Influence of Poly(ε‐caprolactone) Molecular Weight and Coumarin Amount on Photo‐Responsive Polyurethane Properties

Photo‐reversible polyurethane (PU) coatings based on coumarin diol (CD) are obtained. Initially, pre‐polymers based on different amounts of coumarin (5, 15, and 25 mol%) and 1,6‐hexamethylene diisocyanate are prepared to obtain PUs with a large incorporation of CD and high molecular weight. The pre‐polymer is posterior reacted with poly(ε‐caprolactone) diol (PCL‐diol), either with molecular weight = 530 or 2000 g mol^–1. The thermal stabilities of the PUs are studied using thermogravimetric analysis. Polymers with a higher content of CD present higher stability. The thermal transitions and the mechanical response are analyzed using differential scanning calorimetry and strain‐stress tests, respectively. Moreover, the photo‐reversibility of CD‐based PUs is followed by UV absorption. In general, photo‐dimerization induces better mechanical properties of the final PUs. Materials obtained with short PCL‐diol ( = 530 g mol^–1) and the highest amount of CD present higher reversibility processes. Therefore, these polymers are promising for application as coating systems.

     

Mechanical,Tribological, and Thermal Properties of Hot‐Pressed ZrB2‐B4C Composite

The effect of addition of submicrometer‐sized B₄C (5,10 and 15 wt%) on microstructure, phase composition, hardness, fracture toughness, scratch resistance, wear resistance, and thermal behavior of hot‐pressed ZrB₂‐B₄C composites is reported. ZrB₂‐B₄C (10 wt%) composite has V_H1 of 20.81 GPa and fracture toughness of 3.93 at 1 kgf, scratch resistance coefficient of 0.40, wear resistance coefficient of 0.01, and ware rate of 0.49 × 10^?3 mm³/Nm at 10N. Crack deflection by homogeneously dispersed submicrometer‐sized B₄C in ZrB₂ matrix can improve the mechanical and tribological properties. Thermal conductivity of ZrB₂‐B₄C composites varied from 70.13 to 45.30 W/m K between 100°C and 1000°C which is encouraging for making ultra‐high temperature ceramics (UHTC) component.     

Structural and Mechanical Properties Changes of Ethylene‐α‐olefin Copolymer Blends Induced by Thermal Treatments and Composition

Summary: Blends of single‐site catalysed ethylene‐α‐butene (C₄VLDPE) and ethylene‐α‐octene (C₈VLDPE) copolymers were prepared by melt extrusion. The phase morphology, thermal and mechanical properties of the blends have been investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), tensile test and dynamic mechanical analysis (DMA). Depending on the composition and thermal history, significant differences in structure and behaviour were found. It was also found that some degree of co‐crystallization occurred for quenched blends; whereas most of the oven slowly cooled blends showed two well‐defined melting peaks, indicating that the slow cooling favoured partial segregation of the fractions with different degrees of branching to form two morphologies. Moreover, SEM revealed morphology of the thinner crystals distributed in‐between the thicker sheaf‐like crystals for the slowly cooled blends with 20–50% C₈VLDPE. Therefore, the synergism in mechanical properties for the blends with 20–50% C₈VLDPE is due to a combination of larger crystal size, more complete phase separation and interfacial interaction produced by the segregation effect of the slow cooling treatment. DMA studies showed that the storage modulus increased as the addition of C₈VLDPE and modulus for the slowly cooled blends are about twice those measured for the quenched ones, indicating higher stiffness of the blends. The smooth shift of β relaxation temperature with addition of C₈VLDPE for both sets of blends confirmed the miscibility in the amorphous phase.

SEM image of the C₄VLDPE‐C₈VLDPE (50/50) blend after oven slow cooling treatment.     

BaSO4‐, CaF2‐, and Al‐Maleate‐Derived Nanocomposite Coatings with Excellent Mechanical,Thermal, and Optical Properties

Acrylate‐based nanocomposite coatings prepared from uniformly sized, nanoscaled inorganic, i.e., BaSO₄‐ and CaF₂‐ as well as organometallic, i.e., Al‐maleate‐derived nanoparticles were prepared applying photochemical curing. Excellent mechanical and thermal stability as well as high optical transparency was achieved as compared to standard SiO₂‐based coatings. The performance of CaF₂‐based nanocomposites could be further enhanced by addition of nanocorundum. A comprehensive data set on surface and Martens hardness, the penetration depths, glass transition temperatures, and UV–Vis transparency of the final coatings is presented.

