Characterisation of acidic groups in oxycelluloses. II. Estimation of carboxyl groups and lactones by iodometric method

A differentiation between free carboxyl and various lactone groups in oxycelluloses was carried out based on the variation in their reaction rates with KI–KIO₃ solution. An attempt has been made to identify the various lactone groups present by comparison of the results of different oxycelluloses as well as study on some model compounds. A characteristic and group spectrum was determined for each oxycellulose. On blocking the free carboxyl groups by zinc acetate treatment, the results for the nature and amounts of various lactones present are in good agreement with the results for oxycelluloses themselves. Sodium borohydride treatment for 120 hr has been found to be incapable of reducing all the lactones present. An appreciable decrease in the value for glucono-δ-lactone was observed, whiles glucuronic acid lactone was only partially attacked. Treatment with chlorous acid resulted in an increase in the values for free carboxyl as well as lactones for all oxycelluloses.     

Characterization of acidic groups in oxycelluloses IV. Effect of accelerated aging on yellowing as well as carboxyl groups and lactones in pulp

Bleached bamboo pulp as well as two oxypulps were subjected to accelerated aging by heating as well as steaming, and the yellowing or color reversion was studied. The yellowing is increased by the presence of free carboxyl and the reducing groups in oxycelluloses. The again treatments were found to cause an increase in free carboxyl groups accompanied by a reduction in copper number. A differentiation between free carboxyl and various lactone groups in oxidized and also aged samples was carried out based on the variation in their reaction rates with KI/KIO₃ solution, and the characteristic acidic group spectrum showed that on steam again the fastreacting lactones are lost.     

Characterization of acidic groups in oxycelluloses. I. Identification of various functional groups

A large number of oxycelluloses were prepared and modified further by treatment with sodium borohydride as well as chlorous acid, and qualitative color tests were carried out to detect the presence of various functional groups. Uronic acid groups were found to be present in most of the samples. Enediol groups were not detected in any of the samples, although the samples after sodium carbonate treatment gave distinct color tests for enediols, indicating the presence of α-hydroxymonoketo groups. Characteristic color tests for lactones were observed for most of the samples. The intensity of color developed in the lactone test was, however, found to decrease progressively on contact with a KI–KIO₃ mixture for various periods. The difference in the values of carboxyl content between the methylene blue method and the iodometric method is thus mainly caused by the opening of lactones in the latter method.     

Pyrolysis of brown coals. 1. Decomposition of acid groups in coals containing carboxyl groups in the acid and cation forms

The effect of low-temperature pyrolysis (up to 300 °C) on the acid groups of two low-rank coals (a brown coal from Victoria, Australia, and a lignite from Texas, U.S.A.) has been studied for samples in both the acid and cation forms. A preliminary study at temperatures above 300 °C was made on the brown coal. The carboxyl groups of coals in the acid form decompose to give one mole of carbon dioxide for each equivalent of carboxyl content. Cation-form coals yield more carbon dioxide on pyrolysis than can be accounted for by the carboxyl groups present. Water is evolved in proportion to the carbon dioxide evolved from both acid- and cation-form coals, but the ratios differ. Findings have been interpreted as indicating that some other oxygen-containing group is associated with the carboxyl group. In the case of the acid-form coal this group decomposes to give water. When the carboxyl group is in the cation form, decomposition of the associated groups gives carbon dioxide as well as water. Phenolic groups appear to be stable, at least to 300 °C.     

降低聚酯切片端羧基措施的探讨

分析原料性质及生产工艺条件对聚酯切片端羧基的影响,提高酯化段最终酯化率及EG物质的量比、提高缩聚系统真空度、适当降低缩聚反应温度,可以降低切片端羧基。     

Effect of chemical modification of carboxyl groups in apple residues on metal ion binding

AR (apple residue) was used as an alternative and cheap material for binding metal ions due to the presence of carboxyl and phenolic functional groups. The binding capacity of copper, lead, and cadmium by AR was pH dependent. Carboxyl groups of AR were esterified by acidic methanol to determine the contribution of carboxyl groups to metal ions binding. The extent of esterification was determined by analyzing the amount of methanol released in the sample hydrolysates by gas chromatography. The effect of esterification on binding metal ions was investigated in batch experiments by unmodified and modified AR. All esterified AR showed significant decreases in binding copper, lead and cadmium. The loss in the capacity of metal ion binding was proportional to the extent of esterification. The capacity of metal binding decreased with increase in the concentration of methanol in the respective hydrolysates or the modified AR. The data indicate that carboxyl groups on AR play an important role in the metal ion binding.     

