Rheological and thermal properties of stereocomplexed polylactide films

Poly(l-lactide) (PLLA) and Poly(d-lactide) (PDLA) blended films (PLLA/PDLA) were prepared (5/95; 25/75; 50/50, and 75/25) by solvent casting method. Blend of PLLA and PDLA of medium molecular mass led to the formation of stereocomplex which was evidenced by differential scanning calorimetry, rheological measurement and Fourier transform infrared spectroscopy. The stereocomplex had a higher melting temperature (T _m) (more than 50 °C) and crystallized at higher temperature (T _c) (more than 25 °C) from the melt compared to neat PLLA and PDLA. The T _m and T _c gradually decreased with increasing the number of thermal scans. The enthalpy of fusion (?H_m) for stereocomplex crystallites in 50/50 blend films was the highest than that of homo-crystallites. Rheological measurement at a temperature of 180–195 °C revealed that the neat PLA was predominantly liquid-like behavior (G″ > G′) which transformed to extreme solid-like behavior by incorporation of PDLA into PLLA. Among blends, 50/50 PDLA/PLLA showed the maximum mechanical strength (G′) followed by 25/75, 75/25, and 5/95 blends. The significant increase in mechanical strength is believed to be attributed by stereocomplex formation by blends. Thermal and rheological data supported higher mechanical strength and an increase in melting and crystallization temperature adequately.     

Thermal stability,morphology and electronic band gap of Zn(NCN)

The thermal behavior of zinc carbodiimide Zn(NCN) was examined in the temperature range between 200 and 1100 °C in Ar atmosphere. The material starts to partially decompose at about 800 °C. Heat treatment at temperatures beyond 800 °C results in the formation of the byproducts nitrogen-containing bamboo-like multiwall carbon-nanotubes of 20–50 nm in diameter due to a partial decomposition of Zn(NCN) into dicyan (CN)₂, zinc and nitrogen gas followed by the polymerization of the former product to paracyanogen (CN)_n. At 1100 °C, the yield of the residual carbodiimide depends on the dwelling time and the initial amount of powder used for pyrolysis. One hour dwelling at 1100 °C yields ∼50% of the Zn(NCN) separated as pure material. Temperature-induced change in the band structure, namely indirect-to-direct band gap transition, is registered when compared the Zn(NCN) at room temperature with the residual material annealed at 1100 °C. The transition from indirect (E_g = 4.32 eV) to direct band gap (E_g = 4.93 eV) is due to the thermal annealing process which results in healing of crystal defects.     

Synthesis of soluble,thermosetting polymides derived from 1,4-phenylenebis(phenylmaleic anhydride) and aromatic diamines

The dianhydride monomer 1,4-phenylenebis(phenylmaleic anhydride) was polymerized with various aromatic diamines in a one-step solution polymerization to afford high molecular weight, soluble polyimides containing backbone phenylmaleimide structures. The polymides were soluble in amide solvents, chlorinated hydrocarbons, and tetrahydrofuran at 25°C at a concentration of 15% (w/v), displayed molecular weight distributions (M_w/M_n) of 2.0–2.2 as determined by absolute GPC and showed T_g values of 240°C and above as measured by differential scanning calorimetry. In addition, polyimide thermosets were prepared from these materials by thermal cure at 350–360°C. The crosslinked polyimides displayed T_gs 20–25°C higher than their soluble precursors, and chloroform extraction indicated gel fractions ranging from 74–100% after cure. © 1994 John Wiley & Sons, Inc.     

Calorimetric analysis of the multiple melting behavior of melt-crystallized poly(l-lactic acid) with a low optical purity

The polymorphous crystallization and multiple melting behavior of poly(l-lactic acid) (PLLA) with an optical purity of 92 % were investigated after isothermally crystallized from the melt state by wide-angle X-ray diffraction and differential scanning calorimetry. Owing to the low optical purity, it was found that the disordered (α′) and ordered (α) crystalline phases of PLLA were formed in the samples crystallized at lower (<95 °C) and higher (≥95 °C) temperatures, respectively. The melting behavior of PLLA is different in three regions of crystallization temperature (T _c) divided into Region I (T _c < 95 °C), Region II (95 °C ≤ T _c < 120 °C), and Region III (T _c ≥ 120 °C). In Region I, an exothermic peak was observed between the low-temperature and high-temperature endothermic peaks, which results from the solid–solid phase transition of α′-form crystal to α one. In Region II, the double-melting peaks can be mainly ascribed to the melting–recrystallization–remelting of less stable α crystals. In Region III, the single endotherm shows that the α crystals formed at higher temperatures are stable enough and melt directly without the recrystallization process during heating.     

