Oxidation Induction Time Value Research Articles

Thermo‐mechanical properties of polyethylene composites filled with soapstone waste

AbstractIn this study, soapstone waste originated from craftsmanship activities was used as an alternative filler (0–30 wt%) for a high‐density polyethylene (PE) matrix. The aim of this paper is to understand the effect of the filler particles on crystallinity, thermal stability and thermo‐mechanical properties of this newly developed composite material. Physico‐chemical characterization was performed by x‐ray diffraction (XRD) and Fourier‐transform infrared (FTIR) spectroscopy. Thermogravimetric analysis (TGA), oxidation induction time (OIT) and dynamic mechanical thermal analysis (DMA) were performed to assess the effect of the filler on the themo‐mechanical properties of PE. Thermal stability, measured by TGA, was enhanced, while OIT values reduced with filler content. A significant increase on the storage modulus of the composites (up to 148% in comparison with unfilled PE) was observed and this reinforcing effect was even more prominent at higher temperatures. XRD analysis revealed that the degree of crystallinity improved significantly with soapstone loading, which explains the substantial increase in stiffness observed. Increased crystallinity is also associated with higher strength, reduced residual stress, and better dimensional stability of end products, which can be particularly attractive for pressure pipe applications.

Synthesis of a novel organic-inorganic hindered phenol antioxidant derived from polyhedral oligomeric silsesquioxane and its anti-oxidative behavior in polypropylene

To explore antioxidants with high anti-aging efficiency and admirable anti-extraction ability, a novel organic-inorganic hindered phenol antioxidant (AO-POSS) derived from polyhedral oligomeric silsesquioxane (POSS) was successfully synthesized via a nucleophilic substitution reaction. Chlorinated polyhedral oligomeric silsesquioxane with 8 silicon cores was first synthesized by hydrolysis-polycondensation of (3-chloropropyl)trimethoxysilane and further used for preparing AO-POSS by reacting with the sodium salt of hindered phenolic precursor 3-(3,5-Di‑tert‑butyl‑4-hydroxyphenyl)propionic acid (AO). According to the 29Si-NMR spectra, the T8 cores of Cl-POSS occurred cage-rearrangement under the catalytic effect of propionate anion to produce a thermodynamically stable mixed product, AO-POSS (T8, T10, and T12: 23.8 %, 60.5 %, and 15.7 %). When AO-POSS was incorporated into polypropylene (PP), the oxidation induction time (OIT) of the PP/AO-POSS compound (15.8 min) was slightly longer than that of the PP/1010 compound (13.8 min) at the same molar amounts of hindered phenols. Furthermore, the OIT value of PP/AO-POSS/168 (50.7 min) was obviously higher than that of PP/1010/168 (38.1 min), pointing out the enhanced levels of positive synergism between AO-POSS and secondary antioxidants in inhibiting PP oxidation degradation. Hence, it is apparent that AO-POSS possesses high thermo-oxidative stability and anti-aging efficiency in PP. Notably, even after 48 h of Soxhlet extraction, the OIT value of PP/AO-POSS was retained at 69.5 %, while that of PP/1010 was only 32.2 %, indicating the much better anti-extraction ability of AO-POSS.

Influence of Seeds' Age and Clarification of Cold-Pressed Raspberry (Rubus idaeus L.) Oil on the DSC Oxidative Stability and Phase Transition Profiles.

After cold-pressing, small particles of seed residue remain in raspberry seed oil (RSO), even after passing it through cold filtration. The removal of the remaining seed residue is rather an alternative option to improve the visual properties of RSO. This study investigated the influence that the seeds' age (0, 10, 20 months) and clarification process after pressing has on the oxidative stability and phase transition of RSO by means of differential scanning calorimetry (DSC). The results proved that the oil centrifugation process reduces the DPPH radical scavenging activity and oxidative stability measured by p-anisidine value (p-AnV) and DSC oxidation induction time (OIT) at 120 °C of all RSO samples, regardless of the age of the seeds (p ≤ 0.05). No significant differences were observed on the DSC melting and crystallization properties at 1 °C/min after the oil clarification by centrifugation (p > 0.05). The storage time of raspberry seeds, i.e., 10 and 20 months after expiry date, influenced the quality deterioration of RSO, as measured by higher p-AnV, lower DPPH, and OIT values (p ≤ 0.05). The results presented provide new information about oil production processing, suggesting that producers should reconsider giving up the clarification process of oil, since it lowers all quality parameters.

