Preparation method of tray cushion block

Abstract

The invention provides a preparation method of a tray cushion block. The method comprises the following steps: (1) applying an isocyanate adhesive on the surface of a base material; (2) applying an internal release agent on the surface of the base material; (3) applying the modified gamma-polyglutamic acid solution to the surface of the base material; and (4) applying a bishydrazide compound on the surface of the base material to obtain a tray cushion block material, and forming to obtain the tray cushion block. The tray cushion block produced by the method has a double-crosslinking network of isocyanate and modified gamma-polyglutamic acid. The first network is an isocyanate cross-linked network, the second network is a modified gamma-polyglutamic acid network, the network is formed by crosslinking functional carbonyl on modified gamma-polyglutamic acid and a bishydrazide compound through ketone hydrazine, and the double-network cross-linked system improves the mutual entanglement degree of molecular chains, enhances the internal friction force and improves the mechanical property of the composite material. And the tray cushion block has higher screw holding force.

Description

Technical Field

[0001] The present invention belongs to the field of wood processing, and particularly relates to a preparation method of a pallet cushion block with high nail-holding force. Background Art

[0002] Currently, the pallet cushion blocks are mainly divided into four types, namely solid wood cushion blocks, multi-layer board cushion blocks, sawdust cushion blocks and particle board cushion blocks. With the improvement of people's awareness of resource conservation, the usage amount of particle board cushion blocks is increasing. Compared with solid wood cushion blocks and multi-layer board cushion blocks, particle board cushion blocks can utilize all the remaining waste wood, reducing resource waste. Waste furniture can also be broken into particles again to achieve recycling. In addition, due to the smooth surface and high strength of particle board cushion blocks, they can replace solid wood cushion blocks. They are the designated products of the pallet association in Europe, meeting the strict requirements of EPAL, and are exempt from fumigation when exported. Therefore, they are gradually being taken seriously by the packaging industry.

[0003] Currently, the commonly used adhesive in particle board cushion blocks is urea-formaldehyde resin, but urea-formaldehyde resin adhesive has some inherent defects, such as poor nail-holding force, the screw is prone to fall off after being driven into the pallet cushion block; poor mechanical strength, the cushion block is easily damaged, and there is formaldehyde release, etc. With the development of the packaging industry and the improvement of people's environmental protection awareness, the particle board cushion blocks prepared with urea-formaldehyde resin adhesive gradually cannot meet the needs of social development.

[0004] Patent CN212825931U discloses a particle board for improving nail-holding force. By implanting rubber columns in the particle board and positioning, the screw is driven into the rubber columns in the particle board to improve the nail-holding force. The invention patent of Patent CN104945926B is to solve the problem of poor nail-holding force of wooden products. Rubber powder particles are added to the wooden board to form a uniform sea-island structure phase diagram in a submicron phase state, effectively solving the problem of poor nail-holding force. Both of these methods improve the nail-holding force by adding rubber materials, but these methods increase the processing difficulty of the particle board, are difficult to promote on a large scale, and the addition of rubber columns affects the secondary utilization of waste wood boards.

[0005] Therefore, it is very necessary to develop a particle board cushion block with high nail-holding force, good mechanical properties and convenient processing. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of a formaldehyde-free particle board pallet cushion block. The present invention improves the internal bonding degree of the particle board cushion block by constructing a double cross-linking network of an isocyanate cross-linking system and a γ-PGA cross-linking system in the particle board cushion block. The molecular chains of the two cross-linked macromolecules are entangled with each other, and the internal friction force between the molecular chains increases, improving the stability and friction force of the screw entering the pallet cushion block, so that the prepared pallet cushion block has high nail-holding force.

[0007] To achieve the purpose of the present invention, the following technical solutions are adopted:

[0008] A preparation method of a pallet cushion block, the method comprising the following steps:

[0009] (1) Apply an isocyanate adhesive on the surface of the substrate;

[0010] (2) Then apply an internal mold release agent on the surface of the substrate;

[0011] (3) Then apply a modified γ-polyglutamic acid solution on the surface of the substrate;

[0012] (4) Apply a diacylhydrazine compound on the surface of the substrate to obtain a pallet cushion block material, and then through molding, obtain a pallet cushion block.

