فصلنامه مواد پیشرفته و پوشش های نوین
سال یازدهم شماره 44 (پیاپی 42، بهار 1402)

Flammability if polymers has always been a big challenge for plastic industry producers. Therefore, development of flame-retardant polymers has become a necessity in terms of safety standards. In this research, advanced materials based on high-density polyethylene (HDPE), polyamide 6 (PA6) and ethylene vinyl alcohol (EVOH) are manufactured as binary and ternary polymer blends reinforced with ammonium polyphosphate (APP) and clay nanoplatelets (NC) as flame retardants. Microstructure, thermal stability, and flame retardancy behavior of samples were studied by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and cone calorimetry tests. Results show that localization of APP and NC, minor phase domain size and compatibilizer incorporation can considerably affect thermal and flame retardant properties. The presence and increase of amount of APP in HDPE/PA6 binary blends slightly improved flame retardancy and thermal stability, where compatibilizer incorporation led to PA6 size reduction. The presence of third polymer, i.e., EVOH, enhanced compatibility featured by lower PA6 particle size, but compatibilizer was not efficient and did not improve flame retardancy.

In this paper, the piezo-resistivity effect is utilized to experimentally investigate self-diagnostic behavior of composite laminates in determining delamination. In order to do so, composite laminated beams with unidirectional carbon fibers and epoxy resin containing CNT are produced while Teflon tape is placed between layers of some samples to artificially insert delamination. Three-point bending tests are conducted and stress-strain curves and electrical resistance of the samples are measured for not-damaged and damaged beams. The stress-strain curves are applied to interpret and determine damage mechanisms and to extract time data for the evolution of each damage mechanism. This time data is then used to determine the self-diagnostic behavior based on the variation of electrical resistance of the samples. The results show that in general, the electrical resistance of the not-damaged samples is higher than the damaged ones. This fact shows that piezo-resistivity effect can determine the existence of the delamination in the samples. Moreover, the propagation of delamination leads to electrical resistance increase when the delamination is placed far from the neutral axis of the beam. In addition, decreasing the dimension of the delamination reduces the sensitivity of the self-diagnosing behavior, which means that the variation of electrical resistance cannot determine the evolution of small sized delamination. On the other hand, the longitudinal location of delamination does not have a sensible effect on the behavior.

In this paper a three-layer graded magnesium foam with a potential application in bone implants is produced by means of powder metallurgy and spacer method. The gradation is based on the density variation between the layers. In order to so, three different combinations of magnesium powder and carbamide particles (used as the spacer) are considered in three layers and the graded structure is compacted under a pressure of 300 MPa and finally sintered at 400°C for 4 hours. SEM analysis and compression tests are conducted on the produced specimens to determine the microstructure and mechanical properties of the graded foam, respectively. The results show that increasing the percentage of the carbamide spacer can lead to producing open cell foam. This means that this kind of foam can be used for repairing bone tissue scaffolds. In addition, while the mechanical properties of bulk magnesium implants are far from that of a compacted human bone, the produced three-layer graded foam can resemble spongy bone structures properties excellently. Furthermore, similar mechanical properties to human spongy bone can be obtained by gradation of the foam rather than applying single layer foams. This means that potentially, the three-layer graded magnesium foam may be utilized in human bone implants.

Nowadays, with the advancement of nano technology, several researches have been done on using Nano additives to solve the existing problems of the oil industry. One of the main challenges of drilling is thermal degradation of polymer additives in well drilling, which will lead to a decrease in rheological properties, increase in filtration values. Entering large amounts of filtrate into the shale formation will increase pore pressure, shale instability, cause many problems. Solving this problem by using high temperature polymers or carbon materials with high thermal conductivity can prevent thermal degradation of polymers and also block the nanometer pores of shale. In this research, we decided to investigate the effect of carbon nanotubes (FMWCNT) with two polar functional groups, OH and COOH, on rheological properties of light weight water base drilling fluid with a weight of 63 pcf.
In this study, a base fluid sample and 6 fluid samples containing nanotubes (3 samples with OH agent and 3 samples with COOH agent) with concentrations (w/w) of 0.01, and 0.05 and 0.1% were made and under the conditions of laboratory environment temperature. (BHR:77 °F) and mud circulation at the simulated bottom hole temperature (AHR:250 °F) Rheological properties and then filtration values (FL) have also been measured. The results have shown that among the concentrations used, the best effect on the rheological properties was observed at a concentration of 0.05% for the COOH functional group, which increased all rheological properties in both BHR and AHR conditions and also decreased the FL values.

In this research, the potential of using the carbonization of Zn based metal-organic framework under air atmosphere to synthesized C doped zinc oxide nanoparticles to create a fabric with UV protection was investigated. The results of X-ray diffraction spectroscopy, field emission scanning electron microscopy and elemental analysis showed that the coating of zinc oxide nanoparticles on the cotton fabric was successfully done. UV protection of the coated fabric were evaluated by changing the color of Methylene Blue exposed to UV light using a spectrophotometer. Compared to the raw fabric, the coated fabric showed higher UV protection. About 98% decomposition of Methylene blue was achieved in 45 min by ZnO doped with carbon. The results showed that the fabric coated with zinc oxide synthesized through the direct pyrolysis of metal-organic framework has the potential to provide protection against ultraviolet irradiation and can be used in advanced protective textiles. Also, synthesized zinc oxide nanoparticles can be effectively used in wastewater treatment and environmental applications.

Recently, interest in studying lignin as the second most abundant biopolymer in advanced applications has increased. In particular, micro and nano-lignin materials have high value-added applications. The present study investigated the path of lignin synthesis to nano-lignin materials. Subsequently, through performing different tests, the microstructures of these nano-lignin materials were compared with normal lignin.
At first, the GPC test results of lignin and milled lignin showed that the average molecular weight for lignin was 16814.16 Daltons and the average molecular weight for milled lignin was 265 Daltons.
The results of the DLS test also indicated that the average size of the milled lignin particles when dissolved in ethylene glycol is about 0/520 µm. Next, coatings based on milled lignin were synthesized and applied on steel substrates. Finally, FE-SEM and roughness measurement images of the surface of polyurethane coatings based on milled lignin were prepared, and the results clearly indicated the formation of nano-lignin particles during the ultrasonic and ball mill process.

Nearly two decades have passed since the discovery of high-entropy alloys, an idea of alloying that has encouraged materials engineering scientists to explore unusual alloy compositions and multicomponent alloy systems. To increase the performance of this group of alloys in various fields of application, controllable synthesis with favorable phases is required. Based on this, in this research, with the aim of synthesizing a two-phase high entropy alloy based on the principles of thermodynamics, theoretical calculations were performed in the first step, and after feasibility from a theoretical point of view, elemental powders of iron, cobalt, nickel, and copper were used in the solid state method. And high purity aluminum was selected and mechanically mixed and alloyed. Sampling was done from the mechanical alloying chamber at consecutive times of 10, 20, 30, 40 and 50 hours. These samples were characterized by X-ray diffraction (XRD) technique and it was observed that after 50 hours, this alloy has two-phase FCC crystal structure. In this way, the experimental tests confirmed the thermodynamic calculations. Also, the images of the elemental map analysis showed that after 50 hours of mechanical alloying, all elements of the high entropy alloy were completely uniformly dispersed in the field and a uniform solid solution structure was formed. Finally, some insights into the challenges and future prospects in this emerging research field are provided.