Adaptation of polystyrene/multi‐wall carbon nanotube composite properties in respect of its thermal stability

Polystyrene (PS)/multi‐wall carbon nanotube (MWCNT) nanocomposites were prepared by melt mixing and by coagulation of PS/MWCNT sonicated dispersion. Before mixing and coagulation particles of MWCNT were covered with PS nanospheres by microemulsion polymerization to increase their dispersibility and compatibility with the matrix. Microemulsion polymerization was carried out under sonication in the presence of surfactants and a cross‐linking agent. The structure of modified MWCNT filler was revealed by SEM and TEM microscopy analyses. They show that PS is well grafted onto surface of MWCNT in form of ca 30 nm nanospheres or as ca 3–8 nm PS film layer. Significant changes in properties were recorded mainly for the coagulated sample. Although no shift of T_g was recorded for the melt mixed composite, the coagulated sample shows an increase by 9°C. Also the reinforcing effect of MWCNT was more pronounced for the same method of preparation (further supported by the filler modification). The creep response of this material shifts to longer times not only in the T_g area, but also as low as 70°C below it, which is perceived as an improvement of temperature stability (the same properties kept for a longer time). This was also proved by the increase of creep modulus, and consequently by the prolonged time needed to reach the same tensile creep compliance after aging. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Equilibrium and Kinetic Studies of Ni (II) Adsorption using Pineapple and Bamboo Stem Based Adsorbents

This work addresses the preparation and characterization of inexpensive adsorbents for the removal of Ni (II) from aqueous solutions. Activated carbon based adsorbents have been prepared from plant based biomass resources, namely Pineapple stem ( Ananas Comosus ) and Bamboo Stem ( Bambuseae ). Adopting phosphoric acid and heat treatment techniques, it has been observed that the bamboo stem activated charcoal (BSAC) and pineapple stem (PS) adsorbents had a BET surface area of 116 and 11.47 m ² /g, respectively. FTIR analysis indicated that various surface functional groups (such as C ≡ N stretching, stretching vibration of C = O, –CH₃ wagging and C–O stretching vibration) contribute towards Ni (II) adsorption. Batch mode adsorption experiments were conducted for these adsorbents in the range of 50–300 mg/L Ni (II) solution concentration, 2–10 pH, 15–300 min. contact time, and 0.02–0.1 g/50 mL dosage. The BSAC adsorbent has been characterized with a metal uptake and %removal of 121.72 mg/g and 92.47, respectively, which corresponds to 45% higher metal uptake than corresponding bamboo based adsorbents presented in the literature. Further experimentation with BSAC enabled to achieve activated charcoal with surface area values similar to that of the commercial activated carbon adsorbent. The bamboo adsorbent has also been evaluated to perform similar to the commercial activated carbon for the removal and recovery of Pd (II) from synthetic electroless plating solutions. Also, a conceptual cost analysis indicated and affirmed towards the potential of the BSAC adsorbents for waste water treatment applications.     

Structural alterations of polycarbonate/PBT by gamma irradiation for high technology applications

In this work, polycarbonate/polybutylene terephthalate (PC/PBT) was irradiated with different gamma doses ranging from 200 kGy to 1950 kGy. Structural alterations of irradiated PC/PBT polymer blend have been studied using UV–vis spectroscopy, X-ray diffraction, and Fourier transform infrared (FTIR), as well as surface wettability. The results of UV–vis spectra showed that gamma irradiation induced an increase in the optical absorption with an increase in the gamma doses with shift in the optical absorption edge in the irradiated samples toward the higher wavelength. This shift is correlated with the decrease in optical band gap energy. Optical band gap decreases up to 12 and 20% with respect to pristine sample for direct and indirect transition, respectively. The number of carbon atoms per conjugated length has been estimated. The α phase and β phase of the crystalline PBT structure were observed. The α phase reflections are slightly increased due to the irradiation but the accompanying α to β transformation alters the results. FTIR investigation showed slight variation in the absorption spectrum specially in the range from 1300 to 1001 cm^?1 which are related to the O–C–O arrangements that is found to be the most affected part of the molecule by irradiation. A remarkable increase was observed in the wettability, surface free energy, and adhesion work of irradiated samples with an increase in the gamma doses.     

