A biodegradable blocked isocyanate chain extender and its preparation method and application

Abstract

The invention discloses a biodegradable blocked isocyanate chain extender and a preparation method and application thereof. The chain extender is made of multifunctional isocyanate, a capping agent, a polyol and a catalyst, and can be used in the processing of fully biodegradable materials. The chain extender of the invention is biodegradable, has a fast chain extension reaction speed, and has good environmental compatibility. It contains two carbamate groups with different stabilities, and can form a dynamic micro-crosslinked three-dimensional network in which a chemical crosslinked network and a physical crosslinked network coexist in biodegradable plastics, thereby simultaneously improving the strength and toughness of the material. In addition, the unblocked small molecule capping agent has a synergistic effect with the biodegradable material matrix, has an excellent nitrification inhibition effect in the soil, and can effectively reduce nitrogen loss and improve the utilization rate of nitrogen fertilizer.

Description

Technical Field

[0001] The invention relates to a biodegradable blocked isocyanate chain extender and a preparation method and application thereof. Background Art

[0002] Using biodegradable plastics to replace traditional non-degradable plastics is one of the inevitable trends in current global development.

[0003] According to the current national standard GB / T39514-2020, biodegradable plastics are defined as follows: biodegradable polymer materials are plastics that can be degraded by some microorganisms such as bacteria, fungi, algae, etc. in the natural environment or in the body, or under certain composting conditions, and finally converted into carbon dioxide (CO2) and / or methane (CH4), water (H2O) and new biomass. The current fully biodegradable plastics mainly include polylactic acid (PLA), polybutylene succinate (PBS), polycaprolactone (PCL), polymethyl ethylene carbonate (PPC), polybutylene terephthalate-adipate (PBAT), polyhydroxyalkanoate (PHA), etc. Among them, PBAT has great potential and application in the packaging field and agricultural mulch applications due to its good physical and mechanical properties and ductility. However, compared with the performance of traditional plastics such as polyethylene, the performance of PBAT, especially the mechanical properties, is still relatively low, and the melt strength is not high. This has brought some constraints to its production and application.

[0004] Adding a chain extender is one of the methods to improve the mechanical properties and melt strength of fully biodegradable plastics. The active functional groups on the chain extender molecules react with the functional groups such as the terminal hydroxyl group and the terminal carboxyl group in the fully biodegradable plastics to increase the molecular weight of the polymer, thereby increasing its mechanical properties. Traditional chain extenders include epoxy chain extenders, anhydride chain extenders, oxazoline chain extenders, etc. Existing chain extenders have some disadvantages. 1. Most of them are polyolefin structures that are not biodegradable, such as styrene, polyethylene, etc. Adding them as chain extenders to fully biodegradable plastics will affect the biodegradability of the material, resulting in a decrease in the fully biodegradable performance of PBAT. 2. If the active group of the chain extender has low reactivity, the chain extension reaction takes a long time, and the material needs to stay in a high temperature environment for a long time. When fully biodegradable plastics (such as PBAT) are processed, they stay in a high temperature environment for a long time and are prone to thermal degradation, resulting in degradation of material performance. If the active group of the chain extender has high reactivity (such as isocyanate), there are problems such as high toxicity, difficulty in storage and transportation.

[0005] In order to solve the above problems, the present invention provides a biodegradable blocked isocyanate chain extender to improve the mechanical properties of PBAT, achieve a simultaneous improvement in material strength and toughness, and have biodegradability.

[0006] In addition, during the process of planting crops in the soil, nitrogen fertilizer will gradually be converted into nitrate nitrogen by microorganisms in the form of ammonium nitrogen. Ammonium nitrogen is easily fixed by soil colloids, while nitrate nitrogen is easily lost with water, causing water pollution. In addition, nitrate nitrogen will release nitrogen oxides into the air as a substrate for denitrification in the soil, leading to the greenhouse effect and destruction of the ozone layer, thus causing harm to humans and the environment. Common single nitrification inhibitors, such as those disclosed in CN111116259B, have a maximum nitrification inhibition rate of 48%. Shi Yunfeng et al. (Shi Yunfeng, Wu Zhijie, Chen Lijun et al. Effect of 3,5-dimethylpyrazole phosphate (DMPZP) on soil nitrification [J]. Journal of Applied Ecology, 2007 (05): 1035-1039) found that the maximum nitrification inhibition rate of a single pyrazole nitrification inhibitor was about 60%.

