Degradable thermal insulation coating for greenhouse vegetables

Abstract

The invention belongs to the technical field of coatings, and particularly relates to a degradable heat insulation coating for greenhouse vegetables. The invention relates to a degradable heat-insulating coating for greenhouse vegetables. The degradable heat-insulating coating is prepared from the following components: a base material system, a heat-insulating filler, a functional additive and a solvent, wherein the base material system is composed of a PLA / PBAT blend and cross-linked starch; the heat insulation filler is composed of nano cesium tungstate oxide and hollow ceramic microbeads; the solvent is deionized water. Through innovative design of the base material system, the heat-insulating filler, the functional additive and the like, the prepared heat-insulating coating for the greenhouse vegetables has relatively good flexibility, relatively low heat conductivity coefficient and relatively excellent degradation rate, and has remarkable industrial application value and popularization prospect.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a biodegradable heat-insulating coating for greenhouse vegetables. Background Technology

[0002] Greenhouse vegetable cultivation, as a core model for ensuring year-round vegetable supply, relies heavily on temperature control within the greenhouses, which directly impacts crop photosynthetic efficiency, growth cycle, and yield. Thermal insulation coatings are a crucial means of controlling greenhouse temperature. Currently, agricultural greenhouse insulation materials are mainly classified into the following two categories: The first category is traditional non-degradable heat insulation coatings, with commercially available ZS-221 nano heat insulation coating as a typical example. It uses nano hollow ceramic microspheres and water-based acrylic resin to significantly reduce the thermal conductivity. However, it relies on synthetic resins and inorganic fillers, resulting in low degradation efficiency in farmland soil, easy plastic pollution, damage to soil aggregate structure, and impact on subsequent crop root development.

[0003] The second category is biodegradable coatings. Although they can avoid pollution problems, their thermal insulation performance is generally poor. For example, biodegradable coatings based on zein and polycaprolactone rely solely on the substrate itself to block light and achieve cooling. They do not introduce highly efficient thermal insulation fillers, resulting in insufficient thermal insulation performance. In summer, the temperature inside the greenhouse still needs to be regulated by ventilation equipment.

[0004] In addition, radiation insulation coatings commonly used in the construction industry include solvent-based polyurethane coatings containing nano-indium tin oxide. However, solvent-based polyurethane substrates are non-degradable, and indium tin oxide is relatively expensive. In the modification of PE agricultural films in the plastics processing industry, infrared blocking can be achieved by adding nano-cesium tungstate oxide, but the natural degradation cycle of PE substrates is long, and agricultural films need to be applied once and cannot be coated and renewed as needed like coatings.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a biodegradable heat-insulating coating for greenhouse vegetables, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A biodegradable heat-insulating coating for greenhouse vegetables is prepared from the following components: a substrate system, heat-insulating fillers, functional additives, and solvents; wherein, The substrate system is composed of PLA / PBAT blend and cross-linked starch; The heat insulation filler is composed of nano-cesium tungstate tungstate and hollow ceramic microspheres; The functional additives are composed of glycerin, montmorillonite, Streptomyces B2 spore powder, polyether-modified siloxane, and organosilicon. The solvent is deionized water.

[0008] Furthermore, by weight percentage, the biodegradable heat-insulating coating for greenhouse vegetables is prepared from the following components: 20-30% PLA / PBAT blend, 5-10% cross-linked starch, 3-5% nano-cesium tungstate, 15-20% hollow ceramic microspheres, 2-5% glycerol, 1-3% montmorillonite, 0.1-0.5% Streptomyces B2 spore powder, 0.5-1% polyether-modified siloxane, 0.1-0.3% organosilicon, and the balance being deionized water.

[0009] Furthermore, the mass ratio of PLA to PBAT in the PLA / PBAT blend is 3:1.

[0010] Further, the preparation method of cross-linked starch is as follows: corn starch is taken, deionized water is added and stirred to prepare a 35% starch milk, the temperature is raised to 45℃, and stirred for 15 min; 3% sodium trimetaphosphate by weight of corn starch is added, stirred and dissolved, and the pH value of the system is adjusted to 8.5 with 0.1 mol / L NaOH solution, the temperature is raised to 60℃, and the reaction is stirred at a constant temperature for 3 h; the pH value of the system is adjusted to 7.0 with 0.1 mol / L HCl solution, the heating is stopped, and the mixture is allowed to stand for 2 h before filtration and collection of filter cake; the filter cake is vacuum dried at 60℃ to constant weight, pulverized and passed through a 100-mesh sieve to obtain the cross-linked starch.

