دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و چهارم شماره 5 (پیاپی 175، آذر و دی 1400)

In recent years, extensive studies have been conducted on secondary lithium-ion (Li-ion) batteries for innumerable applications, including power source for the portable electronics, electric vehicle, and electric storage reservoir. It is well-known that Li-ion batteries are made up of four different components, i.e., anode, cathode, electrolyte and separator. Even though separators play no roles in the electrochemical reactions, they physically separate the anode and cathode to avoid electrical short circuits when the free flow of Li ions transfers through the liquid electrolyte. According to the above-given statements, a separator takes a key part in the safety and the power capability of Li-ion batteries. Unil today, various separators have been introduced, among which polyolefin membrane separators have proved to be the most promising separators for commercial Li-ion batteries, arising from their outstanding properties, e.g., electrochemical stability, good mechanical strength, cost-efficiency, and thermal shutdown properties. Nevertheless, these membrane separators have faced several key drawbacks for vehicular storage, including non-polarity, low surface energy and poor thermal stability. Accordingly, the aim of this study is to review the types of polyolefin microporous separators which are widely employed in Li-ion batteries and all the intricate approaches taken for their surface modification. Several approaches including grafting by different methods, mussel-inspired technique and functionalization by inorganic nanostructures have been widely utilized to overcome the above- problems. It has been proven in the literature that outstanding properties can be provided through mono- and multilayer polyolefin separators if they are modified by proper strategies and materials, by which stat-of-the-art Li-ion batteries can be introduced..

Amphiphilic systems present efficient ability in solublizing insoluble compounds by self-association to micellar structures. Polyurethanes with amphiphilic feature as polymeric assembling species illustrate specific characteristics such as H-bond assisting stability of arranged structures and functionalizing possibilty. In this respect, an amphiphilic random polyurethane (APU) synthesized from olive oil-based fatty acid was characterized for micellization in non-polar organic invironment along with its loading and transfering capability for insoluble dyes.

The solution of APU in non-polar organic solvent, toluene, at different concentrations was evaluated by turbidimetry and viscometry methods to realize the possibility of micelle formation and determine the aggregation point (RCMC). Morphology of the nanoparticles was investigated by field emision scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and dynamic light scattering (DLS). Capability of these polymeric micells as nano-carrier in encapsulating and solublizing of fushine hydrophilic dye in toluene as well as in phase transfering some hydrophilic cationic dyes from aqueous phase to toluene was investigated. Quantitative transferring capacity was spectroscopically evaluated by recording UV-Vis spectra of the dyes.

APU showed successful self-association into revers micelle at low critical concentration (0.02 mg/mL), expreesing efficent intermolecular interaction between hydrophilic segments of the polymer. Solvating capability of APU in the non-polar organic medium for hydrophilic dyes and phase transfer of this type of dyes from aqueous phase to organic phase illustrate the formation of assembled structures of APU with core-shell nature in the organic solvent and the embedding ability of APU. On the other hand, the reverse micelles formed in the organic phase were able to transfer cationic dyes from aqueous solution to organic medium. Based on the obtained results, APU can be utilized in removing cationic dyes from contaminated water and drug delivering process..

The fabrication of electrospun nanofibers for drug delivery applications has attracted a great attention in recent years. Polycaprolactone (PCL) is a polymer which has been used frequently in medical and tissue engineering applications. However, the hydrophobic nature of PCL is a drawback which could be resolved by biological materials. The synergistic effect of piperine and ellagic acid on different properties and performance of curcumin containing nanofiber mats has been investigated.

Nanofibers based on PCL with certain amounts of plant extracts were prepared and produced through electrospinning. In order to investigate the effect of each plant extract, single systems containing curcumin or piperine, dual systems containing curcumin/piperine and triple systems containing curcumin/piperine/ellagic acid were produced by electrospinning and various analyses were performed to find out whether they were effective in improving the properties of fiber prepared for medical applications.

The study on microstructure of electrospun mats showed that the diameter distribution of nanofibers was between 50-100 nm and the average fiber diameter in single, double and triple samples changed in the range of 73-87 nm. The antibacterial test revealed that piperine is also an active antibacterial agent like curcumin. In addition, the triple system had a good degree of antibacterial activity (79%). The water uptake and water vapor permeability (WVP) of triple samples were about 337% and 11.56 mg(cm2.h)-1, respectively. The prepared mats showed desirable tensile strength, elasticity and flexibility. Cell viability analysis on electrospun mats indicated that they are not toxic to human dermal fibroblasts (HDF). Therefore, taking into account all the results, it can be concluded that the use of two compounds, ellagic acid and piperine, is effective in increasing the bioavailability of curcumin, and the mats can be used in medical applications as wound dressings..

