Preparation method and application of film formed by coffee grounds and waste paper

Abstract

The invention relates to the technical field of high-valued utilization and processing of waste wood fiber raw material coffee grounds, in particular to a preparation method and application of a coffee grounds and waste paper film. Coffee grounds and waste paper are used as main raw materials and pretreated, then a cellulose dissolving agent is added, and a film is prepared; stirring at a certain temperature after freezing, centrifuging to obtain a mixed dissolving solution, cleaning after solidification, performing suction filtration to form a film, and drying to obtain the coffee residue regenerated composite film. The coffee residue film prepared by the method disclosed by the invention has excellent biodegradability, ultraviolet resistance and certain aromaticity, can be reprocessed into other products, and can be used as a high-value utilization method for treating coffee residues and waste paper wastes. In addition, the compounding of the coffee grounds and the cellulose is further proved to improve the strength, biodegradability, ultraviolet resistance, water absorption and other properties of the raw materials.

Description

Technical Field

[0001] The present invention relates to the technical field of high-value utilization processing of waste lignocellulosic raw material coffee grounds, and particularly relates to a preparation method and application of a coffee grounds and waste paper film-forming material. Background Art

[0002] Coffee is an aromatic beverage consumed by millions of people and is also one of the most traded commodities in the world. According to the latest statistical data of the International Coffee Organization, compared with the 2020 / 21 season, global coffee consumption increased by 3.3% in the 2021 / 22 season, reaching 170.3 million 60-kilogram bags (ICO, 2023). Coffee grounds are the main solid residue produced when brewing coffee. It is estimated that 650 kg of SCG (solid coffee grounds) are produced per ton of coffee beans, and 2 kg of wet residue are produced per kg of soluble coffee (Murthy & Madhava Naidu, 2012).

[0003] It is worth noting that at the present stage, coffee grounds are mainly treated by physical burial, but this also brings a series of problems. On the one hand, coffee grounds are prone to absorbing moisture in the air, have good water retention, and contain rich nutrients such as polysaccharides and minerals, making coffee grounds prone to breeding bacteria and molds during daily storage and treatment. In addition, coffee grounds contain substances such as polyphenols and caffeine, which are toxic to the life cycles of many organisms. On the other hand, coffee grounds consume a large amount of oxygen during the decomposition process and produce a large amount of carbon dioxide. The continuous discharge of coffee grounds into the environment due to the sharp increase in coffee consumption will lead to the intensification of the greenhouse effect. Coffee grounds are a potential biological resource, so the reasonable and harmless treatment of coffee grounds has become an issue that cannot be ignored.

[0004] The components of coffee grounds themselves are complex. When using them as a filler to compound with common materials, it is often necessary to modify the coffee grounds or add modifiers to improve the interfacial compatibility of these substances. On the one hand, such treatment requires higher costs. On the other hand, this interfacial compatibility problem often leads to a decline in the physical properties of the composite material and a dark brown appearance, greatly limiting the use scenarios of coffee grounds composite materials and being unfavorable for the large-scale high-value utilization of coffee grounds.

[0005] Some studies have shown that dissolving and regenerating the fibers in coffee grounds can be a way to treat coffee grounds. However, due to the high content of hemicellulose with low polymerization degree and the low content of cellulose with high polymerization degree in the components of coffee grounds, the physical properties of the packaging film after solvent dissolution and regeneration using coffee grounds as the sole raw material are poor.

[0006] Chinese Patent CN115232339B, "Method for Preparing Composite Film with High Strength and High UV Shielding Ability from Coffee Grounds and Pulp Fibers"; CN112064413B, "Paper Containing Coffee Grounds and Preparation Method Thereof". The processes for film-making from coffee grounds and related materials disclosed in the aforementioned patents mainly involve simply compounding coffee grounds and other materials as a filler with polymer materials. Such treatment is troubled by the interfacial compatibility problems existing when coffee grounds are compounded with other materials, resulting in a decline in physical and chemical properties, specifically manifested as a decrease in raw material strength, biodegradability, UV resistance, and water absorption. At the same time, the method of using hot N-methylmorpholine-N-oxide (NMMO) to dissolve the mixed fibers to prepare the composite film in the aforementioned patents has disadvantages such as high solvent preparation cost, instability at high temperatures, difficulty in recycling, and high operating costs for maintaining high temperatures. In addition, the prior art usually only mechanically crushes the fiber materials during the pretreatment. The length of the crushed fibers is relatively long, making them difficult to dissolve under stirring, with a long dissolution time and low solubility. In subsequent processing, problems such as entanglement with each other will also occur, resulting in a series of problems such as wrapping the slag material and being unable to dissolve.

[0007] At present, the matrix materials for preparing films in the industry mostly originate from petroleum-based materials, which are difficult to degrade and do not meet the overall requirements of the country for environmental protection and sustainable development. As a by-product of the coffee industry, coffee grounds have a huge output and are difficult to handle. Moreover, as a lignocellulosic raw material, they have the potential for further utilization. Therefore, it is necessary to study a method for preparing a high-strength composite film from coffee grounds and waste paper fibers to achieve the high-value utilization of waste coffee grounds. Summary of the Invention

[0008] One of the objectives of the present invention is to provide a preparation method for forming a film from coffee grounds and waste paper, which has a simple preparation method, is easy to adjust, and the prepared composite film has excellent biodegradability, UV resistance, and certain aromaticity.