Orientation and structural development of semicrystalline poly(lactic acid) under uniaxial drawing assessed by infrared spectroscopy and X-ray diffraction

The effects of drawing temperature (T_d) and draw strain on the orientation and structure of semicrystalline poly(lactic acid) (PLA) films were investigated by wide angle X-ray diffraction and polarized Fourier transform infrared spectroscopy. Semicrystalline PLA samples with two initial levels of crystallinity, X_c = 1% and 11%, were prepared by cold crystallization at 80 ^°C. Whatever X_c and T_d, the total amount of the ordered phases (i.e. crystalline + mesophase) increased with draw strain, which could be ascribed to the formation of strain-induced mesophase at T_d = 60 or 70 ^°C but crystalline at 80 ^°C. Also, the molecular orientation of both the amorphous and ordered phases increased with draw strain. Whatever X_c, the orientation of the ordered phases was insensitive to T_d, whereas higher orientation in the amorphous phase was achieved at lower T_d, and the trend was more significant for X_c = 1% compared with 11%.     

Molecular characterization of Ulex europaeus biochar obtained from laboratory heat treatment experiments – A pyrolysis–GC/MS study

Gorse species (Ulex sp.) are ubiquitous in the shrublands of NW Spain and have the potential to become key players in an integral biofuel/biochar program in NW Spain. Here we present molecular characterization (using pyrolysis–GC/MS) of a biochar “thermosequence” obtained by laboratory heating of Ulex europaeus wood in a muffle furnace between 200 and 600 °C (T_CHAR). Low temperature chars (T_CHAR ≤ 350 °C) produced significant amounts of pyrolysis products of which the precursor biopolymer could be recognized, while high-temperature chars (T_CHAR ≥ 400 °C) produced mainly phenols and monocyclic and polycyclic aromatic hydrocarbons, which are not specific for any biopolymer. Carbohydrate could hardly be recognized at T_CHAR ≥ 350 °C. The thermal rearrangement of polyphenols, mainly lignin, was reflected in more detail (1) C₃-side chain shortening and probably depolymerization (T_CHAR 200–350 °C), (2) demethoxylation of syringyl and probably also some guaiacyl lignin (T_CHAR 300–400 °C), (3) elimination of virtually all remaining methoxyl groups (T_CHAR 350–400 °C), through dehydroxylation and demethoxylation, (4) almost complete dehydroxylation of lignin and other biopolymers (T_CHAR 400–500 °C), (5) progressive condensation into polyaromatic structures (T_CHAR 300–500 °C) and (6) partial elimination of alkyl bridges between (poly)aromatic moieties (T_CHAR 450–500 °C). These results were supported by Fourier transform infrared spectroscopy (FTIR) of the same samples. We conclude that pyrolysis–GC/MS can be used as a rapid molecular screening method of gorse-derived biochar. Molecular properties elucidation is an essential part of predicting the stability and agronomical behavior of gorse-derived biochar after future implementation in soils.     

Deep eutectic silsesquioxane hybrids with quaternary ammonium/urea derivatives: synthesis and physicochemical and ion-conductive properties