UV-induced Persulfate Oxidation of Organic Micropollutants in Water Matrices

ABSTRACT

The efficacies of UV photolysis, UV-activated persulfate (UV/PS), and combined UV/Fe²⁺-activated persulfate (UV/PS/Fe²⁺) systems for degrading of different organic micropollutants in ultrapure water and groundwater were examined and compared. The studied micropollutants belonging to the different classes involved an artificial sweetener acesulfame K (ACE), beta-lactam antibiotic amoxicillin (AMX), and endocrine disrupting compound 4-nonylphenol (NP). Among the studied systems, the UV/PS/Fe²⁺ process showed the highest performance both in degradation and in mineralization of ACE (UVA-induced systems; k_app = 0.126 1/min and 80.3% TOC removal) and AMX (UVC-induced systems; k_app = 1.383 1/min and 85.4% TOC removal), followed by the UV/PS process. In the case of NP trials, the application of UVC/PS systems was the most promising, and after careful adjustment of oxidant concentration, it demonstrated a considerable improvement in the target compound degradation (at a NP/PS molar ratio of 1/4 k_app = 0.024 1/min) compared with the UVC photolysis (k_app = 0.016 1/min). Irrespective of the applied UV-induced treatment process, the efficacy of target compounds degradation was lower in groundwater as compared with ultrapure water trials.     

Reaction of ozone with polybenzimidazole (PBI)

Ozone reacted with the polybenzimidazole (PBI) film surface and X-ray photoelectron spectroscopy (XPS) detected a rapid increase in O atom concentration up to a saturation level of 27 ± 1 atomic %. Atomic force microscopy measurements showed little change in surface roughness. The water contact angle of the treated film decreased by ca. 60% compared to untreated PBI film indicating an increase in hydrophilicity and hydrogen bonding due the formation of the polar oxygenated functional groups. With treatment, the curve fitting of the XPS chemical states showed a decrease in the C–C sp², C–C sp³, and C=N functional groups, and an increase in C–N, C=O, O–C=O, O–(C=O)–O, and N–C=O moieties which were explained using mechanisms associated with the dissociation of the primary ozonide formed from the addition of ozone to the C=C and C=N bonds and reaction with the amine groups in PBI. Washing the treated surface with water partially washed away the O concentration which indicated the formation of a weak boundary layer due to the breakage of bonds in the decomposition of the primary ozonide.     

Effect of Cu2O thin film on Cu–Sn alloy coated steel surface in promoting interfacial adhesion with rubber

In the present study, effect of Cu₂O film deposited via successive ionic layer adsorption and corresponding chemical reaction (SILAR method) on Cu–Sn coated steel substrate was explored for the purpose of improving the adhesion of steel with rubber. The effect of the relative alkali concentration in the oxide film deposition bath and the number of immersion cycles on the interfacial adhesion affecting the nature of oxide film deposited, its thickness and surface coverage were investigated. In the current study, Cu–Sn coated steel bead wire with coated surface roughness (R_a) around 2 μm showed an improvement of 33% in adhesion (in terms of pull out force) with an optimum alkali/Cu ion concentration of 25:1 with single dipping cycle attributed to an optimum oxide coating thickness of ~70 nm. Surface morphology study exhibited formation of thicker coating with increase in number of dipping cycles. Satisfactory thermal stability of the Cu₂O film was confirmed as no re-oxidation of the Cu₂O film to CuO was observed in the 200 °C heat treated samples.     

