Search results for "Oxidative degradation"

Biochemical and Immunological implications of Lutein and Zeaxanthin

2021

Throughout history, nature has been acknowledged for being a primordial source of various bioactive molecules in which human macular carotenoids are gaining significant attention. Among 750 natural carotenoids, lutein, zeaxanthin and their oxidative metabolites are selectively accumulated in the macular region of living beings. Due to their vast applications in food, feed, pharmaceutical and nutraceuticals industries, the global market of lutein and zeaxanthin is continuously expanding but chemical synthesis, extraction and purification of these compounds from their natural repertoire e.g., plants, is somewhat costly and technically challenging. In this regard microbial as well as microalga…

1990

This lecture summarizes some recent results and ideas about interrelations between degradation and mechanical behaviour of polyolefins. Aspects of the heterogeneous nature of oxidative degradation in the solid state, the feedback mechanism in degradation, effects of morphology, particularly orientation, on the degradation process, and the influence of degradation on plasticity and on the ultimate mechanical behaviour are discussed.

Thermo-oxidative stabilization of poly(lactic acid) with antioxidant intercalated layered double hydroxides

2016

Two antioxidant modified layered double hydroxides (AO-LDHs) were successfully prepared by the intercalation of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (IrganoxCOOH) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) in the layered structure of LDH. It was found that by anchoring the phenolic moieties to the LDH layers the antioxidant power is retained in the case of Trolox, and even amplified in the case of IrganoxCOOH. A small amount of the two AO-LDHs was incorporated into poly(lactic acid), PLA, by solution mixing and melt extrusion. The thermo-oxidative stability of the composites was compared with that of the neat PLA and PLA containing free AOs. SEC analy…

Effectiveness of some protective and self-cleaning treatments: a challenge for the conservation of temple G stone in Selinunte

2021

Abstract The Temple G of the Archaeological Park of Selinunte (Italy), the largest in Europe, is one of the most impressive temples in the Magna Grecia. Today, it is completely destroyed due to a strong earthquake occurred in the Middle Ages. The used stone is a calcarenite coming from the ancient and renowned quarries of Cusa near the acropolis. This work comes from the today’s proposal of Temple G anastylosis. The goal of the work is to provide the results relating the protective effectiveness of three polymer formulations, appropriately selected, on stone samples taken from the “Capitello” quarry, part of “Cusa quarries”. The formulations functionality was deployed by adding TiO2 nanopar…

Ancistrocyclinones A and B, unprecedented pentacyclic N,C-coupled naphthylisoquinoline alkaloids, from the Chinese liana Ancistrocladus tectorius

2018

Two unique pentacyclic N,C-coupled naphthylisoquinolines, the ancistrocyclinones A (5) and B (6), were discovered in the Chinese liana Ancistrocladus tectorius. Furthermore, six known, likewise N,C-coupled alkaloids, viz., ancistrocladinium A (7a) and its mono- and bisphenolic analogs 8a and 9a were isolated, along with their atropo-diastereomers 7b, 8b, and 9b. The stereostructures of 5 and 6 were determined by HRESIMS, 1D and 2D NMR, oxidative degradation, and ECD calculations. The pentacyclic ancistrocyclinones A (5) and B (6) are structurally similar to berberine alkaloids - yet arising from a most different biosynthetic pathway: they are apparently formed by N,C-coupling of their polyk…

Photooxidation and Stabilization of Photooxidized Polyethylene and of its Monopolymer Blends

2003

The increasing use of products from recycled polymers, or from blends with recycled polymers exposed to the outdoors, implies the need for good weathering resistance. This is particularly important when the recycled material comes, in turn, from products exposed during their lifetime to the sun. In this case the presence of C=O groups in the macromolecular chains strongly increases the photooxidative degradation kinetics of these secondary materials. In this work the change of the photooxidative degradation of blends of virgin and photooxidized polyethylene was evaluated as a function of the C=O content present in the material. As expected, the presence of the C=O groups strongly increases …

Time-resolved rheology as a tool to monitor the progress of polymer degradation in the melt state - Part I: Thermal and thermo-oxidative degradation …

2015

Abstract Thermal and thermo-oxidative degradation of polyamide 11 (PA11) in the melt state (T = 215 °C) are studied by resorting to time-resolved mechanical spectroscopy. Such an approach allows to elude the changes in the rheological properties occurring while testing, thus enabling the rigorous study of polymer degradation in the melt state. Different concurrent degradation reactions in oxidative (air) and non-oxidative (N2) environment are promptly guessed by studying the time evolutions of rheological functions. In particular, changes in the zero-frequency complex viscosity reflects changes in the average molecular weight, while the appearance of a yield stress in the complex viscosity …

Nano-hybrids based on quercetin and carbon nanotubes with excellent anti-oxidant activity

2016

Abstract Multi-functional nano-hybrids based on Quercetin (Q), a natural antioxidant, and functionalized Carbon Nanotubes (CNTs) have been formulated and used to prepare Ultra High Molecular Weight PolyEthylene (UHMWPE)-based nanocomposites. The study of the nanocomposites rheological behaviour shows that the immobilization of Q molecules onto CNTs outer surface leads to a beneficial effect on the state of the interface between polymer and nanoparticles. Additionally, the investigation of the thermo- and photo-oxidation processes reveals that the hybrids nanoparticles are able to exert a remarkable stabilizing action, due to strong physical interaction between Q and CNTs. In particular, the…

Oxidative degradation properties of Co-based catalysts in the presence of ozone

2007

Four series of cobalt-based catalysts, such as bare Co3O4 and CoO, CoOx-CeO2 mixed oxides, CoOx supported over alumina and alumina-baria and CoMgAl and CoNiAl hydrotalcites have been synthesized and investigated for the oxidative degradation of phenol in the presence of ozone. Characterizations were obtained by several techniques in order to investigate the nature of cobalt species and their morphological properties, depending on the system. Analyses by XRD, BET, TPR, UV-visible diffuse reflectance spectroscopy and TG/DT were performed. The CoNiAl hydrotalcite exhibits, after 4 h of reaction, the highest phenol ozonation activity followed by Co(3 wt%)/Al2O3-BaO and CoMgAl. The samples Co(1 …

Time-resolved rheology as a tool to monitor the progress of polymer degradation in the melt state – Part II: Thermal and thermo-oxidative degradation…

2015

Abstract Thermal and thermo-oxidative degradation of nanocomposites based on polyamide 11 (PA11) and organo-modified clay (Cloisite® 30B) are studied in the melt state (T = 215 °C) via time-resolved mechanical spectroscopy (TRMS). The goal is assessing the potentiality of rheological analysis for studying polymer degradation in complex systems such as polymer nanocomposites, whose rheological response stems from the combination of the contributions of polymer and nanoparticles. We prove that a thorough analysis grounded on TRMS allows to isolate the effect of degradation of the polymer matrix, whose progress can be hence profitably monitored. Essentially the same degradation mechanisms as i…