[0007] The small molecule end-capping agent after the chain extender of the present invention is unblocked has a synergistic effect with the biodegradable material matrix, has an excellent nitrification inhibition effect in the soil, can effectively reduce nitrogen loss and improve nitrogen fertilizer utilization. Summary of the invention

[0008] The present invention aims to provide a biodegradable blocked isocyanate chain extender and a preparation method thereof, as well as application in fully biodegradable plastics. The chain extender of the present invention can adjust the molecular weight according to the selected main body, has a high chain extension effect, and the fully biodegradable plastic after chain extension is simultaneously strengthened and toughened, and the mechanical properties are improved.

[0009] At the same time, the free end-capping agent of the chain extender of the present invention works synergistically with the biodegradable material matrix, has an excellent nitrification inhibition effect in the soil, and can effectively improve the utilization rate of nitrogen fertilizer.

[0010] The technical solution of the present invention is as follows:

[0011] A biodegradable blocked isocyanate chain extender is prepared from a multifunctional isocyanate, a blocking agent, a polyol and a catalyst;

[0012] The molar ratio of the blocking agent to the multifunctional isocyanate is 0.1 to 2:1, preferably 0.5 to 0.7:1;

[0013] The molar ratio of polyol to multifunctional isocyanate is 0.01 to 0.6:1, preferably 0.01 to 0.02:1;

[0014] The molar ratio of the catalyst to the multifunctional isocyanate is 0.0001 to 0.01:1, preferably 0.0002 to 0.0006:1;

[0015] The multifunctional isocyanate is selected from any one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, methylcyclohexyl diisocyanate, cyclohexane dimethyl diisocyanate, trimethyl-1,6-hexamethylene diisocyanate and cyclic dimers, trimers, pentamers or polyisocyanates with higher polymerization degree thereof; hexamethylene diisocyanate trimer is particularly preferred;

[0016] The end-capping agent is selected from imidazole compounds (e.g., benzimidazole, 2-methylimidazole, 4-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2,4-dimethylimidazole, etc.), oxime compounds (e.g., formaldehyde oxime, acetaldehyde oxime, acetone oxime, methyl ethyl ketone oxime, cyclohexanone oxime, diacetyl monoxime, benzophenone oxime, etc.), pyrazole compounds (e.g., pyrazole, 3,5-dimethylpyrazole, 3,5-diisopropylpyrazole, 3,5-diphenylpyrazole, 3 ,5-di-tert-butylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 3-methyl-5-phenylpyrazole, etc.) any one or more; it should be noted that the end-capping agent is released due to the deblocking reaction during the processing of the fully biodegradable plastic. From the perspective of being beneficial to the environment, pyrazole compounds (particularly 3,5-dimethylpyrazole) are preferred as the end-capping agent used in the present invention;

[0017] The polyol is a biodegradable polysaccharide, selected from, for example, any one or more of starch, cellulose, maltose, dextrin, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, maltodextrin, inulin, etc.; β-cyclodextrin is particularly preferred;

[0018] The catalyst is selected from amine catalysts and / or organic metal catalysts; the amine catalyst is selected from, for example, any one or more of triethylamine, tributylamine, triethylenediamine, N-ethylmorpholine, N,N,N',N'-tetramethyl-ethylenediamine, pentamethyldiethylene-triamine, N,N-methylaniline, N,N-dimethylaniline or 1,8-diazabicycloundec-7-ene; the organic metal catalyst is selected from, for example, any one or more of stannous acetate, stannous octoate, ethylhexyltin, dibutyltin dilaurate, dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin maleate, dioctyltin diacetate, bismuth isooctanoate, bismuth neodecanoate, zinc isooctanoate, and zirconium isooctanoate; dibutyltin dilaurate is particularly preferred.

