摘要:

The elution behaviors of CH4, C2H6, n-C3H8, iso-C4H10, Ar. O2, N2, and SF6were studied in A-type zeolites containing K+, Na+, Li+, Sr2+, Ca2+, and Mg2+and on a 10X zeolite. Temperature- and flow-dependent tailing of peaks and changes in retention volume with flow rate were found for those adsorbates able only to partially penetrate the pores. When diffusivities were large enough to allow total access to the pores, molecular size and the degree of adsorption for the adsorbate had significant effects — on HETP values.

ISSN:0037-2366    

DOI:10.1080/00372367108055547

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A systematic study of the comparative extraction behavior of some transitional metals has been performed with the high molecular weight carboxylic acids, SRS-100 and Versatic-9, using benzene as diluent. The study includes the extraction behavior as a function of pH, effect of diluent, metal ion concentration, solvent concentration, salting-out agent, and finally interference of the associated elements. Exchange reaction for several systems are reported. In almost all cases nearly quantitative extraction has been achiaved. It has been found that the extraction is rapid and complete within 3–4 min but the optimum period of extraction is kept at 5 min. In some cases quantitative separations have also been carried out.

ISSN:0037-2366    

DOI:10.1080/00372367108055548

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A more precise criterion for the formation of a steady-state sorption front is the convergence of the integrals which characterize the quantity of a sorbate in the leading edge of the front and the unused capacity of a sorbent behind the front. Existence of an asymptotic solution of the equation of sorption dynamics is not sufficient for convergence of these integrals, if the line passing through the points of the equilibrium isotherm, which correspond to the initial concentratons in the solution … and in the sorbent, is tangent to the isotherm at one of these points.

ISSN:0037-2366    

DOI:10.1080/00372367108055549

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A method is proposed by which selective radiant heating of a molecular-beam source could be used to enrich volatile, labeled compounds in the minute quantities that are needed for tracer experiments.

ISSN:0037-2366    

DOI:10.1080/00372367108055550

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Chain length distribution of a broad spectrum of wood celluloses and cellulose derivatives was determined by gel permeation chromatography. Relative amounts of short and long chain-length species were characterized, and uniformity indices were calculated. Prefractionation was found to be a desirable approach to amplify low- and high-DP regions. This was accomplished using a 55/45 ethyl acetate/ethyl alcohol mixture to yield the low-DP fraction and with a van-ing composition acetone/water system to obtain high-DP material. Fractions of regenerated cellulose from rayon obtained by treatment with 6.5 and 10% sodium hydroxide and by acid hydrolysis were characterized. Wood celluloses and rayons were analyzed in their nitrate form, whereas cellulose acetates were studied directly. This work was aimed primarily at elucidating the gel fraction that appears in the form of a peak of apparently high-DP material, resulting in a bimodal distribution.

ISSN:0037-2366    

DOI:10.1080/00372367108055551

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

This is the first part in a series of papers describing the application of GPC to studies of the viscose process. In this part the procedures used are described. For these studies THF solutions of nitrocellulose were used. Modifications were made to the standard nitration procedures, resulting in improved efficiency. The importance of sampling homogeneity was studied and precision was-obtained. In addition, a computer program to handle the data was developed.

ISSN:0037-2366    

DOI:10.1080/00372367108055552

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Changes in the distribution of degree of polymerization (DP) of cellulose during the steeping and alkali-crumb aging steps of the viscose process have been studied. A dissolving-grade pulp was used, and two mechanisms of degradation—oxidation and hydrolysis—were considered. Alkaline hydrolysis was relatively unimportant during the steeping, the major change in the DP distribution being a result of the much faster oxida-tive degradation. The extent of oxidation was determined by the solubility of oxygen in the alkali solution. Both oxidation and hydrolysis cause degradation during the aging of alkali crumb. Under the conditions used, hydrolysis was a slow, pseudo-first-order reaction, and oxidation a much faster zero-order reaction. Since there was a large difference in the rates of these reactions, the kinetics of degradation approached zero order.

ISSN:0037-2366    

DOI:10.1080/00372367108055553

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A general method is proposed for obtaining gel permeation chromato-graphic (GPC) molecular weight (MW) and hydrodynamic volume (HDV) calibration curves for polymer-solvent systems where primary polymer standards are unavailable. The method is demonstrated by using a HDV calibration curve based on polystyrene in tetrahydrofuran (THF), in conjunction with integral distribution curves of elution volume for poly(methyl methacrylate) (PMMA) in THF and in 2,2,2-tri-fluoroethanol (TFE) for the generation of a HDV calibration curve in TFE. Transformation methods for generating secondary MW calibration curves from HDV calibration curves are discussed and applied to PMMA in THF and TFE, and to poly(trimethylene oxide), poly(vinyl acetate), and certain polyamides in TFE. The utility and reliability of the secondary calibration curves are demonstrated by comparing MW average and intrinsic viscosites obtained by GPC and by the classical methods. Molecular structural differences among th polyamide samples associated with the distribution of short- and long-chain branches are discussed in relation to their secondary calibration curves.

ISSN:0037-2366    

DOI:10.1080/00372367108055554

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The effect of long- and short-chain branching in polymer molecules on GPC separation is reviewed (1–4). The calculation of branched GPC curves is developed from the uiiiversal calibration techniques, which is based on the concept of hydrodynamic volume (M [η]) and previously established relationships for the effect of branching on molecular dimensions. Typical calibration curves are shown for different branching models and degrees of branching. As the branching level increases, the curves arc shown to approach a limiting value. Methods of characterizing branching level3 and molecular-weight distributions of fractions and whole polymers from GPC and intrinsic viscosity data arc prcsentecl. An iterative computer program is described which was written to calculate the degree of branching in whole polymers. Long-chain branching in beveral low-density polyethylene samples was determined, using both the fraction and the whole polymer methods. Effects of various experimental errors and branching models were investigated. For polyethylene, the data show that the effect of branching in intrinsic viscosity is best described by the relationship (g3)w= [η]br/[η] whre (gsis the Zimin-Stockmeyer expression for trifunctional branch points in a polydisperse sample.

ISSN:0037-2366    

DOI:10.1080/00372367108055555

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Three different techniques involved in the preparation of Stereospecific block copolymers were studied using gel permeation chromatography (GPC). These techniques involved the use of a monofunctional organo-lithium catalyst, a difunctional organolithium catalyst, and a combination of a monofunctional organolithium catalyst and a coupling technique. GPC curves were obtained on the block copolymers using two different column sequences and solvents. The ABA block copolymers studied contained styrene, vinyl toluene, or α-methyl styrene as thermoplastic monomers and butadiene as the elastomeric monomer. The results obtained showed that block copolymers prepared using monomers and catalyst systems free of impurities generally exhibited single peaked GPC curves. In systems where impurities were found to be present, small amounts of A block homopolymer and AB block copolymer were formed. In such cases, the GPC curves were observed to have two or three peaks.

ISSN:0037-2366    

DOI:10.1080/00372367108055556

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor