Dihydromyricetin

A study on the efficiency of bio-based compound as stabilizer for linear low density polyethylene (LLDPE) is reported. A water extract from Ampelopsis grossedentata (Dihydromyricetin) is used. Its stabilizing activity is compared with two commercial phenolic antioxidants: methyl gallate (MG) and Irganox 1010. Based on the measurement of the oxidation onset temperature (OOT) of LLDPE/antioxidant samples, it is found that the antioxidant ability of the three kinds of antioxidants is in the following order: DMY > 1010 > MG. The antioxidant ability and thermal decomposition activation energy (E _a) of antioxidants are further examined by thermal gravimetric analysis. The effects of water extraction on the migration resistance of LLDPE/antioxidants are also evaluated by monitoring the OOT change, demonstrating that DMY retained high stability against migration.     

Evaluation of antioxidants on the thermo-oxidative stability of soybean biodiesel

This work shows the evaluation of three antioxidants (2,6-di-t-butyl-4-methylphenol (BHT)—synthetic antioxidant, hydrogenated cardanol (HC), and alkyl hydrogenated cardanol (AHC)—both derived from cashew nut shell liquid) on the thermo-oxidative stability of the soybean biodiesel. The antioxidants were added at concentrations of 200, 300, and 400 ppm, and the oxidative stability of the biofuel with and without antioxidants were investigated by thermogravimetric analysis (TG-DTG and IPDT) and Metrohm 743 Rancimat per the EN 14112 method. The results showed that all antioxidants contributed for the thermo-oxidative stability of the soybean biodiesel as follows: soybean biodiesel < soybean biodiesel + BHT < soybean biodiesel + HC < soybean biodiesel + AHC. In the Rancimat method, the results showed that the antioxidants influenced the biodiesel stability with an increase of at least 71 %.     

By-products from fruit processing

The oxidative stability of soybean oil added of extracts from by-products generated in the pulp processing of mango (CM), Barbados cherry (CB) and guava (CG), as well as the combination of these extracts with the antioxidants butylated hydroxytoluene (BHT) and tertiary butylhydroquinone (TBHQ), were evaluated by pressurized differential scanning calorimetry (P-DSC) and Rancimat methods. Among the extracts, that obtained from CB showed the highest content of total extractible phenolic. Soybean oil added of CM extract showed greater (p < 0.05) oxidative stability in Rancimat analysis, while by P-DSC method CB was the extract more effective (p < 0.05) to protect soybean oil. Soybean oil added of CB extract showed higher (p < 0.05) OIT values compared to those added of CM, CG and synthetic antioxidants BHT and TBHQ. The combination of CB, CM and CG extracts with TBHQ showed synergistic effects, while CM and CB combined with BHT showed antagonistic effect on oxidative stability in soybean oil. The OIT results obtained from analysis by P-DSC and the OSI results obtained by Rancimat showed Pearson moderate correlation (r = 0.42). These results suggest the CB, CM and CG extracts as good source of antioxidant compounds with potential for combined application with synthetic antioxidants to prevent oxidation in soybean oil.     

Investigation of the interaction between human hemoglobin and five antioxidants by fluorescence spectroscopy and molecular modeling

L-ascorbic acid, α-tocopherol, procyanidin B3, β-carotene, and astaxanthin are five classic dietary antioxidants. In this study, the interaction between the five antioxidants and human hemoglobin (HHb) was investigated by fluorescence spectroscopy and molecular modeling. The quenching mechanisms of HHb by the five antioxidants are all static quenching. The downward curvature of the Stern–Volmer plots for HHb–procyanidin B3 system at higher concentrations of procyanidin B3 come from the reason for the variation in the number of accessible tryptophan (Trp) residues toward HHb. The upward curvature of the Stern–Volmer plots for HHb–β-carotene system at higher concentrations of β-carotene predominantly by the “sphere of action” quenching mechanism. The binding constants of HHb with the five antioxidants are in the following order as: astaxanthin > L-ascorbic acid > β-carotene > α-tocopherol > procyanidin B3 at 298 K. The binding processes of the five antioxidants to HHb are all entropy process. Thermodynamic analysis and molecular modeling suggest that the hydrophobic forces are the main interaction force in the binding of the five antioxidants to HHb and hydrogen bond interactions between HHb and L-ascorbic acid/α-tocopherol/procyanidin B3/astaxanthin should be also considered. The fluorescence experimental results are in agreement with the results obtained by molecular modeling study.     

