Higher Average Molecular Weight Research Articles

Peatlands Versus Permafrost: Landscape Features as Drivers of Dissolved Organic Matter Composition in West Siberian Rivers

AbstractWest Siberia contains some of the largest soil carbon stores on Earth owing to vast areas of peatlands and permafrost, with the region warming far faster than the global average. Organic matter transported in fluvial systems is likely to undergo distinct compositional changes as peatlands and permafrost warm. However, the influence of peatlands and permafrost on future dissolved organic matter (DOM) composition is not well characterized. To better understand how these environmental drivers may impact DOM composition in warming Arctic rivers, we used ultrahigh resolution Fourier‐transform ion cyclotron resonance mass spectrometry to analyze riverine DOM composition across a latitudinal gradient of West Siberia spanning both permafrost‐influenced and permafrost‐free watersheds and varying proportions of peatland cover. We find that peatland cover explains much of the variance in DOM composition in permafrost‐free watersheds in West Siberia, but this effect is suppressed in permafrost‐influenced watersheds. DOM from warm permafrost‐free watersheds was more heterogenous, higher molecular weight, and relatively nitrogen enriched in comparison to DOM from cold permafrost‐influenced watersheds, which were relatively enriched in energy‐rich peptide‐like and aliphatic compounds. Therefore, we predict that as these watersheds warm, West Siberian rivers will export more heterogeneous DOM with higher average molecular weight than at present. Such compositional shifts have been linked to different fates of DOM in downstream ecosystems. For example, a shift toward higher molecular weight, less energy‐rich DOM may lead to a change in the fate of this material, making it more susceptible to photochemical degradation processes, particularly in the receiving Arctic Ocean.

Development of Synthetically Accessible Glycolated Polythiophenes for High‐Performance Organic Electrochemical Transistors

AbstractFour glycolated polythiophene‐based organic mixed ionic‐electronic conductors (OMIECs), PE2gTT, PE2gT, PT2gTT, and PT2gT are prepared by atom‐efficient direct arylation polymerization, avoiding the need for toxic organometallic precursors. PE2gT, PT2gTT, and PT2gT are operable in p‐type accumulation mode organic electrochemical transistors (OECTs), with PT2gT displaying the best device performance with a µC* product figure‐of‐merit of 290 F cm−1 V−1 s−1. A record volumetric capacitance among p‐type glycolated polythiophene OMIECs of 313 F cm−3 is observed for PE2gT, ascribed to the high proportionality of polar components in its materials design. The good OECT performance of PE2gT with µC* = 84.2 F cm−1 V−1 s−1, comparable with state‐of‐the‐art poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) devices, coupled with its synthetic accessibility and favorable accumulation mode operation makes PE2gT an ideal glycolated alternative to PEDOT:PSS in bioelectronics. PE2gT with the least negative threshold voltage also displays the best OECT operational cycling stability, linked to better resistance of its oxidized state against parasitic redox side reactions . Shelf life stability of OECTs stored (without bias) is observed to be better for materials with a more negative threshold voltage and higher average molecular weight (PT2gT), that are less susceptible to ambient auto‐oxidation and film delamination.

Fractionation and physicochemical characterization of dietary fiber of kenaf (Hibiscus cannabinus L.) seed.