The increasing production of non-degradable polymer wastes such as polystyrene (PS) and expandable polystyrene (EPS) is known as one of the most important environmental issues. Pyrolysis is one of the strategic and suitable methods for recycling of non-degradable polymeric wastes to fuels and useful chemicals. Therefore, investigation of pyrolysis kinetic of polystyrene waste, especially for available materials in Iran, is an essential issue for their use in industries. Obtaining the polystyrene pyrolysis kinetic can be used in designing industrial reactors and where it has economic credibility, styrene monomers can be produced in an industrial scale from polystyrene wastes.

Polystyrene (PS) and expandable polystyrene (EPS) samples that are available in Iran were collected, and their TGA analysis was performed in a nitrogen atmosphere in the temperature range of 25 to 600oC, at heating rates of 5, 10, 15, and 20 C/min, and sample mass changes were measured. The activation energy of pyrolysis was estimated by the Coats Redfern (CR), Ozawa Flynn Wall (OFW), Kissinger Akahira Sunose (KAS), Augis Bennetis (AB) and Vyazovkin methods.

The Vyazovkin model can predict the experimental data better than the other models, and therefore this model was used to estimate the activation energy. The activation energies of PS and EPS were calculated in the range of 158-201 kJ/mole and 182-195 kJ/mole, respectively. Furthermore, the pre-exponential factors of PS and EPS were estimated by Vyazovkin approach as 3.08×1012 and 1.05×1015, respectively. The results of kinetic analysis of polystyrene (PS) and expandable polystyrene (EPS) pyrolysis of samples in Iran can help simulate waste recycling processes and consequently reduce the environmental problems.

The desirable tack and viscosity in prepregs are mostly obtained by pre-curing, but the main problem with this method is the decremental storage life of prepreg because of the ongoing curing reaction. One of the appropriate strategies to overcome this problem is to eliminate the pre-curing stage in the prepreg process and achieve the appropriate viscosity through epoxy formulations with different molecular weights. With this method, it is possible to obtain a prepreg with single-stage curability and longer storage life.

By using low molecular weight epoxy resin (Epon828) and solid epoxy resin with high molecular weight (Ker3003) in the presence of MEK as solvent, DICY as curing agent and diuron as accelerator, two types of formulations including 3S7L (30% (wt) Ker3003 and 70% (wt) Epon828) and 4S6L (40% (wt) Ker3003 and 60% (wt) Epon828) were designed. Based on the obtained formulations, prepregs were manufactured and then cured to obtain the final composites. Different characterization techniques including FTIR, DSC, DMTA, ILSS, tensile strength, viscosity and drapability were used to determine the properties of formulated resins, prepregs and composites.

Appropriate prepregs were obtained based on the designed resin formulations without pre-curing stage. The results showed that the curing initiation temperatures of the formulated resins were about 15°C higher than that of Epon828 epoxy resin. The 4S6L formulation maintains the desired tack and viscosity of the prepreg up to 45°C. ILSS for composites based on 3S7L formulation was about 14% and 11% higher than the values obtained for composites based 4S6L and Epon828 resins, respectively. Flexural rigidity as representative of the drapability of the prepregs was obtained 3230 and 3460 μJ/m, respectively. For prepregs based on 3S7L and 4S6L formulations, there is an indication of high drapability of the prepregs based on designed formulations..

Nanocrystalline cellulose (NCC) has received much attention to be used as nanofiller in bioplastics due to its biodegradability, renewability and fantastic mechanical properties. The well distribution of NCC is a key factor in determining the enhanced properties of bioplastics/NCC nanocomposites. Surface modification of NCC using aminosilanes can improve its dispersion in a polymer matrix.

N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane was used for surface modification of nanocrystalline cellulose (NCC) to improve its affinity to polybutylene succinate adipate (PBSA). PBSA-based nanocomposites, containing 0, 0.1, 0.3, 0.5, 1 and 2 phr modified, NCC were prepared by solution mixing. The structural, thermal and physical properties of the prepared samples were characterized using FTIR, RMS, SEM, TGA, DSC and water absorption techniques.

The chemical modification of NCC was confirmed by FTIR, TGA and EDX. Linear viscoelastic measurements show that the incorporation of NCC in PBSA resulted in a non-terminal behavior and viscosity up-turn in the low frequency range, which are pronounced in high loadings of NCCs. The enhanced affinity of NCC toward PBSA, obtained by surface modification, resulted in hydrodynamic interactions between them, leading to the formation of a 3D network structure in the matrix. The SEM results showed well distribution of modified NCC in the PBSA matrix. The TGA results showed that the thermal stability of PBSA increases in the presence of silane-modified NCC. This can be attributed to the interactions formed between the components of nanocomposite, needing higher energy for thermal degradation. Study on DCS results indicated that the crystallization temperature of the nanocomposites containing modified NCC increases as a consequence of well distributed modified NCC. The water absorption results demonstrated that the water uptake of the samples containing modified NCC increases as compared to virgin PBSA...