[0009] Another objective of the present invention is to provide an application of the coffee grounds regenerated composite film.

[0010] The solution adopted by the present invention to achieve the first objective is: a preparation method for forming a film from coffee grounds and waste paper, using coffee grounds and waste paper as the main raw materials, pretreating them, then adding a cellulose solvent, stirring and centrifuging at a certain temperature to obtain a mixed solution, coagulating, washing, filtering, and forming a film, and drying to obtain the coffee grounds regenerated composite film.

[0011] By coagulating after dissolving the cellulose, the problem of interfacial compatibility is solved.

[0012] Preferably, the steps are as follows:

[0013] S1: Use coffee grounds and waste paper as the main raw materials and pre-treat them;

[0014] S2: Prepare a mixed solution of water and alkali as a cellulose solvent;

[0015] S3: Mix the coffee grounds and waste paper after pre-treatment in step S1 according to a mass ratio;

[0016] S4: Mix the mixed raw materials in step S3 with the cellulose solvent prepared in step S2, and stir at a certain temperature to obtain a mixed solution;

[0017] S5: Centrifuge and defoam the mixed solution in step S4 to obtain a viscous fully treated solution;

[0018] S6: Pour the fully treated solution in step S5 into a coagulation bath, and at the same time quickly stir to precipitate the viscous liquid. Remove the supernatant and repeat until it is washed to neutral to obtain regenerated cellulose;

[0019] S7: Filter the regenerated cellulose in step S6 into a film, dry it and seal it for standby to obtain a coffee grounds regenerated composite film.

[0020] Preferably, in step S1, the steps of pre-treating coffee grounds are specifically: mechanically crush and fully grind coffee grounds, and screen them so that the particle sizes of the two are between 0-200 μm, and dry the above materials at 60-70 °C until completely dried. Perform mechanical crushing treatment to break the cell walls of coffee grounds, and screen to increase the solubility of its particles in the solvent.

[0021] Preferably, in step S1, the steps of pre-treating waste paper are specifically: mechanically crush waste paper and then perform ultrasonic crushing, filter long fibers, and dry short fibers at 60-70 °C until completely dried. Perform mechanical crushing treatment and ultrasonic crushing to greatly shorten the length of waste paper fibers and increase their solubility in the solvent. The proposed method of further crushing with an ultrasonic cell disrupter can break the fibers so that their length is within 5 mm.

[0022] Compared with the long fibers produced by mechanical crushing in the prior art, they are easier to dissolve, the dissolution time is low, and the film-making efficiency and raw material utilization rate are increased. Therefore, this new material is very suitable for application in the field of high-value utilization and processing of waste lignocellulosic raw materials such as coffee grounds.

[0023] In the prior art, the pretreatment of fibers is usually only mechanical crushing. The length of the crushed fibers is relatively long, making it difficult to dissolve under stirring, with a long dissolution time and low solubility. In subsequent processing, problems such as entanglement will also occur, resulting in a series of issues such as wrapped slag and inability to dissolve. In the present invention, after mechanical crushing, an ultrasonic cell disruptor is used for further crushing. The length of the crushed fibers is within 5 mm, which is more easily dissolved compared to long fibers, with a lower dissolution time and increased film-making efficiency.

[0024] Preferably, in step S2, the cellulose solvent comprises the following raw materials: 4 wt% - 10 wt% NaOH, 9 wt% - 15 wt% urea, and 78 wt% - 84 wt% water.

[0025] Preferably, in step S3, the mass ratio of coffee grounds to waste paper is 1 - 5:1.

[0026] Preferably, in step S4, the mixing mass ratio of the mixed raw materials to the cellulose solvent is 0.1 - 1.0:99 - 99.9.

[0027] In the step S3: in the mixed raw materials of coffee grounds and waste paper, the mass ratio of the two is any one of (5:1), (4:1), (3:1), (2:1), (1:1);

[0028] In the step S4: the mixing mass ratio of the mixed raw materials to the water / alkali solution is any one of (0.6%:99.4%), (0.5%:99.5%), (0.4%:99.6%), (0.3%:99.7%), or (0.2%:99.8%);

[0029] Preferably, in step S4, the freezing temperature is -10 to -20 °C; the stirring temperature is below 25 °C, and the stirring rate is 100 - 2500 rpm; stir until the material is completely dissolved to form a viscous transparent liquid.

[0030] Preferably, in step S5, the centrifugal defoaming rate is 3800 - 4000 rpm, the time is 10 - 12 min, and the temperature is 5 - 7 °C.

[0031] Preferably, in step S6, pure water is selected as the coagulating liquid for the coagulation bath.

[0032] The solution adopted by the present invention to achieve the second object is: an application of a coffee grounds recycled composite film, the coffee grounds recycled composite film is prepared by the described preparation method, and the coffee grounds recycled composite film is applied to the fields of environmental protection product packaging, anti-ultraviolet decoration, aromatic fabric processing, or agricultural scientific research.

