دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و سوم شماره 2 (پیاپی 166، خرداد و تیر 1399)

Tissue engineering is a triad involves three components of different types of cells, growth factor, small biomolecules and scaffold for the purpose of tissue restore, repair and regeneration. In tissue engineering, attachment, growth, proliferation and differentiation of cells require careful control of external factors such as the physical properties of the scaffold as extra cellular matrix (ECM), type and amount of biologically active molecules like small biomolecules, peptides and proteins. Therefore, the interaction of the synthetic and natural scaffolds with the cells must reflect the cellular microenvironment in the body. In this study, we describe a variety of in situ forming injectable hydrogels synthesis with the medical application and tissue regeneration that are crosslinked by chemical bonding or physical interactions. These types of hydrogels have attracted a lot of attention in tissue engineering applications because they can easily transfer the cells or delivered the biomolecules to the damaged tissue. Lack of severe toxicity, minimal injury and pain during surgery could be the other advantages of the injectable hydrogels. A wide variety of chemical methods have been used to crosslink the injectable hydrogels such as click chemistry, Michael addition, Schiff-base, enzymatic reaction and, etc. Some hydrogels can also be cross-linked using physical interactions such as ionic interactions, hydrogen bonding, supramolecular interaction, etc., without external factors in the physiological conditions of the body. In this study, in addition to various methods of synthesis, the practical aspects of hydrogels in regenerative medicine and their achievements in tissue engineering are discussed.

Design and production of hybrid tire cords is a simple and cost-effective way to improve the physical and thermal properties of the tire. It also affects the fuel consumption of the vehicle.

In this study, to achieve new reinforcing materials with better performance using conventional fibers, a hybrid tire cord has been manufactured by twisting nylon 6.6 and polyester yarns together. The effects of twist level and core ratio were studied on the thermomechanical properties of the hybrid cord. The produced cords have different twist levels of 300, 350 and 400 tpm and core ratios of 1.00, 1.03, and 1.05. The mechanical properties of these cords, including strength and creep, have been studied. The heat shrinkage and shrinkage force were also measured and compared with reference samples, nylon and polyester yarns and cords. The dynamic mechanical thermal analysis (DMTA) was used to examine the shrinkage force and creep of the tire cords.

The results show that the yield strain and shrinkage of all hybrid cords were lower than those of the nylon cord and more than those of the polyester cord. The increase in the twist level leads to a decrease in the load at specific elongation (LASE), and also an increase in the creep due to the helix angle between the cord axis and filament axis. In addition, the LASE, work to rupture and creep increase, as the core ratio increases. Furthermore, a rise in twist level and core ratio leads to an increase in shrinkage and shrinkage force. The hybrid tire cord with a core ratio of 1.05 due to its dimensional stability and good mechanical properties can be used to design high-performance tires.

One method to improve the electrical conductivity of nanocomposites is the use of immiscible blends containing conductive fillers based on the concept of double percolation. In this research, the electrical and rheological properties of high density polyethylene/polyamide 6 (HDPE/ PA6) blend in presence of multi-wall carbon nanotubes (MWCNTs) were investigated.

Samples based on HDPE/PA6 blend with maleic anhydride-grafted high density polyethylene (HDPE-g-MA) as a compatibilizer and also containing 1, 3 and 5% (by wt) MWCNTs were prepared by melt mixing process in an internal mixer. Then different analyses were performed to investigate the morphology, rheology and electrical properties of samples with different weight percentages of MWCNT and the results were studied.

Scanning electron microscopy (SEM) images of an unfilled blend showed co-continuous morphology and the presence of MWCNTs in the blend also resulted in co-continuous morphology1 and compatibility of the blend with reduced interfacial tension. The rheological properties were characterized using melt rheometric mechanical spectroscopy (RMS). The results showed that with increasing MWCNT content, the storage modulus and complex viscosity of the nanocomposites increased compared to the neat blend and the storage modulus eventually reached a low-frequency plateau region, indicating a rheological percolation threshold of nanocomposite. Storage modulus and loss factor of the blend samples were evaluated using dynamic mechanical analysis (DMA). With increasing MWCNT content, the maximum loss factor of PA6 phase in the nanocomposites decreased with respect to similar phase in the unfilled blend, whereas the maximum loss factor of HDPE phase remained almost constant, indicating a higher presence of MWCNTs in PA6 phase. Also the temperature of the maximum loss factor of the PA6 phase shifted to higher temperatures. The electrical conductivity results according to the four-point probe method showed that the electrical conductivity of the nanocomposite increased significantly by adding 5%  (by wt) MWCNTs.

suspension polymerization of styrene in the presence of graphite was carried out. The polymerization reaction kinetics was investigated to gain better insight into manipulating process parameters. The particle size distribution and thermal conductivity of the foams were studied by considering different parameters.

Product characterization and the reaction thermal kinetics were evaluated using differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), particle size distribution and thermal conductivity measurements. The effect of graphite and initiator concentration on the reaction kinetics was investigated.

The results showed that the graphite profoundly reduced the rate of reaction and consequently caused instability in the suspension. By manipulating the process variables such as increasing the amount of stabilizers (1 to 2%) and initiator (up to 0.6% by wt), their frequency and injection time, the polymerization of styrene in the presence of graphite was done. The beads were spherical and the superfine (less than 420 μm) proportion of the product was less than 5%. Through the pre-expansion process, the beads were expanded and the cell structure was uniform. The pentane content of the beads was sufficient (~7% by wt) to successfully sinter the pre-expanded beads in the final molding process. Final foams had 0, 1 and 1.5% graphite. By increasing the graphite content, the thermal conductivity of the foams was decreased. Graphite-containing foams were better thermal insulators than conventional expandable polystyrene. Therefore, for a specific thermal duty, a smaller amount of graphite-containing expandable polystyrene rather than conventional polystyrene is required and consequently, the total cost of the insulation is reduced.

Introducing the porosity into the conductive polymer composite (CPC) sensitive layer improves the performance parameters of the prepared gas detectors.

In this research, porous poly(vinyl alcohol)/carbon nanotube (CNT) composite was used as the sensitive layer for detecting methanol, ethanol, and water (as lung cancer biomarkers). Vapor-induced phase separation method was used for introducing the porosity into the polymer matrix. The solution consisted of 2% (by wt) polymer in water and 4% (by wt) CNT. The film was exposed to the acetone vapor for introducing the porosity. The morphology of the prepared porous composite was investigated by SEM and BET tests. The responses of prepared sensitive layers toward the target analytes were analyzed by a home-made apparatus.     

The SEM images indicated the porous structure of the composite with nodular structures. Also, the BET test indicated the remarkable increase in the specific surface area of the porous composite in comparison with the dense one. The results showed that the specific surface area was increased to10.93 m2/g for porous composite. The final results illustrated the remarkable improvement in performance parameters such as response time and sensitivity in porous composites. The lower level of detection (LLD) of dense and porous composites toward water vapor was equal to 1000 and 50 ppm, respectively. Such enhancement was related to the increasing the specific surface area of the composite, and consequently, increasing the accessibility of analyte molecules to the sensitive sites of CPCs. Also, the response of the prepared sensitive layer was investigated based on the thermodynamic. The final investigations indicated that δa correctly explained the sensitivity of prepared CPCs.

Polyamide 6 (PA6)/nitrile butadiene rubber (NBR) thermoplastic elastomer reinforced by nanoparticles has several applications in various industries. The addition of nanoparticles to thermoplastic elastomers will affect the tensile strength, impact strength, fracture mechanism and thermal properties of nanocomposites. There are different processes to fabricate these nanocomposites such as extruder, internal mixer, and friction stir process.

PA6/NBR/clay nanocomposites were fabricated by internal mixer (IM) and friction stir process (FSP). The mechanical properties and fracture mechanisms of these nanocomposites were investigated by mechanical testing (tensile, impact, and hardness) and essential work of fracture (EWF) methodology. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the morphology of samples.

The results indicated that with addition of nanoclay up to 5% in an elastomer containing internal mixer, the tensile strength increased, and beyond 5%, the tensile strength decreased. The friction stir process sample with 7% nanoclay showed a maximum tensile strength of 35.4 MPa. In the friction stir process sample with 7% nanoclay, the tensile modulus and total work of fracture, respectively, increased by 75% and 56%, while in the internal mixer sample, the modulus increased by 50% and total work of fracture decreased by 5%. With the addition of 7% nanoclay to PA6/NBR blend, the impact strength of friction stir process and internal mixer samples decreased by 4 and 18%, respectively. The addition of 7% nanoclay to PA6/NBR blend with friction stir process improved the thermal behavior as the crystallization temperature and melting temperature increased from 195.3 to 197.1°C and 221.3 to 222.5°C, respectively.