What are the factors that affect the swelling performance of hydroxypropyl methylcellulose HPMC hydrogel?

What are the factors that affect the swelling performance of hydroxypropyl methylcellulose HPMC hydrogel?

Generally speaking, a hydrogel mainly refers to a hydrophilic polymer gel that can swell significantly in water but does not dissolve in water. It can be said to override the interpenetrating network between solids and liquids, or override Three-dimensional network between liquid and solid. The full name of HPMC hydrogel is hydroxypropyl methylcellulose hydrogel. When studying its swelling properties, the weighing method is usually used to study specific influencing factors.

1. Introduction to material preparation and research methods

First, it is necessary to accurately weigh a certain mass of hydroxypropyl methylcellulose HPMC sample on the balance equipment, and then place it in a certain amount of deionized water with a certain amount of heat, and implement stirring measures, with a slight movement When the temperature is cooled to room temperature, a homogeneous solution with a concentration of 0.1g/ml is obtained. In addition, the temperature of the resulting solution needs to be heated to about 60 degrees Celsius, and a certain amount of gel mass is obtained from the gradually turbid solution. The next thing to do is to take out the gel mass material and cut it into shapes. And gel particles of the same size, and then these gel particles are placed in a vacuum oven and dried at about 30 degrees Celsius to become a dry gel.

table Weight average molecular mass and substituent content of HPMC sample of hydroxypropyl methylcellulose

According to the above table, carry out accurate weighing of various dry gel samples of the same quality, and use traditional weighing methods to effectively study the actual swelling kinetics of cellulose ether. By reasonably changing the swelling temperature of the gel, the temperature values ​​are 50°C, 55°C, 60°C, 65°C, 70°C, and finally obtain the gel swelling kinetic curve at different temperatures.

The relationship between equilibrium swelling degree of HPMC hydrogel and temperature

Set the specific swelling temperature at 30 degrees Celsius, swell an equal amount of dry gel samples in dimethyl sulfoxide, pure ethanol solvent, and deionized water, and record the gel quality values ​​at different times , And effectively calculate its specific swelling degree SR.

Set the specific swelling temperature at 30 degrees Celsius, swell dry gels of equal mass in solutions with different pH values ​​(1 and 13), and record the gel quality in each time period. , Implement reasonable calculations for the gel swelling degree in different pH solutions.

2. Factors affecting the swelling properties of HPMC hydrogel

2.1 Temperature

For gel materials, ESR or equilibrium swelling degree is an important parameter, and the specific swelling temperature has a relatively important effect on this parameter. According to experiments, it is not difficult to find that with the continuous increase in temperature, the overall swelling performance of HPMC hydrogel tends to decrease. This is mainly because cellulose ether gel has a different formation mechanism from other general polymer gels. When it is formed, it takes the hydrogen bond of water molecules to release the macromolecules that have been dissolved in the water, and then under the hydrophobic interaction between the macromolecules, they can combine to produce macromolecular aggregates. The aggregates can form the corresponding three-dimensional gel network. At low temperatures, hydrogen bonding is easy to occur, causing water molecules to easily enter the formed gel network. From a macro perspective, the specific performance is that the gel has better swelling ability. As well as water absorption capacity; but at high temperatures, hydrogen bonding is very difficult to be unstable, but it is difficult for water molecules to enter through hydrogen bonding, and the hydrophobicity between macromolecules becomes stronger, making the gel network more compact, from a macroscopic perspective From a point of view, the swelling ability of the gel is relatively weak.

2.2 Types of solvents

The swelling and shrinkage of the hydrogel can be reflected by the interaction between the hydrophilic and hydrophobic groups in the gel and the solvent. If the hydrophilic group in the gel can generate hydrogen bonds with the solvent, the solvent can easily penetrate into the gel, indicating that in this type of solvent, the gel has a stronger swelling ability; if the solvent molecules follow the gel If the hydrophilic group of the gel fails to form a hydrogen bond, or the hydrogen bond formed is relatively poor, the swelling ability of the gel in the solvent is very small. The swelling degree of the gel in dimethyl sulfoxide, deionized water, and pure ethanol solvent shows a decreasing trend, so its swelling degree in dimethyl sulfoxide solvent> deionized water> pure ethanol is mainly because Dimethyl sulfoxide is a strong polar solvent. Compared with pure water, its polarity is very large, and it can easily form hydrogen bonds with the hydrophilic groups in the gel, such as the molecular chain of cellulose ether. Hydroxypropyl and other hydrophilic groups, allowing solvent molecules to quickly penetrate into the gel network. Therefore, the gel swelling is relatively strong in this type of solvent; in addition, because the polarity of ethanol solvent is very weak Compared with pure water, its ability to form hydrogen bonds with the hydrophilic groups in the gel is worse. It can be seen that the swelling ability of the gel in ethanol solvent is even worse than that in water.

2.3 PH value

In the field of sustained drug release, HPMC hydrogels are often used in the human body. Therefore, it is necessary to carry out research on the swelling properties of gels under different pH values. Most polymer hydrogels have relatively strong responsive behavior with pH values, but the hydrogels prepared by HPC radiation cross-linking do not respond significantly to pH values. The main reason for this phenomenon may be that there are no suspicious pH-sensitive related groups on the HPMC hydrogel molecules. Therefore, the hydrogen bond formed between the macromolecules and the water molecules has not been significantly affected.

2.4 degree of substitution

For the swelling properties of hydroxypropyl methylcellulose HPMC, the degree of substitution has a comprehensive and significant specific impact on it. According to experiments, it can be known that whether it is a low-molecular-weight sample or a high-molecular-weight sample, the equilibrium swelling degree of the HF series hydrogel is relatively small compared with the HK series, indicating that the content of the substituted groups determines this The actual performance of the two series of hydrogels. Because the hydroxypropyl content of HK is greater than that of HF, its hydrogen bonding effect is stronger, and water molecules can enter the gel network more quickly, so its initial swelling degree is relatively large. The content of methoxy group is smaller than that of HF, so the hydrophobic interaction between the macromolecules is relatively weak, which leads to its water absorption greater than that of HF series.

3. Summary

In summary, we conclude that the influencing factors of hydroxypropyl methylcellulose HPMC hydrogel include temperature, solvent type, pH value and degree of substitution, etc. In general, HPMC hydrogels will correspondingly reduce the equilibrium swelling degree as the temperature rises; moreover, the change of the type of solvent also has a significant impact on the actual swelling performance of HPMC hydrogels, and the hydrogen bonding effect will As the polarity of the solvent becomes stronger and stronger, the swelling degree of the gel will also be greatly increased. On the contrary, in a solvent with relatively weak polarity, the hydrogen bond effect is not very obvious, which will make the gel The swelling performance is significantly reduced; in general, if the pH value changes, it will not have a significant impact on the swelling performance of the HPMC hydrogel, but if it is in an alkaline environment, the swelling degree of the gel will also decrease Phenomenon: For the swelling behavior of HPMC hydrogel, the degree of substitution has a very significant effect on it. Due to the high hydroxypropyl content and low methoxy content of the HK series gel, its water-absorbing swelling performance is significantly higher than HF series gel.

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