 2 - 3 times to remove impurities, and vacuum dried at 60 - 80 °C for 1 - 2 h to obtain a functionalized modified composite.

[0015] Furthermore, the dosage ratio of the pre-treated high-silica glass fibers, polyethylene glycol sulfate, nickel sulfate, citric acid, and L-cysteine is 20 - 30 g : 1 - 2 g : 800 - 900 mL : 2 - 3 g : 1 - 2 g

[0016] Furthermore, the pre-treated high-silica glass fibers are prepared by the following steps:

[0017] High-silica glass fibers with a length of 50 - 70 μm and an ethanol solution with a mass fraction of 50 - 60% are added to a reaction kettle, stirred at 20 - 25 °C and 500 - 600 r / min for 24 - 26 h, dried in an oven at 100 - 110 °C for 30 - 40 min, transferred to a mixed solution of sulfuric acid with a mass fraction of 3 - 4% and nitric acid with a mass fraction of 1 - 2%, stirred at 60 - 70 °C and 500 - 600 r / min for 30 - 40 min, filtered, and the filter cake is washed with deionized water until the last washing liquid is neutral, and vacuum dried at 60 - 80 °C for 1 - 2 h to obtain pre-treated high-silica glass fibers.

[0018] Furthermore, the dosage ratio of the high-silica glass fibers, ethanol, sulfuric acid, and nitric acid is 40 - 50 g : 800 - 900 mL : 400 - 500 mL : 200 - 300 mL.

[0019] Furthermore, the interpenetrating toughening and flame retardant is prepared by the following steps:

[0020] Ammonium polyphosphate, 2,5-diaminobenzoic acid and deionized water are added into a reaction kettle. Sodium lauryl sulfate is dissolved in an ethanol solution with a concentration of 60-70wt% and then added into the reaction kettle. Stir at 50-60°C and 400-500 r / min for 40-50 min, then add zinc chloride, and continue to stir and react for 3-4 h. Filter by suction, wash the filter cake with deionized water 2-3 times, and dry it under vacuum to obtain a flame-retardant functional ligand; Add the flame-retardant functional ligand, polyether polyol and deionized water into the reaction kettle, stir at 20-25°C and 500-700 r / min for 20-30 min, dissolve epoxy resin powder with a particle size of 20-30 μm and acetone by stirring and then add it into the reaction kettle, continue to stir for 10-15 min, then add isocyanate and a dibutyltin dilaurate solution with a mass fraction of 0.3-0.4%, continue to stir and react for 1-2 h, filter, wash the filter cake with deionized water 2-3 times, and dry it under vacuum at 60-80°C for 1-2 h to obtain an interpenetrating toughened flame-retardant material.

[0021] Furthermore, the dosage ratio of ammonium polyphosphate, 2,5-diaminobenzoic acid, deionized water, sodium lauryl sulfate, ethanol solution and zinc chloride is 10-12 g: 15-20 g: 400-500 mL: 2-3 g: 100-120 mL: 8-10 g.

[0022] Furthermore, the dosage ratio of the flame-retardant functional ligand, polyether polyol, deionized water, epoxy resin powder, acetone, isocyanate and dibutyltin dilaurate solution is 10-12 g: 50-60 mL: 200-300 mL: 15-20 g: 180-200 mL: 30-35 mL: 4-5 mL.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. A degradable polylactic acid-based hot melt adhesive prepared by the present invention uses polylactic acid as the matrix, and has excellent degradation rate, bonding strength, thermal stability, flame retardancy and electromagnetic shielding ability; The functionalized modified composite of the present invention deposits a nickel film on the surface of glass fiber as a catalytic center to adsorb and decompose carbon-containing gases, and also serves as a growth point. When carbon atoms reach supersaturation in the catalyst, they precipitate from the catalyst particles and grow on its surface to form carbon nanotubes, which can improve its compatibility with polylactic acid hot melt adhesive by increasing the surface roughness and active sites of carbon fiber and having good bonding strength; The synergistic effect of glass fiber and carbon nanotubes can significantly enhance the thermal stability of polylactic acid hot melt adhesive.

