At what temperature does HPMC decompose?

Hydroxypropyl methylcellulose (HPMC), a nonionic cellulose ether, exhibits excellent thermal stability, and its decomposition behavior is closely related to temperature. Under normal operating conditions, HPMC maintains a stable structure, but it undergoes gradual thermal decomposition at elevated temperatures.

The decomposition process of HPMC can be divided into several stages:

Below 180°C, primarily physical changes occur, such as water evaporation and material expansion, without chemical bond breakage.

The initial decomposition temperature is approximately 190–200°C, at which point ether bonds begin to break, releasing low-molecular-weight volatiles.

In the 220–250°C range, decomposition intensifies, potentially producing products such as water, methanol, and formaldehyde.

When temperatures exceed 280°C, HPMC rapidly carbonizes, leaving a primarily carbonaceous solid residue.

The thermal decomposition mechanism primarily involves ether bond breakage, hydroxyl group dehydration, and subsequent oxidation or carbonization. Decomposition behavior is influenced by factors such as degree of substitution, molecular weight, system purity, and atmospheric conditions.

In practical applications, such as in the building materials, pharmaceutical, food, and cosmetics industries, HPMC is typically kept at temperatures well below its initial decomposition temperature (generally <100°C), thus maintaining thermal stability that meets most process requirements. However, when processing at high temperatures or storing them for extended periods, careful temperature control is still necessary to prevent degradation of material properties.

In summary, HPMC begins to decompose at around 190°C and rapidly carbonizes above 280°C. Properly controlling operating and storage temperatures is crucial to ensuring its functional stability.