The Role of Carbohydrates in Alkali Anthraqutnone Pulping

The reactions of carbohydrates with anthraquinones in alkaline pulping processes are reviewed. AQ reacts mainly with the short-lived intermediates that are formed in the degradation reactions of wood polysaccharides. Oxidation of the reducing end groups of polysaccharides to stable aldonic acid end groups is marginal and corresponds to less than 1 % of all reactions of AQ. The stabilization of the polysaccharides may be enhanced by the use of salts of alkaline earth metals which increase the relative oxidation rate of sugar enediols and promote the hydride shift reaction of the intermediate aldos-2-ulose end groups to stable hexonic acid end groups. Analysis of the monomeric carbohydrate-derived oxidation products indicates that hardwood lignin probably contains more structures that react with anthrahydroquinone than does softwood lignin. This difference may partly explain the more facile delignification of hardwoods.     

Photodynamic inactivation of bacterial spores on the surface of a photoactive polymer

Novel photoactive polymers were prepared by covalently binding an anthraquinone (AQ) derivative through its 2-position to acid groups of a commercially available ethylene–acrylic acid copolymer, and the photodynamic action of films prepared using these polymers was evaluated. Inoculation of Bacillus cereus spores onto the surface of photoactive polymer films having an AQ content of 35% w/w, followed by exposure to low-power UV-A light, was found to significantly enhance the inactivation of the spores compared with their survival on the surface of inert polymer substrates. It was shown that this effect most likely originates from the photo-induced production of singlet oxygen by the photoactive polymer. These results provide compelling evidence that singlet oxygen produced exogenously by a polymeric substrate can successfully inactivate microbes located on the substrate’s surface.     

UV‐Triggered Optical Response and Oxygen Scavenging Ability of a Water‐Soluble Poly(N,N‐dimethylacrylamide‐co‐2‐vinylbenzylanthraquinone) Copolymer

A vinyl‐modified anthraquinone (AQ) derivative (Vinyl‐AQ) is synthesized through a palladium‐mediated Suzuki coupling reaction between vinylphenylboronic acid and 2‐chloromethylanthraquinone and, subsequently, copolymerized with N,N‐dimethylacrylamide (DMAM) through free radical copolymerization in organic solvent. The chemical structure of the resulting water‐soluble copolymer, P(DMAM‐co‐AQ), is verified using techniques such as proton nuclear magnetic resonance, attenuated total reflection‐infrared spectroscopy, thermogravimetric analysis, and UV–vis spectroscopy. The evolution of the oxygen scavenging abilities of aqueous P(DMAM‐co‐AQ) solutions after UV irradiation is monitored as a function of UV irradiation time, concentration of AQ moieties, and pH. The copolymer is proved an effective UV‐triggered oxygen scavenger, leading to dissolved oxygen contents below 1 ppm for the optimized experimental conditions. This behavior is related with the appearance of novel chemical species with interesting optical properties, as suggested by the respective evolution of the UV–vis absorption and photoluminescence spectra after UV irradiation.     

The effect of polypyrrole-bound anthraquinonedisulphonate dianion on cathodic reduction of oxygen

Functionalized polypyrrole (PPy) films were prepared by incorporation of anthraquinonedisulphonate (AQDS) as doping anion during the electropolymerization of pyrrole (Py) monomer at a glassy carbon electrode from aqueous solution. The electrochemical behavior of the PPy-bound AQDS modified electrode and cathodic reduction of oxygen on the resulting polymer film were studied. An obvious surface redox reaction corresponding to AQ/H₂AQ was observed and the dependence of this reaction on the solution pH was also illustrated. The electrocatalytic ability of the PPy-bound AQDS modified electrode was demonstrated by the electroreduction of oxygen at the optimized pH of 6.3 in a phosphate buffer. The reduced AQDS (H₂AQ) is responsible for the extraordinary catalytic activity to the oxygen reduction reaction. The PPy layers not only act as an electron mediator, but also facilitate the stability of the modified electrode. It was found that the catalytic reaction occurred in the presence of the bound AQDS and O₂ is in agreement with an electrochemical–chemical (EC) mechanism. The kinetic parameters of oxygen reduction were determined using Koutecky–Levich equation and Tafel polarization technique.     