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.     

Preparation and thermal properties of polyquinazolones: Effect of the chemical structure of bisbenzoxazinones on the thermal properties

Four kinds of polyquinazolones were synthesized from 4,4′-diaminodiphenylether and bisbenzoxazinones having different central aromatic nuclei (benzene, biphenyl, benzophenone, diphenylmethane). All the polymers were prepared by solution polycondensation at 190°C at a concentration of 15% solid in m-cresol, and were obtained with intrinsic viscosities in the range of 0.3–0.8 dL/g in 97–98% yield. Their thermal properties were studied by using dynamic thermogravimetry and isothermal weight loss. All the polymers were found to produce high char yields (55–75%) in nitrogen. Oxidative thermal stability of the polymers was dependent on the chemical structure of bisbenzoxazinone and was governed by the stability of the bonds in the quinazolone units. The following order of oxidative thermal stability of the quinazolone units was determined from this study: diphenylmethane < benzophenone < biphenyl < benzene.     

Influence of acid treatment on structure of clinoptilolite tuff and its adsorption of methane

This study presents the results of the methane adsorption properties of clinoptilolite tuff from Bigadic, Turkey and that of acid treated forms at 273 and 293 K up to 100 kPa using volumetric apparatus. In order to assess changes in structural and gas adsorption properties of clinoptilolite, zeolite sample was treated with acid solutions of varying concentrations (0.1, 0.5, 1.0 and 2.0 M) at 70 °C during 3 h. Structural and thermal characterization of natural and acid treated clinoptilolite samples were carried out using a combination of techniques such as X-ray diffraction, X-ray fluorescence, thermogravimetric, differential thermal analysis and nitrogen adsorption methods. At both temperatures, uptake of methane (CH₄) increased in the following order: CLN < CLN-H2 < CLN-H1 < CLN-H05 < CLN-H01. CH₄ adsorption capacities of the original and acid treated clinoptilolites were found in the range of 0.476–0.910 mmol/g and 0.398–0.691 mmol/g at 273 and 293 K, respectively.     

Synthesis, crystal structure, magnetic, DSS cell, lifetime measurement, electrochemical, catecholase activity, and antimicrobial studies of mono and hetero binuclear cryptates

Mono and hetero binuclear cryptates, [GdML(DMF)] [M = VO(IV), Co(II), Cu(II)], were synthesized. The ligand L represents the deprotonated anionic cryptate obtained by the 2+3 condensation of tris-(2-aminoethyl)amine with 2,6-diformyl-4-methylphenol. The crystal structure of [GdL(NO₃)](NO₃)₂·H₂O was determined by single-crystal X-ray diffraction method. The magnetic susceptibility of the complexes was measured by SQUID. The Gd(III)Cu(II) cryptate has ferromagnetic interaction and [Gd(III)VO(IV)] cryptate has weaker intramolecular antiferromagnetic interaction. Fluorescence intensity and excited state lifetime of the cryptates increase in the following order: [GdCoL] < [GdVOL] < [GdL] < [GdCuL]. The efficiency (η) of cryptate based dye-sensitized solar cell increases in the following order: [GdL] < [GdVOL] < [GdCoL] < [GdCuL]. The reduction potential values of [Gd(M)L] M = VO(IV), Co(II), Cu(II) complexes are in the following order: Cu(II) > Co(II) > VO(IV). The catecholase activity of binuclear [GdML] complexes are relatively high compared with the mononuclear [Gd(III)L] complex in the following order: [GdL] < [GdVOL] < [GdCoL] < [GdCuL]. The antimicrobial activity of the binuclear complex Gd(III)Cu(II) is relatively higher than the mononuclear and other binuclear complexes.     

