Low temperature resistant birch plywood for cryogenic liquid storage cabin and preparation method thereof

Abstract

The invention relates to the technical field of plywood, and discloses a low-temperature resistant birch plywood for a cryogenic liquid storage cabin and a preparation method thereof. The invention comprises the following steps: S1: adding epoxidized hydroxy-terminated polybutadiene, dibutyltin dilaurate and composite isocyanate to ethyl acetate in sequence, stirring evenly, heating to 50-55°C for reaction for 3-4h, adding E51 epoxy resin, heating to 80-85°C for reaction for 3-3.5h, and evacuating at 80-85°C until there are no bubbles to obtain a polyurethane modified epoxy resin; S2: adding a polyurethane modified epoxy resin, an alicyclic epoxy resin, octa(epoxycyclohexyl)POSS, diethylene glycol glycidyl ether and a curing agent to obtain an epoxy resin composite adhesive; cutting, pretreating, drying, gluing, aging, assembling, hot pressing, aging and cutting birch veneer raw materials to obtain the low-temperature resistant birch plywood.

Description

Technical Field

[0001] The invention relates to the technical field of plywood, in particular to a low-temperature resistant birch plywood for a cryogenic liquid storage cabin and a preparation method thereof. Background Art

[0002] Birch plywood is a product with relatively mature technology. Finland has developed a birch plywood for building insulation boxes for liquefied natural gas carriers. Birch in Northeast my country grows in the cold temperate zone and its cold resistance is better than that of tree species in other latitudes.

[0003] As an efficient and clean energy source, natural gas will liquefy when the temperature drops to -162℃, and its volume will be reduced to 1 / 600 of its original size, making it more suitable for transportation. The transportation of liquefied natural gas has strict requirements on ships, and the key technology lies in designing insulating boxes that can safely store liquefied natural gas below -162℃.

[0004] The surface of the insulation box that directly contacts the liquefied natural gas is made of low-temperature resistant alloy material, while its main insulation layer is composed of a birch plywood box. This box needs to have sufficient strength and appropriate weight to accommodate insulation materials such as perlite and withstand the pressure of liquefied natural gas. During the entire transportation process, the box must be kept at -162°C when fully loaded, and the temperature must return to normal temperature when empty.

[0005] Therefore, it is of great significance to invent a low-temperature resistant birch plywood to meet the requirements of birch plywood in terms of strength, stiffness, anti-attenuation performance, and anti-deformation ability under large temperature difference conditions. Summary of the invention

[0006] The object of the present invention is to provide a low-temperature resistant birch plywood for a cryogenic liquid storage cabin and a preparation method thereof, so as to solve the problems raised in the above-mentioned background technology.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A method for preparing low-temperature resistant birch plywood for a cryogenic liquid storage cabin comprises the following steps:

[0009] S1: Add epoxidized hydroxy-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate to ethyl acetate in sequence, stir evenly, heat to 50-55°C for reaction for 3-4h, add E51 epoxy resin, heat to 80-85°C for reaction for 3-3.5h, and evacuate at 80-85°C until there are no bubbles to obtain polyurethane-modified epoxy resin;

[0010] S2: polyurethane modified epoxy resin, alicyclic epoxy resin, octa(epoxycyclohexyl) POSS, diethylene glycol glycidyl ether and curing agent are mixed to obtain epoxy resin composite adhesive; birch veneer raw materials are cut, pretreated, dried, glued, aged, assembled, hot pressed, aged and cut to obtain low-temperature resistant birch plywood.

[0011] Furthermore, the low-temperature resistant birch plywood has a 7- or 9-layer structure, and the thickness of the veneer is 1.5-1.55 mm; the amount of veneer glue applied during the gluing process is 1.18-1.21 kg / m 2 During the hot pressing process, the hot pressing temperature is 140-150°C, the hot pressing time is 0.9-1.0min / mm, and the hot pressing pressure is 1.2-1.4MPa.

[0012] Furthermore, the proportions of the components in the epoxy resin composite adhesive, by mass, are 40-60 parts of polyurethane-modified epoxy resin, 10-20 parts of alicyclic epoxy resin, 4-10 parts of octa(epoxycyclohexyl)POSS, 20-40 parts of diethylene glycol glycidyl ether, and 30-50 parts of curing agent.

[0013] Furthermore, the curing agent comprises polyamide and polyetheramine, wherein the mass ratio of polyamide:polyetheramine is (9-9.5):(0.5-1).