[0013] Preferably, the substrate is a wood or non-wood veneer, including but not limited to eucalyptus wood shavings, pine wood shavings, poplar wood shavings, bamboo wood shavings, etc., or fibers of herbaceous plants, wheat straw, peanut shells, cotton stalks, etc., and the moisture content of the substrate is 5%-20wt%, such as 12wt%, 15wt%, 18wt%, etc.;

[0014] Preferably, the isocyanate adhesive is any one or a combination of aliphatic polyisocyanates, aromatic polyisocyanates or their modified isocyanates, preferably a modified aromatic polyisocyanate, more preferably an aromatic polyisocyanate modified by polyethylene glycol or polyethylene glycol - polypropylene glycol; preferably, the -NCO content of the isocyanate adhesive is 22-34wt%.

[0015] Preferably, the application method of the isocyanate adhesive is atomized sizing or pouring sizing;

[0016] Preferably, the application amount of the isocyanate adhesive is 3-10% of the mass of the wood shavings, such as 4%, 5%, 6%, etc.;

[0017] Preferably, the internal mold release agent is a water-based stearate, including but not limited to one or more of zinc stearate, magnesium stearate, calcium stearate, ammonium stearate, and the application method of the internal mold release agent is atomized application or pouring sizing;

[0018] Preferably, the application amount of the internal mold release agent is 0.01-1% of the mass of the substrate, preferably 0.1-1%, and can be configured into an aqueous solution for dilution and use;

[0019] The internal mold release agent used in the present invention is mainly a water-based stearate. The internal mold release agent is added to the formulation. During each molding process, the internal mold release agent migrates to the interface between the foam and the mold, thereby achieving the demolding effect. Generally, the internal mold release agent is easily dispersed in the resin system to form a stable dispersion; it does not change the original reactivity and physical properties; it does not affect the nucleation effect, thus not changing the porous structure or foaming stability; it does not affect the paintability of the molded article.

[0020] Preferably, the modified γ-polyglutamic acid solution is obtained by reacting component I and component II:

[0021] Among them, component I is γ-polyglutamic acid with a number average molecular weight of 10 - 500 kDa; component II is a p-aminobenzoyl compound with the following structural formula, where X is hydrogen or an alkyl group with 1 - 6 carbon atoms.

[0022]

[0023] Preferably, the preparation method of the modified γ-polyglutamic acid includes the following steps:

[0024] (a) Dissolve γ-polyglutamic acid in water and stir evenly;

[0025] (b) Add a carbodiimide condensing agent and an acylation activator to the solution obtained in step (a), and stir for activation;

[0026] (c) Then add a p-aminobenzoyl compound for reaction;

[0027] Preferably, the carbodiimide condensing agent is selected from 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) or dicyclohexylcarbodiimide (DCC), which is used to activate the carboxyl group.

[0028] Preferably, the acylation activator is selected from N-hydroxysuccinimide or N-hydroxyphthalimide, which is used to activate the amino group.

[0029] Preferably, the activation in step (b) is carried out for 4 - 10 h;

[0030] Preferably, the reaction temperature in step (c) is 60 - 80 °C, and the reaction time is 12 - 24 h.

[0031] Preferably, the molar ratio of the carbodiimide condensing agent to the acylation activator is 3 - 1:1;

[0032] Preferably, the molar ratio of the carbodiimide condensing agent to the carboxyl group in γ-polyglutamic acid is 2 - 1:1;

[0033] Preferably, the molar ratio of the carboxyl group in γ-polyglutamic acid to the p-aminobenzoyl compound is 1:1 - 3.

[0034] Preferably, the p-aminobenzoyl compound is selected from one or more of p-aminobenzaldehyde, p-aminoacetophenone, 4-aminopropiophenone, and 4-aminobutyrophenone;

[0035] Preferably, after the reaction is completed, separation is carried out. The system obtained in step (c) is transferred to a dialysis bag and dialyzed in water for 3 to 7 days to separate unreacted small molecule substances and the activator by dialysis; the product after dialysis is freeze-dried to obtain carbonyl-functionalized γ-polyglutamic acid.

