scholarly journals STUDY OF PROPERTIES OF ISOPRENE OLIGOMERS OBTAINED BY MICROWAVE IRRADIATION OF SKI-3 RUBBER

2021 ◽  
Vol 64 (6) ◽  
pp. 56-61
Author(s):  
Marina E. Tsyganova ◽  
Alevtina P. Rakhmatullina
Keyword(s):  
Molecular Weight ◽  
Microwave Irradiation ◽  
Average Molecular Weight ◽  
Physical And Mechanical Properties ◽  
Low Molecular Weight ◽  
Destruction Process ◽  
Experiment Data ◽  
Irradiation Power ◽  
Power Change ◽  
Isoprene Rubber

The present article proposes a method for production of low molecular weight rubber in microwave irradiation field. Isoprene rubber SKI-3 (10% solution in toluene) was used as the initial reactant. The effect of MWI power change (144 W, 450 W, 675 W, 900 W) on the degree of destruction was studied. The degree of destruction was measured based on the change in viscosity average molecular weight. The findings of the experiment data analysis indicate that the destruction process occurs in correspondence with the following dependency: the increase in the microwave irradiation power raises the destruction degree. At the same time, a decrease in molecular weight was observed. Furthermore, it was found that the use of phospholipids as modifiers also affects the destruction process. The increase in phospholipids content in toluene-SKI-3 system reduces the degree of polyisoprene destruction regardless of the microwave irradiation power. It is demonstrated by the fact that rubber molecular weight is subject to a lower decrease in systems with higher phospholipids content. Phospholipids perform two functions. Firstly, they act as a stabilizer that inhibits the rubber destruction process. Secondly, varying their content allows controlling the destruction degree and obtaining oligomers with predetermined molecular weight. The obtained oligomers were used as SKI-3 isoprene rubber modifiers. It is observed that that the introduction of oligomers into rubber mixtures in the amount of 7 and 10 parts by weight per 100 parts by weight of rubber increases its cohesive strength. Furthermore, vulcanizates containing oligomers are characterized by improved physical and mechanical properties.

scholarly journals Characterisation of Sequential Solvent Fractionation and Base-catalysed Depolymerisation of Treated Alkali Lignin

BioResources ◽  
2015 ◽  
Vol 10 (3) ◽  
pp. 4137-4151 ◽  
Author(s):  
Aikfei Ang ◽  
Zaidon Ashaari ◽  
Edi Suhaimi Bakar ◽  
Nor Azowa Ibrahim
Keyword(s):  
Molecular Weight ◽  
Chemical Structure ◽  
Average Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Solubility Parameters ◽  
Low Molecular Weight ◽  
Sequential Fractionation ◽  
Weight Average Molecular Weight ◽  
Solvent Fractionation ◽  
Alkali Lignin

An alkali lignin (OL) with a weight-average molecular weight (Mw) of 11646 g/mol was used to prepare low-molecular weight lignin for resin synthesis. The low-molecular weight lignin feedstock was obtained via base-catalysed depolymerisation (BCD) treatments at different combined severity factors. Sequential fractionation of the OL and BCD-treated lignins using organic solvents with different Hildebrand solubility parameters were used to alter the homogeneity of the OL. The yield and properties of OL itself and OL and BCD-treated OL dissolved in propan-1-ol (F1), ethanol (F2), and methanol (F3) were determined. Regardless of the treatment applied, a small amount of OL was dissolved in F1 and F2. The BCD treatment did not increase the yield of F1 but did increase the yields of F2 and F3. Gel permeation chromatography (GPC) showed that the repolymerization reaction occurred in F3 for all BCD-treated OL, so these lignins were not suitable for use as feedstocks for resin production. The GPC, 13Carbon-nuclear magnetic resonance, and Fourier transform infrared spectroscopy analyses confirmed that the F3 in OL exhibited the optimum yield, molecular weight distribution, and chemical structure suitable for use as feedstocks for resin synthesis.

scholarly journals Influence of Dextransucrase of Weissella Cibaria Nitcsk4 on Low Molecular Weight Dextran Yield: a Statistical Approach using Mixed Level Taguchi Design and Artificial Neural Network

2019 ◽  
Vol 9 (2S2) ◽  
pp. 657-664
Keyword(s):  
Neural Network ◽  
Molecular Weight ◽  
Mean Squared Error ◽  
Sucrose Concentration ◽  
Average Molecular Weight ◽  
Taguchi Design ◽  
Percentage Error ◽  
Low Molecular Weight ◽  
Weight Average Molecular Weight ◽  
Weissella Cibaria

In the present study, the influence of dextransucrase of Weissella cibaria NITCSK4 (DSWc4), sucrose concentration, and reaction temperature on the yield of low molecular weight dextran (LMWD-DexWc4) was investigated using mixed level Taguchi design and back propagation neural network (BPNN). BPNN model with three neurons in a hidden layer generated a low mean squared error (MSE). The determination coefficients (R2 -value) for ANN and Taguchi models were 0.991 and 0.998, respectively. Considering absolute average deviation (AAD) and MSE, Taguchi model is more adequate. Among three factors, the percentage yield of low molecular weight of dextran is invariably dependent on the sucrose concentration. The study suggested that a low sucrose concentration (3% w/v), DSWc4 (0.25 IU/ml) and slightly high temperature (35°C) ultimately favored the production of LMWD-DexWc4 (91.639%). LMW-DexWc4 produced by DSWc4 at optimized conditions was analyzed. The weight average molecular weight of LMW-DexWc4 was calculated using M-H expression, found to be 85775 (≈90 kDa). The relative percentage error between the number and weight average molecular weight was found to be less (4.42%). The polydispersity (PD) index of the LMW-DexWc4 was found to be 0.9576 and the value is close to 1. The PD value depicted that the molecular weight distribution of dextran was narrowly dispersed.

End-Group Method for Molecular Weight Determination of PET Depolymerization under Microwave Irradiation

2012 ◽  
Vol 554-556 ◽  
pp. 1933-1937 ◽  
Author(s):  
Qing Hua Feng ◽  
Qing Hua Tang ◽  
Wei Lu Zhang ◽  
Yan Hua Jia ◽  
Dong Zhang
Keyword(s):  
Molecular Weight ◽  
Microwave Irradiation ◽  
Average Molecular Weight ◽  
Relative Number ◽  
Group Method ◽  
Molecular Weight Determination ◽  
Stannous Oxide ◽  
Hydrolytic Depolymerization ◽  
End Group

A series of catalysis hydrolytic depolymerization of PET catalyzed by zinc acetate, zinc sulfate, stannous oxide respectively under microwave irradiation at different temperature with time was studied, in which the microwave power was 260W, the ratio of water to PET was 10:1 and the dosage of the catalysts was 0.5% of PET. The relative number average molecular weight of the undepolymerized PET was determined by end-group method. The results show that the molecular weight of the undepolymerized PET decreases with the reaction time increasing, and tends to be stable at the end of the depolymerization reaction. Under the same time, the temperature is higher, the molecular weight is smaller. The molecular weight of the undepolymerized PET reduces most quickly with stannous oxide among the three catalysts.

COMPARATIVE CLINICAL PHARMACOLOGY OF LOW MOLECULAR WEIGHT HEPARINS IN MAN

1987 ◽  
Author(s):  
Y Ordu ◽  
J Augustin ◽  
E V Hodenberg ◽  
V Bode ◽  
J Harenberg
Keyword(s):  
Molecular Weight ◽  
Clinical Pharmacology ◽  
Ex Vivo ◽  
Average Molecular Weight ◽  
Factor Xa ◽  
Low Molecular Weight ◽  
Pharmacological Properties ◽  
Clotting Time ◽  
Activity Time ◽  
Low Molecular Weight Heparins

Low molecular weight (LMW) heparins are obtained by diffent chemical procedures from conventional pig intestinal mucosa heparin. The LMW heparins differ in their molecular weight distribution and physicochemical properties. Therefore, we report of comparative studies on the anticoagulant and lipolytic effects of low molecular weight heparins in man.The following LMW heparins were used: BM 21-23 (Braun, Melsungen, FRG), CY 216 (Choay Laboratories, Paris, France), Heparin NM (Sandoz, Niimberg, FRG), Kabi 2165 (Kabi Vitrum AB, Stockholm, Sweden), RD Heparin (Hepar Industries, Franklin, US A), normal heparin (Braun). All heparins were administered intravenously and subcutaneously to six volunteers each.The data show considerable differences in the anticoagulant and lipolytic effects between the different low molecular weight heparins. From the area under the activity time curves (AUC) of the clotting assays for factor Xa (heptest), aPTT and thrombin clotting time the aXa/aPTT ratio ex vivo and aXa/alla ratio ex vivo were determined (table, average values)It can be seen that there are clear differences in the ex vivo ratios of the LMW heparins. There is a good correlation between the average molecular weight of the LMW heparins and the aXa/aPTT ratio after s.c. administration and of the aXa/alla ratio ex vivo after s.c. administration. Therefore, LMW heparins differ significantly in their clinical pharmacological properties.

