Study on Properties of Shellac Resin-Hydroxypropyl Methyl Cellulose Composite Film

Abstract: In order to improve the physical and chemical properties of shellac resin after film formation, a composite film was prepared by physical blending of hydroxypropyl methylcellulose (HPMC) and shellac resin, with ω (HPMC) as 0%, 10%, and 20%, 30%, 40%, and 50% are blended, and the characteristics of the composite film are measured and analyzed. The results show that shellac resin and HPMC can be blended into films by physical blending in water, and the addition of HPMC can improve the compactness of shellac resin films; when ω (HPMC) is 40%, the glass transition temperature of the composite film The lowest, the melting temperature and the required heat are the highest, that is, when used as a heat-resistant material, the anti-melt rheology under this ratio is the best; when ω (HPMC) is 40%, the hydrophilicity of the composite film is the best; The water solubility and hygroscopicity of the film both increased with the increase of HPMC content.

Key words: shellac resin; hydroxypropyl methylcellulose; composite film; blending; properties

Hydroxypropylmethylcellulose (HPMC) has become a commonly used excipient in the pharmaceutical industry because of its good film-forming properties, flexibility, transparency, water vapor barrier properties and biodegradability, and is usually used as a coating material. , that is, HPMC is used as a dense coat on the tablet to protect the drug from light, water vapor, deformation and other factors, and can also cover the smell of the tablet itself. In addition, when HPMC is used as a coating, its toughness and stomach It is superior to sugar-coated tablets in fluidity and enteric properties, and can achieve slow and localized release of drugs. It has been used for more than 30 years. In recent years, sustained-release tablets have been prepared by using its hydrophilic gel matrix, and oral adhesive tablets have been prepared together with other pharmaceutical excipients such as carbomer.

Shellac is a natural non-toxic, degradable and special performance natural resin mixture secreted by lac insects after absorbing plant juice. Its application in the pharmaceutical field has a long history. The earliest application of lac in my country can be traced back to By 69 A.D., the names of Lac at that time included Purple Stem, Buttercup, Purple Mine, Zicao Velvet, and Worm.

Jiao, purple Jiao, ant paint, etc. However, the mechanical properties of shellac resin itself are poor, and aging reactions such as polymerization are prone to occur during long-term storage. Due to its poor hydrophilic properties, it is necessary to use another substance to improve its thermal stability and mechanical properties, while focusing on improving its hydrophilic properties, so that it can be better used in the medical field.

Therefore, the hydrophilic property and film-forming flexibility of HPMC just make it a candidate blending material for improving shellac resin film. Based on this, this study prepared a composite film by mixing shellac resin with HPMC to explore the feasibility of physical blending of the two, and further explored the hydrophilicity and thermal stability of shellac resin and HPMC composite films in different proportions. characteristics, in order to provide a reference for the combined application of the two.

1. Materials and Instruments

1.1 Test material

Alkaline-extracted shellac resin, self-made in the laboratory; low-viscosity hydroxypropyl methylcellulose, KIMA CHEMICAL CO., LTD; ethanol (95%), Guangdong Huaguang Technology Co., Ltd; anhydrous sodium carbonate, Tianjin Fengchuan Chemical reagent factory; deionized water, self-made in the laboratory.

1.2 Test equipment

DSX-90 digital display mixer, Hangzhou Instrument Motor Co., Ltd.; T25 digital dispersing machine, German IKA company; SHZ-D (Ⅲ) circulating water vacuum pump, Gongyi Yuhua Instrument Co., Ltd.; BT-1J peristaltic Pump driver, Baoding Lange Constant Flow Pump Co., Ltd.; DF-101S collector type constant temperature heating magnetic stirrer, Henan Yuhua Instrument Co., Ltd.; AB204-S precision electronic balance, Mettler-Toledo (China) Co., Ltd. Company; TENSOR27 infrared spectrometer, Bruker, Germany; TM3000 desktop high-resolution scanning electron microscope, Hitachi, Japan; HR83-P rapid halogen moisture analyzer, Mettler-Toledo, Switzerland; TG 209FC thermogravimetric analysis Meter, Netzsch Company, Germany; SL200B Dynamic/Static Contact Angle Meter, Kono Industries Co., Ltd., USA; Airflow Dryer for Glass Instruments, Wuhan Keer Instrument Equipment Co., Ltd.

