Structure and mechanical properties of extruded Mg-Gd based alloy sheet

The Mg-8Gd-2Y-1Nd-0.3Zn-0.6Zr (wt.%) alloy sheet was prepared by hot extrusion technique, and the structure and mechanical properties of the extruded alloy were investigated. The results show that the alloy in different states is mainly composed of alpha-Mg solid solution and secondary phases of Mg5RE and Mg24RE5 (RE = Gd, Y and Nd). At aging temperatures from 200 degrees C to 300 degrees C the alloy exhibits obvious age-hardening response. Great improvement of mechanical properties is observed in the peak-aged state alloy (aged at 200 degrees C for 60 h), the ultimate tensile strength (sigma(b)), tensile yield strength (sigma(0.2)) and elongation (epsilon) are 376 MPa, 270 MPa and 14.2% at room temperature (RT), and 206 MPa. 153 MPa and 25.4% at 300 degrees C, respectively, the alloy exhibits high thermal stability.

Structure stability and strengthening mechanism of die-cast Mg-Gd-Dy based alloy

Mg-8Gd-1Dy-0.3Zn (wt.%) alloy was prepared by high-pressure die-casting technique. The thermal stability, mechanical properties at temperature range from room temperature to 573 K and strengthening mechanism was investigated. The results showed that the die-cast state alloy was mainly composed of fine cellular equiaxed grain. The fine porosity-free skin region was related to the aggregation of rare earth elements. The long lamellar-shaped stacking compound containing Zn and polygon-shaped precipitate were observed along the grain boundaries. The die-cast sample exhibited high mechanical properties and good thermal stability until 523 K.

The nanocomposite scaffold of poly(lactide-co-glycolide) and hydroxyapatite surface-grafted with L-lactic acid oligomer for bone repair

Nanohydroxyapatite (op-HA) surface-modified with L-lactic acid oligomer (LAc oligomer) was prepared by LAc oligomer grafted onto the hydroxyapatite (HA) surface. The nanocomposite of op-HA/PLGA with different op-HA contents of 5, 10, 20 and 40 wt.% in the composite was fabricated into three-dimensional scaffolds by the melt-molding and particulate leaching methods. PLGA and the nanocomposite of HA/PLGA with 10 wt.% of ungrafted hydroxyapatite were used as the controls. The scaffolds were highly porous with evenly distributed and interconnected pore structures, and the porosity was around 90%. Besides the macropores of 100-300 mu m created by the leaching of NaCl particles, the micropores (1-50 mu m) in the pore walls increased with increasing content of op-HA in the composites of op-HA/PLGA. The op-HA particles could disperse more uniformly than those of pure HA in PLGA matrix. The 20 wt.% op-HA/PLGA sample exhibited the maximum mechanical strength, including bending strength (4.14 MPa) and compressive strength (2.31 MPa). The cell viability and the areas of the attached osteoblasts on the films of 10 wt.% op-HA/PLGA and 20 wt.% op-HA/PLGA were evidently higher than those on the other composites.

Crystallization Behavior and Mechanical Properties of Crosslinked Plasticized Poly(L-lactic acid)

Enhancing the stability of plasticized poly(L-lactic acid) (PLLA) with poly (ethylene glycol) (PEG) is necessary for its practical application. In this study, plasticized PLLA (PLLA/PEG 80/20 wt/wt) was crosslinked under I-ray (Co-60) in the presence of triallyl isocyanurate (TALC) as crosslinking agent. FTIR analysis revealed that PLLA, PEG, and TALC formed a cocrosslinking structure. Crystallization behavior and mechanical properties of the crosslinked plasticized PLLA were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and tensile tests. Experimental results indicated that the crystallization behaviors of both PEG and PLLA in the blends were restrained after irradiation. The melting peak of PEG in the crystallized samples disappeared at a low irradiation doses about 10 kGy. Although PLLA still owned the behavior of crystallize, its cold crystallization temperature and glass transition temperature shifted to higher temperature. Mechanical properties of the plasticized PLLA were strengthened through crosslinking. Both yield strength and elastic modulus of the samples increased after crosslinking.

Effect of substituting cerium-rich mischmetal with lanthanum on microstructure and mechanical properties of die-cast Mg-Al-RE alloys

Die-cast Mg-4Al-4RE-0.4Mn (RE = Ce-rich mischmetal) and Mg-4Al-4La-0.4Mn magnesium alloys were prepared successfully and their microstructure, tensile and creep properties have been investigated. The results show that two binary Al-RE phases, Al11RE3 and Al2RE, are formed along grain boundaries in Mg-4Al-4RE-0.4Mn alloy, while the phase compositions of Mg-4Al-4La-0.4Mn alloy mainly consist of alpha-Mg phase and Al11La3 phase. And in Mg-4Al-4La-0.4Mn alloy the Al11La3 phase occupies a large grain boundary area and grows with complicated morphologies, which is characterized by scanning electron microscopy in detail. Changing the rare earth content of the alloy from Ce-rich mischmetal to lanthanum gives a further improvement in the tensile and creep properties, and the later could be attributed to the better thermal stability of Al11La3 phase in Mg-4Al-4La-0.4Mn alloy than that of Al11RE3 phase in Mg-4Al-4RE-0.4Mn alloy.

Thermal and mechanical properties of poly(epsilon-caprolactone) crosslinked with gamma radiation in the presence of triallyl isocyanurate

Poly(epsilon-caprolactone) was crosslinked by gamma radiation in the presence of triallyl isocyanurate. The influence of gamma-radiation crosslinking on the thermal and mechanical properties of poly(epsilon-caprolactone)/triallyl isocyanurate was investigated. Differential scanning calorimetry analyses showed differences between the first and second scans. Dynamic mechanical analysis showed an increase in the glass-transition temperature as a result of the radiation crosslinking of poly(epsilon-caprolactone). Thermogravimetric analysis showed that gamma-radiation crosslinking slightly improved the thermal stability of poly(epsilon-caprolactone). The 7 radiation also strongly influenced the mechanical properties. At room temperature, crosslinking by radiation did not have a significant influence on the Young's modulus and yield stress of poly(E-caprolactone). However, the tensile strength at break and the elongation at break generally decreased with an increase in the crosslinking level. When the temperature was increased above the melting point, the tensile strength at break, elongation at break, and Young's modulus of poly(epsilon-caprolactone) were also reduced with an increase in the crosslinking level. The yield stress disappeared as a result of the disappearance of the crystallites.

Processing, microstructure and mechanical properties of W50Al50 bulk alloy obtained by mechanical alloying and hot-pressing

The Al50W50 alloy bulk bodies were fabricated by using mechanical alloying and hot-pressing in this work. The Al50W50 alloy had excellent thermal stability up to 1300 degreesC under vacuum and Its optimum microhardness, bending strength and compressive strength were 10.21 GPa, 570 MPa and 2.07 GPa, respectively.

Thermal mechanical and dynamic mechanical property of biphenyl polyimide fibers

High-performance polyimide fibers possess man), excellent properties, e.g., outstanding thermal stability and mechanical properties and excellent radiation resistant and electrical properties. However, the preparation of fibers with good mechanical properties is very difficult. In this report, a biphenvl polyimide from 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydianiline is synthesized in p-chlorophenol by one-step polymerization. The solution is spun into a coagulation bath of water and alcohol via dry-jet wet-spinning technology. Then, the fibers are drawn in two heating tubes. Thermal gravimetric analysis, thermal mechanical analysis, and dynamic mechanical analysis (DMA) are performed to study the properties of the fibers. The results show that the fibers have a good thermal stability at a temperature of more than 400degreesC. The linear coefficient of thermal expansion is negative in the solid state and the glass transition temperature is about 265degreesC. DMA spectra indicate that the tandelta of the fibers has three transition peaks, namely, alpha, beta, and gamma transition. The alpha and gamma transition temperature, corresponding to the end-group motion and glass transition, respectively, extensively depends on the applied frequency, while the beta transition does not.

Effects of reinforcement filler and temperature on the stability of beta-crystal in glass bead filled polypropylene

The effects of crystallization temperature (T,), glass bead content and its size on the, formation of beta-crystal and structural stability of originally formed beta-crystal in glass bead filled polypropylene (PP) were examined. The differential scanning calorimetry (DSC) measurements indicated that the amount of beta-phase in PP crystals was a function of the crystallization temperature and glass bead content. For a constant crystallization temperature, it was observed that the amount of beta-crystal initially increased with increase in glass bead content up to 30 wt.%, and then decreased slightly with further increase in the filler content. From the DSC data, a disorder parameter (S) was derived to define the structural stability of originally formed beta-crystals. The structural stability of originally formed beta-crystals was enhanced with increase in either the crystallization temperature or the glass bead content. Also, the influence of glass bead size (4-66 mu m) on the formation and stability of beta-crystals in PP/glass bead blends was studied. Large glass bead particles suppressed the formation and decreased the stability of beta-crystals.

Mechanical and thermal properties of high-density polyethylene toughened with glass beads

Glass beads were used to improve the mechanical and thermal properties of high-density polyethylene (HDPE). HDPE/glass-bead blends were prepared in a Brabender-like apparatus, and this was followed by press molding. Static tensile measurements showed that the modulus of the HDPE/glass-bead blends increased considerably with increasing glass-bead content, whereas the yield stress remained roughly unchanged at first and then decreased slowly with increasing glass-bead content. Izod impact tests at room temperature revealed that the impact strength changed very slowly with increasing glass-bead content up to a critical value; thereafter, it increased sharply with increasing glass-bead content. That is, the lzod impact strength of the blends underwent a sharp transition with increasing glass-bead content. It was calculated that the critical interparticle distance for the HDPE/glass-bead blends at room temperature (25degreesC) was 2.5 mum. Scanning electron microscopy observations indicated that the high impact strength of the HDPE/glass-bead blends resulted from the deformation of the HDPE matrix. Dynamic mechanical analyses and thermogravimetric measurements implied that the heat resistance and heat stability of the blends tended to increase considerably with increasing glass-bead content.