CHEMICAL CHARACTERIZATION OF BEECH CONDENSATE

ABSTRACT

Beech (Fagus sylvatica L.) condensate from a steaming operation was collected and analyzed. The condensate exhibited a low pH, and contained carbohydrates and phenolic compounds. A total of five phenolic acids and aldehydes (syringic acid, vanillic acid, p-hydroxybenzoic acid, syringaldehyde, vanillin) were identified. TLC of the carbohydrates showed the presence of glucose, galactose, xylose, mannose and/or arabinose in the condensate. Fructose, saccharose, raffinose and stachyose were also identified. The COD, BOD5, pH, conductivity and suspended solids (TSS) were determined. The chemical oxygen demand (COD) in the beech condensate varied from 2016 to 1393O mg/L. This value is two to three fold higher than the corresponding biological oxygen demand (BOD₅).     

Quinones As Additives During Soda Cooking

Anthraquinone-1-acetic acid is a less effective delignification catalyst than anthraquinone but it gives an enhanced carbohydrate stabilization by converting reducing sugar end groups more effectively to aldonic acid end groups. This reaction produces the hydroquinone form of the additive which is then easily oxidized by oxygen at 80°C. Oxygen treatment favors the end group stabilization. Depolymerization of the cellulose is suppressed by the presence of magnesium hydroxide but cannot be avoided completely.     

枫香树材清洁制浆技术

对速生阔叶木枫香树材的纤维形态、主要化学组成、清洁制浆及绿色漂白工艺进行了一系列探讨。结果显示,枫香木纤维平均长度较长,长宽比均比杨木大,且其综纤维素和戊聚糖含量高而Klason木素含量低,是一种很有发展潜力的制浆造纸原料。采用硫酸盐法制浆,蒸煮后所得细浆得率为49.9%,卡伯值为23.0,白度为23.8%ISO,黏度为734.7 mL/g。利用环境友好型漂白法——氧脱木素技术处理该枫香树材硫酸盐浆,并在此过程中创造性地使用助剂蒽醌。四因素三水平正交试验结果表明:用碱量、氧压、温度和时间对枫香树材硫酸盐浆添加蒽醌氧脱木素后浆料的性能均有很大的影响。其中,温度对得率、卡伯值、白度和黏度等的影响最大,时间对卡伯值、白度和黏度的影响最小。枫香树材硫酸盐浆添加蒽醌氧脱木素的较为适宜的工艺为:用碱量3%,氧压0.7 MPa,温度105℃,保温时间90 min,浆浓20%,MgSO4用量0.5%,蒽醌用量0.1%。在该条件下所得浆料得率90.7%,卡伯值7.0,黏度545.1 mL/g,白度51.0%ISO,脱木素选择性8.42×10-2。与相同条件下常规氧脱相比,卡伯值和白度相近,但得率、黏度和脱木素选择性都有所提高。蒽醌在枫香树材硫酸盐浆氧脱木素过程中可保护碳水化合物,提高脱木素选择性,是一种良好的氧脱木素助剂。     

Redox chemistry of H2S oxidation by the British gas Stretford process part V: Aspects of the process chemistry

Stretford processes use air to oxidize H₂S in process and natural gases to elemental sulphur, by absorption in aqueous solution at about pH 9 and reaction of the resulting HS^– ions with dissolved oxygen, in the presence of anthraquinone disulphonates (AQDS) and vanadium (v) species, which act as catalysts. Kinetic measurements of the reactions (AQ27DS + HS^– ions), (V(v) + HS^– ions) and (AQ27DSH^– + O₂), primarily used stopped flow spectrophotometry, as reported here, following papers on the electrochemical behaviour of the individual redox couples in Stretford Processes. The course of reaction (AQ27DS + HS^– ions) was also followed with a gold bead indicator electrode, the potential of which was determined essentially by the AQ27DS/AQ27DSH^– couple as the former species were reduced to the latter. Attempts to use⁵¹V NMR to characterize aqueous vanadium-sulphur complexes were inconclusive. A possible mechanism for Stretford Processes is postulated, involving polysulphide (S _n ^2–) ions as intermediates, which are oxidized to elemental sulphur by another intermediate, H₂O₂, formed by reaction of AQ27DSH^– ions and dissolved oxygen.     

