مجله ایرانی پلیمر
سال:1393 | دوره: | شماره: |تعداد مقالات:9

Poly (acrylic acid)-g-poly (ethylene glycol) (PAA-g-PEG) comb-like copolymer (PCE) is one of the best kind of superplasticizers for cement suspensions. But PCE can be considered as polyelectrolyte which is easily affected by the ions in cement suspensions. In cement system, calcium ions are the most abundant cations which would have great influence on the performance of polymer superplasticizer. Here, the effects of calcium ion on the surface charge, adsorption and dispersion in cement system with PCE as dispersant are investigated in detail. And the changes in the conformation of PCE before and after adding calcium ions are studied by methods of dynamic light scattering and transmission electron microscopy. Calcium ions increase the zeta potential of cement particles and make the molecular chains of PCE curlier, which induces the changes in adsorption and dispersion behavior. The adding of calcium ions makes the ion bridging between calcium and PCE to take place and the ion bridging makes the PCE molecules shrink to smaller size. In this paper, it tells that the molecular structure of PCE polymer could be changed based on the conclusion to adapt the cement with different content of calcium. In cement suspensions, the effect of calcium ions on the performance of PCE polymer would be weakened by decreasing the content of carboxyl groups in the molecular chain.

Cotton pulp cellulose and butyl methacrylate were used as the main raw materials to synthesize cellulose/butylmethacrylate graft polymer (Cell-g-PBMA) via homogeneous ATRP method, after which the graft polymer was dissolved in N, N-dimethylacetamide to prepare a spinning solution, and the novel oil-absorbent Cell-g-PBMA graft polymer fibers were spun by wet-spinning method. The morphology of the polymer fibers before and after oil absorption was analyzed using a high-powered microscope and scanning electron microscope and the saturated oil absorption rate as well as buoyancy recovery of the fiber products were also studied. The results showed that Cell-g-PBMA polymer fibers had a rough surface and exhibited a void network structure that was specific to oil-absorbent materials. The saturated absorption rates of the Cell-g-PBMA polymer fibers for crude oil, vegetable oil, dichloromethane and diesel were 96.5, 78.7, 38.4, and 27.2 g/g, respectively, which were about 3-6 times that of a commercial polypropylene sorbent. The Cell-g-PBMA fibers also displayed excellent oil/water selectivity and high buoyancy recovery in the clean-up of oil over water. Its excellent oil absorbency demonstrated oil absorbent characteristics of both traditional oil-absorbing materials and synthetic oil-absorbing resins, rendering it an excellent fibrous oil-absorbent material.

Selective cation-exchange membranes are placing a key role in separation processes. The application of selective cation-exchange membranes is wide since there are many kinds of mixtures needed to be separated for reuse. In this study, a facile and efficient one-pot approach was used to obtain monodispersed methyl methacrylate-N-isopropyl acrylamide (MMA-NIPAm) polymer by atom transfer radical precipitation polymerization (ATRPP) and then MMA-NIPAm chiral selective separation membranes were prepared for separating racemic equol. Firstly, using dodecylbenzenesulfonyl chloride (DBSC) as the initiator, bipyridine (bipy)/CuCl as the catalyst system, acetonitrile as the solvent, and S-equol as template molecule by which a MMA-NIPAm copolymer was synthesized and it was characterized by TEM, FTIR, TGA, UV-vis absorption spectrum, and dynamic layer scattering analysis. Lastly, MMA-NIPAm chiral separation membranes were prepared by casting 3 wt% of MMA-NIPAm copolymer dimethyl formamide (DMF) solution on a rimmed glass plate and evaporated the solvent completely at 100 °C under vacuum. Then, the PMMA-PNIPAm chiral selective cation-exchange membranes were prepared by immersing in methanol/acetic acid (95:5, v/v) to remove the template molecules. Most worthy of mention was that the prepared chiral selective separation membranes could separate S-equol and R-equol from the mixture of racemic equol. In application of a thermo-responsive monomer, the separation ability of the prepared PMMA-PNIPAm chiral separation membranes could be tunable according to environment temperature changes.

