A pulp foam cushioning material, its preparation method and application

Abstract

This invention relates to the field of foam material preparation technology, and in particular to a pulp foam cushioning material, its preparation method, and its application. A waxy substance is mixed and dispersed with a nanocellulose solution to obtain a nanocellulose / wax emulsion; pulp fibers are mixed and stirred with a flame retardant solution to obtain a pulp / flame retardant mixture; the nanocellulose / wax emulsion is then mixed with the pulp / flame retardant mixture, the liquid phase is removed, and the mixture is dried to obtain the pulp foam cushioning material. The components of the pulp foam cushioning material are composited through physical interactions, making it easy to mold and process. The entire preparation process is free of chemical cross-linking, making it green and pollution-free. Each component can be disassembled and reprocessed, and is completely biodegradable. It features lightweight, high strength, flame retardancy, water resistance, room temperature and pressure molding, and recyclability.

Description

Technical Field

[0001] This invention relates to the field of foam material preparation technology, and in particular to a pulp foam cushioning material, its preparation method, and its application. Background Technology

[0002] In the process of moving towards a green and low-carbon era, the development of high-performance biomass-based foam materials to replace traditional petroleum-based foam materials (such as polystyrene foam, polyurethane foam, and polyethylene foam) has become a global focus. Widely available and renewable cellulose is an ideal alternative material with significant development and application potential. However, the construction of high-performance cellulose-based foams often involves chemical modification and grafting to achieve cross-linking and promote the stability of the three-dimensional structure. But the introduction of chemical synthesis reagents usually reduces the environmental benefits of the material. Furthermore, cellulose foams typically require freeze-drying and supercritical drying to overcome the capillary pressure of water to achieve uniform molding, greatly increasing the complexity of the preparation process and posing challenges for large-scale production. Therefore, achieving the construction of high-performance cellulose-based foams through a simple and rapid room-temperature and ambient-pressure drying method is of significant research importance.

[0003] Currently, many researchers are dedicated to the development and research of cellulose foam materials. For example, patent CN116903921A discloses a method for preparing pulp foam materials, using pulp fibers as the main body and combining a treatment liquid prepared with gelatin, sodium hydroxide, polyvinyl alcohol, and sepiolite that has undergone calcination, vacuum homogenization, and low-temperature and low-pressure treatment as functional components to achieve the preparation and molding of paper-based foam materials; patent CN103131038A discloses a method for preparing lignocellulose foam, which constructs lignocellulose foam materials by crushing, grinding, dispersing, and freeze-drying lignocellulose; CN109161057A discloses a method for preparing cellulose foam, using pulp, old cotton, and sodium sulfate as raw materials, and achieving the preparation of cellulose-based foam materials through alkalization, sulfonation, dissolution, mixing, molding, heating, washing, static descaling, and rinsing processes. Although the preparation and processing methods of cellulose foam materials are constantly being developed, the above-mentioned patents still have the following problems: (1) The preparation process of cellulose foam materials is accompanied by the use of a large number of chemical synthesis reagents, which have potential pollution and are difficult to completely degrade; (2) The preparation process is complicated; (3) It lacks water resistance and fire resistance and has a single function; (4) It has poor mechanical properties; (5) It is difficult to form at room temperature and pressure after introducing flame retardants with high surface energy. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a pulp foam cushioning material, its preparation method, and its application. The apparent density of the pulp foam cushioning material is 0.08–0.15 g / cm³. 3With a compression modulus of 0.20–1.50 MPa, a limiting oxygen index (LOI) of 25–33%, a vertical burning performance reaching UL-94V0 level, and a hydrophobic angle of 130–142°, this material exhibits excellent comprehensive performance and can be applied in scenarios such as express packaging, cold chain transportation, and building furniture. Using pulp fiber as the main component and nanocellulose as an emulsifier for hydrophobic waxy materials, a nanocellulose / wax emulsion is prepared. The physical composite process between the emulsion and pulp fiber achieves hydrophobic modification and interfacial enhancement of the pulp fiber. Furthermore, a cured waxy coating layer efficiently loads a green flame retardant to impart flame-retardant properties to the foam material, thus realizing the preparation of a high-performance pulp foam cushioning material. Solutions are proposed to address the problems in the preparation process of cellulose-based foam cushioning materials, such as chemical pollution, difficulty in complete foam degradation, complex preparation process, limited functionality, poor mechanical strength, and difficulty in molding during room temperature and pressure drying.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a pulp foam cushioning material, comprising the following steps:

