The Influence of Molecular Polarity of Pressure-Sensitive Adhesives on Peel Strength

The Influence of Adhesive Molecular Polarity on Peel Strength

 

　　Introducing monomers containing polar groups—such as acrylic acid, acrylamide, and hydroxyethyl acrylate—into polyacrylic pressure-sensitive adhesives via copolymerization, or blending highly polar tackifying resins with rubber-based pressure-sensitive adhesives, can both increase the molecular polarity of the pressure-sensitive adhesive. An increase in the molecular polarity of the pressure-sensitive adhesive can significantly enhance the peel strength of pressure-sensitive adhesive products when bonding to polar substrates. As shown in Table 1:

 

 

　　

Table 1 presents a set of typical experimental data. Obviously, the molecular polarity of acrylic acid and acrylamide is greater than that of methacrylic acid and methyl methacrylate; consequently, their contribution to increasing the molecular polarity of the copolymer is also greater, and thus their effect on enhancing the 90° peel strength of the copolymer is more pronounced. Therefore, it is common practice to introduce acrylic acid in order to improve the 180° peel strength performance of polyacrylate pressure-sensitive adhesives. We have previously studied the effect of varying the amount of acrylic acid in solvent-based polyacrylate pressure-sensitive adhesive formulations on the 180° peel strength and other pressure-sensitive adhesive properties of the resulting products. The experimental results are shown in Table 2. The data indicate that as the amount of the polar monomer AA increases, the molecular polarity of the copolymer rises significantly, leading to a marked increase in 180° peel strength and a substantial improvement in the shear creep resistance of the pressure-sensitive adhesive. However, the initial tack of the pressure-sensitive adhesive shows a systematic decline.

 

　　The polarity of pressure-sensitive adhesive molecules not only enhances the intermolecular interaction forces at the adhesive interface and improves the interfacial adhesion conditions, thereby increasing the work of adhesion at the interface. It also alters the mechanical and rheological properties of the pressure-sensitive adhesive layer—for example, by boosting cohesive strength and elastic modulus, and improving resistance to peel-off and bulk viscosity. All these factors influence the 180° peel strength and other adhesive performance characteristics of pressure-sensitive adhesives.