Preparation method of pectin-cellulose composite bioplastic based on fruit peel waste

Abstract

The present application relates to the field of environmental protection treatment and resource recycling, and more relates to the harmless treatment and processing application field of peel waste, and specifically provides a preparation method of pectin-cellulose composite biological plastic based on peel waste, which specifically utilizes the separation and in-situ self-assembly principle of pectin and cellulose in peel cell walls, so that they are tightly wound to form a stable structure similar to carboxylic acid dimers. The prepared biological plastic has high mechanical strength and toughness, has the properties of biological safety, biodegradability, processability and recyclability, has great potential to replace petrochemical plastic products, and can be especially used in the field of food packaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the harmless treatment and processing application field of peel waste, and particularly relates to a pectin-cellulose composite bioplastic based on peel waste and a preparation method thereof. BACKGROUND

[0002] Petrochemical plastics are widely used in the food industry due to their low cost and ideal mechanical and processing properties. However, these plastics are often difficult to degrade, and they accumulate in large quantities in nature, causing serious damage to the environment and ecological systems. More seriously, micro-nano plastics generated by the use of plastics have a great risk of migration into food, posing a major threat to human health. More and more evidence shows that the widespread use of plastics in direct contact with food, such as packaging and tableware, exacerbates the migration of microplastics and nanoplastics into food. Therefore, the use of safe and renewable natural biopolymers (for example, lignocellulose and pectin) to replace traditional petrochemical plastics in the food industry has attracted extensive attention and interest in the development of biodegradable bioplastics.

[0003] Peels and some other agricultural wastes can be considered as good sources of these natural biopolymers, which have the potential to develop biodegradable bioplastics. According to statistics, the food industry produces more than 492 million tons of fruit and vegetable waste every year. These organic solid wastes are highly fermentable, and improper management often poses a serious threat to the environment and human health, including water pollution, eutrophication, and greenhouse gas emissions. In addition, the current common waste management practices (especially incineration and landfill) often do not take into account the high-value utilization of fruit waste, and it is difficult to generate additional economic benefits. Therefore, from the perspectives of environment, economy, resource management and sustainable development, through innovative methods to convert these biomass waste into valuable biodegradable plastics, not only can solve the current serious plastic pollution and inefficient management of organic waste, but also can open up a new way for sustainable materials science, which has important strategic significance.

[0004] However, it is not easy to directly convert peel waste into bioplastics. There are few studies on the use of peel waste to prepare bioplastics, and the reported bioplastics generally exhibit poor performance, such as low mechanical strength, flexibility. In addition, due to the lack of effective energy dissipation and molecular flow, the bioplastic films prepared using natural polymers usually have unsatisfactory reprocessability, which seriously limits their further application. Therefore, how to directly produce high-performance and balanced degradable bioplastics using peels in a simple and sustainable way is challenging and meaningful. SUMMARY

[0005] In order to solve the problems of low management efficiency of organic food waste and plastic environmental pollution in the prior art, and the problems of poor mechanical properties, poor processing performance, difficult recycling and reuse, and the need to add chemical reagents such as film-forming agents and plasticizers of the current biological plastic, the present application provides a pectin-cellulose composite biological plastic based on peel waste and a preparation method thereof, which specifically utilizes the separation and in-situ self-assembly principle of pectin and cellulose in the peel cell wall to make them tightly entangled and form a stable structure similar to carboxylic acid dimer. The prepared biological plastic has high mechanical strength and toughness, and has the properties of biological safety, biodegradability, processability and recyclability, and has great potential to replace petrochemical plastic products, especially in the field of food packaging.

[0006] The present application provides a preparation method of a pectin-cellulose composite biological plastic based on peel waste, comprising the following steps:

[0007] 1) drying and crushing the peel;

[0008] 2) mixing the peel powder with water and performing enzymatic hydrolysis treatment, and centrifuging to obtain the precipitate;

[0009] 3) mixing the precipitate obtained in step 2) with water, adjusting the pH with a saturated citric acid solution, and performing wall breaking treatment under high pressure environment, followed by magnetic stirring at 65-95℃ for 2-4h;

[0010] 4) cooling the mixture obtained in step 3) and placing it in a dialysis bag for dialysis;

[0011] 5) concentrating the mixture after dialysis obtained in step 4), ultrasonic dispersion, and stirring until uniform to obtain a pectin-cellulose composite film-forming slurry;

[0012] 6) degassing the slurry obtained in step 5), uniformly pouring it onto a glass plate, evaporating the water at room temperature, and then peeling off to obtain the biological plastic.

