Films based on xanthan/wheat starch and xanthan/maize starch were prepared in different proportions and analysed in terms of thermal stability in relation to the degradation reaction in an inert atmosphere. The main gaseous decomposition products were identified by infrared spectroscopy. Xanthan was found to be less thermally stable than starch from different sources. The starch addition to xanthan induced an increase in the film thermal stabilities. The thermal degradation mechanism of xanthan starts with scission of the side chain groups with subsequent scission of the main chain. Starches from maize and wheat presented a constant mechanism of thermal degradation. The proportion of xanthan/starch (50/50) presented a synergistic behaviour which may be associated with changes in the mechanism of the thermal degradation process. The FTIR spectra of the gaseous products during thermal degradation of xanthan showed a broad absorption in the 2750–3300 cm−1 region, probably indicating decomposition of β-d-mannopyranosyl groups, present in xanthan side chains. For pure starches, absorptions related to alcohol O–H stretching (3500–3750 cm−1), CO stretching of CO2, CO and carbonyl compounds (2361, 2177 and 1743 cm−1, respectively) were observed. For xanthan/starch mixtures (50/50) the same compounds as those for the pure polymer degradation were evolved. However, a shift of the CO to higher wavenumber values indicates that new carbonyl compounds are being formed due to changes in the thermal degradation mechanism. 相似文献
Infrared (IR) spectra and wide-angle X-ray diffraction (WAXD) patterns of poly(3-hydroxybutyrate) (PHB) and its copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), P(HB-co-HHx) (HHx = 12 mol%) were measured over a temperature range of 20 °C to higher temperatures (PHB, 185 °C, HHx = 12 mol%, 140 °C) to explore their structure change and thermal behavior and molecular interaction. The WAXD measurements revealed that the a lattice parameter increases significantly with temperature, while the b lattice parameter varies a little in the crystalline PHB and P(HB-co-HHx). It seems that the intermolecular interaction between the CO group of one helical structure and the CH3 group of the other helical structure decreases along the a axis of crystalline PHB and P(HB-co-HHx) with temperature. The temperature-dependent IR spectral variations were analyzed for the CH stretching, CO stretching, CH3 deformation, and C O C stretching variation regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It was found from the anomalous frequencies of the CH3 asymmetric stretching and CO stretching bands of PHB and P(HB-co-HHx) and the X-ray crystallographic structure of PHB that there is an intermolecular interaction (C H…OC hydrogen bond) between the CO group and the CH3 group combining two helical structures in PHB and P(HB-co-HHx). In this review paper we discuss the role of the C H…OC hydrogen bonding and the crystal and lamella structure of PHB and P(HB-co-HHx) (HHx = 12 mol %) in comparison with the structure of Nylon. 相似文献
The influence of polycaprolatone-triol (PCL-T) on the thermal degradation properties of soy protein isolate (SPI)-based films was studied by thermogravimetry and infrared spectroscopy under nitrogen atmosphere. The results showed that in the absence of PCL-T the thermal degradation began between 292 °C (pure SPI films) and ca. 264 °C (SPI/SDS films with more than 20% of SDS), and these values decreased further to the range 250-255 °C for SPI/SDS/PCL-T films. At the same time, the temperature of maximum degradation rate (Tmax) decreased from 331 °C (pure SPI film) to ca. 280 °C for SPI/SDS/PCL-T films with 39% PCL-T content. This behavior was also confirmed by the activation energy (E) values associated with the thermal degradation process. Apparently, the low thermal stability of PCL-T as compared to other film constituents, along with its plasticizer characteristics, is responsible for the decreased stability of SPI/SDS/PCL-T films. The FTIR spectra of gas products evolved during the thermal degradation indicated the formation of OH, CO2, NH3 and other saturated compounds, suggesting that the reaction mechanism involved simultaneous scission of the C(O)-O polyester bonds and C-N, C(O)-NH, C(O)-NH2 and -NH2 bonds of the protein. 相似文献
In this study, the possibility of using Tween 80 to disturb the microstructures of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) was investigated under high pressures. The imidazolioum C H absorptions of pure ionic liquids (ILs) are significantly blue-shifted under high pressures. However, mild changes in imidazolioum C H stretching frequencies were observed for IL/Tween 80 mixtures. Tween 80 may hinder cations of ILs to form network structures with anions under high pressures via pressure-enhanced cation-Tween 80 interactions. Based on the experimental results, Tween 80-[BMIM]PF6 interactions are more effective in disturbing the local structure of imidazolium C H than Tween 80-[BMIM]BF4 interactions. 相似文献
