Role of salt on adhesion of an epoxy/aluminum (oxide) interface in aqueous environments

Joints held by polymeric adhesives are commonplace in many engineered products, but normal service can require exposure to environmental conditions that present a significant challenge for maintaining the structural integrity of the interface. In particular, aqueous environments can wreak havoc on the joint strength. Here, a mechanistic approach is used to understand the difference in the debonding behavior of an epoxy/aluminum (oxide) interface when exposed to deionized (DI) water and aqueous sodium chloride by correlating macroscopic failure with the sorption of salt and water into the adhesive and its nanoscale distribution. For the epoxy‐aluminum system examined here, the presence of sodium chloride increases the resistance to crack growth in comparison to DI water. The debonding appears to be controlled by water near the buried interface. Salt water decreases the solubility of water in the epoxy and decreases the concentration of water near the buried interface, but the concentration of salt that enters the epoxy is below the detection limit. Thus, even if ions cannot penetrate or sorb into the adhesive, the presence of salt can significantly alter the water distribution within the adhesive and ultimately the strength of the joint. POLYM. ENG. SCI., 56:18–26, 2016. © 2015 Society of Plastics Engineers     

Microstructure and physicomechanical properties of pressureless sintered multiwalled carbon nanotube/alumina nanocomposites

Multiwalled carbon nanotube (MWCNT)/alumina (Al₂O₃) nanocomposites containing CNT from 0.15 vol.% to 2.4 vol.% have been successfully fabricated by simple wet mixing of as-received commercial precursors followed by pressureless sintering. Extent of densification of nanocomposites sintered at low temperature (e.g. 1500 °C) was <90%, but increased up to ∼99% when sintered at 1700 °C and offered superior performance compared to pure Al₂O₃. Nanocomposites containing 0.3 vol.% MWCNT and sintered at 1700 °C for 2 h in Argon led to ∼23% and ∼34% improvement in hardness and fracture toughness, respectively, than monolithic Al₂O₃. In addition, the highest improvement (∼20%) in bending strength was obtained for 0.15 vol.% MWCNT/Al₂O₃ nanocomposite compared to pure Al₂O₃. Weibull analysis indicated reliability of nanocomposites increased up to 0.3 vol.% MWCNT, whereas, beyond that loading consistency was the same as obtained for pure Al₂O₃. Detailed microstructure and fractographic analysis were performed to assess structure-property relationship of present nanocomposites.     

Factors Impacting the Formation of 3-MCPD Esters and Glycidyl Esters During Deep Fat Frying of Chicken Breast Meat

The effect of the frying temperature, frying duration and the addition of NaCl on the formation of 3‐monochloropropane‐1,2‐diol (3‐MCPD) esters and glycidyl esters (GE) in palm olein after deep frying was examined in this study. The eight frying systems were deep‐fat frying (at 160 and 180 °C) of chicken breast meat (CBM) (with 0, 1, 3 and 5% sodium chloride, NaCl) for 100 min/day for five consecutive days. All oil samples collected after each day were analyzed for 3‐MCPD ester, GE, and free fatty acid (FFA) contents, specific extinctions at 232 and 268 nm (K₂₃₂ and K₂₆₈), p‐anisidine value (pA), and fatty acid composition. There was a significant (p < 0.05) decrease in the 3‐MCPD esters and a significant (p < 0.05) decrease in the GE with the increasing of the frying duration. There were significant (p < 0.05) increases in the 3‐MCPD esters formed when the concentration of NaCl increased from 0 to 5%. The addition of NaCl to the CBM during deep frying had no significant effect on the GE generation. The FFA contents, K₂₃₂ and K₂₆₈ and pA showed that all the frying oils were within the safety limit.     

Induced doping by sodium ion in poly(m-aminophenol) through the functional groups

Poly(m-aminophenol) (PmAP) was synthesized by the oxidative polymerization of m-aminophenol in sodium hydroxide medium using ammonium persulfate oxidant at room temperature. The synthesized polymer showed very good solution processability as it was well soluble in aqueous sodium hydroxide, dimethylsulfoxide (DMSO), dymethylformamide (DMF), etc. A free-standing film was cast from thermal evaporation of DMSO solution of the synthesized PmAP. The film was then doped with aqueous sodium hydroxide and methanol mixture by solution doping technique at room temperature. The doping conditions were standardized in terms of the DC-conductivity of the doped film. The doped PmAP was characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Electron dispersion spectroscopy, X-ray diffraction spectroscopy, elemental analysis by atomic absorption spectroscopy, thermogravimetric analysis and DC-electrical conductivity. The DC-electrical conductivity of PmAP film was increased to 2.34 × 10^?5 S/cm from <10^?12 S/cm due to sodium ion doping. From all the above characterizations it was confirmed that the sodium ions were not the reason for the conduction. The incorporated sodium cation in the polymer through free –OH groups of the polymer chain was induced the electron cloud of the polymer and so the polymer became conducting.     

