Controlled sparse and percolating cross-linking in waterborne soft adhesives.
The effect of low levels of cross-linking on the adhesive and mechanical properties of waterborne pressure-sensitive adhesives was investigated. We have taken advantage of a core-shell latex particle morphology obtained by emulsion polymerization to create a heterogeneous structure of cross-links without major modification of the monomer composition. The latex particles comprise a shell containing cross-linkable diacetone acrylamide (DAAM) repeat units localized on the periphery of a slightly softer core copolymer of very similar composition. Adipic acid dihydrazide was added to the latex prior to film formation to react with DAAM repeat units and affect interfacial cross-linking between particles in the adhesive films. The honeycomb-like structure obtained after drying of the latex results in a good balance between the dissipative properties required for adhesion and the resistance to creep. The characterization of the mechanical properties of the films shows that the chosen cross-linking method creates a percolating lightly cross-linked network, swollen with a nearly un-cross-linked component. With this cross-linking method, the linear viscoelastic properties of the soft films are nearly unaffected by the cross-linking while the nonlinear tensile properties are greatly modified. As a result, the long-term shear resistance of the adhesive film improves very significantly while the peel force remains nearly the same. A simple rheological model is used to interpret qualitatively the changes in the material parameters induced by cross-linking.
Deplace
F
F
Laboratoire de Physico-Chimie des Polymeres et des Milieux Disperses, UMR 7615, UPMC, CNRS-ESPCI, 10 Rue Vauquelin, 75231 Paris Cedex 05, France.
Carelli
C
C
Langenfeld
A
A
Rabjohns
M A
MA
Foster
A B
AB
Lovell
P A
PA
Creton
C
C
D000269:Adhesives; D003432:Cross-Linking Reagents / Q000737:chemistry; D004548:Elasticity; D008422:Materials Testing; D008567:Membranes, Artificial; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D013499:Surface Properties; D013718:Tensile Strength; D014783:Viscosity
D000269:Adhesives; D003432:Cross-Linking Reagents; D008567:Membranes, Artificial; D011108:Polymers