Method for improving anti-cracking performance of special recombinant material for independent liquid cargo tanks of LNG, LPG and LEG ships

Abstract

The invention provides a method for improving the anti-cracking performance of a special recombined material for independent liquid cargo tanks of LNG, LPG and LEG ships. The method comprises the steps that wood is rotationally cut into single plates with the thickness being 1.8-3.0 mm; the veneer is subjected to heat-moisture treatment, first drying, gum dipping and second drying; the second drying means that the moisture content of the impregnated veneer reaches 5-8%; after reinforcing materials are dispersed on the upper surfaces of the impregnated veneers, assembling, hot pressing and balancing are conducted; the reinforcing material is located between the adjacent impregnated veneers, and the reinforcing material comprises a fiber material with the average diameter of 5-8 microns and / or nano particles with the average particle size of 10-50 nm. By means of the method, the cracking rate of the interior or the glue layer of the special recombined material veneer can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of wood processing, and particularly to a method for improving the anti-cracking performance of special recombinant materials used in independent liquid cargo tanks of LNG, LPG, and LEG ships. Background Art

[0002] Liquefied natural gas (LNG), as a clean and efficient energy source, is widely used globally. In the design and construction of medium and small LNG ships and LNG-powered ships, high-performance special recombinant materials are widely used in the thermal insulation support structures of liquid cargo tanks due to their excellent mechanical properties, low thermal conductivity, and water resistance.

[0003] However, special recombinant materials used in LNG ships may face the risk of cracking during long-term use. This is because LNG ships operate in extremely low-temperature environments. For example, the temperature in the cargo tank is usually maintained at about -163°C, and wood will shrink in the cold. Under the action of frequent temperature fluctuations and mechanical loads, microcracks may appear in the recombinant materials, leading to more serious structural cracking. This not only affects the thermal insulation effect of the materials but also may endanger the structural integrity of the liquid cargo tank and the safety of the ship. Therefore, improving the anti-cracking performance of special recombinant materials used in LNG ships is particularly important for extending their service life and ensuring their stability and reliability under various environmental conditions.

[0004] In the research on preventing wood from cracking and deforming, it mainly focuses on how to inhibit the cracking of wood during the drying process, and there is little research on the anti-cracking of high-density special recombinant materials used in the ultra-low-temperature field. Summary of the Invention

[0005] The density of high-density special recombinant materials used in the ultra-low-temperature field is generally 1.30 g / cm 3 Above. As described above, due to the harsh use conditions of such products, especially the frequent ultra-low-temperature changes, they are prone to cracking. The present invention aims to solve at least to some extent the cracking problem of special recombinant materials in this specific application scenario. For this purpose, the present invention proposes a method for improving the anti-cracking performance of special recombinant materials used in independent liquid cargo tanks of LNG, LPG, and LEG ships. By combining raw materials, preparation processes, and structural designs, it can effectively reduce the cracking rate of special recombinant materials in this specific application scenario on the premise of meeting the performance requirements such as the density, thermal conductivity, and water resistance of special recombinant materials, and achieve the preparation of high-density special recombinant materials with a density of 1.30 - 1.36 g / cm 3 , a cracking rate lower than 3%, a thermal conductivity ≤ 0.32 W / (m·K), and a water absorption rate ≤ 0.5%.

[0006] In a first aspect, the present invention provides a method for improving the anti-cracking performance of a recombinant material, which is used for independent liquid cargo tanks of LNG ships, LPG ships or LEG ships, and includes: veneers are sliced from wood with a thickness of 1.8 - 3.0 mm; the veneers are subjected to hydrothermal treatment, first drying, impregnation with glue, and second drying to obtain impregnated veneers; the second drying is to make the moisture content of the impregnated veneers reach 5 - 8%; after the upper surface of the impregnated veneers is dispersed with reinforcing materials, the veneers are assembled into a blank, hot-pressed, and balanced; the reinforcing materials are located between adjacent impregnated veneers; the reinforcing materials include fiber materials with an average diameter of 5 - 8 μm and / or nanoparticles with an average particle size of 10 - 50 nm.

[0007] As described above, ultra-low temperature embrittles the recombinant material, making it more rigid and fragile, and reducing its plastic deformation ability, so that cracks are likely to form and rapidly expand in stress concentration areas. At the same time, there is a large temperature difference between the two ends of the recombinant material of the liquid cargo tank support, and there is thermal stress. The change in ambient temperature will also gradually accumulate the thermal stress inside the recombinant material. If the thermal stress exceeds the fracture strength of the resin, it may cause microcracks in the recombinant material. These microcracks are prone to expand under repeated loading and high and low temperature cycles, ultimately leading to obvious cracking phenomena. The inventor found that hydrothermal treatment can change the internal structure of the veneer and eliminate internal stress. However, hydrothermal treatment can only reduce cracks to a certain extent. The inventor further studied and found that due to the different thermal expansion coefficients of wood and resin, cracks are likely to appear at the glue layer. Therefore, the present invention designs the recombinant material with the above specific structure, especially adding reinforcing materials at the glue layer, which play a passivation role in the crack propagation process. Even if the crack passes through the glue layer, it will be blocked or dispersed at certain points, so as to prevent the crack from rapidly expanding.

[0008] Based on this structural design, the present invention provides the above specific method. Specifically: before impregnation with glue, the veneer is subjected to hydrothermal treatment to change its internal structure and reduce stress concentration. At the same time, the moisture content of the impregnated veneer and the structure of the reinforcing material are controlled. Combining with the subsequent hot-pressing process, it can not only ensure the above functions of the reinforcing material, but also avoid the decrease in bonding strength, thereby enhancing the overall toughness, improving the anti-cracking ability, reducing the cracking rate of the glue layer of the recombinant material, and improving the anti-cracking performance.

[0009] The thickness of the veneer of the present invention can be 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, 2.5 mm, 3 mm, 3.6 mm. The veneer with a suitable thickness is the basis for improving the anti-cracking ability of the recombinant material.

[0010] According to the method provided by the present invention, the hydrothermal treatment includes saturated steam treatment, the temperature of the saturated steam is 180 - 190 °C, the steam pressure is 0.6 - 0.8 MPa, and the treatment time is 15 - 30 min.

[0011] Within the parameter range disclosed in the present invention, performing the hydrothermal treatment can significantly improve the internal stress within the veneer, thereby reducing the cracking rate within the veneer. Specifically, the temperature can be 180°C, 185°C, and 190°C, the time can be 15 min, 25 min, 30 min, and the pressure is generally 0.6 - 0.8 MPa; those skilled in the art can also select a suitable hydrothermal treatment process based on the requirements on the basis of the content disclosed in the present invention.

[0012] According to the method provided by the present invention, the fiber material is selected from at least one of glass fiber, carbon fiber, and basalt fiber cloth.

[0013] According to the method provided by the present invention, the fiber material is a fiber cloth impregnated with resin. The resin is preferably one or a combination of two or more of epoxy resin, isocyanate, and phenolic resin.

[0014] According to the method provided by the present invention, the nanomaterial is selected from at least one of nano-silica and nano-aluminum oxide.

[0015] According to the method provided by the present invention, the nanoparticles are evenly sprayed on the upper surface by spraying, and the addition amount of the nanoparticles on the upper surface is 0.5 - 1.0 g / m 2 For example, the nanoparticles are dispersed in a solvent, such as ethanol, and then sprayed by spraying.

[0016] According to the method provided by the present invention, it further includes coating a protective coating on the surface of the special recombinant material that has undergone the equilibration treatment.

[0017] Preferably, the protective coating includes at least one selected from polyurethane coating, acrylic coating, tung oil, and waterproof paint. Polyurethane coating and acrylic coating can protect the surface and reduce cracking. Using tung oil and waterproof paint can seal the wood surface and prevent cracking caused by water infiltration and humidity change.

[0018] According to the method provided by the present invention, the wood is selected from at least one of birch, cedar, hemlock, beech, and southern pine. Among them, selecting high-quality wood as raw materials, such as birch, cedar, hemlock, beech, southern pine, etc., whose wood texture is delicate and can maintain stability in cold environments, is beneficial for the recombinant material to maintain stable performance in ultra-low temperature environments, reduce cracking, and extend the service life. Southern pine is selected from longleaf pine, shortleaf pine, slash pine, and loblolly pine.