Exploring the Elastic Behavior of Core–shell Organic–Inorganic Spherical Particles by AFM Indentation Experiments

Monodispersed polystyrene (PS)-silica core–shell composite particles were synthesized via the hydrolysis and condensation of tetraethoxysilane (TEOS) on PS colloids at acidic medium. The thickness of silica coating was controlled by the amount of the addition of TEOS during the shell growth process. Transmission electron microscopy results confirmed that a continuous amorphous network of homogenous coating of silica was formed on the PS colloids. After coating by silica, the particle diameter increased from ca. 221 nm for uncoated PS cores to ca. 243–286 nm for PS-silica composite particles observed by scanning electron microscopy, indicating that the silica shell thickness was 11–32 nm. The elastic behavior of the obtained products was investigated by means of atomic force microscopy. The elastic moduli of samples were calculated by fitting the retract curves in force-separation plots based on the Hertzian contact model. The average moduli were 4–8 GPa for the PS-silica composite particles which were much lower than the that of the pure silica (72–75 GPa) and closed to that of the PS cores (2.1 ± 0.5 GPa). The elastic moduli of the PS-silica hybrids increased with increasing of silica shell thickness, suggesting that the elasticity of the PS-silica composite particles might be attributed to the PS cores and the silica shell was stiffening the polymer cores. These results provide a basis for exploring the mechanical properties of core–shell PS-silica hybrids in the application of novel abrasives for chemical mechanical polishing.     

Adhesion optimization for catalyst coating on silicon-based reformer

CMZ (ca. 30.0 wt.% Cu, 20 wt.% Mn, and 50 wt.% Zn) catalyst was chosen for the partial oxidation of methanol (POM) reaction. To enhance adhesion between a silicon-based reactor and catalysts, boehmite and bentonite were used as binders. Changes in conditions such as pH value, ratio of bentonite/boehmite, amount of solid contents per area of substrate, and aging time have crucial effects on adhesion and result in variable performance of catalyst in POM reaction. Regarding optimized adhesion conditions, 13 wt.% weight loss was observed and methanol conversion could be kept at ca. 80–90% of original catalyst performance in a packed-bed reactor. However, poor performance was observed in the micro-channel reactor. The methanol conversion (C_MeOH), H₂ selectivity (S_H2), and H₂ yield (Y_H2) achieved 58%, 67%, 5.7 × 10^?6 mol/min in micro-channel reformer at 250 °C, respectively.     

Photon transmission method for studying film formation from polstyrene latexes with different molecular weights

A photon‐transmission method was used to probe the evolution of transparency during film formation from polystyrene (PS) particles with different molecular weights. The latex films were formed at room temperature from the PS particles having two different average molecular weights and annealed at elevated temperatures in various time intervals above the glass transition (T_g). Onset temperatures (T_H) at given times (τ_H) for the optical clarity of films formed from low (LM) and high molecular (HM) weight PS particles were used to calculate the healing activation energies for the minor chains and found to be 22.0 ± 0.5 and 27.0 ± 0.6 kcal/mol, respectively. The increase in the transmitted photon intensity, I_tr, above the T_H was attributed to increase in the number of interfaces that disappeared. The Prager–Tirrell (PT) model was employed to interpret the increase in crossing density at the junction surface. The backbone activation energies (ΔE) were measured and found to be 127.8 ± 2.5 kcal/mol for a diffusing polymer chain across the junction surface for LM and HM latex films. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 866–874, 2000     

Mixed monolayers of pmas with poly(styrene‐b‐methyl methacrylate) at the air/water interface

Poly(methyl methacrylate) (PMMA) is known to be immiscible with poly(styrene) (PS) in the bulk state. Poly(ethyl methacrylate) (PEMA), poly(propyl methacrylate) (PPMA), and poly(n‐butyl methacrylate) (PBMA) are also known to be immiscible with PMMA (or PS). Therefore, PMAs (PMMA, PEMA, PPMA, and PBMA) are predicted by the mean field theory to be immiscible with poly(styrene‐b‐methyl methacrylate) (PS‐b‐PMMA) in the bulk state. However, the miscibility of PMAs with PS‐b‐PMMA may be different in the two‐dimensional state. Therefore, the mixed monolayer behavior of PMAs and PS‐b‐PMMA was investigated from the measurements of surface pressure‐area per molecule (π‐A) isotherms at three different temperatures (10°C, 25°C, and 40°C). Calculation of compressibility from isotherms provided the inflection data from maximum and minimum peaks. The miscibility and nonideality of the mixed monolayers were examined by calculating the excess area as a function of composition. Mostly, negative deviations from ideality were observed in the mixed monolayers. This is likely because of favorable interaction between PMMA and PMAs in the monolayer state. The positive deviations occurred at 40°C with PBMA at a high surface pressure. Therefore, with confinement in the two‐dimensional state, the miscibility between PMAs and PS‐b‐PMMA was greatly improved in comparison with the bulk state. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Effects of Food Topographical Features on Attachment and Heat Resistance of Salmonella During Drying