[0014] Furthermore, in the polyurethane-modified epoxy resin, the mass ratio of E51 epoxy resin to epoxidized hydroxyl-terminated polybutadiene is 100:(5-10); and the molar ratio of epoxidized hydroxyl-terminated polybutadiene to composite isocyanate is 1:2.

[0015] Furthermore, the composite isocyanate includes diisocyanate POSS and 2,4-toluene diisocyanate, wherein the mass ratio of diisocyanate POSS to 2,4-toluene diisocyanate is (7-9):(1-3).

[0016] Further, the preparation method of the diisocyanate-based POSS comprises the following steps:

[0017] Step (1): adding methyltrimethoxysilane, sodium hydroxide and deionized water to isopropanol, stirring evenly, heating to 95-98°C for reflux reaction for 4-5h, cooling to room temperature for stirring reaction for 15-16h, filtering, washing, and vacuum drying at 45-50°C to obtain a siloxane sodium salt intermediate;

[0018] Step (2): adding the siloxane sodium salt intermediate to tetrahydrofuran, stirring evenly, adding triethylamine under a nitrogen atmosphere, adding methylvinyldichlorosilane under ice bath conditions, keeping the temperature for 4-5 hours, heating to room temperature and stirring for 20-22 hours, rotary evaporation, column chromatography purification, and vacuum drying at 45-50° C. to obtain divinyl POSS;

[0019] Step (3): adding divinyl POSS to tetrahydrofuran, adding 2-tert-butoxycarbonylaminoethanethiol and 2,2-dihydroxymethylacrylic acid, stirring under ultraviolet light for reaction for 10-15 minutes; rotary evaporation, column chromatography purification, and vacuum drying at 45-50° C. to obtain di(2-tert-butoxycarbonylamino)POSS;

[0020] Step (4): adding di(2-tert-butyloxycarbonylamino)POSS to a mixed solvent prepared by dichloromethane and trifluoroacetic acid, stirring at room temperature for 2-2.5 hours, and rotary evaporating; adding the product to dichloromethane, adding a sodium hydroxide aqueous solution as washing liquid, rotary evaporating, and vacuum drying at 45-50° C. to obtain diaminoPOSS;

[0021] Step (5): adding diamino POSS to an inert solvent, stirring evenly, preheating to 60-80° C., adding the diamino POSS solution to the triphosgene solution under a nitrogen atmosphere, heating to 80-100° C., pressurizing to 0.1-0.27 MPa, reacting for 0.5-4.5 h, rotary evaporation, filtering, and drying to obtain diisocyanate POSS;

[0022] Furthermore, in step (1), the molar ratio of methyltrimethoxysilane: sodium hydroxide: deionized water is (6-12): (0.04-0.08): (0.07-0.14);

[0023] Furthermore, in the step (2), the molar ratio of the siloxane sodium salt intermediate: triethylamine: methylvinyldichlorosilane is 1:3:3;

[0024] Further, in the step (3), the molar ratio of divinyl POSS:2-tert-butyloxycarbonylaminoethanethiol is (0.85-1):(4-5.4);

[0025] Furthermore, in step (4), the volume ratio of dichloromethane:trifluoroacetic acid is 1:1, and the concentration of the sodium hydroxide aqueous solution is 1.1.2 mol / L.

[0026] Further, in the step (5), the molar ratio of diaminoPOSS:triphosgene is (1.5-3.6):3;

[0027] Furthermore, the inert solvent includes any one of tetrahydrofuran and dichloromethane.

[0028] Furthermore, the pretreatment step includes using a stabilizer WDJ to perform a stabilizer treatment on the birch veneer.

[0029] Furthermore, the odd-numbered layers of the low-temperature resistant birch plywood are veneers with transverse textures, and the even-numbered layers of the veneers are veneers with longitudinal textures.

[0030] Furthermore, when the low-temperature resistant birch plywood has 7 layers, the total thickness of the plywood is 9 mm; when the low-temperature resistant birch plywood has 9 layers, the total thickness of the plywood is 12 mm.

[0031] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0032] The present invention selects a polyurethane modified resin having both a soft segment structure of a linear carbon chain and a hard segment structure of a rigid benzene ring as a matrix resin, utilizes the advantages of high segment strength, good toughness and high adhesive strength, controls the addition amount of diethylene glycol glycerol ether (the characteristics of aliphatic ether chain structure, high molecular chain flexibility and low chain strength) and alicyclic epoxy resin (the characteristics between the flexibility and chain strength of polyurethane modified resin and diethylene glycol glycerol ether), adjusts the segment length of two cross-linking points in the adhesive system and the flexible segment composition in the cross-linking network, so that the adhesive has excellent mechanical properties and bonding properties both at room temperature and in a low-temperature environment of liquefied natural gas, and gives the plywood excellent low-temperature resistance.