2. Test method

2.1 Preparation process of shellac resin and HPMC composite film

After dissolving shellac resin in absolute ethanol, filter to remove alcohol-insoluble matter, and slowly add the filtrate to high-speed sheared deionized water through a peristaltic pump to prepare shellac resin emulsion for later use; add HPMC in a certain proportion Dissolve in deionized water at 60°C, then cool to room temperature, and set aside; Mix the shellac resin emulsion prepared above with HPMC aqueous solution in a water bath at 49°C and stir for 2 h, then transfer to room temperature and continue stirring for 24 h, use A blower was used to remove air bubbles on the surface of the mixed solution, and finally the liquid was poured into a petri dish, and dried in an electric thermostat incubator at 30 °C for 24 h. After the solvent ethanol and water of the mixed solution were fully volatilized, the mixed solution was dried to form a composite of shellac resin and HPMC. After the film is removed, it is ready to be tested. In the above preparation process, the mass fraction of HPMC in the composite membrane was controlled at 0%, 10%, 20%, 30%, 40%, and 50%, respectively.

During the preparation process, because the shellac resin emulsion will be affected by temperature and other effects, some flocculent shellac resin will be precipitated, and the precipitated resin will account for about 0.5% to 1.0% of the input amount after drying and weighing. In order to eliminate this error, the corresponding input amount of shellac resin was increased at the initial stage of preparation of ethanol solution of shellac resin.

2.2 Performance evaluation of shellac resin and HPMC composite film

2.2.1 Surface morphology observation of the composite film

Use a digital camera to record its appearance and observe the composite film; then it is sprayed with gold, and then magnified 2000 times under a scanning electron microscope for detection, observation and imaging to compare and observe its surface regularity.

2.2.2 Thermal stability analysis of the composite film

1) Differential scanning calorimetry analysis. The differential scanning calorimetry (DSC) test was carried out on the samples. The test conditions were as follows: the temperature was lowered from room temperature to -50 °C, the cooling rate was 10 °C/min, the temperature was kept at a constant temperature for 5 min, and then the temperature was raised to 150 °C at a heating rate of 5 °C/min. ℃, constant temperature for 10min to ensure that the sample absorbs heat sufficiently and the baseline is stable. The heating process is carried out under the atmosphere of sweeping gas and protective gas (both are high-purity N2, of which the sweeping gas is 20 mL/min, and the protective gas is 50 mL/min), and the cooling medium is liquid nitrogen.

2) Thermogravimetric analysis. The thermal stability of the samples was analyzed using a thermogravimetric analyzer (TG). The sample was raised to 100 °C at a heating rate of 20 °C/min at 25 °C and kept for 10 min, and the moisture content of the composite film was compared by comparing the remaining mass of the composite film at different HPMC contents; After the heating rate was increased to 500 °C, the measurement was completed. By comparing the remaining mass of composite membranes containing different masses of HPMC at different temperatures (200, 300, 400, and 500 °C), combined with the corresponding temperature when the mass loss was 5%, The effect of HPMC content on the thermal stability of the composite membrane was analyzed. The mass of the sample used for the measurement is (6.0 ± 0.5) mg.

2.2.3 Measurement of static drop contact angle of composite film

The composite films with different HPMC contents were placed on the glass slide of contact angle meter, and the static drop contact angle of each film with deionized water was measured.

2.2.4 Determination of acid value of composite membrane

The determination procedure of the acid value is carried out according to the method of "Determination of acid value" in GB/T 8143-2008 "Testing methods for shellac products".

2.2.5 Structural analysis of the composite membrane

In order to study whether shellac resin and hydroxypropyl methylcellulose form hydrogen bonds in the process of mixing and forming a film, and whether a chemical reaction occurs to generate new groups, the sample needs to be mixed with KBr powder for tableting. A spectrometer detects its molecular structure.

2.2.6 Determination of water solubility of composite membrane

Cut the composite film into a square of 2.0 cm × 2.0 cm and accurately weigh its dry mass (expressed as W0), then put it into a beaker filled with 100 mL of deionized water, at 25 °C, at 180 rpm The stirring speed was 1 min to make it dissolve for 24 h, and the undissolved fragments were filtered and dried in an oven at 70 °C to a constant mass (expressed as W1), and the percentage of dissolved amount (water solubility) of the composite film was calculated. All samples were measured 3 times and the average value was taken.

2.2.7 Obtaining the moisture absorption isotherm of the composite film

The composite film sample was placed in a constant temperature, controlled humidity environment until it reached equilibrium. Then the film samples were dried in an oven at 70 °C for 3 h until the dry mass was constant (M0). (Oven) Dried samples were placed in desiccators filled with different saturated solutions. First put it into a desiccator containing lithium chloride, its relative humidity is 11.3%, aw=0.113, and it is placed at 25°C for 5-10 days until a constant mass (M1) is obtained. Then the sample was removed from the lithium chloride desiccator and put into magnesium chloride (relative humidity 32.8%, aw=0.328), sodium dichromate (relative humidity 54.4%, aw=0.544), sodium chloride (relative humidity 75.3%, aw=0.753), potassium chloride (relative humidity is 84.3%, aw=0.843), potassium nitrate (relative humidity is 93.7%, aw=0.937) saturated solution and distilled water (relative humidity 100.0%, aw = 1.00), after the mass is constant, record the constant mass under each relative humidity condition, and calculate the water content. Three measurements were performed under each relative humidity condition, and the average value was taken.

3. Results and Analysis

3.1 Surface morphology of the composite membrane

3.1.1 Appearance of the composite film

It can be seen from the appearance of the composite film that with the increase of HPMC content, the color of the composite film gradually becomes lighter, which is due to the colorless transparency of HPMC film formation.

3.1.2 SEM image of the composite film

From the imaging image of the composite film magnified 2000 times, it can be seen that with the increase of HPMC content, the compactness of the composite film increases; when ω (HPMC) is 0%, the shellac resin film gap is larger, indicating that HPMC and shellac The resin has better compatibility when forming a film.

3.2 Thermal stability of the composite film

3.2.1 DSC analysis

From the DSC curves of the composite films with different contents of HPMC, it can be seen that the endothermic peaks of the composite films added with HPMC are sharper, while the endothermic peaks of the shellac resin film without HPMC (ω (HPMC) is 100%) are wider and less severe. The addition of HPMC shortens the melting range of shellac resin. According to the characteristic temperature data of the endothermic peak in each DSC curve, when ω(HPMC) is 40%, its peak temperature is the highest, which is 66.3 ℃, and its melting The required enthalpy change is the largest, which is 53.95 J/g, indicating that the composite film has the best melting resistance under this condition.

It can be seen from the comparison of Tg of composite membranes with different contents of HPMC that when ω (HPMC) is 40%, its Tg value is the smallest, indicating that the energy required for the segments of composite membranes at this content to start moving is the lowest, and does not differ from that of The above-mentioned conclusion that the enthalpy change required for melting under the condition of this ratio is the largest is contradictory, because the mechanisms of melting and glass transition are not the same, the former is the overall movement of molecular chains, while the latter is the movement of chain segments. It shows that when ω(HPMC) is 40%, the heat required for the movement of each molecular chain segment in the composite film is the smallest, and the heat required for the movement of each macromolecular chain as a whole is the largest, that is, only a small amount of heat is needed to A certain segment in the molecular chain can start to move, but to make the whole large molecular chain start to move, it needs to provide a lot of heat.

3.2.2 TG analysis

From the characteristic temperature data of each curve, it can be seen that when ω (HPMC) is 0%, the remaining mass is the largest at 100 °C, indicating that the water content of the pure lac resin film is the smallest.

When the temperature is 200 ℃, the residual mass of pure lac resin film is the largest, indicating that when the temperature is ≤ 200 ℃, the thermal decomposition of lac resin is the least; when the temperature is > 200 ℃, ω (HPMC) is 50% composite The film showed a strong anti-pyrolysis ability, and its mass residual was the largest at 300 °C and 500 °C, which were 91.88% and 21.44%, respectively, and its pyrolysis temperature was the highest at this ratio, which was 274.4 ℃, therefore, when the materials made with this ratio encounter an open flame, if the fire is extinguished in time, the loss rate of this type of material is the smallest.

The composite membrane with ω (HPMC) of 40% has the smallest mass remaining (that is, the largest mass loss) at 100 °C, indicating that the water content (or low boiling point substance content) of the composite membrane is the highest under the condition of this blending ratio. Therefore, ω ( The composite membrane with HPMC) of 40% has the lowest heat required for segment transformation and the highest heat required for molecular chain movement, which is most likely related to the highest water content (or low boiling point substance content) under this ratio.

3.3 Contact angle of the composite film

From the test results of static drop contact angle of composite films with different proportions, it can be seen that when ω (HPMC) is 40%, the average contact angle of the composite film is the smallest, which is 17.96°. At this time, the compatibility of HPMC and shellac resin shows The hydrophilicity of the composite membrane is excellent, so its wettability is the best.

3.4 Acid value of the composite membrane

From the relationship between the HPMC content in the composite film and the acid value of the composite film, it can be known that the acid value of the composite film decreases with the increase of the HPMC content. , so the curve will show a decreasing trend; on the other hand, to a certain extent, it shows that the addition of HPMC does not cause a significant change in the number of carboxyl groups in shellac resin, that is, the probability of chemical reaction between the two is extremely low.

3.5 Infrared spectroscopy analysis of the composite film

From the infrared spectra of the composite films with different contents of HPMC, it can be seen that the composite films with all contents have broad absorption peaks at 3500-3000 cm-1, indicating that the addition of HPMC does not affect the composition of hydroxyl groups on the molecular chain of shellac resin. The associations that occur due to hydrogen bonds, including intramolecular and intermolecular associations, among which the intermolecular associations are mostly concentrated at 3 400 ~ 3 200 cm-1, and the peak shape of the association is relatively broad.

