Supercritical CO2 based processing of amorphous fluoropolymer Teflon-AF: Surfactant-free dispersions and superhydrophobic films

We report the application of a modified RESS process to create and collect in high yield nanoparticles of an amorphous fluoropolymer, Teflon-AF1600. The nanoparticles with diameters ranging from 10 to 100 nm can be synthesized from polymer solutions in supercritical CO₂ at 300 bar and 60 °C. The nanoparticles are collected by formation of dry ice in a liquid nitrogen-cooled trap. Nanoparticles embedded in dry-ice can be dispersed in organic solvents (acetone, ethanol, and n-heptane) creating surfactant-free dispersions. When dispersed in water, the nanoparticles self-assemble at the air–water interface forming a mechanically robust, superhydrophobic film. The film can support large water droplets (up to volume 250 μL) without breaking and is impermeable to water. The films cast from dispersions as well as those lifted-off water surface, are highly porous and superhydrophobic in nature (water contact angle θ_adv = 162°). This work demonstrates the utility of supercritical fluids based processing of fluoropolymers.     

Towards superhydrophobic coatings made by non-fluorinated polymers sprayed from a supercritical solution

The objective of this study was to create a superhydrophobic surface using polymers that are non-fluorinated and applying them to a surface via rapid expansion of a supercritical solution (RESS). Solubility studies of poly(ɛ-caprolactone) (PCL) and a statistical copolymer of vinyl acetate and vinyl pivalate (P(VAc-VPi))in supercritical carbon dioxide (scCO₂) were carried out using an extraction procedure. It was found that the most suitable process parameters for spraying these polymers using the RESS technique were 30 MPa, 40 °C and 10% (v/v) acetone as a co-solvent. The surfaces produced were characterized in terms of their morphology and hydrophobic properties by scanning electron microscopy and contact angle measurements, respectively. The most hydrophobic surfaces were obtained by spraying the P(VAc-VPi) copolymers, giving advancing water contact angles in the range of 120–155° due to the hydrophobic character of the polymer and the microstructure formed with the RESS technique. These results show great promise for the creation of superhydrophobic surfaces using non-fluorinated polymers applied to surfaces via RESS technique.     

Grafting modification of ramie fibers with poly(2,2,2-trifluoroethyl methacrylate) via reversible addition–fragmentation chain transfer (RAFT) polymerization in supercritical carbon dioxide

Reversible addition–fragmentation chain transfer (RAFT) polymerization was used to control the grafting of 2,2,2-trifluoroethyl methacrylate (TFEMA) with ramie fibers in supercritical carbon dioxide (scCO₂). The hydroxyl groups of the ramie fibers were converted to 2-dithiobenzoyl isobutyrate as the RAFT chain transfer agent (cellulose-CTA). Then, the subsequent grafting with TFEMA was mediated by RAFT polymerization in the presence of 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate (ECPDB) as the free RAFT chain transfer agent (free CTA). The modified ramie fibers were highly hydrophobic with water contact angles of up to 149°. Size exclusion chromatography showed narrow polydispersity (PDI = 1.28) of the grafted poly(TFEMA) chains. This grafting polymerization process is a novel and environmentally friendly approach for the preparation of functional grafted copolymers utilizing ramie fiber biomass.     

Enhancement of flexographic print quality on bleached kraft liner using nano-silica from rice husk

Nano-silica from rice husk (nano-RHS) was synthesized and used in a coating agent to enhance the flexographic print quality of bleached kraft liner. The rice husk was refluxed with a 2 M HCl solution and calcined in a muffle furnace at 650 °C for 4 h. The particle size of the resultant rice husk ash was reduced to a very fine nano-RHS by hexadecyl trimethyl ammonium bromide. The synthesized nano-RHS in different proportions – 1%, 2%, 3%, 4% and 5% (w/w_resin) – was added to a water-based coating agent consisting of acrylic resin. The coating agent with nano-RHS additive was applied by gravure rolling onto the surface of a 170 g/m² bleached kraft liner 3–4 μm in thickness. The flexographic print quality was determined with printing details of 31.5 lpc using water-based process colors. The results indicated that the coating agent with 1% nano-RHS was the most promising for improving the flexographic print quality on the bleached kraft liner. At this fraction, the best print quality in terms of high sharpness of fonts and texts, line art, realistic image, and TVI curve (under the requirements of ISO 12647-6) were achieved. In addition, low tone-value and ΔE*_abwith a large, three-dimensional color profile and the widest color gamut were obtained.     