Effect of Ag addition on the corrosion properties of Sn‐based solder alloys

Corrosion properties of three different Sn‐Ag lead free solder alloys have been investigated in 0.3 wt% Na₂SO₄ solution as corrosive environment. As cast solder alloy was analyzed by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Volume fractions of the Ag₃Sn in the solders were determined by image analysis technique. Pitting potential and corrosion potential for the alloys were determined by potentiodynamic tests. Electrochemical impedance spectroscopy (EIS) was carried out to measure the film and charge transfer resistance. Alloys with lower Ag content have been found as better corrosion resistance material.     

Effect of coefficient of thermal expansion on positive temperature coefficient of resistivity behavior of HDPE–Cu composites

Positive temperature coefficient of resistivity (PTCR) characteristics of (high density polyethylene) HDPE–Cu composites has been investigated with reference to the conventional HDPE–CB (carbon black) composites. Plot of resistivity against temperature of HDPE–CB composites showed a sudden rise in resistivity (PTC trip) at 127°C, close to the melting temperature of HDPE. However, the PTC trip temperature (98°C) for HDPE–Cu composites was appeared well below the melting temperature of HDPE. Addition of 1 phr nanoclay in the composites resulted in an increase in PTC trip temperature of HDPE–Cu composites, whereas no significant effect of nanoclay on PTC trip temperature was evident in case of HDPE–CB–clay composites. We proposed that the PTC trip temperature in HDPE–Cu composites was governed by the difference in coefficient of thermal expansion (CTE) of HDPE and Cu. The room temperature resistivity and PTC trip temperature of HDPE–Cu composites were very much stable upon thermal cycling. DMA results showed higher storage modulus of HDPE–Cu composites than the HDPE–CB composites. Thermal stability of HDPE–Cu composites was also improved compared to that of HDPE–CB composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Atomistic simulation of stacking faults in (001), (010), and (100) planes of cementite

Molecular-dynamics method was used to study γ surfaces for the (001), (010), and (100) planes of cementite. Displacement vectors corresponding to stable stacking faults have been determined. The energy of these stacking faults has been calculated by the molecular-dynamics and ab initio methods. The energy of unstable stacking faults, which characterizes the tendency of a material to plastic relaxation, has been estimated. The reactions of the splitting of perfect dislocations have been suggested; the possibility of the propagation of stacking faults in the planes under consideration is discussed.     

Acrylonitrile‐butadiene‐styrene nanocomposites filled with nanosized alumina

A polymer nanocomposite was produced by acrylonitrile‐butadiene‐styrene (ABS) and α‐alumina was prepared through sol‐gel process using aluminum nitrate and citric acid. The particle size was analyzed by X‐ray diffraction and scanning electron microscopy (SEM) studies. The nanocomposites were characterized through tensile strength, Young's modulus, strain% at break, flexural strength, flexural modulus, and impact strength. The ABS/Al₂O₃ nanocomposites are found to have slightly higher Young's modulus, but lower tensile strength, strain% at break, flexural and impact strength than the virgin ABS. But its flexural modulus increases with increasing Al₂O₃ content in ABS matrix. The d‐spacing was calculated in nanocomposites to evaluate the interaction between Al₂O₃ and ABS. The particle distributions in nanocomposites were studied by SEM. The fractured surfaces of tensile test samples were also examined through SEM and show that the ductile fracture of ABS is converted to brittle fracture with addition of Al₂O₃. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Stress relaxation behavior of glass fiber‐reinforced polyester composites prepared by the newly proposed rubber pressure molding

Stress‐relaxation behavior of glass fiber‐reinforced polyester composites, prepared by a recently developed manufacturing method called rubber pressure molding (RPM), is investigated with special reference to the effect of environmental temperature (−70°C to +100°C), fiber volume fraction (30–60%), and initial load level (1–5 kN). It is found that the stress‐relaxation rate decreases with an increase in the applied load of composites and a decrease in temperature. Below glass transition temperature, the rate of stress relaxation increases with an increase in volume fraction of fibers in the composites, whereas above glass transition temperature, it increases with a decrease in the volume fraction of fibers. The experimental results for a given composites are summarized by four values, the slopes of the two straight lines (two separate relaxation processes), and their intercepts upon the stress axis. Both the slopes are dependent upon the applied load, temperature, and volume fraction of fibers in the composites. Relaxation times in both primary and secondary are calculated over the wide range of temperatures, loads, and volume fraction of fibers in the composites. It depends strongly on the temperature, but does not depend strongly on the applied load and volume fraction of fibers. The performances of the composites are also evaluated through conventional compression‐molding process. The rate of stress relaxation is small when the composites are made of newly proposed RPM technique when compared with the conventional process. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers