A high-barrier pulp molded packaging material, its preparation method and application

Abstract

This invention discloses a high-barrier molded pulp packaging material, its preparation method, and its application, belonging to the technical field of molded pulp packaging materials. This invention utilizes the advantages of different fibers by compounding plant fibers (bamboo pulp fiber (BF) and sorghum straw fiber (SF)) with aramid fibers; then, by spraying PVA emulsion, it imparts superior oxygen barrier properties to the molded pulp; by coating the surface with a PBAT film, which has excellent biodegradability and improves the waterproof and oil-proof properties of the molded pulp products; in addition, aramid fibers also have excellent barrier properties. The molded pulp products prepared by this invention have superior mechanical and barrier properties, and can be used for packaging fresh produce and fruits and vegetables, playing an important role in high-performance paper-based packaging products and facilitating high-value-added applications.

Description

Technical Field

[0001] This invention belongs to the technical field of pulp molding packaging materials, and specifically relates to a high-barrier pulp molding packaging material, its preparation method, and its application. Background Technology

[0002] Pulp molding is a three-dimensional papermaking technology that uses virgin pulp or waste paper as the base material. Through processes such as vacuum filtration, molding, and drying, it produces a pollution-free, biodegradable, and environmentally friendly product. It possesses excellent shockproof, impact-resistant, and antistatic properties. Furthermore, it benefits from abundant raw material sources, lightweight construction, high compressive strength, stackability, and low storage capacity, making it widely used in food, tableware, industrial product cushioning packaging, and fine packaging. Because it uses natural plant fibers as raw materials, the finished product is completely biodegradable.

[0003] The production process for ordinary pulp molded products is currently mature; however, certain specialized capabilities need improvement, and high-value-added pulp molded products represent the future development direction. Existing technologies impart waterproof and oil-resistant properties to pulp molded products by adding waterproofing additives or coatings, partially replacing foamed plastic products and effectively eliminating "white pollution." However, the oxygen barrier properties of pulp molded products remain unsatisfactory. Some pulp molded products improve their barrier properties by aluminum plating on plastic followed by paper-plastic composites. This involves using pulp molded products as the skeleton material, aluminum as the barrier material, and plastic as the binder to prepare a composite material based on the pulp molded product skeleton. However, the non-degradable nature of aluminum limits its large-scale application. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing high-barrier pulp molded packaging materials.

[0005] Another object of the present invention is to provide a high-barrier pulp molded packaging material prepared by the aforementioned preparation method.

[0006] Another object of the present invention is to provide the application of the high-barrier pulp molded packaging material.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a high-barrier pulp molded packaging material includes the following steps:

[0009] (1) Pulp preparation: Bamboo pulp fiber (BF) pulp and sorghum straw fiber (SF) pulp are decomposed and dispersed to obtain bamboo pulp fiber dispersion and sorghum straw fiber dispersion, and then the bamboo pulp fiber dispersion and sorghum straw fiber dispersion are mixed evenly and pulped to obtain BF / SF mixed pulp.

[0010] (2) Adding additives: Add the aramid fiber (AF) suspension to the BF / SF mixed slurry obtained in step (1) under stirring conditions, mix evenly to obtain BF / SF / AF compound slurry; then add waterproofing agent and wet strength agent, stir evenly to obtain composite slurry;

[0011] (3) Shaping treatment: The composite pulp obtained in step (2) is molded into pulp, and then vacuum filtered and dehydrated to obtain a pulp molded wet preform. Then, it is hot-pressed to shape and obtain a high-barrier pulp molded packaging material.

[0012] To better achieve the objectives of this invention, it also includes:

[0013] (4) Coating treatment: The high-barrier pulp molding packaging material obtained in step (3) is trimmed to obtain a pulp molding blank; the coating is sprayed onto the pulp molding blank and then dried.

[0014] (5) Coating treatment: The surface of the pulp molded after spraying in step (4) is coated with a film, and the coated pulp molded is cooled and trimmed to obtain a high-barrier pulp molded product.

[0015] The dispersing process described in step (1) involves dispersing the bamboo pulp fiber (BF) slurry at a rotation speed of 16,000 to 22,000 r / min for 5 to 15 minutes.

[0016] The dispersing process described in step (1) involves dispersing sorghum straw fiber (SF) slurry at a rotation speed of 10,000 to 15,000 r / min for 5 to 10 minutes.

[0017] The bamboo pulp fiber (BF) in the bamboo pulp fiber dispersion in step (1) has a length of 1250–4360 nm and a width of 75–610 nm; the sorghum straw fiber (SF) in the sorghum straw fiber dispersion has a length of 530–1420 nm and a width of 50–380 nm.

[0018] The concentration of the bamboo pulp fiber dispersion in step (1) is 4.0 to 4.8 wt%.

[0019] The concentration of the sorghum straw fiber dispersion in step (1) is 4.5–5.2 wt%.

[0020] The pulping process described in step (1) is performed using a high-concentration pulping machine.

[0021] The pulping conditions described in step (1) are: pulping speed of 10,000 to 14,000 revolutions, pulping concentration of 4.2 to 4.8%, and pulping degree of 36 to 40°SR.

[0022] In step (1), the oven-dry mass ratio of bamboo pulp fiber (BF) and sorghum straw fiber (SF) in the mixed system is (5-7):(3-5).

[0023] The aramid fiber (AF) mentioned in step (2) is a meta-aramid short-cut fiber with a length of 3 to 8 mm and a single filament fineness of 1.5D to 2.5D (1D = the weight in grams of a 9000-meter-long fiber).

[0024] The concentration of the aramid fiber (AF) suspension (preferably meta-aramid chopped fiber suspension) mentioned in step (2) is 2.0% to 4.0% by mass.

[0025] The amount of meta-aramid chopped fiber added in step (2) is 1.0 to 3.0% of the oven-dry weight of the BF / SF / AF compound slurry.

[0026] In step (2), the rotation speed used under stirring conditions is 4000-6000 r / min.

[0027] The stirring speed used in step (2) is 8000-10000 r / min, and the stirring time is 5-8 min.

[0028] The waterproofing agent mentioned in step (2) is a wax emulsion (solid content 30%), and the amount added is 1.0 to 3.0% of the oven-dry weight of the composite slurry; the wet strength agent is polyamide polyepoxychloropropane resin, and the amount added is 2.0 to 5.0% of the oven-dry weight of the composite slurry.

[0029] The mass concentration of the composite slurry mentioned in step (3) is 0.1-0.3%.

[0030] The vacuum filtration dehydration described in step (3) is carried out under vacuum of -0.03 to -0.04 MPa for 10 to 20 seconds until the water content is 60 to 70%.

[0031] The hot pressing conditions described in step (3) are: pressure: 40~70kg / cm² 2 Temperature: 180~220℃, Time: 15~20s.

[0032] The coating mentioned in step (4) is a PVA emulsion with a concentration of 4.0–8.0% and a spraying amount of 1.0–4.0 g / m². 2 The average molecular weight of PVA is 100,000 to 150,000.

[0033] The coating process described in step (5) is a poly(butylene adipate) terephthalate (PBAT) film. The film temperature is 220-260°C. After being vacuum-pressed for 1.0-1.6 seconds, it is tightly coated onto the surface of the pulp molded blank. After the coating process is completed, a high-barrier pulp molded product is obtained.

[0034] A high-barrier pulp molded packaging material is prepared by the above-described preparation method.

[0035] The above-mentioned high-barrier pulp molded packaging materials are used in the preparation of high-barrier pulp molded products.

[0036] Preferably, a high-barrier pulp molded product is prepared by the above-described preparation method.

[0037] The performance indicators of the high-barrier pulp molded products are as follows: Basis weight: 30-34 g / m³ 2 Tensile strength index: 65.8~73.4 N·m / g; Bursting strength index: 5.16~5.87 kPa·m 2 / g; Water contact angle: 108–135°; Oxygen permeability: 0.52–0.65cm 3 / m 2 • Day • 0.1 MPa; Water vapor transmission rate: 0.93~1.15 g / m 2 •day; possesses heat-resistant oil properties.

[0038] The high-barrier pulp molded products are mainly used for packaging fresh produce or fruits and vegetables.

[0039] The present invention has the following advantages and effects compared with the prior art:

[0040] (1) The bamboo pulp and sorghum straw used in this invention are non-wood fiber raw materials, which can solve the problem of the shortage of wood fiber raw materials, expand the source of pulp fiber raw materials, realize the use of paper instead of plastic in the field of packaging materials for fresh fruits and vegetables, and conform to the concept of sustainable development.

[0041] (2) By combining plant fibers with aramid fibers, the advantages of different fibers can be fully utilized: bamboo pulp fiber (BF) is long and strong, which can significantly improve physical strength; sorghum straw fiber (SF) is fine and soft, which can ensure that the fibers are tightly bonded; aramid fiber has excellent characteristics such as high strength, high modulus, high temperature resistance, corrosion resistance, flame retardancy, electrical insulation, chemical stability and thermal stability, which can improve the mechanical strength, thermal stability and corrosion resistance of pulp molding.

[0042] (3) This invention imparts superior oxygen barrier properties to molded pulp by spraying a PVA emulsion with good oxygen barrier properties; by coating the surface with a PBAT film, which has excellent biodegradability and can improve the waterproof and oil-proof properties of the molded pulp products; in addition, aramid fibers also have excellent barrier properties. Through the comprehensive design of this invention, the resulting molded pulp products have superior mechanical and barrier properties, and can be used for packaging fresh produce and fruits and vegetables. They play an important role in high-performance packaging products that replace plastic with paper, which is conducive to achieving high value-added applications. Attached Figure Description

[0043] Figure 1 This is a plan view of the high-barrier pulp molded product provided in Embodiment 1 of the present invention.

