Nonisothermal suspension polymerization of vinyl chloride for enhanced productivity

In the present study, a mathematical model is developed to numerically predict nonisothermal batch suspension polymerization of vinyl chloride. Free volume theory was used to consider diffusion‐controlled reactions. Model predictions were validated against field data obtained in a pilot scale stirred tank reactor. Variable temperature trajectory was considered during the course of the reaction to improve productivity by reducing the polymerization time for a certain conversion. Variable temperature during the course of the polymerization was successfully implemented by considering the predefined K value. By using variable temperatures during the course of the reaction, the density of the short branches per 1,000 monomer units as a criterion for structure defect remained relatively unchanged. Maximum reduction in reaction time relative to the isothermal case with the same K value and final conversion was 44% for the best temperature trajectory. J. VINYL ADDIT. TECHNOL., 22:470–478, 2016. © 2015 Society of Plastics Engineers     

The effect of substrate temperature on microstructural evolution and hardenability of tungsten carbide coating in hot filament chemical vapor deposition

Effect of substrate temperature on microstructural evolution and hardenability of tungsten carbide coating produced by hot filament chemical vapor deposition (HFCVD) process was studied. Annealed sheets of 316L stainless steels were used as the substrate. HFCVD technique, with substrate temperatures of 400 and 500°C, was used to deposit tungsten carbide coating on these sheets. Field Emission Scanning Electron Microscope (FE‐SEM) was used to study the evolution of microstructure. X‐Ray Diffraction spectroscopy was used to analyze the phases formed and Raman spectroscopy was employed to differentiate molecular composition of the coatings. The amount of the porosity of the coatings was measured and Vickers hardness measurement was used for hardness assessment. Results show that the tungsten carbide coatings have a honeycomb structure and increasing the temperature of the substrate increases the amount of porosity of the coating. XRD results showed that 3 different crystalline structures containing W, WC, and W₂C were formed in the coating deposited on the 316L stainless steel. Increasing the temperature of the deposition has increased the intensity of the peaks in the XRD results. Raman spectroscopy results indicated the presence of a carbon in the tungsten carbide coatings. Finally, microhardness of the tungsten carbide coating increases with increasing the temperature of the substrate.     

Tribological behaviour of semisolid–semisolid compocast Al–Si matrix composites reinforced with TiB2 coated B4C particulates

The purpose of this paper is to provide a deeper understanding of the wear behavior of the sol–gel coated B₄C particulate reinforced A356 matrix composites. A typical microstructure of the composite consists of relatively large primary phase globules which are surrounded by B₄C particles. In fact the globules themselves are B₄C particles free and consequently the sample is not homogeneous on a scale smaller than the globule size. The wear sliding test disclosed that the wear rate of the coated B₄C reinforced composites is less than that of the unreinforced alloy and decreases with increasing volume fraction of B₄C particulates. As the hardness of the composites is higher, this reduces the cutting efficiency of the abrasives and consequently the abrasion wear loss. Once the particles fracture or loosen from the matrix alloy, they can be removed easily from the matrix, contributing to the material loss. Two kinds of debris present irregular-shaped flake, which has withstood a large of plastic deformation and then pull off from the surface. During the sliding wear, Iron is transferred to the surface of the composites from the steel counterface forming the iron-rich layer on the contact surfaces which increases with increasing the B₄C content and is substantially harder than the bulk material largely because it contains a fine mixture of Fe phase, Al and B₄C.     

