Oxygen Induction Time Research Articles

Utilization of Silybum marianum extract as a high-performance natural antioxidant for polyethylene

In this study, Silybum marianum extract powder was introduced into low density polyethylene (LDPE) as a primary polyphenolic antioxidant via melt blending method. Two synthetic and commercial polyphenol- and phosphite-based antioxidants (Irganox® 1010 and Irgafos® 168) were also used for comparing the antioxidant efficiency and performance of Silybum marianum extract with commercial ones. A systematic formulation study was achieved by varying the amount of Silybum marianum extract in the range of 0.1–1.0 wt% and the primary:secondary antioxidant ratio. Antioxidant efficiency of Silybum marianum extract was quantified with the oxygen induction time (OIT) and oxidation onset temperature values determined by thermal analysis in a differential scanning calorimeter depending on the compositional variations. Some physical properties of specimens such as transparency, color coordinates, contact angle, and degree of crystallinity values were also examined. It was found that 0.2 wt% of Silybum marianum extract and 0.2 wt% of Irgafos® 168 loaded sample showed an OIT value of 22 min. at 210 °C that could be regarded as a very successful commercial potential. Increasing amount of Silybum marianum extract and Irgafos® 168 significantly improved the oxidation stability of polyethylene under isothermal and non-isothermal conditions. It was also found that introducing Silybum marianum extract, even the loading content of 1.0 wt%, did not alter the transparency and physical properties of LDPE. It has been concluded that Silybum marianum extract can be successfully used as a natural antioxidant in polyolefins and these samples could be used in packaging film applications.Graphical

Ground lemon and stevia leaves as renewable functional fillers with antioxidant activity for high-density polyethylene composites

The development of new sustainable material solutions in the processing of thermoplastic polymers concerns both the application of biopolymers and the use of valorized plant derivatives as fillers and modifiers of petrochemical polymers. Herein, the possibility of using unprocessed raw parts of two commonly used in the food industry leaves, i.e., lemon (LL) and stevia (ST), as active and functional fillers for high-density polyethylene (HDPE) has been verified. The series of composites containing 1, 2, and 5 wt% of ground leaves produced in the melt-mixing process were analyzed for thermal properties (DSC and TGA), and the antioxidant potential of the fillers was evaluated. Verifying the active effect of the ground leaves on the resistance to oxidation in the molten state was carried out by oxygen induction time (OIT by DSC) analysis and oscillatory rheology under steady-state shear conditions combined with spectroscopic (FTIR) carbonyl index (CI) analysis. Studies have shown that the introduction of 5 wt% of both types of leaves allows for a significant increase in the melt oxidation resistance (above 2 times longer OIT concerning HDPE, ~ 35 min) of composites without substantial changes in their crystalline structure and thermal stability. Determined after the long-term rheological measurements in an oxidative atmosphere CI showed 70 and 82% lower values for 5 wt% LL and ST composites compared to unmodified polyethylene.Graphical abstract

Clarifying the effects of comonomer distribution between short and long chains on physical and mechanical properties of ethylenic copolymers

AbstractIn this paper, two Zigler‐Natta catalysts (ZNCs) were used to synthesize a commercially available linear low‐density polyethylene (LLDPE), widely used in the packaging industry, on an industrial scale. The catalysts differ only in their ability to distribute comonomers between short and long chains. Both catalysts were fully characterized in the first section, and two similar ethylene/1‐butene copolymers were made using them. Afterward, the produced copolymers were fully characterized using different techniques; namely, differential scanning calorimetry (DSC), successive self‐nucleation and annealing (SSA), oxygen induction time (OIT), melt flow index (MFI), rheometric mechanical spectroscopy (RMS), and a wide range of mechanical experiments. It was revealed that while the presence of comonomers in short chains can reduce their resistance against oxidation (by more than 30%) and can cause a dramatic change in friction coefficients (by more than 20%), some of the other main mechanical properties of the made copolymers were independent of comonomer distribution between long and short chains. In addition, it was shown that ethylenic copolymers' strain hardening modulus (SHM) takes advantage of the homogenous distribution.

Oxygen Scavenger and Antioxidant LDPE/EVOH/PET-Based Films Containing β-Carotene Intended for Fried Peanuts (Arachis hypogaea L.) Packaging: Pilot Scale Processing and Validation Studies.

