Composite film for packaging potassium chloride particles and preparation method thereof

Abstract

The present invention relates to the technical field of potassium chloride packaging, and more specifically to a composite film for packaging potassium chloride granules and a method for preparing the composite film. The composite film preparation method comprises: preparing a solution containing gelatin powder, konjac flour, glycerin, and hydroxyapatite powder; after fully dissolving the solution, treating the solution in a water bath at approximately 100°C for 15 minutes; transferring the solution to a culture dish and baking the solution at 40-60°C for 24-48 hours; and peeling the composite film from the culture dish. The composite film prepared by the present invention utilizes gelatin and konjac flour as primary raw materials during the preparation process, and while having a certain degree of air permeability, its water vapor transmission rate is relatively low. This is likely because the gelatin and konjac flour form a dense membrane structure, while the hydroxyapatite added thereto has a high water absorption capacity, effectively absorbing water and preventing moisture from entering and permeating the membrane, thereby preventing the potassium chloride granules from clumping.

Description

Technical Field

[0001] The invention relates to the technical field of potassium chloride packaging, and in particular to a composite film for packaging potassium chloride particles and a preparation method thereof. Background Art

[0002] Potassium chloride is primarily used as a raw material for various potassium salts in the fertilizer, food, and pharmaceutical industries, with over 90% of its production used as potash fertilizer. However, the resulting potassium chloride granules often clump, which not only affects their appearance and quality but also creates inconveniences in transportation, sales, and use. Therefore, addressing this clumping issue has become a pressing priority for compound fertilizer manufacturers.

[0003] There are two main theories of inorganic salt agglomeration currently accepted: the crystal bridging theory and the capillary adsorption theory. The crystal bridging theory posits that agglomeration is primarily caused by changes in internal factors (such as the properties, chemical composition, particle size, size distribution, and geometry of the inorganic salt crystals) and external factors (such as temperature, humidity, pressure, and impurities). During the drying process, free water in potassium chloride continuously diffuses from the interior to the particle surface, resulting in a saturated solution on the particle surface. When the temperature changes, a supersaturated solution forms, crystals precipitate, and crystal bridges form at the contact points between the particles. Over time, the crystals bond together, forming agglomerates. The capillary adsorption theory posits that the capillary adsorption force between microcrystalline particles causes the saturated vapor pressure on the capillary meniscus to be lower than the external saturated vapor pressure. This creates conditions for water vapor to diffuse between the crystals, making it easier for the crystals to absorb moisture. This cycle proceeds in the following order: moisture absorption → dissolution on the particle surface → evaporation of water and subsequent crystal precipitation → bridging between particles, ultimately forming agglomerates.

[0004] In order to prevent the agglomeration of the food, the existing technology mainly uses different packaging materials to package the food, but this cannot effectively solve the agglomeration problem. Summary of the Invention

[0005] In view of this, the present invention provides a composite film for packaging potassium chloride particles and a preparation method thereof.

[0006] One of the purposes of the present invention is to provide a method for preparing a composite film for packaging potassium chloride granules, comprising the following steps:

[0007] (1) Prepare a solution containing gelatin powder, konjac flour, glycerin, and hydroxyapatite powder, fully dissolve them, and then treat them in a water bath at approximately 100°C for 15 minutes;

[0008] (2) Transfer the solution obtained in step (1) into a culture dish and bake at 40-60°C for 24-48 hours;

[0009] (3) Peeling the composite film off the culture dish.

[0010] Furthermore, the concentration of the solution in step (1) is 2.5 to 6 wt%. Among them, the solution concentration can also be 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3.0wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt%, 3.6wt%, 3.7wt%, 3.8wt%, 3.9wt%, 4.0wt%, 4.1wt%, 4.2wt%, 4.3wt%, 4.4wt%, 4.5wt%, 4.6wt%, 4.7wt%, 4.8wt%, 4.9wt%, 5.0wt%, 5.1wt%, 5.2wt%, 5.3wt%, 5.4wt%, 5.5wt%, 5.6wt%, 5.7wt%, 5.8wt% or 5.9wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0011] Furthermore, in step (1), the weight ratio of gelatin, konjac, glycerol and hydroxyapatite is (100-120):(100-120):(100-120):(2-5).