STUDY ON CYCLODEXTRIN AND ITS INCLUSION COMPLEXES - MOLECULAR MECHANICAL CALCULATION

We studied several inclusion complexes of beta-CD by means of molecular mechanical calculation. The inclusion process and the driving force were discussed, and the conclusion on stability agrees with the results of electrochemical experiments.

Studies on equine milk and comparative studies on equine and bovine milk systems

The composition of equine milk differs considerably from that of the milk of the principal dairying species, i.e., the cow, buffalo, goat and sheep. Because equine milk resembles human milk in many respects and is claimed to have special therapeutic properties, it is becoming increasingly popular in Western Europe, where it is produced on large farms in several countries. Equine milk is considered to be highly digestible, rich in essential nutrients and to possess an optimum whey protein:casein ratio, making it very suitable as a substitute for bovine milk in paediatric dietetics. There is some scientific basis for the special nutritional and health-giving properties of equine milk but this study provides a comprehensive analysis of the composition and physico-chemical properties of equine milk which is required to fully exploit its potential in human nutrition. Quantification and distribution of the nitrogenous components and principal salts of equine milk are reported. The effects of the high concentration of ionic calcium, large casein micelles (~ 260 nm), low protein, lack of a sulphydryl group in equine β-lactoglobulin and a very low level of κ-casein on the physico-chemical properties of equine milk are reported. This thesis provides an insight into the stability of equine casein micelles to heat, ethanol, high pressure, rennet or acid. Differences in rennet- and acid-induced coagulation between equine and bovine milk are attributed not only to the low casein content of equine milk but also to differences in the mechanism by which the respective micelles are stabilized. It has been reported that β-casein plays a role in the stabilization of equine casein micelles and proteomic techniques support this view. In this study, equine κ-casein appeared to be resistant to hydrolysis by calf chymosin but equine β-casein was readily hydrolysed. Resolution of equine milk proteins by urea-PAGE showed the multi-phosphorylated isoforms of equine αs- and β-caseins and capillary zone electrophoresis showed 3 to 7 phosphorylated residues in equine β-casein. In vitro digestion of equine β-casein by pepsin and Corolase PP™ did not produce casomorphins BCM-5 or BCM-7, believed to be harmful to human health. Electron microscopy provided very clear, detailed images of equine casein micelles in their native state and when renneted or acidified. Equine milk formed flocs rather then a gel when renneted or acidified which is supported by dynamic oscillatory analysis. The results presented in this thesis will assist in the development of new products from equine milk for human consumption which will retain some of its unique compositional and health-giving properties.

Chondrogenesis and mineralization during in vitro culture of human mesenchymal stem cells on three-dimensional woven scaffolds.

Human mesenchymal stem cells (hMSCs) and three-dimensional (3D) woven poly(ɛ-caprolactone) (PCL) scaffolds are promising tools for skeletal tissue engineering. We hypothesized that in vitro culture duration and medium additives can individually and interactively influence the structure, composition, mechanical, and molecular properties of engineered tissues based on hMSCs and 3D poly(ɛ-caprolactone). Bone marrow hMSCs were suspended in collagen gel, seeded on scaffolds, and cultured for 1, 21, or 45 days under chondrogenic and/or osteogenic conditions. Structure, composition, biomechanics, and gene expression were analyzed. In chondrogenic medium, cartilaginous tissue formed by day 21, and hypertrophic mineralization was observed in the newly formed extracellular matrix at the interface with underlying scaffold by day 45. Glycosaminoglycan, hydroxyproline, and calcium contents, and alkaline phosphatase activity depended on culture duration and medium additives, with significant interactive effects (all p < 0.0001). The 45-day constructs exhibited mechanical properties on the order of magnitude of native articular cartilage (aggregate, Young's, and shear moduli of 0.15, 0.12, and 0.033 MPa, respectively). Gene expression was characteristic of chondrogenesis and endochondral bone formation, with sequential regulation of Sox-9, collagen type II, aggrecan, core binding factor alpha 1 (Cbfα1)/Runx2, bone sialoprotein, bone morphogenetic protein-2, and osteocalcin. In contrast, osteogenic medium produced limited osteogenesis. Long-term culture of hMSC on 3D scaffolds resulted in chondrogenesis and regional mineralization at the interface between soft, newly formed engineered cartilage, and stiffer underlying scaffold. These findings merit consideration when developing grafts for osteochondral defect repair.