Commercial Phenolic Antioxidant Research Articles

Investigating the impact of Cloisite® 15A nanoclays on the diffusivity of Irganox 1035 antioxidant in high‐density polyethylene nanocomposite

AbstractKnowing the diffusion coefficients of antioxidants in packaging materials is essential to assess their effectiveness in protecting materials against oxidation, but also to prevent their eventual migration to food. In this work, the diffusion of a commercial phenolic antioxidant (Irganox 1035) was measured experimentally in pristine high‐density polyethylene (HDPE) and in HDPE nanocomposite filled with 3 wt% of nanoclays (Cloisite® 15A). Diffusion experiments were performed using the Roe's method between 60 and 100°C. The local concentration of Irganox1035 in each film was measured by UV–Vis spectroscopy from the UV absorbance at 282 nm. The adjustment of the experimental data by Fick's second law allowed us to deduce the values of the diffusion coefficient of Irganox1035 at each temperature and to show that the temperature dependence of this coefficient obeys an Arrhenius' law. It is shown that the incorporation of 3 wt% of Cloisite®15A into HDPE significantly hinders the diffusion of Irganox 1035 and increases its activation energy. Several mechanistic assumptions could explain this result, first the increase in the tortuosity of diffusion paths, but also the possible establishment of strong intermolecular interactions between the antioxidant and some chemical groups on the nanofiller surface, or even the formation of an interphase with reduced molecular mobility around the nanofillers.

Effect of additives on the thermal and thermo-oxidative stability of poly(ethylene furanoate) biobased polyester

Polyesters based on 2,5-furan dicarboxylic acid are a new class of biobased polymers with properties superior of those of their fossil-based homologues. However, similarly to poly(ethylene terephthalate) (PET), poly(ethylene 2,5-furan dicarboxylate) (PEF) degrades during its thermal processing and as a result its molecular weight drops, and discoloration occurs. This is mainly attributed to thermal and thermo-oxidative degradation reactions. The addition of several types of thermal stabilizers during the synthesis or the processing of thermoplastic polyesters is a common practice. In this work, a commercial phenolic antioxidant (Irganox 1098), and two phosphorus-containing thermal stabilizers (phosphoric acid and triphenyl phosphate) were added in PEF polyester during synthesis with the use of antimony acetate catalyst. The effect of these additives on the molecular weight, thermal properties, thermal, thermo-oxidative stability and physical aging of PEF was evaluated. It was found that all additives slightly improved the thermal stability of PEF, with phosphoric acid and mainly triphenyl phosphate being the most efficient ones.

Use of dihydromyricetin as antioxidant for polypropylene stabilization

A study on the efficiency of a flavonoid compound as an antioxidant stabilizer for polypropylene (PP) is reported. Dihydromyricetin (DMY), a 2,3-dihydroflavonol compound, was extracted from Ampelopsis grossedentata. Its stabilizing activity was compared with that of a commercial phenolic antioxidant. Thermogravimetric analysis and oxidation onset temperature measurements performed on samples, as well as a α,α-diphenyl-β-picrylhydrazyl radical assay on DMY, provided evidence for the effectiveness of the DMY. Based on our results, it could be used as an efficient and high value-added additive for PP. DMY was less toxic and highly effective as a good, natural antioxidant for PP.

Synthesis and characterization of gallates for linear low-density polyethylene as antioxidant

In this paper, the synthesis of octyl gallate (OG), dodecyl gallate (DG) and hexadecyl gallate (HG) as antioxidant for linear low-density polyethylene (LLDPE) was reported for the first time. The structure and antioxidation of synthetic gallates were characterized by FTIR 1H NMR and oxidation induction time. The LLDPE-OG, LLDPE-HG and LLDPE-HG of degradation and stabilization were compared with the commercial phenolic antioxidant Irganox 1010. Experimental results indicate that the antioxidant ability of the three synthetic antioxidants is in the following order: DG > HG > OG. Therefore, DG could be used as an efficient and low environmental impact additive of LLDPE. The release of the gallates from LLDPE films was evaluated by monitoring the oxidation induction temperature change upon water extraction, demonstrating that LLDPE-DG retained high stability against migration.