[0025] 2. The interpenetrating toughened flame retardant of the present invention forms an interpenetrating network structure through polyurethane and epoxy resin. The networks are entangled with each other to anchor the flame retardant functional ligands in the composite material to avoid the migration of the flame retardant. The interpenetrating network can disperse stress when subjected to external force, improve the overall toughness of the material, and avoid the problem of high brittleness of polylactic acid. The interpenetrating of the porous zinc skeleton can further enhance the mechanical properties. The porous zinc skeleton has a catalytic effect and can work synergistically with the nickel film to promote the formation of the carbon layer and increase the flame retardant ability.

[0026] 3. The large amount of pyrene groups contained in the end-capped polylactic acid matrix of the present invention can change the surface properties of the carbon nanotubes by combining with the carbon nanotubes through the π-π effect. This change in surface properties helps to reduce the interaction force between the carbon nanotubes, thereby improving their dispersibility and avoiding agglomeration; the functionalized modified composite grows carbon nanotubes on the surface of the glass fiber through the catalytic action of the nickel film. The carbon nanotubes have good wave absorbing ability. The glass fiber can be used as a reinforcement to improve the overall mechanical properties and stability of the material, so that the composite material exhibits better wave absorbing performance within the electromagnetic wave frequency band; and the addition of carbon nanotubes can affect the crystallization behavior of the resin and has a nucleation effect, thereby increasing the cooling crystallization temperature of the hot melt adhesive, which helps to accelerate the curing process and improve production efficiency. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Embodiment 1: A degradable polylactic acid-based hot melt adhesive and a preparation method thereof, comprising the following steps:

[0029] S1: 40 mL of L-lactic acid solution was added to the reactor, stirred at 20 ° C and 500 r / min for 15 min, heated to 110 ° C in an oil bath under a nitrogen atmosphere, vacuum dehydrated for 2 h, and then 1 mL of methanesulfonic acid and 1 g of stannous acetate were added as catalysts, heated to 150 ° C, and the reaction continued for 8 h. Then 500 mL of chloroform was added, precipitated with anhydrous ethanol, filtered, and the filter cake was washed with deionized water twice, and vacuum dried at 60 ° C for 1 h to obtain a polylactic acid prepolymer; 10 g of polylactic acid prepolymer, 14 g of 1,3-diaminopyrene and 300 mL of hexafluoroisopropanol were added to the reactor, stirred at 150 ° C and 500 r / min for 15 min under nitrogen protection, 1 g of sodium dodecylbenzene sulfonate was added, the reaction continued for 4 h, filtered, the filter cake was washed with deionized water twice, and vacuum dried at 60 ° C for 1 h to obtain a capped polylactic acid matrix.

[0030] The amino group of 1,3-diaminopyrene binds to the terminal carboxyl group of the polylactic acid prepolymer to obtain a pyrene-capped polylactic acid matrix. The pyrene group is a relatively stable chemical structure, and pyrene capping can enhance the chemical stability of the polylactic acid matrix at high temperatures.

[0031] S2: Add 40 g of high-silica glass fibers with a length of 50 μm and 800 mL of an ethanol solution with a mass fraction of 50% to a reaction kettle, stir at 20 °C and 500 r / min for 24 h, dry in an oven at 100 °C for 30 min, transfer to a mixed solution of 400 mL of sulfuric acid with a mass fraction of 3% and 200 mL of nitric acid with a mass fraction of 1%, stir at 60 °C and 500 r / min for 30 min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and dry in vacuum at 60 °C for 1 h to obtain pretreated high-silica glass fibers.

