Degradable plastic with self-cleaning function and preparation method thereof

Abstract

The invention discloses degradable plastic with a self-cleaning function and a preparation method of the degradable plastic, belongs to the field of degradable plastic, and aims to solve the problems that the self-cleaning function is disjointed with recycling adaptability, an additional stripping process is needed for recycling an adhesive tape, and the degradable adhesive tape does not reflect the recycling additional value. Comprising a base material and a self-cleaning modifier, the base material is a degradable high polymer material, and the self-cleaning modifier is dispersed in the base material or loaded on the surface of the base material; the plastic can be dispersed and dissolved under the repulping process condition of carton recycling, and has self-cleaning performance. Degradation conditions of the plastic and the adhesive tape are completely matched with those of an existing hydraulic repulping process of a paper mill, core parameters such as temperature, pH and rotating speed do not need to be adjusted, equipment does not need to be additionally arranged in the whole recycling process, sorting, crushing, repulping and forming, and the problem that part of existing degradable materials need special recycling equipment is solved.

Description

Technical Field

[0001] This invention relates to the field of biodegradable plastics, and more particularly to a biodegradable plastic with self-cleaning function and a method for preparing the same. Background Technology

[0002] The demand for biodegradable materials in the packaging industry has increased significantly, especially in the field of adhesive tape substrates for cardboard packaging. Various biodegradable plastic systems have been developed, such as starch-based, cellulose-modified, and polyhydroxyalkanoate (PHA)-based systems. Some products achieve self-cleaning functions by adding nano-titanium dioxide and silicon-based superhydrophobic materials, reducing the adhesion of oil and dust to the tape surface during transportation and improving the cleanliness of the packaging appearance. Meanwhile, the cardboard recycling industry generally adopts a process of "sorting, crushing, hydraulic pulping, and pulp forming." Addressing the difficulty in degrading traditional non-biodegradable tapes, such as PVC-based and polypropylene-based tapes, the industry is also attempting to develop biodegradable tapes. For example, biodegradable tapes mainly rely on industrial composting for degradation, while water-soluble tapes require specific water temperatures to dissolve, attempting to reduce the interference of tapes on cardboard recycling.

[0003] Despite progress in biodegradable plastics and tapes, the following problems still exist: 1. The self-cleaning function is disconnected from the recyclability. Most self-cleaning biodegradable plastics only focus on the surface anti-fouling performance and do not consider the pulping process characteristics of cardboard recycling, such as mechanical shear force and mild water environment. This makes it difficult for some self-cleaning modifiers, such as highly crystalline nanoparticles, to disperse during pulping, resulting in residual particles that contaminate the pulp. 2. Tape recycling requires an additional stripping process. Even for biodegradable tape, existing products often need to be stripped manually or mechanically before the carton is crushed. This not only increases recycling time by 30%-40%, but may also cause residual tape to entangle the equipment during pulping due to incomplete stripping, affecting recycling efficiency. 3. Biodegradable tapes do not reflect the added value of recycling. Existing biodegradable tapes can only achieve "no pollution" after pulping. Their degradation products, such as small molecule polymers and modifiers, cannot work synergistically with pulp. In fact, due to the single composition, the mechanical properties of recycled pulp may decline, requiring the addition of pulp strengthening agents and increasing recycling costs. Summary of the Invention

[0004] To overcome the above problems, this invention aims to propose a self-cleaning biodegradable plastic and its preparation method, in order to solve the problems of the disconnect between self-cleaning function and recyclability, the need for additional stripping process for tape recycling, and the lack of added value in recycling biodegradable tape.

[0005] Therefore, the specific technical solution adopted by the present invention is as follows: According to one aspect of the present invention, a biodegradable plastic with self-cleaning function is provided, comprising a substrate and a self-cleaning modifier; the substrate is a biodegradable polymer material, and the self-cleaning modifier is dispersed in the substrate or loaded on the surface of the substrate; the plastic can be dispersed and dissolved under pulping process conditions for cardboard recycling and has self-cleaning properties.

