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101.
Correlation of antioxidant depletion and mechanical performance during thermal degradation of an HTPB elastomer 总被引:1,自引:0,他引:1
M. Celina J.M. Skutnik Elliott S.T. Winters R.A. Assink L.M. Minier 《Polymer Degradation and Stability》2006,91(8):1870-1879
Thermal degradation studies of a stabilized HTPB based elastomer were conducted at temperatures from 50 °C to 110 °C. The concentration of extractable antioxidant (AO2246) in the polymer was quantified via AO extraction and a gas chromatography-based method using internal standards. The decrease in extractable AO levels as a function of time and temperature was evaluated and correlated with mechanical property changes. Most importantly, AO depletion features were found to be temperature dependent. At elevated temperatures (>80 °C) extractable AO levels decreased rapidly and faster than the concurrent loss in mechanical properties. While extractable AO concentrations decrease quickly, the material is able to maintain some useful mechanical properties, perhaps via non-extractable or grafted AO species formed during degradation providing additional protection. At lower aging temperatures extractable or free AO levels decreased more slowly than the mechanical properties. Therefore, for condition monitoring purposes a universal correlation between AO levels and aging state or material condition could not be established. Most importantly, however, loss of mechanical properties and oxidative degradation is observed at lower temperatures despite significant levels of free antioxidant in the material. The antioxidant appears to be limited in its effectiveness to completely prevent degradation reactions, or only fractions of the total AO available are actually involved in the inhibition process. 相似文献
102.
Daniel Karlsson Jakob Dahlin Åsa Marand Gunnar Skarping Marianne Dalene 《Analytica chimica acta》2005,534(2):263-269
A method for the determination of isocyanates as di-n-butyl amine (DBA) derivatives using tandem mass spectrometry (MS/MS) and electrospray ionisation (ESI) is presented. Multiple-reaction monitoring (MRM) of the protonated molecular ions and corresponding deuterium-labelled d9-DBA derivatives resulted in selective quantifications with correlation coefficients >0.998 for the DBA derivatives of isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (PhI), 1,6-hexamethylene diisocyanate (HDI), 2,4-, 2,6-toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 4,4′-methylenediphenyl diisocyanate (MDI), 3-ring MDI, 4-ring MDI, HDI-isocyanurate, HDI-diisocyanurate, HDI-biuret and HDI-dibiuret. The instrumental precision for 10 repeated injections of a solution containing 0.1 μg ml−1 of the studied derivatives was <2%. Performing MRM of the product ion [DBA + H]+ (m/z = 130) from the protonated molecular ion resulted in the lowest detection limits, down to 10 amol (for TDI). Quantification of concentrations below 10−6 of the occupational exposure limit (OEL) for TDI during 10 min of air sampling was made possible. In an effort to control the formation of alkali adducts, addition of lithium acetate to the mobile phase and monitoring of lithium adducts was evaluated. Having lithium present in the mobile phase resulted in complete domination of [M + Li]+ adducts, but detection limits for the studied compounds were not improved. Different deuterium-labelled derivatives as internal standards were evaluated. (1) DBA derivatives of deuterium-labelled isocyanates (d4-HDI, d3-2,4-TDI, d3-2,6-TDI and d2-MDI), (2) d9-DBA derivatives of the corresponding isocyanates and (3) d18-DBA derivatives of the corresponding isocyanates. An increase in number of deuterium in the molecule of the internal standard resulted in an increase in instrumental precision and a decrease in correlation within calibration series. 相似文献
103.
In this work, the enzymatic degradation of poly(butylene succinate-co-butylene terephthalate) (PBST) copolyesters was studied using the lipase from Pseudomonas (Lipase PS®). The biodegradation behavior was found to strongly depend on the overall impacts of several important factors as the BT comonomer structure and molar content, thermal characteristics, morphology, the enzyme-substrate, and so forth. Further, the biodegraded residual film samples were allowed to be analyzed by means of gel permeation chromatography (GPC), proton nuclear magnetic resonance (1H NMR), differential scanning calorimeter (DSC), small angle X-ray scattering (SAXS), and scanning electron microscope (SEM). On the experimental evidences, an exo-type mechanism of enzymatic chain hydrolysis preferentially occurring in the amorphous region was suggested for the PBST film samples. 相似文献
104.