Study of candeia oil extraction using pressurized fluids and purification by adsorption process

The extraction of oil from wood Candeia (Eremanthus erythropappus) was evaluated using CO₂ and propane as solvents. Experiments were carried out under the following conditions: T = 40 °C, P = 200 bar, T = 60 °C, P = 120 bar, T = 50 °C, P = 200 bar and T = 60 °C, P = 245 bar for carbon dioxide, yield was from 0.30 to 0.72. For propane, the temperature conditions studied were 30, 55 and 80 °C and pressures of 80, 100 and 120 bar, the yield was from 0.44 to 0.59. The α-bisabolol content of oil was evaluated and it was found that the operating conditions of extractions interfere in your concentration. The purification of the candeia oil was evaluated by the combined extraction and adsorption in fixed bed column using silica gel and alumina as the adsorbents. The separation was more efficient when used silica gel as adsorbent.     

Spin–spin interactions between π-electronic edge-localized spins and molecular oxygen in defective carbon nano-onions

π-Electronic edge-localized spin magnetism in defective carbon nano-onions (DCNOs) derived from detonation nanodiamonds was investigated in terms of molecular oxygen adsorption and microwave (MW) irradiation effect. At low MW power (P_MW ⩽ 200 μW) electron paramagnetic resonance (EPR) spectra of air-contained DCNO samples show progressive broadening of the g = 2.0014(2) edge-spin signal on temperature decrease. Below 140 K, the edge-spin signal becomes unobservable and the only weak narrow g = 2.0022(1) signal ascribed to sp³-like defects is observed. Upon higher power (P_MW > 20 mW) MW-irradiation at T < 60 K, that weak signal demonstrates unusual enhancement in peak/integral intensities and line broadening accompanied with upward deviations from the conventional saturation behavior. On abrupt reduction of P_MW to low (P_MW < 1 mW) levels, a new strong narrow signal with the same g = 2.0022(1) emerges. Below 60 K the intensity of the strong signal shows non-Curie–Weiss behavior. This EPR signal is attributed to new magnetic entities originating from antiferromagnetically coupled dimers of edge-spin and negatively charged O₂⁻ molecule. The O₂⁻ molecules, formed by charge transfer from π-electronic reservoir of underlaid nano-graphene sheet, appear in the vicinity of nano-graphene edges in the process of desorption/adsorption of oxygen molecules caused by strong MW-irradiation and subsequent abrupt reduction of P_MW.     

Low shear compounding process for thermoplastic fabrication of ferroelectric lead-free fibres

The thermoplastic ceramic extrusion process involves the shaping of a polymer highly filled with inorganic powder, the so-called ceramic–thermoplastic feedstock. The limitation faced with the process is the amount of raw material required to produce the feedstock. Depending on the density and desired volume of the materials used, the typical amount of ceramic powder required is a minimum of ∼100 g. The validation of a low shear feedstock preparation method against a standard high shear mixing method occurred. Microstructure investigation and single electromechanical fibre characterization of low shear produced KNN (d₃₃ – 49 pC/N; P_r – 3.7 μC/cm³) and PZT (d₃₃ – 392 pC/N; P_r – 32.4 μC/cm³) fibres, in terms of PE, SE loops and d₃₃ measurements, demonstrating the reproducibility of the results when compared to a standard ceramic–thermoplastic high shear mixing process. The repeatability of the measurements showed the proposed procedure to be robust, validating the new compounding method for wide-scale use.     

Poly(N-ethyl-4-vinylpyridinium bromide)–sodium dodecyl sulfate complexes. Formation and supramolecular organization in salt containing aqueous solutions

Formation and supramolecular organization of poly(N-ethyl-4-vinylpyridinium bromide) (PEVP)–sodium dodecyl sulfate (SDS) complexes in aqueous-salt solutions have been studied. PEVP samples of three polymerization degrees (P_w = 570, 1200 and 2350) were used. For PEVP of lower polymerization degree (P_w = 570) only insoluble complexes were observed in the whole range of the reaction mixture composition studied: Z = [SDS]/[PEVP] ≤ 1. For PEVP of higher polymerization degrees (P_w = 1200 and 2350), water-soluble complexes are formed up to a critical value of the reaction mixture composition, Z, that is similar for both PEVP fractions. It was found that water-soluble complex species are either molecularly dispersed (i.e. each complex particle comprises only one macromolecule) or aggregated (includes about 40 polymer chains and 20,000 surfactant ions) depending on the complex composition. Complex composition, in its turn, was shown to be determined by PEVP polymerization degree and the reaction mixture composition.     