[0033] The recycled composite film is used as a raw material for any of the following aspects: environmental protection product packaging, anti-ultraviolet decorative fabric, aromatic cloth raw material, degradable germination bag or degradable seedling-raising bag.

[0034] During the research process of the present invention, the following improvements were obtained through relevant experiments:

[0035] 1. Regarding the preliminary treatment of the slag. It is proposed to treat the slag by grinding and sieving, which can make the particle size of the slag <200 μm, increasing the contact area between the slag and the solvent and facilitating the increase of its solubility.

[0036] 2. Regarding the preliminary treatment of waste paper. The fibers of waste paper are still relatively long after mechanical crushing, with low solubility in subsequent treatment. Moreover, due to the too long fiber length, problems such as entanglement will occur in subsequent treatment, resulting in a series of problems such as wrapping the slag and being unable to dissolve. It is innovatively proposed to further treat the fibers by ultrasonic crushing, which can greatly shorten the length of waste paper fibers, solve the above problems, and thus improve the utilization rate of waste paper and slag.

[0037] 3. Regarding the dissolution of raw materials. Through literature search, it can be found that existing dissolution systems such as lithium chloride / N,N-dimethylacetamide (LiCl / DMAc) system, N-methylmorpholine-N-oxide (NMMO) system, ionic liquid system, etc. have disadvantages such as high solvent preparation cost, instability at high temperature, difficult recovery, and high operating cost for maintaining high temperature. The method of the present invention for dissolving the mixed material fibers with urea / sodium hydroxide / aqueous solution at about -10°C to prepare the coffee residue film has advantages such as low solvent preparation cost, no need for heating, no volatile substances generated during the process, low difficulty in waste liquid recovery, recyclability of urea, economy and environmental protection, and can dissolve both lignocellulose and surface cellulose with high crystallinity without generating cellulose derivatives, providing a simple, efficient, green and low-cost method for cellulose dissolution, indicating that the alkali / urea dissolution system has the potential for large-scale industrial production of regenerated cellulose materials.

[0038] 4. Regarding the ratio of raw materials. Through literature search, it can be found that the sodium hydroxide / urea aqueous solution system usually has a relatively high solubility at 4 wt% cellulose. However, due to the non-pure cellulose composition of the experimental materials, through different ratio experiments, it is innovatively proposed that the film-forming success rate is relatively high after dissolving the raw materials at 0.1 wt% - 1 wt%, solving the problem of the raw material ratio in the film-forming process. And in subsequent experiments, it is innovatively proposed that the film made at 0.2 wt% is optimal in terms of biodegradability and antioxidant ability, the film made at 0.6 wt% is optimal in terms of water absorption, anti-ultraviolet ability and visible light shading ability, and it is confirmed that the compounding of coffee residue cellulose can improve the properties such as raw material strength, biodegradability, anti-ultraviolet and water absorption.

[0039] Combined with the above research results, the technical solution of the present invention is as follows:

[0040] In a first aspect, the present invention provides a preparation method for forming a film from coffee grounds and waste paper. The steps of the method are as follows:

[0041] S1: Grind the coffee grounds, sieve to make the particle size < 200 μm, and dry the above materials at 60 - 70 °C for 24 h until completely dried. Crush the waste paper with a high-speed crusher and further crush the waste paper with an ultrasonic cell crusher, and dry the above materials at 60 - 70 °C for 24 h until completely dried; after mechanical crushing, further crush with an ultrasonic cell crusher. The length of the crushed fibers is within 5 mm, which is easier to dissolve compared to long fibers, with a lower dissolution time and increased film-forming efficiency.

[0042] S2: Use an aqueous solution with a mass ratio of sodium hydroxide / urea / water of 7:12:81 as the cellulose solvent for coffee grounds and waste paper. Take the above materials that have been previously dried and slowly add them to the solvent in different material ratios until they are evenly dispersed in the solvent, and finally obtain a concentration of coffee grounds and waste paper of 0.2 - 0.6 wt%;

[0043] In the prior art, when forming a film from fiber materials such as coffee grounds, the above-mentioned slag materials are often directly added to the raw material fibers, and the interfacial compatibility between the raw materials and the slag materials cannot be solved without further treatment. The present invention discovers that using a cellulose solvent can ingeniously solve the above problems. By using a urea / sodium hydroxide / aqueous solution with good solubility in lignocellulosic raw materials, the fibers in coffee grounds and waste paper are dissolved and then prepared into a composite film, fundamentally solving the interfacial compatibility problem existing when coffee grounds are compounded with other materials. The method of using a urea / sodium hydroxide / aqueous solution to dissolve the mixed fiber at about -10 °C to prepare a coffee grounds film has advantages such as low solvent preparation cost, no need for heating, no volatile substances generated during the process, low difficulty in waste liquid recovery, urea can be recycled, economical and environmentally friendly, and it can dissolve both lignocellulose and surface cellulose with a relatively high crystallinity, without generating cellulose derivatives.