Electrocatalytic reduction of oxygen at glassy carbon electrode modified by polypyrrole/anthraquinones composite film in various pH media

The electrocatalytic reduction of dioxygen by one mono and four dihydroxy derivatives of 9,10-anthraquinone (AQ) incorporated in polypyrrole (PPy) matrix on glassy carbon electrode has been investigated. The electrochemical behaviour of the modified electrodes was examined in various pH media and both the formal potential of anthraquinones and reduction potential of dioxygen exhibited pH dependence. AQ and PPy composite film showed excellent electrocatalytic performance for the reduction of O₂ to H₂O₂. pH 6.0 was chosen as the most suitable medium to study the electrocatalysis by comparing the peak potential of oxygen reduction and enhancement in peak current for oxygen reduction. The diffusion coefficient values of AQ at the modified electrodes and the number of electrons involved in AQ reduction were evaluated by chronoamperometric and chronocoulometric techniques, respectively. In addition, hydrodynamic voltammetric studies showed the involvement of two electrons in O₂ reduction. The mass specific activity of AQ used, the diffusion coefficient of oxygen and the heterogeneous rate constants for the oxygen reduction at the surface of modified electrodes were also determined by rotating disk voltammetry.     

The effect of various catalysts on the monomer reactivity ratios in oxidative copolymerization of styrene and α‐methylstyrene

Oxidative copolymerizations of styrene (St) with α‐methylstyrene (AMS) have been studied under 100 psi (690 kPa) oxygen pressure at 50 °C in the presence of various catalysts, namely 2,2′‐azobisisobutyronitrile, cobalt(II) phthalocyanine pyridine complex and cobalt(II) tetraphenylporphyrin pyridine complex. The rates of copolymerization reactions (R_p) are obtained from oxygen consumption versus time plots. The reactivity ratios are computed with the Fineman–Ross and Kelen–Tüdös methods, using copolyperoxide compositions obtained from ¹H NMR analysis. The effects of these catalysts on R_p, molecular weight and monomer reactivity ratios have been examined. Using all three catalysts, the comonomer incorporation in the copolyperoxide chain is controllable over a wide range by adjusting the comonomer feed ratios. The reactivity ratio results indicate that incorporation of St or AMS in the copolyperoxides is independent of initiating system. © 2014 Society of Chemical Industry     

麦草亚铵法氧脱木素浆蒽醌强化次氯酸盐漂白

对麦草亚铵法氧脱木素浆进行蒽醌强化的次氯酸盐漂白工艺的研究,结果表明:在所选四因素三水平漂白工艺中,影响纸浆白度和卡伯值的主要因素是用氯量,当用氯量为7%时,纸浆白度为71.1%ISO;另外,在50℃和80℃的条件下,对麦草亚铵法氧脱木素浆分别进行添加氨基磺酸和蒽醌的漂白研究,发现次氯酸盐漂白时添加蒽醌比添加氨基磺酸的漂白效果好,不仅漂白浆的白度和黏度均得到提高,而且脱木素能力也显示加强。     

Evaluation of aminoquinoline‐imprinted polymers and the recognition mechanism

Three molecularly imprinted polymers P(2‐AQ), P(3‐AQ), and P(8‐AQ) based on methacrylic acid (MAA)–ethylene glycol dimethacrylate were prepared using isomers 2‐aminoquinoline (2‐AQ), 3‐aminoquinoline (3‐AQ), and 8‐aminoquinoline (8‐AQ) as template, respectively, by non‐covalent bulk polymerization technique. Neither P(3‐AQ) nor P(8‐AQ) exhibited imprinting effect for 3‐AQ or 8‐AQ, whereas P(2‐AQ) showed significant imprinting effect for 2‐AQ. This indicates that the position of amino group on the quinoline ring has crucial influence on imprinting effect. The recognition mechanism of P(2‐AQ) was investigated extensively by such methods as selective experiments, comparative study with 2‐aminopyridine‐imprinted polymer, and effect of different kinds of mobile phases. It is confirmed that there are complementary cavities in P(2‐AQ) both in size and in the arrangement of functional groups to 2‐AQ, and MAA binds 2‐AQ via cyclic hydrogen bond. Furthermore, the influence of synthetic conditions on 2‐AQ‐imprinted polymers was explored. We found 2‐AQ‐imprinted polymer synthesized in acetonitrile porogen showed higher imprinting effect for 2‐AQ than that prepared in chloroform. It is deduced that the morphology of the former might be more favorable to 2‐AQ binding, which is also supported indirectly by the fluorimetric experiments estimating the interaction of 2‐AQ with MAA in these two porogens. Additionally, 2‐AQ‐imprinted polymers prepared using two different amounts of acetonitrile exhibited very different imprinting effects, which suggested that porogen amount used in the imprinting process exerted significant influence. In addition to the in‐depth elucidation of the recognition mechanism of 2‐AQ‐imprinted polymer, this article provides the basis for the separation and enrichment of bioactive 2‐AQ. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Melt grafting of maleic anhydride onto polypropylene with assistance of α‐methylstyrene

Melt grafting of maleic anhydride (MA) and α‐methylstyrene (AMS) onto polypropylene (PP) was performed by reactive extrusion. Effects of AMS on the graft degree of MA, crystallization behavior, and thermal properties of the graft copolymer were investigated. Results show that the addition of AMS as a comonomer can efficiently improve the MA graft degree. When the molar ratio of AMS to MA is 0.9:1, the maximum MA graft degree is attained, which increases about 56% compared with that using single monomer of MA. The results of the graft degree of MA obtained by chemical titration (CT) agree well with those obtained by Fourier transform infrared spectroscopy (FTIR). Melt flow rate (MFR) measurements indicate that the addition of AMS effectively reduces the degradation of PP molecules. The wide‐angle X‐ray diffraction (WAXD) results show that in comparison with the PP‐g‐MA sample, the PP‐g‐(MA‐AMS) sample shows no new crystalline form, but has a slight decrease in the average crystalline domain size. According to the results of thermogravimetry (TG) and differential scanning calorimetry (DSC), the graft PP in the presence of AMS exhibits a lower melting point and a higher crystallization temperature and thermal stability in comparison with that without AMS. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Thermal stability of modified end‐capped poly(lactic acid)

The influence of functional end groups on the thermal stability of poly(lactic acid) (PLA) in nitrogen‐ and oxygen‐enriched atmospheres has been investigated in this article using differential scanning calorimetry, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Functional end groups of PLA were modified by succinic anhydride and l ‐cysteine by the addition–elimination reaction. PLA was synthesized by azeotropic condensation of l ‐lactic acid in xylene and characterized by nuclear magnetic resonance. The values of the activation energies determined by TGA in nitrogen and oxygen atmospheres revealed that the character of functional end groups has remarkable influence on the thermal stability of PLA. Moreover, DMA confirmed the strong influence of functional end groups of PLA on polymer chains motion. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41105.     

Thermally and mechanically enhanced epoxy resin‐silica hybrid materials containing primary amine‐modified silica nanoparticles

In this article, a series of hybrid materials consisted of epoxy resin matrix and well‐dispersed amino‐modified silica (denoted by AMS) nanoparticles were successfully prepared. First of all, the AMS nanoparticles were synthesized by performing the conventional acid‐catalyzed sol–gel reactions of tetraethyl orthosilicate (TEOS), which acts as acceded sol–gel precursor in the presence of 3‐aminopropyl trimethoxysilane (APTES), a silane coupling agent molecules. The as‐prepared AMS nanoparticles were then characterized by FTIR, ¹³C‐NMR, and ²⁹Si‐NMR spectroscopy. Subsequently, a series of hybrid materials were prepared by performing in situ thermal ring‐opening polymerization reactions of epoxy resin in the presence of as‐prepared AMS nanoparticles and raw silica (RS) particles (i.e., pristine silica). AMS nanoparticles were found to show better dispersion capability in the polymer matrices than that of RS particles based on the morphological observation of transmission electron microscopy (TEM) study. The better dispersion capability of AMS nanoparticles in hybrid materials was found to lead enhanced thermal, mechanical properties, reduced moisture absorption, and gas permeability based on the measurements of thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and gas permeability analysis (GPA), respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Spherical carbons: Synthesis,characterization and activation processes