[0044] Figure 2 This is a top view of the high-barrier pulp molded product provided in Embodiment 1 of the present invention. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. Test methods in the following embodiments that do not specify specific experimental conditions are generally performed according to conventional experimental conditions or experimental conditions recommended by the manufacturer. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

[0046] 1. The bamboo pulp fiber (BF) pulp and sorghum straw fiber (SF) pulp involved in the embodiments and comparative examples of this invention are sourced from the State Key Laboratory of Pulp and Paper Engineering. The length of bamboo pulp fiber (BF) is 1250–4360 nm, and the width is 75–610 nm; the length of sorghum straw fiber (SF) is 530–1420 nm, and the width is 50–380 nm. The bamboo used as raw material for bamboo pulp fiber (BF) pulp is sourced from Anji, Jiangxi Province, and the sorghum straw used as raw material for sorghum straw fiber (SF) pulp is sourced from Zhumadian, Henan Province. Both are obtained through a classic chemical pulping process (the raw materials are pretreated with acetic acid, cooked using the sulfate method, oxygen delignified, extracted with cold alkali, and bleached with hydrogen peroxide).

[0047] 2. The meta-aramid chopped fibers involved in the embodiments and comparative examples of this invention are conventional commercially available products in the art, with a length of 3-8 mm and a single filament fineness of 1.5D-2.5D (1D = the weight in grams of 9000 meters of fiber), and can be purchased from a certain special fiber manufacturing company; PVA (i.e., polyvinyl alcohol) is a conventional commercially available product in the art, with an average molecular weight of 100,000-150,000, and can be purchased from a certain chemical company.

[0048] 3. The waterproofing agent involved in the embodiments and comparative examples of the present invention is a wax emulsion with a solid content of 30% (purchased from Shanghai Youen Chemical Co., Ltd.); the wet strength agent is polyamide polyepoxychloropropane resin (Lingchuang, Shandong).

[0049] 4. The detection of various parameters involved in the embodiments of this invention is carried out in accordance with national standard testing methods and industry standards, specifically as follows:

[0050] ① Quantitative (GB / T 451.2-2002);

[0051] ②Tension index (GB / T 453-2002);

[0052] ③ Bursting strength index (GB / T 454-2002);

[0053] ④ Water contact angle (GB / T 30447-2013);

[0054] ⑤ Oxygen transmission rate (GB / T 19789-2005);

[0055] ⑥ Water vapor transmission rate (GB / T 22921-2008).

[0056] Test method for heat-resistant oil properties: Place one drop of 80℃ soybean oil on the surface of the pulp molded product. After 10 minutes, wipe off the oil drop. If there are no oil stains on the surface of the pulp molded product, it indicates that the pulp molded product has heat-resistant oil properties.

[0057] Example 1

[0058] This embodiment provides a method for preparing high-barrier pulp molded products, and the specific preparation steps are as follows:

[0059] (1) Pulp preparation: Bamboo pulp fiber (BF) pulp was dispersed for 5 minutes at 16,000 r / min using a high-frequency de-dispersing machine to obtain a BF solution (concentration 4.0 wt%); sorghum straw fiber (SF) pulp was dispersed for 5 minutes at 10,000 r / min using a high-frequency de-dispersing machine to obtain an SF solution (concentration 4.5 wt%). Then, the BF solution (length: 1250–4360 nm, width: 75–610 nm) and the SF solution (length: 530–1420 nm, width: 50–380 nm) were mixed, with an oven-dry mass ratio of bamboo pulp fiber (BF) to sorghum straw fiber (SF) of 5:5. The mixed pulp was then pulped in a high-concentration refiner at 10,000 rpm, with a pulping concentration of 4.2% and a freeness of 36°SR to obtain a BF / SF mixed pulp.

[0060] (2) Adding additives: Under stirring conditions (4000 r / min), add a 2.0% (w / w) suspension of meta-aramid chopped fibers (3 mm in length, 1.5 D single filament fineness) to the BF / SF mixed slurry solution obtained in step (2), mix evenly to obtain BF / SF / AF composite slurry, wherein the amount of meta-aramid chopped fibers (oven dry) added is 1.0% of the oven dry mass of BF / SF / AF composite slurry. Then add a waterproofing agent (wax emulsion with a solid content of 30%) and a wet strength agent (polyamide polyepoxychloropropylene resin), the amount of waterproofing agent added is 1.0% of the oven dry mass of composite slurry; the amount of wet strength agent added is 2.0% of the oven dry mass of composite slurry, stir for 5 min with an electric mixer (8000 r / min) to obtain composite slurry;

[0061] (3) Shaping and Spraying Treatment: The composite slurry obtained in step (2) is transported to the pulp molding machine through a pipeline at a mass concentration of 0.1%. It is then dewatered under vacuum (vacuum degree -0.03MPa, dewatering under negative pressure for 10s) to obtain a pulp molding wet preform (moisture content 70%). Next, it is subjected to a pressure of 40kg / cm². 2 The pulp molded preform is hot-pressed at 180℃ for 15 seconds to set, and then trimmed to obtain a dry preform. A 4.0% PVA emulsion (average molecular weight of PVA is 100,000–150,000) is then sprayed onto the preform using a spray gun at a rate of 1.0 g / m³. 2 Then it is dried;

[0062] (4) Coating treatment: A layer of polybutylene adipate / terephthalate (PBAT) film is coated onto the surface of the pulp molded material after spraying in step (3). The film temperature is 220℃. After vacuum suction for 1.0s, it tightly coats the surface of the pulp molded blank. The coated pulp molded material is removed from the mold, cooled and trimmed to obtain a high-barrier pulp molded product. The product prepared in this experiment is a bowl-shaped product with an upper diameter of 197mm×197mm, a lower diameter of 186mm×186mm, a height of 40mm, and a thickness of 0.75mm. Figure 1 and Figure 2 ).

[0063] The performance indicators of the high-barrier pulp molded product prepared in this embodiment are as follows: Basis weight: 32 g / m³ 2 Tensile strength index: 65.8 N·m / g; Bursting strength index: 5.16 kPa·m 2 / g; Water contact angle: 108°; Oxygen permeability: 0.65cm 3 / m 2 • Day • 0.1 MPa; Water vapor transmission rate: 1.15 g / m 2 •day; possesses heat-resistant oil properties.

[0064] Example 2

[0065] This embodiment provides a method for preparing high-barrier pulp molded products, and the specific preparation steps are as follows:

[0066] (1) Pulp preparation: Bamboo pulp fiber (BF) pulp was dispersed in a high-frequency de-fiber mill at a speed of 18,000 r / min for 10 min to obtain a BF solution (concentration of 4.4 wt%); sorghum straw fiber (SF) pulp was dispersed in a high-frequency de-fiber mill at a speed of 12,000 r / min for 7 min to obtain an SF solution (concentration of 4.7 wt%). Then, the BF solution (length: 1250–4360 nm, width: 75–610 nm) and the SF solution (length: 530–1420 nm, width: 50–380 nm) were mixed, with an oven-dry mass ratio of bamboo pulp fiber (BF) to sorghum straw fiber (SF) of 6:5. The mixed pulp was then pulped in a high-concentration refiner at a speed of 11,000 rpm, a pulping concentration of 4.4%, and a freeness of 37°SR to obtain a BF / SF mixed pulp.

[0067] (2) Adding additives: Under stirring conditions (5000 r / min), add a 3.0% (w / w) suspension of meta-aramid chopped fibers (5 mm in length, 2.0 D single filament fineness) to the BF / SF mixed slurry solution obtained in step (2), mix evenly to obtain BF / SF / AF composite slurry, wherein the amount of meta-aramid chopped fibers (oven dry) added is 2.0% of the oven dry mass of BF / SF / AF composite slurry. Then add a waterproofing agent (wax emulsion with a solid content of 30%) and a wet strength agent (polyamide polyepoxychloropropylene resin), the amount of waterproofing agent added is 1.5% of the oven dry mass of composite slurry; the amount of wet strength agent added is 3.0% of the oven dry mass of composite slurry, stir with an electric mixer (9000 r / min) for 6 min to obtain composite slurry;

[0068] (3) Shaping and Spraying Treatment: The composite slurry obtained in step (2) is transported to the pulp molding machine through a pipeline at a mass concentration of 0.15%. It is then dewatered under vacuum (vacuum degree -0.034MPa, dewatering under negative pressure for 13s) to obtain a pulp molding wet preform (moisture content 67%). Next, it is subjected to a pressure of 50 kg / cm². 2 The pulp molded preform is hot-pressed at 200℃ for 17 seconds for setting, followed by edge trimming to obtain a dry preform. A 5.5% PVA emulsion (PVA with an average molecular weight of 100,000–150,000) is then sprayed onto the preform using a spray gun at a rate of 2.0 g / m³. 2 Then it is dried;

[0069] (4) Coating treatment: A layer of PBAT film is coated on the surface of the pulp molded after spraying in step (3). The film temperature is 235°C. After vacuum suction for 1.2s, it is tightly wrapped on the surface of the pulp molded blank. The coated pulp molded blank is removed from the mold, cooled and trimmed to obtain a high-barrier pulp molded product.

[0070] The performance indicators of the high-barrier pulp molded product prepared in this embodiment are as follows: Basis weight: 34 g / m³ 2 Tensile strength index: 67.4 N·m / g; Bursting strength index: 5.33 kPa·m 2 / g; Water contact angle: 114°; Oxygen permeability: 0.61cm 3 / m 2 • Day • 0.1 MPa; Water vapor transmission rate: 1.03 g / m 2 •day; possesses heat-resistant oil properties.

[0071] Example 3

[0072] This embodiment provides a method for preparing high-barrier pulp molded products, and the specific preparation steps are as follows:

[0073] (1) Pulp preparation: Bamboo pulp fiber (BF) pulp was dispersed in a high-frequency de-fiber mill at a speed of 20,000 r / min for 12 min to obtain a BF solution (concentration of 4.5 wt%); sorghum straw fiber (SF) pulp was dispersed in a high-frequency de-fiber mill at a speed of 14,000 r / min for 8 min to obtain an SF solution (concentration of 4.9 wt%). Then, the BF solution (length: 1250–4360 nm, width: 75–610 nm) and the SF solution (length: 530–1420 nm, width: 50–380 nm) were mixed, with an oven-dry mass ratio of bamboo pulp fiber (BF) to sorghum straw fiber (SF) of 7:4. The mixed pulp was then pulped in a high-concentration refiner at a speed of 13,000 rpm, a pulping concentration of 4.6%, and a freeness of 38°SR to obtain a BF / SF mixed pulp.