[0019] The method for preparing the biodegradable blocked isocyanate chain extender of the present invention comprises the following steps:

[0020] S1: mixing a blocking agent, a multifunctional isocyanate and an organic solvent to perform a blocking reaction;

[0021] S2: adding polyol into the reaction system of S1 to carry out polycondensation reaction to obtain the chain extender;

[0022] The catalyst can be added at the beginning of the first step reaction or after the beginning of the second step reaction, preferably at the beginning of the first step reaction; the catalyst can be added alone or in the form of a solution, or can be dissolved in a polyol or in an isocyanate in advance before being added;

[0023] Preferably, the polyol and the organic solvent are subjected to vacuum dehydration treatment before the reaction;

[0024] The reaction is preferably carried out under an inert gas atmosphere (such as nitrogen, argon, etc.); the reaction temperature is preferably 40 to 120° C., particularly preferably 70° C.;

[0025] The organic solvent can be selected from: any one or more of ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), aliphatic hydrocarbons (e.g., n-hexane, n-heptane, octane, cyclohexane, methylcyclohexane, etc.), aromatic hydrocarbons (e.g., toluene, xylene, ethylbenzene, etc.), halogenated aliphatic hydrocarbons (e.g., methyl chloride, dichloromethane, chloroform, carbon tetrachloride, methyl bromide, diiodomethane, ethylene dichloride, etc.), polar aprotic hydrocarbons (e.g., N-methylpyrrolidone, dimethylformamide, N,N-dimethylformamide, N,N'-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, etc.); particularly preferred are N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO).

[0026] Furthermore, the preparation method of the biodegradable blocked isocyanate chain extender of the present invention is as follows:

[0027] S1: Under a nitrogen atmosphere, a blocking agent, a multifunctional isocyanate and an organic solvent are mixed, the temperature is raised to 70°C, a catalyst is added, and a blocking reaction is carried out for 3 to 6 hours;

[0028] S2: dissolving the polyol in an organic solvent, and then adding the polyol to the reaction system of S1, and continuing the reaction at 70°C for 3-6 hours under a nitrogen environment, and then washing with deionized water and vacuum drying to obtain the chain extender;

[0029] In the above preparation method,

[0030] The molar ratio of the blocking agent to the multifunctional isocyanate is 0.1 to 2:1, and 0.66:1 is particularly preferred;

[0031] The molar ratio of polyol to multifunctional isocyanate is 0.01 to 0.6:1, particularly preferably 0.018:1;

[0032] The molar ratio of the catalyst to the multifunctional isocyanate is 0.0001 to 0.01:1, and particularly preferably 0.0006:1;

[0033] The volume mass ratio of the organic solvent to the multifunctional isocyanate is 1 to 100:1, mL / g;

[0034] It should be noted that the blocking reaction requires judging the reaction endpoint, and the method is as follows: take the solution after the S1 reaction and quantitatively titrate the isocyanate group content in the product system using the di-n-butylamine method according to the national standard GB / T12009.4-1989 "Method for Determination of Isocyanate Content in Polymethylene Polyphenyl Isocyanate". When the measured isocyanate percentage is ≤0.2%, the reaction reaches the endpoint; it is measured that the blocking reaction needs to be carried out for 3 to 6 hours, preferably 5 hours.

[0035] The biodegradable blocked isocyanate chain extender of the present invention can be used for processing of fully biodegradable materials. The chain extender of the present invention is added to the biodegradable material for chain extension modification, and a dynamic hydrogen bond-micro-crosslinked three-dimensional network of the polymer chain is constructed to achieve simultaneous enhancement and toughening of the mechanical properties of the biodegradable polymer material. The specific processing method is as follows:

[0036] The biodegradable material was vacuum dried at 60° C. for 4 hours, then mixed evenly with the chain extender of the present invention, added into a Hake internal mixer, reacted at 180° C. at a speed of 60 rpm for 10 minutes, then preheated at 180° C. and 10 MPa for 2 minutes using a flat vulcanizer, and hot pressed for 3 minutes to obtain a high-strength and high-toughness fully biodegradable material;

[0037] The mass ratio of the chain extender to the biodegradable material of the present invention is 0.5 to 5:100;

[0038] The biodegradable material can be any one or more of polylactic acid (PLA), polybutylene succinate (PBS), polycaprolactone (PCL), polymethyl ethylene carbonate (PPC), polybutylene terephthalate-adipate (PBAT), and polyhydroxyalkanoate (PHA), preferably polybutylene terephthalate-adipate.

[0039] The fully biodegradable material processed by using the biodegradable blocked isocyanate chain extender of the present invention has the function of inhibiting soil nitrification, and can be further prepared into materials such as agricultural mulch films. The unblocked blocking agent will be free in the material, and when the material is placed in the soil, the blocking agent will be released to produce a nitrification inhibition effect. The nitrate nitrogen content of the sample in the soil can be tested according to the national standard GB / T32737-2016.

[0040] Furthermore, the high-strength and high-toughness fully biodegradable material prepared by the present invention and the blank control group were placed in a glass jar containing 1 kg of fresh soil. During the incubation period, each group of soil samples needed to be wrapped with plastic wrap and several small holes were pierced with a needle to create a breathable environment. Nitrogen fertilizer was applied to each group of samples, and during the experiment, water was applied every day to keep the soil moisture content at 40-60%. Samples were taken on the 0th, 3rd, 5th, 7th, 14th, 28th, and 35th days after the start of the experiment. Each time the samples were taken, five points were sampled, and after sufficient mixing, the measurements were performed. Each group of samples was measured in parallel for 3 times. Finally, the nitrate nitrogen content in the soil was measured, and the nitrification inhibition rate was calculated by the following formula.

[0041] Nitrification inhibition rate = (AB) / A×100%, where A is the difference in nitrate nitrogen content before and after incubation in the soil of the blank group (without sample), and B is the difference in nitrate nitrogen content before and after incubation in the soil of the sample-added group.

[0042] Compared with the prior art, the present invention has the following beneficial technical effects:

[0043] 1. The main body of the biodegradable blocked isocyanate chain extender provided by the present invention is a biodegradable polysaccharide, which has the characteristics of safe raw materials, non-toxicity, biodegradability, and good reusability.

[0044] 2. The biodegradable blocked isocyanate chain extender provided by the present invention contains two different stability carbamate groups. The strong carbamate group is a chemical bond connecting the isocyanate and the biodegradable polysaccharide, and has a high thermal stability and will not decompose below 200°C. Therefore, different performance characteristics can be given to biodegradable plastics by introducing the structure of biodegradable polysaccharides. The weak carbamate group is a chemical bond connecting the isocyanate and the blocking agent. It has a low thermal stability and can be decomposed at 120-180°C to release highly active isocyanate groups. It plays a role in quickly undergoing a chain extension reaction with the end groups in the biodegradable plastic material.

[0045] 3. Compared with isocyanate chain extenders, the biodegradable blocked isocyanate chain extender of the present invention has the advantages of low activity, low volatility, easy preservation, easy transportation and storage; compared with other macromolecular chain extenders, the biodegradable blocked isocyanate chain extender of the present invention has the advantages of biodegradability, fast chain extension reaction speed and good environmental compatibility.

[0046] 4. The biodegradable blocked isocyanate chain extender provided by the present invention can form a dynamic micro-crosslinked three-dimensional network in which a chemical crosslinked network and a physical crosslinked network coexist in the biodegradable plastic, thereby simultaneously improving the strength and toughness of the material.

[0047] 5. The high-strength and high-toughness fully biodegradable material prepared by the present invention can release a capping agent with nitrification inhibition effect in the soil, and has a synergistic effect with the material matrix, thereby effectively improving the nitrification inhibition rate, inhibiting the growth of nitrate nitrogen content in the soil, prolonging the residence time of ammonium nitrogen in the soil, promoting its absorption by crops, improving nitrogen utilization rate, and reducing environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 : The storage modulus of Example 1, Example 2, Example 3, Example 4 and Comparative Example 1.

[0049] Figure 2 : The loss modulus of Example 1, Example 2, Example 3, Example 4 and Comparative Example 1.

[0050] Figure 3 : Stress-strain curves of Example 1, Example 2, Example 3, Example 4 and Comparative Example 1.

[0051] Figure 4 : Nitrate nitrogen content change curve of embodiment 2, embodiment 3, embodiment 4 and blank control group 1. DETAILED DESCRIPTION

[0052] The present invention is described in detail below by way of examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by professionals and technicians in this field based on the content of the present invention above still belong to the scope of protection of the present invention.

[0053] In the following examples and comparative examples, polybutylene terephthalate-adipate (PBAT, TH801T) was purchased from Xinjiang Blue Mountain Tunhe Technology Co., Ltd., with a melt flow rate of 2.5-4.5 g / 10 min (ISO 1133, 190°C / 2.16 kg). Hexamethylene diisocyanate trimer (HDI trimer, N3300) was purchased from Covestro Polymers (China) Co., Ltd. Acetone (AR, ≥99.5%), dibutylamine (AR), and ammonium sulfate (AR) were purchased from Sinopharm Chemical Reagent Co., Ltd. 3,5-Dimethylpyrazole (≥99%), β-cyclodextrin (98%), and dibutyltin dilaurate (DBTDL, 95%) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Dimethyl sulfoxide (DMSO, AR) was purchased from Shanghai Yien Chemical Technology Co., Ltd.

