Synthesis and characterization of poly(styrene‐co‐butyl acrylate)/clay nanocomposite latexes in miniemulsion by AGET ATRP

Polymer/clay nanocomposite latexes in the form of positively charged nanoparticles were synthesized by a newly developed initiating system, activators generated by electron transfer (AGET), which has been employed in atom transfer radical polymerization (ATRP). These clay‐dispersed latexes were synthesized using AGET ATRP of styrene and butyl acrylate in a miniemulsion system in which, ascorbic acid as a reducing agent was added drop wise to reduce termination reactions. Particle size and particle size distribution of resulted nanocomposite latexes were characterized by dynamic light scattering (DLS). These latexes were in the range of 138 to 171 nm in size. Gel permeation chromatography (GPC) was used to characterize the molecular weight and molecular weight distribution of the resultant copolymer nanocomposites. GPC traces showed that polymers of narrow molecular weight distribution and low Polydispersity Index (PDI) have been synthesized; this clearly shows ATRP reaction is conducted successfully. By increasing nanoclay content, molecular weight of the nanocomposites decreases. The presence of the nanofiller increases the thermal stability of the nanocomposites as investigated by thermogravimetric Analysis (TGA). Glass transition temperature of nanocomposites increases compared with the neat copolymer which was studied by differential scanning calorimetry (DSC). scanning electron microscope (SEM) showed sphere morphology of polymer particles synthesized by miniemulsion polymerization. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that mixed intercalated and exfoliated morphology is obtained. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Nanoclay‐encapsulated polystyrene microspheres by reverse atom transfer radical polymerization

Nanoclay‐encapsulated polystyrene microspheres were synthesized using reverse atom transfer radical polymerization in miniemulsion. Conversion and molecular weight were evaluated using gravimetry and gel permeation chromatography, respectively. Accordingly, conversion and molecular weight decrease by adding clay content. However, polydispersity index of the nanocomposites with higher clay content is higher. At high temperatures, thermal stability of the nanocomposites is relatively higher than the neat polystyrene, according to the thermogravimetric analysis results. Differential scanning calorimetry results show that glass transition temperature decreases by increasing clay content. Transmission electron microscopy result is in coincidence with X‐ray diffraction data and shows that clay layers are exfoliated in the matrix of PSNM 1. Scanning electron microscopy images display a homogeneous distribution of spherical particles with sizes in the range of ∼200 nm and also confirm dynamic light scattering (DLS) results. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Evaluation of the confinement effect of nanoclay on the kinetics of styrene atom transfer radical polymerization

The grafting through method was employed to study the effect of nanoclay confinement on the atom transfer radical polymerization (ATRP) of styrene. An ammonium salt containing a double bond on its structure was used as a clay modifier. Employing ATRP to polymerize styrene in the presence of modified montmorillonite resulted in a finely well‐defined polystyrene nanocomposite. The gas chromatography (GC) results showed the linear increase of ln(M₀/M) versus time, which indicated the controlled behavior of the polymerization. Another confirmation of the living nature of the polymerization was the linear increase of molecular weight against monomer conversion concluded from the gel permeation chromatography (GPC) data. Nanoclay exerted acceleration on the polymerization of free polystyrene chains. The polydispersity indexes of polymer chains increased by the addition of nanoclay. In the case of clay‐attached polystyrene chains, number and weight‐average molecular weights were lower than that of freely dispersed polystyrene chains. The polydispersity index of the clay‐attached chains was higher in respect to the freely dispersed polystyrene chains. The living nature of polymer chains was more elucidated by Fourier transform infrared spectroscopy (FTIR). Exfoliation of the clay layers in the polymer matrix of polystyrene nanocomposite containing the lowest amount of nanoclay has proven by Transmission Electron Microscopy (TEM). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of nanoclay‐dispersed polystyrene nanofibers via atom transfer radical polymerization and electrospinning

In this study, clay‐dispersed polystyrene (PS) nanocomposites were prepared with the in situ atom transfer radical polymerization method and were subsequently electrospun to form nanofibers 450–650 nm in diameter. The polymer chains extracted from the clay‐dispersed nanofibers exhibited a narrow range of molecular weight distribution. Thermogravimetric analysis (TGA) confirmed a higher thermal stability of the resulting nanocomposites compared to PS. The effect of the weight ratio of montmorillonite on the thermal properties of the nanocomposites was also studied by TGA. Differential scanning calorimetry revealed that the addition of the nanoclay increased the glass‐transition temperature. Moreover, degradation of the bromide chain‐end functionality took place at low temperatures. Scanning electron microscopy showed that the average diameter of the fibers was around 500 nm. The dispersion of clay layers was also evaluated by Al atoms in the PS matrix with the energy‐dispersive X‐ray detection technique. Transmission electron microscopy confirmed the exfoliation of the nanoclay within the matrix. However, the clay layers were oriented along the nanofiber axis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Quality changes of fish burgers prepared from deep flounder (Pseudorhombus elevatus Ogilby, 1912) with and without coating during frozen storage (−18 °C)

In the present study, chemical and sensory qualities of fish burgers prepared from deep flounder (Pseudorhombus elevatus Ogilby, 1912) with and without coating (Group A and Group B, respectively) or batter and breading materials were determined during frozen storage at ?18 °C for 5 months. According the statistical results, Total volatile base nitrogen of two groups increased significantly (P < 0.05) but a significant decrease (P < 0.05) was observed at the third month for Group A. Thiobarbituric acid value of Group A decreased significantly (P < 0.05) with the storage time from 1.01 to 0.22, whereas a significant increase (P < 0.05) was observed for Group B from 0.15 to 0.62 at the end of storage time. There were significant differences of pH in either the Group A or Group B between the beginning and end of the storage periods (P < 0.05). Parameters of colour, texture, taste and general acceptability for two groups decreased (P < 0.05) but Group B indicated better scores than Group A at the end of the storage period.     

To Sonicate or Not to Sonicate PM Filters: Reactive Oxygen Species Generation Upon Ultrasonic Irradiation

In aerosol research, a common approach for the collection of particulate matter (PM) is the use of filters in order to obtain sufficient material to undertake analysis. For subsequent chemical and toxicological analyses, in most cases the PM needs to be extracted from the filters. Sonication is commonly used to most efficiently extract the PM from the filters. Extraction protocols generally involve 10–60 min of sonication. The energy of ultrasonic waves causes the formation and collapse of cavitation bubbles in the solution. Inside the collapsing cavities the localized temperatures and pressures can reach extraordinary values. Although fleeting, such conditions can lead to pyrolysis of the molecules present inside the cavitation bubbles (gases dissolved in the liquid and solvent vapors), which results in the production of free radicals and the generation of new compounds formed by reactions with these free radicals. For example, simple sonication of pure water will result in the formation of detectable levels of hydroxyl radicals. As hydroxyl radicals are recognized as playing key roles as oxidants in the atmosphere the extraction of PM from filters using sonication is therefore problematic. Sonication can result in significant chemical and physical changes to PM through thermal degradation and other reactions. In this article, an overview of sonication technique as used in aerosol research is provided, the capacity for radical generation under these conditions is described and an analysis is given of the impact of sonication-derived free radicals on three molecular probes commonly used by researchers in this field to detect reactive oxygen species (ROS) in PM.

Copyright 2014 American Association for Aerosol Research