Natural antioxidants for polypropylene stabilization

A study on the efficiency of bio-based compounds as stabilizers for polypropylene (PP) is reported. A water extract from French maritime pine bark (Pycnogenol ®), a by-product containing polyphenols obtained from wine production, and a carotenoid-containing oleoresin from processing of tomatoes were used. Their stabilizing activity was compared with that of a commercial phenolic antioxidant. Thermogravimetric analysis and Oxidative Induction Time measurements performed on unaged samples, as well as infrared spectroscopy on samples aged at 70 °C, provided evidence for the effectiveness of the natural stabilizers. Mechanical characterization was carried out on aged films and injection moulded samples. Experimental results indicated that particularly grape extract could provide long-term stabilization to PP under conditions of oxidative degradation. Therefore, it could be used as efficient and high value-added additive for polypropylene. Pycnogenol ® also showed antioxidant activity, however the achievement of a more homogeneous dispersion in the polymer matrix could improve the mechanical performance of aged samples.

Use of isothermal and nonisothermal chemiluminescence measurements for comparison of stabilizing efficiency of hydroxytyrosol (3,4‐dihydroxy‐phenylethanol), α‐tocopherol and irganox®1076 in polypropylene

AbstractHydroxytyrosol (3,4‐dihydroxyphenylethanol) is a phenolic compound obtained during olive processing in oil manufacturing. It plays a role in enhancing the oxidative stability of olive oil with positive effects on human health. The raising interest towards the use of natural antioxidants as stabilizers in polymer formulations makes hydroxytyrosol a potential candidate to substitute synthetic antioxidants in polyolefin formulations. In this study, hydroxytyrosol was compared in antioxidant efficiency with two other compounds, one of them obtained from natural resources (α‐tocopherol) and a synthetic commercial phenolic antioxidant (Irganox®1076). Chemiluminescence was used to as a tool to assess the increase in the polypropylene stability to thermo‐oxidative degradation. A significant increase in the value of oxygen induction time with the initial concentration of natural antioxidants tested under isothermal conditions at 140, 150 and 160°C was observed. A comparison at the same concentration level (0.1 wt %) between the three antioxidants showed an order of stabilizing efficiency as: α‐tocopherol > Irganox®1076 > hydroxytyrosol, but all them showed clearly their stabilization performance in polypropylene. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Visible-light promoted degradation of the commercial antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT): a kinetic study

Visible-light photo-irradiation of the commercial phenolic antioxidants (PhAs) butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), in the presence of vitamin B2 (riboflavin, Rf), in methanolic solutions and under aerobic conditions, results in the photo-oxidation of the PhAs. The synthetic dye photosensitiser Rose Bengal was also employed for auxiliary experiments. With concentrations of riboflavin and PhAs of ca. 0.02 mM and < 1 mM, respectively, the excited triplet state of the vitamin (3Rf*) is quenched by BHT in a competitive fashion with dissolved ground state triplet oxygen. From the quenching of 3Rf*, the semireduced form of the pigment is generated through an electron transfer process from BHT, with the subsequent production of superoxide anion radical (O2•−) by reaction with dissolved molecular oxygen. In parallel, the species singlet molecular oxygen, O2(1Δg), is also generated. Both reactive oxygen species produce the photodegradation of BHT. In the case of BHA, the lack of any effect exerted by superoxide dismutase drives out a significant participation of a O2•−-mediated mechanism. BHA mainly interacts with O2(1Δg) and exhibits a desirable property as an antioxidant – a relatively high capacity for O2(1Δg) de-activation and a low photodegradation efficiency by the oxidative species. Electrochemical determinations support the proposed photodegradative mechanism.

Modelling light stabilizers as thermal antioxidants

Light stabilizers often display some degree of antioxidant activity against thermal degradation of polymers both in the solid state and the melt. Although this capacity to date has been documented in some instances such features have not been kinetically modelled for many light stabilizers. An understanding of the mechanisms of this activity is crucial in polymer materials due to the close link between prior thermal behaviour and post stabilisation. This paper considers the potential antioxidant activity of three representative UV stabilizers using a model system initiated (2,2′-azo-bisisobutyronitrile, AIBN) cumene oxidation. Kinetic measurements of oxidation rates in the presence of the stabilizers showed that the antioxidant activity as well as the mechanism and mode of inhibition was different for each of the stabilizers. Thus, whilst a triazine UV absorber (Cyasorb UV 1164) did not display any antioxidant activity, a hindered phenol (Cyasorb UV 2908) operated as a peroxy radical acceptor, and a hindered amine (Cyasorb 3529) retarded the model reaction without an induction period like many HAS stabilizers. The Cyasorb 2908 revealed weak antioxidant activity with a rate constant for the addition of cumylperoxy RO 2 radicals to the functional group of the stabilizer k 7 = 10 6.2 ± 0.1 e −(3900 ± 600)/R T , however, the inhibition index f (80 °C) is significantly higher than that of the commercial phenolic antioxidant Irganox 1076. Oxidation rate profiles in the presence of Cyasorb 3529 displayed a strong retarding activity by the stabilizer under conditions of the model experiments. The rates were found to depend linearly on the reciprocal square root of the concentration of the stabilizer over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl R radicals to the Cyasorb molecules. The rate constants for the addition of cumyl R radicals to the Cyasorb were determined to be k (333–353 K) = (2.0 ± 0.8) × 10 8 M −1 s −1. This value surpasses even the rate constants for other related HAS Chimassorb [Zeynalov EB, Allen NS. Effect of micron and nano-grade titanium dioxides on the efficiency of hindered piperidine stabilizers in a model oxidative reaction. Polym Degrad Stab 2006;91(4):931–9.] stabilizers and it follows that Cyasorb 3529 is a powerful retarder of thermal oxidation.

Process efficiency and long‐term performance of α‐tocopherol in film‐blown linear low‐density polyethylene

Abstractα‐Tocopherol was compared with a commercial phenolic antioxidant (Irganox 1076) as a long‐term and process antioxidant in film‐blown and compression‐molded linear low‐density polyethylene. The antioxidant function of α‐tocopherol was high in the film‐blown material, especially in the processing, according to oxygen induction time measurements with differential scanning calorimetry. The residual content of α‐tocopherol after processing, determined with chromatographic techniques, was less than that of the commercial phenolic antioxidant in both the film‐blown and compression‐molded materials. The process stabilizing efficiency was nevertheless higher for the material containing α‐tocopherol. During the long‐term stabilization, the efficiency of α‐tocopherol was less than that of the commercial phenolic stabilizer Irganox 1076 in the thin films, according to chemiluminescence and infrared measurements. The long‐term efficiency in the compression‐molded samples stabilized with α‐tocopherol or Irganox 1076 was equally good because of the low loss of both α‐tocopherol and Irganox 1076 from the thicker films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2427–2439, 2005

A kinetic study on the inhibitory action of sympathomimetic drugs towards photogenerated oxygen active species. The case of phenylephrine