Arsenic (As) frequently exists in pyrite (FeS2) in the form of impurities. The oxidation behavior of As in FeS2 is important in environmental science, mineral processing, and other related fields. The adsorption behaviors of H2O and O2 molecules on the As-bearing pyrite (100) surface (As FeS2(100)) are studied using the density functional theory (DFT). The results show that As prefers the S site on the pyrite (100) surface (FeS2(100)). In the absence of O2, an isolated H2O molecule does not dissociate when adsorbed at an iron (Fe) site and is repelled at an As site. Furthermore, the surface area around the As atoms exhibits a hydrophobic behavior. Adsorption energy analysis reveals that the presence of As atoms is unfavorable for the adsorption of H2O molecules on the pure FeS2 surface, and that the adsorption of H2O molecules on the As FeS2(100) is physical adsorption. In the absence of H2O, it is suggested that the O2 molecule easily dissociates on both the pure FeS2(100) and As FeS2(100). The adsorption of O2 on the As-bearing surface is weaker than that on the pure FeS2(100). For the co-adsorption of H2O and O2, the adsorption energy on the As-bearing surface is more negative than that on the pure surface. This indicates that the presence of As promotes surface oxidation. Additionally, two OH and O (AsO or SO) or O (Fe O) species are formed on the surface of pyrite when the H2O molecule is dissociated. 相似文献
Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal–alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca2+. The role of the metal was evaluated by a study using the metal‐free catalysts: [Ph2N−][Me4N+] and [Ph3C−][Me4N+]. These “naked” amides and carbanions can act as catalysts in the conversion of activated double bonds (CO and CN) in the hydroamination of Ar NCO and R NCN R (R=alkyl) by Ph2NH. For the intramolecular hydroamination of unactivated CC bonds in H2CCHCH2CPh2CH2NH2 the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study. 相似文献
Summary: The laser irradiation at 193 nm of a gaseous mixture of carbon disulfide and ethene induces the copolymerization of both compounds and affords the chemical vapour deposition of a C/S/H polymer, the composition of which indicates the reaction between two to three CS2 molecules and one C2H4 molecule. Polymer structure is interpreted on the basis of X‐ray photoelectron and FT‐IR spectra as consisting of >CS, >CC<, CH2 CH2 , (CC)SnC4 − n, C (CS) S , S (CS) S , and C S S C configurations. The gas‐phase copolymerization of carbon disulfide and ethene represents the first example of such a reaction between carbon disulfide and a common monomer.
Scheme showing the expected reaction of excited CS2 molecules with other CS2 molecules to form dimers, which then react with another CS2 molecule or add to ethene. 相似文献
Summary: Phase separation of aqueous solutions of temperature-responsive polymers such as poly(N-isopropylacrylamide) (PNiPAm) and poly(N,N-diethylacrylamide) (PdEA) was investigated. IR spectroscopy was proved to be a quite useful method observing changes in the hydration states of individual chemical groups of the polymers. For example, the analyses of the amide I and II bands provides important information concerning the hydrogen bonding of the CO group and the N-H group, respectively. Changes in the C H stretching bands indicate hydration changes of the alkyl groups. In addition, molecular simulations based on quantum chemistry give a strong support to the interpretation on molecular level. Our recent progress on this subject was presented and the relationship between the molecular interactions and the macroscopic phase behaviors was discussed. 相似文献
The reactions of Cl3PN P(O)Cl2 ( 1 ) with primary and secondary amines have been studied. The following monophosphazenes, (RRN)3PN P(O)(NRR)2, and bis(phosphinoyl)amines, [(RRN)2P(O)]2NH were isolated: NRR = NHCH2Ph, Net2, NH(CH2)2CH3 groups for monophosphazenes, and Net2, NH(CH2)2CH3 for phosphinoyl amines. The unexpected geminal phosphazene, Cl(RRN)2PN P(O)Cl2, {RRN = N[CH(CH3)2]2}, was also obtained in moderate yield. The spectral data (IR, 1H, 13C, and 31P NMR, and MS) are presented. The structure of 1-(dichlorophosphinyl)-2-chloro-2,2-bis(diisopropylamino)phosphazene ( 5 ) was determined by X-ray crystallography. The basicities of these and related compounds in nonaqueous nitrobenzene solution were obtained by potentiometric titration. 相似文献
The IR spectroscopy study shows miscibility between PMMA-PVC blends due to hydrogen bonding between CO of PMMA and hydrogen from CHCl of PVC. This blend system is doped by Camphor Sulphonic Acid (CSA) in the entire composition range. The doping of CSA in PVC, in PMMA and in PMMA-PVC blends shows changes in FTIR spectra. The interaction between PVC and CSA is through hydrogen bonding between CO of CSA and CHCl of PVC. Doping PMMA with CSA, indicate an interaction between H+ ion of CSA and oxygen atoms of CO and OCH3 of PMMA. Whereas in PMMA–PVC blend interaction between H+ ion of CSA and oxygen atom of CO of PMMA. 相似文献