Effect of natural carbon filler on thermo-oxidative degradation of thermoplastic-based composites

Thermo-oxidative degradation of thermoplastic-based composites filled with two types of carbon filler including bituminous (Pittsburgh No.8, P8) and sub-bituminous (Powder River Basin, PRB) coals were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. Oxidation induction time (OIT) and activation energy (AE) for coal plastic composites (CPCs), HDPE, and commercially available wood plastic composites (WPCs) were determined using isothermal and isoconversional kinetic methods. OIT values for CPC increased with coal content, indicating higher thermo-oxidative stability. AE values obtained using isothermal method were 52–116 kJ/mol for all CPC formulations, 32 kJ/mol for HDPE, and 33–114 kJ/mol for WPCs. AEs for CPCs obtained using isoconversional methods were not constant but rather dependent on the degree of degradation with CPC/ P8 coal possessing higher overall AE. Incorporating coal into HDPE increased thermo-oxidative stability of the resulting composite, indicating coal potentially acts as a natural primary and secondary antioxidant for polymer materials.

Assessment of antioxidant resistance to thermal - oxidative degradation of stabilized polybutadiene binder

polybutadiene is the most common polymeric binder for composite solid propellants. This polymer suffers from oxidative degradation reactions on storing with deterioration in mechanical properties. Certain anti-oxidant materials can retard such reaction offering enhanced aging characteristics. In this study, two different primary antioxidants including phenol-based (AO2246) and amine-based (Flexzone 6H) were employed to stabilize polybutadiene polymer. Oxidation induction time (OIT) was evaluated using isothermal DSC. High OIT value means high resistance to oxidative degradation. The impact of anti-oxidant on mechanical properties was evaluated using shore A. Flexzone 6H significantly improved binder oxidative stability with an increase in OIT value by 20 folds with significant decrease in oxidation enthalpy. Flexzone 6H can offer enhanced resistance toward oxidative reactions; as it can act as efficient H atom donor to break down chain degradation reaction. Additionally, the three stabilized aromatic rings can capture free radicals. AO2246 enhanced the binder mechanical characteristics during aging at 80 0C using Shore A test. In the meantime, AO2246 could enhance the mechanical properties due to its integration into the polymeric matrix due to –OH functional groups. The two anti-oxidants demonstrated controversy effects. Whereas Flexzone 6H offered enhanced resistance to oxidative degradation; AO2246 offered enhanced mechanical properties.

Hindered phenolic antioxidants as heat-oxygen stabilizers for HDPE

The effects of four hindered phenolic antioxidants in the short-term heat-oxygen stability of High-Density Polyethylene (HDPE) was evaluated by the Melt Flow Rate (MFR) and Oxidation Induction Time (OIT) analyses. The results showed that Irganox 1330 and Irganox 1010 had more excellent processing property and oxidation resistance behavior in HDPE than Irganox 1024 and Irganox 3114. The OIT values of HDPE with Irganox 1330 and Irganox 1010 were up to 97.25 min and 89.73 min respectively. The long-term accelerated heat-oxygen stability tests of HDPE containing hindered phenolic antioxidants were carried out at 110°C in deionized water pressurized with pure oxygen at a pressure of 10 MPa. The characterization of the long-term heat-oxygen stability was performed by Fourier Transform Infrared (FTIR), Differential Scanning Calorimetry (DSC) and tensile testing. However, the results exhibited that the aging resistance of HDPE containing Irganox 1010 was inferior to that of HDPE containing Irganox 1024 and Irganox 3114, which is quite contrary to their short-term effect on HDPE stabilization. It may be speculated that the ester groups of Irganox 1010 undergo hydrolysis during the long-term heat-oxygen stability tests, leading to the formation of 3-(3,5-ditert-butyl-4-hydroxy-phenyl) propanoic acid and pentaerythritol.

Study on the thermal stability of stabilized and unstabilized low-density polyethylene films

The oxidation and thermal stability of low-density polyethylene (LDPE) films (stabilized and unstabilized) used as greenhouse covering have been investigated. A mixture of kaolin, UV absorber, hindered amine light stabilizers (HALS) and heavy metals was used to stabilize LDPE films; these films were also compared with unstabilized LDPE films. Both films were exposed to natural weathering in Laghouat, Algeria. The oxidation resistance of unstabilized specimens for different ageing periods was determined by measuring the oxidation induction time (OIT) at 180 °C. It has been found that the highest OIT value was obtained for the unaged film and the values decline with ageing time. On the other hand, the stabilized specimens showed a significant stability under the conditions of OIT determination experiments. Furthermore, the oxidation resistance of these samples was evaluated by measuring the oxidation onset temperature (OOT). The results obtained showed that the OOT of the stabilized films ranges from 219 to 236 °C. Finally, a comparative analysis of the thermal stability results of both films was conducted. The activation energy of the photodegradation process of the both films was calculated by using TGA thermograms following the isoconversional approach. The results revealed that the stability of the stabilized specimens diminishes with ageing time and that the stabilizer additives improve the thermal stability of LDPE films. The influence of the photooxidation on the degree of crystallinity (based on DSC and WAXS techniques) of both films was also reported. Generally, there is a strong correlation between TGA, OIT, OOT, UV and FTIR results.

Effects of Post Anthesis Foliar Application of Sodium Selenite to Soybeans (Glycine max): Lipid Composition and Oil Stability.

This study aimed at determining whether applying selenium to soybean plants affected composition and oil oxidative stability of the seeds. Soybean was cultivated and sodium selenite (Selenite) added by foliar application (0, 200, or 300 g Selenite/Ha). Physical and chemical characterization was performed on the harvested seeds (thousand seed weight, bulk and true densities, fat, fiber, ash, protein, nitrogen free extract and selenium content). Soybean oil was tested in terms of Oxidation Induction Time (OIT), fatty acid, tocopherols, phytosterols, density, refractive index and saponification and iodine values. All seeds showed similar composition: crude fat (around 20%) and crude fiber (from 8.4 to 9.3%). Control seeds and those treated with 200 g Selenite/Ha contained higher protein concentration (37%), compared to the 300 g treatment (35.9%). All seeds showed similar ash content (7%). OIT values for both treatments were slightly lower (from 39.1 to 43.7 min) compared with 45.02 min in the control. Polyunsaturated fatty acids were higher for the 300 g Se/Ha (50.2%) compared with 48.2 to 49.4%of the other treatments. All samples showed similar phytosterols and tocopherols concentrations. Results showed that OIT values maintained an inverse relationship with selenium content, suggesting that foliar fertilization enhanced oil oxidation or acted as a pro-oxidant at the applied rates.

Effect of Processing and Radiation Exposure on the Structure and Properties of Polypropylene

While producing polymers as well as during their processing, a certain amount of stabilizers is introduced into the product, which should ensure polymer properties saving during processing and those of polymer products during storage and operation. However, in cases where medical products based on polypropylene are subjected to radiation sterilization, there are not enough stabilizers in it to save their characteristics during operation. In this regard, we made an assessment of the influence of processing conditions on the properties of polypropylene with a different set of stabilizers in the manufacture of products based on it, in order to assess the degree of influence of each technological operation, including the effects of ionizing radiation during sterilization. Processing and radiation exposure are shown to affect the properties of polypropylene. Nevertheless, the effect of ionizing radiation with an absorbed dose of 40-60 kGy exceeds the negative effect of thermo-oxidative breakdown greatly during the extrusion of PP. Polypropylene containing organophosphorus stabilizers (brand PP 1562R) is more susceptible to breakdown. This is indicated by low values of oxidation induction time, breakdown initial temperature, as well as high values of MFI after exposure to electron radiation. PP brand PP H350FF/1 whose stabilizing complex contains phenol-phosphite antioxidants is more resistant to breakdown during processing and sterilization. For both brands under study, it is apparently necessary to increase the content of stabilizing additives in order to save the properties at the level of the original unexposed material.

