Self-repairing biodegradable mulching film and application thereof in crop cultivation with mulching
By introducing sugar alcohol chain extenders into the PBAT main chain to form a dynamic borate ester crosslinking network, the problems of self-repair and controllable degradation of PBAT mulch film were solved, realizing the self-repair and temperature-responsive switching of the mulch film after mechanical damage.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-16
- Publication Date
- 2026-07-21
AI Technical Summary
Traditional PBAT mulch films cannot self-repair after mechanical damage, have uncontrollable degradation cycles, limited functionality, and cannot responsively switch according to environmental stimuli.
By introducing sugar alcohols containing vicinal diol structures into the PBAT backbone as chain extenders, a dynamic borate ester crosslinking network is formed, achieving self-healing and temperature responsiveness.
The plastic film can self-repair after mechanical damage, with a tensile strength recovery rate of 60-90%. It maintains high strength at low temperatures and degrades more rapidly at high temperatures, meeting the needs of crop growth cycles.
Smart Images
Figure CN122427484A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of biodegradable materials technology, and in particular to a self-healing biodegradable mulch film based on dynamic borate ester crosslinking and its application in crop mulching cultivation. Background Technology
[0002] Polybutylene adipate / terephthalate (PBAT) is an important biodegradable polymer material, widely used in agricultural mulch films due to its excellent flexibility and processing properties. However, traditional PBAT mulch films have the following technical defects: Irreversible mechanical damage: During field operations, the mulch film is susceptible to mechanical damage (such as punctures and tears), and once micro-cracks appear, it cannot self-repair, leading to a rapid loss of its heat preservation and moisture retention functions, requiring early replacement or recycling; Uncontrollable degradation cycle: The degradation rate of existing PBAT mulch films is mainly passively determined by environmental temperature and humidity, and cannot be intelligently controlled according to the crop growth cycle, resulting in a mismatch between "crop not harvested, mulch film already degraded" and "crop harvested, mulch film not degraded"; Single function: Traditional mulch films only have a physical covering function and lack the ability to respond to environmental stimuli, failing to achieve the intelligent switching of "maintaining strength during use and accelerating degradation after harvest".
[0003] In recent years, the development of dynamic covalent bonds and materials has provided new solutions to the above problems. Among them, borate ester bonds are widely used in self-healing hydrogel materials due to their reversible breaking and recombination properties under mild conditions. However, introducing the dynamic crosslinking mechanism of borate esters into the PBAT mulch film system faces the following technical challenges: the PBAT molecular chain itself does not contain vicinal diol structures and cannot directly form borate ester bonds with boric acid / borax; the subsequent addition of small molecules containing vicinal diols is prone to migration and precipitation, leading to instability of the crosslinking network; during melt processing, premature formation of borate ester bonds will cause a sharp increase in melt viscosity, making blown film forming difficult.
[0004] Therefore, there is an urgent need to develop a new type of mulch film material that can stably introduce the 1,000 diol structure into the PBAT backbone and has both processability and self-healing properties. Summary of the Invention
[0005] Based on the technical problems existing in the background technology, the present invention proposes a self-healing biodegradable mulch film and its application in crop mulching cultivation. By introducing a sugar alcohol containing an ortho-diol structure as a chain extender into the PBAT main chain, a copolymer containing an ortho-diol side group structure is constructed, and then a dynamic borate ester crosslinking network is formed with borax, thereby realizing the self-healing function, temperature responsiveness and controllable degradation of the mulch film.
[0006] The present invention proposes a self-healing biodegradable mulch film, which is obtained by dynamically covalently crosslinking a sugar alcohol modified poly(adipate / butyl terephthalate) copolymer containing an ortho-diol structure with borax to form borate ester bonds, and then blow molding the film.
[0007] In this invention, the dynamic borate ester bond has temperature reversibility and can undergo reversible breakage and recombination within the range of 25-80 ℃; the resulting mulch film can achieve self-repair under ambient temperature and humidity after mechanical damage (tensile strength recovery rate ≥60% in 24 h) and has temperature responsiveness (crosslinking density can change reversibly within the range of 25-80 ℃), realizing the intelligent switching of "maintaining strength during service life and promoting degradation after harvest".
