Optical Spectroscopic Analysis of High Density Lead Borosilicate Glasses

Lead borosilicate glasses, of chemical composition 20SiO₂-xPbO-(15 + x)B₂O₃-5WO₂-10ZnO-(50-2x) Na₂O (where x = 5, 10, 15, 20, 25) were prepared using the normal melt-quenching technique. The samples were examined using a Philips Analytical X-ray diffraction system in order to check their amorphous nature. The effect of increasing B₂O₃ and PbO content on glass transition temperature was examined using Differential Thermal Analysis measurements (DTA). The results of DTA showed that both melting and glass transition temperatures decrease with increase of lead and boron oxides. Density and its related parameters have been determined to study the effect of lead-boron content on the structural properties of the prepared samples. Based on the density and DTA results, the network forming role of Pb and B ions was proved. The optical properties of the glass samples have been obtained using UV-VIS measurements. The optical parameters, such as optical band gap, Urbach energy, refractive index, and electronic polarizability were deduced based on the optical data. The observed increase in optical band gap and decrease in Urbach energy as well as the red shift in the absorption spectra arise due to the formation of non-bridging oxygen.     

Influence of nanoclay on urea–glyoxalated lignin–formaldehyde resins for wood adhesive

In this research, the influence of nanoclay on urea–glyoxalated lignin–formaldehyde (GLUF) resin properties has been investigated. To prepare the GLUF resin, glyoxalated soda baggase lignin (15 wt%) was added as an alternative for the second urea during the UF resin synthesis. The prepared GLUF resin was mixed with the 0.5%, 1%, and 1.5% nanoclay by mechanically stirring for 5 min at room temperature. The physicochemical properties of the prepared resins were measured according to standard methods. Then the resins were used in particleboard production and the physical and mechanical properties of the manufactured panels were determined. Finally, from the results obtained, the best prepared resin was selected and its properties were analyzed by differential scanning calorimetry (DSC), Fourier transform infrared spectrometry (FTIR), and X-ray diffractometry (XRD). Generally the results indicated that the addition of sodium-montmorillonite (NaMMT) up to 1.5% appears to improve the performance of GLUF resins in particleboards. The results also showed that nanoclays improved mechanical strength (modulus of elasticity (MOE), Modulus of Rupture (MOR), and internal bond (IB) strength) of the panels bonded with GLUF resins. The panels containing GLUF resin and nanoclay yielded lower formaldehyde emission as well as water absorption content than those made from the neat GLUF resins. XRD characterization indicated that NaMMT only intercalated when mixed with GLUF resin. Based on DSC results, the addition of NaMMT could accelerate the curing of GLUF resins. The enthalpy of the cure reaction (ΔH) of GLUF resin containing NaMMT was increased compared with neat GLUF resin. Also the results of FTIR analysis indicated that addition of NaMMT change the GLUF resins structures.     

<Emphasis Type="SmallCaps">l</Emphasis>-Aspartic acid incorporated optically active poly(amide-imide)s: synthesis and characterization

N-trimelliticimido-l-aspartic acid (1) was prepared from the reaction of trimellitic anhydride with l-aspartic acid in a mixture of glacial acetic acid and pyridine solution (3/2 ratio) under refluxing conditions. The solution polycondensation of the corresponding activated monomer with eight aromatic diamines were carried out in DMAc. The resulting poly(amide-imide)s were obtained in quantitative yields, showed admirable inherent viscosities (0.20–0.36 dl g⁻¹), good optical activity (+7.32o to +15.24o), and were readily soluble in polar aprotic solvents. They start to decompose (T _10%) above 170 °C and display glass-transition temperatures at 120–237 °C. All of the above polymers were fully characterized by UV, FT–IR, and ¹HNMR spectroscopy, elemental analysis, thermogravimetric analyses, DSC, inherent viscosity measurement, and specific rotation.     

