CN113858359A

CN113858359A - Preparation method of plastic-replacing biomass-based cold-chain logistics heat-insulation material

Info

Publication number: CN113858359A
Application number: CN202111230953.3A
Authority: CN
Inventors: 石岩; 孔维炜; 余广荣; 王攀登; 刘子畅
Original assignee: Tianjin University of Commerce
Current assignee: Tianjin University of Commerce
Priority date: 2021-10-22
Filing date: 2021-10-22
Publication date: 2021-12-31

Abstract

The invention discloses a preparation method of a plastic-replacing biomass-based cold-chain logistics heat-insulating material. The invention is carried out according to the following steps: (1) delignification of wood; (2) and (3) freeze drying: soaking the delignified board in the step (1) in water to remove residual solvent until the delignified board is neutral, and then freezing the board with full water at-20 ℃; (3) film covering: and (3) coating the waterproof fireproof environment-friendly adhesive film on the wood nano-fiber porous material obtained in the step (2), and heating in an oven at 100 ℃ for 4-6 minutes. The biomass-based heat-insulating material is a wood nanofiber porous material, so that the biomass-based heat-insulating material has the advantages of light weight, heat insulation and high specific strength, and has excellent buffering performance in the direction perpendicular to the wood nanofiber direction.

Description

Preparation method of plastic-replacing biomass-based cold-chain logistics heat-insulation material

Technical Field

The invention relates to the technical field of preparation and utilization of biomass-based functional materials, in particular to a preparation method for developing a plastic-substitute biomass-based cold-chain logistics heat-insulation material.

Background

In a modern society with highly developed convenience, cold-chain logistics transportation is faster and more efficient, and is closely related to the daily life of people. The foaming material with the functions of heat preservation, heat insulation and buffering perfectly matches with cold chain logistics, and fresh food is safely and quickly delivered to the home of people. The foaming material improves the heat insulation effect of the cold chain equipment, and further effectively reduces the loss rate of food in the conveying link. The large-scale long-distance transportation and storage equipment of the low-temperature products mainly comprises a refrigerator car and a refrigerator, is convenient to use and reliable in performance, but has high construction and transportation cost and large energy consumption; polyurethane foam (EPU) materials, polypropylene foam materials, and polystyrene (EPS) foam materials are currently in wide use in refrigerator-freezers, refrigerated display cases, refrigerated trailers, refrigerated containers, and refrigerated warehouses. More than 95% of all refrigerators or cold storage facilities around the world use polyurethane Foam (PU Foam) as a heat insulation material, and the polyurethane Foam material is a high molecular polymer which is prepared by mixing isocyanate and polyether serving as main raw materials through special equipment under the action of various auxiliary agents such as a foaming agent, a catalyst, a flame retardant and the like, and performing high-pressure spraying and on-site foaming. Has the functions of heat preservation and water prevention, and is the lowest heat conductivity coefficient in all the current organic heat-preservation materials. The polystyrene foaming material (EPS) is prepared by processes of prefoaming, curing, molding, drying, cutting and the like. It can be made into foamed material products with different densities and shapes, and has good heat-insulating, packaging and freezing effects in cold-chain logistics. But the toughness is not very good, the material is easy to crack, and the buffering performance is general. The properties of the polystyrene foam after being processed into a foam package are stable within the range of 0-70 degrees, and if the temperature is over 70 degrees, the polystyrene can generate harmful substances. Under the condition of low temperature, the polystyrene foaming box can not release toxic substances. In recent years, a fire in a refrigerator occurs, which not only causes economic loss but also causes a safety problem. Polyurethane foam and polystyrene foam are also one of the main causes of fire.

For short-distance storage and transportation of low-temperature products, a foam insulation can made of foam plastics such as foamed polyurethane or foamed polystyrene is often used as a main storage method. The low-temperature foam box is low in cost, flexible in transportation mode and convenient to deliver, and can be used for refrigerating and transporting various biological freezing reagents, tin paste, poultry drugs, medicines, blood plasma, vaccines, aquatic products, poultry, aquarium fishes and long-distance foreign trade fresh-keeping food by matching with ice bags. Is particularly suitable for the areas which are difficult to reach by vehicles. The novel packaging box which is put into use at present in cold chain transportation is provided with a composite thermal insulation paper box, a composite corrugated paper box, a polypropylene foam material (EPP) thermal insulation box and the like. The polypropylene foaming material is a high-crystallization type polymeric material with excellent performance, and is a novel environment-friendly compression-resistant buffering heat-insulating material which is the fastest growing at present. PP is used as a main raw material, and a physical foaming technology is adopted to prepare the foaming beads. The polypropylene foamed product has excellent shock resistance and energy absorption performance, high recovery rate after deformation, good heat resistance, chemical resistance, oil resistance and heat insulation, and is a necessary material in cold-chain logistics. In addition, the weight of the product is light, and the weight of the product can be greatly reduced. Has good toughness, difficult fracture and good buffer performance. Can be recycled and reused, and can not cause white pollution. The requirement of cold-chain logistics packaging in the future can be well met from the functional perspective and the environmental protection perspective. From the environmental protection perspective, the polypropylene foaming material box is expected to replace the insulation can made of polyurethane and polystyrene.