The aim of this study was to develop an oxygen scavenger and antioxidant active packaging material for fried peanuts. The packaging solution, which has been made at the laboratory previously, has been developed by cast film extrusion and is composed of low-density polyethylene-ethylene vinyl alcohol-polyethylene terephthalate (LDPE/EVOH/PET)-based films containing β-carotene (CAR). In comparison with film without additive, developed film presented an orange colouring (higher L* and b* values and lower a* values) and an increase in oxygen induction time (OIt) from 4.5 to 14.1 min. The incorporation of β-carotene to the formulation also brings about a significant effect on the thermal stability as maximum degradation temperatures increased around 1%. Regarding the oxygen absorption capacity of the films, values of 1.39 ± 0.10 mL O2 per g of film at laboratory scale and 1.7 ± 0.3 mL O2 per g of multilayer (ML)/LDPE_CAR were obtained, respectively, after 3 days, proving the suitability of the packaging solutions as oxygen absorbers. To validate the packaging solution, the oxidative stability of fried peanuts packed in fabricated multilayer β-carotene bags was evaluated for 3 months at 40 °C. The hexanal content remained constant during this period. Meanwhile, peanuts packed in ML without β-carotene increased their hexanal content to 294%. This fact indicated a lower extent of oxidation in fried peanuts compared to food samples packaged in control films, suggesting the potential of ML/LDPE_CAR films as sustainable and antioxidant food packaging systems to offer protection against lipid oxidation in foods. Sensory evaluation confirmed that ML/LDPE_CAR films provided the peanut samples with an extra aroma due to the volatile degradation products of β-carotene (such as β-cyclocitral or 6-methyl-5-hepten-2-ol).

Chemosensory Device Assisted-Estimation of the Quality of Edible Oils with Repetitive Frying.

This study investigated chemosensory degradations of soybean and canola oils with repeated frying in order to estimate the quality of the oils. Methods: Chemical parameters including oxygen induction time, acid value, p-anisidine value, malondialdehyde, and total polar compounds were measured. Electronic nose and electronic tongue analyses were performed to assess sensory properties. Multivariate analyses were employed to investigate relationships among tastes and volatile compounds using principal component analysis (PCA) and Pearson’s correlation analysis. Results: All chemical parameters increased with repeated frying in both oils. Electronic nose analysis found ethyl butyrate, 2-heptenal, and 2,4-pentanedione as major volatiles for soybean oil and ethyl butyrate and linalool for canola oil. As the numbers of frying increased, all volatiles showed an increased concentration in various extents. In multivariate analyses, ethyl butyrate revealed strong positive correlations with sourness, umami, and sweetness, and umami showed strong positive correlations with sourness and saltiness (p < 0.05). PCA confirmed that in PC1 with 49% variance, sourness, saltiness, and umami were at similar rates while acetyl pyrazine, 2,4-pentadieone, and 1-octanol were found at similar rates. Canola oil was chemically more stable and less susceptible to deterioration in all chemical parameters compared to soybean oil, resulting in a relatively better quality oil when repeatedly fried. Conclusion: The results suggested that minimum repeated frying (5 times) degrades chemosensory characteristics of both oils, thereby compromising their quality. The findings of this study will be utilized as a foundation for quality control of fried foods in food industry, fried food development, and fast-food industry.

Accelerating effect of pigments on poly(acrylonitrile butadiene styrene) degradation

Pigments such as iron oxides are readily used in combination with polymers and evaluating their influence on polymer durability is important to successfully evaluate lifetime of modern polymer products. This work presents heat-treatment at 60 °C of poly(acrylonitrile butadiene styrene) (ABS) compounded with 18 different pigments, with focus on five iron and three copper complex pigments loaded in ABS. The pigments were shown to have an catalysing effect on the thermo-oxidative degradation of ABS, specifically the 1,4-poly(butadiene) phase leading to PB-phase crosslinking, resulting in embrittlement of the polymer. Attenuated total reflectance Fourier transform infrared spectroscopy showed that the oxidation of 1,4-poly(butadiene) was accelerated about six-fold after 1440 h at 60 °C, 50%RH when ABS was compounded with iron oxide based pigments (e.g. PBl11) compared to pure ABS. The degradation of the poly(butadiene) rubbery phase caused ABS to become brittle, demonstrated as a lowered strain a break and impact toughness. The impact toughness of ABS decreased up to four times more when compounded with some iron oxide and copper complex pigments, compared to pure ABS after heat-treatment at 60 °C for 1440 h. However, it was noted that some iron- and copper based pigments did not cause catalytic degradation of ABS, which may be a result of lowered surface area, chelation and sterically hindering of the metal atom. Differential scanning calorimetry oxygen-induction time was utilized to screen the ABS-pigment combination before ageing, and an oxygen-induction time below 10 min lead to significantly increased degradation of the poly(butadiene) phase in ABS.