AlBr3 impact on the thermal degradation of P(S-co-MMA): a study performed by contemporary techniques

Pyrolysis of copolymer, [P(S-co-MMA)], in the presence of AlBr₃ was inspected in an inert atmosphere. Five different proportions (copolymer/additive) were chosen. Films were cast from common solvent. It was noticed that copolymer showed more stability on the basis of T _0, however, regions of stability were also observed for the blends. Copolymer showed T ₀ at 260?°C, whereas blends started degrading around 70?°C. T _max was the same for the copolymer and the blends. Low-temperature decompositions of blends were attributed to the generation of free radicals (Br^?) and the zones of stabilizations were assigned to the formation of a ??complex type?? structure between Al and the carbonyl oxygens of MMA units. Degradation products were collected and identified employing Py-GC?CMS technique. Intermediates (solid) at different temperatures (300, 350 and 400?°C) were examined through FTIR spectroscopy. In the light of gathered data, a degradation mechanism was proposed. New products were encountered, viz., bromobenzene, ??brominated?? anhydride ring, etc., which established the chemical interactions between the constituents of the blends, i.e., copolymer and additive. Anhydride rings were absent when poly (methyl methacrylate) was pyrolyzed in the presence of AlBr₃. Oligomers of styrene were not found hinting at the involvement of additive in ??targeting?? the degrading styrene units. The blends indicate 2?C7% residue of original mass; the additive exhibits 9% while the copolymer does not leave residue at the completion of the TG run. The presence of char in the residues of blends suggests that the additive imparts stability to the copolymer. Horizontal burning rate was lowest (6 times less than that of neat copolymer) for [P(S-co-MMA):AlBr₃, 87.5:12.5%], thereby revealing the efficiency of the additive as thermal stabilizer. The highest activation energy was calculated for the copolymer (169.46?kJ/mol) and the range of this parameter for the blends was found from 52.72 to 27.14?kJ/mol.     

Effect of TiO2 nanoparticle on rheological behavior of poly(vinyl alcohol) solution

In recent years, addition of nanoparticles to fluids and polymers has been used as a way of modifying rheological properties. Poly(vinyl alcohol) (PVA) and titanium dioxide (TiO₂) nanoparticles aqueous composite nanofluids were prepared through the use of ultrasonic vibration. In fact, ultrasonic vibration is an advantageous method for nanoparticle dispersion. The preparation method prevents reduction of the polymer's molecular weight. TiO₂ nanoparticles with different concentrations were employed to investigate the rheological characteristics of composite nanofluids. Rheological characteristics of base fluids and composite nanofluids were measured at different temperatures. Based on the results, all composite nanofluids, as well as base fluids, exhibited non‐Newtonian behavior and rheological characteristics of composite nanofluids, following the Herschel‐Bulkley model. In addition, model parameters are functions of temperature, PVA, and TiO₂ nanoparticle concentrations. Also, two‐way interactions among temperature, PVA, and TiO₂ nanoparticle concentrations affect flow index and consistency index of the Herschel‐Bulkley model. J. VINYL ADDIT. TECHNOL., 23:234–240, 2017. © 2015 Society of Plastics Engineers     

Polyhydroxybutyrate/chitosan/bioglass nanocomposite as a novel electrospun scaffold: fabrication and characterization

Scaffolds and their features play a central role in tissue engineering; so this study is based on the production of a series of electrospun PHB/Chitosan/nBG nanocomposite scaffolds with 9 wt% polyhydroxybutyrate, 10, 15 and 20 wt% chitosan and 7.5, 10 and 15 wt% nanobioglass (nBG). Electrospinning process was performed with optimal conditions of spinning machine including voltage of 16 kV, syringe-collector spacing of 16 cm, and output rate of 1 µl per hour. The developed phases and the formation of chemical bonds between ceramic and polymer bands were studied through XRD and FTIR analyses. The FE-SEM and TEM analyses showed uniform morphology of nanofibers and dispersion of bioglass nanoparticles in the fiber structure. The presence of 10 wt% bioglass nanoparticles and 15 wt% chitosan increased the tensile strength of fibers to 3.42 MPa, which was about four times greater than strength of control sample (pure PHB). The developed fibers were kept 28 days in SBF solution and 60 days in PBS solution to assess their bioactivity and biodegradability. The results showed that the presence of bioglass nanoparticles leads to a dramatic increase in absorption of calcium and phosphorus ions and weight loss of scaffold. The developed scaffold can be used for bone and teeth tissue engineering applications.     