The composite film with ω (HPMC) of 40% has a strong absorption peak at 2 960 ~ 2 850 cm-1 in its infrared spectrum, indicating that the composite film with this ratio has a large amount of saturated hydrocarbons. The dispersion force may be generated due to the appearance of the instantaneous dipole, and the corresponding hydrogen bond will be relatively reduced, so the water drop contact angle of the composite film is the smallest when ω (HPMC) is 40% in the infrared spectrum of the composite film with different proportions, that is It has the strongest affinity for water; and in the TG curves of the composite membranes with different proportions, the Tg value of the composite membranes under this content is the lowest, because the number of hydrogen bonds in the composite membranes under this ratio is small, and due to the instantaneous dipole The resulting dispersion force is relatively strong, and the glass transition temperature produced by the dispersion force whose strength is much lower than that of the hydrogen bond is naturally the lowest. The composite film with ω (HPMC) of 40% has the next strongest absorption peak similar to that of pure lac resin film at 1716 cm-1, indicating that this ratio also better preserves the carbonyl group of lac resin.

At the same time, when ω (HPMC) is 40%, the composite membrane is at 1000

The stretching vibration peak near cm-1 indicates that there are ether bonds in the composite film, and the presence of ether bond can increase the hydrophilicity of the composite film, which is also shown in the infrared spectra of the composite films with different ratios. ω (HPMC) is 40% The water droplet contact angle of the composite film is the smallest.

The composite films with 6 different HPMC contents in the remaining wavenumber range did not show obvious different absorption peaks, so it can be further inferred that the addition of HPMC did not significantly change the chemical structure of shellac resin.

3.6 Water solubility and hygroscopic properties of the composite film

3.6.1 Water solubility of the composite film

From the relationship between the water solubility (dissolution rate in water) of the composite membrane and the HPMC content, it can be known that the water solubility of the composite membrane increases with the increase of the HPMC content. When ω (HPMC) is 50%, the dissolution rate of the composite film is the highest, which is 50.38%. This is because the physical blending process is mainly used in the composite film-forming process of shellac resin and HPMC, and a large part of the molecules are molecular The intermolecular force attracts each other. When the composite membrane is placed in the shearing water, the shear force of the water flow destroys the intermolecular force, and when ω (HPMC) is 50%, the degree of damage is the largest, resulting in Shellac resin molecules and HPMC molecules have been separated to a large extent, while shellac resin has poor water solubility, while HPMC has better water solubility, which finally makes the dissolution rate of the composite film reach the maximum.

3.6.2 Hygroscopic properties of the composite film

From the hygroscopic isotherms of the composite films with different proportions, it can be seen that the hygroscopicity of the pure shellac resin film is the worst, and its water absorption tends to decrease with the increase of humidity, while the composite films with ω(HPMC) between 10% and 50% are all in the The water absorption is the strongest when the humidity is 100%, which provides the possibility for the application of the composite film in the field of artificial skin materials.

4.Conclusion

In this study, shellac resin-HPMC composite membranes containing different qualities of HPMC were prepared by physical blending method, and the appearance, heat absorption capacity, thermal decomposition characteristics, hydrophilicity, acid value, structure, water solubility, Based on the preliminary analysis of hygroscopicity, the following conclusions can be drawn.

1) Shellac resin and HPMC can be blended and formed into films by physical blending method in water phase. The addition of HPMC improves the compactness of shellac resin film, and with the increase of HPMC content, the compactness of the composite film increases. The degree of chemical reaction between the two is relatively low, but the change of the distance between the molecular chains and segments of the two will affect the distribution and effect of the intermolecular force of the composite film. Shellac resin and HPMC have certain physical compatibility.

2) When ω (HPMC) is 40%, the glass transition temperature of the composite film is the lowest, and the melting temperature and heat required are the highest, that is, when used as a heat-resistant material, the anti-melt rheology under this ratio is the best; ω (HPMC) is 40%, the hydrophilicity of the composite membrane is the best;

3) The water solubility and hygroscopicity of the composite film both increased with the increase of the content of the hydrophilic substance HPMC, which further confirmed the greater degree of physical blending of the two composites; Stable (no chemical aging and other reactions occurred at 60 ℃). This study provides basic data for the application of shellac resin in materials that require certain water permeability and hydrophilicity (such as artificial skin, plastic film, etc.), but further research is still needed to determine more physical and chemical properties of the HPMC-shellac resin composite film. Performance, including degradation mechanism and weather resistance, etc.