Kenaf seeds are underutilized kenaf plant by-products, containing essential nutrients including dietary fiber (DF), which can be potentially utilized as food ingredients. The present study aimed to evaluate the physicochemical characteristics of kenaf seed fiber fractions extracted from kenaf seed. Defatted kenaf seed powder yielded four DF fractions: alkali-soluble hemicellulose (146.4 g kg-1 ), calcium-bound pectin (10.3 g kg-1 ) and acid-soluble pectin (25.4 g kg-1 ) made up the soluble fibre fraction, whereas cellulose (202.2 g kg-1 ) comprised the insoluble fraction. All fractions were evaluated for their physicochemical properties. The DF fractions contained glucose, mannose, xylose and arabinose, and a small amount of uronic acid (1.2-2.7 g kg-1 ). The isolated pectin fractions had a low degree of esterification (14-30%). All the isolated DF fractions had high average molecular weights ranging from 0.3 to 4.3 × 106 g mol-1 . X-ray diffractogram analysis revealed that the fractions consisted mainly of an amorphous structure with a relative crystallinity ranging from 31.6% to 44.1%. The Fourier-transform infrared spectroscopy spectrum of kenaf seed and its DF fractions showed typical absorption of polysaccharides, with the presence of hydroxyl, carboxyl, acetyl and methyl groups. Scanning electron microscopy analysis demonstrated that the raw material with the rigid structure resulted in soluble and insoluble DF fractions with more fragile and fibrous appearances, respectively. The soluble DF demonstrated greater flowability and compressibility than the insoluble fractions. These findings provide novel information on the DF fractions of kenaf seeds, which could be used as a potential new DF for the food industry. © 2023 Society of Chemical Industry.

Management of non-compressible hemorrhage and re-bleeding by a liquid hemostatic polysaccharide floccuronic acid

Effective management of excessive bleeding requires liquid hemostatic agents, especially in scenarios involving uncompressible and postoperative hemorrhage. This study introduces the microbial exopolysaccharide floccuronic acid (FA) as a liquid hemostatic agent, characterized by a high weight average molecular weight of 2.38 × 108 Da. The investigation focuses on the flocculation effect, hemostatic efficiency in both in vitro and in vivo settings, elucidating its hemostatic mechanism, and assessing its safety profile. Results reveal that FA solution significantly accelerates the coagulation process, leading to the formation of compact clots while specifically interfering with fibrin. Notably, FA demonstrates excellent hemostatic effects in animal liver models and a rat arterial rebleeding model. The biocompatible and biodegradable characteristics further underscore FA's potential as a valuable liquid hemostatic material, particularly suited for non-compressible and re-bleeding scenarios.

Bio-based high gas barrier polyesters based on furandicarboxylic acid: Trade-off between ethylene and propylene diols

A series of bio-based poly(ethylene-co-propylene furandicarboxylate) (PEPF) copolyesters with different compositions were synthesized from dimethyl-2,5-furandicarboxylate, ethylene glycol and 1,3-propanediol by transesterification and melting polycondensation. Their chemical structure, composition and sequence distribution were confirmed by 1H NMR and 13C NMR. The results of GPC showed that the obtained copolyesters had a high number average molecular weight between 25000 g/mol and 30900 g/mol. The thermal properties characterized by DSC showed that the Tg increased with the mole fraction of EF from 64.4℃ for PEPF-23 to 83.2℃ for PEPF-84 as well as the samples displayed a high Young's modulus between 2800 and 3360 MPa and tensile strength between 56 and 89 MPa. Furthermore, the PEPF copolyesters exhibited excellent CO2, O2 and H2O barrier properties compared with poly(ethylene terephthalate) with the BIFp of 8.7–10 times, 3.7–4.4 times and 1.5–1.6 times, respectively. The transparency of PEPFs was up to 89% by cutoff at 700 nm and had better solvent resistance. This work builds a bridge between poly(ethylene 2,5-furandicarboxylate) and poly(propylene 2,5-furandicarboxylate) and PEPFs owned excellent thermo-mechanical and gas barrier properties could be used in food packaging fields.

Investigations on physical, structural, elastic, optical and radiation shielding properties of boro-tellurite glasses for radiation waste management applications

