Mechanical action in CO₂ dry cleaning

High-pressure carbon dioxide (CO₂) is a potential alternative for perchloroethylene (PER), a common but harmful textile dry cleaning solvent. Previous studies have indicated that the particulate soil removal with CO₂ is lower compared to that with PER, because of the low amount of mechanical action in CO₂. It is the objective of this study to get more insight in the influence of various types of mechanical action on the cleaning results in CO₂ dry cleaning. In the experiments, various mechanisms of mechanical action, such as rotating drum, CO₂ spray, and ultrasound were investigated. Several types of textiles stained with different kinds of particulate soils were cleaned using 25 L and 90 L CO₂ dry cleaning set-ups. The washing results show that liquid CO₂ spray may be a suitable additional mechanism to provide textile movement. The average CPI of CO₂ over all soils using the best combination of commercial machine and process was still 25% lower than the results with PER and 18% lower than the results with water, but 11% higher than K4 solvent while the average redeposition level was significantly lower, showing that CO₂ has a good prospect as an alternative solvent to replace PER. An endoscopic camera has been installed in the 25 L set-up to get an insight in the textile movement inside the rotating drum. The results show that no plug formation occurs and the textile movement in CO₂ is sluggish, which means that the mechanical movement of textile in CO₂ dry cleaning does not follow the simplified tumbling-movement model which was developed in a previous study, and the mechanical action is much less than predicted.