Bio-based thermosetting bismaleimide resins using eugenol,bieugenol and eugenol novolac

5,5′-Bieugenol (BEG) and eugenol novolac (EGN) were synthesized by the oxidative coupling reaction of eugenol (EG) and the addition–condensation reaction of EG with formaldehyde, respectively. The EG, BEG and EGN were prepolymerized with 4,4′-bismaleimidediphenylmethane (BMI) at 180 °C and then compression-molded at finally 250 °C for 6 h to produce cured EG/BMI (EB), BEG/BMI (BB) and EGN/BMI (NB) resins with eugenol/maleimide unit ratios of 1/1, 1/2 and 1/3. The FT-IR analysis of EBs and ¹³C NMR analysis of the model reaction product of EG/N-phenylmaleimide (PMI) 1/3 at 200 °C for 12 h suggested that the ene reaction and subsequent Diels-Alder/ene reactions mainly occurred for EBs. The FT-IR analyses of BBs and NBs supported the occurrence of ene reaction and subsequent thermal addition copolymerization in a similar manner to the well-known curing reaction of 2,2′-diallylbisphenol A and BMI. The glass transition temperature (T_g) and 5% weight loss temperature (T₅) of the cured resin increased with increasing BMI content, and EB 1/3 showed the highest T_g 377 °C and T₅ 475 °C. The flexural strengths and moduli of EBs and NBs were higher than those of BBs, and EB 1/2 showed the most balanced flexural strength and modulus (84.5 MPa and 2.75 GPa). The FE-SEM analysis revealed that there is no phase separation for all the cured resins.     

Synthesis and characterization of a cross-linkable nonlinear optical polymer functionalized with a thiophene- and tricyanovinyl-containing chromophore

This paper reports a novel nonlinear optical polymer BP-AVT-TCV functionalized with a thiophene- and tricyanovinyl-substituted chromophore. BP-AVT-TCV was synthesized by the post-tricyanovinylation of an epoxy-based precursor polymer BP-AVT, and had a high molar functionalization degree of chromophore (70 mol.%). It had an enhanced glass transition temperature (T_g = 164 °C) compared with BP-AVT (T_g = 114 °C), and a high decomposition temperature (T_d,5% = 295 °C). BP-AVT-TCV was further cross-linked to achieve the three-dimensional (3D) network of thermosetting polyurethane (PU). The poled PU films revealed an electro-optic (EO) coefficient (γ₃₃) value of 21 pm/V at a wavelength of 1315 nm. The structures of the polymers were confirmed by FT-IR, UV–Vis, and ¹H NMR spectra.     

Two-step sintering assisted consolidation of bulk titania nano-ceramics by spark plasma sintering

This work investigates the feasibility to the fabrication of high density of nano-grained titanium dioxide ceramics by two-step sintering process under spark plasma conditions. First step is carried out by fast-heating-rate sintering in order to obtain an initial high density and a second step is held at a lower temperature by isothermal sintering aiming to increase the density without obvious grain growth. Experiments are conducted to determine the appropriate temperatures for each step. The temperature range between 840 and 850 °C is effective for the first step sintering (T₁) due to its highest densification rate. The isothermal sintering is then carried out at 810–830 °C (T₂) for various hours in order to avoid the abnormal grain growth and improve the density at the same time. TiO₂ bulk ceramics with nano-sized grain were fabricated successfully by combination of spark plasma sintering (SPS) with the two step sintering method (TSS). Titanium dioxide nano-ceramics with >95% theoretical density could be obtained with T₁ and T₂ taken as 850 °C and 830 °C, respectively. The relative grain growth quotient D/D_o for the used starting powder was almost ～1. Further XRD investigations indicated no obvious anatase–rutile transition was found in the prepared nano-crystalline ceramics.     

Synthesis and photoresponsive behavior of the high-Tg azobenzene polymers via RAFT polymerization

Well-defined photo-responsive alternating copolymers, poly(4-(N-maleimido)azobenzene-alt-styrene)s (PMSts), were successfully synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. A divinyl monomer was used in this polymerization to prepare high molecular weight azobenzene polymers. These polymers had good solubility in most organic solvents, formed films well, and had high glass transition temperatures (T_g = 174–250 °C) and were heat resistant (T_d > 320 °C). The photo-induced trans–cis isomerization of the copolymers was examined in chloroform solution. Surface-relief-gratings (SRGs) formed on the polymer films were also investigated using illumination from a linearly polarized Kr⁺ laser beam.     