Rheological and mechanical properties of composites made from wood flour and recycled LDPE/HDPE blend

The effect of compounding method is studied with respect to the rheological behavior and mechanical properties of composites made of wood flour and a blend of two main components of plastics waste in municipal solid waste, low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The effects of recycling process on the rheological behavior of LDPE and HDPE blends were investigated. Initially, samples of virgin LDPE and HDPE were thermo-mechanically degraded twice under controlled conditions in an extruder. The recycled materials and wood flour were then compounded by two different mixing methods: simultaneous mixing of all components and pre-mixing, including the blending of polymers in molten state, grinding and subsequent compounding with wood flour. The rheological and mechanical properties of the LDPE/HDPE blend and resultant composites were determined. The results showed that recycling increased the complex viscosity of the LDPE/HDPE blend and it exhibited miscible behavior in a molten state. Rheological testing indicated that the complex viscosity and storage modulus of the composites made by pre-mixing method were higher than that made by the simultaneous method. The results also showed that melt pre-mixing of the polymeric matrix (recycled LDPE and HDPE) improved the mechanical properties of the wood–plastic composites.     

Effect of apple cider vinegar agent on the microstructure,phase evolution,and magnetic properties of CoFe2O4 magnetic nanoparticles

In the present study, spinel structure CoFe₂O₄ nanoparticles were successfully synthesized by the sol-gel auto-combustion technique. The effect of apple cider vinegar (ACV) addition as an organic biocompatible agent on the size, morphology, and magnetic properties of CoFe₂O₄ nanoparticles was investigated in detail. The phase evolution, particle size, and lattice parameter changes of the synthesized phase have been estimated by using Rietveld structure refinement analysis of X-ray powder diffraction data. Also, Fourier transform infrared spectra (FT-IR) of the samples verified the presence of two expected bands correspond to tetrahedral and octahedral metal-oxygen complexes within the spinel structure. Furthermore, microstructural observations revealed that ultrafine particles have a semi-spherical morphology. It was shown that the particles size decreased from ~45 to ~17 nm with an increase in the amount of ACV. Magnetic properties were carried out by vibrating sample magnetometer (VSM) at room temperature. Both the saturation magnetization (M_s) and coercivity (H_c) were found to be significantly dependent on the crystallite size and the amount of ACV.     

The Ablation and Oxidation Behaviors of SiC Coatings on Graphite Prepared by Slurry Sintering and Pack Cementation

SiC coatings were generated on graphite using slurry sintering (SS) and pack cementation (PC). The samples’ ablation features were assessed by an oxyacetylene torch. The rates of mass ablation of the PC–SiC and SS–SiC coatings were approximated 2.17?×?10^?3 and 9.52?×?10^?3 g s^?1, respectively, decreased by 84.1 and 29.6% compared to the uncoated samples. It was mainly attributed to the formation of a SiO₂ layer on the surface. The continuous SiO₂ molten film formed via the PC–SiC oxidation generates a sealing mechanism which can be an obstacle against the oxygen diffusion and hinder more ablation. This is while discontinuous SiO₂ film formed from the thin SS–SiC cannot protect the graphite effectively. The non-isothermal oxidation test shows that without the SiC coating, the sample weight is lost largely from 25 to 1500 °C, and its weight loss was 2.2% after the TGA. However, after coating, the samples possessed excellent oxidation protection and weight losses of SS–SiC and PC–SiC coatings are down to 1.3 and 0.6%, respectively. The more oxidation of the graphite substrate occurred due to the formation of macrocracks in the coating during the TGA and also the formation of holes on SiO₂ glass layer owing to release of CO or CO₂.     

Characterization and formation mechanism of nanocrystalline W–Al alloy prepared by mechanical alloying

Tungsten and aluminum elemental powders with composition W–20 wt.% Al were mechanical alloyed in high energy planetary ball mill. Structural and morphological changes of powder particles after different milling times were studied by X-ray diffractometer, scanning electron microscopy and microhardness measurements. Mechanical alloying of this system led to the formation of W–Al alloy as a result of formation of W/Al layered microstructure having faceted interface between layers. This alloy indicated high microhardness value of about 570 Hv.