     

Thermal and Mechanical Properties of Poly(arylene ether ketone)s Based on 5‐tert‐Butyl‐1,3‐bis(4‐fluorobenzoyl)benzene

An aromatic bishalide, 5‐tert‐butyl‐1,3‐bis(4‐fluorobenzoyl)benzene ( 2 ) was synthesized in high yield and purity by the reaction of 5‐tert‐butylisophthaloyl chloride ( 1 ) and fluorobenzene and polymerized by nucleophilic substitution reaction with commercially available aromatic bisphenols to prepare a series of high molecular weight poly(arylene ether ketone)s containing pendant tertiary butyl groups. The effect of molecular structure on the physical, thermal, mechanical and adhesion properties of the polymers was investigated.     

Mechanical Properties and Reliability of Li2O‐Stabilized β″‐Alumina Ceramics: Effect of Synthesizing Method

Li₂O‐stabilized β″‐alumina powder has been synthesized by the solid‐state and double‐zeta processes. It was shown that by the double‐zeta process, the β″‐alumina fraction of sintered samples was 10% higher, showing around 99% of β″‐alumina fraction. Using β″‐alumina powder produced by the double‐zeta process, the sintered density improved, microstructure was more uniform and leads to improvement in hardness, strength and Weibull modulus due to more uniform microstructure and absence of abnormal grain growth. The higher fracture toughness of the solid‐state‐processed samples could be due to crack deflection mechanism.     

The Effect of α‐Zirconium Phosphate Nanosheets on Thermal,Mechanical, and Tribological Properties of Polyimide

In this work, to investigate the addition effect of 2D α‐zirconium phosphate (α‐ZrP) nanosheets on the properties of polyimide (PI), a series of PI/ZrP composites are synthesized by in situ polymerization. The thermal, mechanical, and tribological properties of composites strongly depend on the dispersity and distribution of α‐ZrP nanosheets in the PI matrix. The dispersed α‐ZrP can make rich interfacial interactions with PI matrix, which facilitates the transfer of external stress, heat, antiwear ability, etc., from the PI matrix to the surface of the α‐ZrP nanosheets, leading to the obvious enhancements of the thermal, mechanical, and tribological properties of the PI/ZrP composites. Specially, compared with pure PI, the tensile strength and elongation at break of the optimum sample of PI‐0.6 are increased by 13.7% and 35.7%, while its wear volume is reduced by 85%. This work provides a new paradigm for using other layered 2D nanosheets to prepare high‐performance PI‐based composite materials.     

Correlation between the fracture toughness and β‐crystal fraction in a β‐nucleated propylene‐based propylene–ethylene random copolymer

Propylene‐based propylene–ethylene random copolymer (PPR) has been widely used in the production of hot‐water pipes. To further improve its toughness and thermal resistance, β‐nucleating agents (β‐NAs) are frequently incorporated. In this study, PPR containing 5.6 mol % ethylene units was modified by two kinds of β‐NAs, that is, calcium pimelate and N,N′‐dicyclohexylterephthalamide. The notched Izod impact strength of PPR increased with the addition of the β‐NAs. Drastically different toughening effects were found between the two β‐NAs. The structure of PPR with and without a β‐NA was investigated by calorimetry, X‐ray diffraction, and thermomechanical analysis. The results indicated that the relative fraction of β crystals (k_β) in the injection‐molded specimens was determined by the type and content of β‐NA. The relationship between k_β and the impact toughness was summarized. A critical value for k_β (0.68) was identified for the brittle–ductile transition of PPR. PPR with β‐NA having a k_β greater than 0.68 displayed a higher impact strength than the other mixtures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42930.     

Synthesis and Thermal Expansion of β‐Eucryptite Powders Produced by the Inorganic–Organic Steric Entrapment Method

The characterization of powders prepared using the inorganic–organic steric entrapment method was explored and compared to the conventional solid‐state route, using X‐ray diffraction, differential scanning calorimetry, particle size analysis, and specific surface area measurements. β‐eucryptite was crystallized at 627°C and the properties of the resulting powder allowed for increased densification upon sintering compared to conventional methods. The thermal expansion behavior was also determined in situ using X‐ray diffraction and was found to be similar to other published studies, but thermal expansion in all {hkl} pole directions has been measured.     