[0032] S3: Add 20 g of pretreated high-silica glass fibers, 1 g of polyethylene glycol sulfate as a surfactant, 800 mL of nickel sulfate, 2 g of citric acid as a complexing agent, and 1 g of L-cysteine as a stabilizer, stir at 40 °C and 400 r / min for 40 min, filter, wash the filter cake with deionized water until the last washing liquid is neutral to obtain nickel-plated high-silica glass fibers with a surface nickel film thickness of 20 nm; place the nickel-plated high-silica glass fibers in PECVD, introduce high-purity argon with a gas flow rate of 40 L / h and methane with a gas flow rate of 5 L / h as a carbon source for 10 min, the reactor temperature is 980 °C, the treatment time is 2 h, then wash the treated powder with deionized water 2 times to remove impurities, and dry in vacuum at 60 °C for 1 h to obtain a functionalized modified composite.

[0033] The nickel film can act as a catalyst to adsorb and decompose carbon-containing gases and serve as a growth point. When carbon atoms reach a supersaturated state in the catalyst, they will precipitate from the catalyst particles and start to grow carbon nanotubes on its surface; and the nickel film can cooperate with the porous zinc skeleton structure in the interpenetrating toughening and flame-retardant material to promote the formation of a carbon layer.

[0034] A large number of pyrene groups contained in the capped polylactic acid matrix bind to carbon nanotubes through π-π interactions, which can change the surface properties of the carbon nanotubes. This change in surface properties helps to reduce the interaction force between carbon nanotubes, thereby improving their dispersibility.

[0035] S4: Add 10 g of ammonium polyphosphate, 15 g of 2,5-diaminobenzoic acid and 400 mL of deionized water into a reaction kettle. Dissolve 2 g of sodium dodecyl sulfate in 100 mL of 60 wt% ethanol solution and then add it into the reaction kettle. Stir at 50 °C and 400 r / min for 40 min, then add 8 g of zinc chloride, continue stirring and reacting for 3 h, carry out suction filtration, wash the filter cake with deionized water twice, and dry it under vacuum to obtain a flame-retardant functional ligand; Add 10 g of the flame-retardant functional ligand, 50 mL of polyether polyol and 200 mL of deionized water into the reaction kettle, stir at 20 °C and 500 r / min for 20 min. Stir and dissolve 15 g of epoxy resin powder with a particle size of 20 - 30 μm and 180 mL of acetone and then add it into the reaction kettle, continue stirring for 10 min, then add 30 mL of isocyanate and 4 mL of a dibutyltin dilaurate solution with a mass fraction of 0.3%, continue stirring and reacting for 1 h, filter, wash the filter cake with deionized water twice, and dry it under vacuum at 60 °C for 1 h to obtain an interpenetrating toughened flame retardant.

[0036] Through the formation of an interpenetrating network structure between polyurethane and epoxy resin, and through the entanglement between the networks, the flame-retardant functional ligand is anchored in the composite material to avoid the migration of the flame retardant. Moreover, the interpenetrating network can disperse stress when subjected to external forces, improve the overall toughness of the material, and avoid the problem of high brittleness of polylactic acid; The interpenetration of the porous zinc skeleton can further enhance this mechanical property, and the porous zinc skeleton has a catalytic effect, which can promote the carbonization ability of the flame retardant.

[0037] S5: Add the end-capped polylactic acid matrix, the functionalized modified composite, the interpenetrating toughened flame retardant and butylated hydroxyanisole into the reaction kettle according to a mass ratio of 60:5:18:1, stir at 160 °C and 80 r / min for 2 h, and extrude and pelletize using a twin-screw extruder to obtain a degradable polylactic acid-based hot melt adhesive.

[0038] Example 2: A degradable polylactic acid-based hot melt adhesive and its preparation method, including the following steps:

[0039] S1: Add 45 mL of L-lactic acid solution into a reaction kettle, stir for 18 min at 23 °C and 550 r / min. Under a nitrogen atmosphere, heat it to 115 °C in an oil bath, dehydrate by vacuum for 2.3 h, then add 1.2 mL of methanesulfonic acid as a catalyst and 1.2 g of stannous acetate, heat to 150 °C, and continue the reaction for 8.5 h. Then add 550 mL of chloroform, precipitate with absolute ethanol, filter by suction, wash the filter cake twice with deionized water, and dry it in vacuum at 70 °C for 1.2 h to obtain a polylactic acid prepolymer; Add 11 g of the polylactic acid prepolymer, 15 g of 1,3-diaminopyrene, and 350 mL of hexafluoroisopropanol into the reaction kettle. Under nitrogen protection, stir at 160 °C and 550 r / min for 18 min, add 1.2 g of sodium dodecylbenzenesulfonate, continue the reaction for 5 h, filter, wash the filter cake twice with deionized water, and dry it in vacuum at 70 °C for 1.2 h to obtain a capped polylactic acid matrix.

[0040] S2: Add 45 g of high-silica glass fibers with a length of 60 μm and 850 mL of an ethanol solution with a mass fraction of 55% into a reaction kettle, stir at 23 °C and 550 r / min for 25 h, dry in an oven at 105 °C for 35 min, transfer it to a mixed solution of 450 mL of sulfuric acid with a mass fraction of 3.4% and 250 mL of nitric acid with a mass fraction of 1.2%, stir at 65 °C and 550 r / min for 35 min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and dry it in vacuum at 70 °C for 1.2 h to obtain pretreated high-silica glass fibers.

[0041] S3: Add 25 g of the pretreated high-silica glass fibers, 1.2 g of polyethylene glycol sulfate as a surfactant, 850 mL of nickel sulfate, 2.3 g of citric acid as a complexing agent, and 1.5 g of L-cysteine as a stabilizer, stir at 45 °C and 450 r / min for 50 min, filter, wash the filter cake with deionized water until the last washing liquid is neutral to obtain nickel-plated high-silica glass fibers with a surface nickel film thickness of 25 nm; Place the nickel-plated high-silica glass fibers in PECVD, introduce high-purity argon with a gas flow rate of 45 L / h and methane with a gas flow rate of 6 L / h as a carbon source for 11 min, the reactor temperature is 1000 °C, the treatment time is 2.5 h, then wash the treated powder twice with deionized water to remove impurities, and dry it in vacuum at 70 °C for 1.2 h to obtain a functionalized modified composite.

[0042] S4: Add 11 g of ammonium polyphosphate, 18 g of 2,5-diaminobenzoic acid, and 450 mL of deionized water into a reaction kettle. Dissolve 2.3 g of sodium dodecyl sulfate in 110 mL of 65 wt% ethanol solution and then add it into the reaction kettle. Stir at 55 °C and 450 r / min for 45 min, then add 9 g of zinc chloride, continue stirring and reacting for 3.4 h, carry out suction filtration, wash the filter cake with deionized water three times, and dry it under vacuum to obtain a flame-retardant functional ligand; Add 11 g of the flame-retardant functional ligand, 55 mL of polyether polyol, and 250 mL of deionized water into the reaction kettle, stir at 23 °C and 600 r / min for 25 min. Stir and dissolve 18 g of epoxy resin powder with a particle size of 20 - 30 μm and 190 mL of acetone, then add it into the reaction kettle, continue stirring for 13 min, then add 33 mL of isocyanate and 4.5 mL of a dibutyltin dilaurate solution with a mass fraction of 0.35%, continue stirring and reacting for 1.2 h, filter, wash the filter cake with deionized water twice, and dry it at 70 °C under vacuum for 1.2 h to obtain an interpenetrating toughened flame retardant.

[0043] S5: Add the end-capped polylactic acid matrix, the functionalized modified composite, the interpenetrating toughened flame retardant, and butylated hydroxyanisole into the reaction kettle according to a mass ratio of 65:7:19:1, stir at 165 °C and 85 r / min for 2.3 h, and extrude and pelletize using a twin-screw extruder to obtain a degradable polylactic acid-based hot melt adhesive.