[0013] Preferably, in step 1), the peel is crushed and then passed through a 200-mesh sieve; the present application uses peel as raw material, separates pectin and cellulose therefrom, and performs in-situ self-assembly to obtain a pectin-cellulose composite biological plastic. The peel is selected from one of citrus peel, watermelon peel, cantaloupe peel, pineapple peel, apple peel and residue.

[0014] Preferably, in step 2), the peel powder is mixed with water in a ratio of 1 g:(15-30) mL, then 0.15%-0.25% of hemicellulase based on the mass of the peel is added, and the mixture is treated by oscillation at 40℃ for 15-30min, followed by centrifugation at 5000-6000rpm to obtain the precipitate; the hemicellulase used has an enzyme activity of ≥200 unit / mg solid; and more preferably, the peel powder is mixed with water in a ratio of 1 g:20 mL.

[0015] The enzymatic treatment of hemicellulase can remove the hemicellulose component in the peel, which is beneficial for screening and obtaining the main pectin and cellulose components.

[0016] Preferably, in step 3), the precipitate is mixed with water in a ratio of 1 g: (15-30) mL, and then the pH is adjusted to 1.8-2.2 using saturated citric acid, and the pressure in the high-pressure environment is 2.0-3.0 MPa.

[0017] Preferably, in step 3), the wall-breaking treatment is a microwave-ultrasonic synergistic treatment, the microwave power is 200-500 W, the ultrasonic power is 200-400 W, and the treatment time is 10-20 min.

[0018] Under the synergistic effect of microwave-high pressure-ultrasonic microwave, the cell wall of the peel is quickly disintegrated, and the pectin and cellulose in it are exposed to the acid solution, which accelerates the separation of pectin and cellulose.

[0019] Preferably, in step 4), the molecular weight cut-off of the dialysis bag is 3.5-6.0 KDa, and the dialysis time is 24-48 h, and the water is changed every 6-8 h.

[0020] Under the action of dialysis, the oligosaccharides and other impurities with smaller molecular weight in the mixed solution, including most of the citric acid, can be dialyzed out, while the pectin and cellulose with larger molecular weight are retained, which provides a basis for further in-situ polymerization / crosslinking of pectin and cellulose to prepare pectin-cellulose composite bioplastics.

[0021] Preferably, in step 5), the degree of concentration of the mixed solution after dialysis needs to be determined according to the content of pectin and cellulose, specifically, 10 g of peel raw material should be concentrated to 100 mL, if the concentration volume is too low, the pectin-cellulose composite content ratio will be too high, which will cause part of the acoustic cavitation during the ultrasonic process in step 5), and the polymer near the ultrasonic probe will agglomerate, affecting the energy transmission and making it difficult for the pectin-cellulose composite to disperse uniformly, and such non-uniform slurry cannot be used for film laying. If the concentration volume is too high, the concentration of pectin-cellulose composite in the slurry will be reduced, which will affect the film forming.

[0022] Preferably, in step 5), the ultrasonic dispersion ultrasonic power is 200-500 W, and the ultrasonic time is 5-10 min, followed by stirring until completely and uniformly distributed; the ultrasonic treatment enables the pectin-cellulose to disperse rapidly and uniformly in water and form a uniformly distributed slurry for the production of pectin-cellulose composite bioplastic film.

[0023] Preferably, in step 6), the vacuum degree of the vacuumization for degassing is -0.1 MPa, the slurry is poured onto a glass plate with a thickness of 0.3-0.5 cm, and neither too thin nor too thick is conducive to the stable formation of the film; and the drying condition is natural evaporation of water at room temperature.

[0024] The present application firstly removes the hemicellulose component by enzymatic hydrolysis treatment of the peel, then completes the breakage of the peel cell wall and the separation of pectin and cellulose by microwave ultrasonic-assisted thermal acid treatment under high pressure, and then removes oligosaccharides and other impurities with small molecular weight including most of the citric acid by using a dialysis bag, retains the pectin and cellulose, and preliminarily obtains a pectin-cellulose composite mixed solution, which is concentrated and ultrasonically treated to obtain a pectin-cellulose composite slurry that can be used for the production of bioplastics. The single-component citrus peel cellulose and pectin are difficult to stably form a film without adding other substances, or the performance of the film is poor after being formed, such as high brittleness and low mechanical strength.

[0025] The use of citric acid accelerates the separation of pectin and cellulose, and the small amount of citric acid remaining after dialysis plays a connecting role, so that the pectin and cellulose form a stable structure to form bioplastics.

[0026] The pectin-cellulose composite bioplastics prepared by the above method are prepared in the process, and other impurities (hemicellulose and part of oligosaccharide polysaccharide) are removed through high-pressure microwave ultrasonic treatment and thermal acid treatment in the subsequent dialysis step.