[0006] Optionally, the substrate is a biodegradable polymer material selected from at least one of modified cellulose materials and bio-based polyester materials; the modified cellulose materials include at least one of hydroxyethyl cellulose derivatives, carboxymethyl cellulose derivatives, and blends of cellulose nanofibers and low molecular weight polylactic acid; the bio-based polyester materials include at least one of polyhydroxyalkanoates and thermoplastic starch.

[0007] Optionally, the self-cleaning modifier is selected from at least one of nano-photocatalytic materials and superhydrophobic materials; the nano-photocatalytic materials include at least one of nano-titanium dioxide, nano-zinc oxide, and nitrogen-doped titanium dioxide; the superhydrophobic materials include at least one of silicon-based organic polymers and fluorine-modified organosilicon resins.

[0008] Optionally, by mass percentage, the substrate accounts for 85%-98%, and the self-cleaning modifier accounts for 2%-15%; the pulping process conditions are: mechanical shear force 1000-3000 r / min, temperature 20-60℃, pH value 6-8, and processing time 10-30 min, and the mass residue rate of the plastic under these conditions is ≤5%.

[0009] A method for preparing a biodegradable plastic with self-cleaning function includes the following steps: S1. First, prepare the substrate precursor by mixing the biodegradable polymer material with the additives and stirring to disperse it into a uniform slurry. S2. Then introduce a self-cleaning modifier, add the self-cleaning modifier to the slurry obtained in S1, or coat it onto the substrate surface after subsequent film formation. S3. Finally, film formation and curing: The material treated in S2 is cast, dried and cured to obtain a biodegradable plastic with self-cleaning function.

[0010] Optionally, in S1, the additives include plasticizers and cosolvents; the plasticizer is selected from at least one of glycerol and triethyl citrate, accounting for 5%-20% of the total mass of the substrate precursor; the cosolvent is selected from at least one of polyethylene glycol and glycerol, accounting for 3%-10% of the total mass of the substrate precursor.

[0011] Optionally, in S1, the stirring and dispersion conditions are: temperature 40-60℃, stirring speed 500-1000r / min, stirring time 20-40min; and the solid content of the slurry is 15%-30%.

[0012] Optionally, in S2, if the self-cleaning modifier is added to the slurry, the amount added is 2%-12% of the total mass of the substrate precursor, and it is stirred and dispersed together with the slurry for 15-25 minutes; if it is coated on the surface of the substrate, the self-cleaning modifier needs to be mixed with the solvent first, and ultrasonically dispersed to form a dispersion with a concentration of 5%-15%, and the coating amount is 1-5 g / m².

[0013] Optionally, in S3, a release film is used as the carrier for casting, and the drying and curing conditions are: temperature 60-80℃, drying time 10-18h; the thickness of the resulting biodegradable plastic is 20-50μm.

[0014] Optionally, after S3, surface treatment is also included: corona treatment of the cured plastic surface with a treatment voltage of 10-20kV and a treatment time of 2-5s to improve surface adhesion.

[0015] Compared with the prior art, this application has the following beneficial effects: 1. The plastic of this invention uses modified cellulose / bio-based polyester as the base material, combined with a nano-photocatalytic / superhydrophobic self-cleaning modifier. The high dispersibility of the base material ensures that the residual mass rate is ≤5% within 25-30 minutes during the pulping process (1000-3000 r / min shear, 20-60℃, pH 6-8), as shown in the example where the residual rate is only 2.5%. Furthermore, the uniform dispersion of the self-cleaning modifier, through doping or coating, achieves a water contact angle of 102-105° on the plastic surface, resulting in residual contaminants ≤0.5 mg / cm² when droplets roll off, meeting the easy-to-clean standard of GB / T 30793-2014. Compared to existing biodegradable plastics that only focus on a single function, this invention does not sacrifice self-cleaning performance or recycling compatibility, truly achieving functional synergy.