The mechanical properties of polypropylene random copolymer (PP-R) with different processing parameters were studied. Special attention is devoted to the investigation of the influence of masterbatch addition on the variation in the mechanical properties of injection moulded PP-R. Tensile, instrumented Charpy impact, Shore D hardness, differential scanning calorimeter (DSC) and Vicat softening temperature (VST) tests were conducted on the test samples containing different colour masterbatches varying from 0.5 to 10 wt%. The observed changes in the mechanical behaviour are explained by the type and level of masterbatch content. The natural UV weathering performance of the PP-R material was studied from the masterbatch type point of view. The effect of processing parameters on material performance was studied on samples which were directly obtained from extruded pipes and on injection moulded samples.
Finally, the effects of storage time on the polymer properties were investigated. 相似文献
105.
Sbai K. Abouimrane A. El Kababi K. Vilminot S. 《Journal of Thermal Analysis and Calorimetry》2002,68(1):109-122
We have studied the thermal behaviour under atmospheric pressure of isotypic tetrahydrate cyclotriphosphates MII(NH4)4(P3O9)2x4H2O (M
II=Cu, Ni and Co), between 25 and 1400°C, by X-ray diffraction, thermal analyses (TG and DTA) and infrared spectrometry. This
study shows that the series of the compounds MII(NH4)4(P3O9)2x4H2O (M
II=Cu, Ni and Co) after elimination of water, in two different stages, and ammonia leads, at 400°C to cyclotetraphosphate M2
IIP4O12 crystallized and to a thermal residue with a formula H4P4O12 which undergoes under a thermal degradation by evolving water and pentoxide phosphorus. The kinetic characteristics of the
dehydration and elimination of ammonia have been determinated. The vibrational spectra of Cu(NH4)4(P3O9)2x4H2O were examined and interpreted, in the domain of the valency frequencies, on the basis of the crystalline structure of its
isotypic compound Co(NH4)4(P3O9)2x4H2O whose cycle has the site symmetry C1, of our results of the calculation of the IR frequencies and the successive isotopic substitutions of the equivalent atoms
(3P, 3Oi and 6Oe belonging to the P3Oi3Oe6 ring) of the P3O9
3− cycle with high symmetry D3h.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
106.
《中国化学快报》2021,32(10):3215-3220
Antibiotics such as sulfonamides are widely used in agriculture as growth promoters and medicine in treatment of infectious diseases. However, the release of these antibiotics has caused serious environmental problems. In this paper, photocatalytic oxidation technology was used to degrade sulfadiazine (SDZ), one of the typical sulfonamides antibiotics, in UV illuminated TiO2 suspensions. It was found that TiO2 nanosheets (TiO2-NSs) with exposed (001) facets exhibit much higher photoreactivity towards SDZ degradation compared to TiO2 nanoparticles (TiO2-NPs) with a rate constant increases from 0.017 min−1 to 0.035 min−1, improving by a factor of 2.1. Under the attacking of reactive oxygen species (ROSs) such as superoxide radicals (O2–) and hydroxyl radicals (OH), SDZ was steady degraded on the surface of TiO2-NSs. Based on the identification of the produced intermediates by LC–MS/MS, possible degradation pathways of SDZ, which include desulfonation, oxidation and cleavage, were put forwards. After UV irradiation for 4 h, nearly 90% of the total organic carbon (TOC) can be removed in suspensions of TiO2-NSs, indicating the mineralization of SDZ. TiO2-NSs also exhibits excellent stability in photocatalytic degradation of SDZ in wide range of pH. Even after recycling used for 7 times, more than 91.3% of the SDZ can be efficiently removed, indicating that they are promising to be practically used in treatment of wastewater containing antibiotics. 相似文献
107.
