A method for preparing paper pulp molded products using waste wet-process fiberboard and use thereof

Abstract

The application discloses a method for preparing paper pulp molded products by using waste wet fiber boards and application thereof, and belongs to the technical field of plant fiber solid waste resource utilization and paper pulp molding. The method comprises the following steps: sequentially performing raw material crushing pretreatment, low-temperature and low-pressure hot water pre-hydrolysis-mild mechanical dissociation, multi-stage screening and purification, fiber refining and sizing, vacuum suction filtration forming and hot-pressing drying treatment. The urea-formaldehyde resin in the fiber board is hydrolyzed and becomes brittle in a wet heat environment, and the fiber is dissociated under low shear conditions, so that the fiber length is maximally reserved and the resin agglomerated impurities are removed; then, the functional additives are matched to prepare a molding pulp, and finally, the paper pulp molded products are prepared. The process flow is mild, a strong acid or alkali system is not needed, and the wastewater treatment pressure is small; the regenerated fiber can replace part of commercial waste paper pulp, realizes high-value cyclic utilization of the waste fiber boards, and the mechanical strength and water resistance of the prepared paper pulp molded products meet the use requirements of electronic inner liners, fruit and vegetable supports and industrial cushion packaging, so that the paper pulp molded products have good industrialization popularization prospects.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource recycling technology and pulp molding manufacturing technology. Background Technology

[0002] Wet-process fiberboard is a type of engineered wood product made from wood fibers as raw materials, with the addition of urea-formaldehyde resin adhesive, through a wet-process molding and hot-press curing process. Large quantities of waste wet-process fiberboard that have reached their service life or are generated during processing are often disposed of through landfill or incineration. Landfilling occupies land, and residual formaldehyde in the boards is slowly released, polluting the soil and water sources; incineration produces waste gas, resulting in extremely low resource utilization.

[0003] Existing waste fiberboard recycling processes have significant shortcomings: direct hydraulic pulping cannot remove the cured urea-formaldehyde resin, resulting in a large amount of gum adhering to the fiber surface; the prepared pulp has poor water filtration performance, and the molded products have severe water absorption and insufficient strength, mostly only suitable for the production of low-end fiberboard with low added value. If a high-temperature, strong acid system is used to hydrolyze the resin, the fibers will degrade drastically, the fiber length will decrease significantly, the quality of the recycled fibers will deteriorate, and the cost of acidic wastewater treatment will be high.

[0004] Pulp molding products are environmentally friendly and biodegradable packaging materials. Currently, the main raw materials are waste paper pulp from corrugated board, bagasse pulp, and virgin wood pulp, and raw material prices continue to rise. The industry urgently needs to develop low-cost recycled fiber raw materials and expand high-value utilization pathways for solid waste. Currently, there is no mature process to stably convert waste wet-process fiberboard into qualified pulp molding raw materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing waste wet fiberboard recycling technologies, such as large fiber damage, poor resin removal effect, and difficulty in using recycled fibers for pulp molding. It provides a mild hydrolysis process that decomposes urea-formaldehyde resin while protecting fiber length. After purification and pulp conditioning, pulp molded packaging products can be directly produced, realizing high-value recycling of solid waste.

[0006] The technical solution adopted by the present invention to achieve the above objectives is: a method for preparing pulp molded products using waste wet-process fiberboard, comprising the following steps: S1. Raw material pretreatment: Sorting waste wet fiberboard, removing impurities such as plastic, metal and sand, and crushing to obtain fiberboard fragments with a particle size of 20-80mm. S2. Resin hydrolysis and gentle fiber dissociation: Fiberboard fragments are put into a hydrolysis and dissociation tank, and the water-solid mass ratio is controlled at 4:1 to 7:1. The temperature is 95 to 120℃ and the pressure is 0 to 0.2MPa. The mixture is kept at this temperature for 25 to 60 minutes to hydrolyze and embrittle the urea-formaldehyde resin that has been cured inside the board. Then it is sent to a hydraulic pulper for low-shear dissociation to obtain coarse fiber suspension pulp. S3. Multi-stage purification and screening: The coarse fiber suspension pulp is screened sequentially to obtain purified and regenerated fiber pulp; S4. Fine grinding and pulp preparation: The purified recycled fiber pulp is fed into a disc mill for light fine grinding, and the pulp freeness is adjusted to 22-38°SR; functional additives are added to the pulp and mixed evenly to obtain pulp molding pulp. S5. Vacuum forming and hot pressing: The forming slurry is diluted to a mass concentration of 0.6% to 1.8%, and a wet fiber preform is obtained by vacuum filtration under negative pressure; the wet preform is transferred to a hot pressing mold for pre-pressing and dehydration to a moisture content of 20-25%; S6. Post-drying treatment: After hot pressing, the wet blank is dried with hot air to a moisture content of 6% to 10%, and the edges are trimmed to obtain pulp molded products.