Changes in the topographical features of food during thermal processing, e.g., surface and bulk shrinkage during drying, may protect microbial cells from direct exposure to heat. Knowledge of the effects of the surface topographical features and their changes on microbial cell behavior is thus of interest. The objective of the present study was to investigate the effects of artificially prepared topographical features on the attachment ability and heat resistance of Salmonella on model food surface during hot air drying. Carrot was used as a model food material. Carrot sticks (3 × 1 × 1 cm) were artificially textured on one side with either shark tooth or wavy (crinkle) cut; the cut was artificially made to amplify the possible effect of surface roughness, which resembles topographical features of food surface and their changes, on the bacterial cell behavior. The degree of roughness was varied in the range of 20–80% of the total height of a stick. Approximately 0.2–0.7 log increase in the number of Salmonella was observed on the rough surfaces as compared to smooth control samples since larger surface areas were available for bacterial cell attachment. Salmonella attached on the surfaces with higher wave height also exhibited higher heat resistance (up to 2 h extra drying time was required to achieve 4-log reductions of Salmonella as compared to the time required by the control sample). However, the effect of cut pattern on bacterial cell behavior was not observed.     

Low-energy He-ion beam modifications the surface properties of biomaterial

In the present work, ultra-high-molecular-weight polyethylene (UHMWPE) films were irradiated with 130 keV He ions. The fluence of the ion beam was ranged from 1 × 10¹² to 1 × 10¹⁶ cm^?2. The chemical, morphological, and crystallite structure changes resulted from the ion bombardment were obtained using different spectroscopic techniques. These techniques were Fourier transform infrared spectrometer, scanning electron microscope, X-ray diffraction, and UV–vis spectrophotometry. The surface free energy for untreated and ion-beam-treated samples was determined by means of contact angle measurements of three different liquids. Our results showed a decrease in the crystallinity of UHMWPE and formation of C=O groups on the polymer surface for modified samples as well. A remarkable shifting in the UV–vis spectra toward lower energy and increase in the optical absorption were observed as the ion fluence increases. Measurements of the contact angle indicate remarkable increase in the surface free energy as a function of ion fluence.     

Lipase-Catalyzed Esterification of Triterpene Alcohols and Phytosterols with Oleic Acid

Oleic acid esters of phytosterols (PSs) and triterpene alcohols (TAs), derived from rice bran, were synthesized using lipases under mild conditions. Some lipases, especially from Candida rugosa, type VII, showed very high substrate specificity towards both PSs and TAs, when a mixture of PS and TA (PS/TA mixture) was used as the substrate source. The maximum yield of PS esters was ca. 80 % in each case; however, the maximum yield of TA esters was much lower when the reaction was continued for 7 days. Due to the difficulty in purifying the esters obtained when the PS/TA mixture was used as source of substrate, free PSs and TAs were separated from the PS/TA mixture by silica-gel and reverse-phase chromatography prior to esterification. The pure PSs or TAs were esterified with oleic acid to obtain the corresponding esters with high purity. Differential scanning calorimetric analysis of the resulting esters revealed that their melting points ranged from 7.0 to 42 °C. These values were at least 100 °C lower than those of the free PSs and TAs.     

Influence of temperature,molecular weight,and molecular weight dispersity on the surface tension of PS,PP, and PE. I. Experimental

