دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و یکم شماره 4 (پیاپی 156، مهر و آبان 1397)

Hypothesis: Cellulose is the most abundant source of biomass, and it has a potential ability to become an alternative to fossil resources for sustainable production of chemicals and fuels for preventing global warming by decreasing atmospheric CO2 generated from the consumption of fossil fuels. Mildly hydrothermal method using solid acid catalysts for production of glucose from cellulose can be one of the key technologies for a future sustainable society using cellulose biomass.

In this manuscript, an acidic poly(ionic liquid) coated magnetic nanoparticle catalyst was successfully synthesized by polymerization of vinylimidazolium sulfonic acid in the presence of surface modified magnetic nanoparticles. The poly(ionic liquid) coated magnetic nanoparticle was prepared by distillation-precipitation-polymerization in the absence of any surfactant. Direct attachment of SO3H to imidazole groups in polymeric chains resulted to generation of highly dual acidic poly(ionic liquid) which can be used as a Bronsted acid catalyst. Since, the monomers make the catalyst bed, the catalyst has high loading level of acidic groups comparing to other heterogeneous acid catalysts. The resultant catalyst was characterized by various instrumental analyses such as FTIR, TGA, XRD, VSM, AA and TEM. Finding: The resulting ionic heterogeneous catalyst is shown to be an efficient catalyst in hydrolysis of cellulose and gave high yield of glucose. The synthesized acidic catalyst was compared to industrial and mineral acids and the results showed higher selectivity of the presence catalyst. The catalyst was also separated by using an external magnet and reused in other runs. All the results proved that the present catalyst has better performance compared to other reported catalysts and lower amounts of catalyst was required to complete the reaction. All the results show that the presented catalyst and protocol can be scaled up

Hypothesis: We investigated the effect of thermally-reduced graphene (TRG) nanosheets on electrical conductivity, dielectric constant, electromagnetic interference shielding performance, rheological behavior and thermal stability of polypropylene/polyethylene terephthalate (PP/PET) blend. For this purpose, 50/50 PP/PET blends were prepared through melt compounding in presence of different volume fractions of TRG. The direct current (DC) conductivity, the AC electrical conductivity and EMI shielding effectiveness of composites were measured. The morphology of blends was examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Findings: The morphology of the samples was co-continuous, and preferential localization of the nanoparticles led to a double percolated structure. This structure enhanced electrical conductivity of the samples considerably. The rheological analysis indicated that a percolated network was formed at low volume fractions of TRG. At 0.1 vol% loading, the conductivity of the composites satisfies the antistatic criterion (10−6 S/m) for thin films. At 2 vol% of graphene, a high electrical conductivity of0.16 S/m was achieved which was considered sufficient for electronic device applications. The dielectric constant and the electromagnetic interference shielding efficiency (EMI SE) of the blends significantly increased with TRG addition. By incorporating 2 vol% of TRG, the dielectric constant increased from 4 (for neat sample) to 9×107 at 10 Hz and the EMI SE increased from 1 dB (for neat sample) to 42 dB at 10 GHz, satisfying the target value for commercial applications. Thermogravimetric analysis (TGA) indicated that addition of TRG effectively enhanced the thermal stability of the samples. Incorporation of TRG not only increased the initial decomposition temperatures but also decreased the rate of decomposition. The enhanced thermal stability of the composites was attributed to the high aspect ratio of TRGs, which served as a barrier and prevented the emission of gaseous molecules during thermal degradation.