[0044] Example 3: A degradable polylactic acid-based hot melt adhesive and its preparation method, including the following steps:

[0045] S1: Add 50 mL of L-lactic acid solution into the reaction kettle, stir at 25 °C and 700 r / min for 20 min. Under a nitrogen atmosphere, heat it to 120 °C in an oil bath, evacuate and dehydrate for 3 h, then add 2 mL of catalyst methanesulfonic acid and 2 g of stannous acetate, heat to 160 °C, and continue reacting for 9 h. Then add 600 mL of chloroform, precipitate with absolute ethanol, carry out suction filtration, wash the filter cake with deionized water three times, and dry it at 80 °C under vacuum for 2 h to obtain a polylactic acid prepolymer; Add 12 g of the polylactic acid prepolymer, 16 g of 1,3-diaminopyrene, and 400 mL of hexafluoroisopropanol into the reaction kettle. Under nitrogen protection, stir at 170 °C and 700 r / min for 20 min, add 2 g of sodium dodecylbenzenesulfonate, continue reacting for 6 h, filter, wash the filter cake with deionized water three times, and dry it at 80 °C under vacuum for 2 h to obtain an end-capped polylactic acid matrix.

[0046] S2: Add 50 g of high silica glass fibers with a length of 70 μm and 900 mL of ethanol solution with a mass fraction of 60% into a reaction kettle, stir at 25 °C and 600 r / min for 26 h, dry in an oven at 110 °C for 40 min, transfer to a mixed solution of 500 mL of sulfuric acid with a mass fraction of 4% and 300 mL of nitric acid with a mass fraction of 2%, stir at 70 °C and 600 r / min for 40 min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and dry in vacuum at 80 °C for 2 h to obtain pretreated high silica glass fibers.

[0047] S3: Add 30 g of pretreated high silica glass fibers, 2 g of polyethylene glycol sulfate as a surfactant, 900 mL of nickel sulfate, 3 g of citric acid as a complexing agent, and 2 g of L-cysteine as a stabilizer, stir at 50 °C and 500 r / min for 60 min, filter, wash the filter cake with deionized water until the last washing liquid is neutral to obtain nickel-plated high silica glass fibers with a surface nickel film thickness of 30 nm; place the nickel-plated high silica glass fibers in PECVD, introduce high-purity argon with a gas flow rate of 50 L / h and methane with a gas flow rate of 7 L / h as a carbon source for 12 min, the reactor temperature is 1020 °C, the treatment time is 3 h, then wash the treated powder with deionized water 3 times to remove impurities, and dry in vacuum at 80 °C for 2 h to obtain a functionalized modified composite.

[0048] S4: Add 12 g of ammonium polyphosphate, 20 g of 2,5-diaminobenzoic acid and 500 mL of deionized water into a reaction kettle, dissolve 3 g of sodium dodecyl sulfate in 120 mL of 70 wt% ethanol solution and then add it into the reaction kettle, stir at 60 °C and 500 r / min for 50 min, add 10 g of zinc chloride, continue to stir and react for 4 h, filter, wash the filter cake with deionized water 3 times, and dry in vacuum to obtain a flame retardant functional ligand; add 12 g of the flame retardant functional ligand, 60 mL of polyether polyol and 300 mL of deionized water into a reaction kettle, stir at 25 °C and 700 r / min for 30 min, dissolve 20 g of epoxy resin powder with a particle size of 20 - 30 μm and 200 mL of acetone and then add it into the reaction kettle, continue to stir for 15 min, then add 35 mL of isocyanate and 5 mL of dibutyltin dilaurate solution with a mass fraction of 0.4%, continue to stir and react for 2 h, filter, wash the filter cake with deionized water 3 times, and dry in vacuum at 80 °C for 2 h to obtain an interpenetrating toughened flame retardant.

[0049] S5: Add the capped polylactic acid matrix, the functionalized modified composite, the interpenetrating toughened flame retardant and butylated hydroxyanisole into a reaction kettle according to a mass ratio of 70:8:22:2, stir at 170 °C and 90 r / min for 3 h, and extrude and pelletize using a twin-screw extruder to obtain a degradable polylactic acid-based hot melt adhesive.

[0050] Comparative Example 1: Based on Example 3, the capped polylactic acid matrix in step S1 was replaced with commercially available polylactic acid, and the remaining steps remained unchanged to prepare a degradable polylactic acid-based hot melt adhesive.