[0027] The present application utilizes the separation and in-situ self-assembly principle of pectin and cellulose in the cell wall of the peel, so that they are tightly wound to form a stable structure similar to carboxylic acid dimers. The prepared bioplastics have high mechanical strength and toughness, and have the properties of biological safety, biodegradability, processability and recyclability, and have great potential to replace petrochemical plastic products (especially in the field of food packaging).

[0028] The pectin-cellulose composite bioplastics based on the peel and the preparation method thereof provided by the present application have the following advantages and beneficial effects:

[0029] (1) The present application maximally utilizes the peel waste, which not only avoids the environmental and ecological damage caused by the peel waste, but also improves the application value of the peel waste;

[0030] (2) The obtained bioplastics have high mechanical strength (46.3 MPa) and toughness (5.1 MJ / m 3 ), and can be completely degraded (within one month);

[0031] (3) The obtained bioplastics are recyclable, and the bioplastics after the use cycle can be processed again to form new bioplastics after simple treatment;

[0032] (4) The method adopted does not need other chemical reagents such as film-forming agents and plasticizers, is safe, green, simple and easy to operate, low in cost and easy to realize sustainable batch production;

[0033] (5) The prepared biological plastic is safe and non-toxic, can be used as a substitute for petrochemical plastic, and has great application prospect in the field of food packaging. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 Flow chart for preparing biological plastic according to the present application;

[0035] Figure 2 Fruit peel waste production example, biological plastic formation mechanism, comparison with other plastics in performance and large-scale production schematic diagram for preparing biological plastic according to the present application;

[0036] Figure 3 Density functional theory (DFT) in the production process of the biological plastic prepared in Example 1, wherein (a) is the DFT simulation between pectin, cellulose and citric acid; (b) is the possible structure formed by pectin, citric acid and cellulose according to the DFT simulation;

[0037] Figure 4 Image of load bearing, plasticity and folding of the biological plastic prepared in Example 1;

[0038] Figure 5 Verification of the universality of the process for preparing biological plastic according to the present application in various fruit peels, (a) watermelon peel, (b) pineapple peel, (c) apple residue, (d) cantaloupe peel;

[0039] Figure 6 Weldability, processability and recyclability of the biological plastic prepared in Example 1 under the action of water;

[0040] Figure 7 Biological toxicity test of the biological plastic prepared in Example 1;

[0041] Figure 8 Degradability of the biological plastic prepared in Example 1 in soil and natural environment. DETAILED DESCRIPTION

[0042] The embodiments of the present application will be further described in detail by the following examples, it is necessary to point out that the following examples are only used for further illustrating the present application, and the embodiments of the present application are not limited to this. Some non-essential adjustments and improvements made by the person skilled in the related field according to the above application scheme still belong to the protection scope of the present application.

[0043] The fruit peels used in the scheme are collected from local markets; the rest of the substances and reagents are general commercially available products if not specially mentioned.

[0044] Example 1 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0045] Orange peels were selected, washed, dried, and ground to pass through a 200 mesh sieve to obtain orange peel powder. 10 g of the orange peel powder was mixed with water at a ratio of 1 g:20 mL, 15 mg of hemicellulase (≥200 unit / mg solid) was added, and incubation was performed at 40°C in a water bath constant temperature shaker for 20 min. The precipitate was then centrifuged, mixed with water at a ratio of 1 g:20 mL, and then the pH of the mixture was adjusted to 2 using a saturated citric acid solution. The mixture was placed in a high-pressure environment at 2.0 MPa, and ultrasonic microwave synergistic treatment was performed for 10 min (microwave power: 500 W; ultrasonic power: 300 W). Subsequently, magnetic stirring was performed at 95°C for 2.5 h. After cooling, the mixture was placed in a 3.5 KDa dialysis bag for dialysis for 48 h, and then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated with 300 W ultrasonic waves for 5 min to form a pectin-cellulose composite film-forming slurry, and then magnetic stirring was performed until complete uniformity. After degassing, the slurry was poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm), and dried at room temperature to obtain a film.

[0046] Example 2 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0047] Orange peels were selected, washed, dried, and ground to pass through a 200 mesh sieve to obtain orange peel powder. 10 g of the orange peel powder was mixed with water at a ratio of 1 g:20 mL, 15 mg of hemicellulase (≥200 unit / mg solid) was added, and incubation was performed at 40°C in a water bath constant temperature shaker for 20 min. The precipitate was then centrifuged, mixed with water at a ratio of 1 g:20 mL, and then the pH of the mixture was adjusted to 2 using a saturated citric acid solution. The mixture was placed in a high-pressure environment at 2.0 MPa, and ultrasonic microwave synergistic treatment was performed for 10 min (microwave power: 500 W; ultrasonic power: 300 W). Subsequently, magnetic stirring was performed at 95°C for 2.5 h. After cooling, the mixture was placed in a 3.5 KDa dialysis bag for dialysis for 48 h, and then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated with 300 W ultrasonic waves for 5 min to form a pectin-cellulose composite film-forming slurry, and then magnetic stirring was performed until complete uniformity. After degassing, the slurry was poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm), and dried at room temperature to obtain a film.

[0048] Example 3 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0049] Citrus peel, washed and dried, was ground to pass through a 200-mesh screen to obtain citrus peel powder. 10 g of the citrus peel powder was mixed with water at a ratio of 1 g:20 mL, and 15 mg of hemicellulase (≥200 unit / mg solid) was added. The mixture was incubated in a water bath constant temperature shaker at 40°C for 20 min. Then the precipitate was centrifuged and mixed with water at a ratio of 1 g:20 mL. The pH of the mixture was adjusted to 2 using a saturated citric acid solution, and the mixture was treated by ultrasonic microwave synergy at 2.0 MPa for 5 min (microwave power: 400 W; ultrasonic power: 200 W). Then the mixture was stirred at 95°C for 2.5 h. After cooling, the mixture was dialyzed in a 3.5 KDa dialysis bag for 48 h. Then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated by ultrasonic at 300 W for 5 min to form a pectin-cellulose composite film-forming slurry. The slurry was stirred magnetically until it was completely uniform, degassed, and then poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm). The film was peeled off after air-drying at room temperature.

[0050] Example 4 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0051] Citrus peel, washed and dried, was ground to pass through a 200-mesh screen to obtain citrus peel powder. 10 g of the citrus peel powder was mixed with water at a ratio of 1 g:20 mL, and 15 mg of hemicellulase (≥200 unit / mg solid) was added. The mixture was incubated in a water bath constant temperature shaker at 40°C for 20 min. Then the precipitate was centrifuged and mixed with water at a ratio of 1 g:20 mL. The pH of the mixture was adjusted to 2 using a saturated citric acid solution, and the mixture was treated by ultrasonic microwave synergy at 2.0 MPa for 5 min (microwave power: 400 W; ultrasonic power: 200 W). Then the mixture was stirred at 95°C for 2.5 h. After cooling, the mixture was dialyzed in a 3.5 KDa dialysis bag for 48 h. Then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated by ultrasonic at 300 W for 5 min to form a pectin-cellulose composite film-forming slurry. The slurry was stirred magnetically until it was completely uniform, degassed, and then poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm). The film was peeled off after air-drying at room temperature.

[0052] Example 5 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0053] Citrus peel, washed and dried, was ground to pass through a 200-mesh screen to obtain citrus peel powder. 10 g of the citrus peel powder was mixed with water at a ratio of 1 g:20 mL, and 15 mg of hemicellulase (≥200 unit / mg solid) was added. The mixture was incubated in a water bath constant temperature shaker at 40°C for 20 min. Then the precipitate was centrifuged and mixed with water at a ratio of 1 g:20 mL. The pH of the mixture was adjusted to 2 using a saturated citric acid solution, and the mixture was treated by ultrasonic microwave synergy at 2.0 MPa for 10 min (microwave power: 500 W; ultrasonic power: 300 W). Then the mixture was stirred magnetically at 95°C for 2.5 h. After cooling, the mixture was dialyzed in a 3.5 KDa dialysis bag for 48 h. Then the dialyzed mixture was concentrated to 150 mL. The concentrated mixture was treated by ultrasonic at 300 W for 5 min to form a pectin-cellulose composite film-forming slurry. The slurry was stirred magnetically until it was completely uniform, degassed, and then poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm). The film was peeled off after air-drying at room temperature.

[0054] Example 6 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0055] Citrus peel, washed and dried, was ground to pass through a 200-mesh screen to obtain citrus peel powder. 10 g of the citrus peel powder was mixed with water at a ratio of 1 g:20 mL, and 15 mg of hemicellulase (≥200 unit / mg solid) was added. The mixture was incubated in a water bath constant temperature shaker at 40°C for 20 min. Then the precipitate was centrifuged and mixed with water at a ratio of 1 g:20 mL. The pH of the mixture was adjusted to 2 using a saturated citric acid solution, and the mixture was treated by ultrasonic microwave synergy at 2.0 MPa for 10 min (microwave power: 500 W; ultrasonic power: 300 W). Then the mixture was stirred magnetically at 95°C for 2.5 h. After cooling, the mixture was dialyzed in a 3.5 KDa dialysis bag for 48 h. Then the dialyzed mixture was concentrated to 150 mL. The concentrated mixture was treated by ultrasonic at 300 W for 5 min to form a pectin-cellulose composite film-forming slurry. The slurry was stirred magnetically until it was completely uniform, degassed, and then poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm). The film was peeled off after air-drying at room temperature.

[0056] Example 7 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0057] Select the orange peel, washed and dried, crushed through 200 mesh screen to get orange peel powder. 10 g of orange peel powder, according to 1 g:30 mL of water mixed with the ratio, the addition of 25 mg of hemicellulase (≥200 unit / mg solid), in a water bath constant temperature oscillator 45 ℃ incubation for 20 min. Then centrifugal precipitation, according to 1 g:20 mL of water mixed with the ratio, then using saturated citric acid solution to adjust the pH of the mixture to 2, placed in a high pressure environment for 2.0 MPa, ultrasonic microwave synergistic treatment 10 min (microwave power: 500 W; ultrasonic power: 300 W) and then at 95 ℃ magnetic stirring 2.5 h. After cooling, the mixture is placed in 3.5 KDa dialysis bag dialysis 48 h, then the dialysate after the mixture is concentrated to 100 mL. The concentrated mixture in 300 W ultrasonic treatment 5 min to form pectin-cellulose composite film forming slurry, then magnetic stirring to completely uniform, after degassing to the appropriate size of the glass plate (slurry thickness of about 0.5 cm), room temperature drying and membrane, that is, get.

[0058] Example 8 A preparation method of pectin-cellulose composite bioplastics based on fruit peel waste, comprising the following steps:

[0059] Select the Hami melon peel, washed and dried, crushed through 200 mesh screen to get Hami melon peel powder. 10 g of fruit peel powder, according to 1 g:20 mL of water mixed with the ratio, the addition of 15 mg of hemicellulase (≥200 unit / mg solid), in a water bath constant temperature oscillator 40 ℃ incubation for 20 min. Then centrifugal precipitation, according to 1 g:20 mL of water mixed with the ratio, then using saturated citric acid solution to adjust the pH of the mixture to 2, placed in a high pressure environment for 2.0 MPa, ultrasonic microwave synergistic treatment 10 min (microwave power: 500 W; ultrasonic power: 300 W) and then at 95 ℃ magnetic stirring 2.5 h. After cooling, the mixture is placed in 3.5 KDa dialysis bag dialysis 48 h, then the dialysate after the mixture is concentrated to 100 mL. The concentrated mixture in 300 W ultrasonic treatment 5 min to form pectin-cellulose composite film forming slurry, then magnetic stirring to completely uniform, after degassing to the appropriate size of the glass plate (slurry thickness of about 0.5 cm), room temperature drying and membrane, that is, get.

[0060] Example 9 A preparation method of pectin-cellulose composite bioplastics based on fruit peel waste, comprising the following steps:

[0061] Apple pomace, washed and dried, was ground to pass through a 200-mesh screen to obtain apple pomace powder. 10 g of the pomace powder was mixed with water at a ratio of 1 g:20 mL, and 15 mg of hemicellulase (≥200 unit / mg solid) was added. The mixture was incubated in a water bath constant temperature shaker at 40°C for 20 min. Then, the precipitate was obtained by centrifugation, mixed with water at a ratio of 1 g:20 mL, and then the pH of the mixture was adjusted to 2 using a saturated citric acid solution. The mixture was subjected to ultrasonic-microwave synergistic treatment at 2.0 MPa for 10 min (microwave power: 500 W; ultrasonic power: 300 W), and then stirred magnetically at 95°C for 2.5 h. After cooling, the mixture was dialyzed in a 3.5KDa dialysis bag for 48 h, and then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated with ultrasonic at 300 W for 5 min to form a pectin-cellulose composite film-forming slurry, which was then stirred magnetically until completely uniform. After degassing, the slurry was poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm), and dried at room temperature to obtain the pectin-cellulose composite bio-plastic film.