Evaluation of the durability of lignin-reinforced composites based on wheat straw/recycled polypropylene blends

The influence of a lignin additive at different loading levels on the surface properties, mechanical, and thermal performance of recycled polypropylene composites reinforced with wheat straw, before and after accelerated weathering, was studied. Eight groups of samples were exposed to an ultraviolet (UV) accelerated weathering tester for a total of 1200 h. The weathered surface morphology, chemical change, and color change were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and chroma meter analyses, respectively. Furthermore, the mechanical properties and oxidation induction time (OIT) were tested. It was shown that the use of lignin had a positive effect in improving mechanical properties and in reducing OIT values of filled composites due to the enhanced fiber/matrix interface bonding and its functions of anti-oxidation. Less fibers were falling off and shallower cracks occurred on the weathered surface of the lignin reinforced composites. The carbonyl index of wheat straw fibers reinforced recycled polypropylene composites (WSF/RPP) with 5 wt% lignin content showed a notable decrease of 4.9% when compared with the growth rate of the control groups. When the stabilizer was introduced to the blends, the mechanical properties and antioxidant capacity of the composites were improved during weathering.

Triple‐faced polypropylene: Fire retardant, thermally stable, and antioxidative

A halogen‐free nitrogen‐rich additive was used to make polypropylene (PP) prepared for three different missions: fire retardancy, thermal stability, and antioxidative properties. The prepared additive was composed of a cyclodextrin, a nanohydroxyapatite, and a poly[[6‐[(1,1,3,3,‐tetramethylbutyl)amino]‐1,3,5‐triazine‐2,4‐diyl][(2,2,6,6‐tetramethyl‐4‐piperidinyl)imino]‐1,6‐hexanediyl[2,2,6,6‐tetramethyl‐4‐piperidinyl)imino] (SABO®STAB) integrated into a unique molecule, namely, BSDH. Fire retardancy performance of BSDH in PP was compared with that of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) commercially available additive in terms of cone calorimeter results. Thermal stabilities of PP/BSDH and PP/DOPO composites were compared by changes observed in pyrolysis activation energy values measured in thermogravimetric analysis under nitrogen atmosphere at various heating rates. Flame retardancy of PP/BSDH composite was reflected in a drop in the peak of Heat Release Rate by ca. 31% with respect to neat PP. Very interestingly, the results show that BSDH additive retarded thermal oxidation of PP macromolecular chains when compared with DOPO commercially available flame retardant, as signaled by a rise in oxidation induction time value as well as an increased early‐stage activation energy needed for thermal decomposition of PP in the presence of BSDH. J. VINYL ADDIT. TECHNOL., 25:366–376, 2019. © 2019 Society of Plastics Engineers

Synthesis, Characterization, and Performance Evaluation of Sulfur-Containing Diphenylamines Based on Intramolecular Synergism.

To obtain novel structural antioxidants that have different antioxidant mechanisms, four 2-(alkylthio)-N-(4-(phenylamino)phenyl)acetamides 2a–d as dual functional antioxidants are designed, synthesized, and confirmed by 1H-NMR, FTIR, MS, and elemental analysis. The antioxidant behavior of compounds 2a–d as additives of base oil triisodecyl trimellitate (TIDTM) is evaluated by non-isothermal and isothermal DSC analyses. The results showed all compounds can greatly increase the incipient oxidation temperature (IOT) and oxidation induction time (OIT) of TIDTM, especially, compound 2c exhibited an OIT value of 72.5 min at 230 °C, which is almost 28 times the length of TIDTM. Moreover, compounds 2a–d do not affect the tribological performance of TIDTM. The mechanism of antioxidants involved an intramolecular synergism are proposed. This work demonstrates compound 2c can be used as a novel potential antioxidant additive of TIDTM; in addition, it would inspire the emergence of highly potent antioxidants with different antioxidant mechanisms.