[0011] Furthermore, the nano-sized cesium tungstate has a particle size of 50-100 nm; the hollow ceramic microspheres have a particle size of 5-20 μm.

[0012] The present invention also provides a method for preparing the biodegradable heat-insulating coating for greenhouse vegetables, comprising the following steps: S1. Mix PLA and PBAT at a mass ratio of 3:1, melt-blend at 160℃ and 300r / min for 8min, then add cross-linked starch and glycerol, and continue stirring for 5min to obtain the substrate premix. S2. Add nano-cesium tungstate oxide and hollow ceramic microspheres to 1 / 2 deionized water, and ultrasonically disperse at 500W and 20kHz for 30min to obtain a filler suspension; S3. Mix the substrate premix, filler suspension, montmorillonite and Streptomyces B2 spore powder evenly, and shear emulsify at 8000 r / min for 20 min; S4. Add the remaining deionized water and functional additives, adjust the pH value to 7.0, and mill through a 50μm sieve to obtain the biodegradable heat insulation coating for greenhouse vegetables.

[0013] The present invention also provides a method for using the biodegradable heat-insulating coating for greenhouse vegetables, wherein the coating is applied evenly in two coats onto the plastic film or glass of a vegetable greenhouse, with a dry film thickness of 35-50 μm.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This application, through innovative design of the substrate system, heat-insulating filler, and functional additives, produces a heat-insulating coating for greenhouse vegetables that exhibits good flexibility, low thermal conductivity, and a superior degradation rate. Furthermore, using deionized water as the sole solvent, it contains no organic solvents, thus avoiding chemical pollution to crops and soil; the 180-day degradation rate reaches 92.1%, without affecting subsequent crop root development, which is beneficial to soil ecology; and the raw materials used in its preparation are environmentally friendly. In summary, the biodegradable heat-insulating coating for greenhouse vegetables of this invention possesses significant industrial application value and promising prospects for promotion. Detailed Implementation

[0015] The technical solution of this invention patent will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0016] 1. Materials and Methods 1.1 Coating Formulation A biodegradable heat-insulating coating for greenhouse vegetables is prepared from the following components: a base material system, heat-insulating fillers, functional additives, and solvents; among which, The substrate system consists of a PLA / PBAT blend and cross-linked starch. Specifically, the PLA is Total PLA L175 from Thailand; the PBAT is polybutylene terephthalate (PBAT resin), CAS: 55231-08-8, purchased from Hubei Shiteng Chemical Technology Co., Ltd. The cross-linked starch is prepared as follows: corn starch is added to deionized water and stirred to prepare a 35% starch slurry. The mixture is heated to 45°C and stirred for 15 minutes. 3% sodium tripolyphosphate (sodium tripolyphosphate by weight of corn starch) is added and stirred until dissolved. The pH of the system is adjusted to 8.5 with 0.1 mol / L NaOH solution. The mixture is heated to 60°C and stirred for 3 hours. The pH of the system is adjusted to 7.0 with 0.1 mol / L HCl solution. Heating is stopped, and the mixture is allowed to stand for 2 hours before filtration. The filter cake is collected and vacuum dried at 60°C to constant weight. The filter cake is then pulverized and passed through a 100-mesh sieve to obtain the cross-linked starch. The thermal insulation filler is composed of nano-cesium tungstate and hollow ceramic microspheres; specifically, the nano-cesium tungstate particles are all capable of passing through a 100nm pore size sieve; the hollow ceramic microsphere particles are all capable of passing through a 20μm pore size sieve. The functional additives consist of glycerin, montmorillonite, Streptomyces B2 spore powder, polyether-modified siloxane BYK-333, and organosilicon BYK-024; The solvent is deionized water.

[0017] 1.2 Preparation method S1. Mix PLA and PBAT at a mass ratio of 3:1, melt-blend at 160℃ and 300r / min for 8min, then add cross-linked starch and glycerol, and continue stirring for 5min to obtain the substrate premix. S2. Add nano-cesium tungstate oxide and hollow ceramic microspheres to 1 / 2 deionized water, and ultrasonically disperse at 500W and 20kHz for 30min to obtain a filler suspension; S3. Mix the substrate premix, filler suspension, montmorillonite and Streptomyces B2 spore powder evenly, and shear emulsify at 8000 r / min for 20 min; S4. Add the remaining deionized water and functional additives, adjust the pH value to 7.0, and mill through a 50μm sieve to obtain the biodegradable heat insulation coating for greenhouse vegetables.

