Changes In Chemical Structure Research Articles

Experimental and Theoretical Study of Gamma Radiolysis and Dose Rate Effect of o-Cresol Formaldehyde Epoxy Composites.

Gamma radiolysis behaviors and mechanisms of silica-filled o-cresol formaldehyde epoxy are studied at 2.20 × 10-5 to 1.95 × 10-1 Gy/s. The radiolysis-induced changes in chemical structures do not severely affect its thermostability. The slightly deteriorated mechanical strength at temperature exceeding 100 °C is accompanied by the declining glass transition temperature (from 185.9 to 172.2 °C) and enhanced damping ability. The gas yields of hydrogen, methane, and carbon dioxide manifest a remarkable dose rate effect. Based on the Schwarzschild law, their yields at an extremely low dose rate are accurately predicted by the established master curves. Besides, the latent radiolysis of gas products and postradiation effect are found with caution. The radiation-caused residual spin species are proved to be composed of silica defects and a phenoxy-type free radical with a tert-butyl group, according to the experimental results, theoretical calculations, and spectra simulations. The lower vertical ionization potential (7.6 eV) and adiabatic ionization potential (7.1 eV) are primarily due to the ionization of the benzene ring moiety with the tert-butyl group, which is likely to suffer from radiolysis. The calculated bond dissociation energy (260.8-563.5 kJ/mol) of the typical chemical bonds of epoxy is consistent with its radiolytic vulnerability and degradation mechanisms.

SERS active fibers from wet-spinning of alginate with gold nanoparticles for pH sensing

Functional composite fibers were prepared by a wet-spinning method and used for pH sensing based on surface enhanced Raman scattering (SERS). Alginate solution with gold nanoparticles (AuNPs) was spun to fibers that acting as active substrate showed distinct SERS enhancement for low concentrations of dyes (1.0 × 10-9 M for rhodamine 6G and 1.0 × 10-8 M for crystal violet). After AuNPs were modified with 4-mercaptopyridine (4-MPY), the as-synthesized composite fibers (AuNPs@4-MPY/Ca-ALG fibers) displayed pH dependent SERS spectra due to the changes of chemical structures of 4-MPY under different pH conditions. The AuNPs@4-MPY/Ca-ALG fibers achieved fast response to the pH changes between 1.00 and 13.00. The flexible composite fibers were woven to a wearable “wrist band”, which has potential applications in health monitoring involving pH variation.

Curing Kinetics of Tannin and Lignin Biobased Adhesives Determined by DSC and ABES

The curing process of two biobased adhesives: pine tanninhexamine (TH) and organosolv lignin non-isocyanate polyurethane (NIPU), suitable for interior nonstructural use, were compared with commercial urea-formaldehyde (UF) adhesive. Changes in chemical structure before and after the curing process were observed with Fouriertransform infrared spectroscopy (FTIR). The process of adhesive curing was monitored with differential scanning calorimetry (DSC) and the automated bonding evaluation system (ABES). Both DSC and ABES measurements confirmed UF as the fastest and NIPU as the slowest curing adhesive observed. Taking into account the ABES results, the optimal pressing parameters for the TH adhesive would be 4 min at 175°C, for the NIPU adhesive 7 min at 200°C and for the UF 1.5 min at 100°C. Strong linear correlation was observed between mechanical and chemical curing for the UF and NIPU adhesives, whereas lower correlation was observed for the TH adhesive. At all observed adhesives, the DSC measurements were underestimating the curing process determined by ABES in the first part and overestimating it at the end. The underestimation was the most evident with the TH adhesive and the less with the UF adhesive. When comparing the uncured and cured FTIR spectra of all three types of adhesives, a drastic decrease in the characteristic band of -OH groups at 3330–3400 cm−1 and an increase in the signal intensity at 2920 cm−1 of aliphatic -CH2-groups were observed. For the UF adhesive, the C=O stretching frequency has shifted from 1632 cm−1 for uncured to three different bands at 1766, 1701, and 1655 cm−1 for cured UF. The sharp band for phenolic alcohols at 1236 cm−1 of C–O stretch and hydroxyl O–H functional group at 1009 cm−1 and at 684 cm−1 of uncured TH adhesive diminished during curing, which indicates that a crosslinking reaction occurs via -OH groups. The peak of the C=O group of urethane bridges at 1697 cm−1 for uncured NIPU shifted to lower wavenumber at 1633 cm−1 for cured NIPU.

