Bio-oils employed for various industrial purposes, such as biodiesel production, undergo extensive oxidation and degradation during transformation processes. Therefore, it is extremely important to predict their stability at high temperature. We report herein a new procedure based on the optically detected profile of headspace O₂ concentration during isotherms at 130 °C for evaluating the oxidation kinetic parameters of several bio-oil feedstocks. The slope of O₂ consumption and the induction period duration were related to the oil characteristics (molecular structure, acidity, and presence of intrinsic antioxidants or metals). The increase of the induction time caused by a standardized propyl gallate addition yielded a semiquantitative value of radical generation rate. Investigated oils included used cooking oils; mono-, di-, and triglycerides from natural sources; free fatty acids; transesterified oils; and their blends. With respect to other methods, this characterization presents the advantage of disentangling and evaluating the role of both fatty acids composition and naturally occurring antioxidants, and allows the development of rational strategies for antioxidant protection of oils and of their blends.

The density of trap states in donor/acceptor blends of organic photovoltaic materials is obtained from photogenerated charge-carrier recombination kinetics observed by light-induced electron spin resonance (LESR) at different temperatures. The method, based on an inversion calculation, is applied to experimental LESR data from two P3AT-PCBM blend films with different kinetic behavior, deriving density-of-states profiles and values of the trap depths in agreement with previous literature results obtained using other techniques. DOI: http://dx.doi.org/10.1103/PhysRevB.84.245205 3 More Received 6 July 2011Revised 24 November 2011Published 14 December 2011©2011 American Physical Society

Peroxidation of vegetable oils represents a major problem for the food and biodiesel industries, and it is greatly accelerated by oil degree of unsaturation and by temperature increase. Phenols represent the most common additives used to counteract oil peroxidation, however clear structure-activity relationships at high temperatures are not available. We report, herein, a kinetic study of O₂ consumption during spontaneous peroxidation of sunflower oil at 130 °C in the presence of 18 antioxidants belonging to the main families of natural and synthetic phenols, including α-tocopherol, alkylphenols (BHT, BHA), hydroquinones (TBHD), catechols (quercetin, catechin) and gallates. Results show that TBHQ provide the best protection in terms of induction period (IP) duration and O₂ consumption rate. EPR spectroscopy demonstrated that the inhibition activity is negatively correlated to the stability of the phenoxyl radical of the antioxidant (A^•), suggesting that chain propagation with linoleate (RH) moieties A^• + RH → AH + R^• decreases the efficacy of those antioxidants forming persistent A^• radicals. These results provide important information to optimize the antioxidant activity of phenols and of novel phenol-based materials.