Low-substituted hydroxypropyl cellulose (L-HPC) and hydroxypropyl cellulose (HPC) are cellulose derivatives widely used in pharmaceuticals, food and other industrial fields. Despite their similarities in chemical structures and applications, they have significant differences in degree of substitution, physical properties, solubility, and application areas.

1. Chemical structure and degree of substitution
Hydroxypropylcellulose (HPC) is a product obtained after partial etherification of cellulose, in which some of the hydroxyl groups are replaced with hydroxypropyl groups. The degree of substitution (usually expressed as the molar degree of substitution, that is, the average number of substituted hydroxypropyl groups per glucose unit) is an important factor affecting the performance of HPC. HPC has a higher degree of substitution, usually between 3.0 and 4.5, which means that most of the hydroxyl groups are replaced by hydroxypropyl groups.

Low-substituted hydroxypropylcellulose (L-HPC) is also prepared through a similar etherification reaction, but its degree of substitution is lower, usually between 0.1 and 0.2. Therefore, the hydroxyl groups of L-HPC are only substituted by a small amount of hydroxypropyl groups, and the number of unsubstituted hydroxyl groups is larger. This low degree of substitution makes L-HPC different from HPC in physical and chemical properties.

2. Solubility
Due to the difference in the degree of substitution, the solubility of HPC and L-HPC shows significant differences. HPC is water-soluble and can be dissolved in cold or hot water to form a clear viscous solution. It also has good solubility in polar organic solvents. This solubility makes HPC commonly used as a solubilizer, thickener or gelling agent in pharmaceuticals.

In contrast, L-HPC has different solubility properties due to its low degree of substitution. L-HPC is insoluble in water, but has good water-absorbing swelling ability in water and can form a gel. This property of L-HPC allows it to be used as a disintegrant or filler in tablets, helping the drug to rapidly disintegrate and release in water.

3. Physical properties
HPC usually exhibits higher viscosity and film-forming properties due to its higher degree of substitution and solubility. HPC solutions can form strong films after drying and are therefore commonly used in coatings, film forming and coating materials. In addition, HPC also has good thermal stability and oil resistance, making it suitable for applications requiring good physical strength and chemical stability.

L-HPC exhibits lower viscosity and higher water absorption due to its low degree of substitution. Its insolubility in water and good swelling properties give it unique advantages in tablet manufacturing. L-HPC can absorb water and swell, thereby promoting tablet disintegration and drug release. This disintegration property makes L-HPC widely used as a disintegrant in the pharmaceutical industry.

4. Application areas
HPC is widely used in pharmaceuticals, food, cosmetics and other industrial fields due to its good solubility, film-forming and thickening capabilities. In the pharmaceutical field, HPC is commonly used as a thickener, gelling agent, solubilizer, membrane material and drug carrier. In addition, HPC is also used in food as a thickener and emulsifier, and in cosmetics as a film-forming agent and moisturizer.

L-HPC is mainly used in the pharmaceutical industry, especially in the preparation of tablets. As an effective disintegrant, it can increase the disintegration speed of tablets and promote the release of drugs, thereby improving the bioavailability of drugs. In addition, L-HPC can also be used as a filler and diluent to improve the hardness and stability of tablets.

5. Application examples
In the pharmaceutical industry, HPC is often used in the preparation of controlled-release formulations. It can control the release rate of drugs by forming a viscous gel layer, thereby extending the action time of drugs. Typical applications include controlled release agents in extended-release tablets and capsules.

L-HPC is widely used in immediate-release tablets as a disintegrant. For example, in some rapid-release tablet formulations, the addition of L-HPC can significantly shorten the time for tablets to disintegrate in the body, thereby accelerating the onset of action of the drug.

6. Environmental impact and safety
Both HPC and L-HPC are derivatives derived from natural cellulose and therefore have good biodegradability and environmental friendliness. They are easily decomposed in the natural environment and have less impact on the ecological environment. Additionally, both are considered safe materials and are widely used in the manufacture of food and pharmaceuticals.

Although low-substituted hydroxypropyl cellulose (L-HPC) and hydroxypropyl cellulose (HPC) are both modified products of cellulose, due to differences in substitution degrees, they show differences in solubility, physical properties, and application fields. Significantly different. L-HPC is mainly used in the pharmaceutical field due to its excellent disintegration properties, while HPC is widely used in pharmaceutical, food, cosmetics and other fields due to its good solubility and film-forming properties. The difference between the two lies in the effect of the degree of substitution on the physical and chemical properties, thus determining their suitability for different applications.