[0019] According to the method provided by the present invention, the adhesive used for dipping contains one of epoxy resin, isocyanate, and phenolic resin.

[0020] Preferably, when impregnating with glue, the adhesive is formulated into an adhesive solution. The construction method can be to immerse the veneer after the first drying in the adhesive solution, or to spray the adhesive solution onto the veneer after the first drying, so that the adhesive in the adhesive solution adheres to and penetrates into the veneer after the first drying to a certain extent.

[0021] In the invention, for the veneer after heat and humidity treatment and the first drying, when impregnating with glue, the penetration effect of various types of adhesives mainly depends on the solid content of the adhesive solution.

[0022] When the adhesive is epoxy resin, preferably, the solid content of the adhesive solution is 30-70%. Among them, for specific epoxy resin adhesives, the present invention has no special restrictions. Generally, when the adhesive can be selected from epoxy resin E-44, etc., and epoxy resin adhesives commonly used for the wood selected in the present invention, the achieved technical effects are basically the same.

[0023] When the adhesive is isocyanate, preferably, the solid content of the adhesive solution is 40-70%. Among them, for specific isocyanate adhesives, the present invention has no special restrictions. Generally, when the adhesive can be selected from: Desmodur L 75 (Covestro), Wannate PM-200 (Wanhua Chemical), Bayhydur XP 2655 (Covestro) or Cythane 3160 (Cytec), etc., and isocyanate adhesives commonly used for the wood selected in the present invention, the achieved technical effects are basically the same.

[0024] When the adhesive is phenolic resin, preferably, the solid content of the adhesive solution is 35-45%. Among them, for specific phenolic resin adhesives, the present invention has no special restrictions. Generally, when the adhesive can be selected from: phenolic resin LSR-802 or water-based resole phenolic resin, etc., and phenolic resin adhesives commonly used for the wood selected in the present invention, the achieved technical effects are basically the same.

[0025] According to the method provided by the present invention, the sizing amount of the adhesive is 20-35%. The sizing amount in the present invention is mainly controlled by the solid content of the adhesive solution during impregnation. In actual application, it can be adjusted by controlling the impregnation time until the sizing amount of the adhesive meets the requirements of the present invention.

[0026] According to the method provided by the present invention, the first drying is to make the moisture content of the veneer ≤5%. The present invention controls the moisture content of the first drying and the second drying differently according to the different functions of the drying process. Specifically, in order to achieve a better impregnation effect, the first drying makes the moisture content of the veneer ≤5%, and in order to improve the hot pressing effect, it is necessary to control the second drying to make the moisture content of the impregnated veneer reach 5-8%.

[0027] According to the method provided by the present invention, the temperature of the hot pressing is 125 - 145 °C, the pressure is 8 - 15 MPa, and the hot pressing speed is 0.8 - 1.5 min / mm.

[0028] When assembling the blanks, orthogonal, parallel or any other angle can be adopted for blank assembly. After blank assembly, hot pressing is carried out. The temperature can be 125 °C, 130 °C, 135 °C, 140 °C and 145 °C, and the pressure can be 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa and 15 MPa. The hot pressing process can be any combination of temperature, pressure and speed. Those skilled in the art can also select a suitable hot pressing process according to requirements. Adopting the above hot pressing process is beneficial to improving the anti-cracking ability of the recombinant material.

[0029] According to the method provided by the present invention, the hot-pressed board is subjected to a balance treatment for 5 - 9 days. The present invention has no special restrictions on the conditions of the balance treatment, and it can be implemented under the conventional conditions of the present invention. For example, by carrying out a balance treatment for 5 days, 6 days, 7 days, 8 days and 9 days, the wood will gradually absorb or release moisture until the moisture content reaches a relatively stable state, thereby reducing cracking during later use.

[0030] In a second aspect, the present invention also provides a special recombinant material for an independent liquid cargo tank of an LNG ship, an LPG ship or an LEG ship, which is prepared by the method as described above; the density of the recombinant material is 1.30 - 1.36 g / cm 3 , the cracking rate is less than 3%, the thermal conductivity is ≤ 0.32 W / (m·K), and the water absorption rate is ≤ 0.5%.

[0031] Beneficial effects: By combining the wet-heat treatment and adding reinforcing materials at the adhesive layer, the present invention significantly improves the anti-cracking ability, especially effectively reduces the cracking inside the veneer of the recombinant material and at the adhesive layer; on this basis, the present invention further improves the anti-cracking ability through the selection of wood, the design of the veneer thickness, the selection of adhesives, the control of the moisture content of the board, and the optimization of the hot pressing process. Coating a protective coating on the surface of the hot-pressed board is also beneficial to further improving the anti-cracking performance of the recombinant material.

[0032] Through the above multi-faceted optimized design, the present invention can effectively reduce the cracking rate inside the veneer or at the adhesive layer of the special recombinant material used for LNG ships, LPG ships or LEG ships. Specific embodiments

[0033] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be described clearly and completely below. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts fall within the scope of protection of the present invention.

[0034] For those technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0035] The present invention will be described below with reference to specific embodiments. It should be noted that these embodiments are only descriptive and do not limit the present invention in any way.

[0036] Example 1 A method for improving the anti-cracking performance of a recombinant material, the recombinant material being used for the independent liquid cargo tank of an LNG ship, an LPG ship or an LEG ship, and the steps are as follows: (1) The wood is rotary cut into veneers with a thickness of 2 mm; the wood is selected from birch.

[0037] (2) The veneers in step (1) are treated with saturated steam. The temperature of the saturated steam is 185 °C, the steam pressure is 0.7 MPa, and the treatment time is 20 min. Then, the first drying is carried out to make the moisture content of the veneers reach 5%. Then, the veneers are impregnated with a phenolic resin solution with a solid content of 40% at normal temperature and pressure. The sizing amount of the adhesive is 30%. Then, the second drying is carried out to obtain impregnated veneers with a moisture content of 6%.

[0038] (3) A fiber material with an average fiber diameter of 6 μm (specifically, a fiberglass cloth impregnated with the same phenolic resin as in step (2)) is dispersed on the upper surface of the impregnated veneers in step (2). The addition amount is 0.7 g / m 2 , and then, the veneers are assembled. When assembling, the fiber material is located between adjacent impregnated veneers. Then, hot pressing is carried out under the conditions of a temperature of 130 °C, a pressure of 10 MPa, and a hot pressing speed of 1 min / mm. After the hot pressing is completed, it is balanced for 7 days, and a waterproof coating is applied to obtain the recombinant material.

[0039] Example 2 It is basically the same as Example 1, except that: the fiberglass cloth is replaced with a fiber material with an average fiber diameter of 5 μm (carbon fiber impregnated with phenolic resin) in equal mass Example 3 Basically the same as Example 1, except that: the fiberglass cloth is replaced with a fiber material (basalt fiber cloth impregnated with phenolic resin) having an average fiber diameter of 8 μm in equal mass. Example 4 Basically the same as Example 1, except that: the fiberglass cloth is replaced with nanoparticles (nano-silica) having an average particle size of 25 nm in equal mass. The nanoparticles are first dispersed in ethanol and then sprayed on the upper surface of the impregnated veneer.

[0040] Example 5 Basically the same as Example 4, except that: the nanoparticles are replaced with nanoparticles (nano-aluminum oxide) having an average particle size of 40 nm in equal mass. The nanoparticles are first dispersed in ethanol and then sprayed on the upper surface of the impregnated veneer.

[0041] Example 6 Basically the same as Example 4, except that: the phenolic resin solution with a solid content of 40% is replaced with an epoxy acid ester solution with a solid content of 50%. Accordingly, the adhesive in the fiber material is also replaced with the same epoxy acid ester in equal mass.

[0042] Example 7 Basically the same as Example 4, except that: "impregnating with a phenolic resin solution with a solid content of 40%" is replaced with spraying with an isocyanate solution with a solid content of 50%. Accordingly, the adhesive in the fiber material is also replaced with the same isocyanate in equal mass.

[0043] Example 8 Basically the same as Example 4, except that: birch etc. are replaced with cedar.

[0044] Example 9 Basically the same as Example 4, except that: birch etc. are replaced with hemlock.

[0045] Comparative Example 1 Basically the same as Example 1, except that: the saturated steam treatment is adjusted to the veneer being placed at room temperature for the same time as the saturated steam treatment.