[0008] Preferably, the sugar alcohol modified poly(adipic acid) / butyl terephthalate copolymer is obtained by melt polycondensation of terephthalic acid, adipic acid, 1,4-butanediol and a sugar alcohol containing an ortho-diol structure.
[0009] Preferably, the sugar alcohol is at least one selected from sorbitol, mannitol, isosorbide, or maltitol; Preferably, the molar ratio of the sugar alcohol and 1,4-butanediol to the total diol of the sugar alcohol is 0.05-0.1:1; the molar ratio of terephthalic acid to adipic acid is 1:0.8-1.2; and the molar ratio of the total diol of 1,4-butanediol and the sugar alcohol to the total dicarboxylic acid of terephthalic acid and adipic acid is 1.0-1.5:1.
[0010] Preferably, the melt polycondensation includes: an esterification stage, a pre-polycondensation stage, and a final polycondensation stage; Preferably, the esterification stage includes: heating to 180-220 °C, carrying out the esterification reaction under normal pressure and inert gas protection, and achieving an esterification rate of over 95%; the pre-condensation stage includes: continuing to heat to 220-240 °C, reducing the pressure to 5-10 kPa, and reacting until the stirring torque increases; the final condensation stage includes: continuing to heat to 235-250 °C, evacuating to <100 Pa, and reacting until the target intrinsic viscosity is reached. Preferably, in the melt polycondensation, terephthalic acid, adipic acid and 1,4-butanediol are first mixed and reacted, and then the sugar alcohol is added and reacted after the temperature is raised to 180-220 °C.
[0011] Preferably, the dynamic covalent crosslinking specifically includes: adding the sugar alcohol-modified poly(adipic acid / butyl terephthalate) copolymer and borax dispersion into a twin-screw extruder for melt blending.
[0012] Preferably, the borax dispersion is a glycerol dispersion of borax, which is obtained by grinding borax to D50≤10 μm and then pre-dispersing it with glycerol in a high-speed mixer at a mass ratio of 1:1-2.
[0013] Preferably, the melt blending temperature is not higher than 170 ℃, the screw speed of the twin-screw extruder is 100-150 rpm, and the material residence time is 2-3 min.
[0014] Preferably, when the sugar alcohol-modified poly(adipate) / butyl terephthalate copolymer and borax dispersion are added to a twin-screw extruder for melt blending, coupling agent, opening agent, ultraviolet absorber and antioxidant are also added. Preferably, the coupling agent is at least one of aluminate coupling agent or silane coupling agent, the opening agent is at least one of oleamide, talc or silica, the ultraviolet absorber is at least one of UV-234 or UV-326, and the antioxidant is at least one of antioxidant 1010 or antioxidant 1076. Preferably, by weight, the sugar alcohol modified PBAT copolymer comprises 100 parts, borax pre-dispersion solution comprises 1-10 parts, coupling agent comprises 0.001-5 parts, opening agent comprises 0.001-1 parts, ultraviolet absorber comprises 0.001-1 parts, and antioxidant comprises 0.001-1 parts.
[0015] Preferably, the blown film is formed by blown film forming using a blown film machine, with a blown film forming temperature of 140-165 ℃, a blow-up ratio of 2.0-2.5, a traction speed of 5-15 m / min, and a film thickness of 0.008-0.015 mm.
[0016] The present invention also proposes an application of the above-mentioned mulch film in crop mulching cultivation, wherein after mechanical damage, the mulch film is placed at 25-80 ℃ and relative humidity ≥60% for 12-48 h, and the tensile strength recovery rate reaches more than 60%.
[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The dynamic borate ester crosslinking mechanism was introduced into the PBAT mulch film system for the first time: by introducing sugar alcohol chain extender in the PBAT synthesis stage, the vicinal diol structure was stably embedded in the main chain, which solved the problem of easy migration and precipitation of small molecules added later, and the stability of the crosslinking network was significantly improved.