[0036] The application method of the modified γ-polyglutamic acid solution is atomization application or sizing; the mass fraction of modified γ-polyglutamic acid in the solution is 1% - 10%, the molecular weight is 10 - 500 kDa, and the application amount of the modified γ-polyglutamic acid solution is 1% - 5% of the mass of the substrate;

[0037] In the present invention, another system that forms a double cross-linked network with the isocyanate system is the modified γ-polyglutamic acid system. γ-Polyglutamic acid is a water-soluble macromolecule with a large number of carboxyl groups in its molecular structure. In the present invention, the carboxyl groups in γ-polyglutamic acid are subjected to amidation reaction with p-aminobenzoyl compounds to introduce a large number of carbonyl groups into the γ-polyglutamic acid molecular chain. During the sizing process, the carbonyl groups will undergo ketone-hydrazide cross-linking with dihydrazide compounds to form imine bonds. The ketone-hydrazide cross-linking makes the modified γ-polyglutamic acid molecular chain form a network structure, which is intertwined with the isocyanate cross-linking system to improve the nail-holding force of the pallet cushion block.

[0038] The dihydrazide compound is added in the form of a solution. The mass fraction of the dihydrazide compound solution is 0.1 - 2%, and the application amount of the dihydrazide compound is 1% - 3% of the mass of the wood chips;

[0039] Preferably, the dihydrazide compound is a dicarboxylic acid dihydrazide, selected from one or more of succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, and pimelic acid dihydrazide. The dihydrazide compound can be added in the form of an aqueous solution, and its mass fraction is 0.1 - 2%. The application amount of the dihydrazide compound solution is 1% - 3% of the mass of the substrate.

[0040] The treated substrate is fed into a pallet cushion block molding machine, and the pallet cushion block is molded under certain pressure, temperature, and time conditions to obtain a high nail-holding force and formaldehyde-free added pallet cushion block.

[0041] Preferably, the treated substrate is fed into the molding machine for molding within 0 - 20 minutes.

[0042] Preferably, the temperature for molding the pallet cushion block is 110 - 150 °C, such as 120 °C, 130 °C, 140 °C, etc.;

[0043] The forming pressure of the pallet cushion block is 2-5 MPa, such as 3 MPa, 3.5 MPa, 4 MPa, etc.;

[0044] The pushing time period of the push rod of the pallet cushion block forming machine can be shortened compared with that of urea-formaldehyde resin, specifically 25-60 s / time, such as 30 s / time, 40 s / time, 50 s / time, etc.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] (1) By constructing a double cross-linking system, the present invention utilizes the mutual entanglement between macromolecules formed by the isocyanate cross-linking system and the modified γ-polyglutamic acid cross-linking system to increase the internal friction force between macromolecular chains, enabling the pallet cushion block to have better screw holding force.

[0047] (2) The production process route of the pallet cushion block provided by the present invention requires less modification to the equipment, has strong feasibility, and excellent mechanical properties. Detailed Embodiments

[0048] The following further illustrates the implementation scheme of the present invention in combination with embodiments. However, the present invention is not limited to the listed embodiments, and should also include any other known changes within the scope of the rights required by the present invention.

[0049] For the parts not specifying the specific experimental steps or conditions in the embodiments, the operations or conditions of the corresponding conventional experimental steps in the technical field can be followed. For the reagents or instruments not indicating the manufacturers, they are all conventional products that can be obtained through commercial purchase.

[0050] Modified isocyanate (Wannate 9131FC), with a viscosity of 320-550 cP at 25°C and an -NCO content of 27.5-30%, Wanhua Chemical Group Co., Ltd.;

[0051] Aqueous zinc stearate, with a milky white liquid appearance, easily dispersed in water, a solid content of 38-45%, a viscosity ≤ 1300 cP, Dongguan Hanwei Technology Co., Ltd.;

[0052] γ-Polyglutamic acid (γ-PGA), with a white powder appearance, is a water-soluble, biodegradable, non-toxic polymer with a molecular weight of 70 kDa and 200 kDa, Nanjing Xuankai Biotechnology Co., Ltd.;

[0053] 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), which is often used as a carboxyl activator in the preparation of amides in combination with N-hydroxysuccinimide (NHS) to increase the efficiency of the coupling reaction, Beijing Innochem Technology Co., Ltd.;

[0054] N-Hydroxysuccinimide (NHS), a white crystalline powder, sensitive to moisture, prone to caking, can be used as an activator for amino groups, Beijing Innochem Technology Co., Ltd.;

[0055] p-Acetylacetanilide, with a yellow needle-like crystal appearance, easily soluble in hot water, Yancheng Spring Chemical Technology Co., Ltd.;

[0056] p-Aminobenzaldehyde, with a yellow crystal appearance, soluble in ethanol, insoluble in water, Hubei Wande Chemical Industry Co., Ltd.;

[0057] Succinic dihydrazide, with a white crystalline powder appearance, Hubei Hengjingrui Chemical Industry Co., Ltd.;

[0058] Mixed poplar and pine wood shavings, with a moisture content of 10%;

[0059] Universal testing machine, High Rail Testing Instruments (Dongguan) Co., Ltd.

