CN116715903A - Preparation method of hydrophobic starch-based foaming material - Google Patents

Abstract

The invention discloses a method for preparing a hydrophobic starch-based foaming material. The invention first adds nano-SiO ₂ to starch to prepare the foaming material, then uses hexamethyldisilazane solution for fumigation, and finally coats nano ‑SiO ₂ layer is attached to the surface side of the material. The present invention uses hexamethyldisilazane to generate a "Si-O-C" structure when it meets a large number of hydroxyl groups on the starch surface, and at the same time generates a more stable "Si-O" with nano-SiO ₂ which has a large number of unbonded hydroxyl groups on the surface. O-Si" structure, three methyl silane is finally grafted to the surface of the starch material, which can form an effective hydrophobic layer to effectively block contact with water, and react with the HMDS attached to the fumigation surface to the greatest extent to form a stable The "Si‑O‑Si" water-blocking structure, while the granular shape formed by nano‑SiO ₂ on the surface of the material greatly increases the roughness, quickly improves the hydrophobicity of the material surface, and solves the problem of direct spraying of existing starch foaming materials. The SiO ₂ hydrophobic layer is not tightly combined with the foam and is susceptible to friction, which reduces the hydrophobic ability.

Description

Preparation method of hydrophobic starch-based foaming material

Technical field

The invention belongs to the technical field of starch foaming material modification technology, and more specifically, relates to a preparation method of hydrophobic starch-based foaming material.

Background technique

In recent years, using starch to replace traditional industrial resins to prepare foam products has become a hot research topic. Starch foam products can not only suppress the environmental problems caused by foam plastic waste, but also reduce the consumption of petroleum-based raw materials to a certain extent, which is of sustainable development significance. . Currently, such products have some applications on the market, but they cannot be promoted on a large scale. The main reason is that there are still defects in the production and application of starch-based foaming materials, such as poor mechanical properties and poor water resistance.

Starch is a hydrophilic polymer material with a large number of hydrophilic hydroxyl groups (-OH) distributed in the molecular structure, making it highly water absorbent. When it is made into foam products, the overall structure expands and the specific surface area The size increases and the water absorption capacity is stronger, which greatly limits the application of starch foam products in people's daily life. In order to weaken this defect, starch products often need to be treated with water resistance to reduce sensitivity to water. In current research, the main commonly used methods are grafting and coating. The coating method is to coat a hydrophobic layer on the surface of starch-based materials. For example, CN202110544821.1 discloses a method for preparing a waterproof starch foam material by blending starch, glycerin, NaHCO ₃ and nano-CaCO ₃ , molding and molding to prepare a foam, and then placing the foam in a closed container. Steam fumigation, and finally spray the SiO ₂ ethanol solution onto the surface of the foam after water vapor treatment, add nano-SiO ₂ into the ethanol solution and stir for 10 minutes; spray the prepared solution evenly to the foam; and then spray the foam Place it under dry conditions at room temperature for 6 hours to obtain a hydrophobic layer. This patent uses the water vapor method to improve the hydrophobic effect of the material, and evenly and quickly covers the nano-SiO ₂ /ethanol solution on the foam surface through the spraying method to produce a waterproof starch-based foaming material with excellent performance. However, the hydrophobic layer of this patent is a single nano-SiO ₂ layer, and its hydrophobicity improvement is limited. SiO ₂ has high surface activity and low bonding strength with the starch matrix. When the foamed product is squeezed or rubbed, The hydrophobic layer on its surface is easy to peel off, thereby weakening the hydrophobic ability of the starch foam material.

Contents of the invention

The present invention provides a hydrophobic starch-based material to overcome the problems that existing starch foaming materials using a SiO ₂ hydrophobic layer have poor waterproof performance, and the adhesion between the SiO ₂ hydrophobic layer and the starch surface is not strong and is easy to peel off. Preparation method of foam material.

The present invention is achieved through the following technical solutions:

A method for preparing hydrophobic starch-based foaming materials, characterized in that the steps include:

S1. Mix raw starch, foaming agent and glycerol containing nano-silica evenly, and then prepare starch foaming material;

S2. Place the starch foaming material in a closed space, add hexamethyldisilazane (HMDS) solution for fumigation, and obtain the modified starch foaming material;

S3. Then coat the surface of the modified starch foam material with a nano-silica solution, and then dry it to obtain a hydrophobic starch-based foam material.