UV durability assessment of a thermoplastic epoxy-based hybrid composite rod for structural reinforcement and retrofitting

Recently, a hybrid composite cable has been developed for external strengthening of structures in seismically active zones, containing a novel thermoplastic epoxy matrix. While this resin has advantageous properties such as processability, the UV resistance for outdoor service conditions has not been studied. This paper examines the accelerated UV degradation behavior by using a xenon arc source, and reporting the changes in chemical structure and mechanical properties of both the resin and FRP rods. While the neat resin is susceptible to photo-oxidation and a sharp decline in strength, the hybrid FRP shows no significant changes in tensile properties even after nearly 2000 MJ/m2 of UV radiation (equivalent to seven years in Florida, USA). This was attributed to the fiber-dominant nature of unidirectional composites, further supported by a Curtin-type analytical model.

Thermal stability of filler‐based ethylene/vinyl acetate/vinyl alcohol terpolymer in nitroplasticizer oxidative environment

AbstractTo study the thermal stability of ethylene/vinyl acetate/vinyl alcohol (EVA‐OH) composite with filler particles, systematic thermogravimetric analysis (TGA) investigation was conducted in both nonisothermal and isothermal modes. The effect of polymer concentration on the aging behavior of EVA‐OH was investigated in the nitroplasticizer (NP) environment. Fourier transform infrared spectroscopy was used to probe chemical structural changes in the EVA‐OH polymer before and after thermal aging. The results suggest that filler addition accelerates the rate of NP exudation out of the EVA‐OH composites and deteriorates the thermal stability of NP at moderate temperatures (up to 70°C). The degradation of NP, in turn, accelerates the degradation of EVA‐OH polymer in its composite form through oxidation and hydrolysis indicating the importance of antioxidants in such phase blends.

The influence of plasma gas on changes in chemical composition and structures during the cutting process

Cutting is usually one of initial and basic operations of the manufacturing process of welded structures and realization constructions elements. Thermal cutting, in particular plasma arc cutting is often used to prepare elements. The plasma arc cutting process involves melting and ejecting the liquid metal from the cutting gap with a highly concentrated plasma electric arc which is generated between the non-consuable electrode and the workpiece. The paper presents the results of research on the influence of plasma gas on structural changes and chemical compositions changes resulting unalloyed steel cutting by air plasma arc. It was shown that in the air plasma arc cutting process the amorphous layer with a very high nitrogen content (about 1.6%) and a hardness of 750 HV 0.2 was used. This high nitriding effect is due to the diffusion of nitrogen from the plasma gas. As a result of the interaction of air plasma arc gases on the liquid metal, the cutting surface is carburized (about 0.5%). The alloy components are also burnt according to the theory of selective oxidation of chemical elements. The material structure after the air plasma cutting process shows the structures between the structure formed after oxygen cutting processs and nitrogen plasma cutting process. The process of argon-hydrogen plasma cutting has the least influence on the cut material.

Wear Resistance Improvement of Linear Block-Polyurethanes Under Conditions of Liquid Friction

Abstract A significant disadvantage of parts made of linear block polyurethanes under conditions of friction contact in the presence of an aqueous medium is the intensification of hydrolysis processes and decrease in volume strength. It was proposed to slow down the hydrolysis of polyurethanes in three ways: by directed changes in chemical structure, by electromagnetic radiation of different intensities and by creation of composite materials, based on the principle of additional intermolecular crosslinking at the manufacturing and hot processing stages. The conditions for the formation of a smooth wear-resistant surface that protects the material from rapid destruction are revealed.

A review of nuclear magnetic resonance (NMR) technology applied in the characterization of polymer gels for petroleum reservoir conformance control

Polymer gel systems have been widely applied to control excessive water and improve oil recovery (IOR) in petroleum reservoirs. They are usually divided into two main types, in-situ cross-linked polymer gels, and pre-formed polymer gels. In recent years, nuclear magnetic resonance (NMR) technology has been gradually applied to the research of polymer gel systems due to its unique analysis advantages. This paper is intent to review these works systematically. For in-situ cross-linked polymer gel systems, NMR can be used to characterize the chemical structure changes of the polymer, the cross-linker, and the auxiliary agent in the formulation of the polymer gel systems. Moreover, the gelation time and the gel strength of the in-situ cross-linked polymer gel systems can also be measured by NMR. For pre-formed polymer gels, NMR can be employed to detect the chemical structure of the designed products. Last, the NMR method can evaluate the plugging, water control, and oil improvement performance of the polymer gels in porous media without using dopants. This review can help readers build a more systematic understanding of the application of NMR technology in polymer gel systems for IOR and help researchers to more deeply study the performance of polymer gel systems.

