Biomass-based food-contact water-resistant oil-resistant paper as well as preparation method and application of biomass-based food-contact water-resistant oil-resistant paper

Abstract

The invention relates to the technical field of food packaging materials, in particular to biomass-based food-contactable water-resistant and oil-resistant paper as well as a preparation method and application of the biomass-based food-contactable water-resistant and oil-resistant paper. The preparation method comprises the following steps: dissolving chitosan in an acetic acid aqueous solution to obtain a chitosan oil-proof agent, taking filter paper as a carrier, coating the surface of the filter paper with the chitosan oil-proof agent, drying to obtain chitosan coated filter paper, soaking the chitosan coated filter paper in a phytic acid solution, cross-linking the chitosan on the surface of the filter paper with phytic acid to form a three-dimensional network structure, taking out and drying to obtain the chitosan oil-proof filter paper. The biomass-based food-contact water-resistant oil-resistant paper is obtained. The oil-blocking time of the obtained oil-blocking paper is more than 24 hours, the water-blocking time exceeds 30 minutes, and the oil-blocking paper is environment-friendly and degradable, so that the problem of pollution of traditional plastic packaging is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of food packaging materials, and specifically to a biomass-based food-contact water and oil barrier paper and its preparation method and application. Background Art

[0002] Food packaging paper, as a material directly contacting food, its safety and functionality cannot be ignored. Food packaging not only needs to ensure food safety and prevent harmful substances from contacting food, but also needs to have corresponding barrier properties according to the characteristics of various foods, such as water resistance, oil resistance, air barrier, etc. Among them, oil resistance is extremely crucial because oil penetration can not only damage the packaging, but also may contaminate the food, accelerate the spoilage of the food, and shorten the shelf life of the food.

[0003] The biodegradability of biomass-based oil barrier paper enables it to be rapidly decomposed by microorganisms in nature after being discarded, reducing white pollution and promoting the recycling of renewable resources. This is not only beneficial to alleviating the problem of resource shortage, but also reduces the cost of garbage disposal. The development of biomass-based food-contact water and oil barrier paper will promote technological innovation and progress in the food packaging field, drive the food packaging industry towards a more environmentally friendly direction, and at the same time can bring new directions for the utilization of biomass materials in other fields.

[0004] Currently, biomass materials such as starch, sodium alginate, sodium carboxymethyl cellulose, and gelatin have all been reported for use in the preparation of biomass-based oil barrier paper. However, the natural high water absorbency of biomass materials has somewhat restricted the application of oil barrier paper in the food field. How to further improve the water resistance of biomass-based oil barrier paper is an important problem to be solved. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a biomass-based food-contact water and oil barrier paper and its preparation method and application. The present invention develops a product that not only meets the requirements of food packaging but also meets the needs of biodegradability, and is expected to expand the application of bio-based functional paper in the fields of food packaging and barrier packaging.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: A preparation method of a biomass-based food-contact water and oil barrier paper, comprising the following steps: Dissolve chitosan in an acetic acid aqueous solution to obtain a chitosan oil-proof agent.

[0007] Using filter paper as a carrier, coat the chitosan oil-proof agent on the surface of the filter paper and dry it to obtain chitosan-coated filter paper.

[0008] The chitosan-coated filter paper is immersed in the phytic acid solution for soaking. The chitosan on the surface of the filter paper crosslinks with phytic acid to form a three-dimensional network structure, and then it is taken out and dried to obtain the biomass-based water and oil barrier paper that can be in contact with food.

[0009] In the present invention, first, chitosan is dissolved in an aqueous acetic acid solution to obtain a chitosan oil-proof agent. Using the filter paper as a carrier, the chitosan oil-proof agent is coated on the surface of the filter paper and dried to obtain chitosan-coated filter paper. The coating thickness is adjusted by adjusting the coating amount to endow the paper with good oil barrier performance. The chitosan-coated filter paper is immersed in the phytic acid solution for soaking, and a three-dimensional dense crosslinked network is formed through the electrostatic interaction of chitosan and phytic acid, increasing the crosslinking density of chitosan on the surface of the filter paper, further improving the crosslinking density of the coating, and thus enhancing the water barrier ability of the oil barrier paper.