Chemical Functionalization of Graphene Oxide by Poly(styrene sulfonate) Using Atom Transfer Radical and Free Radical Polymerization: A Comparative Study

Poly(sodium styrenesulfonate)-functionalized graphene was prepared from graphene oxide, using atom transfer radical polymerization and free radical polymerization. In atom transfer radical polymerization route, the amine-functionalized GO was synthesized through hydroxyl group reaction of GO with 3-amino propyltriethoxysilane. Atom transfer radical polymerization initiator was grafted onto modified GO (GO-NH₂) by reaction of 2-bromo-2-methylpropionyl bromide with amine groups, then styrene sulfonate monomers were polymerized on the surface of GO sheets by in situ atom transfer radical polymerization. In free radical polymerization route, the poly(sodium 4-styrenesulfonate) chains were grafted on GO sheets in presence of Azobis-Isobutyronitrile as an initiator and styrene sulfonate monomer in water medium. The resulting modified GO was characterized using range of techniques. Thermal gravimetric analysis, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy results indicated the successful graft of polymer chains on GO sheets. Thermogravimetric analysis showed that the amount of grafted polymer was 22.5 and 31?wt% in the free radical polymerization and atom transfer radical polymerization methods, respectively. The thickness of polymer grafted on GO sheets was 2.1?nm (free radical polymerization method) and 6?nm (atom transfer radical polymerization method) that was measured by atomic force microscopy analysis. X-ray diffractometer and transmission electron microscopy indicated that after grafting of poly(sodium 4-styrenesulfonate), the modified GO sheets still retained isolated and exfoliated, and also the dispersibility was enhanced.     

A new blend of polymeric encapsulation of azithromycin by spray-drying with a pH responsive in drug release

The microencapsulation of macrolides with polymers has been reported to retard the release of the drug in oral cavity. However, these methods are unable to control drug release in gastrointestinal tract. The aim of the present study was to investigate the effect of formulation of a new polymeric encapsulation of azithromycin which is suitable for both masking and sustained release usage. Eudragit E100 and polyethylene glycol (PEG) 4000 were chosen as the barrier coatings. The spray drying technique was used to obtain the microcapsules containing azithromycin. To obtain the initial results, the effects of several parameters were evaluated. A 3:2:1 ratio of E100:PEG 4000:azithromycin at pH 6 gave the best coating condition. Thermogravimetric analysis and IR analysis data confirmed the encapsulation of azithromycin inside polymers. The encapsulated drug was released in different rates from the particles by changing the pH (1.7 and 7.4). An analysis of the kinetic release properties indicates that the release of the drug is a combination of swelling and diffusion mechanism. The synergistic cooperation between polymers and drug due to the existence of several hydrogen bonding is supposed to influence the pH-responsive property of the encapsulated drug. Moreover, the use of mixtures of E100 and PEG 4000 appears to offer a good balance between cost and efficiency.     

Amide–acid functional SiO2 nanocomposites based on new semi‐crystalline poly(ether‐sulfone‐amide): thermal,combustion and mechanical studies

New amide–acid functional SiO₂ nanoparticle (FSNP)‐reinforced semi‐crystalline aliphatic–aromatic poly(ether‐sulfone‐amide) (PESA) was synthesized using a solution method in dimethylformamide. The surfaces of SiO₂ nanoparticles were functionalized with phthalic anhydride, and subsequently PESA was synthesized using direct polymerization with good yield and desired molar mass. PESA / SiO₂ nanocomposites (PSNCs) were prepared with three different contents of FSNP and the morphology and mechanical, thermal and combustion properties of the PSNCs were studied. The results of X‐ray diffraction, field‐emission scanning electron microscopy and transmission electron microscopy showed a uniform dispersion for FSNP in the PESA matrix. According to the results of mechanical tests, the tensile strength and the Young's modulus of PESA were enhanced by FSNP loading. Thermogravimetric analysis and derivative thermogravimetry results showed a substantial improvement in thermal properties of PESA. The temperature at 5% mass loss was increased from 371.7 to 395.8 °C for the PSNC containing 8 mass% of FSNP, as well as the char yield being enhanced greatly, which was about 30% higher than that of neat PESA. Significant improvements in combustion properties were observed for PSNCs from microscale combustion calorimetry. The peak heat release rate showed an obvious improvement and decreased by about 57% compared to that of neat PESA on 8 mass% loading of FSNP. © 2016 Society of Chemical Industry     