[0060] Testing method:

[0061] Adhesive layer shear strength

[0062] Test the samples according to the method in 4.18 of GB / T 17657-2013. Gradually apply a compressive load to the test pieces to cause shear failure of the adhesive layer to determine the gluing quality.

[0063] Modulus of rupture

[0064] Test the samples according to the method in 4.7 of GB / T 17657-2013.

[0065] Screw holding power

[0066] Test the samples according to the method in 4.21 of GB / T 17657-2013.

[0067] 24-hour water absorption thickness swelling rate

[0068] Test the samples according to the method in 4.6 of GB / T 17657-2013.

[0069] Example 1

[0070] Preparation of modified γ-PGA:

[0071] First, dissolve γ-polyglutamic acid (with a molecular weight of 70 kDa) in deionized water and stir until completely dissolved; add EDC and NHS to the obtained solution and stir for activation for 4 h; add p-aminophenylethanone to the activated system, heat in a water bath at 70 °C and react for 12 h; transfer the reacted system to a dialysis bag and dialyze in deionized water for 4 days; after drying with a freeze dryer, carbonyl-functionalized γ-polyglutamic acid is obtained. The molar ratios of the substances in the above reaction are as follows: γ-PGA (-COOH): EDC = 1:1, EDC: NHS = 1:1, γ-PGA (-COOH): p-aminophenylethanone (-NH2) = 1:1.

[0072] Preparation of pallet cushions:

[0073] Obtain poplar wood raw material shavings through chipping and planing, and control the moisture content of the shavings to be about 10% after drying. Apply the modified isocyanate adhesive (Wannate 9131FC) to the surface of the shavings by spraying, and the application amount is 5% of the mass of the substrate shavings; apply the internal release agent aqueous zinc stearate solution to the surface of the above shavings by spraying, and the application amount is 1% of the mass of the substrate shavings. Dilute and spray after mixing with water at a ratio of 1:1 during application; apply the modified γ-PGA solution to the surface of the above shavings by gluing, and the application amount is 2% of the mass of the substrate shavings. The mass fraction of the modified γ-PGA in the modified γ-PGA solution is 5%. Apply the succinic dihydrazide solution (the mass fraction of succinic dihydrazide is 1%) to the surface of the above shavings by spraying, and the application amount is 2.5% of the mass of the substrate shavings. After the substrate shavings are sized, enter the pallet cushion molding machine. The molding temperature is 130 °C, the outlet pressure is 3.5 MPa, the pushing time period of the push rod is 30 s / time, and after molding, obtain the pallet cushions through cutting and aging and cooling.

[0074] Determine the performance of the obtained pallet cushions according to "Appendix A (Normative) Chip Cushions" in "GBT 31148-2022 General Technical Requirements for Wooden Flat Pallets". The results are shown in Table 1.

[0075] Example 2

[0076] Preparation of modified γ-PGA:

[0077] First, dissolve γ-polyglutamic acid (with a molecular weight of 200 kDa) in deionized water and stir until completely dissolved; add EDC and NHS to the obtained solution and stir for activation for 4 h; add p-aminophenetone to the activated system, heat it in a water bath at 70 °C and react for 12 h; transfer the reacted system to a dialysis bag and dialyze it in deionized water for 4 days; after drying with a freeze dryer, carbonyl-functionalized γ-polyglutamic acid is obtained. The molar ratios of the substances in the above reaction are as follows: γ-PGA (-COOH): EDC = 1:1, EDC: NHS = 1:1, γ-PGA (-COOH): p-aminophenetone (-NH2) = 1:1.