Novel organic/inorganic hybrid polyphosphazenes were prepared by free radical UV copolymerization of linear polyphosphazenes and vinyl monomers. In this work, linear polyphosphazenes grafted by allyl amino and n-butylamino groups have been synthesized via nucleophilic substitution reaction at an anhydrous and anaerobic atmosphere. By regulating the molar ratio of allyl amino and n-butylamino groups, five different linear polyphosphazenes were prepared. The hybrid polyphosphazenes have been crosslinked using the linear polyphosphazenes and vinyl monomers including styrene, methyl methacrylate, and lauryl methacrylate as intermediates via free radical UV copolymerization. By changing the quantity of vinyl monomers participating in the crosslinking reaction, series of hybrid polyphosphazene membranes were obtained. The linear polyphosphazenes have been characterized by Nuclear magnetic resonance, Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA), Differential scanning calorimeter, Dynamic mechanical analyzer and Drop Shape Analysis (DSA). The hybrid polyphosphazenes have also been studied via FTIR, TGA and DSA. The test results proved that the linear polymers were successfully synthesized. Moreover, the water contact angles showed that the hybrid crosslinked polyphosphazenes had a better hydrophobicity and thermal stability than the linear polyphosphazenes and the hydrophobicity of hybrid membranes have a regular changing tendency with the quantities of UV-monomers and ratio of allylamino. The initial decomposition temperatures of the hybrid polymers also had a regular change due to the difference and quantities of vinyl monomers.

The corrosion protection of aluminum flake pigments has been extended by means of an encapsulating inorganic/organic silica/polystyrene hybrid nanolayer. A silica nanolayer encapsulated the surface of aluminum flakes (Al) by hydrolysis and polycondensation of tetraethylorthosilicate via sol–gel process to yield Al/Si flakes. Then, 3-methacryloxypropyltrimethoxysilane (MPS) was used as surface modifier which has polymerizable groups to participate in polymerization reaction (Al/Si/MPS). A polystyrene (PS) coating layer was applied on Al/Si/MPS flakes by free radical polymerization of styrene initiating with Azobisisobutyronitrile at 60 °C and subsequent washing of free chains with solvent yielded Al/Si/PS flakes. Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy showed that silica and PS nanolayers were formed on the aluminum flakes. The attached PS chains on the surface were detached by hydrofluoric acid aqueous solution and analyzed by gel permeation chromatography (GPC). Also, a transmission electron microscopy image showed clearly that the encapsulating layers are in the scale of nano. Good results were obtained in terms of corrosion protection in acidic and alkaline solutions, indicating that the silica/polymer hybrid nanolayer coating acts as an efficient protective film. After encapsulating the flakes, the evolved hydrogen volume was dropped and hybrid nanolayer resulted in no evolved hydrogen volume.

Methadone hydrochloride is a narcotic drug used to relieve chronic pain and control withdrawal symptoms in people undergoing detoxification for opiate addiction, but poses some limits. To reduce the limits and increase the drug’s effectiveness, supramolecular hydrogels composed of a-CD (a-cyclodextrin) and PCL/PEG (polycaprolactone/polyethylene glycol) copolymers, which gained attention due to their advantages, were chosen in this study as controlled-release formulations. PCL/PEG/PCL and PCL/PEG copolymers were synthesized by a microwave-assisted method and then supramolecular hydrogels were prepared by mixing the solutions of copolymers/drug and a-CD to make a methadone hydrochloride sustained-release system. Effects of the drug, copolymer, and a-CD concentrations and copolymer structure on gelation time were also investigated. The systems had rheological properties that depended on copolymer construction and component concentrations. The microwave-assisted method provides an accelerated synthesis of the copolymers with yield of 57 % and low level of impurities. The supramolecular hydrogels demonstrated shear thinning and thixotropic behavior and regained their networks quickly after passing through a fine needle. Due to the porous construction of supramolecular hydrogels, they swell in the presence of fluids and absorb large quantities of water, thereby making the system comprehensively biocompatible. In this study, supramolecular hydrogels composed of a-CD with tri- and di-block copolymers were investigated and found to have rheological properties that depended on copolymer construction and component concentrations. Changing one parameter alone like copolymer or a-CD concentration or the length of blocks could not significantly affect on the drug release, but combination of these factors was efficient. Results of the present study indicated that supramolecular hydrogels composed of a-CD and PCL/PEG copolymers are appropriate drug delivery systems that can release methadone hydrochloride in a sustained manner.

