How to control residual carbomer solvent?

1.Carbopol solvent residue: a common quality challenge in the pharmaceutical and daily chemical industries

Carbomer (polyacrylic acid resin) is an indispensable rheological modifier in the fields of medicine, personal care, and industry, with three core functions of thickening, suspension, and emulsification. However, due to the introduction of various organic solvents such as benzene, ethyl acetate, and cyclohexane in its preparation process, residual carbomer solvents have always been a key quality problem that troubles the industry.

According to the 2025 edition of the Chinese Pharmacopoeia, the key limits for residual solvents in carbomer are: benzene should not exceed ≤ 2ppm, ethyl acetate should not exceed 0.5%, and cyclohexane should not exceed 0.3%. For Carbopol products applied in the fields of pharmaceutical excipients, high-end cosmetics, and medical devices, solvent residue control is directly related to product compliance and user safety.

How to control residual solvents in Carbopol? This is a question that every Carbopol production technician is thinking about. Hubei Xindesheng Material Technology Co., Ltd., in collaboration with the Quality Department, has launched a special technical research and development project to address common challenges in this industry.

2.Technical Root Analysis of Carbopol Solvent Residue

To fundamentally solve the problem of residual solvents in Carbopol, the New Desheng Technology Department and Quality Department have established a special research and development team to conduct a systematic investigation of the existing Carbopol production process.

After multiple rounds of analysis and verification, the research team has identified the key factors affecting the residual Carbopol solvent, which mainly focus on the following aspects:

(1) Selection of solvent system for polymerization stage

Traditional carbomers (such as carbomer 940, carbomer 934, etc.) use benzene as the polymerization solvent, which poses a high risk of residual solvents. How to optimize the solvent system while ensuring polymerization efficiency is a key research topic.

(2) The efficiency issue of washing process

After polymerization, the crude carbomer still contains a large amount of unreacted solvents, initiators, polymerization inhibitors, and other residues. The traditional washing process has the problem of insufficient efficiency in removing these impurities.

(3) Insufficient refinement of drying process

Improper control of drying temperature and time may result in incomplete solvent evaporation or thermal discoloration of the product. Research has shown that when the drying temperature exceeds 120 ℃, the product will exhibit varying degrees of light yellow color.

3.Optimization of Carbopol Production Process: Stage Results

After a long period of research and development, the special team has made breakthroughs in optimizing the production process of Carbopol:

(1) Optimization and upgrade of Carbopol washing process

The research team has systematically optimized the washing process of crude carbomer. Research has shown that washing newly prepared carbomer with ethanol aqueous solutions of different mass fractions can effectively remove residual initiators, inhibitors, and other impurities. The team further optimized parameters such as washing temperature, washing frequency, and solvent ratio, resulting in a significant increase in impurity removal rate.

(2) Fine control of Carbopol drying process

The research team has established the core process route of low-temperature vacuum drying, strictly controlling the drying temperature at a certain temperature. At the same time, a temperature time vacuum linkage control model was established to achieve precision and standardization of the carbomer drying process.

(3) Establish a process control system for residual solvents in Carbopol

The quality department has set up sampling and testing points for residual solvents in key processes such as aggregation, washing, and drying, achieving a transition from "terminal inspection" to "process control".

(4) Improvement of Carbopol Solvent Residue Index

After process optimization, the solvent residue of the company's carbomer was significantly reduced. The key residual solvent indicators such as ethyl acetate and cyclohexane have been stably controlled within the limits, and some indicators are better than the internal control standards.

By optimizing the carbomer washing process, refining the drying process, and establishing a process control system, New Desheng has made substantial breakthroughs in controlling residual solvents in carbomer.

The next article will focus on the synchronous upgrade of detection capabilities - providing a detailed introduction to the company's new gas chromatography (GC) equipment configuration, optimization of carbomer residual solvent detection methods, and improvement of quality control systems.