A first-principles based chemophysical environment for studying lignins as an asphalt antioxidant

Abstract

Asphalt binder is an important material for many industrial applications. Oxidative aging of asphalt is a constantly occurring chemical process that involves the reactions between oxygen molecules and component species of bulk asphalt throughout its service life, which could lead to significant alterations to the desired physical properties of asphalt. A common practice to alleviate asphalt aging today is to use different chemical additives or modifiers as antioxidants. The current state of knowledge in asphalt oxidation and antioxidant evaluation is focused on monitoring the degradation in asphalt’s physical properties, mainly the viscosity and ductility, which although meeting direct engineering needs does not contribute to the fundamental understanding of the aging and anti-aging mechanisms. Within this context, this study was initiated to study the chemical and physical bases of general chemical antioxidants, using a biopolymer, i.e., coniferyl-alcohol lignin as an example. A quantum chemistry (QC) based chemophysical environment is developed in this study, which is capable of analyzing the various chemical reactions between asphalt component species and oxygen, as well as the incurred physical changes. The techniques of X-ray photoelectron spectroscopy (XPS) was used to prove the validity of the lignin-modified and unmodified asphalt models, from which the XPS results showed high agreement to the model predictions.