[0054] Embodiment 1:

[0055] First, the DMSO solvent is subjected to vacuum dehydration treatment; then, in a nitrogen atmosphere, in a three-necked flask, 6.6499g (0.0691mol) of a blocking agent 3,5-dimethylpyrazole and 20g (0.10376mol) of a hexamethylene diisocyanate trimer are added to a 50ml DMSO solution, the temperature is raised to 70°C, and 0.04g of a catalyst dibutyltin dilaurate is added to carry out a blocking reaction for 5h; 2.1565g (0.0019mol) of vacuum-dried β-cyclodextrin is weighed and dissolved in 40ml DMSO solution, and the solution is added to the above three-necked flask, and the reaction is continued at 70°C for 5h, the reaction is terminated, and the product is washed with deionized water for 3 to 5 times to remove impurities, and vacuum-dried at 60°C for dehydration for 12h, and then dried and stored in a blast oven for 10h, thereby obtaining 28g of the finished product of the biodegradable blocked isocyanate chain extender.

[0056] 0.3 g of the biodegradable blocked isocyanate chain extender prepared above was weighed and added to PBAT pellets (weighed 60 g) that had been vacuum dried for 4 hours, mixed evenly, added to a Haake internal mixer, and reacted at 180° C. and 60 rpm for 10 minutes. The obtained product was hot-pressed using a flat vulcanizer, preheated at 180° C. and 10 MPa for 2 minutes, and hot-pressed for 3 minutes to prepare a sample with a weight average molecular weight (Mw) of 94002. The mechanical properties were tested, and the tensile strength was 37.82 MPa and the elongation at break was 1255.56%.

[0057] Weigh 5g of the PBAT sample after adding the biodegradable blocked isocyanate chain extender and place it in 1kg of fresh soil, apply 4.72g of nitrogen fertilizer (ammonium sulfate), and during the incubation period, wrap the soil with plastic wrap, poke several small holes with a needle to create a breathable environment, apply water every day to keep the soil moisture content at 40-60%, and take samples on the 35th day after the start of the experiment. When sampling, take samples at five points, mix them thoroughly, and then measure them according to the national standard GB / T 32737-2016, and measure 3 parallel experiments for each group of samples. The nitrate nitrogen content in the soil was measured to be 35.39mg / kg on the 35th day, and the nitrification inhibition rate was 30.17%.

[0058] Embodiment 2:

[0059] First, the DMSO solvent is subjected to vacuum dehydration treatment; then, in a nitrogen atmosphere, in a three-necked flask, 6.6499 g (0.0691 mol) of a blocking agent 3,5-dimethylpyrazole and 20 g (0.10376 mol) of a hexamethylene diisocyanate trimer are added to a 50 ml DMSO solution, the temperature is raised to 70° C., and 0.04 g of a catalyst dibutyltin dilaurate is added at the same time, and a blocking reaction is carried out for 5 hours; 2.1565 g (0.0019 mol) of vacuum-dried β-cyclodextrin is weighed, dissolved in 40 ml DMSO solution, added to the above three-necked flask, and the reaction is continued at 70° C. for 5 hours, the reaction is terminated, the product is washed with deionized water for 3 to 5 times to remove impurities, and vacuum-dried at 60° C. for dehydration for 12 hours, and dried and stored in a blast oven after 10 hours, to obtain 28 g of the finished product of the biodegradable blocked isocyanate chain extender.

[0060] 0.6 g of the biodegradable blocked isocyanate chain extender of Example 2 was weighed and added to PBAT pellets (weighed 60 g) that had been vacuum dried for 4 hours, mixed evenly, and added to a Haake internal mixer. The mixture was reacted at 180° C. and 60 rpm for 10 minutes. The obtained product was hot-pressed using a flat vulcanizer, preheated at 180° C. and 10 MPa for 2 minutes, and hot-pressed for 3 minutes to prepare a sample with a weight average molecular weight (Mw) of 96741. The mechanical properties were tested, and the tensile strength was 42.42 MPa and the elongation at break was 1314.48%.