Cationic grafting from carbon black. III. Grafting of polyesters from carbon black by ring-opening polymerization of lactones initiated by CO+ClO groups on carbon black

It was found that the cationic ring-opening polymerization of δ-valerolactone (VL), ε-caprolactone (CL), and β-propiolactone (PL) was initiated by carbon black containing CO⁺ClO groups, which were introduced by the reaction of COCl groups with AgClO₄. The polyester was propagated from CO⁺ClO groups and effectively grafted onto carbon black surface. The polymerizability of these lactones by CO⁺ClO groups decreased in the following order: VL > CL > PL. The increasing temperature of the polymerization caused an increase in the rate of the chain transfer reaction of the growing chains and brought about the decrease of grafting ratio of polyester onto carbon black.     

Evaluation of the number of carboxyl groups on glassy carbon after modification by 3,4-dihydroxybenzylamine

An electrochemical method for determining the number of carboxyl groups on glassy carbon (GC) has been developed. In this method, a carboxyl group is modified with 3,4-dihydroxybenzylamine (DHBA) by the action of carbodiimide. The number of carboxyl groups can be determined from the peak area of DHBA in cyclic voltammograms of GC. The physical adsorption of DHBA on GC is not desirable for this quantification. Thus, physical adsorption is minimized by thorough washing and optimization of the modification conditions. Physical adsorption was assessed by experiments on DHBA-treatment without carbodiimide. The minimization and assessment of the physical adsorption of DHBA enables the use of this modification to determine the number of carboxyl groups on GC. The method is quantitative and much more rapid than other methods that have been used to evaluate surface oxides. Using this method, the numbers of carboxyl groups on several electrochemically oxidized GCs were determined. The results revealed that strong electrochemical oxidation of GC increases not only the total number of carboxyl groups but also the surface area of the GC. Strong oxidation does not greatly increase the number of carboxyl groups per surface area.     

光度法测定聚酯切片端羧基含量的方法条件优化

容量法测定有色聚酯的端羧基时存在滴定终点无法判断的困扰,本论文使用光度法从溶液搅拌速度、空白溶剂测定、混合溶剂选择、标准滴定液稳定性等方面对聚酯切片端羧基测试结果的准确性展开研究,并探讨了在有色聚酯端羧基测定中的应用。光度法测定结果的准确度较好,解决了容量法无法测定有色聚酯端羧基的困扰,也避免容量法因人为因素导致的分析误差。     

电导滴定法测定桉木浆中酚羟基和羧基

两相含水有机介质中电导滴定法测定接木浆中酚羟基和羟基的方法是可行的。较好的滴定条件是：滴定介质为丙酮：吡啶：乙醇：水（40：10：1：1,体积比）;样品浓度为2g/L,滴定剂KOH-异丙醇浓度为0．01mol/L。     

Active transport membrane for anions. III. Effect of crown ether and tautomeric functional groups

Membranes derived from copolymers having N-hydroxyalkyl groups were prepared, and the active transport for anions through the membranes was investigated in the presence of a crown ether which suppresses the diffusion of counter ions. The maximum of the concentrated anions in one side cell was maintained for a long time by the addition of a crown ether in the cell, and a concentration of anions up to 50% was attained. Various N-hydroxyalkyl groups of different lengths were incorporated in copolymers with styrene, and the transport for anions was investigated in order to establish the carrier mechanism of the tautomeric functional groups. Longer-length alkyl moieties bearing N-hydroxyalkyl groups led to a decrease in the active transport for anions, which supports a carrier mechanism for the membranes.     