The boro-tellurite glasses with the chemical composition 29B2O3+20TeO2+50MO +1Dy2O3 containing different modifiers (where M = Ba, Li2, Sr, Ca, Mg and Zn) have been produced via conventional melt quenching method. The elastic, structural, physical, optical bandgap properties and the high energy photon shielding behavior of the produced glasses were extensively inspected through appropriate characterization techniques. The X-ray diffraction (XRD) pattern confirms amorphous character of the as-quenched samples. The Fourier-Transform Infrared (FTIR) spectral analysis reveals the presence of functional groups by the way of their stretching and bending vibrational modes. The estimation of parameters like Boron–Boron separation (dB−B), Bond density (n0), oxygen molar volume (V0), and Oxygen Packing Density (OPD) were facilitated to understand the detailed structural modifications and the moduli of elasticity (E, K, G, σ) parameters were determined for the fabricated the boro-tellurite glasses. The barium incorporated present boro-tellurite glass possess lower OPD and higher average molecular weight and it might make the glass network densely packed. To ensure the radiation protection ability, defending parameters such as equivalent atomic number, mass attenuation coefficient (MAC), Effective electron density, half-value layer (HVL), mean free path (MFP) and build-up factors of the titled glasses were determined employing the user friendly Phy-X software. Barium cations added boro-tellurite glass found to have the shortest MFP and HVL, as well as the lowest EBF in the low and intermediate energy zones indicating the potential for using the barium cations incorporated boro-tellurite glass as alternatives for conventional concretes in shielding and waste management applications.

Global Consumption Speed of Jet Fuel/Air Flames and the Impact of Fuel Chemistry

ABSTRACT Large hydrocarbon fuels are used for ground and air transportation and will be for the foreseeable future. A key parameter when burning these fuels is the turbulent consumption speed, which is the velocity at which fuel and air are consumed through a turbulent flame front. Such information can be useful as a model input parameter and for validation of modeled results. In this study, turbulent consumption speeds were measured for three jet-like fuels using a premixed turbulent Bunsen burner. The burner was used to independently control turbulence intensity, unburned temperature, and equivalence ratio. Each fuel had similar heat releases (within 2%), laminar flame speeds (within 5–15%), and adiabatic flame temperatures. Despite this similarity, for constant Re D and turbulence intensity, A2 fuel (i.e. jet-A) has the highest turbulent flame speeds and remains stable (i.e. without tip quenching) at lower ϕ than the other fuels. In contrast the C1 fuel, which consists of heavily-branched alkanes, contains no aromatics and has a relatively high average molecular weight, has the slowest turbulent flame speeds and is the most prone to tip quenching. The C1 fuel has the highest stretch sensitivity, in general, as indicated by calculated Markstein numbers. This work shows that turbulent flame speeds and tip stability of multi-component large hydrocarbon fuels can be sensitive to the chemical class of its components.

Efficient isolation of immunostimulatory polysaccharides from Lentinula edodes by autoclaving-ultrasonication extraction and fractional precipitation

A hyphenated process, autoclaving followed by ultrasonication (AU), was evaluated for efficient extraction of polysaccharides (PS) from Lentinula edodes (Shiitake) mushroom. The PS yield (w/w) was 8.44 % from hot-water extraction (HWE), 11.01 % by autoclaving extraction (AE), and 16.3 % by AUE. The AUE water extract was subject to fractional precipitation in four-steps with increasing ethanol concentration of 40 %, 50 %, 70 % and 80 % (v/v), yielding four PS fractions in descending molecular weight (MW), PS40 > PS50 > PS70 > PS80. All the four PS fractions were composed of four monosaccharide residues, mannose (Man), glucose (Glc) and galactose (Gal) but in different mole ratios. The PS40 fraction with the highest average MW (4.98 × 106) was the most abundant fraction, accounting for 64.4 % of the total PS mass and also had the highest glucose molar ratio (~80 %). PS40 also most significantly enhanced the NO, and ROS generation and phagocytic activity in RAW 264.7 cells. The results proved that AUE followed by fractional ethanol precipitation is an efficient strategy with reduced solvent expenditure for isolation of the major immunostimulatory PS from L. edodes mushroom.

