ELECTROCATALYTIC OXIDATION OF STARCH IN TWO-CHAMBER CELL WITH REGENERATION OF OXIDANT IN SITU ON ELECTRODES FROM Pb/PbO2 AND GRAPHITE

Electrocatalytic oxidation of potato starch was investigated potassium iodate in a two-chamber electrolytic cell with in situ regeneration of the oxidant on Pb/PbO2 and graphite electrodes, depending on the current density, electrolyte pH and electrolysis time. To analyze the samples of the starting and oxidized starch, the methods of photometry, X-ray diffraction, gel permeation chromatography, and IR spectroscopy were used. The optimal conditions for starch dialdehyde production were determined: current density 50 mA/cm2, electrolyte pH 7, electrolysis time 80 min. and a temperature of 25 °С. The weight average molecular weights (Mw) of AIBN samples were determined, which are several orders of magnitude lower (104) than the average molecular weight of native starch (108).

Download Full-text

Probing the molecular weights of sweetgum and pine kraft lignin fractions

TAPPI Journal ◽

10.32964/tj20.6.381 ◽

2021 ◽

Vol 20 (6) ◽

pp. 381-391

Author(s):

JULIANA M. JARDIM ◽

PETER W. HART ◽

LUCIAN LUCIA ◽

HASAN JAMEEL

Keyword(s):

Molecular Weight ◽

Black Liquor ◽

Average Molecular Weight ◽

Gel Permeation Chromatography ◽

Systematic Investigation ◽

Kraft Pulping ◽

Molecular Weights ◽

Lignin Recovery ◽

Lignin Reactivity ◽

Kinetics Of

The present investigation undertook a systematic investigation of the molecular weight (MW) of kraft lignins throughout the pulping process to establish a correlation between MW and lignin recovery at different extents of the kraft pulping process. The evaluation of MW is crucial for lignin characterization and utilization, since it is known to influence the kinetics of lignin reactivity and its resultant physicochemical properties. Sweetgum and pine lignins precipitated from black liquor at different pHs (9.5 and 2.5) and different extents of kraft pulping (30–150 min) were the subject of this effort. Gel permeation chromatography (GPC) was used to deter- mine the number average molecular weight (Mn), mass average molecular weight (Mw), and polydispersity of the lignin samples. It was shown that the MW of lignins from both feedstocks follow gel degradation theory; that is, at the onset of the kraft pulping process low molecular weightlignins were obtained, and as pulping progressed, the molecular weight peaked and subsequently decreased. An important finding was that acetobromination was shown to be a more effective derivatization technique for carbohydrates containing lignins than acetylation, the technique typically used for derivatization of lignin.

Download Full-text

Lipase mediated synthesis of polycaprolactone and its silica nanohybrid

Pure and Applied Chemistry ◽

10.1515/pac-2018-1011 ◽

2019 ◽

Vol 91 (6) ◽

pp. 957-965

Author(s):

Meltem Akkulak ◽

Yasemin Kaptan ◽

Yasar Andelib Aydin ◽

Yuksel Avcibasi Guvenilir

Keyword(s):

Average Molecular Weight ◽

Proton Nuclear Magnetic Resonance ◽

Gravimetric Analysis ◽

X Ray Diffraction ◽

Scanning Calorimetry ◽

Structural Investigations ◽

Crystallinity Degree ◽

Molecular Weights ◽

H Nmr

Abstract In this study, rice husk ash (RHA) silanized with 3-glycidyloxypropyl trimethoxysilane was used as support material to immobilize Candida antarctica lipase B. The developed biocatalyst was then utilized in the ring opening polymerization (ROP) of ε-caprolactone and in situ development of PCL/Silica nanohybrid. The silanization degree of RHA was determined as 4 % (w) by thermal gravimetric analysis (TGA). Structural investigations and calculation of molecular weights of nanohybrids were realized by proton nuclear magnetic resonance (1H NMR). Crystallinity was determined by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Scanning Electron Microscopy (SEM) was used for morphological observations. Accordingly, the PCL composition in the nanohybrid was determined as 4 %, approximately. Short chained amorphous PCL was synthesized with a number average molecular weight of 4400 g/mol and crystallinity degree of 23 %. In regards to these properties, synthesized PCL/RHA composite can find use biomedical applications.

Download Full-text

Enzymatic Synthesis of Alkyds

MRS Proceedings ◽

10.1557/proc-174-209 ◽

1989 ◽

Vol 174 ◽

Cited By ~ 1

Author(s):

Shimona Geresh

Keyword(s):

Average Molecular Weight ◽

Enzymatic Catalysis ◽

Gel Permeation Chromatography ◽

X Ray Diffraction ◽

High Melting Point ◽

Molecular Weights ◽

Derivatives Of ◽

Low Solubility ◽

Butane Diol ◽

Sem Analyses

AbstractThis paper describes the application of lipase-catalyzed polytransesterification to the preparation of two series of unsaturated “all trans” polyesters (alkyds): in the first series the starting materials were diesters of fumaric acid and 1,4-butane diol, and in the second, bischloroethyl fumarate and aromatic diols (benzene dimethanol and derivatives of bisphenol A). Most of the reactions were carried out in tetrahydrofuran and acetonitrile. As opposed to the extensive isomerization which occurs during the synthesis of unsaturated polyesters by chemical polycondensation, no isomerization of the double bond was found under the mild conditions of enzymatic catalysis. The “all trans” character of our alkyds was determined by nmr spectroscopy, and average molecular weights and dispersivity were measured by gel permeation chromatography. The average molecular weight was found to vary with the solvent. In acetonitrile a relatively high-melting point alkyd was obtained (m.p. 106–108°C), with low solubility in conventional solvents. Powder X-ray diffraction and SEM analyses revealed crystaUinity and layer-type structures.

Download Full-text

Article

Canadian Journal of Chemistry ◽

10.1139/v98-175 ◽

1998 ◽

Vol 76 (11) ◽

pp. 1699-1706 ◽

Cited By ~ 1

Author(s):

Jonathan Z Knaul ◽

Mohammad R Kasaai ◽

V Tam Bui ◽

Katherine AM Creber

Keyword(s):

Molecular Weight ◽

Average Molecular Weight ◽

Gel Permeation Chromatography ◽

Solvent System ◽

Similar Degree ◽

Degree Of Deacetylation ◽

Molecular Weights ◽

Good Accord ◽

Gel Permeation ◽

Weight Analysis

Starting from a chitosan sample with a degree of deacetylation of 71%, three separate sample sets were generated by successive deacetylation and reacetylation processes. The degree of deacetylation of samples was determined by UV spectrometry supported by thermogravimetric analysis. The molecular weight of chitosan samples was determined in a solvent system of 0.25 M CH3COOH/0.25 M CH3COONa, using viscometry and gel permeation chromatography (GPC) with a TSK-gel column. The first set of samples had a similar degree of deacetylation (DDA) but differing molecular weights. The second set of samples had a similar molecular weight but differing degrees of deacetylation. The Mark-Houwink-Sakurada constants used for the determination of viscosity average molecular weight and the universal calibration of the GPC system were K = 1.40 × 10-4 dL/g and a = 0.83. Results showed that molecular weights determined from both techniques are in good accord only at lower degrees of deacetylation. This may be attributed to the fact that the chemical structure of chitosan samples could have been largely altered with increasing or decreasing degree of deacetylation. Nevertheless, the trend with which the molecular weights vary with the deacetylation time is consistent over a limited DDA range. A literature review of molecular weight analysis of chitosan is included.Key words: chitosan, degree of deacetylation, gel permeation chromatography, molecular weight, viscometry.

Download Full-text

The Application of Organic Phosphate Nucleating Agents in Polypropylene with Different Molecular Weights

Crystals ◽

10.3390/cryst11121543 ◽

2021 ◽

Vol 11 (12) ◽

pp. 1543

Author(s):

Juan Li ◽

Zhaohua Liang ◽

Chengtao Gao ◽

Shanshan Luo ◽

Shaowen Huang ◽

...

Keyword(s):

Molecular Weight ◽

Average Molecular Weight ◽

Gel Permeation Chromatography ◽

Nucleating Agent ◽

Organic Phosphate ◽

Nucleating Agents ◽

Tem Analysis ◽

Molecular Weights ◽

Dispersed Particles ◽

Extrusion Method

Two kinds of organic phosphate nucleating agent (NA-11 and NA-21) were used in PP with different molecular weights through the melt extrusion method. The dispersibility of the nucleating agents in PP, and the effect of the nucleating agents on the molecular weight, rheological behavior and crystallization behavior of PP were investigated. SEM and TEM analysis showed that the average radius of the dispersed particles (nucleating agents) was larger in LPP than that in HPP. The good dispersion of NA-21 also created more nucleation embryos for the adsorption of polypropylene molecules than the agglomerated NA-11. The gel permeation chromatography (GPC) analysis showed that the average molecular weight of HPP and LPP both decreased with the addition of a nucleating agent. The rotational rheometer and capillary rheometer analysis showed that the effect of NA-21 on reducing intermolecular entanglement was more significant, whether in HPP or LPP. The addition of NA-21 had less elastic energy storage and better flow stability, and could be processed at a higher speed. Simultaneously, the relaxation time in the blends with LPP was shorter than that with HPP. It was found that the crystallinity and nucleation efficiency of HPP/nucleating agent blends increased remarkably, while there was a barely perceptible increase in LPP/nucleating agent blends.

Download Full-text

Intrinsic Viscosity-molecular Weight Relationship of Poly (Hexanediol Adipate)

Asian Journal of Chemical Sciences ◽

10.9734/ajocs/2019/v6i218992 ◽

2019 ◽

pp. 1-8

Author(s):

Jiankun Li ◽

Zegang Zong ◽

Dehua Hou ◽

Bojun Tu ◽

Weilan Xue ◽

...

Keyword(s):

Molecular Weight ◽

Intrinsic Viscosity ◽

Average Molecular Weight ◽

Group Analysis ◽

Gel Permeation Chromatography ◽

Molecular Weights ◽

The One ◽

Relationship Of ◽

The Relationship ◽

End Group

In this work, a series of poly(Hexanediol adipate)(PHA) samples (103＜Mn＜104) with narrow molecular weight distribution were prepared by the polymerization between adilic acid and 1,6-hexandiol. End-group analysis was applied to determine the number average molecular weight (Mn) of PHA. Gel permeation chromatography (GPC) was employed to obtain the average molecular weights (Mn, Mv, Mw).The intrinsic viscosity of the samples in the tetrahydrofuran (THF) solution was determined at 298 K by the dilution extrapolation method and the one-point method. The relationship between the intrinsic viscosity and the molecular weight for PHA was studied by the Mark-Houwink-Sakurada (MHS) equation, and the parameters of equation were determined.

Download Full-text

“Nascent” Fe(0)-mediated living radical copolymerization of styrene and acrylonitrile

e-Polymers ◽

10.1515/epoly-2014-0012 ◽

2014 ◽

Vol 14 (3) ◽

pp. 187-192

Author(s):

Guo-Xiang Wang ◽

Mang Lu ◽

Zhao-Hui Hou ◽

Xue-Hui Zhan ◽

Yong Gao ◽

...

Keyword(s):

Gel Permeation Chromatography ◽

Random Copolymer ◽

Monomer Conversion ◽

Radical Copolymerization ◽

Chain Extension ◽

Molar Ratio ◽

Molecular Weights ◽

H Nmr ◽

First Order Kinetics

AbstractIn this work, we reported the synthesis of copolymers of poly(styrene-co-acrylonitrile) via single-electron transfer-living radical polymerization using CCl4 as an initiator and Zn(0)/2,2′-bipyridine (Bpy)/FeCl2 as catalyst complexes. The polymerization was carried out at 25°C. The polymerization proceeded in a living fashion based on “nascent” Fe(0) as the source of the transition metal, which was prepared by Zn(0)/FeCl2 in situ. The kinetic experimental results showed that the copolymerization is first-order kinetics. The molecular weights increased linearly with respect to monomer conversion, and narrow polydispersity index values were obtained. The effect of the molar ratio of [Zn(0)]0/[FeCl2]0 on polymerization was investigated. In addition, the polymerization carried out in different solvents was also investigated. The obtained random copolymer was characterized by 1H NMR and gel permeation chromatography. The living characteristic was demonstrated by chain extension experiment.

Download Full-text

Study on Preparation of Water-Soluble Chitosan with Varying Molecular Weights and Its Antioxidant Activity

Advances in Materials Science and Engineering ◽

10.1155/2019/8781013 ◽

2019 ◽

Vol 2019 ◽

pp. 1-8 ◽

Cited By ~ 3

Author(s):

Dang Xuan Du ◽

Bui Xuan Vuong

Keyword(s):

