Effect of nano-sized calcium carbonate on cure kinetics and properties of polyester/epoxy blend powder coatings

Today's strict environmental laws pose significant challenges for coating's formulators to look for eco-friendly products. Powder coatings, particularly polyester/epoxy blends have demonstrated their ability as alternatives to traditional solvent-borne coatings. Recently, the use of nanoparticles such as nano-CaCO₃ (nCaCO₃) has been suggested as a beneficial strategy towards powder coating application with improved properties. Here, we study the effect of nCaCO₃ on morphology, cure behavior, adhesion and hardness of polyester/epoxy systems. The nanoparticles shape, size and dispersion state were investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) methods. Furthermore, isothermal cure characterization of the neat and filled systems was performed using a torque rheometer. The most important finding based on the rheological studies was the catalytic effect of nCaCO₃ on cure reaction of polyester/epoxy, leading to the shorter curing time. Moreover, the kinetic analyses of rheograms revealed a marked decrease in the activation energy of the cure process upon raising nCaCO₃ content. Interestingly, pull-off adhesion and hardness tests showed that the hardness and adhesion strength were dramatically increased by the addition of nCaCO₃ into the polyester/epoxy system compared to pure blend resin. Therefore, considering the strong competition in powder coating market, the use of nCaCO₃ as a commercial and inexpensive nanofiller is necessary not only to reduce the dwell time which has benefits in terms of the energy consumption and economics, but also to improve the performance of final polyester/epoxy coating.     

Numerical optimization of hole making in GFRP composite using abrasive water jet machining process

Machining of composite materials for the production of bolt holes is essential in the assembly of the structural frames in many industrial applications of glass fiber-reinforced plastic (GFRP). Abrasive water jet cutting technology has been used in industry for such purposes. This technology has procured many overlapping applications and as the life of the joint in the assembled structure can be critically affected by the quality of the holes, so it is important for the industry to understand the application of the abrasive water jet cutting process on GFRP composite materials. The aim of the present work is to assess the influence of abrasive water jet machining parameters on the hole making process of woven-laminated GFRP material and to find the optimum values of the process parameters. Statistical approach was used to understand the effects of the predicted variables on the response variables. Analysis of variance was performed to isolate the effects of the parameters affecting the hole making in abrasive water jet cutting. The results show that the optimum values of cutting feed, fiber density, water jet pressure, standoff distance, and abrasive flow rate upon the response variables are 0.3 m/min, 0.82 g/cm³, 150 MPa, 2 mm, and 100 g/min, respectively.     

Separating stress and time dependent effects in the temperature dependent creep of polyethylene nanocomposites

The nonlinear time dependent creep of linear‐low density polyethylene (LLDPE) reinforced with montmorillonite layered silicate was investigated. A previous study related the time/stress dependence of creep compliance of the material at room temperature using the Burger and Kohlrausch‐Williams‐Watts models. Using both the creep and recovery compliance curves, we employ the Schapery formulation to study the relationship between deformation, time, stress, and temperature of LLDPE nanocomposites. Smooth mastercurves are constructed using time–temperature–stress superposition principles. The stress and temperature‐related creep constants and shift factors were determined for the material using the Schapery nonlinear viscoelastic equation. The prediction results confirm the enhanced creep resistance of nanofillers even at extended time scales and low temperatures. POLYM. ENG. SCI., 50:1646–1657, 2010. © 2010 Society of Plastics Engineers     

Introducing a novel integrated NGL recovery process configuration (with a self-refrigeration system (open–closed cycle)) with minimum energy requirement

In this study a novel process configuration for recovery of hydrocarbon liquids from natural gas is proposed. The required refrigeration in this configuration is obtained by a self-refrigeration system (open–closed cycle). High performance of the multi-stream heat exchangers, high recovery levels of the hydrocarbon liquids and low required compression power (in the internal refrigeration section) are three of most important characteristic of the proposed configuration. The effects of the mixed self-refrigerant flow rate and pressure on the performance of the process are discussed. Various values for feed composition are tested and the results show that the process can work efficiently with different feeds. In order to analyze the need of external refrigeration by a close or open cycle that is related to the composition of the inlet gas, a configuration with external refrigeration is designed the manner that it is similar with the purposed configuration in the separation section.     

Fabrication of self-ordered nanoporous alumina with 500–750 nm interpore distances using hard anodization in phosphoric/oxalic acid mixtures

A hard anodization (HA) technique is employed using different mixtures of phosphoric/oxalic acid for fast fabrication of alumina nanopore arrays in voltages higher than 200 V. The mixtures enable to avoid the breakdown of porous anodic alumina (PAA) in the high voltages. It is revealed for the first time that continuously tunable pore intervals (D_int) from 500 to 750 nm can be controlled by varying the concentrations of oxalic acid at anodization voltages (U_anod) from 230 to 360 V, far beyond the U_anod in the single electrolyte of phosphoric acid or oxalic acid. The ratios of interpore distance, pore diameter and barrier layer thickness to anodization voltage are in the range of conventional HA process for each acid mixture. In this approach, the PAA film growth rate is 26 µm/h, being 7 times larger than that in typical mild anodization.     

Investigation of the Binding Behavior between the S-heterocyclic Aromatic Palladium(II) Complex and Human Serum Albumin: Spectroscopic Approach

The interaction of 1, 10-phenanthroline octhyldithiocarbamato palladium(II) nitrate ([Pd(Oct-dtc)(phen)]NO₃) with human serum albumin (HSA) has been investigated by various spectroscopic techniques under physiological conditions. Here, HSA was titrated with the Pd(II) complex, followed by UV–Vis absorption spectroscopy to estimate a binding constant (K_b) and other thermodynamic parameters. The results indicate that the Pd (II) complex has a high affinity for bind HSA. Thermodynamic analysis showed that the enthalpy (ΔH°) and entropy changes (ΔS°) are positive and Gibbs free energy change (ΔG°) is negative which indicated that hydrophobic interactions played the predominant role in the binding process. Fluorescence spectroscopy were used to show the mechanism and binding parameters of this interaction. Utilizing the Stern–Volmer equation, the Pd(II) complex quenched the intrinsic fluorescence of HSA via a static quenching procedure. The specific binding distances between the tryptophan (donor) proteins and Pd(II) complex (acceptor) were estimated by Forster resonance energy transfer. The CD results also showed the conformational changes on serum albumin upon binding with the Pd(II) complex.     

Investigation of Dissipation,Adsorption, Degradation,and Leaching of Triazophos Pesticide in Various Soils

This study concerns the investigation of dissipation, adsorption, and degradation of triazophos in different soils from Pakistan. These processes help in the disappearance of pesticide from the environment. Gas chromatography was used for dissipation and adsorption analysis while for degradation study mass spectrometer was used in addition of gas chromatography (GC-MS). The dissipation rate of triazophos in three different soils was 90% over 30 days with average half-life of 9.059 days. From dissipation study it was inferred that rate is variable in each soil due to climatic changes, soil nature and soil-pesticide interactions. Adsorption experiment has revealed that the adsorption of this pesticide to soil follows the pseudo first order kinetic model with rate constant value of 0.479/h and Freundlich isotherm with adsorption capacity of 1.832 mol/g. Degradation study has displayed two major metabolites, one is phosphorothioic acid, S-[2-[(1-cyano-1-methylethyl) amino]-2-oxoethyl] O,O-diethyl ester at retention time of 9.136 and the other is sulfotep at 14.304 min. The leaching potential of triazophos was also calculated from its half-life and organic carbon content present in soil which was 1.688 representing it as non leacher pesticide.