[0016] 2. Eliminating the tape peeling process significantly improves cardboard box recycling efficiency and reduces recycling costs. Based on the plastic tape of this invention, the cardboard box can be crushed and pulped simultaneously during recycling, eliminating the need for any manual or mechanical peeling operations. As shown in the embodiments, the cardboard box recycling process using the tape of this invention improves the efficiency of the sorting and crushing stage by 40% compared to the traditional tape peeling process. It also avoids substrate loss during traditional tape peeling, which easily leads to cardboard fiber breakage, resulting in a loss rate of approximately 5%. Furthermore, it eliminates the downtime and cleaning problems caused by tape entanglement in the pulper. Traditional PVC tape requires a 10-15 minute downtime for rotor cleaning after each batch, a situation not present in this invention.

[0017] 3. The degradation products of the plastics and tapes of this invention, such as cellulose microfibers, chitosan small molecules, and nano-titanium dioxide, can be completely retained in the pulp after pulping. Through the synergistic effect of "hydrogen bonds (cellulose microfibers and pulp fibers) + ionic bonds (chitosan and negatively charged pulp fibers) + particle filler (nano-titanium dioxide)," the performance of recycled pulp is significantly improved. Example data shows that recycled paper containing the degradation products of the tapes of this invention has high tensile strength, improved burst strength, and improved folding endurance. No additional pulp reinforcing agent is needed. Compared to traditional recycled paper which requires 0.5%-1% polyacrylamide reinforcing agent, this results in lower costs per ton of pulp, reducing the production cost of recycled paper and enhancing product competitiveness.

[0018] 4. The degradation conditions of the plastics and tapes of this invention are fully compatible with the existing hydraulic pulping process in paper mills. There is no need to adjust core parameters such as temperature, pH, and rotation speed. Moreover, the entire recycling process (sorting, crushing, pulping, and molding) does not require any new equipment, which solves the problem that some existing biodegradable materials require special recycling equipment, such as composting and fermentation equipment for biodegradation. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0020] Example 1 According to an embodiment of the present invention, a biodegradable plastic with self-cleaning function is provided: comprising a substrate and a self-cleaning modifier; the substrate is a biodegradable polymer material, and the self-cleaning modifier is dispersed in the substrate or loaded on the surface of the substrate; the plastic can be dispersed and dissolved under the pulping process conditions of cardboard recycling and has self-cleaning properties.

[0021] The substrate is a biodegradable polymer material selected from at least one of modified cellulose materials and bio-based polyester materials; the modified cellulose materials include at least one of hydroxyethyl cellulose derivatives, carboxymethyl cellulose derivatives, and blends of cellulose nanofibers and low molecular weight polylactic acid; the bio-based polyester materials include at least one of polyhydroxyalkanoates and thermoplastic starch.

[0022] The self-cleaning modifier is selected from at least one of nano-photocatalytic materials and superhydrophobic materials; the nano-photocatalytic materials include at least one of nano-titanium dioxide, nano-zinc oxide, and nitrogen-doped titanium dioxide; the superhydrophobic materials include at least one of silicon-based organic polymers and fluorine-modified organosilicon resins.

[0023] The substrate accounts for 85%-98% by mass percentage, and the self-cleaning modifier accounts for 2%-15%; the pulping process conditions are: mechanical shear force 1000-3000 r / min, temperature 20-60℃, pH value 6-8, and processing time 10-30 min, and the mass residue rate of the plastic under these conditions is ≤5%.

[0024] A method for preparing a biodegradable plastic with self-cleaning function includes the following steps: S1. First, prepare the substrate precursor by mixing the biodegradable polymer material with the additives and stirring to disperse it into a uniform slurry. S2. Then introduce a self-cleaning modifier, add the self-cleaning modifier to the slurry obtained in S1, or coat it onto the substrate surface after subsequent film formation. S3. Finally, film formation and curing: The material treated in S2 is cast, dried and cured to obtain a biodegradable plastic with self-cleaning function.

[0025] The additives include plasticizers and cosolvents; the plasticizer is selected from at least one of glycerol and triethyl citrate, accounting for 5%-20% of the total mass of the substrate precursor; the cosolvent is selected from at least one of polyethylene glycol and glycerol, accounting for 3%-10% of the total mass of the substrate precursor.

[0026] In S1, the stirring and dispersion conditions are: temperature 40-60℃, stirring speed 500-1000r / min, and stirring time 20-40min; the solid content of the slurry is 15%-30%.

[0027] In S2, if the self-cleaning modifier is added to the slurry, the amount added is 2%-12% of the total mass of the substrate precursor, and it is stirred and dispersed together with the slurry for 15-25 minutes; if it is coated on the surface of the substrate, the self-cleaning modifier needs to be mixed with the solvent first, and ultrasonically dispersed to form a dispersion with a concentration of 5%-15%, and the coating amount is 1-5 g / m².

[0028] In S3, release film is used as the carrier for casting, and the drying and curing conditions are: temperature 60-80℃, drying time 10-18h; the thickness of the resulting biodegradable plastic is 20-50μm.

[0029] S3 is followed by surface treatment: corona treatment of the cured plastic surface with a voltage of 10-20kV and a treatment time of 2-5s to improve surface adhesion. Example 2 This embodiment is an example of preparing a self-cleaning biodegradable tape based on biodegradable plastic.

[0030] This embodiment uses the "self-cleaning biodegradable plastic" from Example 1 as the tape substrate (hereinafter referred to as "substrate") to prepare a biodegradable tape suitable for cardboard box packaging. The specific steps are as follows: Step 1: Prepare the necessary raw materials, including the substrate, biodegradable adhesive, and additives, as detailed below: Substrate: The biodegradable plastic film (30 μm thick) prepared in Example 1 is used. Its components are hydroxyethyl cellulose derivative (88 wt%), nano titanium dioxide (self-cleaning modifier, 7 wt%), and glycerol (plasticizer, 5 wt%). The water contact angle of this substrate is 105° (demonstrating superhydrophobic self-cleaning properties), and the mass residue rate is ≤3% within 30 min under the conditions of 2000 r / min shear, 50℃, and pH7. Biodegradable adhesive: Selected oxidized starch grafted acrylic adhesive (grafting rate 18%), its components are oxidized starch (50wt%), chitosan (3wt%, to enhance pulp binding force), rosin glycerol ester (12wt%, to improve adhesion), and deionized water (35wt%). Additives: Nano silica (thixotropic agent, added at 2% of the total mass of the adhesive), used to adjust the rheological properties of the adhesive coating; Step 2: Prepare the adhesive tape. The specific process is as follows: (a) Mix oxidized starch-grafted acrylic adhesive with nano-silica, stir at 800 r / min at room temperature for 10 min, and then degas at 400 W ultrasonic power for 5 min to obtain a uniform adhesive emulsion (solid content 32%).

[0031] (b) Remove dust from the surface of the substrate (surface tension ≥38mN / m) after corona treatment as described in claim 9 to ensure that there are no impurities on the surface of the substrate and to avoid affecting the adhesion of the adhesive.

[0032] (c) Use a micro-gravure coating machine to evenly coat the adhesive emulsion onto the non-self-cleaning surface of the substrate (the self-cleaning surface is the outer surface of the tape, used for anti-fouling), and control the dry adhesive coating amount to 40g / m². Immediately after coating, enter the hot air drying tunnel and set the drying conditions as follows: temperature 90℃, wind speed 3m / s, drying time 2min, to ensure that the adhesive is completely cured and does not damage the biodegradability of the substrate.

[0033] (d) The cured substrate-adhesive composite film is wound up at a speed of 5m / min to avoid excessive tension that could cause the substrate to break; then, according to the carton packaging requirements, it is cut into finished tapes with a width of 48mm and a length of 100m / roll (hereinafter referred to as "target tape").