[0018] (2) The self-repair function of the mulch film is realized: After mechanical damage in the field, the dynamic borate ester bond undergoes reversible breakage and recombination under ambient temperature and humidity. The tensile strength recovery rate reaches 60-90% within 12-48 hours, which significantly extends the service life of the mulch film.
[0019] (3) Imparting intelligent temperature response properties to the mulch film: The temperature reversibility of borate ester bonds enables the mulch film to maintain high cross-linking density and high strength at low temperatures (<40 ℃) to meet the needs of crop growth period; at high temperatures (>60 ℃), the cross-linking density decreases and degradation is accelerated, realizing the intelligent switching of "maintaining strength during use and promoting degradation after harvest".
[0020] (4) Green and sustainable raw material sources: Sugar alcohols (sorbitol, mannitol, etc.) can be obtained from biomass resources, which is in line with the environmental protection concept of biodegradable materials. Attached Figure Description
[0021] Figure 1 This is a schematic diagram illustrating the formation of dynamic borate ester bonds in the self-healing biodegradable mulch film described in this invention. Detailed Implementation
[0022] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.
[0023] Example 1
[0024] A self-healing biodegradable mulch film is prepared by the following method: (1) PTA (1.661 kg, 10 mol), AA (1.461 kg, 10 mol), and BDO (1.983 kg, 22 mol) were added to a stainless steel reactor. Nitrogen gas was purged three times, maintaining a weak nitrogen flow. The temperature was first raised to 180 °C, and tetrabutyl titanate (TBT) (4.68 g, 0.15 wt% relative to total acid) was added as a catalyst. The temperature was then raised to 200 °C at a rate of 1 °C / min, and sorbitol (0.404 kg, 2.22 mol) was added. The temperature was further raised to 220 °C, and the reaction was maintained for 2.5 h. The esterification stage ended when the amount of water distilled reached 97% of the theoretical value. The temperature was then raised to 230 °C, and the vacuum pump was turned on to gradually reduce the pressure to 5 kPa. The reaction was continued for 1.5 h, and the stirring torque increased significantly. The temperature was then raised to 245 °C, and the vacuum was reduced to 80 Pa. The reaction was continued for 2.5 h. h, Nitrogen gas is used to break the vacuum, the material is discharged, cooled, and pelletized to obtain sorbitol-modified PBAT copolymer (PBAT-S10). Its intrinsic viscosity [η] = 1.05 dL / g (phenol / tetrachloroethane, 25℃), number average molecular weight Mn = 45,000 g / mol (GPC, THF phase), and vicinal diol content: 0.55 mmol / g (determined by periodic acid oxidation method). (2) Borax (sodium tetraborate decahydrate, 0.5 kg) was ground in a ball mill to D50=8 μm and mixed with glycerol (0.5 kg) in a high-speed mixer. The stirring speed was set to 2000 rpm and the time was 10 min to obtain a uniform paste-like borax dispersion. The borax dispersion (1 kg) was mixed with PBAT-S10 (10 kg), aluminate coupling agent (0.1 kg), oleamide (0.05 kg), UV-234 (0.05 kg) and antioxidant 1010 (0.05 kg) in a twin-screw extruder for melt blending. The temperature was set to 140 / 150 / 160 / 165 / 160 ℃, the screw speed was 120 rpm, and the material residence time was 3 min to obtain dynamically borate ester crosslinked PBAT granules. (3) Add the dynamically borate crosslinked PBAT granules into a blown film machine for blow molding. Set the temperature to 145 / 155 / 160 / 165 / 160 ℃, the blow-up ratio to 2.2, and the traction speed to 8 m / min to obtain a self-healing biodegradable mulch film with a film thickness of 0.010 mm.