Effects of glycidyl methacrylate content and addition sequence on the acrylic latexes with carboxyl groups

Acrylic latexes with epoxy and carboxyl groups have been synthesized via a two-stage emulsion polymerization process. Different contents of glycidyl methacrylate (GMA) were introduced by three addition modes to copolymerize with methyl methacrylate, butyl acrylate, acrylic acid (AA) in the presence of K₂S₂O₈. To obtain stable latexes, NaHCO₃ was employed as a buffer to compensate for the acidity from the thermal dissociation of K₂S₂O₈, and triethylamine was used to neutralize the carboxyl acid from AA. The results showed that the stable latexes with core/shell structure were synthesized by this method, and higher GMA content or addition at earlier stage led to forming the latexes with higher content of coagulum and bigger sized particles. During the formation of films, the polymer epoxy groups underwent the crosslinking reaction with carboxyl acid. When the GMA content increased or GMA was introduced at a later stage, high crosslinking extent was formed in the films. As a result, the crosslinking provided the films with improved water resistance, chemical resistance, tensile strength, hardness, abrasion resistance, and thermal stability.     

具有不同取代基数量铁酞菁衍生物改性双极膜的性能研究

分别用具有不同取代基数量铁酞菁衍生物加入羧甲基纤维素钠(CMC)阳离子交换膜中,制备改性的CMC/CS双极膜(BPM,CS∶壳聚糖)。结果表明,经铁酞菁改性后,阳膜的离子交换容量、亲水性和双极膜的机械性能均获得提高,双极膜的溶胀度下降。此外,改性后,铁酞菁衍生物可在双极膜中间界面层形成高荷电区,促进水解离,降低膜阻抗和槽电压。当电流密度为60 mA/cm2时,Fe2Pc2(COONa)12-CMC/CS BPM,FePc(COONa)8-C MC/CS BPM,FePc(COONa)4-CMC/CS BPM和CMC/CS BPM的膜电压分别为5.6,6.2,6.5,8.9 V。     

The association constant of macrocyclic ether–cation interactions in 1,4-dioxane/water mixtures. III. Effect of temperature on the binding

The association constant, K_a of Na⁺ with [12]crown-4, [15]crown-5 and [18]crown-6 crown ethers were determined in a binary mixture, 1,4-dioxane/water (50/50) using a Na⁺ ion selective electrode at different temperatures. K_a values were determined with the relationship, 1/K_a [L_o]^n+m–1 = (1–nP′)ⁿ(1–mP′)^m/P′, for various stoichiometries, (n:m), where P′ is the mole fraction of the complexed cation. The exothermic association constants and the thermodynamic data for cation–macrocycle complexes explained in terms of Eigen–Winkler binding mechanism are given. The binding power found for Na⁺, however, was the highest with [18] crown-6.     

Microstructure of cation exchange membranes prepared by the paste method

The microstructure of a cation-exchange membrane (Neosepta CL-25T) prepared by the paste method was investigated by microscopic examination, x-ray microanalysis, scanning electron microscopic observation, and determination of pore size distribution of the porous membrane obtained by selective decomposition of the cation-exchange resin component (R-resin) of the membrane. Both the cloth part and the other part were characterized by uniform distributions of the colloidal R-resin (under 0.1 μm) in poly(vinyl chloride) (PVC). This structural feature made it possible to understand comprehensively the properties of the cation exchange membranes prepared by the paste method. The mechanism of the formation of such microheterogeneity is explained in terms of the microphase separation of the styrene (St)–divinylbenzene (DVB) copolymer from PVC during polymerization.     

The xanthate method of grafting. III. Effect of lignin content on the graftability of wood pulp

Several commercial wood pulps of different chemical origin and with various lignin content were copolymerized with acrylonitrile using the xanthate grafting process. A number of experiments were carried out to evaluate the effects exerted by the residual lignin and by other wood components on the grafting reaction. The results obtained show that graft copolymers can be prepared in good yields with pulps containing as much as 23% lignin. With the aim to investigate the effect of lignin in more detail, two series of pulps were prepared by delignification of a crude sulfite pulp and a crude Kraft pulp to different levels of lignin content. Sodium chlorite was used as a bleaching agent. Copolymerization results obtained with these pulps indicate some fundamental differences in behavior between sulfite and Kraft pulps. In both cases, the copolymerization is afflicted by a short inhibition period whose duration, however, does not depend on the lignin content in the pulp.