High‐Pressure Treatment of Wood – Combination of Mechanical and Thermal Drying in the “I/D Process”

Thermal drying of materials with internal pores is always a time‐consuming and energy‐intensive step within a production process. For chemical and pharmaceutical mass products and, in particular, for wood as an important raw material it is desirable to reduce the water content before thermal treatment by mechanical operations. The wood‐processing industry, facing a rising stress of competition, is forced more than ever to offer high‐quality products at lowest prices. Today, drying of timber is mostly done by air drying or by technical drying in kiln dryers. In any case, drying is necessary to prevent deterioration in quality by shrinkage, formation of cracks, discoloration or infestation. A new process of dewatering wood by combining mechanical and thermal means has been developed at the University of Karlsruhe. Compared to conventional drying processes, short drying times and a low residual moisture content can be achieved and, thus, energy consumption and costs can be reduced. In industrial wood drying only thermal processes (e.g., convective kiln drying, vacuum drying, etc.) have been established because so far no method has been known for removing liquid by mechanical force without significant change in wood structure. With the new I/D process chances for alternatives to conventional thermal drying or for mechanothermal applications are offered.     

Theoretical Prediction and Experimental Investigation on the Thermal and Mechanical Properties of Bulk β‐Yb2Si2O7

The thermal and mechanical properties of β‐Yb₂Si₂O₇ were investigated using a combination of first‐principles calculations and experimental investigations. Theoretically, anisotropic chemical bonding and elastic properties, weak interatomic (010) and (001) planes in the crystal structure, damage tolerance, and low thermal conductivity are predicted. Experimentally, preferred orientation, superior mechanical properties, and damage tolerant behavior for hot‐pressed bulk β‐Yb₂Si₂O₇ are approved. Slipping along the weakly bonded {010}, {001}, or {100} planes, grain delamination, buckling, and kinking of nanolaminated grains are identified as main mechanisms for damage tolerance. The anisotropic linear thermal expansion coefficients (CTEs) are: α_a = (3.57 ± 0.18) × 10^?6 K^?1, α_b = (2.49 ± 0.14) × 10⁶ K^?1, and α_c = (1.48 ± 0.22) × 10^?6 K^?1 (673–1273 K). A low thermal conductivity of ~2.1 W (m·K)^?1 at 1273 K has been confirmed. The unique combination of these properties endow it a potential candidate for thermal barrier coating (TBC)/environmental barrier coating of silicon‐based ceramics.     

Functionalization and Compatibilization of Poly(ε‐caprolactone) Composites with Cellulose Microfibres: Morphology,Thermal and Mechanical Properties

A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic‐acid‐modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT‐IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected by CF and CB content. Composites with PCL‐g‐MAGMA display higher values of tensile modulus, tensile strength and elongation at break.

     

Thermal,Structural, and Enhanced Photoluminescence Properties of Eu3+‐doped Transparent Willemite Glass–Ceramic Nanocomposites

The precursor glass in the ZnO–Al₂O₃–B₂O₃–SiO₂ (ZABS) system doped with Eu₂O₃ was prepared by the melt‐quench technique. The transparent willemite, Zn₂SiO₄ (ZS) glass–ceramic nanocomposites were derived from this precursor glass by a controlled crystallization process. The formation of willemite crystal phase, size, and morphology with increase in heat‐treatment time was examined by X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 18–70 nm whereas the grain size observed in FESEM is 50–250 nm. The refractive index value is decreased with increase in heat‐treatment time which is caused by the partial replacement of ZnO₄ units of ZS nanocrystals by AlO₄ units due to generation of vacancies. Fourier transform infrared (FTIR) reflection spectroscopy was used to evaluate its structural evolution. Vickers hardness study indicates marked improvement of hardness in the resultant glass‐ceramics compared with its precursor glass. The photoluminescence spectra of Eu³⁺ ions exhibit emission transitions of ⁵D₀→⁷F_j (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 395 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 17‐fold with the process of heat treatment. This enhancement is caused by partitioning of Eu³⁺ ions into glassy phase instead of into the willemite crystals with progress of heat treatment. Such luminescent glass–ceramic nanocomposites are expected to find potential applications in solid‐state red lasers, phosphors, and optical display systems.     

Effect of Ta2O5 Substituting on Thermal and Optical Properties of High Refractive Index La2O3–Nb2O5 Glass System Prepared by Aerodynamic Levitation Method

High refractive index glasses with nominal composition of 0.35La₂O₃–(0.65?x)Nb₂O₅–xTa₂O₅ (x ≤ 0.35) were prepared by aerodynamic levitation method. The effect of Ta₂O₅ substituting on their thermal and optical properties was investigated. All the glasses obtained were colorless and transparent. Differential thermal analyzer results show that as the content of Ta₂O₅ increased, the thermal stability of the glasses increased but the glass‐forming ability decreased. The transmittance spectra of all the obtained glasses exhibited a wide transmittance window ranging from 380 to 5500 nm. As the content of Ta₂O₅ increased, the refractive index of the glasses was enhanced from 2.15 to 2.21 and the dispersion was reduced with the Abbe number increasing from 20 to 27.