Effects of annealing on the hierarchical crystalline structures and mechanical properties of injection‐molded bars of high‐density polyethylene

The effect of annealing on the microstructural evolution and mechanical properties of high‐density polyethylene parts molded via gas‐assisted injection molding was investigated using scanning electron microscopy, differential scanning calorimetry, two‐dimensional wide‐angle X‐ray diffraction and tensile testing. The results indicated that a variety of annealing temperatures could induce considerable variations in the hierarchical structures, crystallinity, lamellar thickness and yield stress of the molded bars. According to these results, the annealing temperatures could be divided into three regions. In the low‐temperature region of annealing at 80 °C, the spatial variation of the superstructure developed along the thickness direction and mechanical properties of the annealed sample were mainly unchanged and similar to those of the original specimen. At 100 and 120 °C, the intermediate temperature region of annealing, the thickness of the crystals, degree of orientation and yield stress of annealed samples were greatly improved. Finally, at 127 °C, the degree of orientation decreased and yield stress slightly improved, an indication of the high‐temperature annealing region being characterized by increasing melting/recrystallization and causing relaxation of oriented molecular chains. A model is proposed to interpret the mechanism of the annealing treatment of the samples at various temperatures. © 2013 Society of Chemical Industry     

Enhanced interfacial adhesion via interfacial crystallization between sisal fiber and isotactic polypropylene: direct evidence from single‐fiber fragmentation testing

Bioresource natural sisal fiber (SF) was used to prepare single fiber‐reinforced isotactic polypropylene (iPP) composites. Three kinds of interfacial crystalline morphologies, spherulites, medium nuclei density transcrystallinity (MD‐TC) and high nuclei density transcrystallinity (HD‐TC), were obtained in the single fiber‐reinforced composites by implementing quiescent or dynamic shear‐enhanced crystallization and by modulating the compatibility interaction between SF and iPP. The development of interfacial shear strength (IFSS) during the interfacial crystallization process was demonstrated for the first time using a combination of single‐fiber fragmentation testing and optical microscope observation. A close correlation between IFSS and morphological characteristics of interfacial crystallization was well elucidated. The increases in IFSS were very different for spherulitic, MD‐TC and HD‐TC morphologies. The highest IFSS obtained was 28 MPa, after the formation of HD‐TC, which was about 62% of the tensile strength of neat iPP (45 MPa). These results offer powerful and direct evidence that interfacial crystallization could play an important role in the enhancement of interfacial adhesion of real SF/iPP composites. © 2013 Society of Chemical Industry     

Facile synthesis of ultrathin magnetic iron oxide nanoplates by Schikorr reaction

In this work, a very facile one-pot hydrothermal synthesis approach has been developed for the preparation of ultrathin magnetite nanoplates. The hydrothermal procedure was performed by aging ferrous hydroxide under anaerobic conditions, which is known as Schikorr reaction. Ethylene glycol (EG), which was introduced to the reaction as another solvent, played a critical role in the formation process of these nanoplates. Typically, hexagonal Fe₃O₄ nanoplates with a thickness of 10 to 15 nm and a side length of 150 to 200 nm have been synthesized with EG/H₂O = 1:1 in experiments. Our data suggest that the thickness of Fe₃O₄ nanoplates decreases, and the shape of the nanoplate becomes more irregular when the concentration of EG increases. The as-prepared Fe₃O₄ nanoplates were highly crystallized single crystals and exhibited large coercivity and specific absorption rate coefficient.     

Temperature Dependence of Electric‐induced Light Scattering Performance for PLZT Ceramics

PLZT (7.45/71/29) ceramics with fully dense microstructure and high transmittance were fabricated by a hot‐press sintering method. The effects of temperature on the phase structure, ferroelectric property, and electric‐induced light scattering performance of the PLZT ceramics were examined and analyzed. XRD patterns indicated that the PLZT sample tended to transform from rhombohedral phase to tetragonal phase with the temperature increasing. And the temperature‐dependent ferroelectric hysteresis behavior of the PLZT sample revealed the conversion of a saturated square hysteresis loop to a double‐loop‐like hysteresis loop, accompanied with the significant reduction in coercive field and remnant polarization. Depending on the temperature, the PLZT sample exhibited three different kinds of electric‐induced light scattering performance.     

Phase Evolution of Ga2O3 Produced from Morphology‐Controllable α‐GaOOH Nanocrystals

Fine powders of GaOOH nanocrystals are synthesized via a facile hydrolysis process through the solution–solution interface reactions of anhydrous GaCl₃ and distilled water followed by subsequent solvothermal treatment at mild conditions. Well‐faceted α‐GaOOH hexagonal prism‐like nanorods are prepared through solvothermal treatment at 180°C with CTAB as the morphology controlling surfactant. Ga₂O₃ nanocrystals are fabricated via the pyrolysis of α‐GaOOH hexagonal prism‐like nanostructures at temperatures above 410°C. A peculiar back‐transformation from β‐Ga₂O₃ to α‐Ga₂O₃ has been observed to occur between about 557°C and 719°C, which is considered to be responsible for the coexistence of the two phases. The phase transformation mechanisms of Ga₂O₃ at elevated temperatures, as well as the possible transformation route, have been postulated from a thermodynamic point of view.