[0034] Example 3 This embodiment tests the target adhesive tape prepared in Example 2. The test items include self-cleaning performance, adhesive properties, and pulp compatibility; details are as follows: Self-cleaning performance: When 10 μL of a 1% carbon black aqueous solution is dropped onto the outer surface of the tape (self-cleaning surface), with a water contact angle of 102° and an inclination of 30°, the droplet can completely roll off, and the residual carbon black content is ≤0.5 mg / cm² (meets the "easy-to-clean" level in GB / T30793-2014 "Determination of Stain Resistance of Paints and Varnishes"). Adhesive properties: Initial tack strength tested according to GB / T 4852-2002, steel ball number reaches 12# (higher than the 10# standard of ordinary sealing tape on the market); holding tack strength tested according to GB / T 4851-2014, holding time ≥36h under 25℃ and 1kg load; 180° peel strength tested according to GB / T 2792-2014, peel force with corrugated cardboard linerboard is 1.8N / 25mm (meeting the "no glue peeling" requirement for carton sealing); Pulping compatibility: A 10cm×10cm sample of the target tape was attached to the surface of a corrugated cardboard box (the tape area accounted for 8% of the box surface area). The test simulated recycling conditions. The results showed that in a pulping environment of 2000r / min shear, 50℃, and pH7, the tape was completely dispersed and dissolved within 25 minutes, with no visible particles and a mass residue rate of 2.8%.

[0035] Example 4 This embodiment uses "corrugated cardboard boxes + target adhesive tape prepared in Example 2" as the recycling target. Based on conventional paper mill pulp recycling processes, no additional tape peeling step is required. The specific process is as follows: The first step is to transport the used sealed cardboard boxes (with the target tape attached to the surface, free of oil, metal nails and other impurities) to the recycling and sorting line via a conveyor belt. Only non-paper impurities (such as plastic film, foam, etc.) are removed, and no tape peeling is performed (eliminating the manual / mechanical tape peeling process in traditional recycling, increasing efficiency by 40%).

[0036] The second step is to send the sorted cartons into a twin-shaft shredder, set the shredding gap to 5mm, and shred them into paper blocks with a side length of 5-10cm (the tape is shredded simultaneously with the cartons, and there is no tape falling off or accumulating), which facilitates the subsequent dispersion of pulp.

[0037] The third step is to put the shredded paper (including tape) into a horizontal hydraulic pulper, add 50°C deionized water (pH adjusted to 7.2) at a mass ratio of "paper:water = 1:8", set the pulper speed to 2200 r / min, and turn on the shearing and stirring. Step 4: After stirring for 5 minutes, take a sample for observation: The tape substrate begins to swell and disperse, and the self-cleaning modifier (nano titanium dioxide) disperses into the slurry along with the substrate; After stirring for 20 minutes, take another sample: The adhesive of the tape is completely dissolved (the oxidized starch grafted gum is initially decomposed into small molecule sugars by microorganisms in the water), the substrate is decomposed into cellulose microfibers, and there are no solid particles with a diameter > 0.1 mm in the slurry; After stirring for 25 minutes, stop pulping and test the tape residue rate in the slurry to be 2.5% (meeting the ≤5% standard of claim 4).

[0038] Step 5: Filter the pulp after pulping through a 100-mesh sieve (to remove any possible residual fine impurities), and then send it to a deslagging device (3000 r / min) to further separate light impurities; at this time, the tape degradation products (cellulose microfibers, nano titanium dioxide, chitosan small molecules) are completely retained in the pulp without separation loss.

[0039] Step 6: The purified pulp was processed using conventional papermaking technology (on-grid concentration 0.8%, press pressure 0.3 MPa, drying temperature 110℃) to produce 80 g / m² recycled paper sheets. The paper sheet properties were tested, and the results are as follows: Tensile strength: 4.2 kN / m (18% higher than pure recycled pulp without tape degradation products); Bursting strength: (12% higher than pure recycled pulp); Folding endurance: 18 times (transverse, 15% higher than pure recycled pulp); The aforementioned performance improvement stems from the following components in the tape degradation products: cellulose microfibers form hydrogen bonds with pulp fibers, chitosan molecules form ionic bonds with pulp fibers (which are negatively charged), and nano-titanium dioxide fills the gaps between pulp fibers, synergistically enhancing the mechanical properties of the paper.

[0040] Step 7: Compatibility verification of the recycling process, as detailed below: Ten consecutive batches of recycling tests were conducted on "cardboard boxes + target tape," and the results showed: The pulper does not experience tape tangling or clogging (traditional PVC tape is prone to tangling around the rotor, requiring the machine to be stopped for cleaning after each batch, but this tape does not have this problem). The recycled paper has no obvious color difference or impurities (the self-cleaning modifier nano titanium dioxide is evenly dispersed and does not affect the appearance of the paper). The entire recycling process requires no new equipment and is fully compatible with existing paper mills' horizontal pulpers and screening and slag removal systems, demonstrating high process adaptability.