The mechanism of ultrasonic irradiation effect on viscosity variations of heavy crude oil

Viscosity reduction of heavy oil has economic benefits and applicational value in the field. Applying viscosity reduction technology of heavy oil with ultrasound, this paper examines the influence of ultrasonic irradiation time and the addition of tetralin and ethylene glycol on viscosity reduction of heavy oil. Fourier Transform Infrared Spectrometer (FTIR) and Gas Chromatograph (GC) were used to analyze the chemical compositions and structural changes of oil samples before and after ultrasonic irradiation, and the effects of ultrasound on viscosity changes are presented. The viscosity reduction rate (VRR) was best at an irradiation time of 6 mins under the current experimental conditions, with VRR reaching more than 80%. When the irradiation time reached 12 mins, the viscosity of oil samples increased conversely. Chemical analysis reveals that the light components in the oil samples increased after the ultrasonic irradiation, indicating that the cavitation, thermal, and mechanical effects of ultrasound could play a role in breaking long chains of carbon, thus reducing the viscosity. The increase in viscosity may have been caused by a reassociation between molecules and/or the coking of heavy oil.

Decay resistance of ammonia-plasticised and densified beech wood

ABSTRACT Degradation by wood-rotting fungi has been studied in Lignamon and beech wood modified by the Lignamon process. Different treatments that are used during Lignamon process were applied: gaseous ammonia treatment, densification (20 and 40% compression ratio) and heat treatment (180°C). These specimens were exposed to Trametes versicolor and Coniophora puteana for 16 weeks and the mass loss was evaluated. Changes in chemical structure, nitrogen content and pH caused by individual treatments or by fungal activity were also determined. The wood nitrogen content increased after ammonia treatment (1.0%) and was the highest in Lignamon (1.4%), its release during water leaching was very slow. The chemical analysis of wood revealed slight changes in the polysaccharide and lignin content in wood treated with ammonia. Bonded nitrogen was in the form of amides, which were partially thermally degraded by heat treatment. Neither densification nor heat treatment led to better resistance of wood against fungi, while ammonia treatment significantly restricted mass losses (C. puteana 2.5%; T. versicolor 7.5%) compared to untreated wood (both about 30%). Lignamon showed the best fungi resistance (mass loss < 5%), which was probably caused by the combined effect of hemicellulose degradation, an increased nitrogen content, and wood densification.

Research on Coal Tar Pitch Catalytic Oxidation and Its Effect on the Emission of PAHs during Co-Carbonation with Coal

Coal tar pitch (CTP) is abundant and widely used, but its properties will be affected due to oxidation aging during storage. In this study, CTP was oxidized by simulating the air oxidation process, and the change of chemical structure has been analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and both gas chromatography and mass spectrometry (GCMS). The effects of the oxidized and unoxidized CTP co-carbonization with coal on the polycyclic aromatic hydrocarbons (PAHs) emission were detected by GCMS. The small and medium-molecule aromatic substances were reduced during CTP oxidation, while the intermolecular condensation reaction increased the macromolecules content. The catalytic can effectively facilitate the dehydrogenation and condensation reaction of CTP and the entry of oxygen molecules, which leads to the increase of oxygen-containing groups and the decrease of PAHs. Compared to the raw CTP, the catalytic oxidized CTP significantly reduced the emissions of toxic PAHs during the co-carbonization with coal. A possible catalytic mechanism of CTP catalytic oxidation is proposed.

Lateral Size Effect of Graphene Oxide on Its Surface-Enhanced Raman Scattering Property.

The lateral size effect of graphene oxide (GO) on surfaced-enhanced Raman scattering (SERS) property is systematically investigated by using size-fractionalized GO. For the size fractionalization without changes of chemical structure, large-sized GO (LGO) and small-sized GO (SGO) are separated from the as-synthesized GO (AGO) by centrifugation and membrane filtration, respectively. The size-fractionalized GO sheets are immobilized on a solid substrate for the parallel comparison of their SERS property. As a result, we find that LGO shows considerably higher SERS property than SGO for typical Raman probes such as rhodamine 6G and crystal violet. Furthermore, the lateral size effect of GO derivatives is consistently observed when they are hybridized with plasmonic silver nanoparticles. These results indicate that LGO is superior to AGO and SGO as a SERS platform, and it is also quantitatively confirmed by calculating their enhancement factor.

Effect of advanced oxidation process for chemical structure changes of polyethylene microplastics

Microplastic pollution in the aquatic systems is attracting continued concern globally. Microplastics can be needed a long degradation time due to the structural complexity and hydrophobicity. The advanced oxidation process (AOPs) can generate reactive oxygen such as hydroxyl (OH) radicals. These radicals initiate the plastic degradation process by changes in chemical structure with formed functional groups such as hydroxyl (O-H) and carbonyl (C=O) groups and modified C-H groups. The changes in chemical structure are the alternative to accelerate the degradation of microplastics. In this paper, polyethylene (PE) microplastics were modified the chemical structure by AOPs using the combination of ozonation and hydrogen peroxide (H2O2). The effect of the AOPs in samples of PE microplastics was characterized using Fourier Transform Infrared (FTIR) analysis. The results show increasing the intensity of the O-H and C=O bands and decreasing the intensity of C-H groups. The highest carbonyl index (CI) value was 1.33 at pH 12 with a flow rate of 3 L/min using the combination of ozonation and hydrogen peroxide method.

Correction to: Optimization of Ultrasonic Extraction of Major Phenolic Components from Flowers of Ghav-Patta (Argyreia Speciosa Linn.) Via Response Surface Model

Ultrasound-assisted extraction (UAE) or ultrasonic extraction technology has been used for the isolation of bioactive compounds from Argyreia speciosa (Linn. f.) Sweet plant (family: Convolvulaceae). Argyreia speciosa is an Indian traditional medicinal plant having strong evidence of various properties widely used in Ayurveda. Dried flowers were used for extraction and the response surface methodology (RSM) was used to optimize the conditions of extraction for the yield of total phenolics and antioxidants from A. speciosa flowers (ASF) in respect of three variables: temperature, power, and time. Damage and structural changes of the bioactive compounds were studied by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy techniques. The optimum UAE conditions obtained by RSM for the yield of total phenolic content from ASF were 42.41°C temperature, 43.62 % power, and 26.51 min process time and conditions for the maximum antioxidant activity by DPPH radical scavenging were 41.36°C temperature, 57.02 % power, and 26.63 min. These findings showed that the UAE under optimum conditions increased the percentage yield of bioactive compounds. SEM results showed that there was no relevant damage to the cells, and FTIR spectroscopy verified that there were no changes in chemical structure. It has been concluded that UAE method is an effective technique for enhancing the yields of major phenolic compounds from A. speciosa flowers.

Stability studies of Hollow Microspheres at Refrigerated, Normal and Accelerated Conditions

In the present investigation an attempt was made to focus on the stability aspects of itraconazole hollow microsphere at refrigerated condition, room temperature and at accelerated condition. In stability studies, more emphasis given on the effect of different temperature conditions on appearance, % drug content, % buoyancy and % drug release of formulation over a period of 6 months. Apart from above studies, SEM and FTIR analysis was done to determine any change in morphology or chemical structure. The results showed non-significant changes in pharmaceutical properties. From result findings, it can be concluded that the itraconazole hollow microspheres are stable formulation to sustain the drug in upper GIT for prolonged period of time.

In-Situ FTIR Study of Heterogeneous Oxidation of SOA Tracers by Ozone

Secondary organic aerosols (SOA) play an important role in global climate change and air quality, and SOA tracers can directly characterize the source and reaction mechanism of SOA. However, it is not well known that whether the tracers can be oxidized or how the instability of the tracers in the atmosphere. In this paper, in-situ FTIR was used to analyze the chemical structure changes of erythritol, analogue of 2-methyl erythritol (AME) that is, a tracer of isoprene SOA, and 2, 3-dihydroxy-4-oxopentanoic acid (DHOPA), a tracer of toluene SOA, when exposed to high concentration of ozone for short periods. Under the condition of 20 ppm ozone exposure for 30 min, the change rate of absorption area of AME at 3,480 and 1700 cm−1 was −0.0134 and 0.00117 int.abs/s, respectively, and the change rate of the absorption area of DHOPA at 1,640 and 3340cm−1 was −0.00191 and 0.00218 int.abs/s, respectively. The pseudo-first-order reaction rate constant kapp were 1.89 × 10−8 and 2.12 × 10−7 s−1, and the uptake coefficients of ozone on the surface of AME and DHOPA were (1.3 ± 0.8) × 10−8 and (4.5 ± 2.7) × 10−8, respectively. These results showed the oxidation processes of AME and DHOPA were slow in the presence of high concentrations of ozone, which implied that AME and DHOPA could be considered to be stable in the atmospheric environment with ozone as the main oxidant.

