Average Molecular Weight Measurements Research Articles

Lotus Root Polysaccharide-Phenol Complexes: Interaction, Structure, Antioxidant, and Anti-Inflammatory Activities.

This research aimed to explore the interaction between lotus root polysaccharides (LRPs) and phenolic compounds, and to study the effects of phenolic binding on the structural and functional properties of LRPs. The influences of pH, temperature, and NaCl and phenol concentration on the binding ratio of gallic acid (GA)/epigallocatechin (EGC) to LRPs were evaluated. LRP-GA/EGC complexes with different phenolic binding amounts were then prepared and characterized via ultraviolet-visible (UV-Vis) and Fourier-transform infrared (FTIR) spectroscopy, and average molecular weight (MW) measurements. The results suggest that hydrogen bonds contributed to the binding of GA/EGC and LRPs. The phenolic binding led to significant changes in the structure and MW of LRPs. Moreover, antioxidant activity and the macrophage-stimulating effect of LRPs were improved after binding with GA/EGC, depending on the binding amount and type of polyphenol. Interestingly, LRP-GA/EGC complexes with polyphenol binding amounts of 105.4 mg/g and 50.71 mg/g, respectively, showed better stimulation effects on the anti-inflammatory cytokine IL10 secretion of macrophages when compared to LRPs. These results show the great potential of phenolic binding to be applied to improve the structure and functional activity of LRPs.

Biodegradability study of polypropylene fibers blended with disposable recycledpoly(lactic acid) plastic flakes

Polymer blending as an efficient method for blending at least two~polymers is usually used to create new materials with desirable physical properties. This article focuses on the biodegradability evaluation of polypropylene (PP) fibers modified with disposable recycled poly(lactic acid) (r-PLA) plastic flakes. Biodegradable modified PP fibers containing 30% r-PLA were prepared by melt spinning process and evaluated with different methods of biodegradation assays. The soil burial test method, CO$_{2}$ evolution analysis, weight loss, mechanical properties, and average molecular weight measurements and analysis of surface morphological changes were performed for biodegradability evaluation of the modified PP fibers. Surface morphology of the blend fibers illustrated that by increasing the soil burial period cracks were formed on the surfaces of fibers. While different testing methods showed different values for the biodegradation process, the results obtained from the CO$_{2}$ evolution analysis, weight loss, and variation of mechanical properties confirmed a good agreement between different degradation methods. After incubation in soil for a long period of time, the initial moduli and tenacity of the modified fibers decreased up to 72% and 53%, respectively. In addition, the average molecular weight measurement showed a 28% decrease in average molecular weight after 80 days of soil burial.

GPC/ICP-AES法によるカラギナン分子量測定方法

GPC/ICP-AES法によるカラギナン分子量測定方法

Reprocessing of wood flour reinforced polypropylene composites: Impact of particle size and coupling agent on composite and particle properties

This work aims to understand the degradation induced by multiple injection molding cycles on numerous properties of wood flour reinforced polypropylene (PP) composites. The influence of the initial wood particle size was studied as well as the influence of the addition of polypropylene grafted with maleic anhydride (PPgma) as a coupling agent at a given rate. Biocomposite compounds (20wt% of wood flour) are produced by twin-screw extrusion. Then, multiple injection and grinding cycles were performed (up to 7 cycles) to obtain normalized samples. The evolution of the wood flour particle characteristics is first assessed by SEM observation, size measurements and nanoindentation experiments. Then, the evolution of the PP matrix microstructure is determined by SEC tests (average molecular weight measurements), rheometer tests and DSC (polymer crystallinity). Finally, material mechanical properties are measured at a macro-scale thanks to tensile tests. Our experimental results show that the composite mechanical properties remain quite stable after 7 processing cycles despite wood flour degradation and PP degradation.