Semiaromatic Polyesters from a Rigid Diphenyl-Terephthalic Acid: From Synthesis to Properties

Semiaromatic polyesters with a high glass transition temperature (Tg) are promising materials in demanding fields. Herein, a highly rigid diester, diethyl-2,3-diphenyl-1,4-benzenedicarboxylate (DDB), was synthesized from naturally occurring citric acid and cinnamaldehyde. DDB was used to synthesize a series of biobased polyesters by melt polymerization with linear and cyclic diols. Single-crystal X-ray diffraction analysis revealed that DDB crystallized in the monoclinic crystal system with the pendant phenyl groups almost orthogonal to the central benzene ring. The DDB polyesters based on alkanediols (abbreviated as PD-ms) exhibited high number average molecular weights (Mn) in the range of 10,700–39,800 g mol–1. Thermogravimetric analysis (TGA) demonstrated their excellent thermostability that was comparable to petroleum-based polyesters. The crystallization of the PD-ms series was partially caused due to the π–π stacking of DDB units. The DDB homopolyester based on 1,10-decanediol showed a combination of high modulus, high tensile strength, and high ductility of 762, 17 MPa, and 153%, respectively. This was achieved due to the synergistic effects of the rigid DDB and the flexible 1,10-decanediol units. Lastly, DDB imparted inherent UV-blocking properties to polymers, which made them applicable in UV-protective and transparent films. In view of the fertile chemistry of biobased aromatic aldehydes, this work paves a path to DDB derivatives that are attractive precursors for semiaromatic polyesters.

One-Step Treatment for Upgrading Bleached Bamboo Pulp to Dissolving Pulp High Solvency in Green Alkali/Urea Aqueous Solution.

Bleached bamboo pulp, as a kind of natural cellulose, has received significant attention in the field of biomass materials due to its advantages of environmental protection and the abundance of raw materials. Low-temperature alkali/urea aqueous system is a green dissolution technology for cellulose, which has promising application prospects in the field of regenerated cellulose materials. However, bleached bamboo pulp, with high viscosity average molecular weight (Mη) and high crystallinity, is difficult to dissolve in an alkaline urea solvent system, restraining its practical application in the textile field. Herein, based on commercial bleached bamboo pulp with high Mη, a series of dissolvable bamboo pulps with suitable Mη was prepared using a method of adjusting the ratio of sodium hydroxide and hydrogen peroxide in the pulping process. Due to the hydroxyl radicals being able to react with hydroxyls of cellulose, molecular chains are cut down. Moreover, several regenerated cellulose hydrogels and films were fabricated in an ethanol coagulation bath or a citric acid coagulation bath, and the relationship between the properties of the regenerated materials and the Mη of the bamboo cellulose was systematically studied. The results showed that hydrogel/film had good mechanical properties, as the Mη is 8.3 × 104 and the tensile strength of a regenerated film and the film have values up to 101 MPa and 3.19 MPa, respectively. In this contribution, a simple method of a one-step oxidation of hydroxyl radicals to prepare bamboo cellulose with diversified Mη is presented, providing an avenue for a preparation of dissolving pulp with different Mη in an alkali/urea dissolution system and expanding the practical applications of bamboo pulp in biomass-based materials, textiles, and biomedical materials.

Studies of caprolactam and cyclic oligomer content, molecular weight, and thermal properties during melt post-polycondensation of polycaprolactam in the film state

In industrial application of polycaprolactam, the content of caprolactam monomer and oligomers, as well as their average molecular weight are the key factors. In this work, a liquid-chromatography/time-of-flight mass spectrometry (LC-TOF-MS) method and an advanced polymer chromatography/multi-angle laser light scattering/refractive index detector (APC-MALLS-RID) hyphenated technique have been developed as a quantitative analysis method for monomer and cyclic oligomers, and a means of determining the molecular weight of polycaprolactam. The melt post-polycondensation reaction characteristics of polycaprolactam films and the variation in monomers and cyclic oligomers (C2–C7) content have been systematically investigated. The results showed excellent repeatability and stability of quantitative test results on monomers and cyclic oligomers in polycaprolactam. The content of monomers and cyclic oligomers in the polycaprolactam decreased from 10.21% to 1.52% at 260 °C and 50 Pa for 60 min, and the average molecular weight increased from 1.53×104 g/mol to 2.36×104 g/mol. Additionally, the results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) experiments showed that the thermal stability and crystallization properties of polycaprolactam were improved after the film melt post-polycondensation reaction. Thus, this melt post-polycondensation method can realize the efficient removal of monomers and cyclic oligomers (compared with the traditional hot water extraction method) and afford high-quality polycaprolactam with high average molecular weight.

