Key Engineering Materials Vol. 824

Abstract: The main drawback of low-density polyethylene (LDPE) film for packaging of fresh fruit or vegetables is low moisture breathability. This study developed breathable films by blending LDPE with thermoplastic polyester elastomer (TPEE). LDPE and TPEE in the weight ratios of 95/5, 90/10, 80/20, 70/30, and 60/40 wt% were melt blended and then extruded into films using a cast film extruder. Clarity of films was characterized by UV-VIS spectroscopy. Tensile properties, tear resistance, the degree of crystallinity, and morphology of blend films were evaluated. Water vapour transmission rate (WVTR) was investigated using a desiccant method. The prepared films were transparent. However, the UV-VIS transmittance was reduced slightly. Blending TPEE of more than 10 wt% reduced the modulus but increased elongation at break. It did not impact on the tensile strength of the blends. Since LDPE and TPEE are immiscible, applied stress during extrusion pulled them apart at the interphase boundaries creating micro-pores. As a result, these micro-pores reduce tear resistance significantly but increase WVTR of the blend films. Using a blend ratio of 90/10 wt%, the effect of chill-roll temperature and nip-roll velocity on film properties were studied. It was found that nip-roll velocity had more influence on WVTR than chill-roll temperature due to elongation of the pores.

Abstract: This research is focused on the synthesis and the ability to inhibit scale and corrosion of poly(acrylic acid-co-acrylamide) (PAA-AM copolymers). A series of polymers were synthesized by free radical polymerization having various weight ratios of acrylic acid (AA) to acrylamide (AM). The structures of the synthesized polymers were characterized by UV-Vis Spectroscopy, FT-IR, and ¹H-NMR. The thermal stability of the polymers was analyzed by a TGA technique. The water solubility of the polymers was examined using a turbidity meter. The scale inhibition performance test was performed by titration of calcium ion with ethylene diamine tetraacetic acid (EDTA) solution. After that, the crystal structure of CaCO₃ scale from the scale inhibition test was examined using a scanning electron microscope. The efficiency of the corrosion inhibitor on low carbon steel AISI 1018 was investigated by a potentiodynamic polarization technique. The result show that PAA-AM copolymers having a 9:1 weight ratio with 45.82% at 100 ppm inhibited scale forming. The corrosion resistance of all inhibitors could be achieved when the concentration of the inhibitor was lower than 100 ppm.

Abstract: Silver nanoparticles (AgNPs) have been intensively researched because of their wide range of applications in the areas of catalysis, optics, antimicrobials and biomaterials production. The pH of the reaction mixture is one of the crucial parameters for improving the properties of AgNP, including size, morphology and agglomeration. In this study, AgNPs were synthesized by a biological method using rambutan peel extract. The effect of pH on the resultant biogenic AgNPs was observed by varying the pH values to be 2, 4, 6, 8, 10 and 12. The biosynthesized AgNPs was characterized by UV-Vis spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX) and Zeta potential analysis. The results showed the formation of AgNPs with size ranging from 15-120 nm in diameter. Phytochemical compounds in the extract are likely responsible for the reduction and stabilization of AgNPs. The shape, size and stability of AgNPs depend on the pH of the solution. AgNPs prepared at pH 2, 4 and 6 were of various shapes with a large size distribution. Those synthesized in basic solution (pH 8, 10 and 12) were spherical in shape. The results indicate that pH 8 is optimal for synthesis of AgNP as it offers pureness and fineness with narrow size distribution. Furthermore, biosynthesized AgNP exhibits antibacterial activity against the growth of selected human pathogens.

Abstract: Silica aerogel is a nanostructured porous solid material. It has a low bulk density, low thermal conductivity and can be hydrophobic. In this work, hydrophobic silica gel, a material used to form aerogel, is used instead of its powder form to avoid ultrafine air particles pollution. It is used to surface modified materials to make the materials superhydrophobic and still withstand physical abrasion that ordinary aerogel would not able to do. The superhydrophobic silica aerogel coating was designed by mixing the hydrophobic gel with DOW CORNING^® 2405 resin as binder and varying DOWSIL^™ Z-6137 silane and tetraethyl orthosilicate (TEOS). The coating is characterized by the static contact angles (CA) and abrasion test. Scanning electron micrographs of different coating compositions were investigated. Results show that the hydrophobic gel mixed with resin and Z-6137 silane have contact angle >179º. Superhydrophobic silica aerogel coating can be utilized as material coatings for glass, fiber, polymer, etc.

Abstract: In this report, synthesis and characterization of gold nanoparticles (AuNPs) from gold leaf by electrolysis in two different media (gel and paper) in presence of sodium chloride (NaCl), glucose (C₆H₁₂O₆) and polyvinyl pyrrolidone (PVP) at room temperature were investigated. Graphite was used as two electrodes, NaCl was used as an electrolyte, C₆H₁₂O₆ was used as reducing agent and PVP was used as stabilizer to control the aggregation of the nanoparticles. UV-Visible spectroscopy (UV-Vis) and scanning electron microscopy (SEM) were used to confirm the characteristics and morphologies of the synthesized AuNPs.