Hypothesis: Gas-liquid membrane contactors have been considered as one of the potential alternatives for CO2 removal compared to conventional technologies. However, membranes wetting with liquid absorbents during this process limits membrane contactors application, which indicates the need for the use of hydrophobic membranes in these systems. In recent years, the use of nanoparticles to increase the hydrophobicity of polymer membrane surfaces and fabrication of nanocomposite membranes has been considerably investigated by researchers. In order to reduce the wetting problem of membranes, in the present work, methyl grafted silica nanoparticles (CH3SiO2 NPs) were used to increase surface hydrophobicity of the polypropylene (PP) hollow fiber membranes, which were synthesized by the sol-gel method. Prepared membranes were characterized by ATR-FTIR, XRD, FE-SEM, contact angle, mechanical strength and breakthrough pressure. Findings: The obtained results from ATR-FTIR analysis confirmed the presence of methyl grafted silica NPs on the surface of PP membrane. The results of the contact angle measurement showed that for nanocomposite membranes by increasing the MTES/TEOS molar ratio from 1 to 4, the contact angle increased from 125° to 164°; however, the contact angle decreased with further increase in the molar ratio of MTES/TEOS. Also, with the precision in the results of mechanical strength measurement, it can be seen that the synthesis of NPs on the membrane surface as well as in the cross-section increased the tensile strength of the membrane to 12.8 MPa. Finally, the performance of membranes was investigated in the membrane contactors for CO2 absorption, which results in a significant decrease in the flux for pure membranes compared with nanocomposite membranes

Hypothesis: Short fibers can be incorporated directly into the rubber compound along with other nanoparticles. The state of filler dispersion and orientation in the matrix, their size and aspect ratio as well as the interactions with the rubber chains have been shown to be crucial parameters that determine the reinforcing ability of these fillers. These nanocomposites are light weight and there is tremendous potential in stiffness/weight ratios over conventional materials. In this study, nanocomposites of (NR/SBR) elastomer/short nylon fiber with different amounts of carbon nanotubes were prepared in the presence ofhydrated silica-resorcinol-hexamethylene tetramine (HRH) as bonding agent.

Natural rubber and styrene butadiene rubber (NR/SBR), reinforced with short nylon fibers and carbon nanotubes, were prepared in a two-roll mill mixer. The effect of different amounts of modified and unmodified multiwall carbon nanotubes (MCNTs) between 0 and 3 phr on the mechanical properties, structure and morphology of nanocomposite samples were investigated. The adhesion of the fiber to the rubber matrix was enhanced by the addition of a dry bonding system consisting of HRH. The structure of nanocomposites was studied by scanning electron microscopy (SEM). Findings: By enhancing the amount of modified carbon nanotube and unmodified carbon nanotube, the curing time and the swelling index decreased, while the curing rate and maximum torque increased. The mechanical properties, tear strength, hardness and compressibility were increased as the content of modified and unmodified multi-wall carbon nanotubes increased in both directions of longitudinal (L) and transverse (T) in the nanocomposite. The resilience of nanocomposites was reduced by increasing the carbon nanotube content, and there was a further decrease in the modified nanotube. The microscopy results indicated that by adding carbon nanotubes, specially modified carbon nanotube in longitudinal direction, the fibers pull out and hollow holes decreased at the fracture surface due to the strong bond between the rubber matrix and the fibers and carbon nanotubes. In transverse direction, there was increased pull out and weak bonding

Hypothesis: Glass-reinforced composites are used in the production of passively cooled combustion chambers. To improve the performance of these composites as well as to decrease their costs, the use of micron sized silicon dioxide particles has been widely used. In this work, the possibility of producing glass phenolic composites with nanosized silica as an alternative to micron-scaled silicon dioxide was investigated. In order to disperse nanosilica in composites uniformly, a combination of sonication and high stirring was used. In all cases, the blends were prepared according to following procedure: the resin was weighed and diluted in methyl alcohol, and then the selected amount of nanosilica was added. The resultant mixture was sonicated and stirred for 1 h simultaneously. For preparation of glass fiber nanocopmpsites, a theoretical amount of chopped strands was weighed first and then the fibers were mixed with resin or the nanocomposites. Each produced paste was placed in a cylindrical shaped mold and then the mass was compression molded at a pressure of about 10 bar and cured at 180°C. The thermal resistance properties of the produced materials were studied using an oxy-acetylene torch. In depth temperature profiles taken through the thickness of the samples, ablation and loss of mass data of the post-test surfaces were used to evaluate the effects of nanosilica. Furthermore, to investigate the material post-test microstructure, a detailed morphological characterization was carried out using scanning electron microscopy. Findings: In comparison to neat glass/phenolic composite, the introduction of just 2, 4 and 6 wt% nanosilica particles embedded in the matrix improved the mass loss of nanocomposites about 12, 19 and 31%, respectively