[0078] Preparation of pallet cushion blocks:

[0079] Obtain poplar wood raw material shavings through chipping and planing, and control the moisture content of the shavings to be about 15% after drying. Apply the modified isocyanate adhesive (Wannate 9131FC) to the surface of the shavings by spraying, and the application amount is 8% of the mass of the base material shavings; apply the internal mold release agent aqueous zinc stearate solution to the surface of the above shavings by spraying, and the application amount is 1% of the mass of the base material shavings. Dilute and spray it after mixing with water at a ratio of 1:1 during application; apply the modified γ-PGA solution to the surface of the above shavings by gluing, and the application amount is 3% of the mass of the base material shavings. The mass fraction of the modified γ-PGA in the applied solution is 5%. Apply the succinic dihydrazide solution to the surface of the above shavings by spraying, and the application amount is 2% of the mass of the base material shavings. The mass fraction of succinic dihydrazide in the solution is 1%. After the base material shavings are sized, enter the pallet cushion block molding machine. The molding temperature is 130 °C, the outlet pressure is 3.5 MPa, the pushing time period of the push rod is 30 s / time, and after molding, obtain the pallet cushion blocks through cutting and aging and cooling.

[0080] The performance test of the pallet cushion blocks is the same as that in Example 1. The results are shown in Table 1.

[0081] Example 3

[0082] Preparation of modified γ-PGA:

[0083] First, dissolve γ-polyglutamic acid (with a molecular weight of 70 kDa) in deionized water and stir until completely dissolved; add EDC and NHS to the resulting solution and stir for activation for 4 h; add the ethanol solution of p-aminobenzaldehyde to the activated system and react at room temperature for 12 h; transfer the reacted system to a dialysis bag and dialyze in deionized water for 4 days; after drying with a freeze dryer, carbonyl-functionalized γ-polyglutamic acid is obtained. The molar ratios of the substances in the above reaction are as follows: γ-PGA (-COOH): EDC = 1:1.5, EDC: NHS = 1:1, γ-PGA (-COOH): p-aminophenylethanone (-NH2) = 1:2. The mass fraction of p-aminobenzaldehyde in the ethanol solution of p-aminobenzaldehyde is 10%.

[0084] Preparation of pallet spacers:

[0085] Obtain poplar raw material shavings through chipping and planing, and control the moisture content of the shavings to be about 10% after drying. Apply the modified isocyanate adhesive (Wannate 9131FC) to the surface of the shavings by spraying, with an application amount of 5% of the mass of the base material shavings; apply the aqueous zinc stearate solution of the internal release agent to the surface of the above shavings by spraying, with an application amount of 0.8% of the mass of the base material shavings, and dilute and spray after mixing with water at a ratio of 1:1 during application; apply the modified γ-PGA solution to the surface of the above shavings by gluing, with an application amount of 3% of the mass of the base material shavings, and the mass fraction of the modified γ-PGA in the applied solution is 5%. Apply the succinic dihydrazide solution to the surface of the above shavings by spraying, with an application amount of 1.5% of the mass of the base material shavings, and the mass fraction of succinic dihydrazide in the solution is 1%. After the base material shavings are sized, enter the pallet spacer molding machine, with a molding temperature of 150 °C, an outlet pressure of 3.5 MPa, a push rod pushing time cycle of 30 s / time, and obtain the pallet spacers through cutting and aging and cooling.

[0086] The performance test of the pallet spacers is the same as that in Example 1. The results are shown in Table 1.

[0087] Example 4

[0088] Preparation of modified γ-PGA:

[0089] First, dissolve γ-polyglutamic acid (with a molecular weight of 200 kDa) in deionized water and stir until completely dissolved; add EDC and NHS to the obtained solution and stir for activation for 4 h; add p-aminophenetone to the activated system, heat in a water bath at 70 °C and react for 12 h; transfer the reacted system to a dialysis bag and dialyze in deionized water for 4 days; after drying with a freeze dryer, carbonyl-functionalized γ-polyglutamic acid is obtained. The molar ratios of the substances in the above reaction are as follows: γ-PGA (-COOH): EDC = 1:2, EDC: NHS = 2:1, γ-PGA (-COOH): p-aminophenetone (-NH2) = 1:2.5.

