جستجوی مقالات مرتبط با کلیدواژه "اصلاح شیمیایی" در نشریات گروه "مهندسی شیمی، نفت و پلیمر"

Phase change materials (PCMs) can store latent heat energy during the phase change from solid to liquid. In previous studies, researchers have usually used the microencapsulation method to solve the leakage problem during melting. However, this method has led to issues such as high cost, difficulty of encapsulation, low thermal conductivity, and complexity of product quality control. In this research, to solve the problem of leakage, the method of impregnating PCMs into a porous supporting structure has been used. The porosity of the supporting material allows the phase change material (in liquid state) to flow freely throughout the 3D network and accommodates a greater percentage of PCM. Porous materials prevent the leakage of PCMs due to the improvement of capillary force

To solve the leakage issue of PEG, as the PCM, carbon monofilaments (CF) were used as a supporting material and adapted to improve the compatibility with PEG. After oxidizing CF by acidic solution, its surface modification was done with toluene di-isocyanate and ethylene glycol at a temperature of 90 ºC. The new phase change system was made by impregnating molten PEG in modified CF with a combination of 3 to 6% by weight at 80°C

Chemical modification can create various functional groups on the surface of CF and, as a result, better miscibility with PEG. Due to the physical connection between PEG and modified CF, the leakage of the phase change system reached 2.42%, while the enthalpy efficiency of the system decreased by only 15%. On the other hand, the thermal diffusivity of the phase change system containing CF was found as 1.2 ×10-8 m2. s-1. So an integrated and stable system with a thermal energy absorption of about 44% has been created.

Calix [4] resorcinarene belongs to the calixarenes group. Calix is synthesized via a condensation reaction of resorcinol and aldehydes in acidic conditions. These compounds can be suitable hosts for cations, anions, or neutral molecules. Selective absorption can be created in them by modifying and creating side groups. This research decided to study the optimal conditions for the absorption of cationic blue 41 dye by modified calix[4] resorcinarene oligomer. The optimal conditions were determined using the response surface methodology with three variables: adsorbent amount, time, and pH. The results showed that in the adsorption of dye by modified calix[4], resorcinarene oligomer is the most positive linear effect related to the adsorbent, followed by the time of adsorption process; however, pH has little effect. Also, for more than 61 % absorption, 3.9 % by weight of the adsorbent is required in 180 minutes or 5 % by weight in 127 minutes. Also, with the obtained contour diagram, the adsorption efficiency can be predicted with the amount of adsorbent and time.

The main goal of this study is to investigate the influence of functionalization of silica nanoparticles on the structural properties and gas separation performance of the poly (ether-block-amide) based mixed matrix membranes containing silica nanoparticles. For this purpose, first silica nanoparticles were modified by carboxylic functional groups and used for the preparation of mixed matrix membranes. The prepared membranes were analyzed using the XRD, DSC, FTIR, SEM and gas permeation tests. The results showed that the chemical modification of silica nanoparticles and the incorporating of carboxyl groups on its surface had a strong interaction with the polymer matrix and improved the filler distribution in the membrane matrix. It was observed that by loading 4%wt of silica nanoparticles functionalized with carboxyl groups in the polymer matrix increases the gas permeability at different pressures. The membranes containing 4%wt modified silica nanoparticles had the permeability of CO2, O2 and N2 equal 43.1, 2.8 and 0.42 Barrer, respectively, and the selectivity of O2/N2 (6.71) and CO2/N2 (103.3) at the pressure of 3 bar.

Lignin is a reinforcing filler with properties such as abundantannually renewable, low weight, high biological efficiency, and wide ecological adaptability. These properties are causedincreasing attention from researchers and become an alternative to carbon black in the rubber industry. in this paper, we try to briefly review the lignin. In this regard,initially, the chemical structure of lignin and its structuresareconsidered. it is obvious from the application and process point that this polymer has little tendency to spread in the rubber matrix due to polar functional group and so it will not appear as agglomeration in rubber compoundand thereforewon’t be as reinforcing filler. There have been studies in order to solve this problem and improved the reinforcing properties of lignin. These include modifying the mixing process, increasing the interfacial bonding strength between lignin and the rubber, formation of nano structure with lignin and use of hybrid technologies with other filler.Here some of these methods and the effects of lignin on its curing, mechanical and thermal properties are summarized.