Probiotic Escherichia coli CFR 16 Producing Pyrroloquinoline Quinone (PQQ) Ameliorates 1,2-Dimethylhydrazine-Induced Oxidative Damage in Colon and Liver of Rats

Inflammation of the gastrointestinal tract is associated with reactive oxygen species (ROS) genesis. Alleviation of oxidative stress is achieved by using antioxidants and probiotics. Present study investigates a synergistic effect of the probiotic Escherichia coli CFR 16 containing Vitreoscilla haemoglobin gene (vgb), green fluorescent protein (gfp) gene and pyrroloquinoline quinone (pqq) gene cluster on oxidative stress induced by 1,2-dimethylhydrazine (DMH). Adult virgin Charles foster male rats (3–4 months) weighing 200–250 g were administered with DMH (25 mg/kg body weight, s.c.) twice a week for eight consecutive weeks. Rats receiving only DMH dose showed increased lipid peroxidation in liver and intestinal tissues with reduced activity of antioxidant enzymes, i.e. superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx). Oral dose of E. coli CFR 16::vgb-gfp harbouring pqq gene cluster increased rat faecal PQQ concentration by twofold, reduced lipid peroxidation and retained SOD, CAT and GPx activities close to normal levels in liver and colonic tissues following DMH treatment. In addition, significant protection was found in colonic histological sections of these rat groups. This study demonstrates a protective efficacy in the following order: E. coli CFR 16?<?E. coli CFR 16::vgb-gfp?<?vitamin C?=?PQQ?<?E. coli CFR 16::vgb-gfp (pqq).     

Thermal properties of oxide glasses

A criterion based on the length of induction period of crystallization was used to study the effect of added CoO and NiO oxides on the thermal stability of Li₂O·2SiO₂ glass system against crystallization. It was found out that the thermal stability of studied glasses against crystallization is Li₂O·2SiO₂ < Li₂O·2SiO₂·0.1CoO < Li₂O·2SiO₂·0.1NiO. The addition of CoO and NiO oxides to Li₂O·2SiO₂ glass system increases its thermal stability. These results coincide with the order determined by stability criteria based on the characteristic temperatures.     

Aspects of the thermal and photostabilisation of high styrene-butadiene copolymer (SBC)