Synthesis by Melt-Polymerization of a Novel Series of Bio-Based and Biodegradable Thiophene-Containing Copolyesters with Promising Gas Barrier and High Thermomechanical Properties

Volatile global oil prices, owing to the scarcity of fossil resources, have impacted the cost of producing petrochemicals. Therefore, there is a need to seek novel, renewable chemicals from biomass feedstocks that have comparable properties to petrochemicals. In this study, synthesis, thermal and mechanical properties, and degradability studies of a novel series of sustainable thiophene-based copolyesters like poly(hexylene 2,5-thiophenedicarboxylate-co-bis(2-hydroxyethoxybenzene) (PTBxHy) were conducted via a controlled melt polymerization method. Fourier-transform infrared (FTIR) and nuclear magnetic resonance (1H NMR) spectroscopy techniques elucidated the degree of randomness and structural properties of copolyesters. Meanwhile, gel permeation chromatography (GPC) analysis showed a high average molecular weight in the range of 67.4-78.7 × 103 g/mol. The glass transition temperature (Tg) was between 69.4 and 105.5 °C, and the melting point between 173.7 and 194.2 °C. The synthesized polymers outperformed poly(ethylene 2,5-thiophenedicarboxylate) (PETF) and behaved similarly to polyethylene terephthalate. The copolyesters exhibited a high tensile strength of 46.4-70.5 MPa and a toughness of more than 600%, superior to their corresponding homopolyesters. The copolyesters, which ranged from 1,4-bis(2-hydroxyethyl)benzene thiophenedicarboxylate (TBB)-enriched to hexylene thiophenedicarboxylate (THH)-enriched, offered significant control over crystallinity, thermal and mechanical properties. Enzymatic hydrolysis of synthetized polymers using porcine pancreatic lipase (PP-L) over a short period resulted in significant weight losses of 9.6, 11.4, 30.2, and 35 wt%, as observed by scanning electron microscopy (SEM), with perforations visible on all surfaces of the films. Thus, thiophene-based polyesters with cyclic aromatic structures similar to terephthalic acid (TPA) show great promise as PET mimics. At the same time, PP-L appears to be a promising biocatalyst for the degradation of bioplastic waste and its recycling via re-synthesis processes.

Intramolecular catalyst transfer on N-acyl dithieno[3,2-b:2′,3′-d]pyrroles in nonstoichiometric Suzuki-Miyaura polycondensation toward high molecular weight conjugated copolymers at room temperature

Traditional step-growth polycondensation generally requires a strict stoichiometric balance of monomers, high temperature, and long reaction time conditions to obtain a high number average molecular weight (Mn). To overcome the challenge of these disadvantages, we demonstrate that the nonstoichiometric Suzuki–Miyaura polycondensation using commercially available t-Bu3PPd G2 precatalyst is an efficient method for synthesis of high Mn various alternating π-conjugated copolymers based on N-acyl dithieno[3,2-b:2′,3′-d]pyrroles (N-acyl DTPs) in a short time at room temperature. Initially, the intramolecular transfer ability of t-Bu3P-ligated Pd catalyst on dibromo-N-acyl DTPs was examed by model reaction with 1 equiv of 3-isobutoxyphenylboronic acid. The result showed that disubstituted product was selectively obtained, indicating the Pd catalyst efficiently walked on these N-acyl DTPs. Thus, a series of novel N-acyl DTP-based π-conjugated copolymers with very high Mn (up to 195 kDa) were successfully prepared under nonstoichiometric reaction conditions using excess dibromo-N-acyl DTPs with arylenediboronic acid esters. Notably, the utilization of K3PO4 as a base was essential for fast couplings at room temperature within 3 h. Furthermore, these copolymers showed tunable optical band gaps and exhibited highly fluorescent emission ranges. These findings should be useful for the precision synthesis of N-acyl DTP-based polymers with controlled Mn and narrow dispersity via chain-growth Suzuki–Miyaura polycondensation.