scholarly journals A Systematic Study on the Degradation Products Generated from Artificially Aged Microplastics

Polymers ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1997
Author(s):  
Greta Biale ◽  
Jacopo La Nasa ◽  
Marco Mattonai ◽  
Andrea Corti ◽  
Virginia Vinciguerra ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Degradation Products ◽  
Average Molecular Weight ◽  
Size Exclusion ◽  
Gas Chromatography Mass Spectrometry ◽  
Low Molecular Weight ◽  
Photo Degradation ◽  
Degradation Processes ◽  
Wide Range

Most of the analytical studies focused on microplastics (MPs) are based on the detection and identification of the polymers constituting the particles. On the other hand, plastic debris in the environment undergoes chemical and physical degradation processes leading not only to mechanical but also to molecular fragmentation quickly resulting in the formation of leachable, soluble and/or volatile degradation products that are released in the environment. We performed the analysis of reference MPs–polymer micropowders obtained by grinding a set of five polymer types down to final size in the 857–509 μm range, namely high- and low-density polyethylene, polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET). The reference MPs were artificially aged in a solar-box to investigate their degradation processes by characterizing the aged (photo-oxidized) MPs and their low molecular weight and/or highly oxidized fraction. For this purpose, the artificially aged MPs were subjected to extraction in polar organic solvents, targeting selective recovery of the low molecular weight fractions generated during the artificial aging. Analysis of the extractable fractions and of the residues was carried out by a multi-technique approach combining evolved gas analysis–mass spectrometry (EGA–MS), pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS), and size exclusion chromatography (SEC). The results provided information on the degradation products formed during accelerated aging. Up to 18 wt% of extractable, low molecular weight fraction was recovered from the photo-aged MPs, depending on the polymer type. The photo-degradation products of polyolefins (PE and PP) included a wide range of long chain alcohols, aldehydes, ketones, carboxylic acids, and hydroxy acids, as detected in the soluble fractions of aged samples. SEC analyses also showed a marked decrease in the average molecular weight of PP polymer chains, whereas cross-linking was observed in the case of PS. The most abundant low molecular weight photo-degradation products of PS were benzoic acid and 1,4-benzenedicarboxylic acid, while PET had the highest stability towards aging, as indicated by the modest generation of low molecular weight species.

LOW MOLECULAR WEIGHT HEPARINS s ORAL ABSORPTION IN MONKEYS

1987 ◽  
Author(s):  
S E Lasker ◽  
B Y Lee ◽  
R E Madden
Keyword(s):  
Molecular Weight ◽  
Oral Absorption ◽  
Average Molecular Weight ◽  
Test System ◽  
Maximum Activity ◽  
Low Molecular Weight ◽  
Low Molecular Weight Heparins ◽  
Equilibrium Ultracentrifugation ◽  
Clinical Potential ◽  
Weight Data

An orally administered low molecular weight heparin-like derivative of the commercial polydisperse polysaccharide is desirable clinically. The dissociation of antithrombotic properties and the induction of bleeding as well as minimal effect on platelet function are characteristics of some low-molecular weight heparins; however the circulating level of the anti Xa activity associated with demonstrable theraputic efficacy is not yet defined.The availability of a variety of low molecular weight heparins provided us with the opportunity to evaluate the gastrointestinal absorption characteristics of the preparations in the primate.Average molecular weight is only one of a spectrum of variables associated with absorbability, while Xa/APTT ratio differences and non-equivalent structural alterations may be responsible for functional differences in a living test system. Nevertheless, because of the clinical potential it is instructive to evaluate the GI absorbability of several preparations for which we have precise molecular weight data.Preparations: Low molecular weight heparins were prepared by a variety of methods including isolationby alcohol fractionation from broadly polydisperse commercial or crude heparins, depolymerization of commercial or crude heparin and franctionation of depolymerization products.Methods:Molecular weights were established by equilibrium ultracentrifugation and anti Xa activity was assayed by the Yin-Wessler coagulation method. Faste rhesus monkeys weighing 8-13 kg. were anesthestized and intubated with a radio opaque catheter. One cubic centimeter of a heparin preparation in saline was instilled directly into the duodenum. Blood samples assayed for anti Xa activity and thromboelasticity were drawn at periodic intervals from an indwelling femoral catheter.Results:Standard unfractionated heparin was detectable in blood only after one-half hour. The maximum activity for low molecular weight preparations was achieved after one-half to one hour.One fraction demonstrated activity in the plasma after four hours. Thedose response curve for one fraction at half-hour wascuyvilineal between 7 and 16 Mg/Kg.