[0033] The invention uses homemade POSS containing a diisocyanate structure and epoxidized hydroxyl-terminated polybutadiene as raw materials to prepare modified polyurethane, reacts with E51 epoxy resin to prepare polyurethane-modified epoxy resin, and additionally introduces octa(epoxycyclohexyl)POSS into an adhesive as a reinforcing filler, and the purposes are: 1. the POSS structure introduced into the polyurethane segment can help the octa(epoxycyclohexyl)POSS introduced later to be uniformly dispersed in the adhesive, thereby improving its dispersibility, and avoiding the occurrence of agglomeration effect while increasing the proportion of POSS; 2. utilizing the octa(epoxycyclohexyl)POSS to react with hydroxyl groups and amino groups in the system; ③ Taking advantage of the good flexibility, bond barrier and small internal rotation steric hindrance of the -Si-O-Si- molecular chain in the POSS molecular structure, the activity of the resin molecular chain in the system is improved, and the flexibility of the cross-linked network is improved; ④ Taking advantage of the characteristics of the hollow inorganic nanocage structure of POSS, when subjected to deformation force, it can reduce the stress concentration of the system resin and hinder the crack propagation; at the same time, it can reduce the thermal stress generated inside the resin, deflect the crack, consume a lot of fracture energy, and make the adhesive have excellent mechanical properties regardless of room temperature or low temperature environment.

[0034] The present invention selects polyamide (polar groups such as -CONH in the polyamide structure provide strong hydrogen bonding and fatty chain segments, and have better mechanical strength and low-temperature toughness) and polyetheramine (polyetheramine can improve the wettability of the adhesive to the interface and improve its shear strength) as mixed curing agents, and increases the flexibility of the cross-linked network in a two-component curing agent manner by controlling the amine hydrogen equivalent of the polyamide and the ratio between the polyamide and the polyetheramine, and adjusts the cross-linking density through phase separation caused by the curing reaction, thereby improving the problems of increased low-temperature brittleness of the adhesive, failure of the bonding layer structure, and long-term high-load creep deformation, so that the prepared plywood has excellent low-temperature resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 This is a 7-layer structure diagram of the low-temperature resistant birch plywood of the present invention;

[0037] Figure 2 It is a nine-layer structure diagram of the low-temperature resistant birch plywood of the present invention. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0039] In the following examples, birch veneer specifications: density 0.61-0.63 g / cm 3 , the moisture content is 8-10%; epoxidized hydroxyl-terminated polybutadiene was purchased from Shandong Jiaying Chemical Technology Co., Ltd.; E51 epoxy resin was purchased from Nantong Xingchen Synthetic Materials Co., Ltd.; the alicyclic epoxy resin model is Syna Epoxy S-28, purchased from Nantong Synasia New Materials Co., Ltd.; octa(epoxycyclohexyl) POSS was purchased from Xi'an Qiyue Biology; polyamide specifications: amine value 340-370 / mgKOH / g, amine hydrogen equivalent 130, purchased from Huntsman Advanced Chemical Materials (Guangdong) Co., Ltd.; polyetheramine model is HUNTSMAN D2000 was purchased from Huntsman; the other raw materials were commercially available.

[0040] Example 1: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S1: 6 mol of methyltrimethoxysilane, 0.04 mol of sodium hydroxide, and 0.07 mol of deionized water are added to isopropanol, stirred evenly, heated to 95°C for reflux reaction for 4 hours, cooled to room temperature for stirring reaction for 15 hours, filtered, washed, and vacuum dried at 45°C to obtain a siloxane sodium salt intermediate;

[0041] S2: Add 1 mol of siloxane sodium salt intermediate to tetrahydrofuran, stir evenly, add 3 mol of triethylamine under nitrogen atmosphere, add 3 mol of methylvinyldichlorosilane under ice bath condition, keep warm for 4 hours, heat to room temperature and stir for 20 hours, evaporating, purifying by column chromatography, and drying in vacuum at 45°C to obtain divinyl POSS;

[0042] S3: 0.85 mol of divinyl POSS was added to tetrahydrofuran, 4 mol of 2-tert-butoxycarbonylaminoethanethiol and 0.2 mol of 2,2-dihydroxymethylacrylic acid were added, and the mixture was stirred under ultraviolet light for 10 min; the mixture was subjected to rotary evaporation, purified by column chromatography, and dried under vacuum at 45° C. to obtain di(2-tert-butoxycarbonylamino)POSS;

[0043] S4: adding di(2-tert-butyloxycarbonylamino)POSS to a mixed solvent of dichloromethane and trifluoroacetic acid in a volume ratio of 1:1, stirring at room temperature for 2 hours, and rotary evaporating; adding the product to dichloromethane, adding a 1 mol / L sodium hydroxide aqueous solution as washing liquid, rotary evaporating, and vacuum drying at 45°C to obtain diaminoPOSS;

[0044] S5: Add 3.6 mol of diamino POSS to an inert solvent, stir evenly, preheat to 60°C, add the diamino POSS solution to a triphosgene solution containing 3 mol of triphosgene under a nitrogen atmosphere, heat to 100°C, pressurize to 0.27 MPa, react for 0.5 h, rotary evaporate, filter, and dry to obtain diisocyanate POSS;

[0045] S6: 5g of epoxidized hydroxy-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate were added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin was added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there were no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxy-terminated polybutadiene: composite isocyanate was 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate was 7:3;

[0046] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 4g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of curing agent are mixed to obtain an epoxy resin composite adhesive; the birch veneer raw material is cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; the mass ratio of polyamide:polyetheramine in the curing agent is 9.5:0.5.

[0047] Example 2: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S6: 10g of epoxidized hydroxyl-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate are added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin is added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there are no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxyl-terminated polybutadiene: composite isocyanate is 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate is 7:3;

[0048] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 4g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of curing agent are mixed to obtain an epoxy resin composite adhesive; the birch veneer raw material is cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; the mass ratio of polyamide:polyetheramine in the curing agent is 9.5:0.5.

[0049] The remaining steps are the same as those in Example 1.

[0050] Example 3: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S6: 10g of epoxidized hydroxyl-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate are added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin is added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there are no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxyl-terminated polybutadiene: composite isocyanate is 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate is 9:1;

[0051] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 4g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of curing agent are mixed to obtain an epoxy resin composite adhesive; the birch veneer raw material is cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; the mass ratio of polyamide:polyetheramine in the curing agent is 9.5:0.5.

[0052] The remaining steps are the same as those in Example 1.

[0053] Example 4: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S6: 10g of epoxidized hydroxyl-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate are added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin is added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there are no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxyl-terminated polybutadiene: composite isocyanate is 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate is 9:1;

[0054] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 10g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of curing agent are mixed to obtain an epoxy resin composite adhesive; the birch veneer raw material is cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; the mass ratio of polyamide:polyetheramine in the curing agent is 9.5:0.5.

[0055] The remaining steps are the same as those in Example 1.

[0056] Example 5: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S6: 10g of epoxidized hydroxyl-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate are added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin is added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there are no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxyl-terminated polybutadiene: composite isocyanate is 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate is 9:1;

[0057] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 10g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of curing agent are mixed to obtain epoxy resin composite adhesive; birch veneer raw materials are cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; the mass ratio of polyamide:polyetheramine in the curing agent is 9:1.

[0058] The remaining steps are the same as those in Example 1.

[0059] Comparative Example 1: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S6: 20g of epoxidized hydroxyl-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate are added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin is added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there are no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxyl-terminated polybutadiene: composite isocyanate is 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate is 7:3;

[0060] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 4g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of curing agent are mixed to obtain an epoxy resin composite adhesive; the birch veneer raw material is cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; the mass ratio of polyamide:polyetheramine in the curing agent is 9.5:0.5.

[0061] The remaining steps are the same as those in Example 1.

[0062] Comparative Example 2: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S6: 5g of epoxidized hydroxyl-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate are added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin is added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there are no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxyl-terminated polybutadiene: composite isocyanate is 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate is 7:3;

[0063] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 12g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of curing agent are mixed to obtain epoxy resin composite adhesive; birch veneer raw materials are cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; the mass ratio of polyamide:polyetheramine in the curing agent is 9.5:0.5.

[0064] The remaining steps are the same as those in Example 1.