We report the synthesis of deep eutectic silsesquioxane hybrids (DE-SQs) by simple mixing of quaternary-ammonium-containing SQ and urea derivatives. Cationic SQ, which was prepared by the hydrolytic condensation of a triethoxysilane precursor derived from 2-(dimethylamino)ethyl acrylate, followed by a quaternization reaction with methyl iodide, was used as a quaternary-ammonium-containing SQ component. Cationic SQ reacted with urea at a 1:2 M ratio at 80 °C for 48 h to yield a viscous DE-SQ (2Urea) liquid with a low glass transition temperature (T_g = ?11 °C). Urea derivatives—1,3-dimethylurea (DMU) and 1,3-dimethylthiourea (DMTU)—were additionally used as hydrogen bond donors to form low-T_g DE-SQs. The thermal, physical, and ion-conductive properties of the DE-SQ family of organic–inorganic hybrids were investigated and characterized, and the influences of the nature of the urea derivative and their feed ratios on DE-SQ formation were evaluated. Among the DE-SQs developed in this study, DE-SQ (2Urea) and DE-SQ (2DMTU) achieved the highest ionic conductivity, with DE-SQ (2Urea) exhibiting 2.35 × 10^?6 and 6.63 × 10^?4 S cm^?1 at 25 and 75 °C, respectively, under anhydrous conditions. This is the first report on the synthesis of DE-SQs by simple mixing of two solids, wherein the resulting compounds exhibit low T_g, thermal stability, and characteristic ionic conductivity. The ability to incorporate unique DE units into the SQ structure facilitates the development of advanced organic–inorganic hybrid materials possessing a wide range of functions and applications.     

Preferential crystallization in an unusual case of conglomerate with partial solid solutions

Ethanolamine mandelate (E.M.) crystallizes as a stable conglomerate and has been found to form partial solid solutions. The crystal structure of the pure enantiomer has been solved from single-crystal X-ray diffraction. In order to determine the extreme compositions of the partial solid solutions in equilibrium (87% ee), the isothermal ternary section in the system [(+)-E.M.–(−)-E.M.–(ethanol–water azeotropic mixture)] was established at 25 °C. Several consecutive preferential crystallization attempts (AS3PC method) were undertaken between T_B = 41 °C (starting temperature) and T_F = 25 °C (final temperature) on a 2-L scale.We initially expected to obtain crude crops whose enantiomeric purities would be close to that defined by the isothermal ternary phase diagram (T_F). In fact, the filtered solid phases are of lower enantiomeric excesses: ca. 62% ee. The monitoring of the mother liquor composition over the course of the entrainment shows that the enantiomeric composition of the filtered solid is related to the metastable equilibria involved in the preferential crystallization.     

Water splitting as a tool for obtaining insight into metal–support interactions in catalysis

This review is focused on the use of the water splitting reaction for characterizing oxygen vacancies in supported metal catalysts and more generally to get insight into the high-temperature modifications of metal–support interactions. Three supports widely used in catalysis are considered, namely alumina, silica and ceria. The catalysts were reduced at temperatures T_R ranging from 200 to 1000 °C. The reaction with water was carried out at temperatures T_OX ranging from 100 to 1000 °C. In every case, the metal (Rh or Pt) was chosen among those which are not oxidizable by water. Extensive investigations of the reactivity of water with unsupported metals and films confirmed this choice. The reaction is then selective for the titration of O vacancies, generally associated with reduced cations of the support. On alumina-supported catalysts, reduction at T_R > 600 °C leads to the formation of oxygen vacancies strictly confined to the periphery of metal particles. The amount of hydrogen produced Q_H is coherent with the peripheral oxygen density. Reduction of silica-supported catalysts at T_R > 600 °C generates metal silicides that can be selectively destroyed by water with reformation of silica and metal nanoparticles. Oxygen vacancies are formed on ceria catalysts at 200 °C. These oxygen vacancies are confined to the surface up to 600 °C. At higher temperatures, oxygen vacancies are formed in the bulk: about 50% of CeO₂ would be reduced at 900 °C. The amount of H₂ produced by reaction with water is thus very high on metal-ceria catalysts. At T_R > 900 °C, metal cerides start to form. Remarkably, a significant reactivity of H₂O on a Rh/CeO₂ catalyst reduced at 850 °C is recorded as of 100 °C. However, the quantitative titration of oxygen vacancies required temperatures T_OX > 500 °C. As a rule, the technique of water splitting allows the detection of 1 μmol g⁻¹ of oxygen vacancies, i.e. a few 0.1% of the surface in the case of reducible oxides of 10–20 m² g⁻¹.     