[0012] Furthermore, in step (1), the weight ratio of gelatin, konjac, glycerol and hydroxyapatite is 100:100:120:2.

[0013] Furthermore, in step (1), the weight ratio of gelatin, konjac, glycerol and hydroxyapatite is 120:120:120:2.

[0014] Furthermore, in step (1), the weight ratio of gelatin, konjac, glycerol and hydroxyapatite is 120:120:100:2.

[0015] Furthermore, in step (1), the weight ratio of gelatin, konjac, glycerol and hydroxyapatite is 120:120:100:5.

[0016] Furthermore, in the step (1), during the preparation process, gelatin and konjac are first dissolved in distilled water at approximately 100° C., and then a distilled water solution of hydroxyapatite is prepared in distilled water at approximately 100° C., and finally glycerol is added.

[0017] A second object of the present invention is to provide a composite membrane obtained by the preparation method.

[0018] A third object of the present invention is to provide an application of the composite film obtained by the preparation method in packaging potassium chloride granules.

[0019] The beneficial effects of this solution are:

[0020] 1, because the composite membrane that the present invention makes has adopted gelatin and konjac flour etc. as main raw material in preparation process, has certain gas permeability, but its transmittance to water vapor is lower.May form close membrane structure owing to gelatin and konjac flour, and add wherein hydroxyapatite itself and have high-strength water-absorbent, can effectively absorb water, prevents moisture from going in and sees through film, thereby prevents that potassium chloride granules from caking.

[0021] 2, because the composite film that the present invention makes has added hydroxyapatite and konjac flour itself and composite film form close structure in preparation process, increase the limiting oxygen index of composite film and improve its flame retardancy, and delay the formation of volatility and combustible material of film, delay the degradation rate of film.This makes it can adapt to hot environment as the packaging material of potassium chloride granules, plays the protective effect to potassium chloride granules.

[0022] 3. In addition, through the comparison of the examples and the comparative examples, it was found that the addition of konjac flour helps to disperse the hydroxyapatite, thereby making it easier to obtain a uniform and dense membrane structure.

[0023] 4. In addition, by comparing the examples with the comparative examples, it was found that the composite film prepared in the examples has more excellent mechanical properties and flexibility, and its water vapor permeability is lower, which is more conducive to protecting potassium chloride particles and preventing them from agglomerating. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 These are SEM images of the composite membranes provided in Examples 1 to 4 respectively.

[0025] Figure 2 These are SEM images of the composite films provided in Examples 5-6 and Comparative Examples 1-2, respectively. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following examples. It should be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention. Reagents not described in detail herein are all conventional reagents and are commercially available; methods not specifically described in detail are all conventional experimental methods and are known in the art.

[0027] An embodiment of the present invention provides a method for preparing a composite film for packaging potassium chloride particles, characterized in that it includes the following steps:

[0028] (1) Prepare a solution containing gelatin powder, konjac flour, glycerin, and hydroxyapatite powder, fully dissolve them, and then treat them in a water bath at approximately 100°C for 15 minutes;

[0029] (2) Transfer the solution obtained in step (1) into a culture dish and bake at 40-60°C for 24-48 hours;

[0030] (3) Peeling the composite film off the culture dish.

[0031] The following are typical but non-limiting examples of the present invention:

[0032] Example 1:

[0033] This embodiment provides a composite film for packaging potassium chloride particles and a preparation method thereof. The preparation method comprises the following steps:

[0034] (1) Prepare a 3.5wt% solution containing gelatin powder (food grade, Xinfu Shengde), konjac flour (article number YZ-J-36MY, NY / T494, consistent konjac), glycerol and hydroxyapatite powder (15μm grade, article number SWSW-0715-157, Senwan). The weight ratio of gelatin, konjac, glycerol and hydroxyapatite is 100:100:120:2. During the preparation process, gelatin and konjac are first mixed into distilled water close to 100℃ and fully dissolved, and then glycerol is added. After fully stirring for 30min, it is placed in a water bath close to 100℃ for 15min to deal with the generated foam. During the preparation process, gelatin and konjac are first dissolved in distilled water close to 100℃, and then a distilled water solution of hydroxyapatite is prepared with distilled water close to 100℃. Finally, glycerol is added to facilitate full mixing to avoid the formation of aggregates of hydroxyapatite powder. During the preparation process, the prepared solution was also subjected to ultrasonic treatment (31kHz, acoustic energy density 0.11W / cm 3 ), processing time 1h.