This work describes the influence of silica fillers on the thermomechanical properties of diglycidyl ether of bisphenol A/triethylenetetramine (DGEBA/TETA) epoxy resins during ageing under electron beam irradiation. Whatever be the silica filler (pure micrometric ground and spherical silicas, nanometric silicas and coupling agent treated silicas), the glass transition temperature of the epoxy resins decreases with increasing irradiation dose, meaning that the main effect of the irradiation is chain scission. No influence of the silica fillers has been detected from the changes in the glass transition temperature with the increase in the irradiation dose. The disappearance of the cooperativity of the γ relaxation, the decrease of the α relaxation and the decrease of the elastic modulus at the rubbery plateau observed by dynamic mechanical analyses involve a decrease in the crosslink density of the epoxy resins. The occurrence of chemical reactions between the epoxy resin and the silica surface at high irradiation doses has been shown. Moreover, we show evidence that chemical reactions between the epoxy resin and the silica surface occur at high irradiation dose. 相似文献
108.
Mohammad M. Fares Adeeb S. El-Faqeeh 《Journal of Thermal Analysis and Calorimetry》2005,82(1):161-166
Summary Thermal degradation under N2atmosphere and thermoxidative degradation under air atmosphere of increasingly grafting efficiency values (i.e. GE%=0.0 to 35.5) for starch and starch grafted with N-tert-butylacrylamide thermosensitive copolymers (starch-g-BAM) by Ozawa and Kissinger methods using thermogravimetric analysis
(TG) and differential scanning calorimetry techniques (DSC) at 10, 30 and 50% mass losses respectively have been studied.
Influence of physical inter and intra molecular interactions on grafting and consequently on activation energy of degradation
(Ea,d) was investigated using Ozawa's method, whereas linear dependence of Ea,don GE% by scaling relations using Kissinger's method was determined. Furthermore, the thermoxidative degradation induces the possibility
of molecular rearrangement, cyclization and partial crosslinking that is deduced from the activation energy of degradation
(Ea,d) and residual mass of TG profile. Thermal stability of starch does not alter as a result of different grafting efficiency
percentages. 相似文献
109.
A. Marongiu T. Faravelli G. Bozzano M. Dente E. Ranzi 《Journal of Analytical and Applied Pyrolysis》2003,70(2):519-553
This paper presents an initial attempt at describing poly(vinyl chloride) (PVC) thermal degradation through a semi-detailed and lumped kinetic model. A mechanism of 40 species and pseudocomponents (molecules and radicals) involved in about 250 reactions permits quite a good reproduction of the main characteristics of PVC degradation and volatilization. The presence of the two step mechanism—the first step of which corresponds to dehydrochlorination and the second to the tar release and residue char formation—are correctly predicted both in quantitative terms and in the temperature ranges. The model was validated by comparison with several thermo gravimetric analyses, both dynamic at different heating rates, and isothermal. When compared with the typical one step global apparent degradation models, the approach proposed here spans quite large operative ranges, especially when it comes to predicting product distributions. The initial results of these product predictions, even though quite preliminary, are encouraging and confirm the validity of the model. 相似文献
110.
Fabienne Poncin-Epaillard Barbara Pomepui Jean-Claude Brosse 《Journal of polymer science. Part A, Polymer chemistry》1993,31(11):2671-2680
Polyolefins and their model molecules, some n-alcanes, have been modified by a tetrafluoromethane microwave plasma. The chosen molecules are high-density polyethylene (HDPE) and hexatriacontane (HTC), low-density polyethylene (LDPE) and paraffin, and polycaprolactone (PCL) and octadecyl octadecanoate (ODO). It has been found, except for paraffin, that the model surfaces have the same behavior as the corresponding polymers. Plasma modification is described as the sum of two mechanisms: degradation and fluorination. These reactions seem to be competitive and parallel. Degradation and fluorination rates are dependent on treatment time and are practically independent on substrate position. A domain of fluorination exists near the edge of plasma, whatever the substrate in or outside plasma. © 1993 John Wiley & Sons, Inc. 相似文献