A number balance approach for estimation of microcapsules surface affinity for fabrics: Implications towards sustainable use of microcapsules in consumer care and specialty chemicals

This study proposes a novel number balance approach for evaluating the affinity of microcapsules for a target substrate (e.g., cotton and polyester fabric). Using single particle optical sizing (SPOS) technique, the affinity of polyurea and silica microcapsules was studied by quantifying the capsules present in the dispersions before and after exposure to the fabric. Silica and polyurea microcapsules with encapsulated silicone oil were successfully synthesized and used as model capsules for affinity studies. Accuracy and reproducibility of the data generated from the SPOS were evaluated by relative standard deviation. Results of the affinity experiments revealed that, under the test conditions, not more than one-third of the capsules was deposited on the fabrics with silica capsules showing the highest affinity of 34.4% towards the polyester fabric. The observed affinity trends were explained by surface charge and the structural pattern of the fabrics, with capsules having a greater affinity for oppositely charged fabrics. We also found that the polyester fabric, which inherently contains bigger pores and higher exposed surface area, deposited more capsules than the cotton fabric. We demonstrated that while the microscopic techniques, such as scanning electron microscopy, can only confirm the deposition of capsules on the fabrics, alternative techniques such as SPOS provides an accurate measure of number of capsules, thereby determining the surface affinity of the capsules for the fabric.