Summary:
Chitosan is a natural polymer material with a wide range of sources, with good biodegradability, biocompatibility and antibacterial properties, so it has been widely used in food packaging, controlled drug release and biomedical fields. As one of the important means for the preparation of chitosan membranes, coating technology is of great significance, especially in laboratory research. In this paper, the preparation process of chitosan film is discussed based on the working principle and application of the laboratory coating machine, and the technical parameters, influencing factors and optimization strategies of the film coating machine in the process of chitosan film coating are analyzed. Through specific experiments, the key technical points of the coating machine in coating chitosan films of different thickness and uniformity are demonstrated, and provide a reference for further research and industrial application.
1. Introduction
Chitosan is a natural polysaccharide obtained by deacetylation of chitin, which has good biodegradability, non-toxicity and a wide range of biological activities. Chitosan membranes are widely used in food packaging, controlled drug release, wound dressings, and water treatment due to their adjustability and versatility. However, the preparation of chitosan membranes involves a variety of technologies, among which coating technology, as a common preparation method, has been widely used in laboratory and industrial production. As an important equipment in coating technology, the film coater plays an important role in ensuring the uniformity and stability of the film.
Laboratory film coaters are mainly used to study the performance of coated films, adjust different process parameters to optimize the thickness, transparency, mechanical properties and gas permeability of films. Through the systematic study of the coating experiment of chitosan membrane, it can provide theoretical basis and practical experience for further improving the performance of the membrane and expanding its application field.
2. Preparation of chitosan membranes
The preparation of chitosan membrane is generally carried out by solution coating, impregnation, solution pouring and other methods. Among these methods, the coating method is widely adopted because of its simplicity and adaptability. The coating method usually involves preparing a chitosan solution, evenly coating the solution on the surface of the substrate, and then drying or cross-linking to obtain a thin film.
2.1 Preparation of chitosan solution
The preparation of chitosan membranes first requires the preparation of chitosan solutions. Chitosan is less soluble, so proper solvents and dissolution conditions need to be used. Commonly used solvents include acetic acid solution, chlorinated acid solution, etc. The dissolution process typically consists of the following steps:
1) Mix chitosan with solvent and stir and heat to a certain temperature to dissolve it completely.
2）Depending on the thickness and performance of the required membrane, the concentration of the chitosan solution is adjusted, and the general concentration range is between 1% and 3%.
3）After the solution is prepared, filtration is required to remove insoluble matter and impurities and ensure the uniformity of the membrane.
2.2 Coating process
The use of a laboratory coater is a critical step in the coating process, which controls parameters such as coating speed, coating pressure, and substrate movement speed to achieve uniform coating of the film layer.
Common coating methods are as follows:
Spin coating method - suitable for the preparation of thin films, the spin coating method can control the thickness of the film by adjusting the rotation speed.
Scraper method——The film thickness is adjusted by the gap of the scraper, which is suitable for medium thickness films.
Groove coating method——It is used for the preparation of larger areas and thicker films, and the film thickness is usually adjusted by controlling the liquid level height in the tank.
2.3 Drying and cross-linking
The coated film needs to be dried to remove the solvent and form a solid film. Drying temperature and humidity have a significant impact on the performance of the membrane, typically in the temperature range of 30°C-60°C, and the drying time needs to be adjusted according to the thickness and humidity of the membrane.
In some applications, chitosan membranes also need to be cross-linked to improve their mechanical properties and stability. Common crosslinkers include glutaraldehyde, ferric chloride, etc., which can enhance the water resistance and mechanical strength of the membrane.
3. The working principle and composition of the laboratory film coating machine
A laboratory coater is mainly composed of several key parts: the coating head, the substrate support platform, the drive and the control system.
3.1 Coating head
The coating head is one of the core components of the coating machine, and its function is to evenly coat the coating solution on the surface of the substrate. The design and operation of the coating head directly affect the uniformity and thickness of the film. Common applicator heads include squeegee applicators and groove applicators.
3.2 Substrate support platform
The substrate support platform is used to fix the substrate to be coated to ensure that the substrate moves stably during the coating process. The support platform can be flat or pulley, depending on the coating process and the requirements of the substrate.
3.3 Drives
The drive is responsible for controlling the relative movement of the coating head and the substrate. By precisely controlling the speed and direction of the coating head, the uniformity of the coating and the thickness of the film can be adjusted. The drive unit is usually controlled by an electric motor and combined with a sophisticated transmission system to achieve stable movement.
3.4 Control Systems
The control system is the "brain" of the coater, which adjusts individual operating parameters such as coating speed, pressure, substrate temperature, etc., through computer programs or manual settings. Modern film applicators are often equipped with a touchscreen control interface that allows the operator to monitor and adjust process parameters in real time.
4. Key technical parameters and optimization of laboratory film coating machine
4.1 Coating speed
Coating speed is an important factor affecting film thickness and film uniformity. Higher coating speeds often result in uneven film thicknesses, while lower coating speeds can lead to excessive solution build-up, resulting in inconsistent film thicknesses. Therefore, when using a laboratory coater, it is necessary to set the coating speed reasonably according to the concentration and viscosity of the chitosan solution and the expected thickness of the film.
4.2 Coating pressure
The amount of coating pressure directly affects the quality of the coating layer. Too high a pressure may cause the solution to be overcoated and affect the uniformity of the film; Pressures that are too low may result in under-coating. Therefore, the coating pressure needs to be adjusted according to the thickness requirements of the film and the viscosity of the solution.
4.3 Surface properties of the substrate
The surface finish, surface energy and wettability of the substrate all have an impact on the effect of the coating film. For substrates with strong hydrophilicity, chitosan membranes are easier to adhere; For substrates with strong hydrophobicity, surface treatment or the use of surfactants are required to improve the coating effect.
4.4 Drying conditions
The drying speed and temperature have a significant effect on the morphology and properties of chitosan membranes. Higher drying temperatures can accelerate solvent evaporation, but can also lead to cracks and warpage of the membrane. During the drying process, it is necessary to maintain a constant humidity and temperature to avoid local drying too quickly.
4.5 Environmental factors
Ambient temperature and humidity can also affect the quality of the membrane. Higher humidity may lead to the formation of water droplets on the surface of the membrane, which can affect the uniformity of the membrane. The laboratory environment should maintain an appropriate temperature and humidity to ensure the quality of membrane preparation.
5. Performance test of chitosan membrane
After the coating is completed, it is necessary to test the performance of the chitosan membrane. Common membrane performance tests include:
Film thickness – Measure the average thickness of the film using a tool such as a micrometer or laser scanner.
Breathability——The gas barrier performance of the membrane was tested by gas transmission rate test.
Water vapor transmission rate——To test the water vapor permeability of the membrane, especially in food packaging.
Mechanical properties——The tensile strength, elongation at break, etc. of the membrane are measured by tensile test.
Antimicrobial properties——The antimicrobial effect of the membrane was tested by methods such as colony counting.
6. Conclusion
Laboratory coaters play a crucial role in the preparation of chitosan membranes, and high-quality chitosan films can be obtained by precisely manipulating process parameters such as coating speed, coating pressure, surface treatment of the substrate, and drying conditions. Optimizing every step of the coating process not only improves the performance of the membrane, but also provides technical support for the expansion of chitosan membranes in practical applications. In the future, with the continuous progress of coating technology and equipment, the application of chitosan film in biomedicine, food packaging and other fields will become more and more extensive.