[0007] 1) Mix and disperse the wax with the nanocellulose solution to obtain a nanocellulose / wax emulsion;

[0008] 2) Mix and stir the pulp fibers with the flame retardant solution to obtain a pulp / flame retardant mixture;

[0009] 3) Mix the nanocellulose / wax emulsion obtained in step 1) with the pulp / flame retardant mixture obtained in step 2), remove the liquid phase, and obtain wet pulp.

[0010] 4) Dry the wet pulp obtained in step 3) to obtain pulp foam cushioning material.

[0011] Preferably, the wax in step 1) includes one or more of palm wax, paraffin wax, beeswax, rice bran wax, and rosin;

[0012] The nanocellulose in the nanocellulose solution includes one or more of cellulose nanofibers, cellulose nanocrystals, and cellulose microfibers.

[0013] Preferably, in step 1), the mass percentage of wax in the nanocellulose / wax emulsion is 0.2-0.6%, and the mass percentage of nanocellulose is 0.6-1.8%.

[0014] The dispersion conditions include: a rotation speed of 5000–8000 rpm and a time of 3–8 min.

[0015] Preferably, in step 2), the pulp / flame retardant mixture contains 1-10% by mass of pulp fiber and 0.25-0.75% by mass of flame retardant.

[0016] The stirring conditions include: a rotation speed of 600–1200 rpm and a stirring time of 5–10 min.

[0017] Preferably, the pulp fiber in step 2) includes one or more of bamboo pulp fiber, cotton stalk bark pulp fiber, spruce pulp fiber, Masson pine pulp fiber, red pine pulp fiber, larch pulp fiber and fir pulp fiber;

[0018] The flame retardant includes one or more of phosphoric acid, phytic acid, ammonium polyphosphate, boric acid, and borate.

[0019] Preferably, the mixing conditions in step 3) include: pouring the nanocellulose / wax emulsion into the pulp / flame retardant mixture at a pouring speed of 20-50 mL / s;

[0020] The volume ratio of the nanocellulose / wax emulsion to the pulp / flame retardant mixture is 1:2;

[0021] The mixing speed is 600–1200 rpm.

[0022] Preferably, step 3) involves removing the liquid phase by placing the mixture obtained after mixing in a cylindrical porous mold until no liquid drips; the bottom and sidewalls of the cylindrical porous mold are perforated with a mesh size of 100 mesh and a single-hole spacing of <0.5 mm.

[0023] Preferably, the drying conditions in step 4) include: a temperature of 50–80°C and a time of 8–16 hours.

[0024] The present invention also provides a pulp foam cushioning material prepared by the preparation method described above, wherein the apparent density of the pulp foam cushioning material is 0.08–0.15 g / cm³. 3 It has a compression modulus of 0.20–1.50 MPa, a limiting oxygen index of 25–33%, a vertical combustion performance of UL-94V0, and a hydrophobic angle of 130–142°.

[0025] The present invention also provides the application of the pulp foam cushioning material described in the above technical solution in improving the strength, flame retardant properties and waterproof properties of foam cushioning materials.

[0026] In this invention, pulp fiber, as a common and widely available cellulose aggregate, is biodegradable and renewable. Nanocellulose, characterized by its small size, high aspect ratio, high strength, and abundant hydrogen bonds, exhibits a distinct rod-like or filamentous morphology, making it suitable as a reinforcing component of the main material and an emulsifier for oil-wax materials. By selecting and comparing the hydrophobic properties of various waxes and their auxiliary molding effects on foam materials, the morphology and waterproofing of the foam are systematically controlled. Simultaneously, the wax coating layer solidified on the surface of the pulp fiber allows for efficient loading of various green flame retardants to achieve excellent flame-retardant properties. In summary, this invention addresses existing problems by employing a simple and rapid multi-level interface engineering design strategy and a fully physical composite process. This enables the preparation and structural performance control of high-strength, flame-retardant, room-temperature and room-pressure drying and molding, and waterproof high-performance pulp foam cushioning materials. The excellent comprehensive performance, moldability, and recyclability make pulp foam materials promising for large-scale production.