[0074] (2) Adding additives: Under stirring conditions (speed of 6000 r / min), add a 3.5% (w / w) suspension of meta-aramid chopped fibers (7 mm in length, 2.2D monofilament fineness) to the BF / SF mixed slurry solution obtained in step (2), mix evenly to obtain BF / SF / AF composite slurry, wherein the amount of meta-aramid chopped fibers (oven dry) added is 2.5% of the oven dry mass of BF / SF / AF composite slurry. Then add a waterproofing agent (wax emulsion with a solid content of 30%) and a wet strength agent (polyamide polyepoxychloropropylene resin), the amount of waterproofing agent added is 2.0% of the oven dry mass of composite slurry; the amount of wet strength agent added is 4.0% of the oven dry mass of composite slurry, stir with an electric mixer (speed of 9000 r / min) for 7 min to obtain composite slurry;

[0075] (3) Shaping and Spraying Treatment: The composite slurry obtained in step (2) is transported to the pulp molding machine through a pipeline at a mass concentration of 0.2%. It is then dewatered under vacuum (vacuum degree -0.038MPa, dewatering under negative pressure for 17s) to obtain a pulp molding wet preform (moisture content 64%). Next, it is subjected to a pressure of 60 kg / cm². 2 The pulp molded preform is hot-pressed at 210℃ for 18 seconds for setting, followed by edge trimming to obtain a dry preform. A 6.5% PVA emulsion (PVA with an average molecular weight of 100,000–150,000) is then sprayed onto the preform using a spray gun at a rate of 3.0 g / m³. 2 Then it is dried;

[0076] (4) Coating treatment: A layer of PBAT film is coated on the surface of the pulp molded after spraying in step (3). The film temperature is 250°C. After vacuum suction for 1.4s, it is tightly wrapped on the surface of the pulp molded blank. The coated pulp molded blank is removed from the mold, cooled and trimmed to obtain a high-barrier pulp molded product.

[0077] The performance indicators of the high-barrier pulp molded product prepared in this embodiment are as follows: Basis weight: 30 g / m³ 2 Tensile strength index: 69.8 N·m / g; Bursting strength index: 5.58 kPa·m 2 / g; Water contact angle: 122°; Oxygen permeability: 0.56cm 3 / m 2 • Day • 0.1 MPa; Water vapor transmission rate: 0.97 g / m 2 •day; possesses heat-resistant oil properties.

[0078] Example 4

[0079] This embodiment provides a method for preparing high-barrier pulp molded products, and the specific preparation steps are as follows:

[0080] (1) Pulp preparation: Bamboo pulp fiber (BF) pulp was dispersed in a high-frequency descrambling machine at a speed of 22,000 r / min for 15 min to obtain a BF solution (concentration of 4.8 wt%); sorghum straw fiber (SF) pulp was dispersed in a high-frequency descrambling machine at a speed of 15,000 r / min for 10 min to obtain an SF solution (concentration of 5.2 wt%). Then, the BF solution (length: 1250–4360 nm, width: 75–610 nm) and the SF solution (length: 530–1420 nm, width: 50–380 nm) were mixed, with an oven-dry mass ratio of bamboo pulp fiber (BF) to sorghum straw fiber (SF) of 7:3. The mixed pulp was then pulped in a high-concentration refiner at a speed of 14,000 rpm, a pulping concentration of 4.8%, and a freeness of 40°SR to obtain a BF / SF mixed pulp.

[0081] (2) Adding additives: Under stirring conditions (speed of 6000 r / min), add a suspension of meta-aramid chopped fibers (length of 8 mm, single filament fineness of 2.5D) with a mass concentration of 4.0% to the BF / SF mixed slurry solution obtained in step (2), mix evenly to obtain BF / SF / AF composite slurry, wherein the amount of meta-aramid chopped fibers (oven dry) added is 3.0% of the oven dry mass of BF / SF / AF composite slurry. Then add a waterproofing agent (wax emulsion with a solid content of 30%) and a wet strength agent (polyamide polyepoxychloropropylene resin), the amount of waterproofing agent added is 3.0% of the oven dry mass of composite slurry; the amount of wet strength agent added is 5.0% of the oven dry mass of composite slurry, and stir with an electric mixer (speed of 10000 r / min) for 5-8 minutes to obtain composite slurry;