[0035] (2) The solution obtained in step (1) was transferred into a culture dish and placed in an oven at 55°C for 48 hours to obtain a composite membrane.

[0036] (3) Peel off all the dried films from the culture dish in step (2).

[0037] The composite film prepared in this embodiment has good mechanical properties and flexibility, with a tensile strength of 110 MPa and an elongation at break of 21.4%. The water vapor permeability of the composite film prepared in this embodiment is 5.6×10 -11 (g·m -1 ·Pa -1 ·m -2 ·s -1 ).

[0038] Example 2

[0039] The embodiment provides a composite film for packaging potassium chloride particles and a preparation method thereof. The preparation method comprises the following steps:

[0040] (1) Prepare a 2.5wt% solution containing gelatin powder, konjac flour, glycerol and hydroxyapatite powder. The weight ratio of gelatin, konjac and glycerol is 100:100:120:2. During the preparation process, gelatin and konjac are first mixed into distilled water close to 100°C and fully dissolved, and then glycerol is added. After fully stirring for 30 minutes, it is placed in a water bath close to 100°C for 15 minutes to deal with the generated foam. During the preparation process, gelatin and konjac are first dissolved in distilled water close to 100°C, and then a distilled water solution of hydroxyapatite is prepared with distilled water close to 100°C, and finally glycerol is added to facilitate full mixing to avoid the formation of aggregates of hydroxyapatite powder. During the preparation process, the prepared solution is also subjected to ultrasonic treatment (31kHz, sound energy density 0.11W / cm 3 ), processing time 1h.

[0041] (2) The solution obtained in step (1) was transferred into a culture dish and placed in an oven at 55°C for 48 hours to obtain a composite membrane.

[0042] (3) Peel off all the dried films from the culture dish in step (2).

[0043] The composite film prepared in this embodiment has good mechanical properties and flexibility, with a tensile strength of 102 MPa and an elongation at break of 18.7%. The water vapor permeability of the composite film prepared in this embodiment is 1.4×10 -10 (g·m -1 ·Pa -1 ·m -2 ·s -1 ).

[0044] Example 3

[0045] The embodiment provides a composite film for packaging potassium chloride particles and a preparation method thereof. The preparation method comprises the following steps:

[0046] (1) Prepare a 6.0wt% solution containing gelatin powder, konjac flour, glycerol and hydroxyapatite powder. The weight ratio of gelatin, konjac and glycerol is 100:100:120:2. During the preparation process, gelatin and konjac are first mixed into 100℃ distilled water to fully dissolve, and then glycerol is added. After fully stirring for 30 minutes, the mixture is placed in a water bath at a temperature close to 100℃ for 15 minutes to process the generated foam. During the preparation process, gelatin and konjac are first dissolved in distilled water close to 100℃, and then a distilled water solution of hydroxyapatite is prepared with distilled water close to 100℃, and finally glycerol is added to facilitate full mixing to avoid the formation of aggregates of hydroxyapatite powder. During the preparation process, the prepared solution is also subjected to ultrasonic treatment (31kHz, sound energy density 0.11W / cm 3), processing time 1h.

[0047] (2) The solution obtained in step (1) was transferred into a culture dish and placed in an oven at 55°C for 48 hours to obtain a composite membrane.

[0048] (3) Peel off all the dried films from the culture dish in step (2).

[0049] The composite film prepared in this embodiment has good mechanical properties and flexibility, with a tensile strength of 129 MPa and an elongation at break of 28.4%. The water vapor permeability of the composite film prepared in this embodiment is 0.35×10 -12 (g·m -1 ·Pa -1 ·m -2 ·s -1 ).