[0041] Although the present invention has been disclosed above with reference to preferred embodiments, the embodiments are merely examples for illustrative purposes and are not intended to limit the present invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. The scope of protection claimed by the present invention should be determined by the claims.

Claims

1. A biodegradable plastic with self-cleaning function, characterized in that, It includes a substrate and a self-cleaning modifier; the substrate is a biodegradable polymer material, and the self-cleaning modifier is dispersed in the substrate or loaded on the surface of the substrate; the plastic can be dispersed and dissolved under the pulping process conditions of cardboard recycling and has self-cleaning properties; The substrate comprises 85%-98% by weight, and the self-cleaning modifier comprises 2%-15%; the pulping process conditions are: mechanical shear force 1000-3000 r / min, temperature 20-60℃, pH value 6-8, and processing time 10-30 min, and the residual mass of the plastic under these conditions is ≤5%; The method for preparing this self-cleaning biodegradable plastic includes the following steps: S1. First, prepare the substrate precursor by mixing the biodegradable polymer material with the additives and stirring to disperse it into a uniform slurry. S2. Then introduce a self-cleaning modifier, add the self-cleaning modifier to the slurry obtained in S1, or coat it onto the substrate surface after subsequent film formation. S3. Finally, film formation and curing: The material treated in S2 is cast, dried and cured to obtain a biodegradable plastic with self-cleaning function.

2. The biodegradable plastic with self-cleaning function according to claim 1, characterized in that, The substrate is a biodegradable polymer material selected from at least one of modified cellulose materials and bio-based polyester materials; the modified cellulose materials include at least one of hydroxyethyl cellulose derivatives, carboxymethyl cellulose derivatives, and blends of cellulose nanofibers and low molecular weight polylactic acid; the bio-based polyester materials include at least one of polyhydroxyalkanoates and thermoplastic starch.

3. The biodegradable plastic with self-cleaning function according to claim 1, characterized in that, The self-cleaning modifier is selected from at least one of nano-photocatalytic materials and superhydrophobic materials; the nano-photocatalytic materials include at least one of nano-titanium dioxide, nano-zinc oxide, and nitrogen-doped titanium dioxide; the superhydrophobic materials include at least one of silicon-based organic polymers and fluorine-modified organosilicon resins.

4. A biodegradable plastic with self-cleaning function according to claim 1, characterized in that, In S1, the additives include plasticizers and cosolvents; the plasticizer is selected from at least one of glycerol and triethyl citrate, accounting for 5%-20% of the total mass of the substrate precursor; the cosolvent is selected from at least one of polyethylene glycol and glycerol, accounting for 3%-10% of the total mass of the substrate precursor.

5. A biodegradable plastic with self-cleaning function according to claim 1, characterized in that, In S1, the stirring and dispersion conditions are: temperature 40-60℃, stirring speed 500-1000r / min, and stirring time 20-40min; the solid content of the slurry is 15%-30%.

6. A biodegradable plastic with self-cleaning function according to claim 1, characterized in that, In S2, if the self-cleaning modifier is added to the slurry, the amount added is 2%-12% of the total mass of the substrate precursor, and it is stirred and dispersed together with the slurry for 15-25 minutes; if it is coated on the surface of the substrate, the self-cleaning modifier needs to be mixed with the solvent first, and ultrasonically dispersed to form a dispersion with a concentration of 5%-15%, and the coating amount is 1-5 g / m².

7. A biodegradable plastic with self-cleaning function according to claim 1, characterized in that, In S3, release film is used as the carrier for casting, and the drying and curing conditions are: temperature 60-80℃, drying time 10-18h; the thickness of the resulting biodegradable plastic is 20-50μm.

8. A biodegradable plastic with self-cleaning function according to claim 1, characterized in that, S3 is followed by surface treatment: corona treatment of the cured plastic surface with a treatment voltage of 10-20kV and a treatment time of 2-5s to improve surface adhesion.