Variation in adhesion properties and film morphologies of waterborne pressure-sensitive adhesives containing an acid-rich diblock copolymer additive

摘要

One challenge for waterborne pressure-sensitive adhesives (PSA)s is the typical tradeoff between cohesion and adhesion. Others have shown that waterborne PSA films with thin, hard boundaries formed from short poly(acid) segments surrounding soft particles can have simultaneous improvements in adhesion and cohesion. To study this approach in commercial-type acrylic waterborne PSAs, a diblock copolymer (BCP) composed of poly(acrylic acid)-block-(n-butyl acrylate) (PAA-b-PBA) is added at 1-5 wt to PSAs composed of 100 PBA (PSA (0 acid)) or 99 BA/1 AA (PSA (1 acid)). Films of these blends prepared using industrially relevant conditions reveal complex nanodomains in atomic force microscopy (AFM) images. PSA performance tests showed that 1-2 wt BCP additive nearly tripled adhesion to stainless steel for PSA (0 acid) while improving cohesion. Nonetheless, AFM images of PSA (0 acid) with 1-2 wt BCP display ill-defined morphologies, with clear percolated structures apparent primarily in films with 5 BCP. This indicates that film morphologies which enhance adhesion may not correlate with AFM features. Moreover, the balance of adhesion and cohesion of PSA (1 acid) without BCP exceeds that of any of the BCP blends, demonstrating the challenge of using designed microstructures to improve upon conventional PSAs containing copolymerized acids.