Abstract: Tin-doped indium oxide or indium tin oxide (ITO) has many promising uses in applications, such as, transparent conductive oxides, flat panel displays, and energy-saving windows. In this work, nanorice particles of tin-doped indium oxide (ITO) were obtained by a simple sol-gel method. Indium salts and stannous fluoride precursors were mixed ultrasonically in an aqueous medium. The crystallinity and chemical bonds were studied by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). FTIR spectra before calcination showed the characteristic bonds of In–OH and Sn–OH at 1160 cm^-1 and 1380 cm^-1, respectively. After calcination at 400^°C for 2 h, these characteristic bonds disappeared, confirming the formation of crystalline oxide. Moreover, scanning electron micrographs revealed well-defined structure, called nanorice, emerging from controlled crystal growth at 85^°C for 90 min. The particle size of ITO was approximately 500 nm in length and diameter of 150 nm. The effect of crystallinity was studied by UV absorbance and NIR reflectance. These demonstrated promising results for use as energy-saving windows.

Abstract: Polyacrylamide/polypyrrole (PAM/PPy) hydrogel was developed for the application in controlled drug delivery. PAM/PPy hydrogel was synthesized via free-radical polymerization of acrylamide using ammonium persulfate (APS) as initiator in the dispersion of PPy nanoparticle. N,N’-methylenebisacrylamide (MBA) and N,N,N’,N’-tetra-methylenediamine (TEMED) were utilized as cross-linker and accelerator, respectively. Salicylic acid (SA) was selected as a model drug in this work. The effect of PPy contents on SA-loading and releasing performances was investigated. The more PPy content was incorporated, the greater SA-loading and releasing were found. This is attributed to the increasing pore size of the PAM hydrogel when PPy nanoparticles were incorporated. Drug releasing performance from the SA-loaded PAM/PPy hydrogel were controllable under the applied potential of 1.0 volt. The research exhibits the potential of using conductive polymer hydrogel to control the drug release rate at an optimal desired level.

Abstract: 17α-methyltestosterone (MT) is a synthetic androgen. It is used widely for inducing an all-male population of Nile tilapia (Oreochromis niloticus). In this work, the detection of MT was conducted using screen-printed carbon electrodes (SPCE). These were a bare electrode, a bismuth modified electrode (Bi-SPCE) and an antimony modified electrode (Sb-SPCE). The successful electrode modification was confirmed by scanning electron microscopy. The electroanalytical performance of the SPCE modified electrodes for MT detection was examined by cyclic voltammetry. The highest active surface area of 1.073x10^-4 cm² was obtained on Sb-SPCE. This indicates that Sb-SPCE can enhance the sensitivity of MT detection better than the bare-SPCE and the Bi-SPCE. The Sb-SPCE showed a linear response for MT concentrations ranging from 2 to 8 mg.L^-1. The sensitivity obtained from the slope of a calibration curve was -0.452 mA.mol^-1.L^-1 in a Britton-Robinson buffer pH 4.0 containing Sb 16 mg.L^-1 with deposition potential and deposition time of 1 V and 90 seconds, respectively. A linear relationship between the square root of the scan rate and the peak current revealed that mass transfer of MT to the electrode was driven by a diffusion mechanism. The limit of detection was found to be 1 mg.L^-1.

Abstract: Sodium chloride, commonly known as table salt, is widely used as essential seasoning in food, snacks and deserts worldwide. However, excessive consumption of table salt is a major cause of various health issues, involving high blood pressure, liver cirrhosis, kidney disease, and heart failure. This research aims at creating a portable, low-powered, efficient sensor for detection of sodium ions in body plasma for medical diagnosis purpose. The device was fabricated on a platform of Ion-Sensitive Field-Effect Transistor (ISFET) modified with sodium ionophore (sodium recognizing element), entrapped in polyurethane thin film. Our preliminary studies show that sodium ionophore-modified ISFET sensor yields good sensing performances, having a maximum sensitivity of 43 mV/pNa, and a detection limit of 2.3 millimol/liter.

Abstract: This work presents an enhancement of the voltammetric signal on an electrochemical paper-based analytical device (ePAD) using a graphene oxide (GO) modified carbon electrode. The ePAD is fabricated using a screen printing technique for fabrication of the hydrophobic area and three electrode strips. The graphene film was directly prepared on ePAD by dropping 2 µL of GO dispersed in water onto the working electrode surface and leaving it to dry at room temperature. The electrochemical reduction process of GO was carried out by applying a constant voltage of -1.20 V (vs. Ag/AgCl electrode strip) in 0.1 M KCl for 800 s. The GO-modified carbon working electrode on ePAD was readily obtained and ready to use after removing KCl solution. We tested the enhancement of the voltammetric signal on ePAD with a 6 mM [Fe(CN)₆]^4–/3– redox couple in 0.1 M KCl supporting electrolyte solution. Our results obtained from cyclic voltammograms showed that the unmodified working electrode and the GO-modified working electrode on ePAD provided similar anodic and cathodic peaks. Due to accelerated electron transfer process, it was found that the GO-modified working electrode on ePAD provided approximately a 2-fold increase in voltammetric signals when compared to the unmodified working electrode on ePAD. The reproducibility (inter-day precision) of the voltammetric signal measurement using a GO-modified working electrode on ePAD was acceptable. The relative standard deviation (RSD) was 5-8%. Therefore, the GO-modified carbon working electrode on ePAD offers an effective approach to enhance the signal and sensitivity for chemical analysis.