[0051] Comparative Example 2: Based on Example 3, the nickel-plated high-silica glass fiber in step S2 was replaced with pretreated high-silica glass fiber, and the remaining steps remained unchanged to prepare a degradable polylactic acid-based hot melt adhesive.

[0052] Comparative Example 3: Based on Example 3, the nickel-plated high-silica glass fiber and commercially available carbon nanotubes in step S2 were mixed evenly at a mass ratio of 1:2.5 to obtain a functionalized modified composite, and the remaining steps remained unchanged to prepare a degradable polylactic acid-based hot melt adhesive.

[0053] Comparative Example 4: Based on Example 3, the flame retardant functional ligand in step S4 was replaced with ammonium polyphosphate, and the remaining steps remained unchanged to prepare a degradable polylactic acid-based hot melt adhesive.

[0054] Comparative Example 5: Based on Example 3, the epoxy resin powder in step S4 was removed, and the remaining steps remained unchanged to prepare a degradable polylactic acid-based hot melt adhesive.

[0055] The reagents in the examples and comparative examples were all purchased from regular commercial sources.

[0056] Perform performance tests on the degradable polylactic acid-based hot melt adhesives prepared in Examples 1 - 3 and Comparative Examples 1 - 5. Use a poplar board of 200×200×5 mm, with a coating amount of 300 g / m 2 , hot press and cure for 7 min, the hot press temperature is 220 °C, the hot press pressure is 1.5 Mpa, test the bonding strength of the bonded poplar board, and repeatedly heat 10 times and 20 times and continue to test the bonding strength; place the board in an oven and heat it to 170 °C, after natural cooling, place the board in a constant temperature oven at 65 °C and 75% humidity for accelerated aging for 30 days and then take it out, test the bonding strength after aging;

[0057] Coat the degradable polylactic acid-based hot melt adhesive on high-temperature release paper, with a coating amount of 300 g / m 2 , hot press and cure for 7 min, the hot press temperature is 220 °C, the hot press pressure is 1.5 Mpa, after hot press curing, remove the release paper, cut the hot melt film into 50×50 mm square pieces and weigh them, bury them in the soil, the burial depth is 1 m, dig them out every month, wash and dry them and then weigh them to calculate the degradation rate;

[0058] The electric heating preheating platform is heated to 140 °C, and then the degradable polylactic acid-based hot melt adhesive is placed on the heating preheating platform for preheating for 20 minutes. At the same time, the heating roller temperature of the two-roll calender is heated to 165 °C. The lower roller side uses a 75-μm PET release film as the bottom film, and the upper roller uses a 75-μm thick aluminum film as the upper film. Set the gap between the two rollers to 1.65 mm, place the preheated hot melt adhesive block on the feeding table of the two-roll calender, start the calender for lamination. All materials pass through the calender rollers and are quickly cooled down through the condensation metal plate, and then wound to obtain a hot melt adhesive film. The wave absorption ability is tested, and the results are shown in Table 1:

[0059] Table 1 Test results of the bonding performance and degradation performance of the degradable polylactic acid-based hot melt adhesive

[0060]

[0061]

[0062] As can be seen from Table 1, the degradable polylactic acid-based hot melt adhesive prepared by the present invention still has excellent bonding strength after repeated heating, and the degradation rate reaches more than 50% after 3 months of degradation, with excellent degradation rate, thermal stability, flame retardancy and electromagnetic shielding ability.

[0063] In Comparative Example 1, the end-capped polylactic acid matrix was replaced with commercially available polylactic acid. A large number of pyrene groups are contained in the end-capped polylactic acid matrix. Pyrene is a relatively stable chemical structure. Pyrene end-capping can enhance the chemical stability of the polylactic acid matrix at high temperatures. It can bind to carbon nanotubes through π-π interaction and change the surface properties of carbon nanotubes. This change in surface properties helps to reduce the interaction force between carbon nanotubes, thereby improving its dispersibility.

[0064] In Comparative Example 2, the nickel-plated high-silica glass fiber was replaced with pretreated high-silica glass fiber. A layer of nickel was evenly plated on the surface of the glass fiber, which can catalyze and decompose carbon-containing gases and serve as a growth point. When carbon atoms reach supersaturation in the catalyst, carbon nanotubes grow on its surface. After losing the nickel layer, it affects the number of carbon nanotubes generated and the bonding degree between the glass fiber and the carbon nanotubes. Therefore, the bonding strength is reduced. After repeated heating, the reduction amplitude of the bonding strength is very large, but it has no obvious effect on the dispersibility of carbon nanotubes. Therefore, a good degradation rate can be ensured.

[0065] In Comparative Example 3, nickel-plated high-silica glass fibers and commercially available carbon nanotubes were mixed evenly at a mass ratio of 1:2.5. Carbon nanotubes were grown on the surface of the nickel-plated high-silica glass fibers by chemical deposition to improve the bonding degree. After the nickel-plated high-silica glass fibers and the carbon nanotubes were mixed evenly, there was a strong van der Waals force between the carbon nanotubes. This intermolecular force made the carbon nanotubes prone to agglomeration, which in turn affected the performance test. However, the dispersibility was poor and large agglomerates were easily formed. These structural defects might provide convenient conditions for the intrusion of water molecules, thus accelerating the degradation rate.

[0066] In Comparative Example 4, the flame-retardant functional ligand was replaced with ammonium polyphosphate. The interpenetration of the porous zinc framework could further enhance the ability to disperse stress, and the porous zinc framework had a catalytic effect, which could promote the carbonization ability of the flame retardant.

[0067] In Comparative Example 5, the epoxy resin powder was omitted, and an interpenetrating network structure was formed by polyurethane and epoxy resin. By winding around each other between the networks, the flame-retardant functional ligand was anchored in the composite material to avoid the migration of the flame retardant. Moreover, the interpenetrating network could disperse stress when subjected to external forces, improve the overall toughness of the material, and avoid the problem of high brittleness of polylactic acid.

[0068] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0069] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a degradable polylactic acid-based hot melt adhesive, characterized in that: Prepared by the following steps: The blocked polylactic acid matrix, the functional modified composite, the interpenetrating toughened flame retardant and the butylated hydroxyanisole are added into a reaction kettle in a mass ratio of 60-70:5-8:18-22:1-2, stirred at 160-170°C and 80-90r / min for 2-3h, and extruded and granulated by a twin-screw extruder to obtain a degradable polylactic acid-based hot melt adhesive.

2. The method for preparing a degradable polylactic acid-based hot melt adhesive according to claim 1, characterized in that: The blocked polylactic acid matrix is ​​prepared by the following steps: The L-lactic acid solution is added to the reaction kettle, stirred at 20-25°C and 500-700r / min for 15-20min, heated to 110-120°C in an oil bath under a nitrogen atmosphere, vacuum dehydrated for 2-3h, then added with methanesulfonic acid and stannous acetate, heated to 150-160°C, continued to react for 8-9h, then added with chloroform, precipitated with anhydrous ethanol, filtered, washed the filter cake with deionized water for 2-3 times, and vacuum dried to obtain a polylactic acid prepolymer; the polylactic acid prepolymer, 1,3-diaminopyrene and hexafluoroisopropanol are added to the reaction kettle, stirred at 150-170°C and 500-700r / min for 15-20min under nitrogen protection, added with sodium dodecylbenzene sulfonate, continued to react for 4-6h, filtered, washed the filter cake with deionized water for 2-3 times, and vacuum dried to obtain a capped polylactic acid matrix.

3. The method for preparing a degradable polylactic acid-based hot melt adhesive according to claim 2, characterized in that: The dosage ratio of the L-lactic acid solution, methanesulfonic acid, stannous acetate and chloroform is 40-50 mL: 1-2 mL: 1-2 g: 500-600 mL; The dosage ratio of the polylactic acid prepolymer, 1,3-diaminopyrene, hexafluoroisopropanol and sodium dodecylbenzene sulfonate is 10-12g: 14-16g: 300-400mL: 1-2g.

4. The method for preparing a degradable polylactic acid-based hot melt adhesive according to claim 2, characterized in that: The functionalized modified composite is prepared by the following steps: The pretreated high-silica glass fiber, polyethylene glycol sulfate, nickel sulfate, citric acid and L-cystine are stirred at 40-50° C. and 400-500 r / min for 40-60 min, filtered, and the filter cake is washed with deionized water until the last washing liquid is neutral to obtain a nickel-plated high-silica glass fiber with a surface nickel film thickness of 20-30 nm; the nickel-plated high-silica glass fiber is placed in PECVD, and high-purity argon gas with a gas flow rate of 40-50 L / h and methane with a gas flow rate of 5-7 L / h are introduced for 10-12 min, the reactor temperature is 980-1020° C., the treatment time is 2-3 h, and then the treated powder is washed with deionized water 2-3 times to remove impurities, and vacuum dried to obtain a functional modified composite; The usage ratio of the pretreated high-silica glass fiber, polyethylene glycol sulfate, nickel sulfate, citric acid and L-cystine is 20-30 g: 1-2 g: 800-900 mL: 2-3 g: 1-2 g.

5. The method for preparing a degradable polylactic acid-based hot melt adhesive according to claim 4, characterized in that: The pretreated high-silica glass fiber is prepared by the following steps: Add high-silica glass fiber with a length of 50-70 μm and 50-60wt% ethanol solution into a reactor, stir at 20-25°C and 500-600r / min for 24-26h, dry at 100-110°C for 30-40min, transfer to a mixed solution of 3-4wt% sulfuric acid and 1-2wt% nitric acid, stir at 60-70°C and 500-600r / min for 30-40min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and vacuum dry to obtain pretreated high-silica glass fiber.

6. The method for preparing a degradable polylactic acid-based hot melt adhesive according to claim 4, characterized in that: The usage ratio of the high silica glass fiber, ethanol, sulfuric acid and nitric acid is 40-50g: 800-900mL: 400-500mL: 200-300mL.

7. The method for preparing a degradable polylactic acid-based hot melt adhesive according to claim 5, characterized in that: The interpenetrating toughened flame retardant is prepared by the following steps: Ammonium polyphosphate, 2,5-diaminobenzoic acid and deionized water are added to a reaction kettle, sodium hexadecyl sulfate is dissolved in a 60-70wt% ethanol solution and then added to the reaction kettle, stirred at 50-60°C and 400-500r / min for 40-50min, zinc chloride is added, and the stirring reaction is continued for 3-4h, filtered, the filter cake is washed with deionized water for 2-3 times, and vacuum dried to obtain a flame retardant functional ligand; the flame retardant functional ligand, polyether polyol and deionized water are added Put it into the reactor, stir at 20-25°C and 500-700r / min for 20-30min, stir and dissolve the epoxy resin powder with a particle size of 20-30μm and acetone, add them into the reactor, continue stirring for 10-15min, then add isocyanate and 0.3-0.4wt% dibutyltin dilaurate solution, continue stirring and reacting for 1-2h, filter, wash the filter cake with deionized water 2-3 times, and vacuum dry to obtain an interpenetrating toughened flame retardant.

8. The method for preparing a degradable polylactic acid-based hot melt adhesive according to claim 7, characterized in that: The usage ratio of the ammonium polyphosphate, 2,5-diaminobenzoic acid, deionized water, sodium hexadecyl sulfate, ethanol solution and zinc chloride is 10-12g: 15-20g: 400-500mL: 2-3g: 100-120mL: 8-10g.

9. The method for preparing a degradable polylactic acid-based hot melt adhesive according to claim 7, characterized in that: The usage ratio of the flame retardant functional ligand, polyether polyol, deionized water, epoxy resin powder, acetone, isocyanate and dibutyltin dilaurate solution is 10-12g: 50-60mL: 200-300mL: 15-20g: 180-200mL: 30-35mL: 4-5mL.

10. A degradable polylactic acid-based hot melt adhesive, characterized in that: Prepared by the preparation method described in any one of claims 1 to 9.

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