[0090] Preparation of pallet pads:

[0091] Obtain poplar wood raw material shavings through chipping and planing, and control the moisture content of the shavings to be about 15% after drying. Apply the modified isocyanate adhesive (Wannate 9131FC) to the surface of the shavings by spraying, and the application amount is 3% of the mass of the base material shavings; apply the internal release agent aqueous zinc stearate solution to the surface of the above shavings by spraying, and the application amount is 0.1% of the mass of the base material shavings. When applying, it is diluted and sprayed after mixing with water at a ratio of 1:1; apply the modified γ-PGA solution to the surface of the above shavings by gluing, and the application amount is 3% of the mass of the base material shavings, and the mass fraction of the modified γ-PGA in the applied solution is 5%. Apply the succinic dihydrazide solution to the surface of the above shavings by spraying, and the application amount is 1% of the mass of the base material shavings, and the mass fraction of succinic dihydrazide in the solution is 1%. After the base material shavings are sized, they enter the pallet pad forming machine. The forming temperature is 130 °C, the outlet pressure is 3.5 MPa, the pushing time period of the push rod is 30 s / time, and after forming, the pallet pads are obtained through cutting and aging and cooling.

[0092] Comparative Example 1

[0093] Do not apply the modified γ-PGA solution and the succinic dihydrazide solution; other process conditions are the same as in Example 1.

[0094] The performance test of the pallet pads is the same as in Example 1. The results are shown in Table 1.

[0095] Comparative Example 2

[0096] Do not apply the zinc stearate solution; other process conditions are the same as in Example 1.

[0097] The performance test of the pallet pads is the same as in Example 1. The results are shown in Table 1.

[0098] Comparative Example 3

[0099] Do not apply the succinic dihydrazide solution; other process conditions are the same as in Example 1.

[0100] The number of performance brochures of the pallet cushion blocks is the same as that in Example 1. The results are shown in Table 1.

[0101] Comparative Example 4

[0102] Poplar raw material particles are obtained by chipping and planing, and after drying, the moisture content of the particles is controlled to be about 5%. The urea-formaldehyde resin is applied to the surface of the particles by the method of spraying glue, and the application amount is 17% of the mass of the base material particles; after sufficient stirring, the urea-formaldehyde resin and the base material particles are mixed evenly. After the base material particles are sized, they enter the pallet cushion block molding machine, the molding temperature is 130 °C, the outlet pressure is 3.5 MPa, the pushing time period of the push rod is 70 s / time, and after molding, the urea-formaldehyde pallet cushion blocks are obtained through cutting and aging and cooling.

[0103] The performance test of the pallet cushion blocks is the same as that in Example 1. The results are shown in Table 1.

[0104] Table 1 Summary of the performance test results of the pallet cushion blocks

[0105]

[0106] Note: The shear strength of the glue layer is tested perpendicular to the extrusion direction, and the flexural strength is tested parallel to the extrusion direction.

[0107] The performance test results of the pallet cushion blocks in Examples 1-4 show that using the isocyanate system and the modified γ-PGA system in combination with various additives to prepare the pallet cushion blocks can significantly improve the screw holding force of the particle cushion blocks, and a pallet cushion block with high screw holding force can be prepared.

[0108] The results of Example 1 and Comparative Example 1 show that the screw holding force of the single crosslinking system prepared without using the modified γ-PGA system is significantly reduced compared with that of the double crosslinking system, and the mechanical properties are reduced. It is proved that the double crosslinking system proposed by the present invention can significantly improve the screw holding force of the pallet cushion blocks. The results of Example 1 and Comparative Example 2 show that not using the internal mold release agent may cause slightly difficult demolding of the pallet cushion blocks, the surface of the product is rough, affecting the appearance of the product, and at the same time, it will also have a slight impact on the mechanical properties of the cushion blocks. The results of Example 1 and Comparative Example 3 show that not using the succinic dihydrazide solution will also cause the γ-PGA system to fail to crosslink, resulting in a large decrease in the mechanical properties of the pallet cushion blocks.

[0109] The results of Example 1 and Comparative Example 4 show that compared with the particle cushion blocks currently prepared with urea-formaldehyde resin, the pallet cushion blocks prepared by the present invention can greatly improve the screw holding force and mechanical properties of the pallet cushion blocks.

[0110] Finally, it should be noted that the above embodiments are only used to describe the preferred embodiments of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that various modifications or equivalent replacements made to the technical solutions of the present invention, as well as various variations and improvements, should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of a pallet cushion block, characterized in that, The method comprises the following steps: (1) Applying an isocyanate adhesive on the surface of the substrate; (2) Then applying an internal mold release agent on the surface of the substrate; (3) Then applying a modified γ-polyglutamic acid solution on the surface of the substrate; (4) Applying a diacylhydrazine compound on the surface of the substrate to obtain a tray cushion material, and then forming to obtain a tray cushion.