Enhancement of thermal and mechanical properties of high density polyethylene using commercial clays

The properties required for rainwater containers and pipes were discussed. This work aimed at improving the overall properties of high density polyethylene (HDPE) with commercially available clays for rainwater harvesting system. Ten types of clay were respectively incorporated into HDPE matrix via melt extrusion. Morphological, structural, mechanical and thermal characterizations were performed. The findings show that the clay dispersion state was determined by the thermal stability of their organomodifier. Thermally stable organomodifier dimethyl di(hydrogenated tallow) (2M2HT) prevents clay aggregation and contributes to clay intercalation. The incorporation of high-aspect-ratio clays containing a thermal stable organomodifier improved the mechanical properties of HDPE. Increased Young’s modulus and tensile strength were obtained by addition of appropriate clays. The oxidative induction time (OIT) of clay-HDPE blends were dramatically decreased by the presence of organomodifiers and contaminants. Only unmodified clay with a low impurity content showed less reduction in OIT values. Lastly, it was found that the thermal degradation behavior of blends was related to the dispersion state and the impurity content of clays.

Antiradical Ability of Dendrimer‐Bridged Hindered Phenol and Its Antioxidant Property in Polyolefin

AbstractAntiradical abilities of 1.0 generation dendrimer bridged hindered phenols (1.0G dendritic phenols) are studied by the DPPH method and antioxidant properties in polyolefin are evaluated by melt flow rate (MFR), oxidation induction time (OIT) and accelerated thermal aging test. The results indicate that the antioxidant properties are affected not only by the chemical structure but also by the reaction system for series of 1.0G dendritic phenols. The antiradical ability decreases with increasing of the length of the bridged group of 1.0 G dendritic phenols, and the antiradical abilities at steady state reaction time are better than those at fixed reaction time of 30 min. The reaction of 1.0G dendritic phenols scavenging DPPH free radical belongs to slow kinetic behavior. And 1.0G dendritic phenols have excellent processing property, oxidation resistance behavior and thermo‐oxidative aging resistance in linear low density polyethylene (LLDPE) and polypropylene (PP). The OIT values and the aging coefficient values of polyolefin stabilized with 1.0G dendritic phenols increase with increasing of the length of the bridged group of 1.0G dendritic phenols. The antioxidant abilities 1.0G dendritic phenols in LLDPE are superior to those in PP.

The synergistic mechanism of thermally reduced graphene oxide and antioxidant in improving the thermo-oxidative stability of polypropylene

The feasibility of using thermally reduced graphene oxide (TrGO) to improve the antioxidative efficiency of commercial antioxidant (3,5-di-tert-butyl-4-hydroxycinnamic acid, AO) on unstabilized polypropylene (PP) was evaluated in terms of the oxidation induction time (OIT) and the initial degradation temperature (Ti). It was found that a synergistic effect exist between AO and TrGO in retarding the degradation of PP in oxygen-containing atmosphere. Compared with that of PP/AO (100/0.5) sample, the OIT value of PP/AO/TrGO (100/0.5/1) composite was almost doubled at 180°C and the value of Ti in air was improved by 37.2°C. As verified by using radical scavenging assay with the 1,1-diphenyl-2-picrylhydrazyl radical, the TrGO sheets exhibited a good radical scavenging capacity. The synergistic stabilization mechanism was attributed to the enhanced dispersion of TrGO sheets in the PP matrix in the presence of 0.5wt.% AO, which could improve the oxygen barrier effect and radical scavenging efficiency of TrGO. This synergistic effect between AO and TrGO can efficiently reduce the concentrations of oxygen and peroxy radicals in the PP matrix, leading to the significant improvement in thermo-oxidative stability of PP/AO/TrG composite.