Influence of ultrasonic treatment on the structure and emulsifying properties of peanut protein isolate

Effects of ultrasonic treatment on emulsifying properties and structure of peanut protein isolate (PPI) were evaluated by analysis of particle size distribution, protein surface hydrophobicity, SDS-PAGE, circular dichroism spectra and environmental scanning electron microscopy. The emulsifying properties of the PPI were found to be improved by ultrasonic treatment. The mean particle size decreased from 474.7 nm to 255.8 nm while the molecular weight remained unaffected. The results of intrinsic fluorescence spectroscopy and surface hydrophobicity indicated that ultrasonic treatment induced tertiary structural changes of the proteins in PPI. Emulsifying activity index and emulsion stability index were found to be correlated fairly well with surface hydrophobicity (H₀) (r = 0.712 and r = 0.668, respectively).     

Synthesis of poly(styrene-co-maleimide) and poly(octadecene-co-maleimide) nanoparticles and their utilization in paper coating

Aqueous polymer dispersions comprising of poly(styrene-co-maleimide) (SMI) or poly(octadecene-co-maleimide) (OMI) nanoparticles were synthesized by thermal imidization of the corresponding maleic anhydride copolymer precursors with ammonia using an organic solvent free process. Different reaction parameters such as temperature, time, agitation speed and stirrer geometry, and molar ratio of ammonia-to-anhydride were investigated in order to find optimal conditions. The obtained copolymer nanoparticles exhibited glass transition temperatures (T_g's) between 140 and 170 °C with particle sizes ranging from 50 to 230 nm. The compositional analysis was conducted by recording ¹H NMR and ATR-FTIR spectra. In addition, SMI dispersions were successfully spray dried and analyzed by SEM. Finally, the polymer dispersion's utility as auxiliary organic pigment in paper coating formulations was evaluated.     

Nonlinear optical,poly(amide-imide)–clay nanocomposites comprising an azobenzene moiety synthesised via sequential self-repetitive reaction

Poly(N-acylurea)–clay nanocomposites consisting of a modified montmorillonite and poly(N-acylurea) were prepared from which poly(amide-imide)–clay nanocomposites were subsequently obtained via the sequential self-repetitive reaction of poly(N-acylurea). The moderate T_g of poly(N-acylurea) allows the nonlinear optically active polymer to exhibit high poling efficiency; in situ poling and curing increased the T_gs of poly(amide-imide)–clay nanocomposites. Electro-optical coefficients, r₃₃ of ～17–20 pm/V (830 nm), were achieved; high temporal stability (120 °C) and waveguide optical losses of 3.4–3.9 dB/cm at 1310 nm were also obtained for poly(amide-imide)–clay nanocomposites.     

Novel method for the synthesis of a β-tricalcium phosphate coating on a zirconia implant

A novel method for the synthesis of a thin β-tricalcium phosphate (β-TCP) coating on zirconia implants has been developed. The synthesis procedure involves two steps: (i) rapid wet-chemical deposition of a biomimetic CaP coating and (ii) subsequent post-deposition processing of the biomimetic CaP coating, which includes a heat treatment at 900 °C followed by a short sonication in a water bath. The obtained β-TCP coating showed a uniform and dense morphology with a thickness of ≈500 nm and displayed a roughness in the nanometre range (R_a = 28 nm). The β-TCP coating demonstrated an apatite-mineralization ability in a simulated body fluid and enhanced the adsorption of serum proteins on the zirconia. Moreover, the β-TCP coating adhered firmly to the zirconia substrate, developing a notable scratch resistance (L_c = 97 N) and tensile strength (52 MPa) and showed strong resistance towards mechanical forces present during implantation of the coated zirconia implant into the artificial bone.     