Molecular Weight ◽

Antioxidant Activity ◽

Dose Range ◽

Average Molecular Weight ◽

Gel Permeation Chromatography ◽

Chitosan Solution ◽

Water Soluble ◽

Molecular Weights ◽

Ph Level ◽

The One

The preparation of water-soluble chitosan (WSC) with various molecular weights by gamma Co-60 irradiation of chitosan solution (5%) in the presence of hydrogen peroxide (1%) combined with acetylated reaction was carried out. The average molecular weight (Mw) of chitosan was measured by gel permeation chromatography (GPC). The chemical structure and the crystallinity of chitosan and WSC were characterized by Fourier-transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD), respectively. The antioxidant activity of WSC and chitosan was investigated using the free radical 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS•+). Obtained results showed that chitosan with Mw of 18–90 kDa could be efficiently prepared by this technique in the dose range from 10 to 24.5 kGy. After the acetylated process, the resulting WSC possesses good solubility in a wide pH level of 2–12, and WSC with low molecular weight exhibited significantly higher antioxidant activity than the one with high molecular weight. In detail, the antioxidant activity was 14.7%, 70.5%, 84.2%, 89.4%, and 97.5% for WSC samples prepared from chitosan with Mw of 140.2 kDa, 91.4 kDa, 51.2 kDa, 35.3 kDa, and 18.1 kDa, respectively, at the same reaction time of 90 min. Moreover, the antioxidant activity of WSC was higher than that of chitosan. Thus, WSC prepared by gamma Co-60 irradiation and acetylated process can be potentially applied as a natural antioxidant agent.

Download Full-text

Synthesis and characterization of highly branched polymethacrylates via self-condensing oxyanionic copolymerization

e-Polymers ◽

10.1515/epoly.2005.5.1.172 ◽

2005 ◽

Vol 5 (1) ◽

Author(s):

Zhifeng Jia ◽

Wei Huang ◽

Deyue Yan

Keyword(s):

Gel Permeation Chromatography ◽

Hydroxyethyl Methacrylate ◽

Molecular Weights ◽

Vinyl Group ◽

Branched Structure ◽

Potassium Hydride ◽

Cationic Polyelectrolytes ◽

Reversible Phase

AbstractHighly branched polymethacrylates were successfully synthesized by the self-condensing vinyl copolymerization of 2-dimethylaminoethyl methacrylate (DMAEMA) and methacrylic inimer containing a vinyl group and an oxyanionic active site, which was formed via the in situ reaction of 2-hydroxyethyl methacrylate (HEMA) with potassium hydride. Depending on the comonomer ratio, γ = [DMAEMA]0/[HEMA]0, branched poly(DMAEMA)s with number-average molecular weights between 4800 and 22 000 and degree of branching between 0.09 and 0.38 were obtained, as evidenced by gel permeation chromatography and NMR analysis. Thermally reversible phase transitions were observed for the branched poly(DMAEMA)s produced at higher comonomer ratio (γ ≥ 5). Quaternization of the branched poly(DMAEMA)s with methyl iodide led to cationic polyelectrolytes with branched structure.

Download Full-text

Use of Rubber Process Analyzer for Characterizing the Molecular Weight Parameters of Natural Rubber

International Journal of Polymer Science ◽

10.1155/2015/517260 ◽

2015 ◽

Vol 2015 ◽

pp. 1-6 ◽

Cited By ~ 6

Author(s):

Tianming Gao ◽

Ruihong Xie ◽

Linghong Zhang ◽

Hongxing Gui ◽

Maofang Huang

Keyword(s):

Molecular Weight ◽

Natural Rubber ◽

Milling Time ◽

Laser Light ◽

Average Molecular Weight ◽

Gel Permeation Chromatography ◽

Sweep Frequency ◽

Weight Average Molecular Weight ◽

Molecular Weights ◽

Strain Sweep

The aim of this work is to introduce a simple and rapid method for characterizing the molecular weight parameters and other molecular structure parameters of natural rubber (NR) using a rubber process analyzer (RPA). In this work, NR of different molecular weights was prepared by milling. Molecular weight parameters were measured by gel permeation chromatography coupled with laser light scattering (GPC-LLS) for comparison with RPA results. It was verified that increasing of milling time leads to a decrease of the number-average molecular weight (M-n), weight-average molecular weight (M-w), and molecular weight distribution (MWD). The dynamic and rheological properties were evaluated on RPA by tests of strain sweep, frequency sweep, and stress relaxation. These results were used to characterize the average molecular weight, MWD, and viscosity of NR and were found to agree with those from GPC-LLS. This convenient and rapid technology for characterizing NR molecular weight parameters would be especially useful in the elastomer industry.

Download Full-text