[0062] Example 10 A method for preparing a pectin-cellulose composite bio-plastic based on fruit peel waste, comprising the following steps:

[0063] Pineapple peel, washed and dried, was ground to pass through a 200-mesh screen to obtain pineapple peel powder. 10 g of the peel powder was mixed with water at a ratio of 1 g:20 mL, and 15 mg of hemicellulase (≥200 unit / mg solid) was added. The mixture was incubated in a water bath constant temperature shaker at 40°C for 20 min. Then, the precipitate was obtained by centrifugation, mixed with water at a ratio of 1 g:20 mL, and then the pH of the mixture was adjusted to 2 using a saturated citric acid solution. The mixture was subjected to ultrasonic-microwave synergistic treatment at 2.0 MPa for 10 min (microwave power: 500 W; ultrasonic power: 300 W), and then stirred magnetically at 95°C for 2.5 h. After cooling, the mixture was dialyzed in a 3.5KDa dialysis bag for 48 h, and then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated with ultrasonic at 300 W for 5 min to form a pectin-cellulose composite film-forming slurry, which was then stirred magnetically until completely uniform. After degassing, the slurry was poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm), and dried at room temperature to obtain the pectin-cellulose composite bio-plastic film.

[0064] Example 11 A method for preparing a pectin-cellulose composite bio-plastic based on fruit peel waste, comprising the following steps:

[0065] Selecting watermelon peel, washed and dried, crushed through 200 mesh screen to obtain watermelon peel powder. 10 g of peel powder was mixed with water according to the ratio of 1 g:20 mL, 15 mg of hemicellulase (≥200 unit / mg solid) was added, and incubated in a water bath constant temperature oscillator at 40°C for 20 min. Then centrifuged to obtain the precipitate, mixed with water according to the ratio of 1 g:20 mL, and then the pH of the mixture was adjusted to 2 using saturated citric acid solution. It was placed in a high pressure environment of 2.0 MPa, and treated by ultrasonic microwave cooperation for 10 min (microwave power: 500 W; ultrasonic power: 300 W). Then it was stirred magnetically at 95°C for 2.5 h. After cooling, the mixture was placed in a 3.5 KDa dialysis bag for dialysis for 48 h, and then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated by ultrasonic at 300 W for 5 min to form a pectin-cellulose composite film forming slurry, and then stirred magnetically until completely uniform. After degassing, it was poured into a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm), and dried at room temperature to obtain the film.

[0066] Comparative Example 1 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0067] Selecting orange peel, washed and dried, crushed through 200 mesh screen to obtain orange peel powder. 10 g of peel powder was mixed with water according to the ratio of 1 g:20 mL, 15 mg of hemicellulase (≥200 unit / mg solid) was added, and incubated in a water bath constant temperature oscillator at 40°C for 20 min. Then centrifuged to obtain the precipitate, mixed with water according to the ratio of 1 g:20 mL, and then the pH of the mixture was adjusted to 2 using hydrochloric acid. It was placed in a high pressure environment of 2.0 MPa, and treated by ultrasonic microwave cooperation for 10 min (microwave power: 500 W; ultrasonic power: 300 W). Then it was stirred magnetically at 95°C for 2.5 h. After cooling, the mixture was placed in a 3.5 KDa dialysis bag for dialysis for 48 h, and then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated by ultrasonic at 300 W for 5 min to form a pectin-cellulose composite film forming slurry, and then stirred magnetically until completely uniform. After degassing, it was poured into a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm), and dried at room temperature. Since hydrochloric acid cannot play the cross-linking role of citric acid, a complete film material cannot be obtained without additional addition of other cross-linking agents or plasticizers.

[0068] Comparative Example 2 A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, comprising the following steps:

[0069] Citrus peel, washed and dried, was ground to pass a 200 mesh screen to obtain citrus peel powder. 10 g of the citrus peel powder was mixed with water at a ratio of 1 g:20 mL, and 15 mg of hemicellulase (≥200 unit / mg solid) was added. The mixture was incubated in a water bath constant temperature shaker at 40°C for 20 min. The precipitate was then centrifuged and mixed with water at a ratio of 1 g:20 mL. The pH of the mixture was then adjusted to 2 using a saturated citric acid solution, and the mixture was treated with ultrasonic waves and microwaves in a high pressure environment at 2.0 MPa for 10 min (microwave power: 500 W; ultrasonic power: 300 W). The mixture was then stirred magnetically at 95°C for 2.5 h. After cooling, the mixture was placed in a 3.5 KDa dialysis bag and dialyzed for 48 h. The dialyzed mixture was treated with 300 W ultrasonic waves for 5 min to form a pectin-cellulose composite film-forming slurry, which was then stirred magnetically until completely uniform. After degassing, the slurry was poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm), and dried at room temperature. Since the slurry did not undergo a concentration step, the content of pectin-cellulose composite in the slurry was very low, and thus the film had poor stability or was difficult to form a complete film.

[0070] Comparative Example 3: A method for preparing a pectin-cellulose composite bioplastic based on peel waste, comprising the following steps:

[0071] Citrus peel, washed and dried, was ground to pass a 200 mesh screen to obtain citrus peel powder. 10 g of the citrus peel powder was mixed with water at a ratio of 1 g:20 mL, and 15 mg of hemicellulase (≥200 unit / mg solid) was added. The mixture was incubated in a water bath constant temperature shaker at 40°C for 20 min. The precipitate was then centrifuged and mixed with water at a ratio of 1 g:20 mL. The pH of the mixture was then adjusted to 2 using a saturated citric acid solution, and the mixture was treated with ultrasonic waves and microwaves in a high pressure environment at 2.0 MPa for 10 min (microwave power: 500 W; ultrasonic power: 300 W). The mixture was then stirred magnetically at 95°C for 2.5 h. After cooling, the mixture was placed in a 3.5 KDa dialysis bag and dialyzed for 48 h, and then the dialyzed mixture was concentrated to 100 mL. The concentrated mixture was treated with 300 W ultrasonic waves for 5 min to form a pectin-cellulose composite film-forming slurry, which was then stirred magnetically until completely uniform. After degassing, the slurry was poured onto a glass plate of appropriate size (the thickness of the slurry was about 0.5 cm), and dried at room temperature. Since the slurry did not undergo a concentration step, the content of pectin-cellulose composite in the slurry was very low, and thus the film had poor stability or was difficult to form a complete film.

[0072] The preparation schemes of the above Comparative Examples 1-3 were all difficult to form a complete film.

[0073] Experimental Example

[0074] The mechanical properties were measured by cutting the film into a 100 mm x 50 mm rectangle and using an automatic tensile testing machine to determine the tensile strength, with an initial clamping distance and speed of 50 mm and 1 mm / s, respectively. The test results are shown in Table 1.

[0075] Table 1 shows the performance comparison of the bio-plastic prepared in Example 1 and a commercially available preservative film (PVC).

[0076] Tensile strength Biological toxicity Degradable Recyclable Example 1 46.3 MPa None 1 month degradation Capable of being recycled Commercially available cling film 10.15 MPa Potential hazards of known micro- and nano-plastics None None

[0077] Figure 2 The production of peel waste, the formation mechanism of bio-plastic, the comparison with other plastics, and the schematic diagram of large-scale production are shown. A large amount of peel waste such as kiwi, banana, pineapple, apple, watermelon, and citrus peel is produced worldwide every year (a). Figure 2 a) (M is million tons and HM is hundred million tons in the figure). In the present application, we separate pectin and cellulose in the cell wall of the peel and then self-assemble in situ to form a pectin-cellulose composite bio-plastic. In this process, citric acid acts as a bridge to make pectin and cellulose form a stable structure similar to carboxylic acid dimers (b). Figure 2 b). The common properties of bio-plastic and some other plastics are compared, and the prepared bio-plastic shows obvious advantages in sustainability, cost, mechanical properties, ecological friendliness, and human health (c). The inventors also explored the possibility of large-scale production of this process, and it can be seen that mass production is expected to be realized (d). Figure 2 Figure 2

[0078] Figure 3 The mechanism of the formation process of the pectin-cellulose composite bio-plastic is shown. It can be seen that the binding energy of the most stable addition product geometry predicted by DFT between pectin, cellulose, and citric acid is ΔG = -32.0 kcal / mol (a). Pectin and cellulose are cross-linked together by hydrogen bonds under the action of citric acid. Therefore, based on the DFT results, they finally form a stable structure similar to carboxylic acid dimers (b). Figure 3 Figure 3

[0079] Figure 4 The images of the load-bearing, plasticity, and folding of the bio-plastic prepared in Example 1 are shown. It can be seen that the bio-plastic of very small size can bear a 1 kg weight (a), and it will not break after being folded at will, which corresponds to its high mechanical properties. Figure 4 Figure 4 b and 4c show the images of its folding at will, indicating its excellent flexibility.

[0080] Figure 5 ​​​​​This demonstrates the applicability of the process used in this invention to other fruit peels. It can be seen that the process provided by this invention can process watermelon rind (… Figure 5 a) Pineapple peel ( Figure 5 b) Apple pomace ( Figure 5 c) and cantaloupe rind ( Figure 5 d) Converted into bioplastics. Therefore, this process is applicable to most fruit peels rich in pectin and cellulose.

[0081] Figure 6 The plasticity and processability of the bioplastics prepared in Example 1 are demonstrated. In the presence of water, broken bioplastics can be welded together. They can also be processed into other shapes, such as straws. Based on this property, we crushed the bioplastics and used water as a medium to verify their reprocessability. In the presence of water, the structure formed between pectin, cellulose, and citric acid begins to loosen and break, but with drying and moisture loss, they can rearrange and form a stable structure. Therefore, the bioplastics exhibit hydroplasticity and processability.