[0061] Weigh 5g of the PBAT sample after adding the biodegradable blocked isocyanate chain extender and place it in 1kg of fresh soil, apply 4.72g of nitrogen fertilizer (ammonium sulfate), and during the incubation period, wrap the soil with plastic wrap, poke several small holes with a needle to create a breathable environment, and apply water every day to keep the soil moisture content at 40-60%. Sampling was performed on the 0th, 3rd, 5th, 7th, 14th, 28th, and 35th days after the start of the experiment. Each time sampling, five points were sampled, and after sufficient mixing, the samples were measured according to the national standard GB / T 32737-2016, and each group of samples was measured 3 times in parallel. The nitrate nitrogen content in the soil was measured to be 20.98mg / kg on the 35th day, and the nitrification inhibition rate was 60.38%.

[0062] Embodiment 3:

[0063] First, the DMSO solvent is subjected to vacuum dehydration treatment; then, in a nitrogen atmosphere, in a three-necked flask, 6.6499 g (0.0691 mol) of a blocking agent 3,5-dimethylpyrazole and 20 g (0.10376 mol) of a hexamethylene diisocyanate trimer are added to a 50 ml DMSO solution, the temperature is raised to 70° C., and 0.04 g of a catalyst dibutyltin dilaurate is added at the same time, and a blocking reaction is carried out for 5 hours; 2.1565 g (0.0019 mol) of vacuum-dried β-cyclodextrin is weighed, dissolved in 40 ml DMSO solution, added to the above three-necked flask, and the reaction is continued at 70° C. for 5 hours, the reaction is terminated, the product is washed with deionized water for 3 to 5 times to remove impurities, and vacuum-dried at 60° C. for dehydration for 12 hours, and dried and stored in a blast oven after 10 hours, to obtain 28 g of the finished product of the biodegradable blocked isocyanate chain extender.

[0064] 1.2 g of the biodegradable blocked isocyanate chain extender of Example 3 was weighed and added to PBAT pellets (weighed 60 g) that had been vacuum dried for 4 h, mixed evenly, and added to a Haake internal mixer. The mixture was reacted at 180° C. and 60 rpm for 10 min. The obtained product was hot-pressed using a flat vulcanizer, preheated at 180° C. and 10 MPa for 2 min, and hot-pressed for 3 min to prepare a sample with a weight average molecular weight (Mw) of 98059. The mechanical properties were tested, and the tensile strength was 43.73 MPa and the elongation at break was 1331.62%.

[0065] Weigh 5g of the PBAT sample after adding the biodegradable blocked isocyanate chain extender and place it in 1kg of fresh soil, apply 4.72g of nitrogen fertilizer (ammonium sulfate), and during the incubation period, the soil needs to be wrapped with plastic wrap, and several small holes are pierced with a needle to create a breathable environment. Water is applied every day to keep the soil moisture content at 40-60%. Samples are taken on the 0th, 3rd, 5th, 7th, 14th, 28th, and 35th days after the start of the experiment. Each time the sample is taken, five points are sampled, and after being fully mixed, it is measured according to the national standard GB / T 32737-2016. Each group of samples is measured in parallel 3 times. The nitrate nitrogen content in the soil was measured to be 15.32mg / kg on the 35th day, and the nitrification inhibition rate was 74.28%.

[0066] Embodiment 4:

[0067] First, the DMSO solvent is subjected to vacuum dehydration treatment; then, in a nitrogen atmosphere, in a three-necked flask, 6.6499 g (0.0691 mol) of a blocking agent 3,5-dimethylpyrazole and 20 g (0.10376 mol) of a hexamethylene diisocyanate trimer are added to a 50 ml DMSO solution, the temperature is raised to 70° C., and 0.04 g of a catalyst dibutyltin dilaurate is added at the same time, and a blocking reaction is carried out for 5 hours; 2.1565 g (0.0019 mol) of vacuum-dried β-cyclodextrin is weighed, dissolved in 40 ml DMSO solution, added to the above three-necked flask, and the reaction is continued at 70° C. for 5 hours, the reaction is terminated, the product is washed with deionized water for 3 to 5 times to remove impurities, and vacuum-dried at 60° C. for dehydration for 12 hours, and dried and stored in a blast oven after 10 hours, to obtain 28 g of the finished product of the biodegradable blocked isocyanate chain extender.