At present, the consumption of foam boxes in China is over a billion per year, but the recycling rate is less than 10%, which brings serious burden to the environment and causes great white pollution.

Disclosure of Invention

The invention aims to develop a plastic-substituted biomass-based cold-chain logistics heat-insulating material which is more environment-friendly, has better heat-insulating effect, is waterproof and anti-condensation and does not generate toxic gas during combustion and a preparation method thereof aiming at the environmental problems existing in the existing application materials.

The technical scheme adopted for realizing the purpose of the invention is as follows:

a preparation method of a plastic-substitute biomass-based cold-chain logistics heat-insulating material comprises the following steps:

(1) wood delignification:

cutting natural wood to a thickness of about 1cm, cutting to a width of about 1cm according to the actual required size, and adding acid sodium chlorite solution at a ratio of 1:15-1:25 (g/ml)Soaking in solid-to-liquid ratio for 2-3 days to make the solvent fully soak the board, and steaming at 100 deg.C for 6 hr to remove lignin macromolecules in natural log, and simultaneously, acid sodium chlorite releases ClO₂Bleaching the wood by gas; then, the mixture is cooked in 8 percent sodium hydroxide solution at the temperature of 80 ℃ for about 8 hours to further remove small molecules in hemicellulose and lignin;

(2) and (3) freeze drying:

soaking the delignified board in the step (1) in water to wash away residual solvent until the delignified board is neutral, freezing the fully hydrated board at-20 ℃ to rapidly cool the water-hydrated board, taking the ice crystals filled in pores as a template to retain the pore structure in the delignified wood, transferring the delignified wood to a freeze dryer after freezing, drying the delignified wood for more than 24 hours at-40 ℃ according to different sample sizes, completely subliming water in the sample, retaining a layered porous structure of the delignified board, and enabling the sample to have buffering performance and heat preservation performance;

or directly freeze-drying the delignified board containing 8% sodium hydroxide lye in the step (1) for more than 12 hours, recovering precipitated sodium hydroxide solid, soaking and washing the solid in water to be neutral, freeze-drying the solid, and drying the solid at the temperature of minus 40 ℃ for more than 24 hours;

(3) film covering:

coating the wood nano fiber porous material obtained in the step (2) with a waterproof fireproof environment-friendly adhesive film, heating in a drying oven at 100 ℃ for 4-6 minutes, carrying out hot melting on the adhesive film and coating the adhesive film on the surface of the delignified wood board, realizing the same-direction or cross bonding combination of delignified boards with different thicknesses and different shapes through the coating process, and sealing holes on the surface while coating to enable the material to be in a closed hole structure; the thermal conductivity of the resulting composite material was reduced from 0.08274W/mK for delignified wood to 0.01862W/mK.

The wood is selected from balsawood-balsawood, basswood or paulownia wood.

The environment-friendly adhesive film compounded on the two sides of the wood nano-fiber porous material is waterproof, the thickness (0.1 mm-0.3 mm) of the environment-friendly adhesive film is adjusted according to the use condition, and the number (1-3 layers) of layers bonded in the same direction or in a cross way is adjusted according to the strength and the heat preservation performance requirements of the material of the heat preservation box.

Compared with the existing materials, the invention has the beneficial effects that:

1. the biomass-based heat-insulating material is a wood nanofiber porous material, so that the biomass-based heat-insulating material has the advantages of light weight, heat insulation and high specific strength, and has excellent buffering performance in the direction perpendicular to the wood nanofiber direction. The thermal insulation effect can reach at least 10 ℃ of temperature difference due to better anisotropy, the strength is more than 30 times of that of foamed plastic, the foam plastic is more environment-friendly, the foam plastic is very attractive in actual thermal insulation application, and the actually measured thermal conductivity coefficient is smaller than that of air no matter the porous fiber materials are bonded in an anisotropic cross way or the porous fiber materials are bonded in the same direction, and is not less than that of EPS.