The thermal and photo-oxidative stabilisation of high styrene-butadiene copolymer (SBC) with high styrene content (K-Resin) has been studied using a variety of analytical and spectroscopic methods including yellowness, luminescence and FT-IR spectroscopy coupled with hydroperoxide analysis in order to understand the nature and effectiveness of the processes involved. The next stage of the program was to evaluate the effects of various chemical/solvent treatments on the role of metal ions/residual catalysts and hydroperoxides in the thermal and photostabilisation of SBS as well as combinations of phenolic antioxidants and phosphites/phosphonites. Other additives, such as HALS and a metal deactivator, were also added to the combinations of phenolic and phosphite antioxidants in order to study their behaviour and efficiency. The chemical treatments appeared to stabilise SBS against thermal oxidation to a greater or lesser extent. Phosphoric acid treatment via reflux and zinc dithiocarbamate treatments showed better performances than the rest of the treatments, the latter was particularly effective at inhibiting the discolouration. During photo-oxidation, on the other hand, chemical treatments involving phosphoric acid and pre-thermal effects showed the importance of catalyst effects. The addition of phenolic antioxidants, phosphites/phosphonites, metal deactivator and HALS was found to stabilise the SBS against thermal and photo-oxidation. In thermal oxidation, the combination of Irganox^® 1010/Irgafos^® 168 was found to effectively stabilise the polymer when the finalisation of the polymerisation was with adipic acid. When the same antioxidants were used, but with polymer finalised with BHT, strong yellowing was observed and a higher amount of hydroperoxides and oxidation products. Increasing the amount of antioxidants did not increase the stabilisation efficiency. The stabilisation efficiency of Irganox^® 1010 combined with Alkanox^® P-24 was found to be more effective than when it was combined with Irgafos^® 168. The formulations containing Irgafos^® 168/Irganox^® 1010 and Irgafos^® 168/Irganos^® 1330 were more effective in colour protection and retarding the formation of oxidation products than the combinations of Irgafos^® 168/Irganox^® 3114 and Irgafos^® 168/Lowinox^® 1790. The effect of the addition of HALS, such as Tinuvin^® 770, Tinuvin^® 622 and Chimassorb^® 944, and a metal deactivator, such as Irganox^® MD 1024, to the combination of Irgafos^® 168/Irganox^® 1010 was found to be antagonistic. In photo-oxidation, a combination of Irganox^® 1010/Irgafos^® 168 protected the polymer efficiently, when the polymerisation of the polymer was finalised with adipic acid. When the polymerisation was finalised with BHT, a higher amount of hydroperoxides and oxidation products was found. An increase in the amount of antioxidants did not enhance the stability of the polymer. The addition of Alkanox^® P-24 exhibited an opposite effect to that seen in thermal oxidation, as the stabilisation efficiency was less effective than with Irgafos^® 168. The formulation containing Irgafos^® 168/Irganox^® 1010 was found to be the most efficient compared with the other phenolic antioxidants. The addition of Tinuvin^® 770 to the formulation Irgafos^® 168/Irganox^® 1010 was found to have a synergistic effect. The addition of polymeric HALS or Irganox^® MD 1024, a metal deactivator, had an antagonistic effect on the stabilisation of the polymer. Disruption of the excimer sites in the styrenic phase also correlated with stabilisation effects.     

Thermal stability and sensitivity of RDX-based aluminized explosives

The thermal decomposition characteristics and thermal sensitivity are key indicators for reflecting the thermal stability of explosives in storage and application. The thermal decompositions in different degrees are used to determine the dominant factor which controls the thermal stability of composite explosive. Four kinds of RDX-based aluminized explosives are marked as RA1, RA2, RA3, and RA4 with the Al content increasing from 10 to 40 mass%. The initial thermal decomposition behaviors were studied by DPTA and the complete thermal decompositions were studied by DSC and TG. The thermal sensitivities were characterized by 5-s explosion point. The effects of micron-sized Al particles and their contents on thermal decomposition were investigated. The evolved gas amount (V _i) from DPTA test follows RA3 < RA4 < RA2 < RA1, indicating that RA3 has the best thermal stability at ambient storage conditions. However, according to TG and DSC tests, the characteristic temperatures of thermal decomposition (T _p, T _b, and T _SADT), the thermodynamic parameters (?H _e, ?S ^≠, and ?H ^≠), the kinetic parameters (E _a and A), and the 5-s explosion points all follow RA4 < RA3 < RA2 < RA1. The results indicate that the Al particles play different roles in the different degrees of thermal decomposition. In the initial decomposition, the Al particles have not been activated and are considered as inert materials that hinder the decomposition of explosive. In the complete decomposition, the Al particles catalyze the thermal decomposition, and such catalysis becomes more obvious as the Al content increases to a certain degree.     

Evaluation of the thermal degradation of PC/ABS/montmorillonite nanocomposites

Polycarbonate (PC)/acrylonitrile‐butadiene‐styrene (ABS) polymer alloy/montmorillonite (MMT) nanocomposites were prepared using a direct melt intercalation technique. The pyrolytic degradation and the thermo‐oxidative degradation of the polymer alloy and the nanocomposites were studied by thermogravimetric analysis (TGA). The kinetic evaluations were performed by the model‐free kinetic analysis and the multivariate non‐linear regression. Apparent kinetic parameters for the overall degradation were calculated. The results show that PC/ABS/MMT nanocomposites have high thermal stability and low flammability. Their pyrolytic degradation and the thermo‐oxidative degradation model are different. The pyrolytic degradation reaction of the polymer is a two‐step parallel reaction model: nth‐order reaction model, and ath‐degree autocatalytic reaction with an nth‐order reaction autocatalytic reaction, whereas the thermal oxidative degradation reaction of the polymer is a two‐step following reaction model: A → B → C of nth‐order reaction model, and autocatalytic reaction model. Copyright © 2005 John Wiley & Sons, Ltd.     

