Antioxidant behavior of a novel sulfur-bearing hindered phenolic antioxidant with a high molecular weight in polypropylene

A novel sulfur-bearing hindered phenolic antioxidant with a molecular weight of 1305.9 (SAO) was successfully synthesized via thiol-acrylate Michael addition reaction and its structure was clarified by nuclear magnetic resonance (NMR) and fourier transform infrared spectra (FTIR). The short-term oxidation induction time (OIT) of polypropylene (PP) compounds obtained at 210 °C showed that the OIT value of SAO-containing PP was higher than that of PP using Chinox 1035 with a molecular weight of 642.9 as a stabilizer. Long-term accelerated thermal aging test of PP compounds in an air oven at 150 °C, however, exhibited that the aging resistance of SAO-stabilizing PP was inferior to that of 1035-containing PP, quite contrary to their respective short-term effect on PP stabilization. The possible reasons of this contradiction were discussed from the viewpoint of the antioxidants' molecular structure and the limitations of the OIT approach in lifetime prediction.     

Antioxidant behaviour of a nanosilica-immobilized antioxidant in polypropylene

A nanosilica-immobilized antioxidant was prepared and incorporated into polypropylene (PP) by melt compounding. It has been found that the antioxidant efficiency of the nanosilica-immobilized antioxidant was superior to the corresponding low molecular counterpart (AO), based on the measurement of the oxidation induction time (OIT) of PP/nanosilica-immobilized antioxidant and PP/AO compounds containing an equivalent antioxidant component. By paying attention to the changes of carbonyl absorption and tensile strength of PP compounds with thermal oven aging time, it was observed that the thermal oxidative stability of PP/nanosilica-immobilized antioxidant was much higher than that of PP/AO compound during the long-term accelerated thermal aging.     

Synthesis of polymeric antioxidants based on ring-opening metathesis polymerization (ROMP) and their antioxidant ability for preventing polypropylene (PP) from thermal oxidation degradation

Norbornene derivatives 1-5 bearing hindered phenol groups were synthesized and undergone ring-opening metathesis polymerization (ROMP) with Grubbs 1st generation catalyst to prepare the corresponding polymeric antioxidants. After hydrogenation with p-toluenesulfonylhydrazide (TSH), polymeric antioxidants with saturated polymer chain were prepared. The resulting polymeric antioxidants were characterized by gel permeation chromatography (GPC), ¹H NMR and differential scanning calorimetry (DSC). As to polymerization activity, monomer 1 had the highest ROMP activity, while monomer 5 could not undergo homopolymerization due to the steric hindrance. The antioxidant ability of these polymeric antioxidants which was determined by oxidation induction temperature (OIT) in polypropylene (PP) system is to protect PP against thermal oxidation. Results showed that the OIT of PP increased obviously when PP was stabilized by the adding of polymeric antioxidants.     

ANTIOXIDANT DEPLETION AND OIT VALUES OF HIGH IMPACT PP STRANDS

The service life of a polyolefin product depends to large extent on the type and amount of the antioxidants added. During the manufacturing,storage and use of the product the antioxidants are depleted by physical processes and chemical degradation,and this impairs its long-term performance.The initial and in-use oxidation stability is often characterized and monitored by the measurement of the oxidative induction time(OIT),and service life predictions are based on the rate of decrease of the OIT value.To...     

Investigation of antioxidant and electron beam radiation effects on the thermal oxidation stability of low-density polyethylene

Effect of various antioxidants on the thermal oxidation stability of LDPE and X-LDPE has been investigated. To achieve this purpose, miscellaneous commercial grade antioxidants such as Irganox 1010, Irganox1076, Irgafos168, Irganox B225, and Chimassorb 944 were selected. Then, formulations based on different content of antioxidant were prepared. The samples were crosslinked by exposure to electron beam irradiation. To assess the thermal oxidation stability of samples, oxidation induction time (OIT) test was accomplished on both the irradiated and unirradiated specimens. Ageing tests were carried out in order to evaluate the thermal oxidation stability of irradiated X-LDPE. The results indicate that Irganox 1010 is the most effective antioxidant amongst the selected ones, concerning thermal oxidation stability of LDPE, before and after aging test.     