[0027] The introduction of flame retardants with high surface energy increases the high capillary pressure of the liquid phase on the foam material during the drying process at room temperature and pressure, leading to structural shrinkage. Nanocellulose / wax emulsion composites, fixed to the surface of pulp fibers, can reduce the surface energy of the pulp fibers and simultaneously encapsulate and fix the flame retardant, avoiding interference from the introduction of high surface energy flame retardants on the foam material molding process, thus achieving uniform molding during room temperature and pressure drying.

[0028] The beneficial effects of this invention are:

[0029] The preparation process of this invention does not involve the use of chemical synthesis reagents or chemical cross-linking processes, resulting in no environmental pollution, and the pulp foam material is completely degradable. The preparation of a fiber nanofiber / wax emulsion is achieved through the emulsification of hydrophobic waxes using nanocellulose, which can be uniformly compounded with pulp fibers, thereby achieving hydrophobic modification and interface enhancement of the pulp fibers. This results in a foam hydrophobic angle of 142° and a compressive strength of 1.50 MPa. Simultaneously, the cured wax coating layer allows for efficient loading of green flame retardants, enabling the foam to achieve a limiting oxygen index (LOI) of 33% and a vertical burning performance of UL-94V0. The foam material is compounded through the physical interaction of its components, and the preparation process is simple, fast, moldable, and recyclable. In summary, the foam exhibits excellent comprehensive performance and can be applied in scenarios such as express packaging, cold chain transportation, and building furniture. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0031] Figure 1The images shown are digital photographs of the cellulose nanofiber / palm wax emulsion and optical microscope images of the emulsion droplets in Example 1.

[0032] Figure 2 Examples 1-4 illustrate the effect of cellulose nanofiber dosage on the mechanical properties of pulp foam materials.

[0033] Figure 3 This is an example of the compressive strength of pulp foam material in Example 1 (in a reactor with a foam bearing a mass of 2.5 kg).

[0034] Figure 4 This is an image showing the water contact angle of the pulp foam material in Example 7;

[0035] Figure 5 This is an example of the moldability of foam materials in Example 1;

[0036] Figure 6 The figures show a comparison of the pulp foam cushioning materials prepared in Example 1 and Comparative Example 1. In Example 1, a and b correspond to the uniformly shaped foam materials obtained in Example 1, while c and d show the shaped state and pore structure of the foam materials without the composite nanocellulose / palm wax emulsion. Detailed Implementation

[0037] This invention provides a method for preparing a pulp foam cushioning material, comprising the following steps:

[0038] 1) Mix and disperse the wax with the nanocellulose solution to obtain a nanocellulose / wax emulsion;

[0039] 2) Mix and stir the pulp fibers with the flame retardant solution to obtain a pulp / flame retardant mixture;

[0040] 3) Mix the nanocellulose / wax emulsion obtained in step 1) with the pulp / flame retardant mixture obtained in step 2), remove the liquid phase, and obtain wet pulp.

[0041] 4) Dry the wet pulp obtained in step 3) to obtain pulp foam cushioning material.

[0042] This invention involves mixing and dispersing a waxy substance with a nanocellulose solution to obtain a nanocellulose / wax emulsion. In this invention, the wax preferably includes one or more of palm wax, paraffin wax, beeswax, rice bran wax, and rosin. The wax is preferably composed of wax particles with a particle size of 1–5 mm. This invention does not have a specific limitation on the source of the wax; it can be prepared using conventional commercially available products or conventional preparation methods. In this invention, the nanocellulose in the nanocellulose solution preferably includes one or more of cellulose nanofibers, cellulose nanocrystals, and cellulose microfibers. This invention does not have a specific limitation on the source of the nanocellulose; it can be prepared using conventional commercially available products or conventional preparation methods. In this invention, the mass percentage of wax in the nanocellulose / wax emulsion is preferably 0.2–0.6%, and the mass percentage of nanocellulose is preferably 0.6–1.8%. In this invention, the dispersion conditions preferably include a rotation speed of 5000–8000 rpm and a time of 3–8 min. In this invention, dispersion is preferably achieved using a microfluidic high-speed homogenizer, which emulsifies, disperses, and stabilizes the oil phase with nanocellulose. In this invention, the wax and nanocellulose are preferably mixed and stirred at 90°C, allowing the wax to completely melt into the oil phase.

[0043] This invention involves mixing and stirring pulp fibers with a flame retardant solution to obtain a pulp / flame retardant mixture.

[0044] In this invention, the preferred mass percentage of pulp fiber in the pulp / flame retardant mixture is 1-10%, and the preferred mass percentage of flame retardant is 0.25-0.75%. In this invention, the preferred stirring conditions include a rotation speed of 600-1200 rpm and a stirring time of 5-10 min. In this invention, the preferred pulp fiber includes one or more of bamboo pulp fiber, cotton stalk bark pulp fiber, spruce pulp fiber, Masson pine pulp fiber, red pine pulp fiber, larch pulp fiber, and fir pulp fiber. In this invention, the preferred flame retardant includes one or more of phosphoric acid, phytic acid, ammonium polyphosphate, boric acid, and borate. In this invention, the flame retardant is preferably added to water and stirred for 20 min, then mechanically stirred with the pulp fiber to allow the pulp fiber to absorb water and swell, thereby achieving adsorption of the flame retardant.

[0045] In this invention, the obtained nanocellulose / wax emulsion is mixed with the obtained pulp / flame retardant mixture, and the liquid phase is removed to obtain wet pulp.

[0046] In this invention, the mixing conditions preferably include: pouring the nanocellulose / wax emulsion into the pulp / flame retardant mixture at a pouring speed of 20–50 mL / s. In this invention, the volume ratio of the nanocellulose / wax emulsion to the pulp / flame retardant mixture is preferably 1:2. In this invention, the mixing speed is preferably 600–1200 rpm, and the temperature is preferably 90°C. In this invention, the method for removing the liquid phase preferably includes: placing the mixed mixture in a cylindrical porous mold until no more liquid drips; the bottom and sidewalls of the cylindrical porous mold are perforated with a pore size of 100 mesh and a single-pore spacing of <0.5 mm.

[0047] This invention involves drying the obtained wet pulp to obtain a pulp foam cushioning material. In this invention, the drying conditions preferably include a temperature of 50–80°C and a time of 8–16 hours.

[0048] This invention provides a pulp foam cushioning material prepared by the preparation method described above, wherein the apparent density of the pulp foam cushioning material is 0.08–0.15 g / cm³. 3 It has a compression modulus of 0.20–1.50 MPa, a limiting oxygen index of 25–33%, a vertical combustion performance of UL-94V0, and a hydrophobic angle of 130–142°.

[0049] The present invention also provides the application of the pulp foam cushioning material described in the above technical solution in improving the strength, flame retardant properties and waterproof properties of foam cushioning materials.

[0050] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1

[0052] A method for preparing a pulp foam cushioning material, comprising the following steps:

[0053] Step (1) Preparation of nanocellulose / palm wax emulsion:

[0054] 0.6 g of palm wax particles were added to 100 mL of a 0.6 wt% cellulose nanofiber dispersion (prepared via an organic acid-mechanical method) (Zhao H, Sun L, Yu Y, et al. Low-cost, scale production of nanocellulose from bamboo wastes via a recyclable and stable strategy[J]. Biomass Conversion and Biorefinery, 2024: 1-10.). The mixture was stirred and heated to 90 °C to completely melt the wax particles into an oil phase. The cellulose nanofiber / palm wax dispersion was then rapidly dispersed (6000 rpm for 5 min) using a microfluidic high-speed homogenizer. This allowed the oil phase formed after the palm wax melt to be emulsified, dispersed, and stabilized by the cellulose nanofibers, resulting in a cellulose nanofiber / palm wax emulsion (e.g., ...). Figure 1 (As shown).

[0055] Step (2) Preparation of pulp / flame retardant mixture:

[0056] Phosphoric acid, used as a flame retardant, was added to water and stirred for 20 minutes to obtain a phosphoric acid solution, wherein the mass fraction of phosphoric acid in the phosphoric acid solution was maintained at 0.50 wt%. 6 g of bamboo pulp fiber was added to the phosphoric acid solution, and the pulp / phosphoric acid dispersion was stirred at high speed (800 rpm for 5 minutes) using a mechanical stirrer to obtain a mixture of pulp and phosphoric acid, wherein the pulp fiber absorbed water and swelled, thereby adsorbing phosphoric acid.

[0057] Step (3) Mixing of pulp / phosphate mixture with nanocellulose / palm wax emulsion:

[0058] The pulp / phosphate mixture was heated to 90°C. The prepared cellulose nanofiber / palm wax emulsion was slowly added (20 mL / s) to the pulp / phosphate mixture that was being stirred at high speed. The mixture was then fully dispersed at 800 rpm for 30 min. The volume ratio of the cellulose nanofiber / palm wax emulsion to the pulp / phosphate mixture was 1:2, which allowed the phosphoric acid-loaded pulp fibers to be fully adsorbed by the cellulose nanofiber / palm wax emulsion, thereby achieving the initial binding of each functional component with the pulp fibers.

[0059] Step (4) Drying of pulp foam cushioning material at room temperature and pressure:

[0060] A dispersion of pulp / phosphate / cellulose nanofibers / palm wax was transferred to a cylindrical porous container, and excess liquid phase was naturally removed to obtain wet pulp. The bottom and side walls of the cylindrical porous mold were perforated with a pore size of 100 mesh and a single pore spacing of <0.5 mm. The cured cellulose nanofiber / palm wax coating layer achieved efficient loading of the flame retardant components. The wet pulp was then transferred to an oven for drying (70℃ for 12 hours) to obtain a high-strength, flame-retardant, and waterproof pulp foam cushioning material.

[0061] The composite process involving the complete physical interaction of all components during the preparation of pulp foam materials endows the foam materials with excellent moldability and processability, enabling them to be processed into special shapes (such as...). Figure 5 (As shown).

[0062] Examples 2-4

[0063] By using the mass fraction of cellulose nanofibers in step (1) of Example 1 as a variable, different cellulose nanofiber / palm wax emulsions were obtained.

[0064] In Examples 1-4, the effects of the amount of cellulose nanofiber on the stress-strain curves and compressive modulus of the pulp foam cushioning material during compression are as follows: Figure 2 As shown in Table 1, the foam material supports a 2.5kg reactor. Figure 3 As shown.

[0065] Table 1. Effect of cellulose nanofiber dosage on the compressive modulus of foam materials

[0066]

[0067] As shown in Table 1, under the condition that other variables are kept constant, the compressive modulus of the foam material increases and the compressive strength is improved with the increase of the amount of cellulose nanofibers in the cellulose nanofiber / palm wax emulsion. When the amount of nanocellulose is above 1.8%, the excessive amount of nanocellulose will increase the effect of capillary pressure of water on the system, making molding more difficult and resulting in uneven morphology of the foam material after drying.

[0068] Examples 5-7

[0069] By using the mass fraction of palm wax in step (1) of Example 1 as a variable, different cellulose nanofiber / palm wax emulsions were obtained.

[0070] Table 2 shows the effect of palm wax dosage on the water contact angle of the pulp foam cushioning material under the process conditions of Examples 1 and 5-7; the water contact angle image of the foam material when the mass fraction of palm wax is 0.6 wt% is shown in the figure. Figure 4 As shown.

[0071] Table 2. Effect of palm wax dosage on water contact angle of foam materials

[0072]

[0073]

[0074] As shown in Table 2, with other variables kept constant, the hydrophobic angle of the foam material increases and its waterproofing ability improves with the increase of palm wax content in the cellulose nanofiber / palm wax emulsion. When the AKD content is above 0.6%, AKD is in excess in the system, and further increases do not significantly affect the hydrophobic angle.

