Papers by Keyword: Gelation

Abstract: Thermosets play an important role in composite processing, adhesive bonding and coating. In all these applications, shrinkage my cause a significant amount of residual stress, leading to distortion, reduced load carrying capacity and cracking. The chemical curing reaction is accompanied by a reduction in volume called “chemical shrinkage”. If curing is performed at elevated temperature, cooling to ambient conditions afterwards is accompanied by “thermal shrinkage” and further shrinkage due to so-called “physical ageing”. A skillful combination of available methods makes it possible to separate chemical shrinkage in the viscous state from shrinkage in the gelled and vitrified state. Modeling of the time-and temperature-dependent properties is the prerequisite for the prediction and control of residual stresses caused by shrinkage in thermoset polymers.

Abstract: This study presents the possibilities of using a fire extinguishing agent based on a water-soluble polymer for extinguishing fires at facilities where the fire load is formed by liquid combustible materials. It has been theoretically and experimentally shown that by changing the concentration of gelling additives, the viscosity can be varied, which, in turn, directly affects the characteristics of the protective layer created by applying the gel fire extinguishing agent to the surface of the combustible liquid.. The results of an experimental study of the effectiveness of gel fire extinguishing agents based on a polymer of the ECOFLOC A-18 type are presented. A method for preparing liquid solutions of concentrates of aqueous fire extinguishing agents with a gelling agent concentration of up to 10 %, which are easy to dissolve in water or in a foaming agent, is proposed. It is noted that their concentration should be such that when creating a working solution, the amount of gelling agent in it is not less than 0.05 % for the use of the solution in extinguishing fires.

Abstract: Extinguishing fires in ecosystems has features compared to extinguishing fires in residential and industrial buildings, due to the composition and structure of combustible materials, which can form many foci of smoldering and have the ability to re-ignite, have a relatively low fire load compared to man-made ones. All this leads to high costs of water for extinguishing, carrying out operations for additional extinguishing of fires that occur after the main extinguishing and sets special requirements for aqueous extinguishing agents for their extinguishing.The paper analyzes the current state of the availability and trends of development in the world and domestic practice of effective water extinguishing agents and technologies for their use. Possible ways to improve recipes and increase the efficiency of fire extinguishing substances are outlined, taking into account, first of all, the criteria of efficiency, economy and environmental friendliness.It is noted that the main direction of increasing the fire extinguishing capacity of water is to create combined fire extinguishing solutions that can combine several methods of extinguishing in one technological operation: cooling, isolation and inhibition, which, other things being equal, reduces fire extinguishing consumption and extinguishing efficiency. An integrated direction of increasing the fire-extinguishing capacity of water can be considered to increase the coefficient of active use of water by reducing the surface tension of the fire-extinguishing solution, increasing the wettability and viscosity of water by introducing appropriate additives, obtaining optimal droplet dispersion.

Abstract: In the present study, nanofibers of oxidized cellulose (OC) were prepared from dried bacterial cellulose using a mixture of nitric acid/phosphoric acid and sodium nitrite. Three types of dried bacterial cellulose were used as raw materials. The results revealed that dried sheet bacterial cellulose (DSBC) yielded 86.8% oxidized cellulose with 19.4% carboxyl content, whereas squeeze-dried bacterial cellulose (SDBC) yielded 53.3% OC with 28.6% carboxyl content, and freeze-dried bacterial cellulose (FDBC) yielded 55.6% of OC with 27.6% carboxyl content. The results revealed that OC neutralized with sodium hydroxide from SDBC showed the best swelling property among all types of OC. SDBC indicated the reduction of CFU exceeds 99.99% for gram-negative bacterium Escherichia coli ATCC 25922 and gram-positive bacterium Staphylococcus aureus ATCC 6538.

Abstract: To isolate the surface of toxic liquids, it is proposed to use fast-hardening highly resistant foams. To obtain fast-hardening, highly resistant foams, the process of gel and foaming is combined. For this, solutions of sodium polysilicate and gelation catalyst are mixed. To increase the stability of the foams, it is proposed to add water-soluble polymers to the gel-forming composition. It is shown that a fast-hardening foam of the composition Na₂O·2.5SiO₂ (9%)+NaHCO₃ (9%)+6% foaming agent +0.5% carboxymethyl cellulose with thickness reduces the mass rate of benzene evaporation by more than 5 times. It retains its insulating properties for more than 5 days. It is concluded that it is advisable to use fast-hardening highly resistant foams for the elimination of emergencies with the spill of toxic liquids.