Linking Antioxidant Depletion with Material Properties for Polyethylene Pipes Resins

Plastic pipes used in gas distribution networks are typically made from polyethylene (PE) and are stabilized against degradation by antioxidants. Over time, the antioxidant is consumed and the polymer integrity can become compromised. The rate of antioxidant depletion can be dependent on the specific grade of PE and the surrounding environment. In this research, the crystallinity, tensile strength, Young's modulus, and strain at break were measured for the four most commonly used PE pipe resins in the Australian natural gas distribution network as a function of antioxidant content. A relationship between the changes in material properties with antioxidant consumption was established. By measuring the carbonyl index (CI), which quantifies the amount of degradation products present, and linking this with the oxygen induction time (OIT), it was found that three clear regions exist for all investigated PE resins. These distinct regions of the OIT–CI relationship correlate with regions of substantially different rate of change in material properties, and hence indicate a measure of the integrity of the PE. POLYM. ENG. SCI., 60: 323–329, 2019. © 2019 Society of Plastics Engineers

Polyethylene containing antioxidant moieties exhibiting high thermal-oxidative stability for high temperature applications

A new class of polyethylene-bonded antioxidants (PE-HP), containing several hindered phenol (HP) groups located along the polymer chain, has been prepared and investigated in this paper. The homogeneously distributed HP groups not only provide polymer stability but also form a completely polymer network under elevated temperatures. In a TGA comparative test, the PE-HP copolymer with 1.1 mol% HP concentration demonstrates no weight loss after heating at 190 °C in air for 1000 min, while the commercial HDPE exhibits weight loss within 100 min. A standard ASTM oxygen induction time (OIT) test also shows heat flow to commercial HDPE after 15 min at 190 °C in air, while the PE-HP copolymer with 1.1 mol% HP groups shows a complete flat OIT line up to 230 min, without any detectable onset heat flow into the sample. This new PE-HP copolymer shall expand HDPE application to high temperatures (>150 °C).

Melt stabilization of PE with natural antioxidants: Comparison of rutin and quercetin

The stabilization effect of a flavonoid type natural antioxidant, rutin, was compared to that of quercetin in polyethylene. Additive concentrations changed between 0 and 500 ppm in several steps and also 1000 ppm Sandostab PEPQ phosphorus secondary stabilizer was added to each compound. Stabilization efficiency was determined by changes in vinyl group content, melt flow rate, oxygen induction time, color and the consumption of the secondary antioxidant during multiple extrusions. The results showed that rutin is as efficient melt stabilizer as quercetin used as reference. On the other hand, rutin has a deteriorating effect on the stability of the polymer at small concentrations and partially decomposes during processing. The comparison of bond dissociation enthalpies indicated that the substitution of the hydroxyl group in the ring C of quercetin by saccharide moieties increases their value, but the small increase does not influence the efficiency of the stabilizer. FTIR and DSC measurements indicated the interaction of the natural antioxidant and the phosphonite secondary stabilizer, and the development of interactions was confirmed by molecular modeling. Mainly hydrogen bonds and aromatic, π electron interactions develop between the hydroxyl groups in ring A and the POC group of the phosphonite, as well as between the aromatic rings of PEPQ and the flavonoids, but they do not influence the stabilization efficiency of the antioxidants.

Natural antioxidants as melt stabilizers for PE: Comparison of silymarin and quercetin

The stabilization effect of two flavonoid type natural antioxidants, silymarin (Si) and quercetin (Q), was compared in polyethylene (PE). Additive concentrations changed between 0 and 500ppm in several steps and 1000ppm Sandostab PEPQ phosphorus containing secondary stabilizer was also added to each compound. Stabilization efficiency was determined by changes in functional group (vinyl, residual PEPQ) content, melt flow rate (MFR), oxygen induction time (OIT), color and the consumption of the secondary antioxidant during multiple extrusions. The results showed that silymarin is a much less efficient stabilizer in polyethylene than quercetin. The consumption of vinyl groups is faster, melt flow rate and residual stability is smaller in its presence. Silymarin contains less active phenolic hydroxyls than quercetin, but comparison on equal molar basis also shows the inferiority of the compound. The difference can be partially explained by the larger bond dissociation enthalpies of the hydrogens in silymarin, but this antioxidant also accelerates the consumption of the phosphorous secondary stabilizer that must contribute to its smaller efficiency as well. DSC measurements indicate the interaction of the two compounds probably leading to the faster consumption of the phosphorous antioxidant and poor stabilization. Unlike quercetin and dihydromyricetin, the flavonoid type natural antioxidants studied earlier, silymarin is not a good candidate as stabilizer for practical applications.

Ferulic Acid-Based Bis/Trisphenols as Renewable Antioxidants for Polypropylene and Poly(butylene succinate)

Green chemistry principles recommend the use of renewable feedstocks and biocatalysis to decrease environmental impact of chemicals manufacturing. In this scope, three ferulic acid-based bisphenols and one trisphenol were synthesized using enzymatic catalysis. Their antioxidant activity at polymer processing and service temperature was investigated in polypropylene (PP) and polybutylene succinate (PBS), and benchmarked against the commercial antioxidant Irganox 1010. The analysis of the oxygen induction time of the polymer degradation at high temperatures showed that Irganox 1010 was more efficient to protect PP than the ferulic acid-based bis/trisphenols, whereas, in the case of PBS, the biobased antioxidants, and in particular tris-O-dihydroferuloyl glycerol (GTF), were more efficient. FT-IR analysis of neat and formulated PP with different antioxidants stored for 2 years at room temperature showed no degradation. Aging studies of PBS at room temperature in dry atmosphere showed that all antioxidants had an equal stabilizing effect on the molecular weight averages of the polymer. In conclusion, ferulic acid-based antioxidants can be efficient primary antioxidants for the thermo-oxidative stabilization of polymers.

熱・放射線同時照射した難燃EPRケーブル絶縁体の劣化加速倍率に関する検討

Flame-retardant ethylene-propylene-diene rubbers were subjected to acceleration aging with simultaneous heat and radiation in the air to evaluate the acceleration factor. Mechanical properties under various dose rates, temperatures, and degradation time (0-1050 Gy/h, 80-120°C, 0-42481 hours) were measured to find the optimal shift factor to minimize the data scattering. The estimated shift factor was applied to the oxygen induction time which may correspond to remaining amount of antioxidants. Obtained aging characteristics were found to suggest that the degradation proceeds after consumption of antioxidants. The present study also revealed that the optimum shift parameter of the degradation process may also be applied to aging characteristics obtained under low oxygen pressure conditions.

Dodecyl gallate as a pro-ecological antioxidant for food packing materials

Electrochemical oxidation of dodecyl gallate (lauryl gallate), the main monomer flavanol found in green tea, was investigated on platinum electrodes using cyclic voltammetry (CV) and differential pulse (DPV) methods. The rate constant, electron transfer coefficient and diffusion coefficients were determined for dodecyl gallate electrochemical oxidation. The oxidation mechanism proceeds in sequential steps related to the hydroxyl groups in the aromatic ring of dodecyl gallate. The confirmed antioxidant activity of lauryl gallate justified its use in polymers, for instance, in an environment-friendly stabiliser aimed at improving the resistance to aging of elastomeric materials. Based on energy change during deformation, cross-linking density and oxygen induction time in the TG method, we confirmed the high antioxidant activity of lauryl gallate in polymers. Moreover, the research on biodegradation confirmed the environmentally friendly interest of the antioxidant by the fact that it increases the susceptibility of the elastomeric materials to disintegration by mildew mushrooms.

Stabilized polypropylene synthesis using supported titanium catalyst system in presence of phenolic compounds

Stabilized polypropylene synthesis is carried out using supported titanium catalyst system in presence of phenols. The effect of phenolic compounds such as 2,2′-methylenebis(4-tert-butyl-6-methylphenol) (PH1) and 4,4′-methylenebis(2,6-di-tert-butylphenol) (PH2) is studied on the productivity and stereospecificity of catalyst system as well as on molecular weight characteristics. The extent of stabilization of PP resin by phenolic compounds for oxidative degradation is determined by measurement of oxygen induction time. Molecular weight and b color change are also investigated before and after thermal aging. The catalyst productivity was found to be unaffected by the concentration of phenolic compounds in the studied range. The thermal stability of the polymer resin is, however, found to be dependent on the nature of phenolic compound. The masked PH1 phenolic compound showed better antioxidant characteristic as compared to PH2.

Study on the Structure of Peroxide Cross-Linked Polyethylene Pipes with Several Stabilizers

Cross-linked polyethylene (PEX) pipes used in hot water supply are required for high mechanical strength and high creep resistance at high temperature. Especially PEX-a pipes which are made by peroxide cross-linking have better performance, such as creep resistance and thermal shock resistance than the pipes made by the other cross-linking method. Because the PEX-a pipes indicate the higher cross-link degree as compared with the other PEX pipes. In this study, the PEX-a pipes which were mixed with several stabilizers were tested to evaluate the effects on cross-link degree and the oxygen induction time. And also they are evaluated with the chlorine aqueous solution by the performance of the long-term hydrostatic pressure test and the long-term hydro dynamic pressure test. As a result, it was found that the combination of antioxidants for PEX-a pipes plays an important role to prolong the oxygen induction time without inhibiting the cross-linking. From the results of the 1H pulsed NMR measurement over the melting point of polyethylene, it was found that each peroxide PEX pipe with different antioxidant combinations indicated the different proportion and crosslink density of cross-linked region, in addition, that these pipes had the effective structure of cross-linking for the hydrostatic and hydrodynamic pressure test with the chlorine aqueous solution. Therefore, it was considered to be useful results for studies of the stricture of cross-linking of polyethylene.

Synthesis of triphenyl phosphine oxide‐containing polymers via atom transfer radical polymerization

AbstractBis[(4 ‐β‐(2‐bromopropanoate)ethoxy)phenyl]phenylphosphine oxide was used for the first time as the initiator of atom transfer radical polymerization of styrene and methyl methacrylate in the presence of CuBr/N, N,N′, N″, N″‐pentamethyldiethylenetriamine as catalyst/ligand and dimethyl sulfoxide as solvent. The presence of phosphine oxide linkages in the backbone gives the polymers special properties; low Tg, high char yield, and decreases the oxygen induction time value. A linear increase of number average molecular weight (Mn) versus monomer conversion was observed, and the molecular weight distribution was relatively narrow (Mw/Mn = 1.1–1.3). FTIR, 1HNMR, gel permeation chromatography, ultraviolet spectroscopies were used for the characterization of the related polymers. The thermal properties of these polymers were investigated by differential scanning calorimetry and thermogravimetric analysis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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 &gt; Irganox®1076 &gt; hydroxytyrosol, but all them showed clearly their stabilization performance in polypropylene. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Polyurethane–zinc borate composites with high oxidative stability and flame retardancy

Novel polyurethane zinc borate composites were prepared with the main aim to increase the flame retardancy of the polyurethane. It was discovered that the zinc borate had very significant effects on the oxidative stability of the neat polymer which was first observed by oxygen induction time tests and supported with actual weathering chamber tests. The oxidative stability of zinc borate-filled polyurethane was compared with the polyurethane stabilized with a commercial light stabilizer, Tinuvin B75 from Ciba SC. The performance of zinc borate-filled polyurethane was much better, as shown by oxygen induction time and weathering chamber tests. Additionally the flame retardancy was measured and significant flame retardancy was achieved. Mechanical tests, thermogravimetric analysis and scanning electron microscope studies were performed to characterize the products.

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

Free-radical Reactions and Thermal Effects in PE during Pipe Extrusion

Abstract In this study, various effects on the properties of the material, such as free-radical (FR) processes, oxygen induction time (OIT), melting temperature and melting heat are examined during several stages of the polyethylene (PE) pipe extrusion process. The spectra in the Electron Spin Resonance (ESR) are researched between 77–293 K and in a wide range of magnetic fields. At 77 K a triplet signal in ESR is observed. The parameters of the signal are ΔHm1 ≅ 1:4 – 1:6 mT; ΔHm2 ≅ 1 – 1:2 mT; ΔHm3 ≅ 0:6 – 0:8 mT and g1 ≅ 2:020; g2 ≅ 2:011; g3 ≅ 1:99 and Hyper Fine Structure constant ΔH12 ≅ 2:1 mT; ΔH23 ≅ 5:3 mT. As the temperature increase from 77 K up to 293 K, the signal for g4 ≅ 2:02 (ΔHm4 ≅ 0:7 – 0:8 mT) appears and intensity of signals increase. It is also thought that the triplet observed at 77 K belongs to macroradicals of alkyl (–CH2–CH–CH2), alyl(~CH2 C HCH = CHCH2~), carboanions and the acyl (H C O) radicals of the fourth signal. At room temperature, all the FR's transform into peroxide radicals. The total concentration of the FR's is minimum at 463 K and increases at the outlet of the extruder and the pipe sample. It is observed that the OIT (Oxygen Induction Time) values decrease as one approaches the outlet of the extruder (from 20–30 to 10–15 minutes), while they increase for the processes of 433 K to 463 K. This event proves that the peroxide radicals form as one passes to room temperature. These results support those of the effects of the extrusion stage on the dynamic-mechanical characteristics [2]. Finally, FR's appear as a result of the breaking of the C-C bonds in the main polymer chains starting from the first step in the extrusion process (433 K) and in the later stages, due to the oxygen in the polymer structure, oxidation processes take place.