Graphene network enabled high speed electrical actuation of shape memory nanocomposite based on poly(vinyl acetate)

Here strong electroactive shape memory nanocomposites were prepared by incorporating graphene nanoplatelets into poly(vinyl acetate) (PVAc ) through the simple solvent mixing method. TEM and XRD revealed that well exfoliated graphene nanoplatelets formed a continuous network throughout the matrix with a large amount of interconnectedness. Dynamic mechanical analysis showed that the inclusion of graphene significantly improves both glassy and rubbery moduli of the matrix. Furthermore, the prepared nanocomposites demonstrated a marked electrical conductivity up to 24.7 S m^?1 and thereby surprisingly rapid electrical actuation behaviour exhibiting a 100% recovery ratio in 2.5 s. Moreover, PVAc and its nanocomposites displayed scratch self‐healing capability. This work demonstrates that the PVAc /graphene nanocomposites with high modulus and excellent electroactive shape memory performance can be a promising material in many applications such as sensors and fast deployable and actuating devices. © 2016 Society of Chemical Industry     

Optimizing the mechanical and physical properties of thermoplastic starch via tuning the molecular microstructure through co‐plasticization by sorbitol and glycerol

Nowadays, environmental hazards caused by plastic wastes are a major concern in academia and industry. Utilization of biodegradable polymers derived from renewable sources for replacing common petroleum‐based plastics is a potential solution for reducing the problem. In this regard, starch has become one of the most promising alternatives to non‐biodegradable polymers for depleting plastic waste thanks to its low expense, abundance, renewability and biodegradability. However, the main drawbacks of starch are its poor processability, weak mechanical properties and severe hydrophilicity. In this work, thermoplastic starch (TPS) samples have been prepared using glycerol and sorbitol as co‐plasticizers in a laboratory co‐rotating twin screw extruder. Based on the mechanical test results, glycerol caused higher elongation to break but had lower tensile strength and elastic modulus compared to sorbitol plasticized starch. Fourier transform infrared spectroscopy and DSC results indicated that the hydrogen bond interaction between starch chains and plasticizers could be improved by replacing glycerol by sorbitol, which resulted in higher resistance against retrogradation proved by XRD results. TGA illustrated that the higher the sorbitol to glycerol ratio was, the more stable was the TPS. Using a proper amount of plasticizers (42 wt% total plasticizer, sorbitol to glycerol ratio 2:1) led to the preparation of a TPS sample with optimized properties including enhanced mechanical properties, high thermal stability, strong hydrogen bond formation and high resistance against retrogradation. © 2017 Society of Chemical Industry     

Investigation on the morphological and mechanical properties of (polyamide 6)/(poly[styrene‐co‐acrylonitrile])/(poly[styrene‐b‐{ethylene‐co‐butylene}‐b‐styrene]) ternary blends

In this work, ternary polymer blends based on (polyamide 6)/(poly[styrene‐co‐acrylonitrile])/(poly[styrene‐b‐{ethylene‐co‐butylene}‐b‐styrene]) (SEBS) triblock copolymer and a varying concentration of the reactive (maleic anhydride)‐grafted SEBS were prepared by using a melt‐blending process. The effects of the material parameters (composition of ternary blends and SEBS/[{maleic anhydride}‐grafted SEBS] concentration ratio) and blending sequence on the morphological and mechanical properties of ternary blends were studied. Taguchi experimental design methodology was employed to design the experiments and select the material and processing parameters for the optimized mechanical properties. Tensile properties (Young's modulus and yield stress) and impact strength were considered as the response variables. It was demonstrated that there is a meaningful relationship between the composition of blends, processing parameters, observed phase structure, and obtained mechanical properties. The mechanical tests showed that the highest impact strength was achieved as the dispersion of the rubbery phase achieved an optimum size of about 1 μm. J. VINYL ADDIT. TECHNOL., 23:329–337, 2017. © 2015 Society of Plastics Engineers