[0075] Examples 8-10

[0076] By using the mass fraction of phosphoric acid in step (2) of Example 1 as a variable, different phosphoric acid solutions were obtained.

[0077] Table 3 shows the effect of phosphoric acid dosage on the limiting oxygen index (LOI) and vertical burning performance (UL-94) of pulp foam buffer materials under the process conditions of Examples 1 and 8-10.

[0078] Table 3. Effect of phosphoric acid dosage on limiting oxygen index (LOI) and vertical burning performance (UL-94) of foam materials

[0079]

[0080] As shown in Table 3, under the condition that other variables are kept constant, the limiting oxygen index of the foam material increases with the increase of phosphoric acid content in the phosphoric acid solution; with the phosphoric acid load, the UL-94 vertical burning performance of the foam material can reach the V0 level; the foam material obtains excellent flame retardant ability.

[0081] Comparative Example 1

[0082] The difference from Example 1 is that no nanocellulose / palm wax emulsion was added. The resulting pulp foam cushioning material shrank after molding, as shown in the figure. Figure 6 (c, d).

[0083] In summary, this invention achieves the preparation of recyclable and biodegradable pulp foam cushioning materials through green and pollution-free material selection and a composite method based on physical interactions. The effects of different concentrations and types of nanocellulose, hydrophobic waxes, and green flame retardants on the mechanical, hydrophobic, and flame-retardant properties of pulp foam materials were investigated. Solutions are proposed to address the problems of chemical pollution, incomplete foam degradation, complex preparation processes, limited functionality, and poor mechanical strength in the preparation of conventional cellulose-based foam cushioning materials. This results in the construction and structural control of green, sustainable, high-strength, flame-retardant, and waterproof high-performance paper-based foam cushioning materials.

[0084] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. Application of pulp foam cushioning materials in improving the waterproof performance of foam cushioning materials. The preparation method of the pulp foam cushioning material includes the following steps: 1) Mix and disperse the wax with the nanocellulose solution to obtain a nanocellulose / wax emulsion; 2) Mix and stir the pulp fibers with the flame retardant solution to obtain a pulp / flame retardant mixture; 3) Mix the nanocellulose / wax emulsion obtained in step 1) with the pulp / flame retardant mixture obtained in step 2), remove the liquid phase, and obtain wet pulp. 4) Dry the wet pulp obtained in step 3) to obtain a pulp foam cushioning material; The wax in step 1) is palm wax; The nanocellulose in the nanocellulose solution includes one or more of cellulose nanofibers and cellulose nanocrystals; In step 1), the mass percentage of wax in the nanocellulose / wax emulsion is 0.6%, and the mass percentage of nanocellulose is 0.6-1.8%. The conditions for the dispersion include: The rotation speed is 5000-8000 rpm, and the time is 3-8 minutes; In step 2), the pulp / flame retardant mixture contains 2% pulp fiber by mass and 0.5% flame retardant by mass. The stirring conditions include: a rotation speed of 600–1200 rpm and a stirring time of 5–10 min; The pulp fibers in step 2) include one or more of the following: bamboo pulp fiber, cotton stalk bark pulp fiber, spruce pulp fiber, Masson pine pulp fiber, red pine pulp fiber, larch pulp fiber, and fir pulp fiber; The flame retardant is phosphoric acid; The mixing conditions in step 3) include: pouring the nanocellulose / wax emulsion into the pulp / flame retardant mixture at a pouring speed of 20-50 mL / s; The volume ratio of the nanocellulose / wax emulsion to the pulp / flame retardant mixture is 1:2; The mixing speed is 600–1200 rpm; The method for removing the liquid phase in step 3) includes: placing the mixture obtained after mixing in a cylindrical porous mold until no liquid drips; the bottom and side walls of the cylindrical porous mold are perforated with a pore size of 100 mesh and a single pore spacing of <0.5 mm; The drying conditions in step 4) include: a temperature of 50–80°C and a time of 8–16 hours.

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