Depletion mechanism of antioxidants in MDPE-clay nanocomposites under thermal aging

The depletion behavior of two types of hindered phenolic antioxidants (AO), Irganox^® 1010 (I-1010) and Irganox^®1076 (I-1076), in medium density polyethylene (MDPE)/nanoclay composite was evaluated by incubating samples in a forced air oven at 85 °C. The presence of 4 wt% nanoclay accelerated the depletion of both types of AO, particularly at the surface region of the sample. However, the depletion mechanism in the interior of sample was governed by the AO molecular structure. For samples containing the bulky Irganox®1010, OIT decreased exponentially with aging time consistent with a first order reaction. In contrast, an increase of OIT was detected in first 60 days of heat aging for sample containing I-1076 and afterward the OIT decreased slowly with aging time. The hypothesis for the initial increase of OIT is that the relatively small and linear structure of I-1076 may enable it to be trapped inside the nanoclay galleries and then subsequently released into the polymer matrix during heat aging.     

Synergistic Effect of Phosphite with FuUerene C60 and Fullerenol C60（OH）24 as Antioxidants in Polypropylene

Polypropylene samples with fullerene C60, fullerenol C60（OH）24, 1010, C60/168, C60-OH/168 and 1010/168 as antioxidants were prepared by extrusions. MFR, YI, TGA and OIT of all the samples were tested. According to the results of MFR, during the melt extrusion, fullerene showed excellent stability effect on PP. The antioxidative ability of fullerene was comparable to the traditional antioxidant 1010. The antioxidative ability of fullerenol was not significant in the first extrusion and it accelerated the degradation of PP in the second and the third extrusions. TGA and OIT tests showed that the stability effects of fullerene and fullerenol were slightly lower than antioxidant 1010. In the first time, antioxidant 168 was reported to show great synergistic effects with fullerene and fullerenol as antioxidants, which sussested a simple way to enhance the antioxidative abilities of fullerene and fullerenol.     

Antioxidant capacity of novel amine derivatives of buckminsterfullerene: Determination of inhibition rate constants in a model oxidation system

The radical scavenging efficiency of fullerenes can be significantly activated by means of a connection with hydrogen donating groups of antioxidants such as phenolic, amine and sulfhydryl. The developed system of conjugated σ–π bonds arranged in the fullerene molecule in a closed shape can promote a strong resonance effect on the grafted units and increase the hydrogen atom abstraction efficiency. In this case the known ability of fullerene to trap alkyl radicals might be combined with the strong chain breaking functionality to afford a new class of antioxidants with bimodal action. Explorations in the field of fullerene derivatives on their antioxidant performance provide novel information on the potential stabilization properties of this type of molecular structure. A series of amine derivatives of buckminsterfullerene (C₆₀) with tethered aliphatic chain, cycloaliphatic and aromatic fragments were synthesized and their antioxidant activity was determined. The antioxidant activity of the investigated derivatives was studied by measuring the inhibition rate constants for their reaction with alkyl and peroxy radicals in a model cumene initiated (2,2′-azobisisobutyronitrile, AIBN) oxidation experiments and compared to that recorded under identical experiments for buckminsterfullerene itself and commercial primary aromatic amine stabilizers. The results indicate that linking the amine moieties groups directly to the fullerene core gives rise to a new chain breaking antioxidant mode for the buckminsterfullerene while cyclic fragments containing the same but distant amine group do not reveal this ability. The inhibition rate constants for trapping of peroxy radicals by the amine derivatives were found to be higher than that of known aromatic amine antioxidants Neozone-D and Naugard 445. In addition the C₆₀ part of these molecules acts synergistically by trapping alkyl radicals with inhibition rate constants which exceed that of underivatised fullerene. The amine derivative containing sterically hindered piperidine and pyrrolidine fragments also heighten the inherent rate constant of buckminsterfullerene for scavenging alkyl radicals due to the additional antioxidant contribution promoted by the radical-quenching ability of the formed nitroxyl intermediates. These novel C₆₀–amine conjugates may be considered as promising molecules for broad-spectrum radical scavenging antioxidants.     

Modified cupric reducing antioxidant capacity (CUPRAC) assay for measuring the antioxidant capacities of thiol-containing proteins in admixture with polyphenols

Proteins are not considered as true antioxidants but are known to protect antioxidants from oxidation in various antioxidant activity assays. This study aims to investigate the contribution of proteins, especially thiol-containing proteins, to the observed overall antioxidant capacity measured by known methods. To determine the antioxidant properties of thiol-containing proteins, the CUPRAC method of antioxidant assay using the oxidizing reagent Cu(II)-neocuproine previously used for simultaneous analysis of cystine and cysteine was adopted. While the CUPRAC method is capable of determining all antioxidant compounds including thiols in complex sample matrices, the Ellman method of thiol quantitation basically does not respond to other antioxidants. The antioxidant quantities in the selected samples were assayed with the ABTS and FRAP methods as well as with the CUPRAC method. In all applied methods, the dilutions were made with a standard pH 8 buffer used in the Ellman method by substituting the Na₂EDTA component of the buffer with sodium citrate. On the other hand, the standard CUPRAC protocol was modified by substituting the pH 7 ammonium acetate buffer (at 1 M concentration) with 8 M urea buffer adjusted to pH 7 by neutralizing with 6 M HCl. Urea helps to partly solubilize and denaturate proteins so that their buried thiols be oxidized more easily. All methods used in the estimation of antioxidant properties of proteins (i.e., CUPRAC, Ellman, ABTS, and FRAP) were first standardized with a simple thiol compound, cysteine, by constructing the calibration curves. The molar absorptivities of these methods for cysteine were: ?_CUPRAC = 7.71 × 10³, ?_Ellman = 1.37 × 10⁴, ?_ABTS = 2.06 × 10⁴, and ?_FRAP = 2.98 × 10³ L mol⁻¹cm⁻¹. Then these methods were applied to various samples containing thiols, such as glutathione (reduced form:GSH), egg white, whey proteins, and gelatin. Additionally, known quantities of selected antioxidants were added to these samples to show the additivity of responses.     

Indirect electrochemical determination of antioxidant capacity with hexacyanoferrate(III) reduction using a gold nanoparticle-coated o-phenylenediamine-aniline copolymer electrode

In spite of the many unstandardized literature methods for the determination of the antioxidant activity/capacity (AOA/AOC) of food extracts, there are a very limited number of documented voltammetric nanosensors, despite the fact that commercial electrochemical devices for rapid AOA estimation are on the rise. The mechanism of the developed sensor is based on the chemical reduction of hexacyanoferrate(III) to hexacyanoferrate(II) by antioxidants, followed by the decrement of the cathodic current intensity of hexacyanoferrate(III) in proportion to antioxidant concentration. During voltammetric measurements, the surface of the glassy carbon electrode was coated with an o-phenylenediamine-aniline copolymer and gold nanoparticles were accumulated on this electrode surface to increase the conductivity. It was shown that the developed electrode gave a reversible voltammogram for the hexacyanoferrate(III)/(II) redox couple, and that the cathodic peaks due to strong antioxidants having a standard redox potential less than that of this couple (E^o < 0.36 V) continuously emerged at very close peak potentials. Single antioxidants as well as binary–ternary mixtures were analyzed with this electrode using square wave voltammetry. The trolox-equivalent antioxidant capacities of selected antioxidants were evaluated with this electrode. The modified voltammetric sensor allowed precise measurement of the total antioxidant capacity of plant tea samples such as green tea, lime, and coral moss, and was not interfered by the food preservative sulfite. The results of the developed voltammetric sensor were statistically compared with those of a reference differential pulse voltammetry-cupric reducing antioxidant capacity electrochemical method established in literature.     

Study of antioxidant properties of a water-soluble Vitamin E derivative-tocopherol monoglucoside (TMG) by differential pulse voltammetry

Study of antioxidant properties of tocopherol monoglucoside (TMG), a water-soluble Vitamin E derivative, by differential pulse voltammetry has been carried out in this work. The pH influence on the antioxidant properties of TMG has been also investigated. It was observed that the antioxidant activity of TMG is greater at 6.90<pH<9.18. The reactions between the TMG and reactive oxygen species have been considered. Antioxidant activity of some standard antioxidants including Vitamin E was given for comparison. The results indicate that the TMG is an effective antioxidant in neutral solutions. The oxidation potential for TMG at pH 7.31 has been found (E=0.55±0.03 V versus Ag|AgCl|KCl_sat electrode). Finally the use of TMG for protection against oxidative stress has been recommended.     

Photo‐stabilization of EPDM–clay nanocomposites: effect of antioxidant on the preparation and durability

The present study is to examine the photo‐stabilization effect of an antioxidant on the photo‐oxidation of ethylene‐propylene‐diene monomer (EPDM)–clay nanocomposites. During the preparation of EPDM–clay nanocomposites via melt processing antioxidants are usually incorporated along with clay, which allows phenolic antioxidant molecules to get adsorbed onto acidic clay platelets and their interaction with metallic impurities reduces the stabilizing efficiency of the antioxidant. The nanocomposites were obtained by solution dispersion followed by melt compounding of EPDM and organophilic montmorillonite (OMMT). The samples were characterized by conventional tools such as X‐ray diffraction (XRD), Fourier Transform Infra Red (FT‐IR) spectroscopy, and thermo‐gravimetric analysis (TGA). It was found, upon photo‐irradiation (λ > 290 nm) studies by following the changes in functional groups and surface morphology, that photo‐degradation was lowered by the antioxidant and the efficiency of the antioxidant could be improved by initial incorporation of antioxidant in the EPDM matrix. In EPDM–clay nanocomposites, a stabilizing activity of the antioxidant was observed above some threshold concentration of the antioxidant. The relationship between the nanoclay reinforcement and stabilizing efficiency in terms of photo‐oxidation and surface morphology for their applicability are discussed. The methodology adopted for this study is also justified through our observation. Copyright © 2007 John Wiley & Sons, Ltd.     

Study on the antioxidant activities of benzofuranones in melt processing of polypropylene

The antioxidant activities of four benzofuranones in melt processing of polypropylene (PP) have been investigated using multiple extrusions. The antioxidant activities of those four benzofuranones with different substituent groups have been evaluated using melt flow index (MFI) and yellowness index (Y.I.) of multiple-extruded PP stabilized with those antioxidants. The change of MFI values indicates as follows: firstly, the position of substituent group has a very important effect on the antioxidant activity of benzofuranone in the melt processing of PP i.e. methyl group of 2′-position may prevent the hydrogen donation of benzofuranone toward PP radicals and make the antioxidant activity of benzofuranone in PP decrease; secondly, electronic property of substituent group of para position to 3-reactive hydrogen has little influence on the antioxidant activity. Furthermore, the theory that the formation of antioxidative products due to the dimerization and disproportionation of benzofuranyl radicals is the main reason that induces the discoloration of stabilized PP has been predicted for the first time.     

Determination of phenolic compounds,in vitro antioxidant activity and characterization of secondary metabolites in different parts of Passiflora cincinnata by HPLC-DAD-MS/MS analysis

Abstract

Ethanol extracts of different parts of Passiflora cincinnata were obtained by maceration. The total phenolic and flavonoid contents were evaluated. The antioxidant activities were determined by β-carotene-linoleic acid bleaching test, 2,2-diphenyl-1-picrylhydrazil (DPPH), and 2,2’-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging. The crude ethanol stem extract showed the highest amount of total polyphenols (45.53?mg gallic acid equivalent/g) while the highest total flavonoid contents (1.42?mg of quercetin equivalent/g) were observed in the leaf extract. The lowest IC₅₀ (25.65?μg/ml) by the DPPH method was observed for the stem extract. The ABTS method showed a significant antioxidant activity for all investigated extracts. The secondary metabolite composition of ethanol extracts was assessed by HPLC-DAD-MS/MS analysis, leading to the identification of fourteen secondary metabolites in P. cincinnata extracts. These results showed the potentiality of this species as a source of phenolic compounds and antioxidants.     

Molecular weight determination of bulk polymer surfaces by static secondary ion mass spectrometry

The determination of molecular weights at surfaces of bulk polymer materials can be accomplished by static secondary ion mass spectrometry (SIMS) via fragments originating from repeat units and end groups. The intensity ratio of these fragments depends on the polymer chain length as seen for bisphenol-A-polycarbonate and perfluorinated polyethers (Krytox). A kinetic model of fragment ion formation explains the molecular weight dependent fragment intensities and links them to properties of the molecular weight distribution. In the most simple case one obtains the number average molecular weight <M_n> at the surface. This technique can be used for the determination of the molecular weight at bulk polymer surfaces such as a CD-ROM made from polycarbonate by injection molding.     

