فهرست مطالب

Iranian polymer journal
Volume:18 Issue: 9, 2009

  • تاریخ انتشار: 1388/06/11
  • تعداد عناوین: 8
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  • Ismaeil Ghasemi, Behzad Kord Page 683
    Recently, to improve the properties of wood plastic composite (WPC), incorporation of nanofiller has been considered. In this study, hybrid composite of polypropylene/wood flour/nanoclay with different concentrations of nanoclay and maleated polypropylene (MAPP) as compatibilizer were fabricated in an internal mixer. The long-term water absorption of the composites was evaluated by their immersion in water at room temperature for several weeks (up to 3000 h). Water diffusion coefficients were evaluated. The results indicate that water absorption decreases with increase in clay loading. The morphology of nanoclay was determined by X-ray diffraction (XRD) and transmission electron microscope and the effect of morphology on water absorption is discussed. Due to inadequate compatibilizer, exfoliated morphology of nanoclay is not obtained but the intercalation has occurred. The order of intercalation for samples containing 3 phc is higher than that of 6 phc at the same MAPP content due to some agglomerations of organoclay. The effect of compatibilizer has been positive in terms of enhancing the dimensional stability of the composites and mechanical properties. The maximum elastic modulus may be related to 3 phc of nanoclay and 4 phc of MAPP. The maximum water absorption and diffusion coefficients are decreased by increasing the clay and MAPP contents. The mechanism of water absorption of the composites under study followed the kinetics of a Fickian diffusion process.
  • Jarugla Jayaramudu, Dandu Jeevan Prasad Reddy, Babu Rao Guduri, Anumakonda Varada Rajulu Page 693
    The natural fabric from the tree Sterculia urens was found to be composed of ligno-cellulosic fibres arranged in a rarely occurring uniaxial direction. In order to assess the suitability of Sterculia fabric as reinforcement and polycarbonate as matrix, this uniaxial fabric was coated with polycarbonate. The tensile properties of both uncoated and polycarbonate coated fabrics were studied. The tensile parameters such as maximum stress, Young''s modulus, and elongation-at-break were determined using the Universal Testing Machine. The effect of alkali treatment, coupling agent and the polycarbonate coating on tensile properties was studied. The morphology of the fabric before and after alkali treatment and polycarbonate coating was studied using the scanning electron microscopy and polarized optical microgram techniques, respectively. The improved tensile properties of polycarbonate coating was attributed to the filling up of void regions of uniaxial fabrics with polycarbonate facilitating continuity and also better interfacial bonding between the fabric and polycarbonate. The effect of the coupling agent on the structural changes, morphology and the tensile properties of the neat and alkali treated Sterculia fabric was also studied. Marked changes on the surface of the fabrics were noticed when the coupling agent was used.
  • Liying Wu, Deben Chen, Anyong Zhong, Ming Wang, Xixiang Zhang Page 703
    Apolyacrylate/organic montmorillonite (OMMT) nanocomposite was synthesized by in-situ emulsion polymerization with intercalated structure as demonstrated by X-ray diffractometry. The emulsions and the films obtained from the emulsions prepared were characterized with rotary viscometer, laser light scattering, transmission electron micrograph, scanning electron micrograph, differential scanning calorimetry, the 180ºC peeling intensity test, etc. The results indicated that addition of OMMT improved the engineering properties of emulsions. Among the samples tested, the modified polyacrylate emulsion which was prepared by intercalating 2 wt% OMMT and pretreated with immersion disposal showed the most desirable effect and obtained the following advantages: smaller particle size, stronger pseudo-plastic, better thermal stability, and better adhesion property. The morphology of emulsion particles became a polygon from approximate sphericity. It was also demonstrated by SEM that OMMT addition improved the ductility of the polyacrylate film. Furthermore, the peeling strength was likewise improved with the increased amount of OMMT.
  • Dariush Salari, Heidar Ranjbar, Ali Olad, Aligoli Niaei Page 713
    The effects of weathering on the flow, microstructure, and physico-mechanical properties of an unstabilized poly(acrylonitrile-butadiene-styrene) (ABS) were investigated by irradiating the ABS samples with a wavelength distribution comparable to solar light at 45ºC and relative humidity of 50 percent. A series of ABS samples were prepared by melt mixing of SAN and high rubber content g-ABS. All specimens were characterized by melt flow index (MFI) measurements, heat distortion temperature (HDT), Fourier transform infrared spectroscopy (FTIR), impact strength (Izod), tensile testing and measuring of CIEL*a*b* colour components (data of L*,a*,b* and YI). Alteration in the flow and physical properties was observed. The samples underwent extensive reduction in Izod impact strength, elongation-at-break, workto- break, and turned yellow upon irradiation. The MFI, HDT, and FTIR results showed that upon weathering of ABS, cross-linking and chain scission of rubber phase were the governing degradation and yellowing mechanisms. The loss of unsaturation (disappearance of 1,4-polybutadiene) and alteration in carbonyl group as well as the hydroxyl group were observed. Significant amounts of photoproducts were detected in the directly irradiated surface layer. The colour difference of yellowing ΔYI exhibits a systematic tendency to higher values with increasing irradiation time.