In this work, the influence of temperature, molecular weight (M?_n), and molecular weight dispersity (MWD) on the surface tension of polystyrene (PS) was evaluated using the pendant drop method. The influence of temperature on the surface tension of isotatic polypropylene (i‐PP) and of linear low‐density polyethylene (LLDPE) was also studied here. It was shown that surface tension decreases linearly with increasing temperature for all the polymers studied. The temperature coefficient ?dγ/dT (where γ is the surface tension, and T, the temperature) was shown to decrease with increasing molecular weight and to increase with increasing MWD. The surface tension of PS increased when the molecular weight was varied from 3400 to 41,200 g/mol. When the molecular weight of PS was further increased, the surface tension was shown to level off. The surface tension was shown to decrease with increasing molecular weight distribution. Contact angles formed by drops of diiomethane and water on films of PS with different molecular weights were measured at 20°C. The surface energies of those polymers were then evaluated using the values of the different pairs of contact angles obtained here using two different models: the harmonic mean equation and the geometric mean equation. It was shown that the values of the surface energy obtained are slightly less than are the ones extrapolated from surface‐tension measurements in the rubbery state. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1907–1920, 2001     

Surface modification of poly(styrene) by the attachment of an antimicrobial peptide

Polymers that directly inhibit the growth of microorganisms at their surface are potentially useful. To investigate the feasibility of such materials, poly(styrene) (PS) resin beads that had had poly(ethyleneglycol) (PEG) grafted onto the surface were further derivatized by covalently linking an antimicrobial peptide onto the surface. The antimicrobial peptide was composed of 8 lysine and 7 leucine (6K8L) residues. The resulting surface‐modified polystyrene (SMPS) was microcidal in a concentration and time‐dependent manner against several micro‐organisms including E. coli O157 : H7, L. monocytogenes, S. aureus, P. fluorescens, and K. marxianus when suspended in phosphate buffer. The SMPS inhibited the growth of pathogenic E. coli O157 : H7 in trypticase soy broth. SMPS was bactericidal at pH 3.5 to 7, retained activity after heating to 200°C for 30 min, and could be extensively washed without loss of antimicrobial activity. Bioassays and HPLC analyses of buffer that had been preincubated with SMPS indicated that antimicrobial activity may have been due, at least in part, to the slow release of a peptide–PEG ligand from the PS to the buffer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 609–616, 2001     

Chemical Scarification and Ozone in Seed Dormancy Alleviation of Wild and Domesticated Opuntia,Cactaceae

Protocols for seed germination in the Opuntia genus are different and unsuitable for all their species. Dormancy of Opuntia seeds can be modified by the combination of scarification and an oxidizing agent such as O₃, which could induce antioxidant and DNA-repair mechanisms or dormancy-breaking effects in hydrated seeds. The objective of this study was to evaluate the effects that the combination of mechanical and chemical scarification with exposition to sub-lethal O₃ doses have on seed germination and seedling growth of O. streptacantha Lem., O. megacantha Salm-Dyck, and O. ficus-indica (L.) Mill. Our hypothesis was that O₃ favors germination on scarified seeds and that the magnitude of the effect is species-dependent. Water uptake and germination were quantified in seeds every 48 h, until their roots reached a 5-mm length. The results were analyzed with an analysis of variance and multiple means comparisons with the Tukey test. Accelerated water uptake was observed during the first 48 h; the maximum average was 33.5% in all species. The combination of acid scarification and imbibition in the presence of O₃ increased (P ≤ 0. 05) germination (between 17.8 and 44.4%), mainly in O. streptacantha. O₃ increased germination, regardless of the species. O₃ can be used in sublethal doses to increase seed germination and seedling development in Opuntia genus.     

Preparation,characterization, and biodegradation of PS:PLA and PS:PLA:OMMT nanocomposites using Aspergillus niger

Poly(lactic acid) (PLA) was synthesized using l ‐lactic acid by condensation polymerization. Polystyrene (PS) and surface modified montmorillonite (OMMT) was used for the preparation of PS:PLA composites and PS:PLA:OMMT nanocomposites. The composite materials prepared had varying amount of PLA (10–30%) and OMMT (0.5–5 phr). These composites were subjected to degradation in minimal medium using the fungi Aspergillus niger (A. niger) under controlled conditions. Scanning electron microscopy (SEM) showed the growth of microorganism on the polymer surface and fracture within the polymer matrix as a result of degradation. Fourier transform infra red spectroscopy (FTIR) was further used to determine the mechanism leading to biodegradation. It was found that the biodegradation of both PS:PLA and PS:PLA:OMMT took place mainly via break down and utilization of ester group, as can be seen from disappearance of absorption peak of ester group and simultaneous appearance of a typical IR absorption of microbial mass at 1450 cm⁻¹. The thermal stability of PS:PLA:OMMT nanocomposites was found to increase with increasing concentration of OMMT, as observed from thermo gravimetric analysis (TGA), while mechanical property was found to be decreased after degradation at 30% of PLA and 5 wt% of OMMT content. Change in extracellular protein content, biomass production and % degradation with respect to time (up to 28 days) were studied and correlated to evaluate the effectiveness of A. niger in biodegradation of the composites. POLYM. COMPOS., 35:263–272, 2014. © 2013 Society of Plastics Engineers     

