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Meysam Ranjbar,Reza Miresmaeili,Mohammad Reza Naimi‑Jamal,Majid Mirzaei 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10
This study investigated the influence of microstructure on the mechanical properties and fracture toughness of API X65pipeline steel in the presence of hydrogen. In this study, electrochemical method was used for hydrogen charging and indentationtechnique was applied to obtain the fracture toughness. The results showed that in the presence of hydrogen, elongation(EL%), reduction of area (RA), ductile fracture percentage, and fracture toughness of all microstructures decreased. Themicrostructure of martensite (M) + bainite (B) + ferrite (F), had the highest hydrogen trapping and uptake (Capp) as 8.58 × 10–6 mol cm−3 and the lowest apparent hydrogen diffusivity (Dapp) as 5.68 × 10−10 m2 s−1; thus, the maximum decrements of33% in fracture toughness, 40% in ductile fracture percentage, 47% in RA, and 35% in EL% were observed. However, themicrostructure of ferrite (F) + degenerated perlite (DP) + martensite-austenite micro constituent (M/A), where the lowestvalue of 5.85 × 10–6 mol cm−3 for Cappand the highest value of 8.5 × 10–10 m2 s−1 for Dapphad the minimum decrements as2% in fracture toughness, 10% in ductile fracture percentage, 4% in RA, and 7% in El%. According to the obtained results,depending on the type of microstructures, hydrogen-induced work softening or hardening were observed by decreasing orincreasing the yield stress respectively.
Marziyeh Ranjbar-Mohammadi,Vida Sa’di,Meysam Moezzi,Reza Saghafi 한국섬유공학회 2022 Fibers and polymers Vol.23 No.6
Antibacterial suture yarns containing antibiotic drugs can play an important role in preventing the infection andholding tissues together to achieve wound closure. In this research, the possibility of production drug loaded nano yarns froma mixture of chitosan/polyvinyl alcohol (PVA/CS) (70:30) and poly(lactic acid) (PLA) was assessed by combiningdual‐electrospinning technique with aligned fibers collection. For this, CS/PVA solution was injected from one syringe andPLA from another one. The effect of weight ratio of PLA-PVA/CS (100:0, 80:20 and 60:40), collector speed (500, 800,1100 rpm) and voltage (10, 15 and 20 kV) on the diameter and morphology of fabricated nanofibers was assessed. Fabricatednanofibers with the length of 70 cm were twisted for manufacturing suture yarns. The results showed that fabrication ofstructure with the finest diameter was possible with the weight ratio of PLA-PVA/CS (60:40), the applied voltage of 15 kV,spinning distance of 17 cm and the rotational speed of about 1100 rpm. The diameter of produced nanofibers in this conditionwas about 290±42 nm. Then, tetracycline hydrochloride (T) loaded PLA-PVA/CS nanofibers (PLA/T-PVA/CS) wereproduced with optimum condition and the drug (5 wt. %) was loaded in PLA solution. FTIR analysis of drug loaded yarnexhibited the most important functional groups of chitosan, PVA, tetracycline hydrochloride and PLA in PLA-PVA/CSstructure. Contact angle data for PLA-PVA/CS and PLA/T-PVA/CS was about 89±3 ° and 30±2 °, respectively. The result ofthe antibacterial test indicated that the PLA/T-PVA/CS nanofibrous yarns were the most suitable sample with the prominentantibacterial activity against both gram-positive bacterium Staphylococcus aureus and gram-negative bacterium Escherichiacoli with inhibition zones of 17.5 and 20 mm, respectively. It seems that the fabricated nanofiber based yarns with suitablemorphological characteristics, hydrophilicity nature, and prevention of the surgical infections without affecting the cellviability can be an excellent structure for utilization as suture yarn.