Papers by Author: Li Ping He

Abstract: Natural fiber reinforced polypropylene composites (NF/PP) have attracted a lot of attention because of their light weight, good mechanical properties, recyclable and environmental friendly features. This work has successfully fabricated ramie fiber reinforced polypropylene composites (RF/PP) with a hybrid method of melt-blending and injection molding. Different RF/PP eco-materials have been fabricated by varying the fiber length, fiber content and way of fiber pre-treatment. This paper studied the mechanical properties of the fabricated RF/PP composites in depth by investigating the mechanical behaviors of RF/PP and microstructures of the ruptured surfaces. The results show that the increases of fiber length and fiber content can improve the tensile strength, flexural strength and compression strength apparently, but result in negative influences on the impact strength and elongation behaviors of RF/PP composites. The optimal addition amount of ramie fiber is around 20 wt%. The pre-treatment of ramie fiber in 10%~15% NaOH is good to the mechanical properties of RF/PP. The fiber length can be varied in the range of 3-8 mm. It is expected that the fabricated RF/PP composites can be applied to automobile industry as environmental friendly eco-materials.

Abstract: Ca-containing anodic alumina (CAA) has been successfully prepared by anodizing Al film in an alkali solution at a constant voltage and subsequently electro-depositing calcium salts on and into porous anodic alumina. This paper studied the induction ability of Ca-containing anodic alumina (CAA) for calcium phosphates salts by immersing CAA in a simulated body fluid (SBF). The morphologies and compositions of the inductive coating are studied in depth using SEM and XRD. The results show that the porous Ca-containing anodic alumina (CAA) exhibits good induction ability of calcium phosphates in SBF. The Ca/P atomic ratio of the inductive coating on CAA after 7 days immersion in SBF is of 1.68 and the inductive coating on CAA is apatite. Consequently apatite /Al2O3 (anodic) composite has been obtained after apatite inductively formed on Ca-containing anodic alumina. Tafel polarization test indicates that apatite /Al2O3 composite has good anti-corrosion ability in simulated body environment. Therefore, Ca-containing anodic alumina films are promising substrates for fabricating functional coatings and its inductively formed apatite/Al2O3 composite is a promising material for hard tissue repair applications.

Abstract: Ca-containing anodic alumina (CAA) has been successfully prepared by anodizing Al film in an alkali solution at a constant voltage and subsequently electro-depositing calcium salts on and into anodic alumina. This paper investigated the anodic behavior of Al, deposition behavior of calcium salt, and microstructure of CAA. The results show that the anodic behavior of Al in Na3PO4 electrolyte can be described as three continuous stages as of initial growth of the compact barrier layer, formation of porous alumina and further development of its pores and columnar holes. It is also found that cell voltage of electro-deposition process plays an important role at the deposition behavior of calcium slat and the microstructure of Ca-containing anodic alumina (CAA). The higher the cell voltage is, the faster the deposition rate, and the more calcium being deposited at the surface of anodic alumina and into the columnar holes or at the walls of the holes of anodic alumina. It is expected that Ca-containing anodic alumina films are promising substrates for fabricating functional bio-coatings for prosthetic applications.

Abstract: A novel hydroxyapatite/Al2O3 (anodic) biocomposite coating has been successfully fabricated on titanium using a multi-step technique including physical vapor deposition (PVD), anodization, electrodeposition and hydrothermal treatment. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD) were employed to investigate morphologies and compositions of the pre- and post-hydrothermally treated hydroxyapatite/Al2O3 (anodic) biocomposite coatings. The results showed that plate-like Ca-deficient hydroxyapatite coating was directly elctrodeposited onto anodic Al2O3 at a constant current density of 2.0 mA/cm2 using NaH2PO4 as the phosphorous source. The plate-like Ca-deficient hydroxyapatite was converted into network-like Ca-rich hydroxyapatite after hydrothermal treatment.