[0082] (3) Shaping and Spraying Treatment: The composite slurry obtained in step (2) is transported to the pulp molding machine through a pipeline at a mass concentration of 0.3%. It is then dewatered under vacuum (vacuum degree -0.04MPa, dewatering under negative pressure for 20s) to obtain a pulp molding wet preform (moisture content 60%). Next, it is subjected to a pressure of 70 kg / cm². 2 The pulp molded preform is hot-pressed at 220℃ for 20 seconds for setting, followed by edge trimming to obtain a dry preform. An 8.0% PVA emulsion (with an average molecular weight of 100,000–150,000) is then sprayed onto the preform using a spray gun at a rate of 4.0 g / m³. 2 Then it is dried;

[0083] (4) Coating treatment: A layer of PBAT film is coated on the surface of the pulp molded after spraying in step (3). The film temperature is 260°C. After vacuum suction for 1.6s, it is tightly wrapped on the surface of the pulp molded blank. The coated pulp molded blank is removed from the mold, cooled and trimmed to obtain a high-barrier pulp molded product.

[0084] The performance indicators of the high-barrier pulp molded product prepared in this embodiment are as follows: Basis weight: 31 g / m³ 2 Tensile strength index: 73.4 N·m / g; Bursting strength index: 5.87 kPa·m 2 / g; Water contact angle: 135°; Oxygen permeability: 0.52cm 3 / m 2 • Day • 0.1 MPa; Water vapor transmission rate: 0.93 g / m 2 •day; possesses heat-resistant oil properties.

[0085] Comparative Example 1

[0086] This comparative example provides a method for preparing high-barrier pulp molded articles, and the specific preparation steps are as follows:

[0087] (1) Pulp preparation: Bamboo pulp fiber (BF) pulp was dispersed for 5 minutes at 16,000 r / min using a high-frequency de-dispersing machine to obtain a BF solution (concentration 4.0 wt%); sorghum straw fiber (SF) pulp was dispersed for 5 minutes at 10,000 r / min using a high-frequency de-dispersing machine to obtain an SF solution (concentration 4.5 wt%). Then, the BF solution (length: 1250–4360 nm, width: 75–610 nm) and the SF solution (length: 530–1420 nm, width: 50–380 nm) were mixed, with an oven-dry mass ratio of bamboo pulp fiber (BF) to sorghum straw fiber (SF) of 5:5. The mixed pulp was then pulped in a high-concentration refiner at 10,000 rpm, with a pulping concentration of 4.2% and a freeness of 36°SR to obtain a BF / SF mixed pulp.

[0088] (2) Adding additives: Add waterproofing agent (wax emulsion with a solid content of 30%) and wet strength agent (polyamide polyepoxychloropropylene resin) to the BF / SF mixed slurry. The amount of waterproofing agent added is 1.0% of the oven-dry weight of the composite slurry; the amount of wet strength agent added is 2.0% of the oven-dry weight of the composite slurry. Stir with an electric mixer (speed of 8000 r / min) for 5 min to obtain the composite slurry.

[0089] (3) Shaping and Spraying Treatment: The composite slurry obtained in step (2) is transported to the pulp molding machine through a pipeline at a mass concentration of 0.1%. It is then dewatered under vacuum (vacuum degree -0.03MPa, dewatering under negative pressure for 10s) to obtain a pulp molding wet preform (moisture content 70%). Next, it is subjected to a pressure of 40kg / cm². 2 The pulp molded preform is hot-pressed at 180℃ for 15 seconds to set, and then trimmed to obtain a dry preform. A 4.0% PVA emulsion (average molecular weight of PVA is 100,000–150,000) is then sprayed onto the preform using a spray gun at a rate of 1.0 g / m³. 2 Then it is dried;

[0090] (4) Coating treatment: A layer of PBAT film is coated on the surface of the pulp molded after spraying in step (3). The film temperature is 220°C. After vacuum suction for 1.0s, it is tightly wrapped on the surface of the pulp molded blank. The coated pulp molded blank is removed from the mold, cooled and trimmed to obtain a high-barrier pulp molded product.

[0091] The performance indicators of the high-barrier pulp molded products prepared in this comparative example are as follows: Basis weight: 32 g / m³ 2 Tensile strength index: 47.3 N·m / g; Bursting strength index: 3.85 kPa·m 2 / g; Water contact angle: 102°; Oxygen permeability: 0.93cm 3 / m 2 • Day • 0.1 MPa; Water vapor transmission rate: 1.47 g / m 2 •day; possesses heat-resistant oil properties.

[0092] Comparative Example 2

[0093] This comparative example provides a method for preparing molded pulp articles, and the specific preparation steps are as follows:

[0094] (1) Pulp preparation: Bamboo pulp fiber (BF) pulp was dispersed for 5 minutes at 16,000 r / min using a high-frequency de-dispersing machine to obtain a BF solution (concentration 4.0 wt%); sorghum straw fiber (SF) pulp was dispersed for 5 minutes at 10,000 r / min using a high-frequency de-dispersing machine to obtain an SF solution (concentration 4.5 wt%). Then, the BF solution (length: 1250–4360 nm, width: 75–610 nm) and the SF solution (length: 530–1420 nm, width: 50–380 nm) were mixed, with an oven-dry mass ratio of bamboo pulp fiber (BF) to sorghum straw fiber (SF) of 5:5. The mixed pulp was then pulped in a high-concentration refiner at 10,000 rpm, with a pulping concentration of 4.2% and a freeness of 36°SR to obtain a BF / SF mixed pulp.