Superconducting properties of homoepitaxial CVD diamond

Superconductivity was achieved above 10 K in heavily boron-doped diamond thin films deposited by the microwave plasma-assisted chemical vapor deposition (CVD) method. Advantages of the CVD method are the controllability of boron concentration in a wide range, and a high boron concentration, compared to those obtained using the high-pressure high-temperature method. The superconducting transition temperatures of homoepitaxial (111) films are determined to be 11.4 K for T_C onset and 8.4 K for zero resistance from transport measurements. In contrast, the superconducting transition temperatures of (100) films T_C onset = 6.3 K and T_C zero = 3.2 K were significantly suppressed.     

Micronization of fenofibrate by rapid expansion of supercritical solution

Micronization of fenofibrate was investigated using rapid expansion of supercritical solution (RESS) process. Effects of pressure, temperature and nozzle on particle size were optimized using Taguchi's orthogonal array and analyzed using XRD, DSC, FT-IR, SEM, laser diffractometer and dissolution testing. Processed fenofibrate retained crystalline structure and has a similar chemical structure with unprocessed fenofibrate. The average particle size of fenofibrate was reduced from its original 68.779 ± 0.146 μm to 3.044 ± 0.056 μm under the optimum condition (T at 35 °C, P at 200 bar and nozzle diameter at 200 μm). The processed fenofibrate showed an enhanced dissolution rate by 8.13 times.     

Microstructure and electrical properties of (Ba0.98Ca0.02)(Ti0.94Sn0.06)O3-modified Bi0.51Na0.50TiO3 lead-free ceramics

(Ba_0.98Ca_0.02)(Ti_0.94Sn_0.06)O₃-modified Bi_0.51Na_0.5TiO₃ [(1 ? x)BNT–xBCTS] ceramics were prepared by the normal sintering. A stable solid solution is well formed between BNT and BCTS, and the morphotropic phase boundary of (1 ? x)BNT–xBCTS ceramics is identified in the compositional range of 0.05 ≤ x ≤0.06. The temperature dependence of the dielectric loss and the poling temperature dependence of the d₃₃ value are used to determine the depolarization value (T_d). The T_d value of these ceramics gradually decreases with increasing BCTS content, together with the gradual increase of the dielectric constant. An enhanced electrical behavior of d₃₃ ～ 170 pC/N, k_p ～ 32.8%, P_r ～ 38.5 μC/cm², and E_c ～ 34.3 kV/cm is demonstrated for the ceramic with x = 0.06, which is double than that of pure BNT ceramic.     

Microphase separated structures in the solid and molten states of double-crystal graft copolymers of polyethylene and poly(ethylene oxide)

Transitions from one microphase separated structure in the solid state to a different one in the molten state in polyethylene-graft-poly(ethylene oxide) copolymers, PE-g-PEO, were investigated by variable temperature X-ray scattering measurements and thermal analyses. Small-angle X-ray scattering patterns from polymers with PEO grafts with 25, 50 and 100 ethylene oxide (EO) units show that the polymer passes through three distinct structures at ～10 nm length scales with increase in temperature (T): lamellar structures of PE and PEO at T < T_m^PEO, PE lamellae surrounded by molten PEO at T_m^PEO < T < T_m^PE, and microphase separated structures at T > T_m^PE when both PE and PEO are molten (T_m refers to the melting temperature). These phase transformations also occur during cooling but with hysteresis. Crystalline phases of PEO side chains and PE main chains could be identified in the wide-angle X-ray diffraction profiles indicating that the PE backbone and PEO grafts crystallize into separate domains, especially with longer grafted chains (50 and 100 units). At EO segment lengths > 50, PEO shows the expected increase in melting and crystallization temperatures with the increase in the grafted chain length. PE does not affect T_m^PEO but does decrease the onset of crystallization upon cooling. PEO grafts result in fractionation of PE, decrease the melting point of PE and increase the undercooling for the onset of crystallization of PE.     

