Bio-Microcapsules of Polybutylene Succinate (PBS) and Isocyanates: Towards Sustainable, Safer, and Efficient Adhesives

Abstract

This work describes the encapsulation of three different aliphatic isocyanates to reduce the risks associated with isocyanates’ direct handling. The use of bio-based polybutylene succinate (bio-PBS) increases the sustainability factor as it allows for the use of microcapsules (MCs) from renewable sources with biodegradable features. The three different MCs (MCs-Monomer, MCs-Trimer, and MCs-Polymer) are spherical, crack-free, and matrix-type, containing an isocyanate payload between 67 wt% and 70 wt%. Protection against environmental moisture was improved, resulting in losses of less than 10% for most cases after one month. The bio-PBS MCs were found to be suitable as crosslinking agents in high-performance adhesive formulations for the footwear industry. Adhesive joints with encapsulated isocyanate exhibited peel strength values ranging from 3.28 to 4.56 N/mm, well above the minimum requirements for the intended footwear application. Additionally, these joints demonstrated improved creep resistance compared to those using non-encapsulated isocyanates. In this context, the MCs-Trimer stood out, providing exceptional thermal robustness to the joints, as they showed no failure or opening at 90 °C, consistent with commercial adhesives. These results confirm that bio-PBS MCs can be excellent components for future adhesive formulations and that matrix-type MCs can also be utilised for this purpose.