In this research, firstly Bentonite was treated by Hyamine, a cationic surface active agent, and then its capacity for the adsorption of acidic dyes was investigated. Correlation coefficient of equilibrium adsorption study showed that the surfactant adsorption is predominantly described by Freundlich adsorption isotherm. The maximum adsorption capacity was calculated about 94.7 mg/g at 30 oC. This was measured for the adsorption of the dye onto the modified adsorbent around 86.3 mg/g at 30 oC which was higher than the ones obtained at room temperature and 40 oC. Kinetics of adsorption significantly fitted by pseudo second order equation for both Hyamine and acid dye adsorption onto the adsorbent. Initial adsorption rate was increased by increasing of temperature. Intraparticle diffusion study revealed that the diffusion of the cationic surface active agent and the acid dye in the related adsorption structure was concurrently done by film diffusion.

Eliminating and preventing the spread of microbes from the past has been considered. Antimicrobial coatings are one of the ways to fight pathogens. Acrylic and methacrylic resins, cationic conjugated polyelectrolytes, siloxane resins, hyperbranched resin, tetrachloride resins, resins with quaternary ammonium end group, heterogeneous resins with nitrogen, guanidine-containing resins, natural mimic peptides resins, synthetic peptides, resins with main chain of arylamide and phenylethylene, halogenated resins containing phosphorus and sulfur derivatives, phenol and benzoic acid derivatives resins, and organometallics compounds are the materials studied. Also, to create antimicrobial activity in them, other operations such as covalent integration of low molecular weight antimicrobial compounds, antimicrobial peptide binding, grafting other antimicrobial resins, addition of low molecular weight antimicrobial compounds, alloying with antimicrobial resins, and addition of antimicrobial inorganic compounds to resins by different researchers has taken place. In this article, examples of these studies are briefly presented.

In the recent decades, many articles have been published on the development of lignin and mostly related to the chemical modification of lignin.The direct use of lignin often leads to the synthesis and production of low-value added materials. Hence, chemical modification of lignin not only increases its activity in the reactions but also represents a fine dispersion in the polymer materials. Chemical structure of lignin contains phenyl propane units, originating from three aromatic alcohol precursors of p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. The main uses of lignin can be classified into two different methods. In the first method, without chemical modification, lignin is directly incorporated into a polymer matrix to give new or improved properties. In the second method, a large range of polymer materials is synthesized via chemical modification of the lignin. Chemical modification of the lignin has been studied frequently for various purposes. Lignin modification through reaction with formaldehyde, epichlorohydrin, phenol, propylene oxide, propylene carbonate, polyethylene glycol and synthesis of lignin-based copolymers are among reactions studied in the literature. However, this article has been restricted to the discussion on chemical modification of lignin and its use as a source of monomer in the polymerization process.

Thermoset polymers have excellent properties of high dimensional stability at elevated temperatures, low creep and good resistance against solvents due to their three-dimensional crosslinking structure. Proper thermal-mechanical properties for these polymers are based on such cured structures with high crosslink density. Due to its excellent mechanical properties, epoxy resin has been widely used in coatings, adhesives and composites. In recent years, a variety of modification procedures have been introduced for toughening of cured resin structure in order to minimize crack formation and improve their impact resistance. Chemical modification of epoxy resins with polyurethanes is one of the most efficient procedures to achieve this goal. Polyurethanes have unique properties including good abrasion resistance, ease of processing and high rupture strength. After a brief introduction of epoxy and polyurethane resins, the procedures and the mechanisms of fracture toughness in polyurethane-modified epoxy are reviewed in present article. Different polyurethanes with wide range of chemical structures are able to toughen the epoxy structure efficiently and provide improved resins for use indifferent applications.