[0046] Comparative Example 2 Basically the same as Example 1, except that: the fiberglass cloth is replaced with a fiberglass cloth having an average fiber diameter of 10 μm in equal mass.

[0047] Comparative Example 3 Basically the same as Example 4, except that: the nanoparticles are replaced with nanoparticles (nano-aluminum oxide) having an average particle size of 60 nm in equal mass.

[0048] For the properties of the recombinant materials obtained from the examples and comparative examples, the testing methods are as follows: Cracking rate: Visual inspection combined with image method. Among them, sample size: 300 mm × 300 mm or select a representative area according to the crack distribution; Environmental conditions: Immerse the sample in liquid nitrogen for 1 h, then take out the sample and thaw it at room temperature for 2 h, then immerse it in liquid nitrogen for 1 h again and then thaw it at room temperature for 2 h, and repeat this 10 cycles; Shooting conditions: Diffused natural light or standard light source (CRI>90), avoiding shadows; Cracking rate R The calculation formula of (%) is as follows: ; Among them, L c is the total crack length (mm), A is the sample observation area (mm2).

[0049] Water absorption rate: Refer to ISO 62:2008 Plastics Determination of water absorption.

[0050] The test results are as follows: Table 1

[0051] As can be seen from Table 1, the method of the present invention can prepare recombinant materials with a density maintained in the range of 1.30 - 1.36 g / cm³. Moreover, when the hydrothermal treatment is removed or the particle size / fiber diameter of the reinforcing material is used unreasonably, the cracking performance decreases significantly, and the comprehensive performance of the recombinant materials prepared by the method of the present invention is the best.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the cracking resistance of a recombinant material, wherein the recombinant material is used for an independent liquid cargo tank of an LNG ship, an LPG ship or a LEG ship, characterized in that: include: The wood is peeled into veneers with a thickness of 1.8~3.0mm; The veneer is subjected to wet heat treatment, first drying, dipping, and second drying to obtain a dipping veneer; the second drying is to make the moisture content of the dipping veneer reach 5-8%; After the reinforcing material is dispersed on the upper surface of the impregnated veneer, the veneer is assembled, hot pressed, and balanced; The reinforcing material is located between adjacent dipped veneers; The reinforcing material includes fiber material with an average diameter of 5-8 μm and / or nanoparticles with an average particle size of 10-50 nm.

2. The method according to claim 1, characterized in that: The wet heat treatment includes saturated steam treatment, the temperature of the saturated steam is 180-190° C., the steam pressure is 0.6-0.8 MPa, and the treatment time is 15-30 min.

3. The method according to claim 1 or 2, characterized in that: The fiber material is selected from at least one of glass fiber, carbon fiber and basalt fiber cloth; Preferably, the fiber material is fiber cloth impregnated with resin.

4. The method according to claim 1 or 2, characterized in that: The nanoparticles are selected from at least one of nano-silicon dioxide and nano-aluminum oxide; Preferably, the nanoparticles are uniformly sprayed on the upper surface by spraying, and the amount of nanoparticles added on the upper surface is 0.5-1.0 g / m 2 .

5. The method according to any one of claims 1 to 4, characterized in that: After said equilibration a protective coating is also applied.

6. The method according to claim 5, characterized in that: The wood is selected from at least one of birch, cedar, hemlock, beech and southern pine.

7. The method according to any one of claims 1 to 6, characterized in that: The adhesive used in the dipping is selected from one of epoxy resin, isocyanate and phenolic resin; Preferably, the amount of adhesive applied is 20-35%.

8. The method according to any one of claims 1 to 8, characterized in that: The first drying refers to making the moisture content of the veneer ≤5%; And / or, the hot pressing temperature is 125-145° C., the pressure is 8-15 MPa, and the hot pressing speed is 0.8-1.5 min / mm.

9. The method according to any one of claims 1 to 8, characterized in that: The equilibration time is 5 to 9 days.

10. A special recombinant material for an independent liquid cargo tank of an LNG ship, an LPG ship or a LEG ship, characterized in that: Prepared by the method according to any one of claims 1 to 9; the density of the recombinant material is 1.30 to 1.36 g / cm 3 , cracking rate is less than 3%, thermal conductivity ≤0.32W / (m·K), and water absorption ≤0.5%.

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