Storage stability of vacuum-dried probiotic bacterium Lactobacillus paracasei F19

There is still lack of the insight into the storage stability of dry probiotics produced by vacuum drying. Therefore, in this study we assessed the stability of a vacuum-dried Lactobacillus paracasei F19 under varying storage conditions. L. paracasei F19 was vacuum-dried with and without sorbitol and trehalose. The dried cells were stored at 4, 20 and 37 °C, and at a_w = 0.07, 0.22 and 0.33. The survival was determined by viable counts on MRS agar plates. The inactivation rate constants were determined for each storage condition. The survival after drying of cells dried without and with trehalose and sorbitol was 29, 70 and 54%, respectively. All vacuum-dried cells were very stable at 4 °C. However, high stability at non-refrigerated temperatures was obtained only in the presence of sorbitol. In contrast to sorbitol, the supplementation of trehalose did not stabilize cells during storage. This is supposedly due to the rapid crystallization of trehalose during storage. While glass transition temperatures of dry cell-sorbitol increased from ?32 °C to 12 °C during storage at 37 °C and a_w = 0.07, T_g of dry cell-trehalose (?15 °C after drying) could not be determined after storage for only 24 h. In conclusion, we showed that high stability of probiotic cells at non-refrigerated temperatures could be obtained by vacuum drying process with appropriate protectant.     

Contact residual stress relaxation in soda-lime glass: Part II. Aspects relating to strength recovery

Strength recovery of Vickers indented soda lime glass was measured and compared after annealing at two temperatures: one below and one above T_g. The atomic force microscope was used to study the cracks. At 540 °C, no changes were observed in crack morphology either below the surface or on the surface relative to the pre-anneal state. At 630 °C, both sub-surface and surface crack morphology changes were observed. The trends in strength recovery were compared with residual stress relaxation as measured by a new method of stress estimation based on nanoindentation elastic response. At short hold times at 630 °C, and regardless of the length of hold time at 540 °C, strength recovery of only ∼30% was measured while at moderately long hold times at 630 °C, strong recovery of fracture strength, ∼132% was measured. Trends in strength recovery above T_g are shown to match those of crack tip radius instead of trends in stress relaxation across the residual stress field.     

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.     

The design,synthesis and nonlinear optical properties of a novel,Y-type polyurethane containing tricyanovinylthiophene of high thermal stability

A novel, Y-type polyurethane containing 1-(2,4-dioxyethoxy)phenyl-2-{5-(2,2-dicyanovinyl)-2-thiophenyl}ethenes as nonlinear optical chromophores present within the polymer backbone, was prepared and characterized. The compound was soluble in common organic solvents and displayed thermal stability up to 260 °C and a glass transition temperature (T_g) of 163 °C. The second harmonic generation coefficient (d₃₃) of poled polymer films at the compound's fundamental wavelength of 1560 nm was ～3.72 × 10^?9 esu. Dipole alignment exhibited high thermal stability up to the T_g, and there was no decay in d₃₃ below 148 °C owing to the partial main-chain character of the polymer structure.     

Influence of polymer type on adhesion performance of a blended cement mortar

The purpose of this study was to examine the influence of various polymeric materials on the adhesion characteristics of a rapid setting, minimum defect mortar based upon a blend of calcium sulfoaluminate (CSA) cement and ordinary Portland cement (OPC). Four different polymer powders were added to the base mortar at a polymer/cement ratio (p/c) of 0.15. The water/cement (w/c) ratio remained constant for all mortars at 0.42. The polymeric materials consisted of an acrylic polymer powder with T_g=−10 °C, a styrene butadiene rubber (SBR) polymer powder with T_g=15 °C and two vinyl acetate/ethylene (VAE) polymer powders, one with T_g=−7 °C and the other with T_g=20 °C. Mortars were tested for direct tensile strength following ASTM C307 and pull-off strength following a variant of ASTM C1583 after curing for either 24 h or 13 days at ambient laboratory temperature of 23 °C. Mortars were cast over concrete, wood, metal and glass substrates. Pull-off tests over concrete substrate resulted in substrate failure for all polymer modified mortars. Pull-off tests cast over wood, glass and metal substrate materials highlighted the SBR polymer for demonstrating the poorest adhesion performance. Statistical analysis was performed with Minitab software.     