Furthermore, the raw materials described in S1 also include a binder and a foaming assistant. The binder is preferably polyvinyl alcohol, and the foaming assistant is preferably zinc oxide.

Further, the amount of nanosilica added in S1 is 1 to 5% of the starch mass. Preferably, the amount of nanosilica added is 3% of the starch mass.

Further, the amount of foaming agent added in S1 is 4 to 8% of the starch mass.

Preferably, the ingredients of the raw materials in S1 are 100 phr of starch, 20 phr of glycerin, 4 phr of nano-silica, 5 phr of binder, 6 phr of foaming agent, and 2 phr of foaming assistant.

Further, the fumigation time described in S2 is 10 to 40 minutes.

Further, the nano-silica solution described in S3 is a nano-silica ethanol solution, and the content of nano-silica is 2 to 8 wt%. Preferably, the content of the nano-silica is 5 to 7 wt%.

The hydrophobic starch-based foaming material prepared by the preparation method of the hydrophobic starch-based foaming material is used as buffer packaging materials for electronics, food, medicine, and agricultural and sideline products.

Compared with existing technology, the beneficial effects are:

The present invention adds nano-SiO ₂ to the starch-based foaming material, which can not only enhance the strength of the starch foaming material, but also during the fumigation process using hexamethyldisilazane solution, hexamethyldisilazane interacts with the starch surface When a large number of hydroxyl groups meet to form a "Si-OC" structure, it also forms a more stable "Si-O-Si" structure with nano-SiO ₂ which has a large number of unbonded hydroxyl groups on the surface, and finally grafts three methyl silane To the surface of the starch material, it can effectively block contact with water. The silane trimethyl structure on the outside increases the micro-roughness of the surface of the starch foam material and can show better hydrophobicity. In the present invention, a layer of nano-SiO ₂ is coated on the foamed material after HMDS fumigation and adheres to the surface of the material to react with the HMDS on the fumigated surface to the greatest extent possible to generate a stable "Si-O-Si" barrier. The water structure improves the bonding strength between the surface nano-SiO ₂ and the foam material. More importantly, the granular nano-SiO ₂ greatly increases the roughness of the surface of the material and quickly improves the hydrophobicity of the material surface.

Description of the drawings

Figure 1 is an FTIR image of the outer side of the starch foam material in Example 3 without HMDS fumigation treatment and without HMDS fumigation treatment.

Figure 2 is a diagram showing the influence of preparation solutions with different nano-SiO ₂ contents on the surface morphology in Example 4.

Figure 3 is the XRD pattern of the surface of the foam material under different nano-SiO ₂ contents in Example 4.

Figure 4 is a diagram of the hydrophobic mechanism for spraying nano-SiO ₂ solution.

Detailed ways

The following further explains and illustrates the invention in conjunction with the examples, but the specific examples do not limit the invention in any way. Unless otherwise specified, the methods and equipment used in the examples are conventional methods and equipment in the art, and the raw materials used are all conventional commercially available raw materials.

Corn starch (amyl chain content 60%), Hebei Yanhua Starch Co., Ltd.; Glycerin (analytical grade), Huihong Chemical Reagent Co., Ltd.; PVA (088-20), China Petrochemical Corporation; Nano-SiO ₂ (Grade HL- 200), Jibisheng Technology Co., Ltd.; AC foaming agent (H700), Changzhou Tonghe Chemical Co., Ltd.

Example 1

This embodiment provides a method for preparing hydrophobic starch-based foaming materials. The preparation steps include:

S1. Dry 100phr of cornstarch in a drying oven at 40°C for 30min, uniformly disperse 5phr of nano- _SiO2 into 20phr of glycerin through ultrasonic treatment, and then mix the glycerin containing nano- _SiO2 , powdered PVA, 6 phr of azodicarbonamide (AC) and 2 phr of ZnO were blended with starch in a high-speed mixer for 30 min, then taken out and placed at room temperature for 24 h.

S2. Mill the mixed raw materials multiple times in a double-roller mill at 120°C to obtain thermoplastic starch TPS. Then put the thermoplastic starch TPS into the mold in the middle of the molding press to preheat for 30 minutes. Set the molding temperature to 165°C and the pressing time to 20 minutes. After the mold is opened, the starch foam material is obtained.

S3. Put the starch foaming material and HMDS solution into a sealed fumigation container, and fumigate at 60°C for a period of time to obtain the modified starch foaming material.