[0010] In a preferred embodiment of the present invention, the mass fraction of the aqueous acetic acid solution is 1%.

[0011] In a preferred embodiment of the present invention, the mass percentage of chitosan in the aqueous acetic acid solution is 1.0% - 2.5%.

[0012] In a preferred embodiment of the present invention, the coating amount of the chitosan solution coated on the surface of the filter paper is 20 g / m² - 30 g / m².

[0013] In a preferred embodiment of the present invention, the mass concentration of the phytic acid solution is 1% - 5%.

[0014] In a preferred embodiment of the present invention, the further coating amount of the chitosan solution coated on the surface of the filter paper is 30 g / m².

[0015] In a preferred embodiment of the present invention, the soaking time of the chitosan-coated filter paper immersed in the phytic acid solution is 5 min - 15 min.

[0016] In a preferred embodiment of the present invention, the further soaking time of the chitosan-coated filter paper immersed in the 5% phytic acid solution is 5 min - 10 min.

[0017] Another object of the present invention is to provide a biomass-based water and oil barrier paper that can be in contact with food prepared by the preparation method described in any one of the above.

[0018] The application of the biomass-based water and oil barrier paper that can be in contact with food described in the present invention in food packaging.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 2. The present invention dissolves chitosan in an aqueous acetic acid solution to obtain a chitosan oil-proof agent; using filter paper as a carrier, the chitosan oil-proof agent is coated on the surface of the filter paper and dried to obtain chitosan-coated filter paper; the chitosan-coated filter paper is immersed in a phytic acid solution for soaking, and the chitosan on the filter paper surface crosslinks with phytic acid to form a three-dimensional network structure, then taken out and dried to obtain a biomass-based food-contact water and oil barrier paper. After chitosan coating, as the coating amount increases, the pore structure between the fibers on the filter paper surface is gradually filled by the chitosan film layer, and a dense film layer structure is formed on the filter paper surface. Such a structure can well block grease and is beneficial to improving the oil barrier performance of the paper sample. Then, the chitosan-coated paper is immersed in a phytic acid solution for soaking for a period of time, and a crosslinking reaction occurs between chitosan and phytic acid, enabling the sample to obtain the P element of phytic acid, thereby enhancing the oil and water barrier ability and expanding the application of bio-based paper functional paper in the fields of food packaging and barrier packaging.

[0020] 3. The present invention can facilitate the formation of a dense film layer structure on the surface by adjusting the coating amount of the chitosan oil-proof agent, thereby improving its grease barrier performance. And after the chitosan-coated paper is immersed in the phytic acid solution, a crosslinking reaction occurs to enhance the oil and water barrier ability.

[0021] 4. The present invention prepares a functional paper with excellent oil and water barrier performance by coating a chitosan oil-proof agent and crosslinking modification with phytic acid. A three-dimensional network structure is formed on its surface, increasing the chitosan crosslinking density on the surface of the functional paper and further improving the water barrier performance of the coating. Brief Description of the Drawings

[0022] Figure 1 It is the SEM diagram of the biomass-based food-contact water and oil barrier paper prepared in Examples 1 - 5 of the present invention.

[0023] Figure 2 It is the infrared analysis diagram of the unmodified filter paper prepared in Comparative Example 1, the chitosan oil-proof agent-coated filter paper prepared in Comparative Example 5, and the biomass-based food-contact water and oil barrier paper prepared in Example 5 of the present invention.

[0024] Figure 3 It is the XRD diagram of the chitosan oil-proof agent-coated filter paper prepared in Comparative Example 1 and Comparative Example 4 and the biomass-based food-contact water and oil barrier paper prepared in Example 5 of the present invention.

[0025] Figure 4 It is the total surface element distribution spectrum diagram of the biomass-based food-contact water and oil barrier paper prepared in Example 3 of the present invention.

[0026] Figure 5 It is the broken line diagram of the total surface element distribution spectrum of the biomass-based food-contact water and oil barrier paper prepared in Example 3 of the present invention.