Kinetics and mechanism of the aerobic Riboflavin (Rf, vitamin B2) sensitized photodegradation of Phenylephrine (Phen), a phenolamine belonging to the sympathomimetic drugs family, has been studied in water, employing continuous photolysis, polarographic detection of oxygen uptake, steady-state and time-resolved fluorescence spectroscopy, time-resolved IR-phosphorescence and laser flash photolysis. Results indicate the formation of a weak dark complex Rf–Phen, with an apparent association constant of 5.5 ± 0.5 M −1, only detectable at Phen concentrations much higher than those employed in the photochemical experiments. Under irradiation, an intricate mechanism of competitive reactions operates. Phen quenches excited singlet and triplet states of Rf, with rate constants of 3.33 ± 0.08 and 1.60 ± 0.03 × 10 9 M −1 s −1, respectively. With the sympathomimetic drug in a concentration similar to that of dissolved molecular oxygen in water, Phen and oxygen competitively quench triplet excited Rf, generating superoxide radical anion and singlet molecular oxygen (O 2( 1Δ g)) by processes initiated by electron- and energy-transfer mechanisms respectively. As a global result, the photodegradation of the vitamin, a known process taking place from its excited triplet state, is retarded, whereas the phenolamine, practically unreactive towards these oxidative species, behaves as a highly efficient physical deactivator of O 2( 1Δ g). The phenolamine structure in Phen appears as an excellent scavenger of activated oxygen species, comparatively superior, in kinetic terms, to some commercial phenolic antioxidants.

Technologiczne aspekty oddzialywania przeciwutleniaczy fenolowych z nadtlenkiem dikumylu w procesach sieciowania poliolefin

Results of UV/VIS investigations of the interactions between dicumyl peroxide and two commercial phenolic antioxidants (Fig. 1), used in the processes of polyolefins' crosslinking, were presented. It was found that at temperature as low as 90 ° C, significantly lower than the temperature of rapid decomposition of peroxide investigated, the reactions between peroxide and phenolic antioxidant proceed. As a result, the colored compounds are formed (Fig. 2) what can be undesirable in some applications of crosslinked polyolefins. These reactions undergo in an air or nitrogen atmosphere. Presence of oxygen intensifies their courses. Results of the work can be useful in practice because disadvantageous phenomena can be minimized by proper selection of parameters of technological process.

Comparison of Antioxidant Activity Between Aromatic Indolinonic Nitroxides and Natural and Synthetic Antioxidants

In view of the possible employment of nitroxide compounds in various fields, it is important to know how they compare with other synthetic antioxidant compounds currently used in several industries and with naturally occurring antioxidants. To address this issue, the antioxidant activity of two aromatic indolinonic nitroxides synthesized by us was compared with both commercial phenolic antioxidants (BHT and BHA) and with natural phenolic antioxidants (α-hydroxytyrosol, tyrosol, caffeic acid, α-tocopherol). DPPH radical scavenging ability and the inhibition of both lipid and protein oxidation induced by the peroxyl-radical generator, AAPH, were evaluated. The results obtained show that overall: (i) the reduced forms of the nitroxide compounds are better scavengers of DPPH radical than butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) but less efficient than the natural compounds; (ii) the nitroxides inhibit both linolenic acid micelles and bovine serum albumin (BSA) oxidation to similar extents as most of the other compounds in a concentration-dependent fashion. Since the aromatic nitroxides tested in this study are less toxic than BHT, these compounds may be regarded as potential, alternative sources for several applications. The mechanisms underlying the antioxidant activity of nitroxides were further confirmed by UV–Vis absorption spectroscopy experiments and macroscale reactions in the presence of radicals generated by thermolabile azo-compounds. Distribution coefficients in octanol/buffer of the nitroxides and the other compounds were also determined as a measure of lipophilicity.

Evaluation of novel 4,4-dimethyloxazolidine derivatives as thermal and UV stabilisers in linear low density polyethylene (LLDPE) film

Three novel doxyl derivatives have been synthesised and characterised as thermal and light stabilisers for linear low density polyethylene (LLDPE). The three additives (C2, C3, U2) when mixed with a commercial phenolic antioxidant Irganox 3114, gave rise to good thermal antioxidant activity, similar to that of a commercial HALS (Hindered Amine Light Stabiliser), Chimassorb 944. Furthermore, when the additives are mixed with a mixture of a commercial antioxidant and HALS synergism is observed. On the other hand whilst the three additives exhibit a light stabilising function they are not as exceptional as the commercial mixture of HALS and phenolic antioxidant. Using FTIR analysis interesting comparisons are made between the respective growths in various functionalities. During thermal oxidation the hydroxyl and double bond vinyl and trans-vinylene absorbances (909 and 966 cm −1) begin to growth at the same time and rate as the carbonyl groups. In the case of samples under UV oxidative conditions the ratio of the 1718/1774 keto/peracid value in is lower than that observed on thermal oxidation. Inferences are made form the relative rates of growth and decay in the double bond and carbonyl group concentrations and how these relate to the relative stabilities of the stabilised films.