Abstract: The quaternary phase bioactive glasses (SiO₂-CaO-Na₂O-P₂O₅) were synthesized by the sol-gel process. Pluronic P123, using surfactant as structure-directing agents as well as phase separation inducers. The obtained bioactive glasses were characterized regarding morphology by using the scanning electron microscopy (SEM). Polymer colloidal crystals (CCTs) as the template component yielded either three-dimensionally ordered macroporous (3DOM) structure or hollow spheres shaped bioactive glass. The other type of morphology generation is related to the polymerization-induced phase separation (PIPS) in the gelation process. The heterogeneous precursor i.e. silica-rich regions caused the microspheres and solvent-rich areas produced micrometer-scale void space in bicontinuos structure. While the lower pH of starting precursor in 45S4P showed stronger precursor-template interactions than the 53S4P by generating the completely hollow spheres structure.

Abstract: Thermoset adhesives convert from liquid to solid due to chemical reactions. Once cured, these adhesives carry the potential to create strong load-bearing joints, resisting even severe detrimental service conditions. In the progress of curing of a thermoset adhesive the viscoelastic properties of the resin and hardener formulation change as the chemical reaction proceeds. Gelation occurs once a continuous 3-dimensional network of polymer chains has been created. After gelation, the microstructure of the resin is fixed and further cure is affected by diffusion limitations [1]. Mastering of the curing kinetics and the physicochemical changes in the transition from the liquid to the solid-state is essential to reliably process adhesives in industrial applications. Rheological experiments in parallel plate configuration have become a well-established practice in investigating viscoelastic properties in the progress of curing. In practice, it has shown to be challenging to access the full range of viscoelastic parameters of thermoset resins with a low initial viscosity from the very beginning of the curing reaction to the post-cure consolidation of the vitrified polymer. This paper will discuss experimental methods and criteria for the viscoelastic analysis of curing thermoset adhesives and present experimental data of the time-, temperature-, and frequency-dependent viscoelastic properties of a curing thermoset epoxy in relation to the features of its time-temperature-transformation-diagram.

Abstract: In this study, oxidized cellulose nanofiber was prepared from squeeze dried Nata de Coco sheet by the oxidation system of HNO₃/H₃PO₄-NaNO₂ at 30 °C for 24 hours. The ratio between HNO₃ and H₃PO₄ was 1:3 v/v and the concentration of NaNO₂ was 1.4% w/v. The carboxyl content and %yield of oxidized cellulose nanofiber from Nata de Coco (Nata-OC) was 28.6% and 68.4%, respectively. Then the Nata-OC was treated by several types of bases. Sodium hydroxide (NaOH) or triethanolamine (TEA) treated Nata-OC showed superior in gelation property to the original Nata-OC. The powder of base-treated Nata-OC gave stable Nata-OC aqueous dispersion, which might be applicable for spray-typed materials. The test papers obtained from 10% of base-treated Nata-OC dispersion showed good blood agglutinating property as same as dry sheet of pure Nata-OC. Moreover, the dispersion of base-treated Nata-OC could be coated on the surface of gauze without any additive.

Abstract: The change law of gel time of calcium carbonate-acid water glass grouting material with the content of calcium carbonate is researched in this paper. But the gel time does not increase evenly with reduction calcium carbonic reducing. It increases suddenly because there is sudden exceeding range with the solution pH value increasing. Meanwhile, the change relation of strength of pure gelation with suitable gel time and time is measured. Firming sand strength experiment is conducted by the better mixture ratio. The strength of pure gelation body increases with the time and the content of calcium carbonate increasing. It is closely related with the reaction mechanism of calcium carbonate-acid water glass. The active Ca²⁺ in this system can react with a series of silicate ion to form silicate precipitate which is filled with colloid and forming skeletonation. And the correlation between firming sand strength and the calcium carbonic acid content is non-significant. Finally, the contrast test of the water glass-glyoxal is done, which is the preparation for the subsequent engineering application.

Abstract: Rice starch played an important role in the processing of rice noodles. There were significant differences in physicochemical properties such as gelatinization, swelling power, RVA paste viscosities and textural properties between rice flour and rice starch. Spectroscopic properties and crystalline properties of rice flour and rice noodles were studied by fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results revealed that rice starch played an important role in the preparation of rice noodles. Rice protein could affect the pasting properties and textural properties of rice flour. XRD results showed during rice noodles preparation, rice starch crystal type changed from A-type to V-type. Differential scanning calorimeter (DSC) results showed that in the processing of rice noodles, the crystalline structure re-formed which indicated some amylopectin were associated orderly. We conclude that both amylose and amylopectin were associated during the processing of rice noodles.