[0025] According to the national standard GB / T 1040.3, the above-mentioned self-healing biodegradable mulch film was cut into standard samples. Using a blade, a cut of about 50% width was made in the middle of the sample perpendicular to the tensile direction to form a through crack. The samples were placed at 40 ℃ and 75% relative humidity for 24 h. The results are shown in Table 1 below: Table 1. Test results of the self-healing performance of the mulch film in Example 1
[0026] Macroscopic observation: The incision has completely closed, and there are no obvious cracks visible to the naked eye.
[0027] The above-mentioned PBAT granules were hot-pressed into 1 mm thick sheets on a flat vulcanizing machine, cut into 25 mm diameter discs, and subjected to temperature scanning tests on a rotational rheometer. The test conditions were: frequency 1 Hz, strain 0.5%, heating rate 2 ℃ / min, and temperature range 30-90 ℃. The results are shown in Table 2 below. Table 2 Test results of the temperature response performance of the mulch film in Example 1
[0028] As shown in Table 2 above, the energy storage modulus decreases significantly with increasing temperature, dropping to 40.6% of that at 30℃ at 60℃, indicating that the dynamic borate ester bonds dissociate at high temperatures and the network relaxes.
[0029] Example 2
[0030] A self-healing biodegradable mulch film is prepared by the method described in Example 1, except that in step (1) mannitol is used instead of sorbitol in equal molar amounts to obtain mannitol-modified PBAT copolymer (PBAT-M10).
[0031] Following the national standard GB / T 1040.3, the aforementioned self-healing biodegradable mulch film was cut into standard specimens. A blade was used to cut approximately 50% of the width of each specimen perpendicular to the tensile direction in the middle of the specimen, creating a through crack. The specimens were then placed at 40 ℃ and 75% relative humidity for 24 h. The results are shown in Table 3 below. Table 3. Test results of the self-healing performance of the mulch film in Example 2
[0032] Macroscopic observation: The incision has completely closed, and there are no obvious cracks visible to the naked eye.
[0033] As shown in Table 3 above, the tensile strength of the mulch film in Example 2 is higher than that in Example 1, and the recovery rate after 24 hours of self-healing is 83.6%, which is also slightly higher than that of Example 1. This indicates that the mannitol-modified system has better mechanical properties and comparable self-healing effect.
[0034] Example 3
[0035] A self-healing biodegradable mulch film is prepared by the method described in Example 1, except that sorbitol (0.194 kg, 1.05 mol) is added in step (1).
[0036] Following the national standard GB / T 1040.3, the aforementioned self-healing biodegradable mulch film was cut into standard samples. A blade was used to cut approximately 50% of the sample's width perpendicular to the tensile direction in the middle of the sample, creating a through crack. The samples were then placed at 40 ℃ and 75% relative humidity for 24 h. The results are shown in Table 4 below. Table 4. Test results of the self-healing performance of the mulch film in Example 3
[0037] Macroscopic observation: The incision has completely closed, and there are no obvious cracks visible to the naked eye.
[0038] As shown in Table 4 above, the amount of sorbitol added in Example 3 was reduced, which led to a decrease in the portion of the system connected with boric acid, thereby reducing the self-repairing ability of the system.
[0039] Example 4
[0040] A self-healing biodegradable mulch film is prepared by the method described in Example 1, except that borax dispersion (0.5 kg) is added in step (2).
[0041] Following the national standard GB / T 1040.3, the aforementioned self-healing biodegradable mulch film was cut into standard samples. A blade was used to cut approximately 50% of the sample's width perpendicular to the tensile direction in the middle of the sample, creating a through crack. The samples were then placed at 40 ℃ and 75% relative humidity for 24 h. The results are shown in Table 5 below: Table 5. Test results of the self-healing performance of the mulch film in Example 4
[0042] Macroscopic observation: The incision has completely closed, and there are no obvious cracks visible to the naked eye.
[0043] As shown in Table 5 above, the amount of borax added in Example 4 was reduced, resulting in fewer dynamic borate ester bonds in the system, thereby reducing the self-healing ability of the system.
[0044] Comparative Example 1 A biodegradable mulch film is prepared by the method described in Example 1, except that the addition of sorbitol is omitted in step (1), thereby obtaining a pure PBAT mulch film.
[0045] The biodegradable mulch film obtained in the above comparative examples was compared with that in Example 1, and the results are shown in Table 6 below: Table 6 Comparison of self-healing and temperature responsiveness of mulch film in Example 1 and Comparative Example 1
[0046] As shown in Table 4 above, the pure PBAT mulch film described in Comparative Example 1 does not contain a sugar alcohol structure and cannot introduce dynamic borate ester bonds, thus lacking the self-healing and temperature-responsive functions.
[0047] Comparative Example 2 A biodegradable mulch film is prepared by the method described in Example 1, except that sorbitol (0.643 kg, 3.53 mol) is added in step (1).
[0048] The results showed that crystal points appeared in the mulch film described in Comparative Example 2 during the preparation process. This was because excessive sorbitol content would lead to excessive cross-linking and excessive melt strength, making it difficult to blow the film.
[0049] Comparative Example 3 A biodegradable mulch film is prepared by the method described in Example 1, except that borax dispersion (1.5 kg) is added in step (2).
[0050] The results show that the mulch film described in Comparative Example 3 is difficult to inflate and cannot be processed during the preparation process. The reason is that the high content of borate ester bonds will lead to excessive cross-linking of the system and excessive melt strength, making it difficult to blow the film.
[0051] Comparative Example 4 A biodegradable mulch film is prepared by the method described in Example 1, except that the addition of sorbitol is omitted in step (1), and sorbitol (0.404 kg) is added in step (2).
[0052] After 7 days of placement, the plastic film described in Comparative Example 4 showed white precipitates (borax-glycerol complex migrating to the surface) on its surface, and its self-healing performance decreased to less than 20% of its original value. This result indicates that adding small molecule polyols cannot achieve a stable dynamic cross-linking network, demonstrating the necessity of introducing a sugar alcohol structure into the main chain.
[0053] Comparative Example 5 A biodegradable mulch film is a PBAT mulch film grafted with sorbitol via 1,6-hexamethylene diisocyanate (HDI). To verify the technical effect of "introducing sorbitol through post-modification grafting," the mulch film is prepared according to the following steps: (1) Following the procedure in Example 1 (1), omitting the addition of sorbitol, pure PBAT copolymer was synthesized; (2) Using HDI as a chain extender, HDI (0.420 kg, 2.50 mol) and pure PBAT were melt-plasticized in a twin-screw extruder (160℃) so that the terminal hydroxyl groups of HDI and PBAT reacted for 5 min to obtain HDI-modified PBAT. (3) Sorbitol melt (0.404 kg, 2.22 mol) was reacted with HDI modified PBAT in a mixer at 160 °C for 8 min to achieve sorbitol grafting and obtain sorbitol modified PBAT copolymer. (4) Following steps (2) and (3) of Example 1, the above-mentioned sorbitol-modified PBAT copolymer is blended with borax and blown into a film.
[0054] The results showed that the sorbitol-modified PBAT copolymer had uneven melt viscosity, the film surface was milky white and translucent with many gel points; the tensile strength was 13.8 MPa, the elongation at break was 210%; the self-healing recovery rate after 24 h was only 28%; and yellowing occurred after 30 days (caused by oxidation of residual isocyanate groups in HDI).
[0055] Analysis of causes: HDI grafting only introduces a small amount of sorbitol at the PBAT chain ends, resulting in a sparse and unevenly distributed crosslinking network; the addition of excessive HDI itself causes gel points in PBAT; the multi-step thermal history leads to a decrease in the molecular weight of PBAT; the introduced carbamate bonds may affect biodegradability. Conclusion: Although post-grafting is superior to physical blending, it is still far inferior to in-situ copolymerization; only by introducing sugar alcohols as comonomers during PBAT synthesis can a high-density, uniformly distributed vicinal diol side groups be achieved, constructing an efficient dynamic borate crosslinking network.
[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A self-healing biodegradable mulch film, characterized in that, It is obtained by dynamically covalently crosslinking a sugar alcohol-modified poly(adipate / butyl terephthalate) copolymer containing an ortho-diol structure with borax to form borate ester bonds, followed by blow molding to form a film.
2. The self-healing biodegradable mulch film according to claim 1, characterized in that, The sugar alcohol-modified poly(adipic acid) / butyl terephthalate copolymer is obtained by melt polycondensation of terephthalic acid, adipic acid, 1,4-butanediol and sugar alcohols containing vicinal diol structures.
3. The self-healing biodegradable mulch film according to claim 2, characterized in that, The sugar alcohol is at least one of sorbitol, mannitol, isosorbide or maltitol; The molar ratio of the sugar alcohol and 1,4-butanediol to the total diol of the sugar alcohol is 0.05-0.1:1; the molar ratio of terephthalic acid to adipic acid is 1:0.8-1.2; and the molar ratio of the total diol of 1,4-butanediol and sugar alcohol to the total dicarboxylic acid of terephthalic acid and adipic acid is 1.0-1.5:
1.
4. The self-healing biodegradable mulch film according to claim 2, characterized in that, The melt polycondensation includes: an esterification stage, a pre-polycondensation stage, and a final polycondensation stage; The esterification stage includes: heating to 180-220 ℃ and carrying out the esterification reaction under normal pressure and inert gas protection, with an esterification rate of over 95%; the pre-condensation stage includes: continuing to heat to 220-240 ℃, reducing the pressure to 5-10 kPa, and reacting until the stirring torque increases; the final condensation stage includes: continuing to heat to 235-250 ℃, evacuating to <100 Pa, and reacting until the target intrinsic viscosity is reached. In the melt polycondensation process, terephthalic acid, adipic acid and 1,4-butanediol are first mixed and reacted, and then sugar alcohol is added after the temperature is raised to 180-220°C.
5. The self-healing biodegradable mulch film according to any one of claims 1-4, characterized in that, The dynamic covalent crosslinking to form borate ester bonds specifically includes: adding the sugar alcohol-modified poly(adipate / butyl terephthalate) copolymer and borax dispersion into a twin-screw extruder for melt blending.
6. The self-healing biodegradable mulch film according to claim 5, characterized in that, The borax dispersion is a glycerol dispersion of borax, which is obtained by grinding borax to D50≤10 μm and then pre-dispersing it with glycerol in a high-speed mixer at a mass ratio of 1:1-2.
7. The self-healing biodegradable mulch film according to claim 5, characterized in that, The melt blending temperature is not higher than 170 ℃, the screw speed of the twin-screw extruder is 100-150 rpm, and the material residence time is 2-3 min.
8. The self-healing biodegradable mulch film according to claim 5, characterized in that, When the sugar alcohol-modified poly(adipate) / butyl terephthalate copolymer and borax dispersion are added to a twin-screw extruder for melt blending, coupling agents, opening agents, ultraviolet absorbers and antioxidants are also added. The coupling agent is at least one of aluminate coupling agent or silane coupling agent; the opening agent is at least one of oleamide, talc or silica; the ultraviolet absorber is at least one of UV-234 or UV-326; and the antioxidant is at least one of antioxidant 1010 or antioxidant 1076. By weight, the sugar alcohol modified PBAT copolymer comprises 100 parts, borax pre-dispersion solution comprises 1-10 parts, coupling agent comprises 0.001-5 parts, opening agent comprises 0.001-1 parts, ultraviolet absorber comprises 0.001-1 parts, and antioxidant comprises 0.001-1 parts.
9. The self-healing biodegradable mulch film according to any one of claims 1-4, characterized in that, The blown film is formed by blown film forming machine with a blowing temperature of 140-165 ℃, a blow-up ratio of 2.0-2.5, a traction speed of 5-15 m / min, and a film thickness of 0.008-0.015 mm.
10. The application of the mulch film according to any one of claims 1-9 in crop mulching cultivation, characterized in that, After mechanical damage, the plastic film is placed at 25-80 ℃ and relative humidity ≥60% for 12-48 h, and the tensile strength recovery rate reaches more than 60%.