دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و دوم شماره 5 (پیاپی 163، آذر و دی 1398)

 Dehumidification of a gas stream was carried out by one of the newest separation techniques. Different processes have been proposed for gas humidification such as absorption process using an absorbent and adsorption process with higher capital and operating costs than the former. The former process is more common.

For humidification/dehumidification process two hollow fiber membrane contactor modules were made using polyetherimide hollow fiber membranes. At first, the dry inlet gas was humidified in the first contactor module and then, the dehumidification process was performed by the second module. In dehumidification process, monoethylene glycol (as the absorbent) was allowed to flow through the shell side of the contactor while the wet gas flowed through the fibers. The different operating parameters such as the pressure and flow rate of the wet gas were studied in relation to the performance of dehumidification system.

The results showed that by increasing the wet gas flow rate from 1 SLPM (standard liter per minute) to 3 SLPM, the water vapor absorption flux increased by 133%, indicating that the effect of decrease in gas phase mass transfer resistance in dehumidification process overcomes the effect of reduction in humidity content of the inlet gas to the dehumidification system. Furthermore, by increasing the gas pressure from 1 bar to 5 bar, the water vapor absorption flux decreased by 55% which showed that drop in humidity content of the inlet gas to dehumidification system (due to the pressure enhancement) affects the water vapor absorption process. Therefore, the operating conditions of the dehumidification process should be selected based on the effective parameters.

 Today, the use of modern methods for producing clean and renewable energy such as thermal energy is more requested. One of the most important methods for storing thermal energy is phase change materials (PCMs), which are used as clean and renewable materials in thermal regulating fibres for smart textiles. Polyethylene glycol (PEG), a solid-liquid phase change material, with proper properties, needs to be encapsulated. A single-phase combination electrospinning composed of matrix polymer and PCM is a method of encapsulation. On the other hand, adding metal oxide can increase the thermal conductivity of the phase change materials. This research was conducted with the aim of producing thermal regulating nanofibers from poly(vinyl alcohol) (PVA) and PEG polymers with titanium dioxide nanoparticles (TiO2).

TiO2 nanoparticles were added to an optimal combination solution containing PVA and PEG and the resultant solution was electrospun by a single-phase method and its thermal regulating performance was investigated. For this purpose, DSC, DTG, and also FT-IR and XRD tests were used and FE-SEM, EDS and mapping images were obtained from the nanofibers.

Based on the results of DSC test, the enthalpy of melting and crystallization of the produced nanofibers were higher than those of pure PEG powder. Also, according to FE-SEM, EDS and mapping images, the presence of TiO2 nanoparticles in the mentioned nanofibres was confirmed. Based on the DTG test, the presence of TiO2 nanoparticles and PVA increased the degradation temperature of PEG in nanofibers compared to PEG powder. The FTIR spectrum showed the presence of polymers and TiO2 nanoparticles. The XRD pattern showed a crystalline structure for nanofibres. According to the results, the prepared nanofibres can be used as a form-stable thermo-regulating material in various applications.

 Fatigue crack growth (FCG) of rubber composites as controlled by the viscoelastic losses, is strongly dependent on the polymer-filler interfacial phenomena. The type of filler-polymer bonding at the interface and the extent of mobility restriction of rubber chains resulting from the interaction by the filler are of the critical ones. In highly filled rubber compound, the amount of mobility restriction is almost dictated by the filler-filler interaction. Regulating the surface energy of the filler can be an effective method to control the filler-filler interaction, to distinguish the two interfacial phenomena, and to pave the way of studying their significance.

Ultrasil VN3 and solution styrene-butadiene rubber (SSBR) were of the base composite materials. Using two silanes with a short and a long aliphatic chain length, the surface of Ultrasil was modified in our lab to a certain level of grafting density which could bring the required surface energy and the filler-filler interaction. By controlling the surface energy of silica treated in the lab, and by making a systematic comparison of the resulting composites, it was possible to study the role of covalent bonding at the interface, the role of filler-filler interaction and severity of mobility restriction and finally the role of silane chain length.

Fatigue crack growth experiment revealed that the severity of mobility restriction and the filler-filler interaction of the composite have the highest impact on the amount of viscoelastic dissipation and the rate of crack growth.  The covalent bonding at the interface can deviate the crack from growing in the original direction and thus it may act as a physical barrier to improve crack growth resistance. For highly filled compounds where the properties are almost dictated by the filler-filler interaction, the role played by the chain length of silane is minor.