[0050] Example 4

[0051] The embodiment provides a composite film for packaging potassium chloride particles and a preparation method thereof. The preparation method comprises the following steps:

[0052] (1) Prepare a 3.5wt% solution containing gelatin powder, konjac flour, glycerol and hydroxyapatite powder. The weight ratio of gelatin, konjac and glycerol is 120:120:120:2. During the preparation process, gelatin and konjac are first mixed into distilled water close to 100°C and fully dissolved, and then glycerol is added. After fully stirring for 30 minutes, it is placed in a water bath close to 100°C for 15 minutes to deal with the generated foam. During the preparation process, gelatin and konjac are first dissolved in distilled water close to 100°C, and then a distilled water solution of hydroxyapatite is prepared with distilled water close to 100°C, and finally glycerol is added to facilitate full mixing to avoid the formation of aggregates of hydroxyapatite powder. During the preparation process, the prepared solution is also subjected to ultrasonic treatment (31kHz, sound energy density 0.11W / cm 3 ), processing time 1h.

[0053] (2) The solution obtained in step (1) was transferred into a culture dish and placed in an oven at 55°C for 48 hours to obtain a composite membrane.

[0054] (3) Peel off all the dried films from the culture dish in step (2).

[0055] The composite film prepared in this embodiment has good mechanical properties and flexibility, with a tensile strength of 115 MPa and an elongation at break of 20.8%. The water vapor permeability of the composite film prepared in this embodiment is 1.08×10 -11 (g·m -1 ·Pa -1 ·m -2 ·s-1 ).

[0056] Example 5

[0057] The embodiment provides a composite film for packaging potassium chloride particles and a preparation method thereof. The preparation method comprises the following steps:

[0058] (1) Prepare a 3.5wt% solution containing gelatin powder, konjac flour, glycerol and hydroxyapatite powder. The weight ratio of gelatin, konjac and glycerol is 120:120:100:2. During the preparation process, gelatin and konjac are first mixed into distilled water close to 100°C and fully dissolved, and then glycerol is added. After fully stirring for 30 minutes, it is placed in a water bath close to 100°C for 15 minutes to deal with the generated foam. During the preparation process, gelatin and konjac are first dissolved in distilled water close to 100°C, and then a distilled water solution of hydroxyapatite is prepared with distilled water close to 100°C, and finally glycerol is added to facilitate full mixing to avoid the formation of aggregates of hydroxyapatite powder. During the preparation process, the prepared solution is also subjected to ultrasonic treatment (31kHz, sound energy density 0.11W / cm 3 ), processing time 1h.

[0059] (2) The solution obtained in step (1) was transferred into a culture dish and placed in an oven at 55°C for 48 hours to obtain a composite membrane.

[0060] (3) Peel off all the dried films from the culture dish in step (2).

[0061] The composite film prepared in this embodiment has good mechanical properties and flexibility, with a tensile strength of 121 MPa and an elongation at break of 25.7%. The water vapor permeability of the composite film prepared in this embodiment is 0.72×10 -11 (g·m -1 ·Pa -1 ·m -2 ·s -1 ).

[0062] Example 6

[0063] The embodiment provides a composite film for packaging potassium chloride particles and a preparation method thereof. The preparation method comprises the following steps:

[0064] (1) Prepare a 3.5wt% solution containing gelatin powder, konjac flour, glycerol and hydroxyapatite powder. The weight ratio of gelatin, konjac and glycerol is 120:120:100:5. During the preparation process, gelatin and konjac are first mixed into distilled water close to 100°C and fully dissolved, and then glycerol is added. After fully stirring for 30 minutes, it is placed in a water bath close to 100°C for 15 minutes to deal with the generated foam. During the preparation process, gelatin and konjac are first dissolved in distilled water close to 100°C, and then a distilled water solution of hydroxyapatite is prepared with distilled water close to 100°C, and finally glycerol is added to facilitate full mixing to avoid the formation of aggregates of hydroxyapatite powder. During the preparation process, the prepared solution is also subjected to ultrasonic treatment (31kHz, sound energy density 0.11W / cm 3 ), processing time 1h.

