Mingxing Zhang

Significant Improvement in Thermal and UV Resistances of UHMWPE Fabric through in Situ Formation of Polysiloxane–TiO2 Hybrid Layers

Anatase nanocrystalline titanium dioxide coatings were produced on ultrahigh molecular weight polyethylene (UHMWPE) fabric by radiation-induced graft polymerization of γ-methacryloxypropyl trimethoxysilane (MAPS) and subsequent cohydrolysis of the graft chains (PMAPS) with tetrabutyl titanate, followed by boiling water treatment for 180 min. The resulting material was coded as UHMWPE-g-PMAPS/TiO2 and characterized by attenuated total reflection infrared spectrometry, differential scanning calorimetry, X-ray diffraction, thermal gravimetry, and ultraviolet absorption spectroscopy, among others. The predominant form of TiO2 in the thin film was anatase. The coating layer was composed of two sublayers: an inner part consisting of an organic-inorganic hybrid layer to prevent photocatalytic degradation of the matrix by TiO2 film, and an outer part consisting of anatase nanocrystalline TiO2 capable of UV absorption. This UHMWPE-g-PMAPS/TiO2 composite exhibited much better thermal resistance than conventional UHMWPE fabric, as reflected by the higher melting point, decreased maximum degradation rate, and higher char yield at 700 °C. Compared with UHMWPE fabric, UHMWPE-g-PMAPS/TiO2 exhibited significantly enhanced UV absorption and excellent duration of UV illumination. Specifically, the UV absorption intensity was 2.4-fold higher than that of UHMWPE fabric; the retention of the break strength of UHMWPE-g-PMAPS/TiO2 reached 92.3% after UV irradiation. This work provides an approach for addressing the issue of self-degradation of TiO2-coated polymeric materials due to the inherent photoactivity of TiO2.

Functionalized and reusable polyethylene fibres for Au(III) extraction from aqueous solution with high adsorption capacity and selectivity

A new chelating polyethylene fibre was synthesised by the radiation-induced graft copolymerisation of glycidyl methacrylate (GMA) onto ultrahigh-molecular-weight polyethylene (UHMWPE) fibres and subsequent ring-opening reaction with 4-amino-1,2,4-triazole. The chemical structure and surface morphology of the modified fibres were characterised by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The adsorption behaviour of the fibrous sorbent for Au(III) was investigated in terms of aqueous-solution pH, contact time, initial metal concentration and competition of coexisting metal ions. Resultant fibres exhibited much higher affinity and selectivity for Au3+ ions than all other metal ions (Mg2+, Fe3+, Cu2+, Ca2+, Ni2+ and Cr6+). The affinity coefficient obtained was as high as 97.5–99.9%. The maximum adsorption amount for Au3+ was 429.4 mg g−1. The adsorption of Au(III) followed the pseudo-second-order kinetics model controlled by chemical adsorption. The equilibrium data fitted the Langmuir isotherm model well. In particular, this fibrous adsorbent can be regenerated by treatment in 0.5 M thiourea and 0.5 M H2SO4 solution. The high adsorption capacity can be maintained after at least five adsorption–desorption cycles.

Supercritical CO2 Foaming of Radiation Cross-Linked Isotactic Polypropylene in the Presence of TAIC

Since the maximum foaming temperature window is only about 4 °C for supercritical CO2 (scCO2) foaming of pristine polypropylene, it is important to raise the melt strength of polypropylene in order to more easily achieve scCO2 foaming. In this work, radiation cross-linked isotactic polypropylene, assisted by the addition of a polyfunctional monomer (triallylisocyanurate, TAIC), was employed in the scCO2 foaming process in order to understand the benefits of radiation cross-linking. Due to significantly enhanced melt strength and the decreased degree of crystallinity caused by cross-linking, the scCO2 foaming behavior of polypropylene was dramatically changed. The cell size distribution, cell diameter, cell density, volume expansion ratio, and foaming rate of radiation-cross-linked polypropylene under different foaming conditions were analyzed and compared. It was found that radiation cross-linking favors the foamability and formation of well-defined cell structures. The optimal absorbed dose with the addition of 2 wt % TAIC was 30 kGy. Additionally, the foaming temperature window was expanded to about 8 °C, making the handling of scCO2 foaming of isotactic polypropylene much easier.