Multiscale Structural Characterization of Biobased Diallyl–Eugenol Polymer Networks

Abstract

Biosourced eugenol-based polymer networks have a potential functionality for antibacterial coating applications. The presence of carvacrol, a phenol compound, improves these properties. However, the relationship between the network structure and the macroscopic thermomechanical behavior is not known for these biopolymers. Thus, this work details a robust study of this relationship through a multiscale experimental approach combining Dielectric Spectroscopy, Dynamic Mechanical Analysis, tensile testing, and Time Domain Double-Quantum proton Nuclear Magnetic Resonance (DQ 1H NMR). It was shown that carvacrol has an influence on the molecular mobility of the materials. Namely, it induces the appearance of a shouldering on the γ relaxation and a diminishing of the main molecular α relaxation, Tα. More surprisingly, up to 20% wt, carvacrol increases the elastic E′ and Young’s E moduli. This observation can be interpreted as an increase of the crosslink density of the networks. Time Domain DQ 1H NMR shows that the residual dipolar coupling constant also increases. Thus, carvacrol seems to act as both a thermal plasticizer and mechanical reinforcement, which may seem to be antagonistic trends. For carvacrol contents over 20% wt, these properties diminish because of a saturation of this molecule in the networks and the onset of a phase separation. By combining the aforementioned techniques, it was proven that carvacrol linearly increased the measured crosslink density and thermomechanical properties by physically bonding to the networks through π–π interactions. These interactions would act as physical crosslinks. This work demonstrates that by correlating the results of various multiscale experimental techniques, a better comprehension of the structure–property relationship can be established for biobased functional polymer networks.