[0065] (2) The solution obtained in step (1) was transferred into a culture dish and placed in an oven at 55°C for 48 hours to obtain a composite membrane.

[0066] (3) Peel off all the dried films from the culture dish in step (2).

[0067] The composite film prepared in this embodiment has good mechanical properties and flexibility, with a tensile strength of 123 MPa and an elongation at break of 27.4%. The water vapor permeability of the composite film prepared in this embodiment is 0.72×10 -12 (g·m -1 ·Pa -1 ·m -2 ·s -1 ).

[0068] Comparative Example 1:

[0069] This embodiment provides a composite film for packaging potassium chloride particles and a preparation method thereof. The preparation method comprises the following steps:

[0070] (1) Prepare a 3.5wt% solution containing gelatin powder, konjac powder and glycerol. The weight ratio of gelatin, konjac and glycerol is 100:100:120. During the preparation process, gelatin and konjac are first mixed into distilled water close to 100°C and fully dissolved, and then glycerol is added. After fully stirring for 30 minutes, it is placed in a water bath close to 100°C for 15 minutes to deal with the generated foam. During the preparation process, gelatin and konjac are first dissolved in distilled water close to 100°C, and then a distilled water solution of hydroxyapatite is prepared with distilled water close to 100°C, and finally glycerol is added to facilitate full mixing to avoid the formation of aggregates of hydroxyapatite powder. During the preparation process, the prepared solution is also subjected to ultrasonic treatment (31kHz, sound energy density 0.11W / cm 3 ), processing time 1h.

[0071] (2) The solution obtained in step (1) was transferred into a culture dish and placed in an oven at 55°C for 48 hours to obtain a composite membrane.

[0072] (3) Peel off all the dried films from the culture dish in step (2).

[0073] The composite film prepared in this embodiment has good mechanical properties and flexibility, with a tensile strength of 86 MPa and an elongation at break of 13.5%. The water vapor permeability of the composite film prepared in this embodiment is 2.57×10 -9 (g·m -1 ·Pa -1 ·m -2 ·s -1 ).

[0074] Comparative Example 2:

[0075] This embodiment provides a composite film for packaging potassium chloride particles and a preparation method thereof. The preparation method comprises the following steps:

[0076] (1) Prepare a 3.5 wt% solution containing gelatin powder, glycerin, and hydroxyapatite powder. The weight ratio of gelatin, konjac, and hydroxyapatite is 100:120:2. First, dissolve the gelatin and konjac in distilled water at approximately 100°C. Then, add glycerin, stir thoroughly for 30 minutes, and then place in a water bath at approximately 100°C for 15 minutes to remove any foam.

[0077] (2) The solution obtained in step (1) was transferred into a culture dish and placed in an oven at 55°C for 48 hours to obtain a composite membrane.

[0078] (3) Peel off all the dried films from the culture dish in step (2).

[0079] The composite film prepared in this embodiment has good mechanical properties and flexibility, with a tensile strength of 89 MPa and an elongation at break of 16.4%. The water vapor permeability of the composite film prepared in this embodiment is 5.35×10 -8 (g·m -1 ·Pa -1 ·m -2 ·s -1 ).

[0080] 1. Microstructure of membrane

[0081] The microstructure of the membrane surface was determined by scanning electron microscopy (SEM). The membrane surface was fixed with gold spray to improve conductivity. The accelerating voltage was 15kV. Figure 1As shown in the SEM of Examples 1 to 6, dense and consistent composite films were formed without obvious aggregated particles and gaps. Figure 2 D) Obvious aggregated particles appear (white dots in the figure). Figure 2 D and Figure 1 Compared with Comparative Example A, the raw materials in the composite membrane preparation process provided in Comparative Example 2 do not use konjac flour. It can be seen that the addition of konjac flour helps to disperse hydroxyapatite, thereby making it easier to obtain a uniform and dense composite membrane structure.