One novel and unprecedented one-dimensional zinc coordination polymer with a N,O-donor chelating phenolic ligand, 3-n-butyl-2-(2-hydroxyphenyl)-3H-benzimidazole: synthesis,structure, characterization,photoluminescence and theoretical calculations

One novel and unprecedented 1D zinc coordination polymer with an unsymmetrical N,O-donor phenolic ligand, [Zn(bpbm)₂]_n (1) (Hbpbm · HCl · H₂O = 3-n-butyl-2-(2-hydroxyphenyl)-3H-benzimidazole hydrochloride hydrate) has been prepared and characterized crystallographically, and the geometric structure and photoluminescent properties, investigated experimentally and theoretically by DFT level. The deprotonated ligands, bpbm^?, as μ₂-bridging, adopt uncommon (O,N)-bridging poly(oligo)merization coordination mode, and not the common O-bridging poly(oligo)merization coordination mode. The photoluminescent property is assigned to π → π¹ ligand-to-ligand charge transfer transition (LLCT).     

Environmentally friendly PBS-based copolyesters containing PEG-like subunit: Effect of block length on solid-state properties and enzymatic degradation

The use of biodegradable polymers could contribute to mitigate the huge environmental problems caused by the massive use of conventional non-biodegradable plastics, especially in the case of time-limited applications. In this framework, in the present study we propose a new class of multiblock eco-friendly copolyesters containing butylene succinate (BS) and triethylene succinate (TES) sequences. In particular, four copolyesters with the same chemical composition but different block lengths – P(BS₁₀TES₁₀), P(BS₅TES₅), P(BS₃TES₃), and P(BS₂TES₂) – were synthesized by reactive blending. For sake of comparison, homopolymer PBS was also considered. Physicochemical characterization (DSC, WAXS, tensile tests, WCA) of the copolymers synthesized demonstrated that it is possible to control polymer crystallinity, thermal and mechanical properties and wettability of the final product by simply varying block length. As a matter of fact, melting point, crystallinity degree, elastic modulus and surface wettability decreased with the block length; on the contrary, elongation to break significantly increased. Enzymatic hydrolysis performed with lipase from Candida cylindracea ([E] = 50 U/mL, T = 30 °C and pH = 7.0), showed that copolymers biodegradation is much higher than that of PBS homopolymer. Moreover, copolymers displayed a tunable range of degradation rates, related to their crystallinity degree and hydrophilic/hydrophobic ratio, which render them promising for different time-span applications, ranging from long-term (P(BS₁₀TES₁₀) to very short-term (P(BS₂TES₂)).     

Effects of ultrasound on glass transition temperature of freeze-dried pear (Pyrus pyrifolia) using DMA thermal analysis

The effect of ultrasound pretreatment at various power (360 W, 600 W and 960 W, frequency 20 kHz) on the glass transition temperature of freeze dried pear (Pyrus pyrifolia) has been studied. DMA temperature plots were divided into four sections (A – glassy region, B – transition region, C – Rubbery plateau region and D – terminal region) with the aim to analyze their properties changed with sonication. Under the same freeze drying condition, with the increase in ultrasonic power, dried pear showed higher glass transition in terms of storage modulus, loss modulus and loss tangent peak. Also a decrease in a_w (0.31–0.23) and in moisture content (0.12–0.08 g/g d.b.) has been observed. Samples pretreated with ultrasound showed a better texture profile and much porous structure compared to control one. The results from the study indicated that, ultrasound pretreatment prior to freeze drying can improve the stability during storage of freeze dried pear.     

Oxidation behavior of electrically conductive α/β SiAlON composites with segregated network of TiCN

The oxidation behavior of novel electrically conductive α/β SiAlON composites with a continuous network of 2.5–10 vol% TiCN particulates was investigated. Composites, produced by coating spray dried granules with nano TiCN particles by a simple blending method, were gas pressure sintered at 1990 °C for 1 h under 10 MPa N₂ pressure. Oxidation tests were carried out between 800 °C and 1200 °C in air for 2 and 48 h in atmosphere of dry air. Below 1000 °C, the formation of TiO₂ crystals on the surfaces of TiCN particles was observed. Before the glass transition temperature of intergranular phase (T_g < 1000 °C), it was revealed that oxidation is controlled by the diffusion of oxygen into pre-formed TiO₂ particles. Above T_g, liquid glass dissolves the intergranular phase elements such as Ti, Y, and Si at the interface between TiCN and SiAlON particles. Migration of Ti towards the (opening point of the TiCN network) surface was found to be the main reason for the formation of subsurface porosity that slows down Ti diffusion through the surface. Moreover, it was detected that at high temperatures surface porosity filled by the intergranular glassy phase. Consequently, the oxidation rate was found to be decreased due to the slower oxygen diffusion.