Plasticizers are normally used in polymeric systems to soften or to improve the processability of a composition. This is the basic definition of a plasticizer, with the caveat that the plasticizer needs to be at least partially compatible with the polymer being used. Because pressure-sensitive adhesives (PSAs) are a unique class of adhesives characterized by their ability to form bonds when light pressure is applied, additives such as plasticizers can play a key role in the formulation to enhance performance.
To measure a plasticizer’s effectiveness in a composition, the reduction of the glass-transition temperature (Tg) of the polymer can be used as an indicator; the degree of suppression of the glass transition is also an indication of the compatibility of the plasticizer with the polymer and the other ingredients. The workability or processability of a plasticized composition may be more important than the actual softening of the polymer for some applications, as is the case in PSAs.1