Towards Compostable Pressure Sensitive Adhesives

Abstract

Polymers play a crucial role in modern society, yet their widespread use has led to environmental challenges, particularly due to their persistence and reliance on petroleum-based feedstocks. The transition toward sustainable polymer reaction engineering requires innovations in polymer synthesis, including water-based polymerization, bio-based monomers, and degradable structures that enable responsible end-of-life disposal. Among polymeric materials, pressure-sensitive adhesives (PSAs) are widely used in packaging, medical, and industrial applications, but conventional PSAs are synthesized via solution polymerization using petroleum-derived monomers, resulting in non-biodegradable materials that contribute to long-term waste accumulation. This study develops sustainable, compostable PSAs via emulsion polymerization, incorporating bio-based monomers and renewable nanomaterials to achieve a balance between adhesive performance and environmental degradability. A key innovation is the integration of 2-methylene-1,3-dioxepane (MDO) into butyl acrylate (BA)/vinyl acetate (VAc) terpolymers, introducing hydrolyzable ester bonds to enhance degradability. The reactivity ratios of MDO, BA, and VAc were estimated using the Error-in-Variables Model (EVM) to provide crucial insights into monomer distribution and polymer structure. A major challenge in emulsion polymerization was MDO’s hydrolysis sensitivity and ring retention, which was mitigated through optimized reaction conditions, including pH control (7.8–8.8) and reaction temperatures (40–50°C). These optimizations minimized ring retention, ensuring the effective incorporation of degradable linkages. To further enhance PSA performance, carboxylated cellulose nanocrystals (cCNCs) were incorporated via post-polymerization blending, reinforcing the polymer matrix and simultaneously improving tack, peel strength, and shear adhesion without compromising sustainability and biodegradability. The biodegradability of these formulations was evaluated under controlled composting conditions following ASTM D5338, using a lab-scale composting setup. Among the tested formulations, BMV10-NEW-cCNC (containing 10 wt% MDO and cCNC) exhibited the highest degradation rate. The elevated polymerization temperature (50°C) led to nearly complete MDO ring opening, as confirmed by 13C-NMR, with CO₂ evolution indicating 12.49 wt% biodegradation over 60 days. While these findings demonstrate the potential of MDO-based PSAs for compostable adhesive applications, further improvements in MDO content and polymerization strategies are needed to achieve complete degradation under industrial composting conditions. This study highlights the potential of integrating bio-based polymer chemistry, nanomaterials, and controlled water-based polymerization techniques to develop high-performance, compostable PSAs, advancing the field of sustainable polymer reaction engineering and contributing to a circular economy.