دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و هفتم شماره 5 (پیاپی 133، آذر و دی 1393)

Simultaneous increase in the permeance coefficient and mechanical strength and decrease in membrane fouling pose a challenge to polymeric membrane researchers. In this work، polyethylene (PE) polymer membranes، to which ZSM-5 zeolite particles have been added، were fabricated via thermally induced phase separation (TIPS) method. The fabrication of membranes is done in two steps; in the first step، in a constant coagulating bath temperature، the ratio of zeolite to polymer varies within 0-30% range and the changes in the pure water permeance and mechanical strength were assessed. The results are indicative of 60% increase in pure water permeancy، 300% increase in the mechanical strength and 400% increase in the ultimate tensile strength in pure water permeancy test in the membrane containing 30 wt% of zeolite. In the second step of optimization of the membrane’s structure and performance، the experimental design and response surface methodology (RSM) is applied to measure the individual and mutual effects of zeolite concentration، membrane’s thickness and bath temperature parameters on the water permeancy and mechanical strength. The results indicated that the water permeancy improved with any increase in the zeolite concentration and coagulation bath temperature while the membrane’s thickness scarcely affected the water permeancy. The interesting point was that any increase in the membrane thickness improved mechanical strength. Finally، the performance of membranes was evaluated using the collagen solution. The results showed that the membranes containing zeolites were more fouling resistant and the degree of resistance increased by increasing the zeolite content.

The mechanical properties of epoxy resin including tensile and flexural modulus، tensile and flexural strength for static conditions are currently studied. The frequency effect as significant parameter at room temperature is investigated and fatigue behavior of the epoxy resin in tension-tension loading conditions for different frequencies of 2، 3 and 5 Hz are obtained. The epoxy resin has been taken under flexural bending fatigue loading and fatigue life is investigated. The results of the experiments show the values of 2. 5 and 3 GPa of tensile and flexural modules and 59. 98 and 110. 02 MPa of tensile and flexural strengths for the resin، respectively. To achieve a linear load-deflection relationship in a three-point bending experiment، a maximum allowable deflection of 5 mm is acquired. The relationship between the frequency and fatigue life shows higher frequency results in lower fatigue life. Loading with frequency of 2 Hz has provided 5. 8 times more fatigue life compared with 5 Hz loading. For a tension-tension fatigue loading condition، the variation of tensile module of epoxy resin shows no noticeable change during the fatigue loading condition. This module decreases significantly only in the primary and failure cycles close to the fracture point. In further experiments، fatigue behavior of epoxy resin was tested under flexural bending fatigue loadings with controlled deflection at room temperature. Maximum applied normalized stresses versus the number of cycles to failure curve are illustrated and it can be performed in order to predict the number of cycles to failure for the resin in arbitrary applied normal stresses as well.

Crystallization behavior of nanocomposite based on semicrystalline polymers and graphene nanoplatelets (GNp) has been considered due to its critical effect on the performance of the final product. In this study، nanocomposite based on poly (lactic acid) /graphene nanoplatelets (PLA/GNp، 0. 5 and 1 wt %) was prepared via solution method using dimethylformamide as a solvent. PLA has the largest contribution in the current biopolymer research. To present time، it is well accepted that nanoparticles would be recognized as efficient heterogeneous nucleating agents for various semicrystalline polymers. To improve the dispersion of graphene in the matrix، functionalization using acid treatment and acylation reaction was accomplished. Characterization of functionalization reaction and grafting reaction between PLA and functionalized graphene (FGNp) was tracked by Fourier transform infrared spectroscopy، elemental analysis، and thermogravimetry analysis. Scanning electron microscopy results demonstrated that a relatively fine dispersion of FGNp is achieved in the PLLA matrix. Non-isothermal and isothermal crystallization behavior was studied using differential scanning calorimetry. The isothermal tests were conducted at test temperatures 130°C، 125°C، 120°C and 115°C. The results indicated that crystallization percentage for the samples containing FGNp nanoparticles were higher than those of pristine-containing samples. With increase of temperature in isothermal test onset time for crystallization decreased due to higher mobility of polymeric chains in the samples. It seems that the presence of functionalized nanoparticles facilitated formation of β format of crystals.

Nowadays، due to environmental concerns، there has been great attention to recycling and reclaiming of tires. Different methods have been used for reclaiming or desulfurization of rubber. One of these methods، in which desulfurization of rubber happens with no damage to the polymer structure، is desulfurization by biological microorganisms. In this research the application and performance of thermophilic and sulfur oxidizing bacteria، Acidianus brierleyi for this purpose was investigated. Ground tire rubber was detoxified with organic solvents، and the optimum conditions for growing microorganisms in the existence of rubber powder in the shaker flasks were determined. In order to accelerate the process، the suitable conditions for growth of bacteria and desulfurization in the bioreactor were adopted. Fourier transfer infrared spectroscopy and scanning electron microscopy were employed to characterize desulfurization of bio-treated powder from bioreactor. The results indicated that morphological changes on powder surface and reduction of sulfur bonds have occurred. Samples from bioreactors، with and without bacteria and also untreated rubber powder were compounded with virgin styrene butadiene rubber. Tensile and dynamic properties were investigated using uni-direction tensile test and dynamic-mechanical-thermal analysis، respectively. Although some differences in dynamic-mechanical-thermal properties of samples pointed to stronger interaction between rubber matrix and treated rubber powder، no significant improvements in the mechanical properties of vulcanizates containing A. brierleyi-treated powder were observed. Low concentration of sulfur in rubber vulcanizates، chemical bonds of sulfur، and low efficiency of A. brierleyi in breaking sulfur bonds and reclaiming rubber were considered as the reasons for low efficiency of this treatment process.