[0095] (2) Adding additives: Under stirring conditions (4000 r / min), add a 2.0% (w / w) suspension of meta-aramid chopped fibers (3 mm in length, 1.5 D single filament fineness) to the BF / SF mixed slurry solution obtained in step (2), mix evenly to obtain BF / SF / AF composite slurry, wherein the amount of meta-aramid chopped fibers (oven dry) added is 1.0% of the oven dry mass of BF / SF / AF composite slurry. Then add a waterproofing agent (wax emulsion with a solid content of 30%) and a wet strength agent (polyamide polyepoxychloropropylene resin), the amount of waterproofing agent added is 1.0% of the oven dry mass of composite slurry; the amount of wet strength agent added is 2.0% of the oven dry mass of composite slurry, stir for 5 min with an electric mixer (8000 r / min) to obtain composite slurry;

[0096] (3) Hot pressing and setting treatment: The composite pulp obtained in step (2) is transported to the pulp molding machine through a pipeline at a mass concentration of 0.1%. It is then dewatered under vacuum (vacuum degree -0.03MPa, dewatering under negative pressure for 10s) to obtain a wet pulp molding preform (moisture content 70%). Next, it is heated under a pressure of 40 kg / cm². 2 The pulp molded blank is formed by hot pressing at 180℃ for 15 seconds and then trimming the edges.

[0097] (4) Coating process: In step (3), a layer of PBAT film is coated on the surface of the pulp molding. The film temperature is 220°C. After vacuum suction for 1.0s, it is tightly wrapped on the surface of the pulp molding blank. The coated pulp molding is removed from the mold, cooled and trimmed to obtain the pulp molding product.

[0098] The performance indicators of the pulp molded products prepared in this comparative example are as follows: Basis weight: 32 g / m³ 2 Tensile strength index: 54.3 N·m / g; Bursting strength index: 4.78 kPa·m2 / g; Water contact angle: 104°; Oxygen permeability: 3.14cm 3 / m 2 • Day • 0.1 MPa; Water vapor transmission rate: 1.76 g / m 2 •day; possesses heat-resistant oil properties.

[0099] Comparative Example 3

[0100] This comparative example provides a method for preparing molded pulp articles, and the specific preparation steps are as follows:

[0101] (1) Pulp preparation: Bamboo pulp fiber (BF) pulp was dispersed for 5 minutes at 16,000 r / min using a high-frequency de-dispersing machine to obtain a BF solution (concentration 4.0 wt%); sorghum straw fiber (SF) pulp was dispersed for 5 minutes at 10,000 r / min using a high-frequency de-dispersing machine to obtain an SF solution (concentration 4.5 wt%). Then, the BF solution (length: 1250–4360 nm, width: 75–610 nm) and the SF solution (length: 530–1420 nm, width: 50–380 nm) were mixed, with an oven-dry mass ratio of bamboo pulp fiber (BF) to sorghum straw fiber (SF) of 5:5. The mixed pulp was then pulped in a high-concentration refiner at 10,000 rpm, with a pulping concentration of 4.2% and a freeness of 36°SR to obtain a BF / SF mixed pulp.

[0102] (2) Adding additives: Under stirring conditions (4000 r / min), add a 2.0% (w / w) suspension of meta-aramid chopped fibers (3 mm in length, 1.5 D single filament fineness) to the BF / SF mixed slurry solution obtained in step (2), mix evenly to obtain BF / SF / AF composite slurry, wherein the amount of meta-aramid chopped fibers (oven dry) added is 1.0% of the oven dry mass of BF / SF / AF composite slurry. Then add a waterproofing agent (wax emulsion with a solid content of 30%) and a wet strength agent (polyamide polyepoxychloropropylene resin), the amount of waterproofing agent added is 1.0% of the oven dry mass of composite slurry; the amount of wet strength agent added is 2.0% of the oven dry mass of composite slurry, stir for 5 min with an electric mixer (8000 r / min) to obtain composite slurry;

[0103] (3) Shaping and Spraying Treatment: The composite slurry obtained in step (2) is transported to the pulp molding machine through a pipeline at a mass concentration of 0.1%. It is then dewatered under vacuum (vacuum degree -0.03MPa, dewatering under negative pressure for 10s) to obtain a pulp molding wet preform (moisture content 70%). Next, it is subjected to a pressure of 40kg / cm². 2The pulp molded preform is hot-pressed at 180℃ for 15 seconds to set, and then trimmed to obtain a dry preform. A 4.0% PVA emulsion (average molecular weight of PVA is 100,000–150,000) is then sprayed onto the preform using a spray gun at a rate of 1.0 g / m³. 2 Then, the pulp is dried and trimmed to obtain molded pulp products.