Control of Ethylene and Propylene Polymerisation Processes

Many polymerisation processes can be accurately controlled by the regulation of chain growth through rheological measurement of average molecular weight. This article looks at the new developments in rheological analysers that can reintroduce closed-loop control into a variety of polyethylene and polypropylene manufacturing processes. Through the study of the exact flow patterns in Melt Flow Index test, computer fluid dynamics has enabled this industry standard test method to be faithfully replicated in the some of the more advanced instruments. These instruments can now be classed as analysers and serve the intended purpose of better control of the polymerisation processes. The whole of the polymer industry can benefit from this combined system of measurement and control technology. Closed-loop control of the primary polymer manufacture can ensure that the product is made to close tolerances instead of the present permitted ±10% passband. The manufacturer can benefit from improved plant efficiency by making the desired product as well as being able to guarantee a highly consistent product. The downstream processor can benefit from reduced material usage and elimination of process set-up wastage. A large variety of recyclers and the raw material manufacturers can benefit from the new technology by introducing reaction grades of polymer into the existing processes or by improving the measurement and control of those processes that are already producing reaction grades.

Solvent free synthesis of polyaniline with improved molecular weight through solid state mechanochemical milling at ambient temperature

Mechanochemical synthesis of polyaniline was conducted by our self-designed pan mill equipment, which has a unique and smart structure and can exert fairly strong squeezing and shearing forces on the milled materials. The obtained product was examined by SEM, Fourier transform infrared (FTIR) and UV–Vis spectroscopy, viscometric average molecular weight measurement, X-ray diffraction (XRD) and thermogravimetric analysis. Comparative analysis of polyaniline prepared by solid state mechanochemical milling and mortar grinding was carried out. The formation of polyaniline was confirmed by FTIR and UV–Vis spectroscopy. Measurement of viscosity molecular weight showed that the molecular weight of pan milling prepared polyaniline was over three times higher than that of the mortar ground ones. The analysis of XRD patterns showed that polyaniline exposed to longer time shearing force tends to have a higher degree of crystallinity, and after milling for a certain time, pan milling prepared polyaniline would be more crystalline than the mortar ground polyaniline. Enhanced thermal stability of the pan milling prepared polyaniline further confirmed the improvement of the molecular weight.

Comparing microcrystalline with spherical nanocrystalline cellulose from waste cotton fabrics

Microcrystalline cellulose (MCC) and spherical nanocrystalline cellulose (SNCC) were successfully prepared from waste cotton fabrics through acid hydrolysis. The comparative analysis of the morphology and structure between the obtained MCC and SNCC was carried out. The SNCC suspension exhibited higher stability than the MCC suspension. Transmission electron microscopy in combination with atomic force microscopy showed that the cellulose nanospheres with average size of 35 nm were achieved, while the average particle size of MCC was 49 μm. The MCC and SNCC had similar functional groups and crystalline structure as confirmed by Fourier transform infrared spectroscopy and X-ray diffraction analysis, respectively. Viscometric average molecular weight measurement and thermo gravimetric analysis indicated that the degree of polymerization and thermal stability of SNCC was lower than that of MCC. These results should improve understanding of the characteristics of MCC and SNCC derived from waste cotton fabrics and lead to many new applications.

Hydrogenation of Alkali Lignin Catalyzed by Pd/C

Hydrogenation of alkali lignin was carried out in the presence of Pd/C catalyst at hydrogen pressure 1∼5 MPa. Catalytic activity of Pd/C catalyst was investigated according to the structure changes of alkali lignin, which were characterized by UV and 1H-NMR spectroscopy. The measurement of average molecular weight undertook by gel permeation chromatography (GPC). Changes on function groups of alkali lignin were analyzed through chemical methods. Results show that total hydroxyl, phenolic hydroxyl and alcoholic hydroxyl increase 64.23%, 37.10% and 89.67%, respectively, while carbonyl and carboxyl decrease separately 43.50% and 53.41%. No significant differences of the total acidic groups and the phenyl structure were found after reaction. GPC analysis shows the weight average molecular weight (Mw) and number average molecular weight (Mn) are both decreased, and the polydispersity of alkali lignin is increased The active function groups of alkali lignin are increased obviously, and reactive activity of alkali lignin is enhanced as a result. The present results demonstrate Pd/C catalyst shows an excellent catalytic activity on reductive reaction of alkali lignin and hydrogen.