Reducing cycle time in injection molding process is important because it can save operational cost and increase product yield. Cycle time can be categorized by six criteria, which are metering time, time for closing a mold, packing time, holding time, cooling time, and the time needed to open a mold and to eject the molded product. It was found that the metering time is crucial to predict the cycle time of glass fiber reinforced syndiotactic polystyrene (sPS/GF, 60/40 by weight). In many cases, however, cycle time could be reduced by saving cooling time. This study is motivated by the demand to reduce the cycle time of sPS/GF composite. Since the increase of thermal conductivity leads to the reduction of cooling time, silicon carbide (SiC) is employed to evaluate if it can increase the thermal conductivity of sPS/GF composite. When SiC is added to replace entire GF in sPS/GF composite, the mechanical property of the resulting sPS/SiC (60/40 by weight) composite was not satisfied even though its thermal conductivity was enhanced to about 62 %. Within tolerable ranges in mechanical properties, SiC was added to replace a half amount of existing GF filler. sPS/GF/SiC (60/20/20 by weight) composite achieved the enhancement of thermal conductivity from 0.230 to 0.308 W/m K (34 %) which resulted in the effective reduction of both cooling time and cycle time from 16 to 10 s and from 47 to 38 s, respectively. It should be noted that additional time saving was obtained by 3 s between 6 s in cooling and 9 s in overall cycle time. It can be interpreted by the fact that the increase of thermal conductivity also accelerated the heating rate of sPS/GF/SiC composite.

The chemically modified oil palm ash (OPA) with the cetyltrimethylammonium bromide (CTAB) solution was prepared prior to compounding with the natural rubber and other curing ingredients. The aging resistance and thermal stability of CTAB-modified OPA-filled natural rubber composites were evaluated in the same manner as non-modified OPA samples. The retention tensile properties after thermal aging was measured and based on the result shown, the CTAB-modified OPA-filled natural rubber composites imparted insignificant effect to aging resistance as compared to the non-modified OPA-filled natural rubber composites at very low OPA loading; however, the effect became apparent beyond 3 phr OPA loading where the CTAB-modified OPA-filled natural rubber composites provided better aging resistance than the corresponding non-modified OPA-filled natural rubber composites. The thermogravimetric analysis indicated that the CTAB-modified OPA-filled natural rubber composites exhibited lower thermal stability which showed lower temperature at their respective weight loss and lesser char residue than that of non-modified OPA-filled natural rubber composites. This was attributed to the CTAB which started to decompose at the temperature of 210 °C. However, for the range from ambient temperature to 210 °C, the CTAB-modified OPA-filled natural rubber composites produce better thermal stability than those of non-modified OPA-filled natural rubber composites.

Composite nanofibers of polyacrylonitrile/multi-wall carbon nanotubes (PAN/MWCNTs) were prepared via electrospinning. Samples contained 0, 0.5, 1, 2, 3, and 3.5 wt% of MWCNTs. The viscosity and electrical conductivity of electrospinning solutions were measured. Results revealed that, with the addition of multi-wall carbon nanotubes, viscosity was increased and electrical conductivity was improved. Rheological behavior was studied using two different viscometers. Moreover, morphology and diameters of the composite nanofibers were studied by scanning electron microscopy (SEM) and nanofiber diameter distributions were presented. SEM micrographs showed that by adding MWCNTs, the average diameter of nanofibers was increased. Furthermore, the effect of MWCNTs on glass transition temperature, T g, was investigated using differential scanning calorimetry (DSC) technique. The results showed that T g was increased with the addition of MWCNTs. In addition, Fourier transform infrared spectroscopy (FTIR) results showed that MWCNTs can affect the orientation ability of polymer chains. The effects of adding salt, increasing voltage and changing the tip-to-collector distance on the morphology and diameters of composite nanofibers were examined. The electrical conductivity results of electrospun mats were measured by a two-probe method. Electrical conductivity was increased by addition of MWCNTs and its behavior followed the percolation theory. Finally, it was observed that mats with smaller diameters have higher electrical conductivity.