Melt-reprocessing of mixed polyurethane thermosets†
The melt-reprocessing of thermosets such as polyurethanes (PUs) and epoxy network materials has been a constant technical challenge. Here we report, for the first time, melt-reprocessing of mixed PUs made of aliphatic and aromatic feedstocks. Our methodology consists of using Zn(II) catalysts combined with a slight excess of diols. The use of diols was sufficient to partially reverse the gel-point and reclaim the melt-processability as demonstrated for aliphatic, aromatic, and mixed PUs. Zinc acetate was not effective in imparting melt-processability to PU samples. Furthermore, the mixed PU samples were successfully melt-processed in an extruder on a large scale. This work holds the promise to facilitate the recycling of post-consumer mixed PUs with immense benefits for science, the economy, and the environment. This work has the capability to divert multi-million tons/year of waste PUs into valuable feedstock for manufacturing, thus saving energy and chemicals that are used to generate virgin PUs. Consequently, this work fits the very first principle of green chemistry, which is the prevention of waste creation.