Influence of Natural Aging on the Physicochemical and Structural Characteristics of Green Bio‐Based Polymers

The natural aging of polymers obtained by polymerization of chemically modified oleic or lauric acids with a precursor based on soybean oil was evaluated by comparing infrared spectra, color parameters, contact angles, thermal degradation temperatures, dynamic mechanical properties, and the characteristic nanoscale parameters of positron annihilation lifetime spectra, obtained for samples recently prepared and aged at room temperature for 24 months. The results denoted that physicochemical changes occurred in the materials due to aging, which were evidenced as variations in some structural and physical properties in all the studied polymers. These changes were explained in terms of the network characteristics (i.e., crosslinking density, pendant dangling chains, steric impediment, presence of labile double bonds) and the competitive degradative processes (i.e., crosslinking, chain scission, formation of small volatile molecules) that take place during aging. Results from positron annihilation lifetime spectroscopy indicated that although the average free volume of the tested samples remained almost constant after aging, the number of nanoholes decreased because smaller voids disappeared, thus changing free volume hole size distribution. This study is the result of a careful and systematic experimental design, lasting more than 2 years, therefore representing a considerable investment of time, effort, and resources to produce findings that are not only scarce but also crucial for advancing the development of new materials, especially those based on biomass. Practical Applications : The physicochemical and mechanical characteristics of these polymers, with high green carbon content and environmental benefits, can be tailored for use in different applications by selecting the type and proportion of the precursor in the formulation. In turn, the effects of natural aging are of fundamental importance when defining the type and duration of use. Their characteristics, both before and after natural aging, make them good candidates for structural, decorative, and surface protection applications, especially in indoor environments.