Low temperature synthesis of ferromagnetic (LaK)MnO3 from KCl,KBr and KI fluxes

Potassium doped lanthanum manganites have been synthesized from KCl, KBr and KI fluxes at 900, 850 and 750 °C respectively. While all the flux-grown oxides are ferromagnetic metals (T_c=290–330 K), the oxides grown from KCl and KBr fluxes crystallize in the rhombohedral structure and that synthesized from KI flux adopts the cubic structure. The enhancement in T_c correlates with the increasing tendency of the flux to get oxidized and decreasing melting points of the flux. Nearly stoichiometric (LaK)MnO₃ with 33 % of Mn⁴⁺ concentration could be prepared at temperature as low as 750 °C. Composition of all the phases have been obtained from the chemical analysis of the elements present.     

Synthesis of borosiloxane/polybenzoxazine hybrids as highly efficient and environmentally friendly flame retardant materials

A series of novel borosiloxane/polybenzoxazine hybrids were synthesized through the copolymerization of 3,3′‐phenylmethanebis(3,4‐dihydro‐2H‐1,3‐benzoxazine) and phenol‐functionalized borosiloxane (BSi‐OH) oligomer. The structures were characterized using nuclear magnetic resonance and fourier transform infrared. The thermal and flame retardant properties of hybrids were investigated by dynamic mechanical analysis, thermogravimetric analysis, and oxygen index instrument. The results showed that the addition of BSi‐OH oligomer is not only highly efficient in environmentally friendly flame retardancy of polybenzoxazine, but also enhances its thermal property. Only 25 wt % content of BSi‐OH oligomer was able to increase the glass transition temperature, 5% weight loss temperature (T_d5), 10% weight loss temperature (T_d10), and limited oxygen index (LOI) value from original 211 °C, 374 °C, 395 °C, and 29.5 °C to 244 °C, 408 °C, 448 °C, and 40.1, respectively. This work provides a facile and useful method for the preparation of new polybenzoxazines possessing highly efficient and environmentally friendly flame retardance as well as heat resistance. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2390–2396     

Synthesis and properties of poly(isosorbide 2,5-furandicarboxylate-co-ε-caprolactone) copolyesters

Bio-based poly(isosorbide 2,5-furandicarboxylate-co-ε-caprolactone) (PIFCL) copolyesters were synthesized from 2,5-furandicarboxylic acid, isosorbide and ε-caprolactone. The obtained copolyesters were characterized by ¹H NMR, ¹³C NMR, intrinsic viscosity, GPC, DSC, TGA and tensile testing. The NMR characterization results confirmed the insertion of lactones units into poly(isosorbide 2,5-furandicarboxylate) (PIF) chains. All PIFCL copolyesters were amorphous with T_{D, 5%} higher than 300 °C. The glass transition temperatures of PIFCLs with FDCA molar ratio from 74% to 45% were within the range of 132.1 °C and 72.4 °C. Tensile testing revealed that introduction of ε-caprolactone into PIF chain imparted PIFCL with excellent mechanical performance, typically, PIFCL polyseter with FDCA molar ratio of 45% had a Young's modulus 858 ± 92 MPa, a tensile strength 44 ± 4 MPa and an elongation at break 480 ± 45%.     

Dimorphic cerium(III) oxoarsenate(III) Ce[AsO3]

Colourless, water- and air-stable single crystals of cerium(III) oxoarsenate(III) Ce[AsO₃] were prepared by the reaction of cerium metal (Ce) and arsenic sesquioxide (As₂O₃) in the presence of cesium chloride (CsCl) as fluxing agent at 750 °C in an evacuated silica ampoule. Ce[AsO₃] crystallizes monoclinically (a = 902.89(8), b = 782.54(7), c = 829.68(7) pm, β = 103.393(3)°, Z = 8) in the space group P2₁/c and is isotypic with α-Pb[SeO₃]. There are two crystallographically different Ce³⁺ positions. (Ce1)³⁺ is coordinated by nine oxygen atoms (d(Ce–O) = 244–286 pm) and (Ce2)³⁺ by only eight (d(Ce–O) = 239–273 pm). Both crystallographically different As³⁺ cations form discrete ψ¹ tetrahedra [AsO₃]³⁻ (d(As–O) = 174–179 pm), which are attached to the Ce³⁺ cations via edges and corners. The second monoclinic modification of Ce[AsO₃] with the lattice parameters a = 439.32(4), b = 529.21(5), c = 617.34(6) pm and β = 105.369(3)° with Z = 2 was obtained by high-pressure synthesis (11 GPa, 1200 °C) and has both a higher density (6.31 vs. 6.13 g · cm⁻³) and a higher calculated Madelung part of the lattice energy (15,155 vs. 15,132 kJ · mol⁻¹). It adopts the space group P2₁/m, crystallizing isotypically with La[AsO₃], β-Pb[SeO₃], Pb[SO₃] (scotlandite) or K[ClO₃] and exhibits nine-fold coordinated Ce³⁺ cations exclusively (d(Ce–O) = 254–287 pm) along with tripodal [AsO₃]³⁻ anions (d(As–O) = 175–176 pm). Raman spectroscopy on both phases of Ce[AsO₃] shows stretching vibrations between 769 and 731 cm⁻¹ as well as asymmetric vibrations in the range of 659–617 cm⁻¹. The symmetric bending mode vibrations emerge in an interval from 340 to 410 cm⁻¹ and the asymmetric bending modes range between 230 and 290 cm⁻¹.     