[0018] 1.3 Influence of Substrate System on Coating Performance 1.3.1 Coating Formulation See Table 1.

[0019] Table 1. Coating Formulation and Dosage (by weight)

[0020] 1.3.2 Coating performance test (5 parallel samples for each formulation, and the average value of the results is taken) a. Film-forming properties Referencing GB / T 1727-1992, the coating was uniformly applied to a glass substrate (30cm long, 30cm wide, and 3mm thick), resulting in a dry film thickness of 50μm. After drying at room temperature for 24 hours, the coating was rated through visual observation and physical verification. The rating criteria are as follows: Level 5: The membrane layer is continuous and smooth, without cracks, pinholes, or peeling, and shows no damage after bending 180°; Level 4: The film layer is basically continuous, with only a few microcracks (length <1mm) at the edges, and no peeling occurs after bending 180°; Level 3: The film has a small number of short cracks (1-3 mm in length) or local shrinkage cavities, and there is no obvious peeling after bending 180°; Level 2: Numerous film cracks (length > 3 mm) or localized detachment (area < 5%). Level 1: Large-area membrane detachment (area > 5%) or inability to form a continuous membrane.

[0021] b. Elongation at break Referring to GB / T 1040.3-2006 Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets, the coating was prepared into a film (without a glass substrate) measuring 100 mm in length, 15 mm in width, and 0.2 mm in thickness. A tensile testing machine was used to test the film at a rate of 50 mm / min, and the elongation at break was calculated.

[0022]

[0023] The results are shown in Table 2.

[0024] Table 2. Influence of Substrate System on Coating Performance

[0025] Table 2 shows that adding PBAT to PLA affects the performance of the coating. When the mass ratio of PLA to PBAT is 3:1 and the amount of cross-linked starch added is 5%, the overall performance of the coating is optimal: film-forming grade 5 and elongation at break 24.6%. This indicates that the vegetable coating of this invention forms a stable film and has good flexibility.

[0026] 1.4 The Influence of Thermal Insulation Coatings on Coating Performance 1.41 Coating Formulation See Table 3.

[0027] Table 3. Coating Formulation and Dosage (by weight)

[0028] 1.4.2 Coating performance testing (3 parallel samples for each formulation, and the average value of the results is taken) a. Thermal conductivity Following GB / T 10294-2008, the coating was uniformly applied to a glass substrate (30cm long, 30cm wide, and 3mm thick), resulting in a dry film thickness of 50μm. The substrate was then dried at room temperature for 24 hours. The coated sample was fixed between a hot plate (40℃) and a hot plate (20℃). Once the system reached steady state, the heat flux density was recorded, and the thermal conductivity was calculated.

[0029]

[0030] The results are shown in Table 4.

[0031] Table 4. Influence of thermal insulation coating on coating performance

[0032] As shown in Table 4, the thermal insulation effect of nano-cesium tungstate and hollow ceramic microspheres on the coating is limited. However, when the two are used in combination, the thermal conductivity can be further reduced. In particular, the effect of reducing the thermal conductivity is optimal when nano-cesium tungstate and hollow ceramic microspheres are mixed in a mass ratio of 1:5. This indicates that the thermal insulation coating for greenhouse vegetables of the present invention has excellent thermal insulation effect.

[0033] 1.5 Effects of Functional Additives on Coating Performance 1.5.1 Coating Formulation See Table 5.

[0034] Table 5. Coating Formulation and Dosage (by weight)

[0035] 1.5.2 Coating performance test (3 parallel samples for each formulation, and the average value of the results is taken) a. Degradation rate over 150 days.

[0036] The coating was made into a film (without a glass substrate) measuring 10 cm long, 10 cm wide, and 0.2 mm thick, and vacuum-dried at 60°C to constant weight (initial mass). It was then buried 10 cm deep in soil simulating a vegetable garden environment with 3.5% organic matter, a temperature of 30±1°C, a pH of 6.8, and a humidity of 60±5%. After 150 days, it was removed, rinsed thoroughly with deionized water, and vacuum-dried at 60°C to constant weight (residual mass). The degradation rate after 150 days was calculated by weighing.

[0037]

[0038] Similarly, the degradation rates at 90 days and 180 days were measured.

[0039] The results are shown in Table 5.