Quercetin-albumin nano-complex as an antioxidant agent against hydrogen peroxide-induced death of spinal cord neurons as a model of preventive care study

Herein, the quercetin-human serum albumin (HSA) nano-complex was formulated and its capability to decrease H₂O₂-stimulated cytotoxicity against spinal cord neurons as a model of preventive care study was investigated by cellular assays. Quercetin molecules were first encapsulated into HSA as a shell and the loading efficiency along with drug release and different properties of formulated nano-complex were determined using TEM, SEM, and DLS approaches. Afterwards using CD spectroscopic method and theoritical analysis, the structural changes and binding redisues of HSA after interaction with quercetin were investigated, respectively. Finally, the antioxidant activity of quercetin-HSA nano-complex against H₂O₂ (200 µM)-stimulated cytotoxicity in spinal cord neurons was explored by MTT, SOD and CAT activity, and morphological changes assays. It was shown that the fabrication of quercetin-HSA nano-complex resulted in the improved bioavailability of quercetin with an entrapment efficiency of 68.99% and percent yield of 53.19%. Also, molecular docking study showed that quercetin molecules spontaneously bind to HSA through hydrogen bonds and van der Waals interactions. Furthermore, CD data indicated that the quercetin did not change the secondary structure of HSA. Finally, cellular assays displayed that the pre-treatments of spinal cord neurons with quercetin-HSA nano-complex attenuated the H₂O₂-triggerd neuron mortality through a significant increase in the activity of SOD and CAT and prevention of morphological changes. In conclusion, it may be suggested that the formulation of quercetin into nano-complex can improve its medical properties and this new developed drug formulation may hold a great promise in the advancement of antioxidant compounds in preventive care services.     

Mechanisms of antioxidant action: polymer grafted antioxidants

It is shown that the antioxidant 3,5-di-tert-butyl-4-hydroxybenzyl acrylate, may be grafted to the surface of polymer artefacts. The antioxidant activity of the resulting “efficiently dispersed” antioxidant is very much higher than that of low molecular weight antioxidants containing the same functional group. Even after extraction with an effective solvent for the antioxidant-monomer and derived polymer, the oxidative stability of the polymer films is very much greater than that of polymer containing the antioxidant-monomer or antioxidant-polymer incorporated by a conventional melt technique without extraction. Optimum activity is believed to be associated with the formation of frequent short chain grafts in the surface of the polymer and is achieved by the use of a polymerization photo-activator such as benzophenone which also terminates kinetic chains.Surface grafted antioxidants are also found to be effective u.v. stabilizers for polypropylene in contrast to the normal ineffectiveness of chain terminating antioxidants incorporated into the polymer by conventional techniques.     

A microfluidic system for evaluation of antioxidant capacity based on a peroxyoxalate chemiluminescence assay

A microfluidic system incorporating chemiluminescence detection is reported as a new tool for measuring antioxidant capacity. The detection is based on a peroxyoxalate chemiluminescence (PO-CL) assay with 9,10-bis-(phenylethynyl)anthracene (BPEA) as the fluorescent probe and hydrogen peroxide as the oxidant. Antioxidant plugs injected into the hydrogen peroxide stream result in inhibition of the CL emission which can be quantified and correlated with antioxidant capacity. The PO-CL assay is performed in 800-μm-wide and 800-μm-deep microchannels on a poly(dimethylsiloxane) (PDMS) microchip. Controlled injection of the antioxidant plugs is performed through an injection valve. Of the plant-food based antioxidants tested, β-carotene was found to be the most efficient hydrogen peroxide scavenger (SA _HP of 3.27 × 10⁻³ μmol⁻¹ L), followed by α-tocopherol (SA _HP of 2.36 × 10⁻³ μmol⁻¹ L) and quercetin (SA _HP of 0.31 × 10⁻³ μmol⁻¹ L). Although the method is inherently simple and rapid, excellent analytical performance is afforded in terms of sensitivity, dynamic range, and precision, with RSD values typically below 1.5%. We expect our microfluidic devices to be used for in-the-field antioxidant capacity screening of plant-sourced food and pharmaceutical supplements. Figure Assembled PDMS microchip sandwiched between two glass plates with the top plate containing capillary reservoirs