  • Chuanmei Jiao, Xilei Chen Page 723
    The flammability characterization and synergistic flame retardant mechanism of lanthanum oxide (La2O3) in the ethylene-vinyl acetate/aluminium hydroxide (EVA/ATH) composites were studied by limiting oxygen index (LOI), UL 94 test, cone calorimeter test (CCT), and thermogravimetric analysis (TGA). The results showed that the addition of a given amount of La2O3 apparently increased the LOI value, which for the sample with 1.5 wt% La2O3 reached 37.5. However, the addition of La2O3 cannot enhance the ratings of UL 94 test. The data obtained from the CCT indicated that the addition of La2O3 greatly prolonged the time to ignition, increased the fire performance index (FPI), and predictably reduced the fire growth index (FGI). It has been found that there is a synergistic flame retardant effect between La2O3 and ATH in EVA/ATH/La2O3 composites. The synergistic mechanism between La2O3 and ATH is due to its physical process in the condensed phase, as revealed by CCT data showing that the addition of La2O3 can make the formation of a more thermally stable barrier, and the residual char of the system with La2O3 is higher than that of the system without La2O3. A compact barrier produced by La2O3 collaborating with ATH consequently leads to the decrease of heat release rate, mass, and total release rate as detected by CCT. TGA results showed that La2O3 can enhance the thermal stability of the flame retardant composites at high temperature.
  • Ali Akbar Entezami, Hassan Namazi, Khadijeh Didehban Page 731
    Different generations of dendritic macromolecules based on triazine were synthesized by the divergent growth approach and functionalization with mesogenic units based on peripherally located dihydroxybiphenyl derivatives. Thermotropic liquid crystal dendrimers, containing poly(ethylene glycol) (PEG) as a core and triazine dendrons with peripherals mesogenic groups were synthesized. First generation (G1) was prepared by coupling of hydroxyl group of PEG with cyanuric chloride in dichloromethane at 0-5ºC. Reaction of compound G1 with amino group of ethanolamine in dichloromethane resulted G1.5. Second generation of linear dendritic compounds (G2) was synthesized using coupling reaction of hydroxyl groups of compound G1.5 and cyanuric chloride in dichloromethane. Reaction of compound G2 with amino group of ethanolamine in water/dioxane resulted G2.5. The growth of dendrons on the PEG core and their structures were investigated using common spectroscopy methods. In the next step, compounds Cn with different alkyl tail groups were synthesized via nucleophilic displacement of bromine from 1-bromoalkane by potassium-4,4''-biphenoxide in DMF. The mesogenic compounds 4-bromo-(4-alkyloxybiphenyl- 4''-oxy) butane (CnC4Br) were synthesized by reaction with Cn and 1,4- dibromobutane undergoing SN2 substitution. Liquid crystalline dendrimers (LCD) weresynthesized via coupling of hydroxyl group of G2.5 and bromine from mesogenic units,4-bromo-(4-alkyloxy-biphenyl-4''-oxy) butane. The liquid crystal property of mesogeniccompound has been studied in details with differential scanning calorimetry and opticalpolarization microscopy. The experiments showed that the thermal properties areinfluenced with the spacer length
  • Chao, Can Zhang, Wen, Bing Sun Page 743
    α,ω-Di((N-ethyl)amino(2-methyl)propyl) polydimethylsiloxane (DEAMP-PDMS) together with siloxane-containing epoxy resin with different number average molecular weights, as reactive and functional polymers, were obtained through a three-step synthetic procedure. At first, α,ω-di((N-ethyl)amino(2-methyl)propyl) tetramethylsiloxane (DEAMP-TMS) was prepared by hydrosilylating tetramethyldi-siloxane with N-ethyl-2 methylallylamine in the presence of dihydrogen hexachloroplatinate catalyst. Then, DEAMP-PDMS was synthesized by a base-catalyzed equilibrium reaction of DEAMP-TMS with octamethylcyclotetrasiloxane (D4). Finally, a series of novel siloxane-containing epoxies (SEs) with different number average molecular weights were synthesized through ring opening addition reaction of DEAMP-PDMS with diglycidyl ether of bisphenol A epoxy (DGEBA). The structural elucidation of DEAMPPDMS and SE was carried out by FTIR, 1H NMR and 13C NMR spectroscopy methods. In addition, the purification methods and the factors influencing the synthetic process, such as reaction temperature, time, solvent, and catalyst as well as the relative amount of reactants utilized, are also discussed in detail. Number average molecular weight was determined by end group titration method. The results from spectroscopic analysis and end group titration show that the structure and number average molecular weights of target molecules are consistent with the designed molecular structure. As an advantage, the resultant SE exhibits good room-temperature mobility. Viscosity of SE decreases with the increase in number average molecular weights, which can be explained by the relative content of hydroxyl and the length of siloxane segment in SE.
  • Mehdi Barikani, Ekhlas Eltayeb, Ali Reza Mahdavian, Hengameh Honarkar Page 753
    The widespread use of polyethylene films as packaging materials is due to its exceptional mechanical properties and reasonable cost. These films are usually discarded after single use and because of their high molecular weight and absence of functionalities the degradation time is very slow and their wastes cause major pollution problem in our land fields. Increasing the degradation rate of these materials by incorporation of initiator and sensitizer is a major issue of research topics in this field. In this work, the effects of cobalt naphthenate and 2-hydroxy-4-methoxybenzophenone on photo-oxidative degradation of low density polyethylene (LDPE) have been studied. The degradation was monitored by measuring the changes in the carbonyl index, changes in tensile strength, elongation-at-break, crystallinity, and density. The measurements were performed before and after UV-irradiation at 30 days interval for 3 months. From the results of these measurements, it was observed that the UV-irradiation affects the LDPE and the rate of degradation increases with increasing the concentration of the cobalt naphthenate. The increasing rate of degradation becomes more obvious by varying the concentration of cobalt naphthenate and irradiation time. 2-Hydroxy-4-methoxybenzophenone shows a retarding effect on UV-degradation