[0027] Figure 6Among them, A-F are SEM images of the unmodified filter paper of Comparative Example 1 of the present invention and the chitosan oil-proof agent-coated filter papers prepared in Comparative Examples 2-6 under the same magnification of the microscope.

[0028] Figure 7 Among them are the optical pictures of the modified filter papers prepared in Comparative Examples 4-6 after 24 hours of oil resistance, taking castor oil as an example.

[0029] Figure 8 Among them are the SEM images of the modified filter papers prepared in Comparative Example 7 and Comparative Example 8.

[0030] Figure 9 Among them are the SEM images of the modified filter papers prepared in Comparative Example 9, Comparative Example 10, and Comparative Example 11.

[0031] Figure 10 Among them, a1~a3, b1~b3, and c1~c3 are the optical pictures of the oil resistance contact angles of the filter papers prepared in Comparative Example 1, Comparative Example 6, and Example 5 changing with time.

[0032] Figure 11 Among them, a1~a3, b1~b3, and c1~c3 are the optical pictures of the water resistance contact angles of the filter papers prepared in Comparative Example 1, Comparative Example 6, and Example 5 changing with time.

[0033] Figure 12 Are the optical pictures of the oil resistance and water resistance contact angles of the biomass-based food-contactable water and oil resistant paper prepared in Example 5 changing with time. Detailed implementation mode

[0034] The following combines the embodiments of the present invention, and uses the preferred embodiments and the accompanying drawings to cooperate with a detailed description. The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0035] It should be noted that all the professional terms used in the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the following embodiments of the present invention can be obtained through the market or prepared by existing methods.

[0036] Example 1 A preparation method of a biomass-based food-contactable water and oil resistant paper, comprising the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%; (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 20 g / m², place it in an oven and dry it at 80 °C for later use to obtain chitosan-coated filter paper; (3) Immerse the chitosan-coated filter paper in a 5%wt phytic acid aqueous solution for 5 minutes. The chitosan on the filter paper surface crosslinks with phytic acid to form a three-dimensional network structure. After taking it out, place it in an oven and dry it at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0037] Example 2 A method for preparing a biomass-based water and oil barrier paper for food contact, comprising the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 2.5%; (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 25 g / m², place it in an oven and dry it at 80 °C for later use to obtain chitosan-coated filter paper; (3) Immerse the chitosan-coated filter paper in a 5%wt phytic acid aqueous solution for 5 minutes. The chitosan on the filter paper surface crosslinks with phytic acid to form a three-dimensional network structure. After taking it out, place it in an oven and dry it at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0038] Example 3 A method for preparing a biomass-based water and oil barrier paper for food contact, comprising the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1%; (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry it at 80 °C for later use to obtain chitosan-coated filter paper; (3) Immerse the chitosan-coated filter paper in a 5%wt phytic acid aqueous solution for 5 minutes. The chitosan on the filter paper surface crosslinks with phytic acid to form a three-dimensional network structure. After taking it out, place it in an oven and dry it at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0039] Example 4 A method for preparing a biomass-based water and oil barrier paper for food contact, comprising the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 2%; (2)Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry it at 80 °C for standby to obtain chitosan-coated filter paper; (3)Immerse the chitosan-coated filter paper in a 5%wt phytic acid aqueous solution for 15 min. The chitosan on the filter paper surface crosslinks with phytic acid to form a three-dimensional network structure. After taking it out, place it in an oven and dry it at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0040] Example 5 A preparation method of a biomass-based water and oil barrier paper for food contact, comprising the following steps: (1)Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%; (2)Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry it at 80 °C for standby to obtain chitosan-coated filter paper; (3)Immerse the chitosan-coated filter paper in a 5% phytic acid solution for 10 min. The chitosan on the filter paper surface crosslinks with phytic acid to form a three-dimensional network structure. After taking it out, place it in an oven and dry it at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0041] Example 6 A preparation method of a biomass-based water and oil barrier paper for food contact, comprising the following steps: (1)Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%; (2)Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry it at 80 °C for standby to obtain chitosan-coated filter paper; (3)Immerse the chitosan-coated filter paper in a 5%wt phytic acid aqueous solution for 15 min. The chitosan on the filter paper surface crosslinks with phytic acid to form a three-dimensional network structure. After taking it out, place it in an oven and dry it at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0042] Comparative Example 1 A preparation method of unmodified filter paper, comprising the following steps: Cut the qualitative filter paper into filter paper with a size of 10*10 cm to obtain unmodified filter paper.