In Silico Prediction of Human Clinical Pharmacokinetics with ANDROMEDA by Prosilico: Predictions for an Established Benchmarking Data Set, a Modern Small Drug Data Set, and a Comparison with Laboratory Methods

There is an ongoing aim to replace animal and in vitro laboratory models with in silico methods. Such replacement requires the successful validation and comparably good performance of the alternative methods. We have developed an in silico prediction system for human clinical pharmacokinetics, based on machine learning, conformal prediction and a new physiologically-based pharmacokinetic model, i.e. ANDROMEDA. The objectives of this study were: a) to evaluate how well ANDROMEDA predicts the human clinical pharmacokinetics of a previously proposed benchmarking data set comprising 24 physicochemically diverse drugs and 28 small drug molecules new to the market in 2021; b) to compare its predictive performance with that of laboratory methods; and c) to investigate and describe the pharmacokinetic characteristics of the modern drugs. Median and maximum prediction errors for the selected major parameters were ca 1.2 to 2.5-fold and 16-fold for both data sets, respectively. Prediction accuracy was on par with, or better than, the best laboratory-based prediction methods (superior performance for a vast majority of the comparisons), and the prediction range was considerably broader. The modern drugs have higher average molecular weight than those in the benchmarking set from 15 years earlier (ca 200 g/mol higher), and were predicted to (generally) have relatively complex pharmacokinetics, including permeability and dissolution limitations and significant renal, biliary and/or gut-wall elimination. In conclusion, the results were overall better than those obtained with laboratory methods, and thus serve to further validate the ANDROMEDA in silico system for the prediction of human clinical pharmacokinetics of modern and physicochemically diverse drugs.

A comparative study of a modified unsaturated polyester resin with dicyclopentadiene and methyl dicyclopentadiene blends

Dicyclopentadiene (DCPD) has been a widely used chemical compound in many sectors of chemical industry and materials engineering, from fragrances to composites, from simple adducts to polymeric materials. Unsaturated polyesters resin (UPR), one of the major sectors of resins in terms of production volumes, have been the downstream market of choice for DCPD application for many years. An innovative distillation production route designed by Orlen Unipetrol can produce DCPD in a high purity, but also production of methyl dicyclopentadiene (MeDCPD). This yet only superficially studied material could be applied in some of the numerous areas where DCPD has already been implanted, particularly in UPR. In this work the properties of two unsaturated polyesters with the same formulation were compared, only the type of DCPD purity was variable. Indeed, a polyester grade DCPD was used as standard against a technical MeDCPD. Overall higher average molecular weights, viscosity and color values were measured in the uncured materials for MeDCPD modified polyesters. In the cured state the latter showed higher stiffness both during tensile and flexural tests. Finally, DCPD UPR had higher glass transition temperatures (Tg), curing exotherms and shrinking, the latter representing a disadvantage for large parts manufacturing. Finally, compositions of both type of polyesters during the first stage of syntheses revealed a highly complex behavior of MeDCPD isomers during their addition on carboxy functional molecules. These reactions should be further studied to understand and control processes where this latter molecule is involved.

The Structural and Functional Differences between Three Species of Fish Scale Gelatin and Pigskin Gelatin.