Structure of Aggregates of Dialkyl Urea Derivatives in Solutions

Combined IR spectroscopy, dipole moment, and average molecular weight measurements and DFT calculations on the self-aggregation of N,N'- and N,N-dialkylureas in solvents of different polarities were performed. It was found that, to acquire a better understanding of the mechanisms of associations, the simultaneous use of all of these methods is required. It was found that symmetric dialkyl derivatives of urea associate much more strongly, giving in CCl(4) even a 12-fold mass of monomers, in contrast to asymmetric ones, where the average molecular weight reaches only a 2-fold mass of monomers. The very strong influence of solvents was discovered. The aggregation is much weaker in more polar chloroform and 1,2-dichloroethane leading to only a 2-fold increase in the average molecular weight. A strong influence of the symmetry of dialkylurea molecules was also found. Dipole moments of symmetric N,N'-dialkylurea increase with concentration, suggesting a rather linear arrangement of vectors in an aggregate. For asymmetric N,N-derivatives dipole moments decrease with concentration. DFT calculations were used to predict the form of aggregation.

Polybithiophene and its bilayers with polyaniline coatings on stainless steel by electropolymerization in aqueous medium

For the first time, electrosynthesis of polybithiophene (PBTh) and its bilayers with polyaniline (PAni) coatings on stainless steel (SS) in aqueous oxalic acid solutions containing monomer and sodium dodecyl sulfate (SDS) was carried out by potentiodynamic synthesis technique. Smooth and adherent films were obtained on the steel surfaces. Homopolymers and bilayers were characterized by cyclic voltammetry, FTIR, UV–vis spectroscopies and SEM. Homopolymers were also characterized by means of conductivity and the number average molecular weight measurements. The effects of the scanning potential limits on electrosynthesis of PBTh and its bilayer coatings were investigated. The test for corrosion protection of the polymer coated and uncoated SS substrates were performed in highly aggressive 0.5 M NaCl and 0.5 M HCl solutions by linear potentiodynamic polarization and Tafel test technique, respectively. Corrosion test revealed that among the protective coatings obtained, PBTh as homopolymer and PAni/PBTh as bilayer exhibited the most effective anticorrosive properties. According to linear potendynamic polarization test, the dissolution current of these coatings at 1.6 V decreased to 99.8% and 99.6% in NaCl solution, respectively, when compared to that of uncoated SS surfaces.

Synthesizing UHMWPE Using Ziegler‐Natta Catalyst System of MgCl2(ethoxide type)/ TiCl4/tri‐isobutylaluminum

AbstractSummery: A Ziegler‐Natta catalyst of MgCl2 (ethoxide type)/TiCl4 has been synthesized. In order to obtain ultra high molecular weight polyethylene (UHMWPE) tri‐isobutylaluminum which is less active to chain transfer was used as cocatalyst. Slurry polymerization was carried out for the polymerization of ethylene while, dilute solution viscometry was performed for the viscosity average molecular weight (Mv) measurement. The effect of [Al]/[Ti] molar ratio, temperature, monomer pressure and polymerization time on the Mv and productivity of the catalyst have been investigated. The results showed increasing [Al]/[Ti] ratio in the range of 78–117, decreased the Mv of the obtained polymer from 7.8 × 106 to 3.7 × 106 however, further increase of the ratio, resulted in decreased of by much slower rate up to [Al]/[Ti] = 588. The higher pressure in the range of 1–7 bars showed the higher the Mv of the polymer obtained, while increasing temperature in the range of 50 to 90 °C decreased the Mv from 9.3 × 106 to 3.7 × 106. The Mv rapidly increase with polymerization time in the first 15 minutes of the reaction, this increase was slowly up to the end of the reaction (120 min). Increasing [Al]/[Ti] ratio raised productivity of the catalyst in the range studied. Rising reaction temperature from 50 to 75 °C increased the productivity of the catalyst however, further increase in the temperature up to the 90 °C decreased activity of the catalyst. Monomer pressure in the range 1 to 7 bars yields higher productivity of the catalyst. Also by varying polymerization conditions synthesizing of UHMWPE with Mv in the range of 3 × 106 to 9 × 106 was feasible.