S4. Use a spray gun to evenly spray the ethanol solution containing nano-SiO ₂ onto the surface of the fumigated modified starch foam material, let it stand for 30 minutes, then press it with a hot press for 10 minutes, and then place the starch foam material at room temperature. After 6 hours, a starch-based foaming material containing a hydrophobic layer was obtained.

Hexamethyldisilazane (HMDS, molecular formula Si(CH ₃ ) ₃ NHSi(CH ₃ ) ₃ ) is a solution that is easily volatile when heated appropriately. The method of the present invention uses heated fumigation to hydrophobically modify starch-based composite foaming materials. When HMDS is used as a surface hydrophobic agent, it easily reacts with the hydroxyl structure to generate trimethylalkoxysilane, which can react with starch materials containing a large number of hydroxyl groups. When meeting, a "Si-OC" structure can be generated, and a more stable "Si-O-Si" structure can be generated with nano-SiO ₂ which has a large number of unbonded hydroxyl groups on the surface. The reaction mechanism is as follows:

Finally, three methyl silane is grafted to the surface of the starch material, which can effectively block contact with water. At the same time, the trimethyl structure of the outer silane increases the microscopic roughness of the surface of the material, which will present a larger appearance. Good hydrophobicity.

Compared with water vapor fumigation, the hydrophobic modification of HMDS fumigation generates a barrier bond structure, and the hydrophobic effect is more obvious. As shown above, the sprayed nano-SiO ₂ particles are attached to the surface of the material and react with the HMDS on the fumigated surface to the greatest extent to form a stable "Si-O-Si" water-blocking structure. More importantly, the granular Nano-SiO ₂ greatly increases the roughness of the surface side of the material and quickly improves the hydrophobicity of the material surface.

Example 2

This example uses different HMDS fumigation times to explore the impact on the hydrophobicity of starch foam materials. The steps include:

S1. Dry 100phr of cornstarch in a drying oven at 40°C for 30min, uniformly disperse 5phr of nano- _SiO2 into 20phr of glycerin through ultrasonic treatment, and then mix the glycerin containing nano- _SiO2 , powdered PVA, 6 phr of azodicarbonamide (AC) and 2 phr of ZnO were blended with starch in a high-speed mixer for 30 min, then taken out and placed at room temperature for 24 h.

S2. Mill the mixed raw materials multiple times in a double-roller mill at 120°C to obtain thermoplastic starch TPS. Then put the thermoplastic starch TPS into the middle mold of the molding machine to preheat for 30 minutes. Set the molding temperature to 165°C and the pressing time to 20 minutes. After the mold is opened, the starch foam material is obtained.

Experimental Group 1: This group did not fumigate the starch foam materials;

Experimental Group 2: The fumigation time of starch foam materials in this group is 10 minutes;

Experimental Group 3: The fumigation time of starch foam materials in this group is 20 minutes;

Experimental Group 4: The fumigation time of starch foam materials in this group is 30 minutes;

Experimental Group 5: The fumigation time of starch foam material in this group is 40 minutes.

The hydrophobicity of the hydrophobic starch-based foaming materials prepared in Groups 1 to 5 was tested, and the contact angles of each group were obtained as shown in Table 1 below:

Table 1

As shown in Table 1, the HMDS fumigation time has a significant impact on the contact angle of the surface layer of the starch foam material. As the fumigation time increases, the combination reaction of HMDS with starch and nano-SiO ₂ floating on the starch surface generates "Si-OC" and The hydrophobic layer of "Si-O-Si" has a surface contact angle that gradually increases, with a maximum contact angle of 120°. As the fumigation time increases, the amount of nano-SiO ₂ floating on the surface of the starch foam material that contacts HMDS decreases, so the stable "Si-O-Si" structure no longer increases, and the increase in contact angle slows down in the later stage of fumigation. .

Analyzing the FTIR of Experimental Group 1 and Experimental Group 5 that were not fumigated, it can be seen from Figure 1 that in the 1000-900cm ^-1 band (corresponding to Si-O-Si), the unfumigated outer side (a) is different from the HMDS fumigated The sharpness of the waveform on the outer outer side (b) is obviously different. This shows that HMDS reacts with nano-SiO ₂ in starch to form a "Si-O-Si" structure. HMDS can better adhere to the surface of the starch foam material and effectively form a waterproof barrier layer.