[0065] Comparative Example 3: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S6: 5g of epoxidized hydroxyl-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate are added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin is added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there are no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxyl-terminated polybutadiene: composite isocyanate is 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate is 7:3;

[0066] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 4g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of curing agent are mixed to obtain an epoxy resin composite adhesive; the birch veneer raw material is cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; the mass ratio of polyamide:polyetheramine in the curing agent is 8.5:1.5.

[0067] The remaining steps are the same as those in Example 1.

[0068] Comparative Example 4: A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage cabins: S6: 5g of epoxidized hydroxyl-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate are added to ethyl acetate in sequence, stirred evenly, heated to 50°C for reaction for 3h, 100g of E51 epoxy resin is added, heated to 80°C for reaction for 3h, and vacuumed at 80°C until there are no bubbles to obtain a polyurethane modified epoxy resin; the molar ratio of epoxidized hydroxyl-terminated polybutadiene: composite isocyanate is 1:2; in the composite isocyanate, the mass ratio of diisocyanate-based POSS: 2,4-toluene diisocyanate is 7:3;

[0069] S7: 60g of polyurethane modified epoxy resin, 20g of alicyclic epoxy resin, 4g of octa(epoxycyclohexyl) POSS, 40g of diethylene glycol glycidyl ether, and 50g of 4,4'-diaminodiphenylmethane are mixed to obtain an epoxy resin composite adhesive; birch veneer raw materials are cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood.

[0070] The remaining steps are the same as those in Example 1.

[0071] Experiment: The longitudinal bending elastic modulus and bending strength of plywood were tested according to standard EN310;

[0072] 10 plywood samples were tested in an environment of 20°C and 55% humidity, and another 10 plywood samples were placed in a liquid nitrogen storage container, injected with liquefied natural gas and immersed for 48 hours, then taken out and placed normally for 2 hours before testing, and the average value of the test was taken.

[0073] Test the shear strength of plywood according to standard EN314;

[0074] Thermal shock test was performed by immersing 10 plywood specimens in liquid nitrogen at -196°C for 1 hour and returning them to room temperature;

[0075] Soak 10 plywood samples in boiling water for 4 hours, take them out and place them in a 60℃ oven to dry for 20 hours, boil them again within four hours, cool the water to room temperature, and test them immediately in the wet state;

[0076] Low temperature resistant birch plywood has a 7-layer structure, and the veneer thickness is 1.5mm; the veneer glue application during the gluing process is 1.18kg / m 2 During the hot pressing process, the hot pressing temperature was 140°C, the hot pressing time was 0.9 min / mm, and the hot pressing pressure was 1.2 MPa.

[0077] Table 1 Low temperature resistant birch plywood performance test data

[0078]

[0079] Conclusion: The low-temperature resistant birch plywood prepared by the present invention has excellent low-temperature resistance.

[0080] In the process of preparing the polyurethane-modified epoxy resin in Comparative Example 1, excessive epoxidized hydroxy-terminated polybutadiene was added, which caused the loss of internal strength of the colloid and easily aggregated in the matrix to form macroscopic phase separation, resulting in reduced mechanical properties of the plywood.

[0081] In Comparative Example 2, excessive octa(epoxycyclohexyl)POSS was added, which caused the agglomeration effect of POSS in the matrix, resulting in reduced mechanical properties of the plywood.

[0082] In Comparative Example 3, the proportion of polyetheramine in the curing agent is too high, resulting in a decrease in the cross-linking density of the system and a decrease in the mechanical properties of the plywood.

[0083] In Comparative Example 4, 4,4'-diaminodiphenylmethane is used as a curing agent, which cannot provide excellent mechanical strength and low-temperature toughness, resulting in reduced mechanical properties of the plywood.