Solubility and diffusion coefficient of supercritical-CO2 in polycarbonate and CO2 induced crystallization of polycarbonate

The solubility and diffusion coefficient of supercritical CO₂ in polycarbonate (PC) were measured using a magnetic suspension balance at sorption temperatures that ranged from 75 to 175 °C and at sorption pressures as high as 20 MPa. Above certain threshold pressures, the solubility of CO₂ decreased with time after showing a maximum value at a constant sorption temperature and pressure. This phenomenon indicated the crystallization of PC due to the plasticization effect of dissolved CO₂. A thorough investigation into the dependence of sorption temperature and pressure on the crystallinity of PC showed that the crystallization of PC occurred when the difference between the sorption temperature and the depressed glass transition temperature exceeded 40 °C (T − T_g ≥ 40 °C). Furthermore, the crystallization rate of PC was determined according to Avrami's equation. The crystallization rate increased with the sorption pressure and was at its maximum at a certain temperature under a constant pressure.     

Decomposition of nonionic surfactant on a nitrogen-doped photocatalyst under visible-light irradiation

A visible-light-active N-containing TiO₂ photocatalysts were prepared from crude amorphous titanium dioxide by heating amorphous TiO₂ in gaseous NH₃ atmosphere. The calcination temperatures ranged from 200 to 1000 °C, respectively. UV–vis/DR spectra indicated that the N-doped catalysts prepared at temperatures <400 °C absorbed only UV light (E_g = 3.3 eV), whereas samples prepared at temperatures ≥400 °C absorbed both, UV (E_g = 3.10–3.31 eV) and vis (E_g = 2.54–2.66 eV) light. The chemical structure of the modified photocatalysts was investigated using FT-IR/DRS spectroscopy. All the spectra exhibited bands indicating nitrogen presence in the catalysts structure. The photocatalytic activity of the investigated catalysts was determined on a basis of a decomposition rate of nonionic surfactant (polyoxyethylenenonylphenol ether, Rokafenol N9). The most photoactive catalysts were those calcinated at 300, 500 and 600 °C. For the catalysts heated at temperatures of 500 and 600 °C Rokafenol N9 removal was equal to 61 and 60%, whereas TOC removal amounted to 40 and 35%, respectively. In case of the catalyst calcinated at 300 °C surfactant was degraded by 54% and TOC was removed by 35%. The phase composition of the most active photocatalysts was as follows: (a) catalyst calcinated at 300 °C—49.1% of amorphous TiO₂, 47.4% of anatase and 3.5% of rutile; (b) catalyst calcinated at 500 °C—7.1% of amorphous TiO₂, 89.4% of anatase and 3.5% of rutile; (c) catalyst calcinated at 600 °C—94.2% of anatase and 5.8% of rutile.     

Effects of heat treatment conditions on the structural and magnetic properties of MgCuZn nano ferrite

Mg_0.5Cu_0.05Zn_0.45Fe₂O₄ nanoparticles were prepared through sol–gel method using polyvinyl alcohol as a chelating agent. The as prepared sample was annealed at three different temperatures (500 °C, 700 °C and 900 °C). The phase formation, morphology and magnetic properties with respect to annealing temperature were studied using the characterisation techniques like X-ray diffraction (XRD) as well as Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM), respectively. The crystallite size and magnetisation showed increasing trend with annealing temperature. The coercivity increased up to a particular annealing temperature and decreased thereafter, indicating transition from single domain to multi domain state with increasing annealing temperature. Further, to know the suitability of the material, as a ferrite core, in multilayer chip inductors, the powder sample annealed at 500 °C was compacted in the form of torroids and sintered at three different temperatures (800 °C, 900 °C and 950 °C). The permeability showed increasing trend with the increase of sintering temperature since the permeability depends on microstructure. The frequency dispersion of permeability, for the sintered samples, demonstrated high frequency stability as well as high operating frequency. The cut-off frequency for the sintered samples 800 °C, 900 °C and 950 °C is 32 MHz, 30.8 MHz and 30.4 MHz, respectively.     