Changes in protein composition during grain development in wheat

2001 ◽  
Vol 52 (4) ◽  
pp. 485 ◽  
Author(s):  
J. F. Panozzo ◽  
H. A. Eagles ◽  
M. Wootton
Keyword(s):  
Molecular Weight ◽  
Maximum Rate ◽  
Average Molecular Weight ◽  
Protein Composition ◽  
Grain Filling ◽  
Triticum Aestivum L ◽  
Logistic Function ◽  
Low Molecular Weight ◽  
Grain Development ◽  
Glutenin Subunits

Changes in glutenin, gliadin, glutenin subunit composition, and polymer size distribution were monitored for 4 cultivars of wheat (Triticum aestivum L.) throughout grain filling in an irrigated and non-irrigated environment over 2 seasons. The synthesis of glutenin and gliadin was modelled using a logistic function to determine the rate and duration of synthesis in response to environmental conditions. The maximum rate of synthesis of glutenin occurred approximately 6–8 days after the maximum rate of gliadins, with the duration extended by a similar period. High molecular weight glutenin subunits (HMWGS) were detected earlier than low molecular weight glutenin subunits (LMWGS). After the initial synthesis of HMWGS, there was a period at approximately mid grain filling when the rate of synthesis was reduced, followed by a period of more rapid synthesis in the latter stages of grain filling. In contrast, once detected, LMWGS increased at a faster rate than, and were in excess with respect to, HMWGS. Cultivar and environmental differences were observed, but in all cases the average molecular weight of polymeric glutenin increased throughout grain filling. Large polymers (>400 kD) increased continuously during grain filling, whereas polymers in the range 150–400 kD remained relatively constant and smaller polymers <150 kD decreased. As grain filling approached physiological maturity, there was a rapid increase in the synthesis of large polymers. The gliadin to glutenin ratio was almost the same in grain from adjacent irrigated and non-irrigated environments subjected to high temperatures at mid grain f illing, but the proportion of highly polymeric glutenin was greater from the non-irrigated environment.

Polyamide 6 and high molecular weight phenol novolac blend having excellent mechanical properties in humid conditions

2018 ◽  
Vol 32 (6) ◽  
pp. 778-794 ◽  
Author(s):  
Takayuki Hirai ◽  
Kenzo Fukumori ◽  
Taiji Ikawa ◽  
Tetsuya Oda
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Glass Transition ◽  
High Molecular Weight ◽  
Room Temperature ◽  
Glassy State ◽  
Physical And Mechanical Properties ◽  
Polyamide 6 ◽  
Low Molecular Weight ◽  
Melt Mixing

Polymer blends of polyamide 6 (PA6) and phenol novolac (PN) were prepared by melt mixing. Up to 30 wt% of high molecular weight PN (HPN) or low molecular weight PN (LPN) was blended with PA6, and the physical and mechanical properties were examined. The water absorption of PA6 is inhibited by PN, and this effect is independent of the molecular weight of PN. PA6 and PN are miscible, and their blends show a single glass transition temperature ( T g) that is higher than that of PA6. HPN can enhance the T g of PA6 more efficiently than LPN because of its high T g. PA6 and the PA6/LPN blend after immersion in water had lower-than-room-temperature T gs transitioning to rubbery states. In contrast, the PA6/HPN blend after immersion in water had a higher-than-room-temperature T g. The PA6/HPN blend in water has excellent mechanical properties in its glassy state compared to those of PA6 in the dry state. Thus, the PA6/HPN blend can be used to broaden the applications of PA6, especially in humid conditions.

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