[0084] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing low-temperature resistant birch plywood for cryogenic liquid storage tanks, characterized in that: The following steps are involved: S1: Add epoxidized hydroxy-terminated polybutadiene, dibutyltin dilaurate, and composite isocyanate to ethyl acetate in sequence, stir evenly, heat to 50-55°C for reaction for 3-4h, add E51 epoxy resin, heat to 80-85°C for reaction for 3-3.5h, and evacuate at 80-85°C until there are no bubbles to obtain polyurethane-modified epoxy resin; S2: polyurethane modified epoxy resin, alicyclic epoxy resin, octa(epoxycyclohexyl) POSS, diethylene glycol glycidyl ether, and curing agent are mixed to obtain epoxy resin composite adhesive; birch veneer raw materials are cut, pretreated, dried, glued, aged, assembled, hot pressed, aged, and cut to obtain low-temperature resistant birch plywood; The proportion of each component in the epoxy resin composite adhesive, by weight, is 40-60 parts of polyurethane modified epoxy resin, 10-20 parts of alicyclic epoxy resin, 4-10 parts of octa(epoxycyclohexyl) POSS, 20-40 parts of diethylene glycol glycidyl ether, and 30-50 parts of curing agent; The curing agent comprises polyamide and polyetheramine, wherein the mass ratio of polyamide to polyetheramine is (9-9.5):(0.5-1); The mass ratio of E51 epoxy resin to epoxidized hydroxyl-terminated polybutadiene in the polyurethane-modified epoxy resin is 100:(5-10); the molar ratio of epoxidized hydroxyl-terminated polybutadiene to composite isocyanate is 1:2; The composite isocyanate comprises diisocyanate-based POSS and 2,4-toluene diisocyanate, wherein the mass ratio of diisocyanate-based POSS to 2,4-toluene diisocyanate is (7-9):(1-3); The preparation method of the diisocyanate-based POSS comprises the following steps: Step (1): add methyltrimethoxysilane, sodium hydroxide and deionized water to isopropanol, stir evenly, heat to 95-98°C for reflux reaction for 4-5h, cool to room temperature for stirring reaction for 15-16h, filter, wash, and vacuum dry at 45-50°C to obtain a siloxane sodium salt intermediate; Step (2): Add the siloxane sodium salt intermediate to tetrahydrofuran, stir evenly, add triethylamine under nitrogen atmosphere, add methylvinyldichlorosilane under ice bath condition, keep warm for 4-5h, heat to room temperature and stir for 20-22h, evaporating by rotary evaporation, purifying by column chromatography, and drying under vacuum at 45-50°C to obtain divinyl POSS; Step (3): adding divinyl POSS to tetrahydrofuran, adding 2-tert-butoxycarbonylaminoethanethiol and 2,2-dihydroxymethylacrylic acid, stirring under ultraviolet light for reaction for 10-15 minutes; rotary evaporation, column chromatography purification, and vacuum drying at 45-50° C. to obtain di(2-tert-butoxycarbonylamino)POSS; Step (4): adding di(2-tert-butyloxycarbonylamino)POSS to a mixed solvent prepared by mixing dichloromethane and trifluoroacetic acid, stirring at room temperature for 2-2.5 hours, and performing rotary evaporation; adding the product to dichloromethane, adding a sodium hydroxide aqueous solution as washing liquid, rotary evaporation, and vacuum drying at 45-50° C. to obtain diaminoPOSS; Step (5): Add diamino POSS to an inert solvent, stir evenly, preheat to 60-80° C., add the diamino POSS solution to the triphosgene solution under a nitrogen atmosphere, heat to 80-100° C., pressurize to 0.1-0.27 MPa, react for 0.5-4.5 h, rotary evaporate, filter, and dry to obtain diisocyanate POSS.

2. The method for preparing low-temperature resistant birch plywood for a cryogenic liquid storage tank according to claim 1, characterized in that: The low-temperature resistant birch plywood has a 7- or 9-layer structure, and the veneer thickness is 1.5-1.55 mm; the veneer glue application amount during the gluing process is 1.18-1.21 kg / m2; the hot pressing temperature during the hot pressing process is 140-150°C, the hot pressing time is 0.9-1.0 min / mm, and the hot pressing pressure is 1.2-1.4 MPa.

3. The method for preparing low temperature resistant birch plywood for cryogenic liquid storage tank according to claim 1, characterized in that: In the step (1), the molar ratio of methyltrimethoxysilane: sodium hydroxide: deionized water is (6-12): (0.04-0.08): (0.07-0.14); in the step (2), the molar ratio of siloxane sodium salt intermediate: triethylamine: methylvinyldichlorosilane is 1:3:3; in the step (3), the molar ratio of divinyl POSS: 2-tert-butyloxycarbonylaminoethanethiol is (0.85-1): (4-5.4); in the step (4), the volume ratio of dichloromethane: trifluoroacetic acid is 1:1, and the concentration of the sodium hydroxide aqueous solution is 1.1.2 mol / L.

4. The method for preparing low temperature resistant birch plywood for cryogenic liquid storage tank according to claim 1, characterized in that: In the step (5), the molar ratio of diaminoPOSS:triphosgene is (1.5-3.6):

3.

5. The low-temperature resistant birch plywood prepared according to the method for preparing low-temperature resistant birch plywood for a cryogenic liquid storage cabin according to any one of claims 1 to 4.

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