[0068] 1.8 g of the biodegradable blocked isocyanate chain extender of Example 4 was weighed and added to PBAT pellets (weighed 60 g) that had been vacuum dried for 4 h, mixed evenly, and added to a Haake internal mixer. The mixture was reacted at 180° C. and 60 rpm for 10 min. The obtained product was hot-pressed using a flat vulcanizer, preheated at 180° C. and 10 MPa for 2 min, and hot-pressed for 3 min to prepare a sample with a weight average molecular weight (Mw) of 100461. The mechanical properties were tested, and the tensile strength was 39.26 MPa and the elongation at break was 1201.67%.

[0069] Weigh 5g of the PBAT sample after adding the biodegradable blocked isocyanate chain extender and place it in 1kg of fresh soil, apply 4.72g of nitrogen fertilizer (ammonium sulfate), and during the incubation period, wrap the soil with plastic wrap, poke several small holes with a needle to create a breathable environment, and apply water every day to keep the soil moisture content at 40-60%. Sampling was performed on the 0th, 3rd, 5th, 7th, 14th, 28th, and 35th days after the start of the experiment. Each time sampling, five points were sampled, and after sufficient mixing, the samples were measured according to the national standard GB / T 32737-2016, and each group of samples was measured 3 times in parallel. The nitrate nitrogen content in the soil was measured to be 12.76mg / kg on the 35th day, and the nitrification inhibition rate was 79.64%.

[0070] Blank control group 1:

[0071] Weigh 1 kg of fresh soil in a glass jar as a blank control group, apply 4.72 g of nitrogen fertilizer (ammonium sulfate), wrap the soil with plastic wrap during the culture period, poke several small holes with a needle to create a breathable environment, apply water every day to keep the soil moisture content at 40-60%, and take samples on the 0th, 3rd, 5th, 7th, 14th, 28th, and 35th days after the start of the experiment. Each time the sample is taken, five points are sampled, and after sufficient mixing, it is measured according to the national standard GB / T 32737-2016. Each group of samples is measured 3 times in parallel. The nitrate nitrogen content in the soil was measured to be 50.68 mg / kg on the 35th day.

[0072] Comparative Example 1:

[0073] Weigh 60 g of PBAT pellets dried in vacuum for 4 hours, add them to a Haake internal mixer, react at 180 ° C and 60 rpm for 10 minutes, and use a flat vulcanizer to hot press the product, preheat at 180 ° C, 10 MPa for 2 minutes, and hot press for 3 minutes to prepare a sample with a weight average molecular weight (Mw) of 92101. The mechanical properties test showed that the tensile strength was 35.75 MPa and the elongation at break was 1175.8%.

[0074] Weigh 5g of the PBAT sample prepared above and put it in 1kg of fresh soil, apply 4.72g of nitrogen fertilizer (ammonium sulfate), and during the cultivation period, the soil needs to be wrapped with plastic wrap, and several small holes are pierced with a needle to create a breathable environment. Water is applied every day to keep the soil moisture content at 40-60%. Sampling was performed on the 35th day after the start of the experiment. When sampling, five points were sampled, and after sufficient mixing, it was measured according to the national standard GB / T32737-2016. Each group of samples was measured 3 times in parallel. The nitrate nitrogen content in the soil was measured to be 39.09mg / kg on the 35th day, and the nitrification inhibition rate was 24.35%.

[0075] Comparative Example 2:

[0076] Weigh 3.31g 3,5-dimethylpyrazole and put it in 1 kg fresh soil, apply 4.72g nitrogen fertilizer (ammonium sulfate), during the cultivation, the soil needs to be wrapped with plastic wrap, and several small holes are pierced with a needle to create a breathable environment. Water is applied every day to keep the soil moisture content at 40-60%. Samples are taken on the 35th day after the start of the experiment. When sampling, five points are sampled, and after sufficient mixing, they are measured according to the national standard GB / T32737-2016. Each group of samples is measured 3 times in parallel. The nitrate nitrogen content in the soil was measured to be 32.73mg / kg on the 35th day, and the nitrification inhibition rate was 35.42%.

