Poly(ethylene terephthalate) (PET) and polyethylene (PE) are two of the most commonly used polymers in the packaging industry, and they make up a large portion of the recycling stream. Adhesion between these two immiscible polymers is poor without compatibilization. Maleic anhydride (MAH) grafted PE is a popular compatibilizer for PET/PE but is limited by the slow rate of reaction. In this study, we propose tin additives for improving adhesion and explore the mechanism of that improvement. We demonstrate that either dibutyltin oxide (DBTO) or di-n-octyltin oxide (DOTO) can dramatically enhance adhesion with only 60 s of contact time during lamination. A range of MAH and DOTO concentrations are examined, yielding adhesion up to 1300 J/m2. Possible reactions at the interface are investigated with small molecule model compounds, namely 1-hexadecanol, octylsuccinic anhydride (OSA), and ethylene glycol dibenzoate. DOTO does not improve the reaction rate in the hexadecanol-OSA system. This suggests that another reaction is responsible for the adhesion improvement. We provide evidence that tin oxides can open the ring of alkylsuccinic anhydrides and form complexes that can interesterify PET. This overall reaction appears to be third order with an activation energy of 100 kJ/mol. Extrapolating these kinetic results to 270 °C, the lamination temperature, we estimate that interfacial interesterification is very fast. Thus, adhesion development is limited by diffusion of the tin additives.
Bibliographical noteFunding Information:
This research was funded by a grant from Dow. We thank Dr. Barry Morris of Dow for helpful discussions.