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With the continuous development of unconventional oil and gas in recent years,researchers have set higher requirements on crosslinker performance.Therefore,research on the crosslinking agent that is suitable for the high-temperatu...
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With the continuous development of unconventional oil and gas in recent years,researchers have set higher requirements on crosslinker performance.Therefore,research on the crosslinking agent that is suitable for the high-temperature/high-pressure(HT/HP)fracturing fluid system is particularly important.This work reviews the development status of a crosslinker for the HT/HP fracturing fluid system.Our results show that the cost of a boron crosslinking agent is low;however,it is not suitable under very high temperatures.Metal crosslinking agents are suitable for a wide range of pH but have poor shear resistance.Meanwhile,the nano crosslinking agent has a high applicable temperature and a strong comprehensive performance but is relatively expensive.How to further improve the adaptability of crosslinking agents to high temperature and pressure and reduce the additive dosage are the focus of future research.
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Hydrogels based on crosslinked polymethacrylic acid were synthesized via free-radical polymerization in aqueous solution, using N,N'-methylene bisacrylamide as a crosslinking agent and 2,2'-azobis-[2(2-imidazolin-2-yl)propane] dih...
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Hydrogels based on crosslinked polymethacrylic acid were synthesized via free-radical polymerization in aqueous solution, using N,N'-methylene bisacrylamide as a crosslinking agent and 2,2'-azobis-[2(2-imidazolin-2-yl)propane] dihydrochloride as an initiator. The influence of the reaction parameters (the neutralization degree ofinethacrylic acid and the initial monomer concentration) on the equilibrium swelling degree, the swelling kinetic parameters and the basic structural properties of xerogels, was investigated. The change of synthesis parameters leads to the change of the basic structural parameters of xerogel, as well as the equilibrium swelling degree and the initial swelling rate of the hydrogels. It is found that there are power form relationships between the equilibrium swelling degree, the initial swelling rate and the structural xerogel's properties and the change of the neutralization degree of monomer, i.e. the monomer concentration. The examined correlations proved that the crosslinking density is the crucial parameter which determines all the other investigated structural and swelling parameters.
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Purpose: To evaluate crosslinking of cornea in vivo using green light activation of Rose Bengal (RGX) and assess potential damaging effects of the green light on retina and iris.
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Properties of polyolefins can be modified by crosslinking process.Different methods of crosslinking and effect of process parameters,selection of crosslinking agents and applications are briefly discussed.Polyethylenes are commodi...
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Properties of polyolefins can be modified by crosslinking process.Different methods of crosslinking and effect of process parameters,selection of crosslinking agents and applications are briefly discussed.Polyethylenes are commodity plastics.They account for more than 70% of total plastics market.Polyethylene is easily available,at relatively low cost and easily processable.It finds applications in household items,packaging,insulation,net ropes,fishing rods or medical applications,etc.Polyethylene is processed at temperature in the range 150-250deg C.Most polyethylene compounds contain reasonably good amount of fillers.Polyethylenes are thermoplastic in nature and therefore they can be reprocessed repeatedly.Polyethylene,however,will soften and flow,and lose critical physical properties at elevated temperature thereby limiting its applications.Therefore,crosslinking of polyethylene is carried out to retain desirable properties at high temperature.Crosslinking will change the nature of polymer from thermoplastic to thermoset to yield a non melting,more durable polymer matrix.
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Repaglinide, an oral antidiabetic agent, has a rapid onset of action and short half-life of approximately 1 h. Developing a controlled and prolonged release delivery system is required to maintain its therapeutic plasma concentrat...
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Repaglinide, an oral antidiabetic agent, has a rapid onset of action and short half-life of approximately 1 h. Developing a controlled and prolonged release delivery system is required to maintain its therapeutic plasma concentration and to eliminate its adverse effects particularly hypoglycemia. The present study aimed to develop controlled release repaglinide loaded beads using sodium alginate and pectin with dual cross-linking for effective control of drug release. The prepared beads were characterized for size, percentage drug entrapment efficiency, in vitro drug release and the morphological examination using scanning electron microscope. For the comparative study, the release profile of a marketed conventional tablet of repaglinide (Prandin (R) tablets 2 mg, Novo Nordisk) was determined by the same procedure as followed for beads. The particle size of beads was in the range of 698 +/- 2.34-769 +/- 1.43 mu m. The drug entrapment efficiency varied between 55.24 +/- 4.61 to 82.29 +/- 3.42%. The FTIR results suggest that there was no interaction between repaglinide and excipients. The XRD and DSC results suggest partial molecular dispersion and amorphization of the drug throughout the system. These results suggest that repaglinide did not dissolve completely in the polymer composition and seems not to be involved in the cross-linking reaction. The percent drug release was decreased with higher polymer concentrations. In conclusion, the developed beads could enhance drug entrapment efficiency, prolong the drug release and enhance bioavailability for better control of diabetes. (C) 2017 Elsevier B.V. All rights reserved.
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Since the launching of tertiary oil recovery, the performance requirements of polymer solution increasing, the polymer solution is more difficult to meet the needs of the scene. It could solve poor profile control, salt-tolerant, ...
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Since the launching of tertiary oil recovery, the performance requirements of polymer solution increasing, the polymer solution is more difficult to meet the needs of the scene. It could solve poor profile control, salt-tolerant, and poor performance that crosslinking agent was added to polymer solution. Therefore, chromium acetate crosslinker was synthesized, and the synthesis conditions were optimized, and the performance of crosslinking agent was evaluated. Through optimization, the optimum conditions of chromium acetate synthesis was: reaction time 10 h, reaction temperature 80°C, the molar ratio of acetic acid and potassium dichromate than or equal to 24: 1. Performance evaluation showed that adding crosslinking agent could significantly increase the viscosity of the polymer solution, could significantly improve the resistance coefficient and residual resistance of the polymer solution, and could play a good role profile flooding. Studies showed that when salinity and ion content changed, the crosslinking mechanism of changed. Through the study of molecule coil size at room temperature, the molecule coil size would slightly decline after 1 h, suggesting that crosslinking mechanism was intramolecular crosslinking reaction occurs at first, and then intermolecular crosslinking reaction.
