Advanced Materials Research Vols. 152-153

Abstract: Five series SnO2/C Morph-genetic composite materials were prepared using ramie fiber as biological templates, Sn(OH)4 sol as impregnant, and phenolic resin as supplementary adhesive. The influences of calcination temperature, holding time, and phenolic resin treatment on the mechanical wear property of the SnO2/C morph-genetic materials were studied. The results showed that when the calcination temperature reached 630 and holding time increased, SnO2 was reduced by C and CO to needle-like flakes and pellet mixed SnO/SnO2 tissue, and their pinning and supportive effects significantly increased wear resistance of the samples. Glass Carbon derived from phenolic resin decomposition and ramie carbon were difficult to distinguish, but glass carbon had obvious supportive and strengthening effects on ramie carbon walls. With the formation of homogeneous carbon membrane in the process of friction, the alternative distribution of soft carbon and hard carbon could effectively improve wear resistance of the matrix ramie carbon.

Abstract: The aim of this study was to investigate the effect of electrospinning process on the physical properties of fibers made from shellac. Electrospun shellac fiber was prepared by dissolving shellac in ethanol and then transferred to the electrospinning system. The influences of process parameters; including electric field voltage, tip to collector gap, feeding rate and concentration of shellac solutions; on the spinnability and properties of obtained shellac fibers were elucidated. The result demonstrated that micro-nano fibers of shellac were easily formed after spinning. The concentration of shellac solution was a crucial parameter that determined the spinnability. The electro-sprayed particles of shellac were achieved at the concentration of 35% w/w and lower while the electrospun fibers was formed in the concentration range of 40-45 % w/w. SEM pictures demonstrated that the beaded fiber structure obtained at 40-43% w/w was changed to the continuous fiber structure at 45% w/w. The diameter of fiber showed a tendency to increase while the size distribution of diameter was narrower as increasing voltage. The other optimized electrospinning parameters including feeding rate, tip to collector gap were 0.5-2 ml/h and 15-20 cm, respectively. In conclusion, the study demonstrated the critical parameters that determined the properties of required fibers. The knowledge gained should support the development of the drug incorporated electrospun shellac fiber in near future.

Abstract: Using 1,3,5-benzenetrioxyundecanol (mTU) as the core, and L-lactic acid (L-LA) as starting material, a novel star-shaped poly(L-lactic acid) (SPLLA) was synthesized via direct melt polycondensation with simple process and low-cost. The obtained biodegradable polymer SPLLA was systematically characterized with the intrinsic viscosity [η], FTIR, 1H-NMR, GPC and XRD. The Mw, Tg, Tm, ΔH, crystallinity, crystallite size of all SPLLA basically increased with the increase of the molar feed ratio n(L-LA) : n(mTU). When n(L-LA) : n(mTU) was 500:1, the biggest Mw was 8600, but all Mw meet the requirement for drug delivery application.

Abstract: Poly(glycolic acid) (PGA) fibers produced by melt-spinning technology with different parameters may possess different structures, which may lead to different degradation behavior. In this paper, PGA fibers produced by different technology parameters were placed in phosphate buffer solution (PBS) (pH=7.4) at 37 °C up to 2 weeks to investigate the effect of melt-spinning technology on the degradation in vitro. Changes in weight loss and tensile strength of PGA fibers during degradation were investigated. The results showed that drawing multiple, drawing temperature and inherent viscosity of polymer had the influence on the performance of PGA fiber during degradation. The changes in weight loss and tensile strength during degradation in vitro indicated that the PGA fiber produced with higher drawing multiple degraded more slowly. The PGA fiber produced on higher drawing temperature degraded faster. The PGA fiber made from higher inherent viscosity polymer degraded more slowly.

Abstract: The microstructure, fracture surface topography and mode of hexagonal nut cracked in assembling under air pressure were analyzed with optical microscope and scanning electronic microscope, which are made in contrast with that of hexagonal nut cracked in man-made. The research results show that the man-made fracture of nut was of dimple shape and cracked in toughness mode, which accorded with the fracture behavior of 2Al2 duralumin material. The air-pressure fracture of nut was of right shape and cracked in brittle mode. The fracture mechanism is concluded that crack fountain is formed in surface of nut because of scoring during assembling and then the crack expands rapidly, leading to brittle fracture of the nut.

Abstract: In this study, nano-hydroxyapatite (HA) powders were synthesized via a simple sol-gel method using Ca(NO3)2•4H2O and P2O5 as starting materials. Two different precursors, with and without citric acid (CA), were prepared. The transformation process of HA from precursors, purity and particle size of the obtained HA powders were evaluated. HA derived from the precursor with CA showed a different transformation process from that without CA. It was observed that the content of CaO as an unavoidable major impurity was reduced due to the addition of CA. In the calcined powders from the CA-free precursor, X-ray diffraction (XRD) patterns revealed an intense CaO peak. For the calcined powders from the CA-addition precursor, XRD analysis showed a very weak CaO peak. It was also found that the synthesized HA powders from precursor with CA were finer than those without CA. The mechanism of the influence of CA on the formation, purity and particle size distribution of HA powders was discussed.

Abstract: Before and after heat and wet treatment, the fineness and strength of PLA sample fibers were measured. Temperature, rather than moisture, was reckoned the major factor weakening the strength and fineness of PLA fiber. Acidic and alkali environments activated the hydrolysis of the fiber and lead to obvious fiber damage. Compared with the acidic environment, alkali condition resulted in far faster hydrolysis, caused more reduction of fiber diameter and strength. In addition, vertical cracks appeared on the fiber surface in alkali conditions, but did not occur in acidic environment. Finally, it was found that heat and wet treatment in a neutral environment did not make obvious harm to PLA fiber.

Abstract: Metal structural crack monitoring is a significant and difficult task for structural health monitoring. A special coating sensor was employed in this study to monitor aluminum structural cracks. The coating sensor was deposited on the hot spots of the aluminum structure by modern surface technology. Fatigue experimental results show that the information of the structural crack origination and propagation can be obtained through analyzing the changes of the electrical conductivity of the coating sensor, and the fatigue performance of the specimen is not obviously changed after the coating sensor deposited on it.

Abstract: The epoxy/polyurethane coating has high electrical isolation, anti-corrosion and high adhesive bond strength with magnesium alloy substrate. The coating can effectively block or reduce the substrate erosion induced by water, oxygen as well as the corrosive ions such as , and . The mechanism and efficiency of corrosion protection of the polyurethane coating and epoxy/polyurethane coating on magnesium alloys were studied experimentally. The results indicate that both kinds of coatings improved the anti-corrosion property of magnesium alloy evidently. The anti-corrosion property of the epoxy/polyurethane coating is better than that of the polyurethane coating. The experimental results, which were obtained by the immersion tests in 3.5wt% NaCl solution, loss weight tests, salt spray tests, adhesive force tests, hardness tests, electrochemical tests and stereo microscope photos, definitely support the previous conclusions.

Abstract: The nanosized silica with different morphologies such as sphere, granule, needle, short rod, hollow tubule, has been in turn synthesized by using cetyltrimethylammonium bromide (CTAB) as template and mixed chlorosilane (silicon tetrachloride and trichlorosilane) as silicon source in aliphatic alcohol aqueous solution. The as-prepared products were characterized by x-ray diffraction (XRD), transmission electron microscope (TEM), and Fourier transform infrared spectroscopy (FT-IR), and BET nitrogen adsorption technique was employed for determination of specific surface area of the powdery silica. The formation conditions and mechanism of the nanosized silica with special and diverse shapes are preliminarily discussed.