Hypothesis: Thermally stable nanocomposites were prepared by incorporation of carbon nanotubes (CNT) into the epoxy resin matrix cured by novolac resin. CNT modified with epoxy functional groups is capable of reaction with hydroxyl groups of novolac resin. Therefore, a new and robust method was planned for development of covalent bonding between the filler and matrix. On the other hand, due to slow reaction of epoxy and hydroxyl groups in the absence of catalyst, triphenylphosphine was used as the catalyst to accelerate the curing process.

CNT was modified with nitric acid to obtain oxidized CNT (CNTCOOH). After grafting of butane diol at the surface of CNTCOOH, hydroxyl-containing CNT (CNTOH) was prepared. Afterward, epoxy functional groups were applied at the surface of CNTOH through its modification with (3-glycidyloxypropyl) triethoxysilane in order to prepare epoxy-containing CNT (CNTG). Finally, CNTG and epoxy resin were placed in the hybrid network through the curing process with novolac resin. Finding: The results of FTIR-spectroscopy and X-ray photoelectron spectroscopy showed that modification of CNT was effectively carried out. X-ray diffraction analysis confirmed uniform distribution of CNTG in the matrix of cured epoxy resin. As thermogravimetric analysis exhibited, char yield of the cured epoxy resin (26.6%) was considerably increased to 32.8% and 38.2% through incorporation of 2 and 4 wt% of CNTG into the network, respectively. According to the scanning electron microscopy and transmission electron microscopy images, CNT showed tubular and entangled structure with smooth and uniform surface which even retained its structure after modification reaction. Finally, this approach can be successfully used for production of thermally-resistant thermoset hybrids for thermal protection applications

Hypothesis: Discovering new chemical modifications for polymers is an interesting way to change the properties and final applications of the polymers. Poly (vinyl alcohol) (PVA) and ethylene-vinyl alcohol copolymer (EVA) are useful in practical investigations of functional polymers because they can be modified through their hydroxyl groups. In this st وینیل udy, PVA and EVA were modified to incorporate different reactive functional groups using esterification reaction. Then, substitution reaction was used to incorporate benzimidazole groups into the modified EVA. Azolated EVA can be utilized in other applications such as fuel cell as a proton exchange membrane. Functional modification of PVA was carried out by acryloyl chloride and maleic anhydride in 1-methyl-2-pyrolydone (NMP, room temperature) and dimethyl sulfoxide (DMSO, 100°C), respectively. Similarly, EVA was modified with chloroacetyl chloride and α-bromoisobutyryl bromide via esterification reaction in NMP at room temperature. Next, benzimidazole group was incorporated into the α-bromoisobutyrylated EVA through substitution nucleation reaction with sodium-2-mercaptobenzimidazole in THF at 80°C. Findings: Chemical structures of polymers were investigated by FTIR and
1H NMR. Functionalization of PVA with acryloyl chloride and maleic anhydride was calculated to be 9. 31 and 46. 28 mol% and that of EVA with chloroacetyl chloride and α-bromoisobutyryl bromide was obtained to be 71. 50 and 63. 46 mol%. The high yield obtained in all of the different proposed routes makes them feasible for activation of EVA copolymers. Moreover, to predict the solubility behavior of functionalized polymers, the Hansen solubility parameters of original and modified polymers were calculated via Hoftyzer-Van Krevelen's (HVK) and Hoy's group contribution methods. Calculations showed that, among studied solvents, dimethylacetamide is the best solvent for acryloylated PVA, carboxyvinylated PVA and EVA copolymer, while acetone is the best one for copolymers modified with chloroacetyl chloride and α-bromoisobutyryl bromide and azolated copolymer, which was in good agreement with the experimental results.