Moisture sorption isotherms of whole and fractionated date-pits: Measurement and theoretical modelling

Moisture sorption properties of whole date-pits (WDP) and three fractionated date-pits; defatted date-pits (DDP), residue (REP) and supernatant (SUP) fractions were studied. Sorption isotherms were measured using Differential Thermal and Humidity chamber at different temperatures (10, 30, 50, 70 and 90 °C) and relative humidity ranged from 0.05 to 0.9. Crossovers of isotherm curves were observed for all fractions between different temperatures. At 30 °C, BET-monolayers of WDP, DDP, REP and SUP were 4.9, 4.2, 3.8 and 3.2 g/100 g ds, respectively. The complete isotherms (i.e. 0.05–0.90 water activity) were modelled by GAB with high coefficient of determination (i.e. 0.944 to 0.999). In the cases of WDP and DDP, the isosteric heat plots showed increasing trends with the decreased moisture and peaks at moisture 0.025 and 0.040 g/100 g ds. Unlike all fractions, DDP isokinetic temperatures T_is (i.e. 97.4 °C) was lower than isobound temperatures T_ib (i.e. 145.0 °C) indicating complete removal of bound water occurred at higher temperature as compared to the temperature when all reactions reached at the same. The moisture sorption isotherm characteristics could be used in determining the end point of drying and storage stability as well as packaging design of the date-pits and their fractions.     

Crystallization kinetics, melting behavior, and RAP of novel etheroatom containing naphthyl polyesters

The changes in crystalline phase of poly(butylene naphthalate) (PBN), poly(diethylene naphthalate) (PDEN) and poly(thiodiethylene naphthalate) (PTDEN) upon thermal treatments were evaluated by X-ray diffraction technique. The melting behavior and the crystallization kinetics of the polymers under investigation were investigated by means of differential scanning calorimetry. Multiple endotherms were evidenced in PBN and PTDEN, due to melting and recrystallization processes. By applying the Hoffman?CWeeks?? method, the T _m° of PBN, PDEN, and PTDEN was derived: the introduction of ethero-atoms along PBN polymer chain causes a decrement of T _m° value. The isothermal crystallization kinetics was analyzed according to the Avrami??s treatment: the presence of ether-oxygen or sulphur atoms in the chain deeply reduces the PBN ability of crystallizing. Finally, no interphase was evidenced both in PDEN and PTDEN.     

Homopolyimides containing both benzimidazole and benzoxazole with high Tg and low coefficient of thermal expansion

A pair of isomer diamines containing both benzimidazole and benzoxazole and derived homopolyimides were synthesized for the first time. Due to rich rigid and linear benzoazole units, as well as the strong intermolecular interactions from the hydrogen bonding and the charge transfer complexation (CTC), the obtained polyimides (PIs) exhibited outstanding thermal properties, including high thermal weight loss temperature (T_d5% = 540–561°C), high glass transition temperature (T_g = 392–421°C), and low coefficient of thermal expansion (CTE = 1.3–20.9 ppm/°C). In addition, the obtained PIs also showed ideal mechanical properties (T_S = 189–240 MPa, T_M = 4.1–5.0 GPa and E_B = 2.9%–4.7%). These potential novel PI films with high T_g and low CTE were expected to be applied to next generation of flexible display substrate material.     