[0082] 2. Mechanical properties test

[0083] The mechanical properties of the membrane mainly include breaking strength and breaking elongation. The membrane samples were placed in an environment of 20°C and 60% RH and tested after 48 hours of equilibrium. The membrane was cut into 100mm×20mm strips and fixed on a microcomputer-controlled electronic universal testing machine. The initial stretching distance was set to 50mm and the stretching rate was 50mm / min. Each sample was tested at least three times. The breaking strength (TS), breaking elongation (EB) and Young's modulus (EM) were calculated by formula (1), formula (2) and formula (3), respectively.

[0084] TS = Fmax / A; Formula (1)

[0085] Fmax represents the maximum load when the membrane breaks (N), A represents the cross-sectional area of ​​the test sample (mm 2 , thickness × width).

[0086] EB=ΔL / L0;Formula (2)

[0087] ΔL represents the length difference (mm) when the sample breaks, and L0 represents the initial length (mm) of the test sample.

[0088] EM=Fmax×L0 / A×ΔL;Formula (3)

[0089] 3. Water vapor transmission rate test

[0090] At 20°C, add distilled water to a 25×25 mm weighing bottle, 2 mm below the bottle mouth (100% RH; vapor pressure at 20°C is 2.337×10 3 The membrane was cut into 30 × 30 mm sheets, which were placed over the mouth of a weighing bottle and sealed. The weighing bottle was then placed in a desiccator containing silica gel (1.5% RH; vapor pressure 28.044 Pa at 20°C). The change in the cup's mass was recorded every hour for 8 hours. Each sample was repeated at least three times, and the water vapor transmission rate (WVP) of the membrane was calculated using Equation (5).

[0091] WVP=L×WVTR / ΔP;Formula (5)

[0092] In formula (5), WVTR is the measured water vapor transmission rate of the sample (g·m -2 ·s -1 ), L is the thickness of the membrane (m), and ΔP is the vapor pressure difference on both sides of the membrane (Pa).

[0093] 4. Anti-caking test

[0094] The sample used in this experiment is potassium chloride food particles (80 (mesh). The packaging bag material is the composite film prepared in Examples 1 to 6 and Comparative Examples 1 to 2 respectively. The standing bags of these composite film materials were subjected to a sealing test. The instrument used in the sealing test was a GB-M sealing tester, the instrument manufacturer was Guangzhou Biaoji Packaging Equipment Co., Ltd., and the reference standard was GB / T15171-94.

[0095] The experimental principle involves evacuating a vacuum chamber to create a pressure differential between the inside and outside of a sealed stand-up pouch in water. The pressure is then measured to determine the pouch's sealing performance and breaking strength. The experimental conditions were a maximum vacuum level of 85 kPa, and a sealing time of 50 seconds at this pressure. The experiments revealed that the stand-up pouches used in this experiment, namely those made from the composite films provided in Examples 1-6 and Comparative Examples 1-2, exhibited gas leakage, while the packaging remained intact and undamaged. These packaging materials were deemed qualified according to the standard and met the experimental requirements.

[0096] Secondly, this product was sealed and packaged as a regular product with a 320g composite film stand-up bag packaging machine. Finally, under the same temperature and humidity conditions, the samples made from different composite films were boxed with existing cartons, with 40 bags per box, and each bag of product weighed 320g. According to Examples 1 to 6 and Comparative Examples 1 to 2, they were grouped respectively and placed in a laboratory under the same conditions (placed 0, 3, 6, and 9 months under the conditions of about 20°C and 45% to 75% humidity in a cool place). Each month, a bag of the surface layer was regularly taken and the sample was observed. The caking weight in each sachet was recorded for each observation, and the caking rate (the percentage of caking weight to total sample weight) of the statistical sample was observed 3 times. Under the same temperature, humidity, and pressure conditions, the sample caking situation was observed, as shown in Table 1.