In this paper, gelatin was extracted from the scales of Coregonus peled, Carp and Bighead carp by the acid method, and the structure and functional properties of the obtained scale gelatin and food-grade pigskin gelatin (FG) were compared. The results showed that all gelatins exhibited relatively high protein (86.81-93.61%), and low lipid (0.13-0.39%) and ash (0.37-1.99%) contents. FG had the highest gel strength, probably because of its high proline content (11.96%) and high average molecular weight distribution. Low β-antiparallel was beneficial to the stability of emulsion, which led FG to have the best emulsifying property. The high content of hydrophobic amino acids may be one of the reasons for the superior foaming property of Bighead carp scales gelatin (BCG). The gel strength of Carp scales gelatin (CG) and BCG, the ESI of Coregonus peled scales gelatin (CPG) and the foaming property of BCG indicate that fish gelatin has the potential to be used in food industry as a substitute for pig skin gelatin.

Chromophores and chemical composition of brown carbon characterized at an urban kerbside by excitation–emission spectroscopy and mass spectrometry

Abstract. The optical properties, chemical composition, and potential chromophores of brown carbon (BrC) aerosol particles were studied during typical summertime and wintertime at a kerbside in downtown Karlsruhe, a city in central Europe. The average absorption coefficient and mass absorption efficiency at 365 nm (Abs365 and MAE365) of methanol-soluble BrC (MS-BrC) were lower in the summer period (1.6 ± 0.5 Mm−1, 0.5 ± 0.2 m2 g−1) than in the winter period (2.8 ± 1.9 Mm−1, 1.1 ± 0.3 m2 g−1). Using a parallel factor (PARAFAC) analysis to identify chromophores, two different groups of highly oxygenated humic-like substances (HO-HULIS) dominated in summer and contributed 96 ± 6 % of the total fluorescence intensity. In contrast, less-oxygenated HULIS (LO-HULIS) dominated the total fluorescence intensity in winter with 57 ± 12 %, followed by HO-HULIS with 31 ± 18 %. Positive matrix factorization (PMF) analysis of organic compounds detected in real time by an online aerosol mass spectrometer (AMS) led to five characteristic organic compound classes. The statistical analysis of PARAFAC components and PMF factors showed that LO-HULIS chromophores were most likely emitted from biomass burning in winter. HO-HULIS chromophores could be low-volatility oxygenated organic aerosol from regional transport and oxidation of biogenic volatile organic compounds (VOCs) in summer. Five nitro-aromatic compounds (NACs) were identified by a chemical ionization mass spectrometer (C7H7O3N, C7H7O4N, C6H5O5N, C6H5O4N, and C6H5O3N), which contributed 0.03 ± 0.01 % to the total organic mass but can explain 0.3 ± 0.1 % of the total absorption of MS-BrC at 365 nm in winter. Furthermore, we identified 316 potential brown carbon molecules which accounted for 2.5 ± 0.6 % of the organic aerosol mass. Using an average mass absorption efficiency (MAE365) of 9.5 m2g−1 for these compounds, we can estimate their mean light absorption to be 1.2 ± 0.2 Mm−1, accounting for 32 ± 15 % of the total absorption of MS-BrC at 365 nm. This indicates that a small fraction of brown carbon molecules dominates the overall absorption. The potential BrC molecules assigned to the LO-HULIS component had a higher average molecular weight (265 ± 2 Da) and more nitrogen-containing molecules (62 ± 1 %) than the molecules assigned to the HO-HULIS components. Our analysis shows that the LO-HULIS, with a high contribution of nitrogen-containing molecules originating from biomass burning, dominates aerosol fluorescence in winter, and HO-HULIS, with fewer nitrogen-containing molecules as low-volatility oxygenated organic aerosol from regional transport and oxidation of biogenic volatile organic compounds (VOC), dominates in summer.