[0044] S3: Place it in a refrigerator at -20 °C for 1 h to make its temperature between -10 and -20 °C, and then stir at a speed of 1500 rpm in an environment temperature below 25 °C for 3 - 8 h until the materials are completely dissolved to form a viscous transparent liquid;

[0045] S4: Centrifuge at a speed of 4000 rpm for 10 minutes at 5 °C to remove air bubbles;

[0046] S5: Use pure water as the coagulation bath, slowly pour the centrifuged solution into pure water, and quickly stir with a glass rod at the same time. Wait for the viscous liquid to precipitate, pour off the supernatant and then pour in pure water. Repeat this step until it is washed to neutral.

[0047] S6: Use a disposable dropper to drip the precipitated regenerated cellulose into a suction filtration device and filter it into a film. Then, place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, press the film flat with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film. Seal it for later use. The prepared composite packaging film has excellent biodegradability, ultraviolet resistance, and a certain aromaticity, providing a new solution for the large-scale and high-value utilization of coffee grounds.

[0048] Specifically, previous studies have pointed out that cellulose is most suitable for dissolution at 0.0 - 4.0 wt%. However, the experimental materials are not pure fibers. Therefore, a large mass fraction may be unfavorable for fiber dissolution. This means that we need to reduce the material ratio to address the above deficiencies. The research of this invention has found that after adjusting the material ratio to 0.2 - 0.6 wt%, there are advantages such as less material, easy crushing, fast dissolution, fast dissolution rotation speed, stable rotation speed, short experimental period, high film-forming success rate, high demolding success rate, and improved film stability. Therefore, in this invention, the material ratio within this range is innovatively proposed to explore the raw material ratio and process improvement of film formation of fiber materials such as coffee grounds under a new solvent.

[0049] In the second aspect, the present invention provides the application of the regenerated composite film prepared by the above method in many fields, which can specifically involve applications in technical aspects such as environmental protection product packaging, ultraviolet protection decoration, and aromatic fabrics; it can also involve applications in research fields related to plants and soil. Specifically, the above regenerated composite film is used as a raw material for any one of environmental protection product packaging, ultraviolet protection decoration fabric, aromatic fabric raw material, degradable germination bag, or degradable seedling raising bag.

[0050] The present invention has the following advantages and beneficial effects:

[0051] The coffee grounds film prepared by the method of the present invention has excellent biodegradability, ultraviolet resistance, and a certain aromaticity. It can be reprocessed into other products and can be used as a high-value utilization method for treating coffee grounds and waste paper. In addition, it is further confirmed that the composite of coffee grounds cellulose can improve properties such as raw material strength, biodegradability, ultraviolet resistance, and water absorption.

[0052] Compared with the prior art, it solves the interfacial incompatibility of raw materials such as coffee grounds during film formation. It can solve the disadvantages of high cost, instability at high temperature, difficult recovery, and high operating cost for maintaining high temperature in the N-methylmorpholine-N-oxide (NMMO) system for heating and dissolving the cellulose system. At the same time, it has advantages such as no volatiles generated during the process, low difficulty in recovering waste liquid, urea can be recycled, and it is economical and environmentally friendly.

[0053] The present invention is different from the method of simply compounding coffee grounds with polymer materials as a filler. Instead, it uses a urea / sodium hydroxide / aqueous solution that has good solubility in lignocellulosic raw materials to dissolve the coffee grounds and the fibers in waste paper and then prepares a composite film. This fundamentally solves the interfacial compatibility problem that exists when coffee grounds are compounded with other materials and ensures the maintenance of the physical and chemical properties of the composite film. The prepared composite packaging film has excellent biodegradability, ultraviolet resistance, and a certain aromaticity. It provides a new solution for the large-scale and high-value utilization of coffee grounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is the process flow chart of the present invention;

[0055] Figure 2 From A to E are the morphologies of the materials after dissolution in Examples 1-5;

[0056] Figure 3 is the back view morphology of the films prepared in Comparative Example 1 and Examples 1-5. Among them, F is the back view morphology of the film in Comparative Example 1, and G-K are the back view morphologies of the films in Examples 1-5;

[0057] Figure 4 is the front view morphology of the films prepared in Comparative Example 1 and Examples 1-5. Among them, L is the front view morphology of the film in Comparative Example 1, and M-Q are the front view morphologies of the films in Examples 1-5;

[0058] Figure 5 is the front view morphology of the film prepared in Comparative Example 2;

[0059] Figure 6 is the performance test results of the films in Comparative Example 1 and Examples 1-5;

[0060] Figure 7 is the absorbance relationship of the films in Comparative Example 1 and Examples 1-5;

[0061] Figure 8 is the absorbance relationship of Comparative Examples 2-4 and the control. DETAILED DESCRIPTION OF THE INVENTION

[0062] To better understand the present invention, the following examples further illustrate the present invention, but the content of the present invention is not limited to the following examples.

[0063] Example 1

[0064] Prepare 99.8 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 0.1 g of dry coffee grounds with a particle size of 0 - 200 μm, then add 0.1 g of shredded and ultrasonically broken and dried waste paper. Stir mechanically to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h at an ambient temperature below 25°C until the material is completely dissolved to form a viscous transparent liquid.