[0097] Table 1 Agglomeration of potassium chloride particles in each group

[0098] Grouping 30th 60 days 90 days Example 1 No lumps No lumps No lumps Example 2 No lumps No lumps 2% of pseudo-agglomerates Example 3 No lumps No lumps No lumps Example 4 No lumps No lumps No lumps Example 5 No lumps No lumps No lumps Example 6 No lumps No lumps No lumps Comparative Example 1 Agglomeration rate 5% Agglomeration rate 20% Agglomeration rate 25% Comparative Example 2 No lumps No lumps 5% of pseudo-agglomerates

[0099] The "false lumps" in Table 1 are lumps that break apart with a light touch, whereas true lumps are compacted and cannot be easily broken apart. As shown in Table 1, the stand-up pouches made with the composite films provided in Examples 1-6 are effective in preventing the lumps of potassium chloride granules from clumping.

[0100] 5. Flame retardant performance test

[0101] (1) Limiting oxygen index test

[0102] All membrane samples were cut into rectangles (100 mm × 20 mm). Four membrane sheets were compacted and fixed on a limiting oxygen index tester. The oxygen concentration was adjusted from low to high, and the oxygen concentration when the membrane began to burn was recorded.

[0103] (2) Thermal stability test

[0104] The thermal stability of the membrane was tested using a thermogravimetric tester at a temperature range of 35°C to 600°C at a heating rate of 10°C / min.

[0105] Table 2 Thermal stability performance of each group of composite films

[0106]

[0107] The limiting oxygen index can roughly determine the combustion performance of a material. The higher the limiting oxygen index value, the higher the oxygen content required for combustion, indicating that the material is less flammable. When the limiting oxygen index of a material is lower than 22%, it is considered to be flammable, and when it is higher than 27%, it is considered to be flame retardant. The limiting oxygen indexes of the composite films provided by Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 1. It can be seen from Table 1 that the limiting oxygen indexes of the composite films provided by Examples 1 to 6 are all lower than 27%, indicating that they can be regarded as flame retardant materials, while the composite films provided by Comparative Examples 1 to 2 behave as flammable materials. Comparative Example 1 does not add hydroxyapatite relative to Example 1, and Comparative Example 2 does not add konjac flour relative to Example 1, indicating that the addition of hydroxyapatite and konjac flour can increase the limiting oxygen index of the composite film and improve its flame retardancy.

[0108] Thermogravimetric analysis was used to study the thermal stability of the membrane in a nitrogen atmosphere to evaluate the thermal degradation behavior of hydroxyapatite on the composite membrane. The thermal stability is similar to the flammability experiment, but there is no ignition source. The thermogravimetric test results of the five membranes are shown in Table 2. The initial degradation temperature and the temperature corresponding to the maximum initial degradation rate of the composite membranes provided by Examples 1 to 6 are higher than those of Comparative Examples 1 to 2, and the residual weight percentage at 600°C is also higher than that of Comparative Examples 1 to 2, indicating that the composite membranes provided by Comparative Examples 1 to 2 degrade rapidly and more thoroughly at high temperatures, indicating that the addition of hydroxyapatite and konjac flour delays the formation of volatile and combustible substances in the membrane and delays the degradation rate of the membrane, which may be related to the formation of a crystalline structure of the two in the composite membrane.

[0109] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a composite film for packaging potassium chloride particles, characterized in that: The following steps are involved: (1) A 3.5 wt% solution containing gelatin powder, konjac flour, glycerol, and hydroxyapatite powder was prepared. After fully dissolving, the solution was treated in a water bath at approximately 100°C for 15 min. The weight ratio of gelatin, konjac flour, glycerol, and hydroxyapatite was 120:120:100:

5. (2) Transfer the solution obtained in step (1) into a culture dish and bake at 40-60°C for 24-48 hours; (3) Peeling the composite film from the culture dish.

2. The preparation method according to claim 1, characterized in that In the step (1), during the preparation process, gelatin and konjac are first dissolved in 100° C. distilled water, and then a distilled water solution of hydroxyapatite is prepared in 100° C. distilled water, and finally glycerol is added.

3. A composite film obtained by the preparation method according to any one of claims 1 to 2.

4. Use of the composite film obtained by the preparation method according to any one of claims 1 to 2 in packaging potassium chloride granules.

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