Iranian Journal of Polymer Science and Technology
Year:2019 | Volume:32 | Issue:4 |Papers Count:6

Recently, the supply of electrical energy from sustainable and renewable energies such as mechanical, thermal and solar energy has been expanded. Piezoelectric materials are one of the best alternatives for supplying electrical energy from the mechanical energy available in nature such as mechanical force, vibration and human body movements. The applications for piezoelectric energy harvester include low power electronics or wireless sensing at relatively lower power levels (nW to mW) with an aim to reduce a reliance on batteries or electrical power through cables and realize fully autonomous and self-powered systems. In fact, the piezoelectric property is the property of a special material that enables the conversion of mechanical energy into electrical energy and vice versa. Piezoelectric property was discovered in ceramics for the first time. However, because of the need to piezoelectric materials with large surfaces and high flexibility in many applications, and the relatively low price and simple manufacturing technology of polymers in comparison with ceramics, polymers are used extensively. Poly(vinylidene fluoride) (PVDF) is a semicrystalline polymer with ferroelectric and piezoelectric properties. It has five distinctive configurations (a, b, g, d and e). b-phase is a polar phase showing significant piezoelectricity and pyroelectricity due to the highest dipolar moment and spontaneous polarization. In this review, PVDF polymer is introduced and then the different strategies for identification and quantification of PVDF phases are summarized. Finally, various methods including stretching, high pressure, ultrafast cooling, melt quenching, using polar solvents, poling, copolymerization, polymer blending, electrospinning and filler addition such as carbon nanotube, clay, metals and metal salts, ceramics and etc., have been discussed for β-phase enhancement.

Hypothesis: Production of polyethylene (PE) of a relatively high molecular weight with improved properties and acceptable processability has been allocated to many research efforts. In the slurry polymerization, immobilization of homogeneous metallocene catalyst on a nano-sized support leads to improved mechanical and thermal properties in addition to controlled morphology and appropriate particle size distribution of product. Specific surface area of support particles can be an effective parameter affecting the immobilization process of catalyst and product properties. In this research the main purpose was to produce PE/nanosilica nanocomposite, using an in-situ polymerization technique, in a disentangled state. Methods: A metallocene catalyst, such as zirconocene dichloride (Cp2ZrCl2), was immobilized on the surface of modified nano-fumed silica particles. Three grades of nano-fumed silica having specific surface areas of 380, 200 and 50 m2/g were used. First the surface of thermally pretreated nanosilica was chemically modified using methylaluminoxane. Then, by adding the catalyst, Cp2ZrCl2, immobilization reaction and activation of the catalyst were performed simultaneously. Finally ethylene polymerization was conducted using the prepared catalyst under the atmospheric pressure of monomer at 30° C. Findings: The maximum polymerization yield was related to the heterogenized catalyst on nanosilica with a specific surface area of 200 m2/g. The results of solid state drawability and buildup of modulus in time sweep rheometry exhibited that the synthesized polyethylene is in the less entangled state. Reducing the concentration and density of the active sites on the heterogenized catalyst resulted in the reduced number of chain entanglements. Tensile test results showed that nanocomposite samples possess better mechanical properties compared to the pure polyethylene, an indication of appropriate distribution of silica nanoparticles into the polyethylene matrix which was evidenced using SEM images.

Hypothesis: Energy-absorbing materials and structures have many uses, especially in protecting human lives. As a result, interest in discovering the applied new materials have increased. Polyurethane foams are used in a variety of energy absorbers. In this study, the mechanical properties of a pentanediolreinforced methylene diphenyl diiscocyanate (MDI) polyurethane foam have been investigated. Methods: Foams were prepared by direct mixing of the reactants. Standard samples have been developed to study the compressive and tensile properties. The specimens were made by adding 5 and 10% pentanediol to a same polyurethane compound. Quasi-static strength and compression tests have been performed and the results have been reported. The microstructure of the foam has been investigated using scanning electron microscopy (SEM). Findings: Comparison of the results showed that, despite the strengthening of the compressive strength of the polyurethane foams by adding some other chain-extenders, the compressive properties of polyurethane foams, including the strength and absorbed energy with the pentanediol as an additive, are not significantly altered, but the elastic modulus and plateau modulus increased significantly. The specific absorbed energy of foam is also increased by adding 5 and 10 percent pentanediol to 11. 7% and 12. 6%, respectively. The results of tensile tests also showed a high sensitivity to the addition of pentanediol. With addition of 10% pentanediol, strength, fracture strain and foam toughness increased by 37. 9%, 57. 1% and 137. 5%, respectively. The elastic modulus of the tensile samples was also increased by 6. 9% in adding 10% pentanediol. Also, the results showed that the substance exhibited smaller cells and a more uniform structure by adding 1, 5-pentane diol.