[0043] Comparative Example 2 A preparation method of chitosan-coated filter paper, comprising the following steps: (1) Dissolve chitosan in an aqueous acetic acid solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%.

[0044] (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 5 g / m², and place it in an oven at 80 °C for drying and standby to obtain chitosan-coated filter paper.

[0045] Comparative Example 3 A method for preparing chitosan-coated filter paper, comprising the following steps: (1) Dissolve chitosan in an aqueous acetic acid solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%.

[0046] (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 10 g / m², and place it in an oven at 80 °C for drying and standby to obtain chitosan-coated filter paper.

[0047] Comparative Example 4 A method for preparing chitosan-coated filter paper, comprising the following steps: (1) Dissolve chitosan in an aqueous acetic acid solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%.

[0048] (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 15 g / m², and place it in an oven at 80 °C for drying and standby to obtain chitosan-coated filter paper.

[0049] Comparative Example 5 A method for preparing chitosan-coated filter paper, comprising the following steps: (1) Dissolve chitosan in an aqueous acetic acid solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%.

[0050] (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 20 g / m², and place it in an oven at 80 °C for drying and standby to obtain chitosan-coated filter paper.

[0051] Comparative Example 6 A method for preparing chitosan-coated filter paper, comprising the following steps: (1) Dissolve chitosan in an aqueous acetic acid solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%.

[0052] (2) Using a 10 * 10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry it at 80 °C for standby to obtain a chitosan oil-proof agent-coated filter paper.

[0053] Comparative Example 7 A preparation method of chitosan-coated filter paper includes the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 0.5%.

[0054] (2) Using a 10 * 10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry it at 80 °C for standby to obtain a chitosan oil-proof agent-coated filter paper.

[0055] Comparative Example 8 A preparation method of chitosan-coated filter paper includes the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 3%.

[0056] (2) Using a 10 * 10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry it at 80 °C for standby to obtain a chitosan oil-proof agent-coated filter paper.

[0057] Comparative Example 9 A preparation method of chitosan-coated filter paper includes the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%; (2) Using a 10 * 10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 20 g / m², place it in an oven and dry it at 80 °C for standby to obtain a chitosan-coated filter paper; (3) Immerse the chitosan-coated filter paper in a 1% phytic acid solution and soak for 1 h. The chitosan on the filter paper surface crosslinks with phytic acid to form a three-dimensional network structure. Take it out and place it in an oven to dry at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0058] Comparative Example 10 A preparation method of a biomass-based water and oil barrier paper for food contact includes the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%; (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry at 80 °C for later use to obtain chitosan-coated filter paper; (3) Immerse the chitosan-coated filter paper in a 5% phytic acid solution and soak for 20 min. The chitosan on the surface of the filter paper crosslinks with phytic acid to form a three-dimensional network structure. After taking it out, place it in an oven and dry at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0059] Comparative Example 11 A method for preparing a biomass-based water and oil barrier paper for food contact, comprising the following steps: (1) Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1% to obtain a chitosan oil-proof agent with a mass fraction of 1.5%; (2) Using a 10*10 cm qualitative filter paper as a carrier, coat the surface of the filter paper with a chitosan oil-proof agent at a coating amount of 30 g / m², place it in an oven and dry at 80 °C for later use to obtain chitosan-coated filter paper; (3) Immerse the chitosan-coated filter paper in a 5% phytic acid solution and soak for 30 min. The chitosan on the surface of the filter paper crosslinks with phytic acid to form a three-dimensional network structure. After taking it out, place it in an oven and dry at 80 °C to obtain a biomass-based water and oil barrier paper for food contact.