Quantification of hindered phenols in polyamide 11 during thermal aging

Polyamide 11 films stabilized by Irganox^® 1098, Irganox^® 1010 or Irganox^® 245 were subjected to thermal oxidation at 110 °C. The residual phenol content was assessed by comparing three analytical methods: high performance liquid chromatography (HPLC), determination of the Oxidation Induction Time (OIT) and Onset Oxidation Temperature (OOT) by thermal analyses. Both OIT and OOT are reliable for virgin PA11 after a relevant calibration by HPLC measurement. In the case of oxidized samples, OOT measurements have the benefits of being more easily interpretable than OIT and less time-consuming than HPLC measurements.     

Effect of organophosphate antioxidant on the thermo-oxidative degradation of a mineral oil

This study shows the synthesis, characterization, and evaluation of the effect of organophosphate antioxidant on the thermo-oxidative degradation of a mineral oil. The organophosphate was synthesized by nucleophilic substitution (S_N2) of hydrogenated cardanol. For this study, were employed thermogravimetry, derivative thermogravimetry, differential scanning calorimetry, and differential thermal analysis techniques. The results showed that organophosphate contributed for thermo-oxidative stability of mineral oil (initial decomposition temperature (IDT) mineral oil: 91.28 °C < IDT mineral oil + organophosphate (1%): 156.42 °C). The organophosphate obtained shows significant thermal stability when compared with other compound of the same class (diphenyl phosphate).     

Improving electrochemical performance of poly(vinyl butyral)-based electrolyte by reinforcement with network of ceramic nanofillers

This study has concerned the development of polymer composite electrolytes based on poly(vinyl butyral) (PVB) reinforced with calcinated Li/titania (CLT) for use as an electrolyte in electrochemical devices. The primary aim of this work was to verify our concept of applying CLT-based fillers in a form of nano-backbone to enhance the performance of a solid electrolyte system. To introduce the network of CLT into the PVB matrix, gelatin was used as a sacrificial polymer matrix for the implementation of in situ sol–gel reactions. The gelatin/Li/titania nanofiber films with various lithium perchlorate (LiClO₄) and titanium isopropoxide proportions were initially fabricated via electrospinning, and ionic conductivities of electrospun nanofibers were then examined at 25 °C. In this regard, the highest ionic conductivity of 2.55 × 10⁻⁶ S/cm was achieved when 10 wt% and 7.5 wt% loadings of LiClO₄ and titania precursor were used, respectively. The nanofiber film was then calcined at 400 °C to remove gelatin, and the obtained CLT film was then re-dispersed in solvated PVB-lithium bis(trifluoromethanesulfonyl)imide (PVB-LiTFSI) solution before casting to obtain reinforced composite solid electrolyte film. The reinforced composite PVB polymer electrolyte film shows high ionic conductivity of 2.22 × 10⁻⁴ S/cm with a wider electrochemical stability window in comparison to the one without nanofillers.

     

Preparation of polysulfone-<Emphasis Type="Italic">graft</Emphasis>-monoazabenzo-15-crown-5 ether porous membrane for lithium isotope separation

Several co-monomers were co-grafted with acrylonitrile onto polyethylene nonwoven fabric to prepare amidoximated sorbents. The grafted co-monomer was found to play an important role in the uranium adsorption capacity and sorption selectivity of amidoximated sorbent in natural seawater in the following order: acrylamide (AAm) < acrylic acid (AA) < itaconic acid (ITA) < methacrylic acid (MAA), which agreed well with the result in U-spike brine. The amidoximated sorbent co-grafted with MAA exhibited the highest uranium adsorption capacity (1.05 mg/g) and the best uranium/vanadium sorption selectivity (U/V mass ratio: ~ 0.95) after 56 days of immersion in natural seawater.     