2. The biomass-based heat-insulating material disclosed by the invention can prevent water and dew after being coated with a layer of environment-friendly glue film with adjustable thickness on two sides, the coated environment-friendly glue film can resist the low temperature of-70 ℃, a chemical foaming agent is not used, and the death of human body by suffocation caused by toxic gas generated by combustion can be avoided by adhesion forming.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

Example 1

(1) Sawing the purchased natural Barsha wood plate to a thin cuboid of 5cm multiplied by 1cm by using an electric saw, and configuring 2% (w/w) NaClO₂200ml of the solution, 70ml of 2% (w/w) NaClO was added into a 500ml beaker according to a solid-to-liquid ratio of 1:25₂The solution was then adjusted to pH 4.6 by adding glacial acetic acid dropwise and then weighing 3.3 g of Barsha wood in NaClO₂Soaking in the solution for 48h, and sealing with preservative film to make the solvent fully soak the Barsha wood. Then cooking for 6h on a constant temperature oil bath pan at 100 ℃ for delignification.

(2) And (2) taking the wood blocks cooked in the step (1) out of the solution, washing the residual solvent on the surface by using deionized water, and then cooking the wood blocks in 8% (w/w) NaOH solution at 80 ℃ for 8h to further remove residual lignin.

(3) Soaking the delignified wood blocks in the step (2) in water to wash away residual sodium hydroxide solution until the delignified wood blocks are neutral, placing the wood blocks with full water on a culture dish, sealing the wood blocks by using a preservative film, then transferring the wood blocks to a freeze dryer for freezing at-20 ℃ for 24 hours, transferring the wood blocks to the freeze dryer after freezing, drying the wood blocks at-40 ℃ for more than 24 hours according to the size of a sample, completely subliming the water in the sample, and taking ice crystals frozen in pores of the delignified wood blocks as templates to keep a layered porous structure of the delignified wood so as to prepare the wood nanofiber porous material.

Or directly freeze-drying the delignified wood blocks containing 8% sodium hydroxide lye in the step (2) for more than 12 hours, recovering precipitated sodium hydroxide solid, soaking in water, washing to neutrality, and freeze-drying under the drying conditions as described in the previous paragraph.

(4) The glue film with the thickness of 0.1mm and the density of 0.98g/cm is placed on the surface of a freeze-dried delignified wood block and is heated in a drying oven at 100 ℃ for 4-6 minutes, the glue film is coated on the surface of delignified wood after hot melting, and the surface sealing is carried out during coating, so that the material has a closed-pore structure to block the exchange of air inside the wood and the outside, and the heat transfer is effectively reduced.

(5) The thermal conductivity of the prepared film-coated wood nanofiber-based thermal insulation material is measured by a transient plane heat source method by using a thermal conductivity meter (Hot Disk, 2500S, Sweden). The method comprises the steps of placing a planar heat source clamping piece of an instrument on two wood nanofiber materials which are coated with films on two sides and are in the same direction (parallel), adjusting the height to enable the clamping piece to be flat and fastened, respectively measuring the heat conductivity coefficient of the wood nanofiber materials coated with films on two sides under the environment temperature and humidity, testing each sample for 3 times, taking an average value, measuring the time for 20s, and heating power for 800 mW. The measured thermal conductivity of the insulation material is shown in table 1.

Example 2

(1) Sawing the purchased natural Barsha wood plate to a thin cuboid of 5cm multiplied by 1cm by using an electric saw, and configuring 2% (w/w) NaClO₂200ml of the solution, 70ml of 2% (w/w) NaClO was added into a 500ml beaker according to a solid-to-liquid ratio of 1:25₂The solution was then adjusted to pH 4.6 by adding glacial acetic acid dropwise and then weighing 3.3 g of Barsha wood in NaClO₂Soaking in the solution for 48h, sealing with preservative film to make solvent fully soak Barex sandAnd (7) log. Then cooking for 6h on a constant temperature oil bath pan at 100 ℃ for delignification.

(3) And (3) directly freeze-drying the delignified wood blocks containing 8% sodium hydroxide lye in the step (2) for more than 12 hours, recovering precipitated sodium hydroxide solid, soaking in water, washing to neutrality, freeze-drying, and drying at-40 ℃ for more than 24 hours to completely sublimate water in the sample.

(5) The thermal conductivity of the prepared film-coated wood nanofiber-based thermal insulation material is measured by a transient plane heat source method by using a thermal conductivity meter (Hot Disk, 2500S, Sweden). Placing a planar heat source clamping piece of the instrument on a wood nanofiber material with films coated on two surfaces in different directions (intersecting), adjusting the height to enable the clamping piece to be flat and fastened, respectively measuring the heat conductivity coefficient of the wood nanofiber material with films coated on two surfaces under the ambient temperature and humidity, testing each sample for 3 times, taking an average value, measuring the time for 20s, and heating power for 800 mW. The measured thermal conductivity of the insulation material is shown in table 1.

Table 1 comparison of thermal Properties of Biomass-based insulation materials with conventional materials

	Thermal conductivity (W/m. K)	Thermal diffusivity (mm)²/s）	Specific heat (MJ/M)³K）	Depth of investigation (mm)
					Double-faced film-coated Barsha wood nanofiber material placed in parallel along fiber direction	0.01885	0.02028	0.9296	1.26
Double-faced film-coated Barsha wood nanofiber material arranged in fiber direction in crossed mode	0.023	0.03644	0.6531	1.69
					Tilia wood nanofiber material with double-sided coated films placed in parallel along fiber direction	0.02009	0.02215	0.5326	2.04
Tilia wood nanofiber material with two-sided coated films arranged in fiber direction in crossed mode	0.02384	0.03872	0.4063	1.45
					Paulownia wood nanofiber material with double-faced film-covered and placed in parallel along fiber direction	0.02261	0.04174	0.5098	1.58
Paulownia wood nanofiber material with double-faced film covering and arranged in fiber direction in crossed mode	0.02397	0.04938	0.4199	1.58
					Air (a)	0.01~0.04	/	/	/
Expanded Polystyrene (EPS)	0.041	/	/	/
					Foamed polyurethane (EPU)	0.024	/	/	/
Foamed polyethylene (EPE)	0.0329~0.036	/	/	/

Example 3

The experimental procedure was the same as in example 1 except that the test wood species were basswood having a thickness of about 1 cm. The thermal conductivity of the prepared thermal insulation material is shown in table 1.

Example 4

The experimental procedure was the same as in example 1, except that the test wood species were paulownia wood 1cm thick, and 2.5% (w/w) NaClO was disposed in the delignification treatment conditions₂And (3) solution. The thermal conductivity of the prepared thermal insulation material is shown in table 1.

The invention provides a plastic-replacing biomass-based cold-chain logistics heat-insulating material and a preparation method thereof. Materials with a low thermal conductivity are often referred to as insulating materials. Thermal conductivity of less than or equal to 0.2W/(mK) is generally referred to as thermal insulation. The national standard of China stipulates that materials with the thermal conductivity coefficient not more than 0.12W/(mK) when the average temperature is not higher than 350 ℃ are called thermal insulation materials, and materials with the thermal conductivity coefficient below 0.05W/(mK) are called high-efficiency thermal insulation materials. From the currently developed materials (see table 1), the thermal conductivity of the lightweight wood-based thermal insulation material prepared by placing the fibers in the same direction or in different directions is smaller than that of Expanded Polystyrene (EPS), Expanded Polyurethane (EPU) and Expanded Polyethylene (EPE), and is close to the lowest value of the air thermal conductivity. The light wood-based heat-insulating material developed at present can be completely used for plastic-replacing heat-insulating materials.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a plastic-substitute biomass-based cold-chain logistics heat-insulating material is characterized by comprising the following steps:

(1) wood delignification:

cutting natural wood to a thickness of about 1cm, cutting according to the actual required size, soaking in acidic sodium chlorite solution at a solid-to-liquid ratio of 1:15-1:25 (g/ml) for 2-3 days to make the solvent fully soak the wood, and cooking at 100 deg.C for 6 hr to remove lignin macromolecules in natural log, wherein the acidic sodium chlorite releases ClO₂Bleaching the wood by gas; then, the mixture is cooked in 8 percent sodium hydroxide solution at the temperature of 80 ℃ for about 8 hours to further remove small molecules in hemicellulose and lignin;

(2) and (3) freeze drying:

film covering:

2. The method for preparing the plastic-substitute biomass-based cold-chain logistics insulation material as claimed in claim 1, wherein the wood is selected from balsa wood, basswood or paulownia wood.

3. The preparation method of the plastic-replacing biomass-based cold-chain logistics heat-insulating material as claimed in claim 1, wherein the environment-friendly glue film compounded on the two sides of the wood nanofiber porous material is waterproof, and the thickness of the environment-friendly glue film is adjusted according to the use conditions: 0.1mm-0.3mm, adjusting the number of layers of homodromous or cross bonding according to the requirements of the strength and the heat preservation performance of the heat preservation box material: 1-3 layers.