The comparative effectiveness of some commercial antioxidants as studied by lyoluminescence

Lyoluminescence is an interesting tool to study the reactivity of different antioxidants towards the free RȮ 2 radicals which are frequently involved in the oxidative processes of different polymeric materials. In the present paper we have used lyoluminescence to characterize the effectiveness of the following commercial phenolic antioxidants: Topanol OC, Irganox 1076, Ionox 220, Etanox 330, Cyanox 2246 and Irganox 1010. The antioxidant efficiency of these products in the thermal oxidation of polyethylene was compared on the basis of the results of oxyluminescence and thermal analysis methods.

Flash photolysis and antioxidant activity

The photo-chemical behaviour of a number of mono- and polyfunctional commercial phenolic antioxidants has been examined using kinetic micro-second flash photolysis. The technique provides useful information on the relationship between antioxidant structure and the efficiency of phenoxy radical production. The kinetics of decay of the phenoxy radicals are also found to be dependent on structure. Mono-functional antioxidants give phenoxy radicals which decay by a second-order process whereas polyfunctional antioxidants give phenoxy radicals that decay by a first-order process. In the former case dimerisation to give bisphenolic coupling products is observed whereas, with the latter, this process is sterically inhibited. The value of flash photolysis as a probe for studying antioxidant activity is discussed.

Thermoplastic Polyurethane Elastomer Melt Polymerization Study

Abstract It is concluded from the present study that the slightly modified Brabender PlastiCorder torque rheometer is well suited to the study of thermoplastic polyurethane elastomer melt polymerization. The instrument is sensitive and responsive enough over a broad range to sense and record continuously even small changes in polymerizate temperature and viscosity as a function of time. This capability has enabled us to follow the full course of such polymerizations, with the exception of the final polymer maturation process which customarily is effected in the quiescent state. In our study, the effects of several polymerization variables were clearly and quantitatively apparent, including the effects on the course of polymerization and its degree of: macroglycol acidity; antioxidant (stabilizer); temperature; catalyst; polymer composition; presence of shortstop; and reactant balance. The results demonstrate the known acid catalysis of the hydroxyl-isocyanate reaction as well as polyurethane molecular weight modification by polyester glycol acidity. The inclusion of a commercial phenolic antioxidant in the polymerization charge did not have any obvious effect on the course of polymerization but may have limited degree of polymerization somewhat. Increased urethane content greatly speeds the viscosity increase, demonstrating urethane autocatalysis as well as its viscosity contribution, and even low stannous octoate catalyst levels appreciably speeded the inherently rapid polymerization. The shortstopping action of fugitive and persistent primary alcohols is prompt and effective, but excessive amounts produce some irreversible polymer reversion as they readjust the polymer chain molecular weight distribution present in maintaining the urethane equilibrium. This equilbrium also showed clear response to polymerization temperature, reversible urethane dissociation reducing viscosity with increasing temperature. The effect of polymerization reactant imbalance was readily apparent in the appreciably reduced rate and degree of polymerization attending minor isocyanate deficiency. Mastication experiments in the PlastiCorder show dried preformed polyurethane elastomer to drop quickly to viscosity levels much below that reached by the same compositions during polymer formation. The viscosity loss of the former is attributed to polyurethane chain rupture promoted by virtual network restrictions to chain slippage, while the virtual network has not yet developed in the forming polymer.