According to Wenzel's theory, the relationship between the contact angle change and roughness of the solid surface is analyzed, as shown in formula (1):

cosθ _W =rcosθ (1)

In the formula, θ _W is the contact angle of the rough surface; r is A _rough /A _flat , which is the ratio of the total surface of the rough surface to the horizontal projected area; θ is the contact angle on a smooth flat surface. The use of Wenzel's theory is based on the assumption that droplets fill the entire rough structure of the solid surface, so r in the equation is always greater than 1. It can be seen from the formula that increasing the surface roughness of the substrate can make the material surface hydrophobic.

On the basis of Wenzel's theory, Cassie and Baxter proposed to imagine the rough and uneven solid surface as a composite surface, that is, when a water droplet drips onto a rough surface, the water droplet does not completely fill the rough microstructure of the surface, but makes composite contact with the solid surface. . In the case of composite contact, the apparent solid-liquid contact surface is actually composed of a solid-liquid contact surface and a gas-liquid contact surface. After taking the air factor of the composite interface into account, Cassie and Baxter revised the Wenzel formula and derived the Cassie-Baxter formula, as shown in formula (2):

cosθ _W ＝f ₁ cosθ-f ₂ (2)

In the formula, θ _W represents the contact angle between the rough surface and water, f ₁ represents the proportion of contact between solid microstructure and water in the composite interface, f ₂ represents the proportion of contact between air and water in the composite interface, and f _{1 +} f ₂ =1, so formula (2) can be transformed into formula (3):

cosθ _W =f ₁ (cosθ+1)-1 (3)

Since the value of f ₁ is always less than 1, in the part where the water droplet contacts the solid surface, the smaller f ₁ is, the greater the apparent contact angle of the solid surface is, that is, the greater the proportion of air to water contact in the composite contact interface, The greater the contact angle corresponding to the solid surface.

Example 3

This example uses ethanol solutions with different contents of nano-SiO ₂ to explore the effect on the hydrophobicity of starch foam materials. The steps include:

S1. Dry 100phr of cornstarch in a drying oven at 40°C for 30min, uniformly disperse 5phr of nano- _SiO2 into 20phr of glycerol through ultrasonic treatment, and then mix the glycerin containing nano- _SiO2 , powdered PVA, 6 phr of azodicarbonamide (AC) and 2 phr of ZnO were blended with starch in a high-speed mixer for 30 min, then taken out and placed at room temperature for 24 h.

S2. Mill the mixed raw materials multiple times in a double-roller mill at 120°C to obtain thermoplastic starch TPS. Then put the thermoplastic starch TPS into the middle mold of the molding machine to preheat for 30 minutes. Set the molding temperature to 165°C and the pressing time to 20 minutes. After the mold is opened, the starch foam material is obtained.

S3. Put the starch foaming material and HMDS solution into a sealed fumigation container, and fumigate at 60°C for 30 minutes to obtain the modified starch foaming material.

S4. Use a spray gun to evenly spray the ethanol solution containing nano-SiO ₂ for 3 seconds onto the surface of the fumigated modified starch foam material, let it stand for 30 minutes, then press it with a hot press for 10 minutes, and then put the starch foam material at room temperature. After leaving for 6 hours, a starch-based foaming material containing a hydrophobic layer was obtained.

Experimental group 1: The components of the nano-SiO ₂ /ethanol solution in S4 are: nano-SiO ₂ 2phr, ethanol 100phr;

Experimental group 2: The components of the nano-SiO ₂ /ethanol solution in S4 are: nano-SiO ₂ 4phr, ethanol 100phr;

Experimental group 3: The components of the nano-SiO ₂ /ethanol solution in S4 are: nano-SiO ₂ 6phr, ethanol 100phr;

Experimental group 4: The components of the nano-SiO ₂ /ethanol solution in S4 are: nano-SiO ₂ 8phr, ethanol 100phr.