 The basic limitation of biopolymers compared to the petroleum-based polymers is their weak physical and mechanical properties. In recent years, efforts have been made to properly incorporate nanoparticles into the polymer to reduce the limitation of their use in the packaging industry by partially improving the physical and mechanical properties of these films. This study aimed to incorporate zinc oxide nanoparticles into gelatin-biopolymer-based nanocomposite films, in order to improve their physical, mechanical and thermal properties.

Gelatin-based nanocomposite films were prepared by adding different amounts of zinc oxide nanoparticles (0, 0.5, 1.5 and 3%) using the so-called casting method. By performing several tests, different properties of the manufactured nanocomposite films including thickness, density, water vapor permeability, mechanical properties, degree of transparency, color properties and finally, their biodegradability were investigated.

the results showed that increasing the concentration of zinc oxide nanoparticles increased the tensile strength and decreased the elongation-at-break of this biofilm. The results of physical tests showed that increase in nanoparticles concentration reduced the permeability to water vapor from 0.76 to 0.48. Incorporating zinc oxide nanoparticles affected the transparency of the biofilms i.e. their transparency reduced by increasing nanoparticles concentration. By adding nanoparticles to gelatin-based films, thermal properties including glass transition temperature and melting temperature increased. Also, the thermal stability of the biofilms increased from 533.38°C (0.5% nanoparticles) to 559.53°C (1.5% nanoparticles). The results of biodegradability in soil and light showed that with increasing the concentration of nanoparticles, the biodegradability was reduced. This is mainly due to the addition of nanoparticles, which results in a greater bond strength between the components, and consequently the delay in biodegradation.

 Aerogels are new nanostructured materials that have attracted much attention in recent decades. In the meantime, polymeric aerogels have found special applications due to their lightness and cost-effectiveness. In this study, the carbon aerogels were used to filter the gases from fossil fuels. The challenge of this research is to try to increase the efficiency of gas separation, which is proportional to the surface area and structure of the separator.

Carbon nanocomposite aerogel was made using pre-polymeric material with a high specific surface area and with nanostructure morphology during carbonization process at temperatures 600 and 1200°C. Novolac resin was selected for its low cost and solubility in alcohols as a polymer matrix in sol-gel polymerization. Expanded graphite due to its unique properties and relatively good distribution and for reaction with novolac was used as reinforcement. In this study, a sample with a distribution of fine colloids was selected by examining the distribution of carbon aerogel colloids by combining different percentages of novallac solid in primary sol. Again, by examining the size of the cavities, the production of the aerogel was made by combining the selected precursor composition with four percentages of expanded graphite. Then, the samples were pyrolized at two different temperatures. In the following, the effect of expanded graphite nanoparticles and degree of crystallinity of carbon nanocomposite aerogel on the filtration efficiency of gases from fossil fuels was investigated. To evaluate the effect of different crystallinity of aerogel, carbon aerogels were prepared at temperatures of 600 and 1200°C with different degree of crystallinity.

The results of this study showed that samples of carbon aerogel with 0.75% wt expanded graphite and pyrolized at 1200°C showed 40% higher carbon dioxide absorption efficiency than pure samples.

 Today, thermoset resins are one of the most widely used resins in various industries including aerospace and automotive industries. In this respect, epoxy resins are of particular importance. Strengthening the mechanical properties of this resin for use in special applications has always been a requirement of the industry. Thereby, an attempt was made to improve the tensile modulus of epoxy resin using benzoxazine resin based on aniline and bisphenol A (BA-a) and silica nanoparticles (Si).

Due to the lack of availability of epoxy resin and to achieve the scientific ability of producing epoxy-benzoxazine composites, benzoxazine resin was synthesized by solvent method and then the solvent was removed. Subsequently, Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1HNMR) and differential scanning calorimetry (DSC) tests were used to verify the structural nature of the synthesized resin and evaluate its thermal properties. After making sure that the benzoxazine resin was produced and familiarized with its process properties, epoxy resin blending was performed.

The results of this work showed that the tensile modulus of epoxy-benzoxazine-based composite (80:20 wt/wt%) (EB-82) (3.9 GPa) is 17% higher than a neat epoxy resin (3.33 GPa). By increasing the amount of benzoxazine resin to 30%, the mechanical properties did not change. Therefore, EB-82 was used to make other composites. In nanocomposites with 2 and 4 wt% nanosilica, the tensile modulus increased to about 26 and 51% (4.1 and 1.5 GPa, respectively). These interesting results were attributed to the good interaction between the components and the good filler dispersion.