The effect of chemical composition on the degradation kinetics of high molecular weight poly(trimethylene carbonate-co-L-lactide)

Biodegradable poly(trimethylene carbonate) (PTMC) and its copolymers have been widely used in the biomedical field. However, the unclear degradation behavior and kinetics of these biodegradable polymers are major obstacles to their practical application. The precise control of their degradation kinetics remains a challenge, and the relationship between chemical structure and degradation behavior requires further elucidation. In this work, poly(trimethylene carbonate-co-L-lactide) (PTLA) with different chemical compositions at a high number average molecular weight (Mn, ∼550 kDa) has been prepared via ring-opening copolymerization. The in vitro enzymatic degradation and in vivo degradation of PTLA were investigated and the degradation behaviors were found to change from surface to bulk degradation with the increase of lactide content. PTLA with lactide content of 10–30 mol% followed a surface degradation similar to PTMC, with a linear decrease of mass loss rate constant from 1.49 to 0.51 mg/cm2/d, and thickness loss from 15.08 to 4.06 μm/d. PTLA with lactide content > 30 mol% showed typical bulk degradation behaviors similar to aliphatic polyesters, with the polymer chain experiencing an autocatalytic scission occurring prior to the matrix collapse. Therefore, the in vivo degradation kinetics of PTLA with tunable degradation behaviors by chemical composition was finally obtained.

Utilization of CO2 in supercritical conditions for the synthesis of cyclic poly (N-isopropylacrylamide) via emulsion and homogeneous reactions

In this study, cyclic poly (N-isopropylacrylamide) (cPNIPAAM) was synthesized in supercritical carbon dioxide (SC-CO2) using emulsion and homogeneous reactions for the first time. This was accomplished by applying free radical polymerization and nitroxide compounds to produce low molecular weight precursors in the SC-CO2 solvent. The cyclization reaction occurred in a homogeneous phase in the SC-CO2 solvent, with dimethylformamide (DMF) serving as a co-solvent for dissolving the linear precursor. This reaction was also conducted in emulsion of SC-CO2 in water. The effects of pressure and time on the morphology, molecular weight, and yield of a difunctionalized chain were investigated, where a higher pressure led to a higher yield. The maximum yield was 64% at 23 MPa, and the chain molecular weight (Mw) was 4368 (gr/mol). Additionally, a lower pressure reduced the solubility of materials (particularly terminator) in SC-CO2 and resulted in a chain with a higher molecular weight 9326 (gr/mol), leading to a lower conversion. Furthermore, the effect of cyclization reaction types on the properties of cyclic polymers was investigated. In cyclic reactions, the addition of DMF as a co-solvent resulted in the formation of a polymer with a high viscosity average molecular weight (Mv) and a high degree of cyclization (100%), whereas the CO2/water emulsion resulted in the formation of a polymer with a lower Mv and increased porosity. Polymers were characterized by 1HNMR, FTIR, DSC, TLC, GPC, and viscometry tests. The results were presented and thoroughly discussed.

Structural evolution of in situ polymerized poly(L-lactic acid) nanocomposite for smart textile application

This present study demonstrated the preparation of a highly crystalline anatase (ana) form of titanium oxide (TiO2) doped silk nanocrystal (SNC) nanohybrid (ana-TCS) of diameter (7.5 ± 1.4 nm) by the sol–gel method using titanium (IV) butoxide as the hydrolysis material. This prepared nanohybrid with surface hydroxyl groups acted as a co-initiator for the synthesis of poly(L-lactic acid) (PLLA)-g-ana-TSC nanocomposite with grafted PLLA chains via the in situ polymerization technique, using tin-octoate as a catalyst. The fabricated nanocomposite had a high number average molecular weight of 83 kDa with good processibility. This prepared nanocomposite was hydrophobic in nature, with a contact angle of 105°, which was further enhanced to 122 ± 1° when processed via electrospinning technique into a non-woven fabric. The prepared nanocomposite could degrade up to 43% methylene blue dye in 15 days. This nanocomposite showed no significant molecular weight reduction after 1 h of aqeous treatment, which could be attributed to its hydrophobic nature, inhibiting its degradation. However, 50% degradation was observed for the nanocomoposite whereas, PLLA demonstrated 25% degradation in 15 days, after its end-of-life. Thus, this study revealed that the in situ synthesized PLA-ana-TCS nanocomposite could be targeted for use as a hydrophobic, self-cleaning, dye-degradable fabric.