Empirical models for end-use properties prediction of LDPE: application in the flexible plastic packaging industry

The objective of this work is to develop empirical models to predict end use properties of low density polyethylene (LDPE) resins as functions of two intrinsic properties easily measured in the polymers industry. The most important properties for application in the flexible plastic packaging industry were evaluated experimentally for seven commercial polymer grades. Statistical correlation analysis was performed for all variables and used as the basis for proper choice of inputs to each model output. Intrinsic properties selected for resin characterization are fluidity index (FI), which is essentially an indirect measurement of viscosity and weight average molecular weight (MW), and density. In general, models developed are able to reproduce and predict experimental data within experimental accuracy and show that a significant number of end use properties improve as the MW and density increase. Optical properties are mainly determined by the polymer morphology.

In Defense of Vapor Pressure Osmometry for Measuring Molecular Weight

The value of the average molecular weight of petroleum asphaltenes continues to be controversial. Usually the disagreement is about the measurement of a single asphaltene fraction when the need is for a consistent picture that comprises all fractions of petroleum and includes chemical changes during processing. By using one of the better solvents for carbonaceous materials, o‐dichlorobenzene, at the maximum instrument temperature, vapor pressure osmometry provides a consistent measurement of number average molecular weight not achieved by any other technique. This average molecular weight is consistent among petroleum fractions and gives predictable changes in asphaltene molecular weight with thermal processing.

Kinetics and Modelling of Bulk and Solution Diallyl Terephthalate Polymerization

Free radical polymerization kinetics of diallyl terephthalate (DAT) in solution was investigated with two different peroxide initiators: dicyclohexyl peroxydicarbonate (CHPC) and benzoyl peroxide (BPO) in temperature range from 50°C to 110°C, where ortho-xylene was used as a solvent. Conversion points were measured using Fourier Transform Infrared (FTIR) measurements. Previously developed kinetic model for bulk DAT polymerization, was extended to solution DAT polymerization. The ratio of solvent chain - transfer rate constants to propagation rate constants of the polymerization system were found between 1.25 10-4 to 1.68 10-4 for various reaction conditions. They were obtained using the calculated initial polymerization rates and the number average molecular weight measurements made by GPC. The effect of different solvent fractions and initiator concentrations on the diffusion limitations were investigated. Only two kinetic parameters, kpd0 and ktd0 were obtained by fitting the kinetic model onto measured conversions for various reaction conditions at 0.2, 0.5 and 0.8 solvent fractions. Thus obtained kpd0 and ktd0 kinetic parameters were extrapolated to zero solvent fractions and from obtained values of kinetic parameters the conversion points for bulk DAT polymerization were calculated and compared to measured conversion points.

Polyhydroxyetheresters from resin acids

Summary — Six new polyetheresters were synthesized in polyaddition reaction in solution or in bulk. Polyaddition reactions have been carried out using the equimolar amounts of the adducts (RAAA), obtained in Diels-Alder reaction from resin acids (RA) and acrylic acids (AA), with three various epoxy resins with addition of adipic acid (AAd) or without it. The products obtained were characterized using FT-IR and 1 H NMR methods as well as on the basis of average molecular weight, nitrogen content and inherent viscosity measurements. The results of spectroscopic investigations confirmed RAAA adducts structures and epoxy ring opening in polyaddition reaction of epoxy resins with RAAA as well. Thermal stability of the products has been tested using TGA method. It was found they were rather stable at temperature up to 250—300 o C. The presence of AAd in the reaction mixture increases slightly thermo-oxidizing degradability but brightens the color and increases molecular weight of polyhydroxyetheresters. These products dissolve in majority of organic solvents because of the chemical structure (presence of OH groups and hydrophenantrene fragments).

MOLECULAR WEIGHT STUDIES ON THE GAMMA IRRADIATION DEGRADATION OF POLY(METHYLMETHACRYLATE) IN THE ABSENCE AND PRESENCE OF SULFANILAMIDE DERIVATIVES, PART I: TETRAOXALYLSULFANILAMIDE AND ITS COBALT (II) COMPLEX

Protection of some poly (methylmethacrylate) samples against gamma rays has been investigated in the absence and presence of Tetraoxalylsulfanilamide and its Cobalt (II) complex. The pure PMMA (without additives), PMMA-Ligand and PMMA - Cobalt (II) complex composite samples were irradiated with gamma rays for different exposure doses (5, 15, 25, 35, 50, 75 and 100 KGy). Viscosity average molecular weight (Mv-values) and thin layer chromatographic measurements were carried out after each irradiation dose.The maximum protection against gamma ray is found when 3% of the organic ligand or its Cobalt (II) complex is used in the polymer matrix.The radiation chemical yield for chain scission (Gs) is calculated and has its lower values in the case of the organic ligand, which means that the protection is stronger in the case of the organic ligand than its Cobalt (II) complex. From TLC studies, it is noticed that both the Rf-values and polydispersity of the PMMA samples increase with increasing exposure dose.