Design calculation of a horizontal thermal neutronic beam for neutron radiography at the Syrian MNSR

The computer code MCNP4C and the ENDF/B-V cross-section library were used to design calculation of a horizontal thermal beam for neutron radiography (NR) at Syrian MNSR and to evaluate the safety of the reactor after installation of the NR facility (NRF). Thermal, epithermal and fast neutron energy ranges were selected as <0.30 eV, 0.30 eV–10.0 keV and >10.0 keV, respectively. To produce a good neutron beam in terms of intensity and quality, bismuth (Bi) and silicon (Si) were used as photon and neutron filters, respectively. The ratio of L/D of the NRF ranges between 90 and 125. The thermal neutron flux at the beam exit plane can be varied from 1.836 × 10⁵ to 3.057 × 10⁵ n/cm² s. If such thermal neutron beam would be built into the Syrian MNSR, many scientific applications of the NR would be available.     

Dielectric properties of oxydianiline‐based polyimide thin films according to the water uptake

For polyimide thin films, the dielectric properties were investigated with the capacitance and optical methods. The dielectric constants of the 4,4′‐oxydianiline (ODA)‐based polyimide thin films varied from 2.49 to 3.10 and were in the following decreasing order: 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA)–ODA > 1,2,4,5‐benzenetetracarboxylic dianhydride (PMDA)–ODA > 4,4′‐hexafluoroisopropylidene diphthalic dianhydride (6FDA)–ODA. According to the absorption of water, the diffusion coefficients in the films varied from 4.8 × 10^?10 to 7.2 × 10^?10 cm²/s and were in the following increasing order: BPDA–ODA < PMDA–ODA < 6FDA–ODA. The dielectric constants and diffusion coefficients of the polyimides were affected by the morphological structures, including the molecular packing order. However, because of the water uptake, the changes in the dielectric constants in the polyimide thin films varied from 0.49 to 1.01 and were in the following increasing order: BPDA–ODA < 6FDA–ODA < PMDA–ODA. Surprisingly, 6FDA–ODA with bulky hexafluoroisopropylidene groups showed less of a change in its dielectric constant than PMDA–ODA. The total water uptake for the polyimide thin films varied from 1.43 to 3.19 wt % and was in the following increasing order: BPDA–ODA < 6FDA–ODA < PMDA–ODA. This means that the changes in the dielectric constants in the polyimide thin films were significantly related to the morphological structure and hydrophobicity of hexafluoroisopropylidene groups. Therefore, the morphological structure and chemical affinity in the polyimide thin films were important factors in controlling the dielectric properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2190–2198, 2002     

Simultaneous Determination of Impurities in Ropinirole Tablets by an Improved HPLC Method Coupled with Diode Array Detection

A gradient HPLC method coupled with diode array detection was developed and fully validated for the analysis of impurities in ropinirole using a Kromasil^® C8 100 Å (250 × 4.6 mm, 5 μm) column with a flow rate 1.0 mL min^?1 and detection at 250 nm. The mobile phase component A consisted of a mixture of 19.6 mM aqueous potassium dihydrogen phosphate–acetonitrile (98:2 v/v), pH adjusted to 7.0 with triethylamine and the mobile phase component B consisted of acetonitrile. The method was validated in terms of linearity, sensitivity, precision, accuracy and stability. The calibration curves for ropinirole and its five impurities showed good linearity (r > 0.998) within the calibration ranges tested. The intra- and inter-day RSD values were <3.9 %, while the relative percentage error E _r was <5.8 % for all compounds. Accelerated stability studies performed under various stress conditions including oxidation, hydrolysis and UV light irradiation at 254 nm proved the selectivity of the procedure. Long-term stability studies performed on blistered tablets and under various conditions of heat and humidity indicate the presence of four of the studied impurities in less than 0.07 %. The method was applied successfully to the detection and determination of ropinirole impurities in pharmaceutical formulations.