[0007] In step S2, the pH of the hydrolysis system is controlled to be 4.5–7.0; organic acid (formic acid) is selectively added to promote resin hydrolysis. The amount of organic acid added is 0.1%–0.5% of the oven-dry fiber mass, and the organic acid is formic acid.

[0008] In step 3, the coarse fiber suspension is sequentially passed through a 1.6mm round-hole coarse screen, a hydrocyclone sand separator, and a 0.6-0.9mm slotted pressure fine screen to separate resin residue and inorganic ash, thereby obtaining purified and regenerated fiber pulp. The functional additives mentioned in step S4, calculated based on the weight of oven-dried regenerated fibers, are: cationic starch 1.5%–4%, waterproof sizing agent 0.8%–2.5%, and fiber dispersant 0.1%–0.3%.

[0009] In step S5, the vacuum suction filtration negative pressure is controlled at -0.04 to -0.08 MPa; the hot pressing temperature is 130 to 180°C; the hot pressing pressure is 0.3 to 1.2 MPa; and the holding time is 30 to 120 seconds.

[0010] In step 4, the purified recycled fiber pulp can be mixed with one or two of waste paper pulp and bamboo pulp, and the recycled fiber accounts for 0 to 50% of the oven-dry weight of the mixed pulp.

[0011] The pulp molded products prepared according to the above method are used as industrial cushioning packaging liners, electronic product protective paper trays, or fruit and vegetable preservation trays.

[0012] The present invention has the following beneficial effects: 1. It adopts a low-temperature and low-pressure hot water pre-hydrolysis system, without using concentrated strong acids and alkalis, which gently destroys the urea-formaldehyde resin adhesive layer, reduces the degradation of wood fibers, effectively preserves the fiber length, and results in higher quality regenerated fibers. 2. Low-shear hydraulic dissociation combined with multi-stage screening efficiently removes resin agglomerates and inorganic impurities, solving the defects of poor slurry filtration and easy water absorption of products; 3. The entire process can be implemented by modifying existing pulp molding production lines without the need for new large-scale special equipment, resulting in low industrialization investment; 4. Waste wet-process fiberboard is recycled as solid waste, replacing part of the commercial pulp, reducing the cost of packaging raw materials, and reducing the environmental pressure caused by solid waste incineration and landfill. 5. The resulting pulp molded products meet the standards for general biodegradable packaging in terms of mechanical strength and water resistance, and have a wide range of applications. Attached Figure Description Figure 1 This is a flowchart illustrating the overall process flow of an embodiment of the present invention.

[0013] Process flow: Waste wet-process fiberboard → impurity removal and crushing → hot water pre-hydrolysis → low-speed hydraulic pulping → multi-stage sand removal and screening → disc mill fine grinding → additive preparation of slurry → vacuum suction filtration molding → hot pressing dewatering → hot air drying → finished product finishing. Detailed Implementation

[0014] Example 1: A method for preparing pulp molded products using waste wet-process fiberboard, comprising the following steps: S1: Waste wet-process hardboard is manually sorted to remove impurities and crushed to obtain 30-60mm boards; S2: Water-to-solid ratio 5:1, hydrolysis temperature 105℃, pressure 0.12MPa, heat treatment for 40min; followed by low-speed dissociation in a hydraulic pulper; S3: The resin residue and silt are removed by passing through a 1.6mm round hole coarse screen, a hydrocyclone sand remover, and a 0.6-0.9mm gap pressure fine screen in sequence. S4: Lightly grind with a disc mill, adjust the percussion degree to 30°SR; add 2.5% cationic starch, 1.2% AKD waterproofing agent, and 0.15% polyethylene oxide dispersant by weight of oven-dry fiber, and stir thoroughly; S5: The slurry is diluted to a concentration of 1.0%, and vacuum filtered and formed at -0.06MPa; the wet blank is dehydrated by hot pressing at 150℃ and 0.6MPa for 60s. S6: Dry with hot air at 120℃ to a moisture content of 8%, trim the edges, and obtain pulp molded cushioning packaging.

[0015] Finished product inspection: The product has a uniform structure, excellent static bending strength, and a water absorption rate of less than 18%, making it suitable for inner packaging of electronic products.

[0016] Example 2: The process steps are the same as in Example 1, except that: the recycled fiber pulp and the waste paper pulp of the boxboard are mixed at a ratio of 3:7 by oven-dry weight; composite fiber pulp molded fruit and vegetable trays are prepared, and the impact resistance is further improved.

[0017] Comparative example: The raw materials were not pre-hydrolyzed with hot water, but were directly crushed and pulped. The remaining parameters for pulping, molding, and drying were the same as in Example 1.

[0018] Results: The slurry contained a large number of urea-formaldehyde resin particles, resulting in slow water filtration. The water absorption rate of the molded products increased significantly, and the strength decreased by 35%, failing to meet the requirements for packaging.

[0019] This invention has been described through embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this invention.

Claims

1. A method for preparing pulp molded products using waste wet-process fiberboard, characterized in that: Includes the following steps: S1. Raw material pretreatment: Sorting waste wet fiberboard, removing impurities, and crushing to obtain fiberboard fragments with a particle size of 20-80mm. S2. Resin hydrolysis and gentle fiber dissociation: Fiberboard fragments are put into a hydrolysis and dissociation tank, and the water-solid mass ratio is controlled at 4:1 to 7:

1. The temperature is 95 to 120℃ and the pressure is 0 to 0.2MPa. The mixture is kept at this temperature for 25 to 60 minutes to hydrolyze and embrittle the urea-formaldehyde resin that has been cured inside the board. Then it is sent to a hydraulic pulper for low-shear dissociation to obtain coarse fiber suspension pulp. S3. Multi-stage purification and screening: The coarse fiber suspension pulp is screened sequentially to obtain purified and regenerated fiber pulp; S4. Fine grinding and pulp preparation: The purified recycled fiber pulp is fed into a disc mill for light fine grinding. The pulp freeness is adjusted to 22-38°SR. Functional additives are added to the pulp and mixed evenly to obtain pulp molding pulp. S5. Vacuum forming and hot pressing: The forming slurry is diluted to a mass concentration of 0.6% to 1.8%, and the fiber wet preform is obtained by vacuum suction forming under negative pressure. The wet preform is then transferred to a hot pressing mold for pre-pressing and dehydration. S6. Post-drying treatment: The wet blank after hot pressing is dried with hot air to a moisture content of 6% to 10%, and then trimmed to obtain pulp molded products.

2. The method for preparing pulp molded products using waste wet-process fiberboard according to claim 1, characterized in that: The pH of the hydrolysis system in step S2 is controlled at 4.5 to 7.0; organic acids are selectively added to promote resin hydrolysis, and the amount of organic acid added is 0.1% to 0.5% of the oven-dry fiber mass, wherein the organic acid is formic acid.

3. The method for preparing pulp molded products using waste wet-process fiberboard according to claim 1, characterized in that: In step 3, the coarse fiber suspension pulp is passed sequentially through a 1.6mm round hole coarse screen, a hydrocyclone sand separator, and a 0.6-0.9mm gap pressure fine screen to separate resin residue and inorganic ash residue, thereby obtaining purified and regenerated fiber pulp.

4. The method for preparing pulp molded products using waste wet-process fiberboard according to claim 1, characterized in that: In step S4, the functional additives, calculated based on the weight of oven-dried recycled fibers, include: 1.5%–4% cationic starch, 0.8%–2.5% waterproof sizing agent, and 0.1%–0.3% fiber dispersant.

5. The method for preparing pulp molded products using waste wet-process fiberboard according to claim 1, characterized in that: In step S5, the vacuum suction negative pressure is -0.04 to -0.08 MPa; the hot pressing temperature is 130 to 180°C; the hot pressing pressure is 0.3 to 1.2 MPa; and the holding time is 30 to 120 seconds.

6. The method for preparing pulp molded products using waste wet-process fiberboard according to claim 1, characterized in that: In step 4, the purified recycled fiber pulp is mixed with one or two of waste paper pulp and bamboo pulp, and the recycled fiber accounts for 0 to 50% of the oven-dry weight of the mixed pulp.

7. The pulp molded articles prepared by the method according to any one of claims 1 to 6 are used for industrial cushioning packaging liners, electronic product protective paper trays, or fruit and vegetable preservation trays.

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