[0060] Result analysis Figure 1 This is the SEM image of the water and oil barrier papers prepared in Examples 1-5 of the present invention. It can be seen from the figure that a dense film layer structure is uniformly coated on the surface of the modified filter papers prepared under different conditions, providing a guarantee for the water and oil barrier performance of the modified filter papers.

[0061] Figure 2 This is the infrared analysis image of the unmodified filter paper prepared in Comparative Example 1, the chitosan oil-proof agent-coated filter paper prepared in Comparative Example 5, and the biomass-based water and oil barrier paper for food contact prepared in Example 5 of the present invention. It can be seen from the figure that after coating chitosan on the surface, a bending vibration absorption peak of NH2 in chitosan appears at 1544 cm -1 and a vibration peak of C-O-C glycosidic bond in chitosan appears at 1096 cm -1 After crosslinking with phytic acid, a stretching vibration peak of P-O in phytic acid appears at 1090 cm -1 and a vibration peak of the C-C backbone of the inositol ring of phytic acid appears at 979 cm -1 Since the intermolecular hydrogen bond network is enhanced after the crosslinking of chitosan and phytic acid (hydrogen bond interaction between chitosan -OH and phytic acid -P-OH), the infrared spectrum after crosslinking is in the range of 3200-3600 cm -1The intensity of the -OH characteristic peak increases (hydrogen bonds are enhanced), and the amino group (-NH2) of chitosan and the phosphate group (-PO 3- ) of phytic acid undergo electrostatic interaction (protonation to form -NH…O-P=O or covalent crosslinking, resulting in a decrease or even disappearance of the bending vibration peak intensity of the amino group, causing the -NH2 peak at 1544 cm -1 of chitosan to weaken significantly. Therefore, it can be proved that chitosan was successfully coated on the filter paper surface, and a crosslinking reaction occurred between chitosan and phytic acid.

[0062] Figure 3 XRD patterns of the filter paper coated with the chitosan oil-proof agent prepared in Comparative Example 1 and Comparative Example 4 of the present invention and the biomass-based food-contact oil-resistant paper prepared in Example 7. It can be seen from the figure that the characteristic derivative peaks of cellulose appear at 2θ = 14.96° and 22.56° for the unmodified filter paper, and there is no obvious difference in the diffraction peaks of the three samples, indicating good compatibility between the filter paper, chitosan, and phytic acid. Moreover, the crystallinity peak area of cellulose in the filter paper crosslinked with chitosan and chitosan and phytic acid becomes smaller, and the intensity of the diffraction peak at 2θ = 22.56° decreases slightly. These are caused by the crosslinking of chitosan, phytic acid, and the cellulose of the paper, proving that chitosan has successfully formed a film on the paper surface.

[0063] Figure 4 This is the total surface element distribution spectrogram of the biomass-based food-contact water and oil-resistant paper prepared in Example 3 of the present invention. Figure 5 This is the total surface element distribution spectrogram of the biomass-based food-contact water and oil-resistant paper prepared in Example 3 of the present invention. It can be seen from the figure that after crosslinking with phytic acid, the P element of phytic acid appears on the filter paper surface. That is, after immersing the filter paper@chitosan sample in the phytic acid solution, a crosslinking reaction occurs between chitosan and phytic acid, enabling the sample to obtain the P element of phytic acid, thereby enhancing the oil and water resistance ability.

[0064] Figure 6 In the figure, A-F are SEM images of the unmodified filter paper in Comparative Example 1 of the present invention and the filter paper coated with the chitosan oil-proof agent prepared in Comparative Examples 2-6 at the same magnification. It can be seen from the figure that the structure of cellulose fibers intertwined vertically and horizontally can be clearly seen on the surface of the unmodified filter paper, and there are a large number of pores between the fibers. After coating with the chitosan oil-proof agent, and with the increase of the coating amount (15 g / m 2 - 30 g / m 2 ), the pore structure between the fibers on the filter paper surface is gradually filled with the chitosan film layer, and a dense film layer structure is formed on the filter paper surface. Such a structure can effectively block grease and is beneficial to improving the oil resistance performance of the paper sample.

