دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و هشتم شماره 2 (پیاپی 136، خرداد و تیر 1394)

Nanocomposite materials have recently attracted much attention because of their desirable and unique physical and mechanical properties. Today، many studies have focused on the preparation of high performance new nanocomposites made of biobased and biodegradable materials as both the matrix and reinforcement phases. Because of biocompatibility، biofunctionality، and biological safety in the body، hydroxyapatite-polyvinyl alcohol composites are vastly used in medical applications، specially in the bone tissue regeneration. The properties of a new generation of nanocomposites consisting of hydroxyapatite nanoparticles and cellulose nanofibers، dispersed in polyvinyl alcohol matrix، were investigated. The percentage by weight of each component in the final formulation and the time of ultrasonication were studied as factors affecting the physical and mechanical properties. Tensile strength، elastic modulus and resistance to water dissolution were evaluated. The results showed that by increasing the percentage by weight of PVA and cellulose nanofibers and ultrasonication time، the tensile strength and elastic modulus increased and the resistance to water dissolution and weight loss decreased. On the other hand، with increasing the amount of hydroxyapatite nanoparticles in the final formulation، the elastic modulus and resistance to water solubility increased، while the tensile strength decreased significantly. Scanning electron microscopy (SEM) micrographs were used to find exact correlations between the observed physical and mechanical properties and the structural morphology.

Most of porous polymer materials are mainly prepared by solution phase inversion method. The de-mixing process can be initiated by diffusive solvent/non-solvent exchange of binary، ternary or multicomponent mixture. Recently، supercritical CO2 (ScCO2) is used as a non-solvent to prepare porous polymers. ScCO2 possesses excellent properties، such as environmental friendliness، liquid-like density and gas-like diffusivity in comparison with conventional liquid non-solvents. Porous polyurethane was prepared from polymer/N-dimethylformamide (DMF) solution using a supercritical fluid-phase inversion process in which carbon dioxide acted as the non-solvent. The effects of time delay، casting temperature and ratio of polyol/chain extender (POL/CE) on the membrane morphology and structure (size and distribution of cells and pores، thickness of dense layer and porosity) were studied. According to the results، a minimum time delay of 120 min was determined for formation of a suitable structure. The dense layer of 77. 6 μm thickness was decreased to 43. 1 μm by lowering casting temperature from 55°C to 35°C. The ratio of POL/CE influenced the thermodynamic and kinetic properties. A decrease in POL/CE ratio led to formation of smaller and uniform cells and increased porosity. On decreasing the ratio of POL/CE from 2 to 0. 25، the mean diameter of the cells at 6. 3 μm dropped to 3 μm.

In comparison with conventional concrete، the polymer concrete has considerably better mechanical properties. Meanwhile، polymer concrete is more expensive than traditional cement concretes. Considering the good mechanical properties of polymer concrete، its applications can be developed by reducing manufacturing costs. In this study، in order to improve the mechanical properties and reduce the manufacturing costs of polymer concrete، a new formulation is presented. In this formulation، the more common mixture of large and small aggregates was replaced by silica sand. In addition، in order to reduce the manufacturing costs، polyester resin was used instead of epoxy resin as the base material. The compressive and three-point bending tests showed that the polyester-based concrete had a higher compressive strength (20%) in comparison with the epoxy-based concrete، while their bending strength was approximately the same. As a result، the manufacturing cost for the polymer concrete prepared using this new formulation can be reduced without decrements in mechanical properties. Moreover، a two-phase micromechanical model was applied to estimate the compressive strength of the polymer concrete. Using the two-phase micromechanical model، the mechanical properties of the polymer concrete were predicted. The results obtained from the modeling and experiments were in good agreement with each other (6. 8% error). The excellent mechanical properties of polyester-based concrete developed in the present research and its low cost in comparison with the epoxy-based concrete are key factors that can help its wider applications.