[0040] Table 5. Influence of thermal insulation coating on coating performance

[0041] As shown in Table 5, the combination of montmorillonite and Streptomyces B2 spore powder can improve the degradation rate of the coating. Moreover, the combination of 1% montmorillonite and 0.5% Streptomyces B2 spore powder can achieve controlled degradation in 90-180 days, thus adapting to the growth period of different facility vegetables such as cucumber, tomato and eggplant.

[0042] In summary, this application, through innovative design of the substrate system, heat-insulating filler, and functional additives, produces a heat-insulating coating for greenhouse vegetables that exhibits good flexibility, low thermal conductivity, and a superior degradation rate. Furthermore, using deionized water as the sole solvent, it contains no organic solvents, thus avoiding chemical pollution to crops and soil; the 180-day degradation rate reaches 92.1%, without affecting subsequent crop root development, which is beneficial for protecting the soil ecosystem; and the raw materials used in its preparation are environmentally friendly. Therefore, the biodegradable heat-insulating coating for greenhouse vegetables of this invention possesses significant industrial application value and promising prospects for promotion.

[0043] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A biodegradable heat-insulating coating for greenhouse vegetables, characterized in that, It is prepared from the following components: a substrate system, heat-insulating fillers, functional additives, and solvents; among which, The substrate system is composed of PLA / PBAT blend and cross-linked starch; The heat insulation filler is composed of nano-cesium tungstate tungstate and hollow ceramic microspheres; The functional additives are composed of glycerin, montmorillonite, Streptomyces B2 spore powder, polyether-modified siloxane, and organosilicon. The solvent is deionized water.

2. The biodegradable heat-insulating coating for greenhouse vegetables according to claim 1, characterized in that, By weight percentage, the biodegradable heat-insulating coating for greenhouse vegetables is prepared from the following components: 20-30% PLA / PBAT blend, 5-10% cross-linked starch, 3-5% nano-cesium tungstate, 15-20% hollow ceramic microspheres, 2-5% glycerol, 1-3% montmorillonite, 0.1-0.5% Streptomyces B2 spore powder, 0.5-1% polyether-modified siloxane, 0.1-0.3% organosilicon, and the balance being deionized water.

3. The biodegradable heat-insulating coating for greenhouse vegetables according to claim 1, characterized in that, The mass ratio of PLA to PBAT in the PLA / PBAT blend is 3:

1.

4. The biodegradable heat-insulating coating for greenhouse vegetables according to claim 1, characterized in that, The preparation method of cross-linked starch is as follows: corn starch is taken, deionized water is added and stirred to prepare a 35% starch milk, the temperature is raised to 45℃, and stirred for 15 min; 3% sodium trimetaphosphate by weight of corn starch is added, stirred and dissolved, and the pH value of the system is adjusted to 8.5 with 0.1 mol / L NaOH solution, the temperature is raised to 60℃, and the reaction is stirred at a constant temperature for 3 h; the pH value of the system is adjusted to 7.0 with 0.1 mol / L HCl solution, the heating is stopped, and the mixture is allowed to stand for 2 h before filtration and collection of filter cake; the filter cake is vacuum dried at 60℃ to constant weight, pulverized and passed through a 100-mesh sieve to obtain the cross-linked starch.

5. The biodegradable heat-insulating coating for greenhouse vegetables according to claim 1, characterized in that, The nano-sized cesium tungstate has a particle size of 50-100 nm; the hollow ceramic microspheres have a particle size of 5-20 μm.

6. A method for preparing a biodegradable heat-insulating coating for greenhouse vegetables according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix PLA and PBAT at a mass ratio of 3:1, melt-blend at 160℃ and 300r / min for 8min, then add cross-linked starch and glycerol, and continue stirring for 5min to obtain the substrate premix. S2. Add nano-cesium tungstate oxide and hollow ceramic microspheres to 1 / 2 deionized water, and ultrasonically disperse at 500W and 20kHz for 30min to obtain a filler suspension; S3. Mix the substrate premix, filler suspension, montmorillonite and Streptomyces B2 spore powder evenly, and shear emulsify at 8000 r / min for 20 min; S4. Add the remaining deionized water and functional additives, adjust the pH value to 7.0, and mill through a 50μm sieve to obtain the biodegradable heat insulation coating for greenhouse vegetables.

7. A method of using the biodegradable heat-insulating coating for greenhouse vegetables as described in any one of claims 1-5, characterized in that, Apply the coating evenly in two coats to the plastic film or glass of the vegetable greenhouse, with a dry film thickness of 35-50 μm.

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