[0065] Figure 8SEM images of the chitosan-modified filter papers prepared in Comparative Example 7 and Comparative Example 8. As can be seen from the figures, the chitosan concentration is relatively low (0.5% wt). To achieve a coating amount of 30 g / m 2 2, the coating amount of the chitosan aqueous solution is relatively large. Since a low chitosan concentration results in a low viscosity, the chitosan aqueous solution easily overflows from the surface of the filter paper, leading to a decrease in the chitosan content forming the film on the filter paper surface and making it difficult to cover the pore structure on the filter paper surface, resulting in poor oil and water resistance. When coating the filter paper with a relatively high solid content (3% wt), due to the high solid content and large viscosity of chitosan, the leveling property is poor, and it is difficult for chitosan to penetrate into the internal pore structure of the filter paper, resulting in the formation of a chitosan film on the filter paper surface and also poor oil and water resistance.

[0066] Figure 9 SEM images of the modified filter papers prepared in Comparative Example 9, Comparative Example 10 and Comparative Example 11. As can be seen from the figures, after cross-linking the filter paper with a 1% wt phytic acid aqueous solution for 1 hour, fiber void structures are exposed on the filter paper surface. This is because chitosan is easily dissolved in the weakly acidic phytic acid solution, resulting in a thinner chitosan film layer and a decrease in oil and water resistance; after cross-linking the filter paper with a 5% wt phytic acid aqueous solution for 20 min and 30 min, it can be seen that there is also a problem of dissolution and shedding of chitosan on the filter paper surface, making the oil and water resistance of the modified filter paper poor. Therefore, it is particularly important to select an appropriate concentration of the phytic acid aqueous solution and an appropriate cross-linking time.

[0067] Figure 10 In a1~a3, b1~b3 and c1~c3, the optical pictures of the oil contact angles of the filter papers prepared in Comparative Example 1, Comparative Example 6 and Example 5 changing with time are shown respectively. To further evaluate the oil resistance and permeability of the coated paper, the oil contact angle test was carried out using castor oil ( Figure 10 ). The results show that the untreated filter paper (a1 - a3) rapidly absorbs the oil droplet after contacting the oil droplet and cannot form an obvious contact angle, indicating that it has almost no oil resistance. In contrast, the chitosan-coated filter paper (b1 - b3) shows a certain degree of oil resistance at the initial stage (CA = 30.8°), but as time goes by (3 min, 10 min), the contact angle gradually decreases (down to 25.8°), indicating that the oil droplet gradually spreads and the oil resistance performance decreases. For the chitosan-coated filter paper (c1 - c3) treated with phytic acid cross-linking, although the initial contact angle is slightly lower (CA = 21.0°), its oil resistance performance shows extremely high stability, and the contact angle hardly changes during the test time (only drops to 20.5°), indicating that phytic acid cross-linking significantly enhances the oil resistance and permeability of the coating and effectively maintains the long-term stability of the oil resistance performance.

[0068] Figure 11Among them, a1 - a3, b1 - b3, and c1 - c3 are respectively the optical pictures of the water - repellent contact angles of the filter papers prepared in Comparative Example 1, Comparative Example 6, and Example 5 changing with time, and the effects of different treatment methods on the water - penetration resistance ability of the filter papers were evaluated. The results showed that the untreated filter paper (such as a1 - a3) could hardly block the penetration of water droplets due to its porous structure and hydrophilicity. The water droplets spread rapidly on the surface of the filter paper and could not form a stable contact angle. Although the chitosan coating could temporarily improve the hydrophobicity (81.3°), the coating was prone to swelling and failure after contacting water droplets for 3 minutes, and the water - blocking performance decreased significantly (such as b1 - b3). In contrast, the phytic acid - crosslinked chitosan coating showed excellent water - repellent stability (such as c1 - c3). Its dense cross - linked network structure could effectively resist the penetration of water droplets, and the contact angle retention rate was high, indicating that phytic acid cross - linking significantly enhanced the water resistance and structural integrity of the chitosan coating.