Preparation and characterization of surface modified silicon carbide/polystyrene nanocomposites

A simple method is reported to coat silicon carbide (SiC) nanoparticles with polystyrene (PS) to improve the interfacial adhesion between polymer matrix and SiC nanoparticles. The morphology of untreated SiC nanoparticles, PS coated SiC (p‐SiC) nanoparticles, SiC/PS nanocomposites, and p‐SiC/PS nanocomposites are observed. The HRTEM image of p‐SiC shows that the thickness of PS on the surface of SiC is about 1.5–2.0 nm, which is consistent with the TGA results. With 24.7 vol % untreated SiC nanoparticles dispersed into PS matrix, the thermal conductivity (λ) of the SiC/PS composites increases by about 192%. However, when the same volume fraction of p‐SiC nanoparticles is used, the increase is about 353%. This big difference could be attributed to the promoted dispersion of the p‐SiC in the PS matrix. The measurements of glass transition (T_g), dielectric constant (ε), and tensile strength at break (σ_b) also support this explanation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

High temperature surface neutralization process with random copolymers for block copolymer self‐assembly

Hydroxyl terminated poly(styrene‐r ‐methyl methacrylate) (P(S‐r ‐MMA )) random copolymers (RCPs ), with molecular weight (M _n) spanning from 1700 to 69 000 g mol^?1 and equal styrene unit content, were grafted at different temperatures onto a silicon oxide surface and subsequently used to study the orientation of nanodomains with respect to the substrate, in cylinder forming polystyrene‐b ‐poly(methyl methacrylate) (PS ‐b ‐PMMA ) block copolymer thin films. When the grafting temperature increases from 250 to 310 °C, a substantial increase in the grafting rate is observed. In addition, an increase in the surface neutralization efficiency occurs thus resulting in an increase in the robustness of the surface neutralization step. These data revealed that the neutralization of the substrate is the result of a complex interplay between RCP film characteristics and underlying substrate properties that can be finely tuned by properly adjusting the temperature of the grafting process. © 2016 Society of Chemical Industry     

IN-SITU FT-IR SPECTROSCOPIC STUDIES OF FUEL CELL ELECTRO-CATALYSIS: FROM SINGLE-CRYSTAL TO NANOPARTICLE SURFACES

The work presented in this article shows the power of the variable temperature, in-situ FT-IR spectroscopy system developed in Newcastle with respect to the investigation of fuel cell electro-catalysis. On the Ru(0001) electrode surface, CO co-adsorbs with the oxygen-containing adlayers to form mixed [CO + (2 × 2)–O(H)] domains. The electro-oxidation of the Ru(0001) surface leads to the formation of active (1 × 1)–O(H) domains, and the oxidation of adsorbed CO then takes place at the perimeter of these domains. At 20°C, the adsorbed CO is present as rather compact islands. In contrast, at 60°C, the CO_ads is present as a relatively looser and weaker adlayer. Higher temperature was also found to facilitate the surface diffusion and oxidation of CO_ads. No dissociation or electro-oxidation of methanol was observed at potentials below approximately 950 mV; however, the Ru(0001) surface at high anodic potentials was observed to be very active. On both Pt and PtRu nanoparticle surfaces, only one linear bond CO adsorbate was formed from methanol adsorption, and the PtRu surface significantly promoted both methanol dissociative adsorption to CO and its further oxidation to CO₂. Increasing temperature from 20° to 60°C significantly facilitates the methanol turnover to CO₂.