A theoretical and experimental study was conducted on the mechanical behavior of nanocomposites based on PA6/NBR thermoplastic elastomer reinforced by single wall carbon nanotubes (SWNTs). The selected samples include 60 and 40% NBR with 0. 5، 1. 0 and 1. 5% SWNT. The modeling methodology was based on the use of two-dimensional «representative volume elements» (RVE). The Abaqus/standard code was employed to carry out the non-linear finite element calculations. Plane stress elements were selected for discretization of the domain. Linear elastic and isotropic hardening elastic-plastic models were utilized to describe the mechanical behaviors of the carbon nanotubes and polymer matrix، respectively. The samples were simultaneously prepared using melt mixing method in a laboratory internal mixer. Different orientations including regular in both longitudinal and transverse directions and random were selected for the nanotubes in the matrix. Also، two structural forms including hollow and solid for the carbon nanotubes were chosen. The highest and lowest predicted moduli were obtained from models with regular orientation in longitudinal and transverse directions، respectively. On the other hand، comparison between the predicted elastic modulus and elastic-plastic behaviors of the samples with their corresponding experimental data revealed that the random orientation in conjunction with hollow structural form gives the best results. Moreover، the selected material model for the thermoplastic elastomer i. e.، isotropic hardening can precisely describe the mechanical behavior in both tension and compression modes. It is also concluded that the main source of error in this modeling methodology can be attributed to the effects of interface between polymer and nanotubes and orientation in perpendicular directions.

The main purpose of this paper is the experimental study on the tensile and dynamic - mechanical thermal properties of polypropylene (PP) and polypropylene foam reinforced with mesoporous silica (MCM-41)، hydroxyapatite (HA) and the composite of mesoporous silica and hydroxyapatite (MCM41-HA) nanoparticles. Nanocomposites and nanocomposite foams containing PP، maleic anhydride grafted polypropylene، different nanoparticles and chemical blowing agent (for foam samples) are mixed using the melt-compounding technique in a twin-screw extruder. The results of the tests show that at the same nanoparticles content، all the nanofillers cause better mechanical properties than neat PP and PP foam. Also، due to the porous structure of the foam samples، these samples have the higher damping characteristics and lower tensile properties than the solid samples. Because of higher rigidity and higher strength of HA nanoparticles، the greatest increase in modulus and tensile strength occurs by adding these nanoparticles to neat PP and PP foam. The highest damping factor is obtained by adding MCM-41-HA nanoparticles to PP and PP foam، because of the porous nature of the MCM-41 particles which were reinforced by HA particles. The results of differential scanning calorimetry show that the addition of different nanoparticles does not have any significant effect on crystallinity and melting behavior of PP. Scanning electron microscopy images show that the nanomaterials were fine and uniformly dispersed within the polymer matrix. Furthermore، the addition of different nanoparticles to PP foam causes to increase the cell density، to reduce the cell sizes and to improve the cell sizes distribution. In this respect، the lowest cell sizes and the highest cell density are created by adding HA and MCM41-HA nanopaticles to PP foams.

The effects of through-the-thickness yarn fineness and distance on the damage behavior of vacuum resin infused 3D carbon-phenolic composites were investigated. For this purpose، the carbon/phenolic composites with different tufting thread fineness (count) and distance ranging from 5. 5 mm to 16. 5 mm were produced to determine an optimum distance and count in the composites. Three-point bending test results show that the flexural strength of tufting composites may drop 17% to 34 % while through thickness reinforcements set up a mechanical connection between the plies and bridge over delamination cracks to avoid their penetration. The weakness is attributed to damaging effect of tufting method، misallignments of X-Y fibers in presence of Z direction reinforcement and stress concentration effect of produced holes for tufting. On the other hands، Z direction reinforcements prevent fibers delamination. Therefore، the laminate strength was increased and failure mechanism was changed from brittle to ductile fracture. In addition at the same through-thickness yarn count of tufting composites، with the increase in tufting distance، the flexural strength is reduced. But i in the case of samples with tufting distance of 5. 5 mm، the flexural strength reduced with increase in thorough-the-thickness yarn count، but for samples with tufting distance of 16 mm، showed some increases with the same count variations. After the failure stress in stress-displacement curve was increased for specimens with Z direction reinforcements.