Screening of twelve Clostridium botulinum (group I) spores for high-pressure resistance at elevated-temperatures

Twelve strains of Clostridium botulinum group I spores, suspended in phosphate buffer (0.1 M) at approximately 10⁷ CFU/ml concentration, were subjected to high pressure treatments (800 and 900 MPa; 0.5–15 min) at elevated temperatures (90 and 100 °C). The treatments were chosen to have a range of pressure/temperature severity to be able to discriminate the spore strains for their pressure resistance. An insulated test chamber was used to achieve temperature stability during treatment. Preliminary tests showed the need for an 8 day anaerobic incubation for enumeration. Results showed that strains PA9508B, HO9504A and CK2-A had higher pressure resistance than others among the 12 strains studied. Strain 62A was least resistant and completely inactivated by the treatment. Estimated D values of the more resistant strains were in the 0.66–1.8 min range at 900 MPa at 100 °C treatment. The temperature sensitivity parameter (Z_P value) in the 800–900 MPa pressure range varied between 10 and 16 °C, and pressure sensitivity parameter (Z_T value) in the 90–100 °C temperature range varied between 340 and 760 MPa. The most pressure resistant strain was PA9508B with an estimated Z_P value of 16.0 °C and Z_T value of 470 MPa. Since the pathogenic strains of C. botulinum have different pressure resistance, the most resistance strain should be selected as the basis for process establishment.     

Single-source-precursor synthesis of soft magnetic Fe3Si- and Fe5Si3-containing SiOC ceramic nanocomposites

We present here the single-source-precursor synthesis of Fe₃Si and Fe₅Si₃-containing SiOC ceramic nanocomposites and investigation of their magnetic properties. The materials were prepared upon chemical modification of a hydroxy- and ethoxy-substituted polymethylsilsesquioxane with iron (III) acetylacetonate (Fe(acac)₃) in different amounts (5, 15, 30 and 50 wt%), followed by cross-linking at 180 °C and pyrolysis in argon at temperatures ranging from 1000 °C to 1500 °C. The polymer-to-ceramic transformation of the iron-modified polysilsesquioxane and the evolution at high temperatures of the synthesized SiFeOC-based nanocomposite were studied by means of thermogravimetric analysis (TGA) coupled with evolved gas analysis (EGA) as well as X-ray diffraction (XRD). Upon pyrolysis at 1100 °C, the non-modified polysilsesquioxane converts into an amorphous SiOC ceramic; whereas the iron-modified precursors lead to Fe₃Si/SiOC nanocomposites. Annealing of Fe₃Si/SiOC at temperatures exceeding 1300 °C induced the crystallization of Fe₅Si₃ and β-SiC. The crystallization of the different iron-containing phases at different temperatures is considered to be a consequence of the in situ generation of a Fe–C–Si alloy within the materials during pyrolysis. Depending on the Fe and Si content in the alloy, either Fe₃Si and graphitic carbon (at 1000–1200 °C) or Fe₅Si₃ and β-SiC (at T > 1300 °C) crystallize. All SiFeOC-based ceramic samples were found to exhibit soft magnetic properties. Magnetization versus applied field measurements of the samples show a saturation magnetization up to 26.0 emu/g, depending on the Fe content within the SiFeOC-based samples as well as on the crystalline iron silicide phases formed during pyrolysis.     

Effects of Ta-substitution on the dielectric properties of Ba6Ti2(Nb1−xTax)8O30 thin films

Tunable Ba₆Ti₂(Nb_1−xTa_x)₈O₃₀ (BTN-xTa; x = 0, 0.25, 0.4) thin films with a tetragonal tungsten bronze structure (TTB) were deposited on platinized Si substrates using the pulsed laser deposition (PLD) technique and their properties were investigated from the viewpoint of orientation and ferroelectric phase transition. Crystal structures and dielectric properties were characterized using an X-ray diffractometer and an impedance analyzer. Pure BTN (BTN-0Ta) thin films showed tunability as high as 60% and the tunability decreased as the amounts of Ta-substitution increased at 150 kV/cm and at 1 MHz. The dielectric constants also decreased from 436 to 88 at 1 MHz through the Ta-substitution. The low tunability and dielectric constants of Ta-substituted thin films were mainly ascribed to the lowered ferroelectric transition temperature (T_c). Ferroelectric BTN (BTN-0Ta) thin films may have been changed into a paraelectric state through the Ta-substitution since the T_c of BTN thin films were shifted to temperatures far below room temperatures (approximately −60 °C).     