[0077] The mechanical properties, molecular weight and soil nitrification inhibition rate of the fully biodegradable plastic PBAT added with a biodegradable blocked isocyanate chain extender prepared in Examples 1 to 4 were compared with those in Comparative Examples 1 to 2. The results are shown in Table 1:

[0078] Table 1

[0079]

[0080] The present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A biodegradable blocked isocyanate chain extender, characterized in that: The chain extender is made of multifunctional isocyanate, a blocking agent, a polyol and a catalyst; The molar ratio of the blocking agent to the multifunctional isocyanate is 0.1 to 2:1; The molar ratio of polyol to multifunctional isocyanate is 0.01 to 0.6:1; The molar ratio of the catalyst to the multifunctional isocyanate is 0.0001 to 0.01:1; in, The end-capping agent is selected from pyrazole compounds; The polyol is dextrin; The catalyst is selected from amine catalysts and / or organic metal catalysts.

2. The biodegradable blocked isocyanate chain extender according to claim 1, characterized in that: The multifunctional isocyanate is selected from any one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, methylcyclohexyl diisocyanate, cyclohexane dimethyl diisocyanate, trimethyl-1,6-hexamethylene diisocyanate and cyclic dimers, trimers, pentamers or polyisocyanates with higher polymerization degree thereof.

3. The biodegradable blocked isocyanate chain extender according to claim 1, characterized in that: The pyrazole compound capping agent is selected from pyrazole, 3,5-dimethylpyrazole, 3,5-diisopropylpyrazole, 3,5-diphenylpyrazole, 3,5-di-tert-butylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole.

4. The biodegradable blocked isocyanate chain extender according to claim 1, characterized in that: The polyol is selected from any one or more of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin and maltodextrin.

5. The biodegradable blocked isocyanate chain extender according to claim 1, characterized in that: The amine catalyst is selected from triethylamine, tributylamine, triethylenediamine, N-ethylmorpholine, N,N,N',N'-tetramethyl-ethylenediamine, pentamethyldiethylene-triamine, N,N-methylaniline, N,N-dimethylaniline or 1,8-diazabicycloundec-7-ene; the organic metal catalyst is selected from stannous acetate, stannous octoate, ethylhexyltin, dibutyltin dilaurate, dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin maleate, dioctyltin diacetate, bismuth isooctanoate, bismuth neodecanoate, zinc isooctanoate, zirconium isooctanoate.

6. The method for preparing the biodegradable blocked isocyanate chain extender according to claim 1, characterized in that: The following steps are involved: S1: mixing a blocking agent, a multifunctional isocyanate and an organic solvent to perform a blocking reaction; S2: adding polyol into the reaction system of S1 to carry out polycondensation reaction to obtain the chain extender; The catalyst is added at the beginning of the S1 or S2 reaction; The reaction is carried out under an inert gas atmosphere; the reaction temperature is 40 to 120°C; The organic solvent is selected from any one or more of ketones, aliphatic hydrocarbons, aromatic hydrocarbons, halogenated aliphatic hydrocarbons, and polar aprotic hydrocarbons.

7. The method for preparing a biodegradable blocked isocyanate chain extender according to claim 6, characterized in that: The preparation method is as follows: S1: Under a nitrogen atmosphere, a blocking agent, a multifunctional isocyanate and an organic solvent are mixed, the temperature is raised to 70°C, a catalyst is added, and a blocking reaction is carried out for 3 to 6 hours; S2: After dissolving the polyol in an organic solvent, add the polyol into the S1 reaction system, continue the reaction at 70°C for 3 to 6 hours under a nitrogen environment, then wash with deionized water and dry in vacuum to obtain the chain extender.

8. A fully biodegradable material processed using the biodegradable blocked isocyanate chain extender according to claim 1.

9. The fully biodegradable material according to claim 8, characterized in that: The processing method is as follows: The biodegradable material is vacuum dried at 60° C. for 4 hours, then mixed evenly with the biodegradable blocked isocyanate chain extender according to claim 1, added to a Hake internal mixer, reacted at 180° C. at a speed of 60 rpm for 10 minutes, then preheated at 180° C. and 10 MPa for 2 minutes using a flat vulcanizer, and hot pressed for 3 minutes to obtain a high-strength and high-toughness fully biodegradable material; The mass ratio of the chain extender to the biodegradable material is 0.5 to 5:100; The biodegradable material is any one or more of polylactic acid, polybutylene succinate, polycaprolactone, polymethylethylene carbonate, polybutylene terephthalate-adipate, and polyhydroxyalkanoate.

10. Use of the fully biodegradable material according to claim 8 in inhibiting soil nitrification.

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