Hydroxypropyl Methylcellulose (HPMC) is a multifunctional chemical substance commonly used in pharmaceuticals, food, cosmetics and construction materials. Its shelf life refers to the length of time it can maintain its physical, chemical and functional properties under specific conditions. Factors that affect the shelf life of HPMC include environmental conditions, storage conditions, chemical stability, etc.

1. Environmental conditions
1.1 Temperature
Temperature is one of the important factors affecting the shelf life of HPMC. High temperature will accelerate the degradation reaction of HPMC, resulting in changes in its physical and chemical properties. For example, HPMC may turn yellow and reduce its viscosity at high temperatures, affecting its effectiveness. Therefore, the ambient temperature in which HPMC is stored should be kept at low temperatures, generally below 25°C, to extend its shelf life.

1.2 Humidity
The effect of humidity on HPMC is equally significant. HPMC is a hydrophilic polymer material that easily absorbs moisture. If the humidity in the storage environment is too high, HPMC will absorb moisture in the air, causing its viscosity to change, its solubility to decrease, and even condensation to occur. Therefore, HPMC should be kept dry when stored, and it is recommended that the relative humidity be controlled below 30%.

2. Storage conditions
2.1 Packaging
Packaging materials and sealing have a direct impact on the shelf life of HPMC. High-quality packaging materials can isolate air and moisture and prevent HPMC from getting wet and deteriorating. Commonly used packaging materials include aluminum foil bags, polyethylene bags, etc., which have good barrier properties. At the same time, well-sealed packaging can reduce the contact of HPMC with the external environment and extend its shelf life.

2.2 Lighting
Light, especially ultraviolet irradiation, can cause photooxidative degradation of HPMC and affect its physical and chemical properties. When exposed to light for a long time, HPMC may undergo color changes, molecular chain breakage, etc. Therefore, HPMC should be stored in a light-proof environment or use opaque packaging materials.

3. Chemical stability
3.1 pH value
The stability of HPMC is significantly affected by pH value. Under acidic or alkaline conditions, HPMC will undergo hydrolysis or degradation reactions, leading to problems such as a decrease in viscosity and a change in solubility. In order to ensure the stability of HPMC, it is recommended that the pH value of its solution be controlled within the neutral range (pH 6-8).

3.2 Impurities
The presence of impurities affects the chemical stability of HPMC. For example, impurities such as metal ions may catalyze the degradation reaction of HPMC, shortening its shelf life. Therefore, the impurity content should be strictly controlled during the production process and high-purity raw materials should be used to ensure the purity of HPMC.

4. Product form
The product form of HPMC also affects its shelf life. HPMC usually exists in the form of powder or granules. The impact of different forms on its shelf life is as follows:

4.1 Powder form
HPMC powder form has a large specific surface area and is easily hygroscopic and contaminated, so its shelf life is relatively short. To extend the shelf life of powdered HPMC, sealed packaging should be reinforced to avoid contact with air and moisture.

4.2 Particle morphology
HPMC particles have a smaller specific surface area, are relatively less hygroscopic, and have a longer shelf life. However, granulated HPMC may generate dust during storage and transportation, resulting in a shortened shelf life. Therefore, granular HPMC also requires good packaging and storage conditions.

5. Use additives
In order to improve the stability and extend the shelf life of HPMC, some stabilizers or preservatives can be added during the production process. For example, adding antioxidants can prevent oxidative degradation of HPMC, and adding moisture-proofing agents can reduce the hygroscopicity of HPMC. However, the selection and dosage of additives need to be rigorously experimentally verified to ensure that they do not affect the functional properties and safety of HPMC.

The shelf life of HPMC is affected by many factors, including environmental conditions (temperature, humidity), storage conditions (packaging, light), chemical stability (pH value, impurities), product form (powder, granules) and use of additives. In order to extend the shelf life of HPMC, these factors should be considered comprehensively and appropriate measures should be taken for control. For example, maintain a low-temperature and dry storage environment, use high-quality sealed packaging, control solution pH, reduce impurity content, etc. Through scientific and reasonable management and storage, the shelf life of HPMC can be effectively extended and its effectiveness in various fields can be guaranteed.