Polyaniline-montmorillonite (PANI-MMT) nanocomposite was synthesized by chemical polymerization of aniline in the presence of montmorillonite (MMT) nanostructures. The triple hybrid of polyaniline-polyvinylchloridemontmorillonite (PANI-PVC-MMT) was prepared by mixing of the synthesized PANIMMT nanocomposite with a solution of polyvinylchloride (PVC) in tetrahydrofurane (THF). In addition، PANI-PVC composite was prepared by mixing of pure synthesized PANI and PVC solution in THF. To investigate the mechanical properties، the PANIPVC composite and PANI- PVC-MMT nanocomposite films were prepared with 5، 10 and 15 wt% of pure PANI and PANI-MMT nanocomposite، respectively. The results showed that the PANI- PVC-MMT nanocomposite film having 10 wt% of PANIMMT nanocomposite displayed the best mechanical properties. Therefore، it was chosen as optimum film and its physico-chemical properties were characterized. The cyclic voltammetry (CV) technique confirmed that the triple hybrid of PANI-PVCMMT nanocomposite was electroactive. Also، Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques were used to characterize the composition and structure of the PANI-PVC-MMT triple hybrid nanocomposite. X- Ray diffraction (XRD) technique showed an intercalated structure for the PANI-PVC-MMT nanocomposite. The thermal stability improvement of the PANI-PVC-MMT nanocomposite in comparison with the pure PVC was established by thermogravimetric analysis (TGA).

The effect of NH2-MIL 53 metal organic framework (MOF) on gas transport properties of poly (4-methyl-1-pentyne) (PMP) was investigated. Various characterization methods such as FTIR، DSC، SEM and gas adsorption test as well as a series of CO2/CH4 gas separation tests (i. e.، pure and mixed gas test) were conducted in order to determine the effect of ligand functionalization (–NH2) on the properties of the prepared mixed matrix membranes and their gas transport characteristics. The results of DSC showed that glass transition temperature (Tg) increased by increasing NH2-MIL 53 loading. The SEM images also demonstrated that the NH2-MIL 53 particles were dispersed well in the PMP matrix with no noticeable agglomeration. The gas adsorption test of NH2-MIL 53 particles revealed there was a selective adsorption behavior with respect to CO2. It was also found that، incorporation of NH2-MIL 53 into the PMP resulted in an increase in gas permeability (especially towards CO2) and a higher CO2/CH4 selectivity. Adding 30 wt% NH2-MIL 53 into the polymer matrix increased CO2 permeability and CO2/CH4 selectivity of the mixed gas from 83. 35 to 210. 21 barrer and 7. 61 to 19. 88، respectively. Rising the temperature from 30 to 60°C led to the permeability increment of both CO2 and CH4 in the mixed gas test، while the CO2/CH4 selectivity decreased. Moreover، the results showed that amino groups required no regeneration and their performance did not decline during 120 h of permeation test. A comparison between the permeation data and those calculated from permeation models revealed that the Bruggeman model could fit the CO2 permeability data better than the Maxwell and Lewis models.

The adjustment of material composition in fabrication of modified polymeric membrane has been considered the most efficient and easiest method. For this purpose blended membranes of high density polyethylene (HDPE) –ethylene vinyl acetate (EVA) were prepared by thermally induced phase separation method. The impact of EVA in the presence of diluent on the crystalization temperature was assessed using differential scanning calorimetry (DSC). The obtained results showed that EVA has no significant effect on the crystalization temperature of HDPE. The absorption frequencies at 1248 and 1749 cm-1، respectively، due to C-O and C=O streching vibrations of EVA functional groups، confirmed the existence of EVA in HDPE membrane. The pure water permeability of HDPE/EVA blend was measured and compared with that of neat HDPE membrane. The results showed that an EVA content up to 2. 5 wt% raised water permeability considerably and the leafy structure of the membranes contracted and the pure water permeation dropped with higher EVA content. The results of porosity measurement and scanning electronic microscopic (SEM) analysis also confirmed these findings. Contact angel measurements and atomic force microscopy (AFM) examinations and static absorption of collagen protein on the membrane surfaces revealed that EVA content up to 5 wt% lowered the hydrophobicity of the membrane. By EVA content above 10 wt%، due to the structural alteration on the membrane surface، the contact angel and the collagen absorption on the surface of membrane increased. The measurement of tensile strength showed that with increasing EVA content the mechanical properties of the membranes improved due to interactions of polar groups in EVA.