[0104] The performance indicators of the pulp molded products prepared in this comparative example are as follows: Basis weight: 32 g / m³ 2 Tensile strength index: 58.3 N·m / g; Bursting strength index: 4.75 kPa·m 2 / g; Water contact angle: 96°; Oxygen permeability: 0.98cm 3 / m 2 • Day • 0.1 MPa; Water vapor transmission rate: 1.46 g / m 2 •day; does not have the effect of heat-resistant oil.

[0105] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing high-barrier pulp molded products, characterized in that: Includes the following steps: (1) Pulp preparation: bamboo pulp fiber BF slurry and sorghum straw fiber SF slurry are decomposed and dispersed to obtain bamboo pulp fiber dispersion and sorghum straw fiber dispersion, and then the bamboo pulp fiber dispersion and sorghum straw fiber dispersion are mixed evenly and then pulped to obtain BF / SF mixed slurry. (2) Adding additives: Add aramid fiber AF to the BF / SF mixed slurry obtained in step (1) under stirring conditions, mix evenly to obtain BF / SF / AF compound slurry; then add waterproofing agent and wet strength agent, stir evenly to obtain composite slurry; (3) Shaping treatment: The composite pulp obtained in step (2) is molded into pulp, and then vacuum filtered and dehydrated to obtain a pulp molded wet preform. Then it is hot-pressed to shape and obtain a high-barrier pulp molded packaging material. (4) Coating treatment: The high-barrier pulp molding packaging material obtained in step (3) is subjected to edge trimming treatment to obtain pulp molding blank; The coating is sprayed onto the molded pulp blank and then dried. (5) Coating treatment: The surface of the pulp molded after spraying in step (4) is coated with a film, and the coated pulp molded is cooled and trimmed to obtain a high-barrier pulp molded product; The disintegration described in step (1) involves dispersing the bamboo pulp fiber BF slurry at a rotation speed of 16,000 to 22,000 r / min for 5 to 15 minutes. The dispersing process described in step (1) involves dispersing sorghum straw fiber SF slurry at a rotation speed of 10,000 to 15,000 r / min for 5 to 10 minutes. The bamboo pulp fiber in the bamboo pulp fiber dispersion in step (1) has a length of 1250–4360 nm and a width of 75–610 nm. The sorghum straw fiber in the sorghum straw fiber dispersion in step (1) has a length of 530–1420 nm and a width of 50–380 nm. The concentration of the bamboo pulp fiber dispersion in step (1) is 4.0–4.8 wt%; The concentration of the sorghum straw fiber dispersion in step (1) is 4.5–5.2 wt%; In step (1), the oven-dry mass ratio of bamboo pulp fiber to sorghum straw fiber in the mixed system is (5-7):(3-5). The pulping conditions described in step (1) are: pulping speed of 10,000 to 14,000 revolutions, pulping concentration of 4.2 to 4.8%, and freeness of 36 to 40 °SR; The aramid fiber AF mentioned in step (2) is a meta-aramid short-cut fiber with a length of 3 to 8 mm and a single filament fineness of 1.5D to 2.5D; The amount of meta-aramid chopped fibers added is 1.0% to 3.0% of the oven-dry weight of the BF / SF / AF compound slurry; The concentration of the aramid fiber AF suspension mentioned in step (2) is 2.0% to 4.0% by mass. The waterproofing agent mentioned in step (2) is a wax emulsion with a solid content of 30%, and the amount added is 1.0 to 3.0% of the oven-dry weight of the composite slurry; The wet strength agent mentioned in step (2) is polyamide polyepoxychloropropane resin, and the amount added is 2.0-5.0% of the oven-dry weight of the composite slurry; The mass concentration of the composite slurry mentioned in step (3) is 0.1% to 0.3%. The hot pressing conditions described in step (3) are: pressure: 40–70 kg / cm² 2 Temperature: 180~220 ℃, Time: 15~20 s; The coating mentioned in step (4) is a PVA emulsion with a concentration of 4.0–8.0% and a spraying amount of 1.0–4.0 g / m². 2 Among them, the average molecular weight of PVA is 100,000 to 150,000; The coating process described in step (5) is a poly(adipate) / butyl terephthalate film. The film temperature is 220-260°C. After being vacuum-pressed for 1.0-1.6 seconds, it is tightly wrapped on the surface of the pulp molded blank. After the coating process is completed, a high-barrier pulp molded product is obtained.

2. The preparation method according to claim 1, characterized in that: In step (2), the rotation speed used under stirring conditions is 4000-6000 r / min; The stirring speed used in step (2) is 8000-10000 r / min, and the stirring time is 5-8 min; The vacuum filtration dehydration described in step (3) is carried out under vacuum of -0.03 to -0.04 MPa for 10 to 20 seconds until the water content is 60 to 70%.

3. A high-barrier molded pulp product, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 2.

4. The application of the high-barrier pulp molded article according to claim 3, characterized in that: The high-barrier pulp molded products are used for packaging fresh produce.

5. The application of the high-barrier pulp molded article according to claim 3, characterized in that: The high-barrier pulp molded products are used for packaging fruits and vegetables.

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