Thermal,IR, Raman characteristics,Raman gain coefficient and bandwidths in quaternary glasses

Tellurite glasses with composition 75TeO₂–5WO₃–15Nb₂O₅–5M_xO_y in mol%, where M_xO_y = (Na₂O, Ag₂O, ZnO, MgO, CuO, NiO, TiO₂, MnO₂) have been prepared by using the conventional melt-quenching method. Thermal characteristic of prepared glasses were investigated by using DTA techniques. It was found that the glass with the composition 751TeO₂–5WO₃–15Nb₂O₅–5TiO₂ had high thermal stability (ΔT = 122 °C at heating rate 15 K/min). Raman gain coefficients and bandwidths of prepared glasses for Raman gain media were evaluated. The glass with composition 75TeO₂–5WO₃–15Nb₂O₅–5Na₂O had the maximum value of Raman gain coefficient (g = 4.43 × 10⁻¹² m/W) and it was 24 times as large as silica glass. The highest value of full width half maximum (FWHM ≈ 185 cm⁻¹) was observed in glass system 75TeO₂–5WO₃–15Nb₂O₅–5NiO. Finally, the structure of the glasses was investigated through deconvolution Raman and IR spectra.     

Thermal behavior and kinetic modeling of (NH4)4UO2(CO3)3 decomposition under non-isothermal conditions

The thermal behavior and kinetic analysis of ammonium uranyl carbonate decomposition has been studied in inert gas, O₂, and 90%Ar–10%H₂ atmospheres under non-isothermal conditions. The results showed a dependence on specific surface area with the decomposition temperature of ammonium uranyl tri-carbonate (AUC). Specific surface area increases and reaches a maximum between 300 and 400 °C and decreases at T > 400 °C. The reaction paths of AUC decomposition under the three atmospheres were proposed. The integral methods Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) were used for the kinetic analysis. The activation energy averages are 58.01 and 56.19 kJ/mol by KAS and FWO methods, respectively.

     

Tailoring thermoresponsive nanostructured poly(N-isopropylacrylamide) hydrogels made with poly(acrylamide) nanoparticles

The thermoresponsive behavior and mechanical properties of nanostructured hydrogels, which consist of poly(acrylamide) nanoparticles embedded in a cross-linked poly(N-isopropylacrylamide) hydrogel matrix, are reported here. Nanostructured hydrogels exhibit a tuned volume phase transition temperature (T _VPT), which varies with nanoparticle content in the range from 32 up to 39–40 °C. Moreover, larger equilibrium water uptake, faster swelling and de-swelling rates, and larger equilibrium swelling at 25 °C were obtained with nanostructured hydrogels compared with those of conventional ones. Elastic and Young’s moduli were larger than those of conventional hydrogels at similar swelling ratios. The tuned T _VPT and the de-swelling rate were predicted with a modified Flory–Rehner equation coupled with a mixing rule that considers the contribution of both polymers. These behaviors are explained by a combination of hydrophilic/hydrophobic interactions and by the controlled inhomogeneities (nanoparticles) introduced by the method of synthesis.     

Effect of silver content on the phase transition and electrical properties of 0.95[(K0.5Na0.5)NbO3]–0.05LiSbO3 ceramics

Lead free 0.95[(K_0.5Na_0.5)_1−xAg_xNbO₃]–0.05LiSbO₃ (KNAN–LS) ceramics with x = 0, 0.02, 0.04, 0.06 and 0.08 have been synthesized by conventional solid state reaction route (CSSR). X-ray diffraction (XRD) analysis confirmed the transformation of mixed structure to pure tetragonal structure with the increase in Ag content in KNN–LS ceramics. The Curie temperature (T_c) of the ceramics decreased from 385.5 °C to 331 °C with the increase in silver (Ag) content. The poling temperature was optimized for better piezoelectric properties. The KNAN–LS ceramics with x = 0.06 showed better piezoelectric and ferroelectric properties (d₃₃ = 227 pC/N, k_p = 42.5%, T_c = 368 °C and P_r = 21.9 μC/cm²).