Characterization and relative ionization efficiencies of end-functionalized polystyrenes by matrix-assisted laser desorption/ionization mass spectrometry

The properties and relative ionization efficiencies of a series of polystyrenes (PS) with hydroxyl, hydrogen, tertiary amine, and quaternary amine end-functionalities were examined by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). The hydrogen and hydroxyl functionalized PS ionized via attachment of a single Ag + cation, as expected. However, tertiary amine PS oligomers were found in (M − H) + and (M + H) + forms, in addition to M + Ag +, while the quaternary amine PS oligomers only ionized to the M + form. Analysis of tertiary amine PS spectra revealed varying ratios of the three ionic forms depending on the oligomer length, pointing to a change in ionization efficiency. When the bulk samples were compared, the quaternary amine end-functionalized PS gave a ten-fold higher ionization efficiency over all others studied, likely because of the preexisting charge on the functionality. Samples with hydroxyl and hydrogen functionalities had similar ionization efficiencies, with the tertiary amine slightly higher, depending on the molecular weight. Changes in molecular weight affected the relative ionization efficiencies in varying fashion depending on the end functionality, though average molecular weight measurements were largely unaffected by end-functionality. Quantification of end-functionalized polystyrenes with different ionization efficiencies was found to be possible if due care was taken.

Comparison of properties of acrylic–polyurethane hybrid emulsions prepared by batch and semibatch processes with monomer emulsion feed

AbstractAqueous acrylic–polyurethane hybrid emulsions were prepared by batch and semibatch polymerization of acrylic monomer mixtures (butyl acrylate, methyl methacrylate and acrylic acid) in the presence of polyurethane dispersion. The acrylic component was introduced in the monomer emulsion feed. The weight ratio between acrylic and polyurethane components was varied to obtain different emulsion properties, microphase structure and mechanical film properties. Scanning electron microscopy, average particle size and molecular weight measurements were performed to characterize the latex systems. Mechanical properties were examined by measuring Koenig hardnesses of dried films. The average particle size increased with the acrylic/polyurethane ratio. Particles of larger than average size and, to some extent, higher than average molecular weights by batch process were formed. Koenig hardnesses decreased with increasing acrylic/polyurethane ratio. Properties of emulsions synthesized by semibatch processes were compared with the results reported for a different polyurethane dispersion. Copyright © 2003 Society of Chemical Industry

SEQUENTIAL LINEARIZATION ADAPTIVE CONTROL OF SOLUTION POLYMERIZATION OF METHYL METHACRYLATE IN A BATCH REACTOR

A sequential linearization adaptive PI controller was designed to control the temperature of a batch MMA polymerization reactor. Using the mechanistic model of the polymerization, a transfer function was derived to relate the reactor temperature to the power of the heaters. The coefficients of the transfer function were calculated along the selected temperature trajectory by sequential linearization. In addition, a PI adaptive controller was designed, based on an integral type tuning criteria, to track the temperature trajectory. The controller showed an excellent performance and the maximum deviation was about 0.9°C around 90°C. Measurement of the viscosity average molecular weight shows the possibility of molecular weight control.

The influence of polymer concentration on the radiation-chemical yield of intermolecular crosslinking of poly(vinyl alcohol) by γ-rays in deoxygenated aqueous solution

The effect of polymer concentration on G value of intermolecular crosslinking of poly(vinyl alcohol) (PVA) during γ-ray irradiation is reported here. The G value, determined by the measurement of weight average molecular weight ( M w) from static light scattering, increased initially due to the polymer concentration and approached a maximum value of 0.5 × 10 −7 mol J −1. It then markedly decreased for the more concentrated water-swollen PVA film (polymer concentration C p>300 g dm −3). Our results suggest that polymer concentration plays an important role in the crosslinking and degradation reactions of PVA during γ-ray irradiation.