[0069] Figure 12 It is the optical picture of the oil - and water - repellent contact angle of the biomass - based food - contactable water - and oil - blocking paper prepared in Example 5 changing with time. The phytic acid - crosslinked chitosan coating showed excellent water - repellent stability. Its dense cross - linked network structure could effectively resist the penetration of water droplets, and the contact angle retention rate was high, indicating that phytic acid cross - linking significantly enhanced the water resistance and structural integrity of the chitosan coating. For the chitosan - coated filter paper treated by phytic acid cross - linking, although the initial contact angle was slightly lower (CA = 21.0°), its oil - blocking performance showed extremely high stability, and the contact angle hardly changed during the test time (only decreased to 20.5°), indicating that phytic acid cross - linking significantly enhanced the oil - penetration resistance ability of the coating and effectively maintained the long - term stability of the oil - blocking performance.

[0070] Table 1 shows the oil - proof grade test results of the chitosan oil - proof agent - coated filter papers prepared in Comparative Examples 1 - 6 of the present invention. It can be seen from the figure that when the coating amount of the chitosan oil - proof agent is above 15 g / m 2 the oil - proof grade reaches above grade 12. Combining Figure 7 with the optical pictures of the biomass - based oil - blocking papers prepared in Comparative Examples 4 - 6 of the present invention after blocking castor oil for 24 hours, it can be concluded that when the coating amount of chitosan is above 15 g / m 2 the oil - proof effect of the coated filter paper can basically meet the daily use requirements.

[0071] Based on the above analysis, when the coating amount of the chitosan oil - proof agent is 20 - 30 g / m 2, and the obtained chitosan-coated filter paper has the best effect on the biomass-based food-contact water- and oil-resistant paper soaked in 1-5 wt% phytic acid solution for 5-15 minutes. The time for water droplets to penetrate the paper is more than 30 minutes, and the time for ordinary castor oil to penetrate the paper can reach more than 24 hours. Therefore, the biomass-based food-contact water- and oil-resistant paper prepared by the present invention can effectively solve the problem of traditional plastic packaging pollution and is expected to expand the application of bio-paper-based functional paper in the fields of food packaging and barrier packaging.

[0072] Table 1 shows the oil-proof grades of chitosan oil-proof agents with different coating amounts (√ indicates that the corresponding oil-proof grade can be achieved, and × indicates that the corresponding oil-proof grade cannot be achieved). Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, these changes and modifications are also intended to be included.

Claims

1. A preparation method of a biomass-based water and oil barrier paper for food contact, characterized in that, It includes the following steps: Dissolve chitosan in an acetic acid aqueous solution to obtain a chitosan oil-proof agent; Using filter paper as a carrier, coat the surface of the filter paper with the chitosan oil-proof agent and dry it to obtain chitosan-coated filter paper; Immerse the chitosan-coated filter paper in a phytic acid solution for soaking. The chitosan on the surface of the filter paper crosslinks with phytic acid to form a three-dimensional network structure, take it out and dry it to obtain a biomass-based water and oil barrier paper for food contact.

2. The preparation method of the biomass-based water and oil barrier paper for food contact according to claim 1, characterized in that, The mass percentage of chitosan in the acetic acid aqueous solution is 1.0% - 2.5%.

3. The preparation method of the biomass-based water and oil barrier paper for food contact according to claim 1, wherein, The coating amount of the chitosan solution on the surface of the filter paper is 20 g / m² - 30 g / m².

4. The preparation method of the biomass-based water and oil barrier paper for food contact according to claim 1, wherein, The mass concentration of the phytic acid solution is 1% - 5%.

5. The preparation method of the biomass-based water and oil barrier paper for food contact according to claim 1, characterized in that, The soaking time for immersing the chitosan-coated filter paper in the phytic acid solution is 5 min - 15 min.

6. A biomass-based water and oil barrier paper for food contact prepared by the preparation method according to any one of claims 1 - 5.

7. The application of the biomass-based water and oil barrier paper for food contact according to claim 6 in food packaging.

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