The hydrophobicity of the hydrophobic starch-based foaming materials prepared in Groups 1 to 4 was tested respectively, and the contact angles of each group were obtained as shown in Table 2 below:

Table 2

As shown in Table 2 above, the contact angle of the foam material sprayed with nano-SiO ₂ /ethanol solution on the modified starch foam material is significantly improved compared with the contact angle of only HMDS fumigation. In experimental groups 1-3, as the nano-SiO ₂ content in the prepared solution increases, on the basis that the modified starch-based foaming material after fumigating HMDS has a certain hydrophobic ability, nano-SiO ₂ continues to adhere The roughness of the material surface is greatly increased, and the contact ratio of air and water droplets in the composite contact interface increases, corresponding to the greater the contact angle on the surface of the foaming material. When the nano-SiO ₂ content is 6 phr, the contact angle reaches the maximum in this system. Value 155°. However, as the sprayed nano-SiO ₂ content continues to increase, the nano-SiO ₂ on the surface of the material is excessively accumulated, resulting in a tighter arrangement. The initial rough structure becomes "blunt" and shows a gentle trend. The results of experimental group 4 On the contrary, the contact angle decreased slightly.

As can be seen in Figure 2, when the nano-SiO ₂ content reaches 2phr, the number of nano-SiO ₂ particles on the surface shown in Figure a is not large, the surface is relatively flat, and the hydrophobicity improvement is limited; when the nano-SiO ₂ content reaches At 4phr, the surface in Figure b becomes somewhat rough, and the aggregation of nano-SiO ₂ particles begins to increase significantly; when the nano-SiO ₂ content reaches 6phr, more nano-SiO ₂ agglomerates are formed on the surface shown in Figure c The nano-protrusions present a more regularly arranged rough shape, and the contact angle test reaches the best at this time. After that, as the nano-SiO ₂ content continued to increase to 8phr, the surface nanoparticles shown in Figure d accumulated too much, and the rough structure formed became "blunt", showing a gentle trend. The air and water droplets in the composite contact interface The contact ratio becomes smaller, the contact angle becomes smaller, and the hydrophobicity decreases.

The above four experimental groups and the experimental group without spraying nano-SiO ₂ /ethanol liquid (marked 0 ^# ) were selected for XRD analysis of the outer surface. The results are shown in Figure 3. The experimental XRD spectra of the four groups of sprayed nano-SiO ₂ solutions are similar. When 2θ is 18.3°, a sharp peak appears indicating the presence of nano-SiO _2. The 3 ^# curve has the highest sharpness. This also confirms that when the mass ratio of nano-SiO ₂ to ethanol is 6:100, the effective nano-SiO ₂ accumulated on the surface of the starch foam material is more accumulated, corresponding to more nano-protrusions.

Obviously, the above-mentioned embodiments of the present invention are only examples to clearly illustrate the present invention, and are not intended to limit the implementation of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. An exhaustive list of all implementations is neither necessary nor possible. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (10)

1. A method for preparing hydrophobic starch-based foaming materials, characterized in that the steps include: S1. Mix raw starch, foaming agent and glycerol containing nano-silica evenly, and then prepare starch foaming material; S2. Place the starch foaming material in a closed space, add hexamethyldisilazane solution for fumigation, and obtain the modified starch foaming material; S3. Then coat the surface of the modified starch foam material with a nano-silica solution, and then dry it to obtain a hydrophobic starch-based foam material. 2. The preparation method of hydrophobic starch-based foaming material according to claim 1, characterized in that the raw materials described in S1 also include a binder and a foaming assistant. 3. The preparation method of hydrophobic starch-based foaming material according to claim 1, characterized in that the added amount of nano-silica in S1 is 1 to 5% of the starch mass. 4. The preparation method of hydrophobic starch-based foaming material according to claim 3, characterized in that the added amount of nano-silica in S1 is 3% of the starch mass. 5. The preparation method of hydrophobic starch-based foaming material according to claim 1, characterized in that the amount of foaming agent added in S1 is 4 to 8% of the starch mass. 6. The preparation method of hydrophobic starch-based foaming material according to claim 2, characterized in that the ingredients of the raw materials in S1 are starch 100phr, glycerin 20phr, nano-silica 4phr, binder 5phr, foaming agent 6phr, assistant foaming agent 2phr. 7. The method for preparing hydrophobic starch-based foaming material according to claim 1, characterized in that the fumigation time described in S2 is 10 to 40 minutes. 8. The preparation method of hydrophobic starch-based foaming material according to claim 1, characterized in that the nano-silica solution in S3 is a nano-silica ethanol solution, and the content of nano-silica is 2 to 8wt. %. 9. The method for preparing hydrophobic starch-based foaming material according to claim 8, characterized in that the content of the nano-silica is 5 to 7 wt%. 10. The hydrophobic starch-based foaming material prepared according to the preparation method of the hydrophobic starch-based foaming material according to any one of claims 1 to 9 is used for cushioning packaging materials.