Papers by Author: Jian Yu

Abstract: Alginate calcium fibers were prepared through wet spinning with good tensile strength which can be used for cloth materials. The morphology, mechanical property and combustion property of alginate calcium fibers were investigated. Blending yarns and textile of alginate calcium fibers and combed cotton was fabricated with good hand feeling and strength. Alginate salt fiber was prepared with wet spinning machine designed according to viscose fiber spinning machine. The diameter of alginate calcium fibers was about 10-15µm in diameter with smooth surface. The tensile strength of alginate salt fiber was larger than 4.8 cN in the dry state. The value of Limited Oxygen Index (LOI) of alginate calcium fibers was 34%. The average heat release rates (HRR) of the alginate fiber is about 21 kW/m2 which was much lower than that of most synthetic and natural fibers analysized with Cone. Alginate calcium fibers is an inherent flame-retardant fiber.

Abstract: The natural photo-oxidation of PP bars containing nucleating agent (TMB-5) were studied by using infrared microscope (IM), differential scanning calorimetry (DSC), scanning electron microscope (SEM) and polarizing optical microscope (POM). The results indicated that nucleating agent accelerated the oxidation of PP significantly. The oxidation began from the surface and developed into the interior with time. There is a transition region near the surface, caused by the fast cooling during the injection moulding. This region is prior to be oxidized because of the low density. Therefore, it corresponded to the surface oxidation layer in PP and PP/TMB-5 bars. The nucleating agent helped to reduce the spherulite size of PP and broaden the transition region greatly – from about 25 μm to more than 200μm, covering the morphology of amorphous, fine crystals to relatively perfect crystals. More crystal boundaries, i.e. low density, and broad transition region led to higher oxidation degree and further oxidation along the depth. However, the thickness of the surface oxidation layer maintained nearly constant till the fragments dropped from the seriously damaged surface.

Abstract: Photo-oxidation of polyethylene (PE) has been studied thoroughly these years owing to its high output and various applications, which makes knowledge about its degradation of vital practical importance. Polyethylene products often suffer from service environment factors including ultraviolet, heat or chemicals, which may deteriorate their mechanical properties. The degradation behavior varies with the chain structure and morphology of polyethylene, e.g., branches, linear segments length and crystallization. Natural degradation of three kinds of polyethylene (HDPE, LDPE and LLDPE) has been examined in samples using different annealing conditions in this work. The extent of degradation, described as carbonyl index, was evaluated by Fourier transform infrared spectroscopy (FTIR). Crystallinity measurements were made using differential scanning calorimetry(DSC). The investigation indicates that the branch structure plays a dominant role in the photo-oxidation of polyethylene. Annealing will change the crystallinity of polyethylene before aging, but do not show obvious dependence on the oxidation.

Abstract: This work deals with a novel processing method that combined extrude with laminate molding for preparing polymeric graded material (PGM). The variations of inhomogeneous property were generated by altering the feeding speed and/or weight ratio of the components as well as changing the order or numbers of the folded layers. Three modes of polypropylene (PP)/ talcum powder (talc) flat PGM (signed with T1, T2, T3) are fabricated successfully by using this new technique. The preparation, structure and property of the resultant PP/talc graded composite were investigated. Results indicate that the composition, morphology and properties show a gradient variation along their thickness direction of the flat PGMs.

Abstract: The photo-oxidation stability is crucial for the materials that are exposed to outdoor application. For polyethylene, it has been investigated thoroughly and the auto-oxidation mechanism has been widely accepted. Nevertheless, the photo-oxidation of polyethylene composites, the most widely used materials, has not attracted enough attention yet. It is well known that the mechanical properties of composites are of great difference to that of matrix polymers, due to the introduction of the fillers and the different interfacial interactions between the matrices and the fillers. Also the oxidation behavior of composites have interesting characteristics owing to the various fillers and interfacial interactions, which always depend on the coupling agents. In the present work, the natural photo-oxidation of high-density polyethylene composites was studied. The results showed that the coupling agent had the most important but different influence on the oxidation stability of the composites, according to the different fillers.

Abstract: Stearic acid coated nanometer CaCO3 was encapsulated by polystyrene (PS) network via emulsion polymerization, where a polyfunctional monomer trimethyol propane trimethacrylate (TMPTMA) or divinyl benzene (DVB) was used as crosslinker. The feed modes of monomer and initiator are investigated. Batch mode is shown to be more convenient than semi-continuous mode in view of network perfection. With the amount of crosslinkers increased from 1 wt% to 7 wt%, the percentage of unextractable PS is high (not lower than 95%) for all samples in the system of TMPTMA, while this value decreases sharply from 74% to 3% in the system of DVB. The yield in the system of DVB is higher than that of TMPTMA. With increased amount of CaCO3, encapsulation ratio can be varied from 5.2 to 2.6, while the yield and unextractable PS decrease. FT-IR spectra of the products after extraction indicate tight encapsulation between PS and CaCO3, and TEM photographs of composite particles give direct evidence of encapsulation.