Preparation and thermal performance of nitrocellulose coated by polydopamine

AbstractThe existing stabilizers for nitrocellulose (NC) have various disadvantages of harming human health and polluting the environment, which does not meet the requirements of “green” propellants. This research work investigates the self‐polymerization of dopamine to prepare polydopamine (PDA) coated NC composites, and explores the effects of PDA on the thermal stability of NC. SEM, FT‐IR, and RAMAN were applied to investigate the changes of NC surface morphology and chemical structure. The results show that PDA is effectively coated on the NC surface and form a dense PDA film. The thermal decomposition behavior of NC was studied by TG and DSC, and the thermal decomposition activation energy was calculated. The results showed that the thermal stability of the physical mixture did not improve. The thermal stability of the complex increases first and then decreases with increasing of the concentration of dopamine hydrochloride. The optimal reaction conditions are that the concentration of dopamine hydrochloride is 3 g/L and the reaction time is 24 h. The thermal decomposition activation energy of the sample under the optimal conditions is 190.00 kJ/mol, 8.91% higher than that of NC (174.45 kJ/mol), which proves that PDA has the ability to improve the thermal stability of NC.

Using Dissipative Particle Dynamics to Model Effects of Chemical Reactions Occurring within Hydrogels.

Computational models that reveal the structural response of polymer gels to changing, dissolved reactive chemical species would provide useful information about dynamically evolving environments. However, it remains challenging to devise one computational approach that can capture all the interconnected chemical events and responsive structural changes involved in this multi-stage, multi-component process. Here, we augment the dissipative particle dynamics (DPD) method to simulate the reaction of a gel with diffusing, dissolved chemicals to form kinetically stable complexes, which in turn cause concentration-dependent deformation of the gel. Using this model, we also examine how the addition of new chemical stimuli and subsequent reactions cause the gel to exhibit additional concentration-dependent structural changes. Through these DPD simulations, we show that the gel forms multiple latent states (not just the “on/off”) that indicate changes in the chemical composition of the fluidic environment. Hence, the gel can actuate a range of motion within the system, not just movements corresponding to the equilibrated swollen or collapsed states. Moreover, the system can be used as a sensor, since the structure of the layer effectively indicates the presence of chemical stimuli.

Lipid A-Mediated Bacterial-Host Chemical Ecology: Synthetic Research of Bacterial Lipid As and Their Development as Adjuvants.

Gram-negative bacterial cell surface component lipopolysaccharide (LPS) and its active principle, lipid A, exhibit immunostimulatory effects and have the potential to act as adjuvants. However, canonical LPS acts as an endotoxin by hyperstimulating the immune response. Therefore, LPS and lipid A must be structurally modified to minimize their toxic effects while maintaining their adjuvant effect for application as vaccine adjuvants. In the field of chemical ecology research, various biological phenomena occurring among organisms are considered molecular interactions. Recently, the hypothesis has been proposed that LPS and lipid A mediate bacterial–host chemical ecology to regulate various host biological phenomena, mainly immunity. Parasitic and symbiotic bacteria inhabiting the host are predicted to possess low-toxicity immunomodulators due to the chemical structural changes of their LPS caused by co-evolution with the host. Studies on the chemical synthesis and functional evaluation of their lipid As have been developed to test this hypothesis and to apply them to low-toxicity and safe adjuvants.

Solid-State Nanochannel with Multiple Signal Outputs for Furin Detection Based on the Biocompatible Condensation Reaction.

Utilizing ionic current and fluorescent dual-signal-output nanochannels to achieve the detection of specific target species has received much attention. The introduction of an optical signal could not only improve the selectivity of the detection systems, but also make it possible to observe the reduction of the ionic current that originated from stimulus-triggered nanochannel changes. However, the resolution of an optical signal can only verify issues of the presence or absence and cannot precisely analyze the detailed chemical structural changes within nanochannels. Here, we employed a biocompatible condensation reaction between 2-cyanobenzothiazole (CBT) and d-cysteine, and synthesized molecules PCTC that can be polymerized by cutting off short peptide sequences in the presence of furin to realize the detection of furin with multiple signal outputs. Through the introduction of a UV light-sensitive DNA sequence to the capture probes (CPs) inside the nanochannels, the blocking of the nanochannels can be confirmed to the formed oligomers by mass spectrometry analysis.