Effect of high temperatures on antioxidant depletion from different HDPE geomembranes

The effect of elevated temperatures, typically 95–115 °C, on antioxidant depletion from a high-density polyethylene (HDPE) geomembrane (GMB) incubated in air, water and synthetic leachate is examined. It is shown that the antioxidant depletion in synthetic leachate at 95–115 °C is consistent with what would be expected from Arrhenius modeling based on data from lower temperatures (25–85 °C). A similar finding is reached for incubation in air. However, when incubated in water the antioxidant depletion is more complicated. At temperatures above 100 °C a four-parameter exponential model was needed to fit oxidative induction time data that exhibited quite different early-time and later-time depletion rates. The early-time depletion rate decreases with an increase of the temperature while the later-time depletion rates follow the more typical pattern of increasing with increasing temperature. Three additional HDPE GMBs with different antioxidant packages are examined at elevated temperatures in air. The GMB with the lowest initial standard (Std) oxidative induction time (OIT) and without hindered amine light stabilizer (HALS) has the longest antioxidant depletion stage based on Std-OIT at these elevated temperatures. GMBs stabilized with HALS showed only a slight change in their high pressure OIT during the current study. It is shown also that degradation in physical properties can start at Std-OIT values above the residual OIT values.

Contact probe electrochemical characterization and metal speciation of silver LLDPE nanocomposite films

A contact probe methodology, based on the voltammetry of immobilized microparticle approach, is used for characterizing silver species present in linear low density polyethylene (LLDPE) films with different Ag(I)/Ag(0) ratios and silver nanoparticle features usable as food contact polymers. The films displayed characteristic voltammetric features in contact with aqueous acetate buffer, in particular signals for the stripping oxidation of nanoparticulate Ag systems. Significant differences between the studied films were also observed by means of electrochemical impedance spectroscopy and detected at the nanoscopic scale using electrochemical scanning microscopy. Differences in optical and thermal properties of the studied films are associated with the presence of silver nanoparticles. The silver oxidation state as well as nanoparticle size also had influence on the oxidative resistance of the LLDPE films; indeed, films containing cationic silver showed the lowest oxidation induction time value.

Validation of the estimation of oxidation induction time from non-isothermal DSC measurements

In this paper, correctness of the method for estimation of the oxidation induction time (OIT) from a set of non-isothermal DSC measurements is verified for two samples of sunflower oil in the temperature range of 110–160 °C. It can be concluded on the basis of root-mean-square deviations between the experimental and predicted values of OIT in the high-temperature region (above 110 °C) that both the Arrhenius and non-Arrhenian models lead to a very good agreement of the calculated values of OIT with the experimental ones without any statistically significant bias. Moreover, the uncertainties in the predicted values of OIT are practically identical for all three models applied.

Synthesis of a novel sulfur-bearing secondary antioxidant with a high molecular weight and its comparative study on antioxidant behavior in polypropylene with two commercial sulfur-bearing secondary antioxidants having relatively low molecular weight

A novel sulfur-bearing secondary antioxidant with a high molecular weight of 2252 (OS-POSS), successfully synthesized via photoinitiated thiol-ene click reaction, was compared with two commercial sulfur-bearing secondary antioxidants on the stabilization of polypropylene (PP). The results of their oxidation induction time (OIT) via differential scanning calorimeter measurement (DSC) showed that the higher the molecular weight of secondary antioxidant is, the longer the OIT value, whether such sulfur-bearing antioxidant is used singly or in combination with primary antioxidant. The study of their long-term accelerated thermal aging in the air oven at 150 °C displayed that the molecular structure of sulfur-bearing secondary antioxidant, besides molecular weight, is another highly important factor determining the antioxidant efficiency, i.e., physical loss of antioxidants with the relatively low molecular weight may determine antioxidant efficiency, whereas thioether groups having neighboring ester carbonyl moieties may decompose more hydroperoxides with quicker rate.

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.