Design of emulsion polymer adhesives

The adhesion force after brief contact is called tack (Zosel, 1985,1986). Table 9.2 shows the tack of some acrylic homopolymers. The higher the amount of carbon atoms (C ) in the side chain the higher is the maximum tack, and the lower is the temperature T (max-tack) at which the maximum tack occurs. Low Tg monomers give soft and tacky polymers, in particular polyethylhexyl and polybutyl acrylate have the best tack at room temperature (Druschke, 1987). 

The molar mass and crossMnking of the polymer also affects the adhesion properties. All monomer units having activated H-atoms in a-position to a C=0 or C=C double bond (such as acrylic acid and esters, butadiene, vinyl acetate) are accessible to radical transfer. This leads to branching and crosslinking. Above a certain degree of crosslinking the polymer 

Molar mass and crosslinking can be influenced in addition by the amount of initiator, by the process conditions (e.g. monomer-starved conditions versus monomer-flooded conditions) and by using crosshnking monomers, such as divinyl benzene, butanediol diacrylate or allyl methacrylate. 

Functional monomers are used to improve the adhesive properties. One important functional monomer is acrylic acid. It strongly increases cohesion of PSA and improves compatibility with fiUers, such as CaC03, for construction adhesives. 

Hydroxy alkyl acrylate and water-dispersible polyisocyanates 

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