[0065] If there is still solid present, put it back in the freezer for 1 h, then take it out and stir until the cellulose in the material is completely dissolved. Centrifuge at a speed of 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0066] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the supernatant, and then pour in pure water again. Repeat this step until it is washed to neutral. Use a disposable dropper to drip the precipitated regenerated cellulose into the suction filtration device and filter it into a film. Then place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, flatten the film with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film "Concentration 1".

[0067] Example 2

[0068] Prepare 99.7 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 0.2 g of dry coffee grounds with a particle size of 0 - 200 μm, then add 0.1 g of shredded and ultrasonically broken and dried waste paper. Stir mechanically to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h at an ambient temperature below 25°C until the material is completely dissolved to form a viscous transparent liquid.

[0069] If there is still solid present, put it back in the freezer for 1 h, then take it out and stir until the cellulose in the material is completely dissolved. Centrifuge at a speed of 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0070] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the supernatant, and then pour in pure water again. Repeat this step until it is washed to neutral. Use a disposable dropper to drip the precipitated regenerated cellulose into the suction filtration device and filter it into a film. Then place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, flatten the film with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film "Concentration 2".

[0071] Example 3

[0072] Prepare 99.6 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 0.3 g of dried coffee grounds with a particle size of 0 - 200 μm, then add 0.1 g of shredded and ultrasonically broken and dried waste paper. Stir mechanically to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h at an ambient temperature below 25°C until the material is completely dissolved to form a viscous and transparent liquid.

[0073] If there is still solid present, put it back in the freezer for 1 h, then take it out and stir until the cellulose in the material is completely dissolved. Centrifuge at 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0074] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the upper clear liquid, and then pour in pure water again. Repeat this step until it is washed to neutral. Use a disposable dropper to drip the precipitated regenerated cellulose into the suction filtration device and filter it into a film. Then place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, press the film flat with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film "Concentration 3".

[0075] Example 4

[0076] Prepare 99.5 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 0.4 g of dried coffee grounds with a particle size of 0 - 200 μm, then add 0.1 g of shredded and ultrasonically broken and dried waste paper. Stir mechanically to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h at an ambient temperature below 25°C until the material is completely dissolved to form a viscous and transparent liquid.

[0077] If there is still solid present, put it back in the freezer for 1 h, then take it out and stir until the cellulose in the material is completely dissolved. Centrifuge at 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0078] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the upper clear liquid, and then pour in pure water again. Repeat this step until it is washed to neutral. Use a disposable dropper to drip the precipitated regenerated cellulose into the suction filtration device and filter it into a film. Then place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, press the film flat with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film "Concentration 4".

[0079] Example 5

[0080] Prepare 99.4 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 0.5 g of dry coffee grounds with a particle size of 0 - 200 μm, then add 0.1 g of shredded and ultrasonically fragmented and dried waste paper. Stir mechanically to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h at an ambient temperature below 25°C until the material is completely dissolved to form a viscous transparent liquid.

[0081] If there is still solid present, put it back in the freezer for 1 h, then take it out and stir until the cellulose of the material is completely dissolved. Centrifuge at a speed of 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0082] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the supernatant, and then pour in pure water again. Repeat this step until it is washed to neutral. Use a disposable dropper to drip the precipitated regenerated cellulose at the bottom into a suction filtration device and filter it into a film. Then place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, press the film flat with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film "Concentration 5".

[0083] Figure 2 From A - E are the morphologies after the materials in Examples 1 - 5 are dissolved.

[0084] Comparative Example 1

[0085] Prepare 99.9 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 0.1 g of shredded and ultrasonically fragmented and dried waste paper. Stir mechanically to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h at an ambient temperature below 25°C until the material is completely dissolved to form a viscous transparent liquid.

[0086] If there is still solid present, put it back in the freezer for 1 h, then take it out and stir until the cellulose of the material is completely dissolved. Centrifuge at a speed of 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0087] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the supernatant, and then pour in pure water again. Repeat this step until it is washed to neutral. Obtain a flat and dry regenerated cellulose film "Control".

[0088] Comparative Example 2 (Previous application by the inventor, Chinese Patent Application CN118599150A)

[0089] Prepare 94 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 2 g each of dry coffee grounds and tea leaves with a particle size of 0 - 200 μm, then add 2 g of shredded and ultrasonically broken and dried waste paper, and mechanically stir to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h at an ambient temperature below 25°C until the material is completely dissolved to form a viscous transparent liquid.

[0090] If there is still solid present, put it back in the freezer for 1 h, then take it out and stir until the cellulose in the material is completely dissolved. Centrifuge at a speed of 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0091] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the supernatant, and then pour in pure water again. Repeat this step until it is washed to neutral. Use a disposable dropper to drip the precipitated regenerated cellulose into the suction filtration device and filter it into a film. Then place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, press the film flat with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film A.

[0092] Comparative Example 3 (Previous application by the inventor, Chinese Patent Application CN118599150A)

[0093] Prepare 97 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 1 g each of dry coffee grounds and tea leaves with a particle size of 0 - 200 μm, then add 1 g of shredded and ultrasonically broken and dried waste paper, and mechanically stir to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h at an ambient temperature below 25°C until the material is completely dissolved to form a viscous transparent liquid.

[0094] If there is still solid present, put it back in the freezer for 1 h, then take it out and stir until the cellulose in the material is completely dissolved. Centrifuge at a speed of 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0095] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the supernatant, and then pour in pure water again. Repeat this step until it is washed to neutral. Use a disposable dropper to drip the precipitated regenerated cellulose into the suction filtration device and filter it into a film. Then place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, press the film flat with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film B.

[0096] Comparative Example 4 (Previous application by the inventor, Chinese Patent Application CN118599150A)

[0097] Prepare 98.5 g of an aqueous solution containing 7 wt% NaOH and 12 wt% urea. At room temperature, add 0.5 g each of dry coffee grounds and tea leaves with a particle size of 0 - 200 μm, and then add 0.5 g of shredded waste paper that has been ultrasonically broken and dried. Stir mechanically to mix evenly. Place the mixture in a freezer at -20°C for 1 h, and stir at a speed of 1500 rpm for 3 - 8 h in an environment with a temperature below 25°C until the material is completely dissolved, forming a viscous and transparent liquid.

[0098] If there is still solid present, put it back in the refrigerator and freeze for 1 h, then take it out and stir until the cellulose in the material is completely dissolved. Centrifuge at a speed of 4000 rpm for 10 minutes at 5°C to remove air bubbles.

[0099] Using pure water as the coagulation bath, slowly pour the centrifuged solution into pure water while quickly stirring with a glass rod. Wait for the viscous liquid to precipitate, pour off the supernatant, and then pour in pure water again. Repeat this step until it is washed to neutral. Use a disposable dropper to drop the regenerated cellulose at the bottom into a suction filtration device and filter it into a film. Then place the regenerated cellulose film in an oven to dry. To prevent the film from wrinkling during drying, press the film flat with a glass slide and place a heavy object on the glass slide to obtain a flat and dry regenerated cellulose film C.

[0100] Test Example 1 Biodegradability Test

[0101] Cut the film into small pieces of 40 mm × 40 mm and place them in a 50 m beaker, and dry at 105°C for 24 h. The control is the "control" film in Comparative Example 1.

[0102] Weigh the mass of the dried film (M1, g), and measure 25 mL of distilled water and pour it into the beaker. Immerse the dried film in it at room temperature for 24 h, drain the immersion liquid, and then dry at 105°C for 24 h.

[0103] Weigh the mass of the dried film (M2, g), calculate the water solubility (WS), and repeat the measurement 3 times for each group:

[0104] WS% = (M2 - M1) × 100 / M1

[0105] The test results are shown in Table 1 and Figure 6 as follows.

[0106] Table 1 Water Solubility Test Results

[0107]

[0108] The level of water solubility can infer the biodegradability of the material. The higher the water solubility, the more hydrophilic components in the material, the easier it is to absorb water and swell, form a porous structure, increase the contact area between microorganisms and the material, thereby enhancing the biodegradability of the material and improving the biodegradability.

[0109] From the data in Table 1, it can be seen that, after experiments, it is believed that the control film has no biodegradability or extremely weak degradation ability when the experimental error is allowed. All experimental films have biodegradability, proving that the addition of coffee grounds fiber can act on other materials during compounding and improve their biodegradability.

[0110] Among all the experimental films, the experimental film with concentration 1 performed best, had the highest water solubility, had the best biodegradability, and had significant differences from other experimental films (P<0.05). The biodegradability of the other experimental films decreased with the increase of concentration, and the biodegradability of concentration 5 was the weakest, which was basically significantly different from other experimental films (P<0.05).

[0111] Test Example 2 Water absorption test

[0112] The composite films prepared in Examples 1-5 and the control film prepared in Comparative Example 1 were cut into small pieces of 30 mm x 40 mm, placed in a 50 mL beaker, placed in a forced air drying oven, set the temperature to 105° C., and dried for 24 h.

[0113] The membrane was taken out, its mass (M3, g) was measured, and the membrane was immersed in deionized water for 10 min, and then centrifuged at 5000 rpm for 10 min to remove excess water from the membrane.

[0114] The above membrane was taken out, its mass (M4, g) was weighed, and the water absorption was calculated. The measurement was repeated 3 times for each group.

[0115] Water absorption (%) = (M4-M3) x 100 / M4

[0116] The test results are shown in Table 2 and Figure 6 shown.

[0117] Table 2 Water absorption test results

[0118]

[0119] It can be seen from the data in Table 2 that in terms of water absorption, the water absorption capacity of each experimental membrane is stronger than that of the control membrane, and there is a significant difference (P<0.05), which proves that the composite membranes prepared in Examples 1-5 have significantly strong water absorption capacity. At the same time, it proves that the addition of coffee grounds fiber can act on other materials during compounding and improve their water absorption.

[0120] The water absorption capacity of the membranes at concentrations 2, 3, 4 and 5 in each experiment was significantly different from that at concentration 1 (P<0.05), proving that the water absorption capacity of the membranes at the above four concentrations was significantly stronger than that of the membrane at concentration 1. In contrast, the membrane at concentration 5 had both strong water absorption capacity and a smaller capacity error, proving that it had an outstanding water retention capacity.

[0121] Test Example 3 Antioxidant Property Test

[0122] The composite films prepared in Examples 1 - 5 and the control film prepared in Comparative Example 1 were cut into small pieces of 20 mm x 20 mm, placed in a 50 mL test tube, 4 mL of methanol was added thereto, and it was left to stand in the dark at room temperature for 2 h.

[0123] 3 mL of the sample solution was taken and mixed evenly with 1 mL of DPPH methanol solution (150 μmoL / L), and it was left to stand in the dark at room temperature for 30 min to allow the reaction to proceed sufficiently.

[0124] Using methanol as a blank background for zero adjustment, 3 mL of methanol was mixed evenly with 1 mL of DPPH methanol solution (150 μmoL / L) as a reference, and the absorbance value of the sample solution at 517 nm was measured.

[0125] The DPPH radical scavenging rate was calculated, where A1 was the absorbance of the reference, A0 was the absorbance of the sample solution, and each group was measured 3 times repetitively.

[0126] DPPH radical scavenging rate (%) = (A0 - A1) x 100 / A0

[0127] The test results are shown in Table 3 and Figure 6 as follows.

[0128] Table 3 Antioxidant Property Test Results

[0129]

[0130] It can be seen from the data in Table 3 that in terms of antioxidant property, except for the film at concentration 1, the DPPH radical scavenging ability of the remaining experimental films decreased compared with the control film, and there were significant differences (P < 0.05), which proved that except for the film at concentration 1, the antioxidant property of the raw materials was significantly reduced for the remaining composite films. This means that the addition of coffee residue fibers in a large concentration range could not improve the antioxidant ability of other materials during compounding, and even weakened the relevant antioxidant property.

[0131] If judged solely based on the average DPPH radical scavenging rate, the film at concentration 1 had a slight improvement in antioxidant effect. Whether the addition of coffee residue fibers in a low concentration range could improve the antioxidant ability of other materials during compounding remains to be studied.

[0132] Test Example 4 Film Strength Test

[0133] The integrity of the back side of the film after the composite film was demolded was used as a reflection of the film strength.

[0134] The test results are as Figure 3As shown, it can be seen that there are large peeling patches on the back of the control film, and there are also a small number of peeling patches around the films with concentrations 1 and 2, and there are also slight peeling patches in the middle of the film with concentration 3. These are exactly the traces of the fibers adsorbed on the filter paper and finally peeled off during the demolding process, which can reflect that the films with concentrations 1 and 2 have poor strength. There are no peeling patches on the films with concentrations 4 and 5. Compared with the control, it can be considered that the addition of coffee residue fibers can crosslink with other materials during compounding, improving the strength of the material itself. The films with a concentration of 3 or above have the best strength.

[0135] Comparison Figure 4 and Figure 5 It can be seen that compared with Comparative Example 2 (from the previous Chinese patent application CN118599150A of the same inventor, with a larger raw material ratio and the addition of tea residues), the morphology of the films with concentrations 1-5 is more uniform and thick. Comparative Example 2 is brittle in texture and lacks strength compared with the films with concentrations 1-5. Therefore, it shows that after improvement, by reducing the raw material ratio and removing the tea residues in the raw materials, the components of the film can be more uniform, the texture can be more stable, and the strength can be higher.

[0136] Test Example 5 Ultraviolet Blocking Performance Test

[0137] The composite films prepared in Examples 1-5 and the control films prepared in Comparative Examples 1-4 were cut into small pieces of 10 mm × 40 mm, and scanned within the range of 200-800 nm using an ultraviolet spectrophotometer to determine the light transmittance of the fresh-keeping film. Among them, the Figure 7 control is the result of the control film prepared in Comparative Example 1, and the Figure 8 film A pair is the result of the control film prepared in Comparative Example 2, film B is the result of the control film prepared in Comparative Example 3; film C is the result of the control film prepared in Comparative Example 4, and the control is a commercially available degradable film.

[0138] The test results are as Figure 7 shown. It can be seen that in the ultraviolet light band (within the wavelength range of 200-400 nm), the light absorption ability of each experimental film is stronger than that of the control, confirming that the composite film has excellent ultraviolet resistance, and at the same time proving that the addition of coffee residue fibers can act on other materials during compounding to improve their ultraviolet resistance.

[0139] Among the experimental films, the experimental film with a concentration of 4 shows the best performance and the strongest ultraviolet absorption ability; the ultraviolet absorption ability of the film with a concentration of 5 is not much different from that of the film with a concentration of 4, and is slightly inferior to that of the film with a concentration of 4 mainly in the range of 300-360 nm; the experimental films with concentrations 2 and 3 also have excellent ultraviolet absorption ability, but are less than those of the experimental films with concentrations 4 and 5; the experimental film with a concentration of 1 shows far inferior performance to the other four groups of experimental films and has the weakest ultraviolet resistance.