Studying structure–property relationships in oligomeric engineering thermoplastics by controlled preparation of low molecular weight polymers

The preparation of a series of oligomeric engineering thermoplastics (PS, PES, PEI and PAI) is reported. ¹H and ¹³C NMR and FT-IR/ATR spectroscopic techniques are combined to determine the chemical structure of the synthetic polymers, which are produced in good yield and purity. GPC measurements show the weight average molecular weight (M_w) of the synthesised thermoplastics fall in the range 5454–33,866 g mol⁻¹ and display polydispersity indices in the range 1.33–1.82. Glass transition temperatures (T_g) values measured by DSC, occur between 107 and 257 °C and fall in the pattern PS < PES < PEI < PAI. Molecular simulation is used to probe the structure property relationships displayed by PS and PES and reproduces the elastic properties of PS well within the range of the literature; while the values of PES are less well reproduced. The simulated T_g values of both oligomers agree well with those obtained empirically using DSC.     

Study of high glass transition temperature thermosets made from the copper(I)-catalyzed azide–alkyne cycloaddition reaction

Thermal properties of polymers made from the copper(I)-catalyzed cycloaddition reaction between azides and alkynes have been investigated. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to measure the glass transition temperatures (T_g) of these materials. The polymers were found to have unusually high T_g values, up to 60 °C higher than the curing temperature. It has been shown that the increase of T_g was time dependant, thus, depending on the state of cure of the material.     

Microstructure and mechanical properties of SiC-SiC joints joined by spark plasma sintering

The development of reliable joining technology is of great importance for the full use of SiC. Ti₃SiC₂, which is used as a filler material for SiC joining, can meet the demands of neutron environment applications and can alleviate residual stress during the joining process. In this work, SiC was joined using different powders (Ti₃SiC₂ and 3Ti/1.2Si/2C/0.2Al) as filler materials and spark plasma sintering (SPS). The influence of the joining temperature on the flexural strength of the SiC joints at room temperature and at high temperatures was investigated. Based on X-ray diffraction and scanning electron microscopy analyses, SiC joints with 3Ti/1.2Si/2C/0.2Al powder as the filler material possess high flexural strengths of 133 MPa and 119 MPa at room temperature and at 1200 °C, respectively. The superior flexural strength of the SiC joint at 1200 °C is attributed to the phase transformation of TiO₂ from anatase to rutile.     

Preparation and catalytic activity of K4Zr5O12 for the oxidation of soot from vehicle engine emissions

Pure phase K₄Zr₅O₁₂ is synthesized via solid state method in the present work. Various K/Zr ratios and temperatures are applied, and the synthesis process is investigated in detail by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Its catalytic activity for soot oxidation is studied by temperature programmed oxidation with different types of soot/catalyst contacts. It is revealed that K₄Zr₅O₁₂ is very active in the presence of 2–10% O₂ for both tight and loose contacts (T_p(tight) = 335 °C, T_p(ethanol) = 355 °C and T_p(shaking) = 370 °C). Thermal stability study shows that K₄Zr₅O₁₂ is highly stable up to at least 900 °C.     

The production of amorphous regions in carbon nanotubes by 140 keV He ion irradiation

The production of amorphous regions in carbon nanotubes irradiated with 140 keV He ions was studied using Raman spectroscopy and transmission electron microscopy (TEM). Intensity ratios of Raman D to G bands (I_D/I_G) initially increase and then decrease as a function of ion fluence at all investigated irradiation temperatures (room temperature, 200 and 400 °C). The critical ion fluences corresponding to the maximum in I_D/I_G ratios increase with increasing irradiation temperature because of the enhanced defect annealing. The displacement per atom (dpa) values, consistent with a maximum in I_D/I_G ratios, are determined to be 0.15 dpa at room temperature and 200 °C, and 0.3 dpa at 400 °C. TEM examination of all irradiated specimens supports Raman results indicating that the maximum in I_D/I_G correlates to the formation of amorphous regions. The study shows that after formation of amorphous regions at high fluences, I_D/I_G ratio can be no longer used to measure amorphous/graphitic content in CNTs.