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Purpose: To investigate the outcomes of accelerated (A-CXL) and iontophoresis (I-CXL) corneal crosslinking in a large retrospective cohort with progressive keratoconus. Methods: This retrospective observational cohort study includ...
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Purpose: To investigate the outcomes of accelerated (A-CXL) and iontophoresis (I-CXL) corneal crosslinking in a large retrospective cohort with progressive keratoconus. Methods: This retrospective observational cohort study included consecutive patients treated by A-CXL (9 mW/5.4 J/cm2) or I-CXL with a minimal follow-up of 12 months. Visual acuity, manifest refraction, topography, specular microscopy, and corneal optical coherence tomography (OCT) were evaluated at baseline and at the last visit. Progression was defined as an increase in the maximum topographic keratometry (Kmax) of 1D. Results: 302 eyes of 241 patients with a mean age of 25.2 ± 7.5 years were included from 2012 to 2019: 231 and 71 eyes in the A-CXL and I-CXL groups, respectively. The mean follow-up was 27.2 ± 13.2 months (maximum: 85.7 months). Preoperatively, the mean Kmax was 51.8 ± 4.0D, with no differences between groups. Mean topographic measurements and spherical equivalent remained stable during the follow-up. At the last visit, CXL failure was reported in 60 eyes (19.9%): 40 (14.7%) versus 20 (28.2%) in A-CXL versus I-CXL, respectively, p = 0.005. The likelihood of progression after CXL was significantly higher following I-CXL: RR = 1.62, CI95 = [1.02 to 2.59], p = 0.04. Demarcation line presence at 1 month was positively correlated with higher efficacy of CXL, p = 0.03. No endothelial damage was reported, especially in 51 thin corneas (range = 342-399 μm). Conclusions: A-CXL seems more effective than I-CXL in stabilizing keratoconus; this is to be taken into account when a therapeutic indication is posed according to the aggressiveness of the keratoconus.
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In this paper, the crosslinking of PVC with a new crosslinking agent the hexakisal-lylaminocyclotriphosphazatrine, one hexafunctional monomer was studied. Ionizing radiation was carried out with mixtures of PVC (Mw 64000) and 5 % ...
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In this paper, the crosslinking of PVC with a new crosslinking agent the hexakisal-lylaminocyclotriphosphazatrine, one hexafunctional monomer was studied. Ionizing radiation was carried out with mixtures of PVC (Mw 64000) and 5 % of crosslinking agent. The radiochemical parameters: dose of incipient gel(R_g), does of threshold dose (R_n), radiochemical yield of crosslinking (G_c) and scission(G_s) was determined using the Charlesby Pinner equation.
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In this work, the synthesis of crosslinked chitosan hydrogels was performed by ionic and covalent interactions using tripolyphosphate (TPP) and formaldehyde (CH_2O), respectively. The hydrogels synthesis was performed using a D-Op...
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In this work, the synthesis of crosslinked chitosan hydrogels was performed by ionic and covalent interactions using tripolyphosphate (TPP) and formaldehyde (CH_2O), respectively. The hydrogels synthesis was performed using a D-Optimal combined experiment design with two mixing variables, A and B representing the TPP weight fraction (slack variable) and CH_2O weight fraction, respectively, and three (3) process variables C-chitosan concentration, D-cross-linker concentration, and E-Contact time. The response variables studied were the point of zero charge (pH_(PZC)), the swelling ratio (SW), and the equilibrium water content (EWC), which are relevant physicochemical properties in applications such as the pollutant removal from water. According to the ANOVA results, the model obtained was significant; this means it can be adequately used to predicting pH_(PZC), SW, and EWC from the mixing and process variables, obtaining coefficients of determination R~2 of 0.9572, 0.8900, and 0.8447, respectively. The pH_(PZC) is affected by chitosan concentration, while the crosslinker concentration in-fluences the SW, and the contact time most significantly affected the EWC. Morphology and hardness tests, thermal stability, infrared spectroscopy, and scanning electron microscopy, allowed verifying the types of crosslinking of chitosan with TPP and CH_2O.
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The epsilon-caprolactam monomer having a triphenylimidazole moiety such as DL-3-[alpha-4-(4,5 diphenyl-1H-imidazole-2-yl)-phenylacryloyl-amine]-epsilon-caprolactam (1) was synthesized by the Heck reaction of 2-(4-bromophenyl)-1-(m...
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The epsilon-caprolactam monomer having a triphenylimidazole moiety such as DL-3-[alpha-4-(4,5 diphenyl-1H-imidazole-2-yl)-phenylacryloyl-amine]-epsilon-caprolactam (1) was synthesized by the Heck reaction of 2-(4-bromophenyl)-1-(methoxymethyl)-4,5-diphenylimidazole and the epsilon-caprolactam derivative having an acryloyl group in a good yield. The copolymerization of 1 and epsilon-caprolactam was carried out at 250 degrees C by using H2O as an initiator to give copolymer (4) in a good yield. The crosslinking reaction of the obtained 2 proceeded with K-3[Fe(CN)(6)] and KOH in a mixed solvent of ethanol and phenol. The resulting crosslinked polymer (5) was de-crosslinked under irradiation with visible light. Consequently, the thiol-capped de-crosslinked polymer (6) was obtained in a good yield.
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