[0082] Figure 7 The cytotoxicity results of the bioplastics prepared in Example 1 are presented. As can be seen, the cell viability of the bioplastics remained at a high level (>85%) after 48 hours, demonstrating excellent biocompatibility. Therefore, these bioplastics are biosafe. Since bioplastics are derived from natural, non-toxic plants or edible food ingredients, this biosafety is particularly advantageous for their application in the food packaging field.

[0083] Figure 8 The biodegradability of the bioplastics prepared in Example 1 is demonstrated. Common commercially available PVA plastics are used as a control. It can be seen that whether buried in soil or simply left in the natural environment, they degrade rapidly. In contrast, commercially available plastics are difficult to degrade, illustrating the environmental advantages of the bioplastics provided in this application.

[0084] This invention makes maximum use of fruit peel waste, not only avoiding its damage to the environment and ecology, but also enhancing the application value of fruit peel waste; it has the properties of being biosafe, biodegradable, processable and recyclable, and has great potential to replace petrochemical plastic products (especially in the field of food packaging).

[0085] The above embodiments are preferred embodiments of the present invention, mainly demonstrating and describing the main features and basic principles of the present invention. However, the implementation of the present invention is not limited to the above embodiments. Any modifications, alterations, substitutions, combinations, or simplifications made by those skilled in the art without departing from the spirit and scope of the present invention should be considered within the scope of the present invention.

Claims

1. A method for preparing a pectin-cellulose composite bioplastic based on fruit peel waste, characterized by, Comprising the following steps: 1) drying and crushing the peel; 2) mixing the peel powder with water and performing enzymatic hydrolysis, and centrifuging to obtain the precipitate; 3) mixing the precipitate obtained in step 2) with water, adjusting the pH to 1.8-2.2 using saturated citric acid solution, and performing wall breaking treatment under high pressure environment, followed by magnetic stirring at 65-95℃ for 2-4 h; 4) after cooling the mixture obtained in step 3), placing it in a dialysis bag for dialysis; 5) concentrating the dialyzed mixture obtained in step 4), ultrasonic dispersion, and stirring until uniform to obtain a pectin-cellulose composite film forming slurry; 6) degassing the slurry obtained in step 5), uniformly pouring it onto a glass plate, evaporating the water at room temperature, and then peeling off to obtain the bioplastic; In step 2), the peel powder is mixed with water at a ratio of 1g: 15-30mL; the enzyme used is hemicellulase, and the hemicellulase enzyme activity is ≥200 unit / mg solid, the enzyme addition amount is 0.15%-0.25% of the mass of the peel, and the enzymatic hydrolysis treatment is oscillation treatment at 40℃ for 15-30 min, followed by 5000-6000 rpm centrifugation to obtain the precipitate; In step 3), the pressure of the high pressure environment is 2.0-3.0 MPa; In step 3), after mixing the precipitate with water at a ratio of 1g: 15-30mL, the pH is adjusted to 1.8-2.2 using saturated citric acid solution; the wall breaking treatment is ultrasonic microwave synergistic treatment, the microwave power is 200-500W, the ultrasonic power is 200-400W, and the treatment time is 10-20 min.

2. The preparation method of the pectin-cellulose complex bioplastic based on fruit peel waste according to claim 1, characterized in that, In step 1), the peel is crushed to pass through a 200 mesh sieve, and the peel is selected from one of citrus peel, watermelon peel, cantaloupe peel, pineapple peel, apple peel and residue.

3. The preparation method of the pectin-cellulose complex bioplastic based on fruit peel waste according to claim 1, characterized in that, In step 4), the molecular cut-off of the dialysis bag is 3.5-6.0KDa, and the dialysis time is 24-48h.

4. The preparation method of the pectin-cellulose complex bioplastic based on fruit peel waste according to claim 1, characterized in that, In step 5), 10g of the peel raw material in step 1) is concentrated to 100mL.

5. The preparation method of the pectin-cellulose complex bioplastic based on fruit peel waste according to claim 1, characterized in that, In step 5), the ultrasonic power for ultrasonic dispersion is 200-500W, the ultrasonic time is 5-10min, and then magnetic stirring is performed until completely uniform.

6. The preparation method of the pectin-cellulose complex bioplastic based on fruit peel waste according to claim 1, characterized in that, In step 6), the vacuum degree during degassing is -0.1MPa, the slurry is spread on the glass plate, the thickness of the slurry is 0.3-0.5cm, and after natural evaporation of water at room temperature, the bioplastic is obtained by peeling off.

7. A pectin-cellulose composite bioplastic prepared by the preparation method of any one of claims 1-6.

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