Spherical carbons have been prepared through hydrothermal treatment of three carbohydrates (glucose, saccharose and cellulose). Preparation variables such as treatment time, treatment temperature and concentration of carbohydrate have been analyzed to obtain spherical carbons. These spherical carbons can be prepared with particle sizes larger than 10 μm, especially from saccharose, and have subsequently been activated using different activation processes (H₃PO₄, NaOH, KOH or physical activation with CO₂) to develop their textural properties. All these spherical carbons maintained their spherical morphology after the activation process, except when KOH/carbon ratios higher than 4/1 were used, which caused partial destruction of the spheres. The spherical activated carbons develop interesting textural properties with the four activating agents employed, reaching surface areas up to 3100 m²/g. Comparison of spherical activated carbons obtained with the different activating agents, taking into account the yields obtained after the activation process, shows that phosphoric acid activation produces spherical activated carbons with higher developed surface areas. Also, the spherical activated carbons present different oxygen groups’ content depending on the activating agent employed (higher surface oxygen groups content for chemical activation than for physical activation).     

Carbohydrate stabilization with anthraquinone during alkaline pulping

Summary Treatment of wood meal with aqueous alkali in the presence of anthraquinone at 80°C leads to a conversion of reducing hexose end groups in the polysaccharides to mannonic and gluconic acid end groups. Xylose end groups are oxidized to xylonic and lyxonic acid groups. This leads to a stabilization of the polysaccharides against endwise alkaline degradation.     

Voltammetric quantification of the spontaneous chemical modification of carbon black by diazonium coupling

Surface coverage limits obtained through the spontaneous and reductive reaction of 1-diazo-anthraquinone ions with Vulcan XC72 carbon black have been studied using cyclic voltammetry. The effect of modifying the surface structure of the carbon, varying reaction conditions and time, and the use of sequential reactions were studied. The maximum loading of AQ that could be obtained was 1.0 × 10⁻⁴ mol g⁻¹, consisting in the best case of a 3:1 ratio of covalently bound to adsorbed species. Based on literature specific area values for the carbons and measured specific capacitances, it is concluded that only ca. 25% of the BET area of the pristine Vulcan XC72 is accessible to the diazonium ions, and that a loosely packed monolayer of bound and adsorbed species is formed on this accessible area. Carboxylic acid groups on the carbon surface were not found to limit the total loading of AQ, but did significantly favor covalent bonding over adsorption.     

Synthesis of functionalized polylactide by cationic activated monomer polymerization

Functionalized polylactides (PLAs) containing acryloyl, methacryloyl or propargyl end groups have been obtained by cationic ring-opening polymerization performed in the presence of appropriate alcohols (HEMA, HEA, propargyl alcohol) as initiators and triflic acid as a catalyst. ¹H NMR, MALDI TOF and GPC analysis indicated almost quantitative initiation and confirmed the expected structure and molecular masses of the obtained PLAs. The conditions were found in which transesterification process (usually accompanying the cyclic esters propagation) can be avoided. PLAs functionalized with double bond were successfully homopolymerized and copolymerized with butyl acrylate in the presence of AIBN. PLA with triple bond at one chain end was effectively coupled with a model azide by 1,3-dipolar Huisgen cycloaddition (“click” reaction) in order to prove its ability to be further functionalized.     

Electroreduction of oxygen on glassy carbon electrodes modified with in situ generated anthraquinone diazonium cations

The electrochemical reduction of oxygen on glassy carbon (GC) electrodes modified with in situ generated diazonium cations of anthraquinone (AQ) has been studied using the rotating disk electrode (RDE) technique. The electrografting of the GC electrodes was carried out in two different media: in acetonitrile and in an aqueous acidic solution (0.5 M HCl). 1- and 2-Aminoanthraquinone were used as starting compounds for the formation of the corresponding diazonium derivatives. The anthraquinone diazonium cations were generated by reaction of the aminoanthraquinones with tert-butyl nitrite and sodium nitrite in acetonitrile and in 0.5 M HCl, respectively. For comparison purposes, the previously synthesised and crystallised diazonium tetrafluoroborates of anthraquinone were used for the GC surface modification. Cyclic voltammetry was employed to determine the surface concentration of AQ in O₂ free 0.1 M KOH. The electrocatalytic behaviour towards O₂ reduction was similar for all the AQ-modified electrodes studied. The kinetic parameters of oxygen reduction were determined using a surface redox catalytic cycle model. The rate constant of the reaction between the semiquinone radical anion of AQ and molecular oxygen was virtually independent of the point of attachment of the quinone to the electrode surface.