[0140] In the visible light band (within the wavelength range of 400-800nm), the light absorption capacity of each experimental film is stronger than that of the control, confirming that it also has excellent ability to block visible light. It also proves that the addition of coffee grounds fiber can act on other materials during compounding and improve their visible light blocking ability.

[0141] Unlike the ultraviolet light band, the experimental film with a concentration of 5 has the best blocking ability; the performance of concentration 4 is still excellent, ranking second; the experimental film with a concentration of 1 is also far inferior to the other four groups of experimental films, and its ability to block visible light is the weakest. In the visible light band, the light absorption capacity of each experimental film shows a trend of decreasing as the film concentration decreases.

[0142] contrast Figure 7 and Figure 8 It can be seen that compared with Comparative Examples 2-4 (derived from the former Chinese patent application CN118599150A of the same inventor, the raw material ratio is larger and tea residues are added), the absorbance peak distribution of the concentration 1-5 film is more uniform and regular. And the absorbance peak distribution of Comparative Examples 2-4, especially in the ultraviolet region, is messy and irregular. It is speculated that the process method of the previous application may lead to problems such as uneven film components and unstable properties after film formation. This shows that after improvement, the raw material ratio is adjusted down and the tea residues in the raw materials are removed, the components of the film can be more uniform and the properties are more stable. In addition, the difference between the concentration 1-5 film and the control in the ultraviolet region is more significant compared to Comparative Examples 2-4, indicating that the ultraviolet absorption ability of the film after improvement is better and has stronger anti-ultraviolet ability.

[0143] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A preparation method of a film formed by coffee grounds and waste paper, characterized in that: Using coffee grounds and waste paper as the main raw materials, pretreating them, then adding a cellulose solvent, freezing, stirring at a certain temperature, and centrifuging to obtain a mixed solution. After solidification, it is washed and suction-filtered into a film, and dried to obtain a coffee ground regenerated composite film.

2. The preparation method of the film formed by coffee grounds and waste paper according to claim 1, characterized in that: The steps are as follows: S1: Using coffee grounds and waste paper as the main raw materials and pretreating them; S2: Preparing a mixed solution of water and alkali as the cellulose solvent; S3: Mixing the coffee grounds and waste paper pretreated in step S1 according to a mass ratio; S4: Mixing the mixed raw materials in step S3 with the cellulose solvent prepared in step S2, freezing, and stirring at a certain temperature to obtain a mixed solution; S5: Centrifuging the mixed solution in step S4 to remove bubbles to obtain a viscous fully treated solution; S6: Pouring the fully treated solution in step S5 into a coagulation bath, quickly stirring at the same time to precipitate the viscous liquid, removing the supernatant and repeating until it is washed to neutrality to obtain regenerated cellulose; S7: Suction-filtering the regenerated cellulose in step S6 into a film, drying, and sealing for standby to obtain a coffee ground regenerated composite film.

3. The preparation method of the film formed by coffee grounds and waste paper according to claim 2, characterized in that: In step S1, the steps of pretreating coffee grounds are specifically: mechanically crushing and fully grinding coffee grounds, sieving so that the particle size of the two is between 0 - 200 μm, and drying the above materials at 60 - 70 °C until completely dried; The steps of pretreating waste paper are specifically: mechanically crushing waste paper and then performing ultrasonic crushing, filtering long fibers, and drying the short fibers at 60 - 70 °C until completely dried.

4. The preparation method of the film formed by coffee grounds and waste paper according to claim 2, wherein: In step S2, the cellulose solvent includes the following raw materials: 4wt% - 10wt% NaOH, 9wt% - 15wt% urea, 78wt% - 84wt% water.

5. The preparation method of the film formed by coffee grounds and waste paper according to claim 2, characterized in that: In step S3, the mass ratio of coffee grounds to waste paper is 1 - 5:

1.

6. The preparation method of the film formed by coffee grounds and waste paper according to claim 2, characterized in that: In step S4, the mixing mass ratio of the mixed raw materials to the cellulose solvent is 0.1 - 1.0:99 - 99.

9.

7. The preparation method of the coffee grounds and waste paper film according to claim 2, characterized in that: In step S4, the freezing temperature is -10 to -20 °C; the stirring temperature is below 25 °C, and the stirring rate is 100 - 2500 rpm; stir until the material is completely dissolved to form a viscous transparent liquid.

8. The preparation method of the film formed by coffee grounds and waste paper according to claim 2, characterized in that: In step S5, the centrifuging and defoaming rate is 3800 - 4000 rpm, the time is 10 - 12 min, and the temperature is 5 - 7 °C.

9. The preparation method of the film formed by coffee grounds and waste paper according to claim 2, characterized in that: In step S6, pure water is selected as the coagulation liquid for the coagulation bath.

10. Application of a regenerated composite film from coffee grounds, characterized in that: The coffee ground regenerated composite film is prepared by the preparation method described in any one of claims 1 - 9, and the coffee ground regenerated composite film is applied to the fields of environmental protection product packaging, anti-ultraviolet decoration, aromatic fabric processing, or agricultural scientific research.

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