Hypothesis: Aromatic polyamides are well known as a main group of high performance and heat-resistant polymers. One of the drawbacks to utilize these polymers is the difficulty in processing due to their insoluble nature in aprotic organic solvents in addition to their high melting point or glass transition temperature. One way of overcoming the main problem of heat-resistant polymers-i. e., enhancing solubility without too much scarifying of the thermal stability is designing new monomers. Methods: Firstly, bis(4-oxybenzoic acid)-1, 5-anthraquinone (DA1) and bis(3-oxybenzoic acid)-1, 5-anthraquinone (DA2) were prepared through aromatic nucleophilic substitution reaction of 4-hydroxybenzoic acid and 3-hydroxybenzoic acid with 1, 5-dichloro anthraquinone, respectively. In the next step, the Yamazaki method was applied for synthesis of novel polyamides by polycondensation reaction of the obtained new diacids with commercial aromatic diamines such as oxydianiline (ODA), p-phenylene diamine (PPDA), 2, 6-diaminopyridine (DAP), and diaminodiphenyl methane (DADPM) in presence of triphenylphosphite and pyridine as the activating agents and N-methyl-2-pyrolidone (NMP) as a solvent. Findings: The structures of prepared novel monomers and polymers were characterized using different spectroscopy methods. The thermal and physical properties of novel polymers such as thermal stability and behavior, solubility, viscosity and ultra violet absorption were studied and the structure-property relationship of these polymers was investigated. The prepared polymers showed defined UV-Vis absorption bands at the range of 344-370 nm. Inclusion of an aromatic and bulky anthraquinone unit to the main chain of polymers led to high thermal stability while their solubility was improved in polar aprotic solvents.

Hypothesis: Poly(tetrafluoroethylene) (PTFE) powder, due to its low surface energy, reduces the friction of nitrile rubber (NBR) composite. Moreover, due to its chemical stability PTFE improves the resistance of the composite to oil solvents. Due to thermal stability, it can improve thermal resistance of rubber compound. However, the dispersion of PTFE particles in the rubbery matrix is limited and the latter may reduce in mechanical properties. Methods: To create better polymer-filler interactions and improve the dispersion of rubber, the type of irradiated PTFE powder was used. Samples were prepared and evaluated well by melt mixing. Findings: Distribution and dispersion of irradiated PTFE powder particles are suitable for filled samples. The irradiated PTFE powder not only does not endanger the sulfur curing of nitrile rubber compounds reinforced with carbon black, but also improves the Young's modulus and hardness of the samples. Thus, contrary to the references, irradiated PTFE powder, probably by affecting the reduction in the energy level of rubber compounds, could significantly reduce the friction coefficient and improve tribological properties. So that, with a reduction of mechanical strength about 4-5%, for 20 phr loading of the lubricant, under the test conditions the reduction in friction coefficient was 40%. For the aging properties, a small change in the strength-at-break was obtained after solvent conditioning and under its thermal aging a very small reduction in the strength-at-break was obtained for compounds. For a composite containing 20 phr of PTFE, about 7% decrease in strength and strain-at-break was observed after thermal aging and about 8. 5% improvement after solvent aging.

Hypothesis: In recent years, with the shortage of conventional energy resources, there has been a great advancement in the study of fuel cells particularly hydrogen-methanol types as an important energy alternative. One of the main components in such fuel cells is an electrolyte membrane whose main function is to carry protons and capture methanol. The electrolyte membrane must have a high chemical and electrochemical stability plus mechanical resistance. In addition, high proton conductivity is required to support better fuel cell performance. Methods: In this research, novel nanocomposite membranes were prepared as electrolyte for application in fuel cells. For this purpose, two types of membranes, including sulfonated polyethersulfone (SPES) and its blend with polyurethane (PU), were chosen as base membranes. At first, polyethersulfone was sulfonated by using sulfonic acid and blended with PU. Then, silica nanoparticles with different percentages (3, 5, and 8 wt%) were added to blend membrane (SPES/PU/SiO2). The prepared membranes properties were studied by Fourier transform spectroscopy (FTIR), X-ray diffraction analysis, thermogravimetry (TGA), water and methanol uptake test, proton conductivity test and scanning electron microscopy (SEM). Findings: The results suggested that there was a proper distribution of PU into the prepared membrane through forming hydrogen bonds between polar groups of SEPS and PU. Hence, by the mechanism of increasing polarity, the conductivity in SPES/PU blend membrane was increased (74%), comparing to its pure samples without intense increase in water and ethanol uptake. Additionally, by adding the silica nanoparticles to a SEPS/PU blend membrane and forming SPES/PU/SiO2 nanocomposite membrane, these particles formed a higher adhesion between the phases by forming covalent bonds with sulfonic acid groups of SPES and forming hydrogen bond with polar groups of PU and SPES. As a result, the morphology was modified by the mechanism of decreasing cavities and voidages. Finally, the conductivity of SPEC/PU/SiO2 nanocomposite membrane compared to that of the SPES pure sample increased by 53. 13% only by an increase of 11% and 8% in water and methanol uptake, respectively.