2. The preparation method according to claim 1, characterized in that, The substrate is wood or non-wood veneer or fibers of herbaceous plants, and the moisture content of the substrate is 5%-20wt%.

3. The preparation method according to claim 1, characterized in that, The isocyanate adhesive is any one or a combination of aliphatic polyisocyanates, aromatic polyisocyanates or their modified isocyanates. Preferably, it is a modified aromatic polyisocyanate, and more preferably an aromatic polyisocyanate modified by polyethylene glycol or polyethylene glycol-propylene glycol. Preferably, the -NCO content of the isocyanate adhesive is 22-34wt%; Preferably, the application method of the isocyanate adhesive is atomized sizing or pouring sizing; Preferably, the application amount of the isocyanate adhesive is 3-10% of the mass of the wood chips.

4. The preparation method according to any one of claims 1-3, characterized in that, The internal mold release agent is a water-based stearate, including but not limited to one or more of zinc stearate, magnesium stearate, calcium stearate, ammonium stearate in water. The application method of the internal mold release agent is atomized application or pouring sizing; Preferably, the application amount of the internal mold release agent is 0.01-1% of the mass of the substrate, preferably 0.1-1%, and it can be formulated into an aqueous solution for dilution before use.

5. The preparation method according to any one of claims 1-4, characterized in that, The modified γ-polyglutamic acid solution is obtained by the reaction of component I and component II: Among them, component I is γ-polyglutamic acid, and component II is a p-aminobenzoyl compound with the following structural formula, where X is hydrogen or an alkyl group with 1-6 carbon atoms; Preferably, the number average molecular weight of the γ-polyglutamic acid is 10-500 kDa; Preferably, the p-aminobenzoyl compound is selected from one or more of p-aminobenzaldehyde, p-aminoacetophenone, 4-aminopropiophenone, 4-aminobutyrophenone.

6. The preparation method according to any one of claims 1-5, characterized in that, The preparation method of the modified γ-polyglutamic acid comprises the following steps: (a) Dissolving γ-polyglutamic acid in water and stirring evenly; (b) Adding a carbodiimide condensing agent and an acylation activator to the solution obtained in step (a), and stirring for activation; (c) Then adding a p-aminobenzoyl compound for reaction; Preferably, the carbodiimide condensing agent is selected from 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride or dicyclohexylcarbodiimide; Preferably, the acylation activator is selected from N-hydroxysuccinimide or N-hydroxyphthalimide; Preferably, the activation time in step (b) is 4-10 h; Preferably, the reaction temperature in step (c) is 60-80 °C, and the reaction time is 12-24 h. Preferably, the molar ratio of the carbodiimide condensing agent to the acylation activator is 3-1:1; Preferably, the molar ratio of the carbodiimide condensing agent to the carboxyl group in γ-polyglutamic acid is 2-1:1; Preferably, the molar ratio of the carboxyl group in γ-polyglutamic acid to the p-aminobenzoyl compound is 1:1-3.

7. The preparation method according to any one of claims 1-6, characterized in that, The application method of the modified γ-polyglutamic acid solution is atomized application or pouring sizing; Preferably, the mass fraction of the modified γ-polyglutamic acid in the solution is 1%-10%. Preferably, the application amount of the modified γ-polyglutamic acid solution is 1%-5% of the mass of the substrate.

8. The preparation method according to any one of claims 1-7, characterized in that, The bis-hydrazide compound is added in the form of a solution, and the mass fraction of the bis-hydrazide compound solution is 0.1-2%; Preferably, the application amount of the bis-hydrazide compound is 1%-3% of the mass of the wood chips; Preferably, the bis-hydrazide compound is a dicarboxylic acid dihydrazide, selected from one or more of succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, and pimelic acid dihydrazide, and the application amount of the bis-hydrazide compound solution is 1%-3% of the mass of the substrate.

9. The preparation method according to any one of claims 1-8, characterized in that, The treated substrate is formed. Preferably, the treated substrate is fed into a forming machine for forming within 0-20 minutes; Preferably, the forming temperature of the tray cushion block is 110-150 °C; Preferably, the forming pressure of the tray cushion block is 2-5 MPa; Preferably, the pushing time of the push rod of the tray cushion block forming machine is 25-60 s / time.

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