Controlled sparse and percolating cross-linking in waterborne soft adhesives

Area of Science:

• Materials Science
• Polymer Chemistry
• Adhesion Science

Background:

• Investigating waterborne pressure-sensitive adhesives (PSAs) is crucial for developing sustainable and high-performance adhesive solutions.
• Controlling cross-linking in PSAs is key to balancing adhesive and mechanical properties, but traditional methods can be complex.
• Heterogeneous cross-linking strategies offer a novel approach to tailor PSA performance.

Purpose of the Study:

• To investigate the impact of low-level cross-linking on the adhesive and mechanical properties of waterborne PSAs.
• To explore a core-shell latex particle morphology for creating heterogeneous cross-link structures.
• To understand how interfacial cross-linking affects film properties and performance.

Main Methods:

• Emulsion polymerization was used to synthesize core-shell latex particles with a cross-linkable shell (diacetone acrylamide - DAAM) and a softer core.
• Adipic acid dihydrazide was added to induce interfacial cross-linking between particles during film formation.
• Characterization involved mechanical testing (linear viscoelasticity, nonlinear tensile properties) and rheological modeling.

Main Results:

• The core-shell morphology and interfacial cross-linking created a honeycomb-like structure with a balance of dissipative properties and creep resistance.
• Low-level cross-linking resulted in a percolating network swollen with a nearly un-cross-linked component.
• Linear viscoelastic properties remained largely unaffected, while nonlinear tensile properties were significantly modified, leading to improved long-term shear resistance with unchanged peel force.

Conclusions:

• Heterogeneous cross-linking via core-shell morphology is an effective strategy for enhancing PSA performance.
• This method significantly improves long-term shear resistance while maintaining desirable peel forces.
• The findings provide insights into tailoring PSA properties through controlled cross-linking for specific applications.