Meng Linghui

Depolymerization of poly(butylene terephthalate) using high-temperature and high-pressure methanol

Poly(butylene terephthalate) (PBT) was depolymerized in excess methanol at high-temperature (473–523 K) and high-pressure (4–14 MPa) conditions. Considering the critical point of methanol (512.6 K, 8.09 MPa), the reaction pressure was varied over the range of 6–14 MPa at the reaction temperature of 513 K. As a result, ca. 20 min was required to recover dimethyl terephthalate and 1,4-butanediol, quantitatively, at any pressure, indicating that the supercritical state of methanol is not a key factor of degradation of PBT and that the effect of pressure is little. On the contrary, when the reaction temperature was varied over the range of 473–523 K at the pressure 12 MPa, the decomposition rate constant of PBT at the reaction temperatures (503–523 K) higher than the melting temperature of PBT (500 K) was much higher than that at 473–483 K. This result indicates that melting of PBT is an important factor for the short-time depolymerization of PBT.

Interface enhancement of carbon fiber reinforced unsaturated polyester composites with sizing agent containing carbon nanotubes

A liquid sizing agent containing carbon nanotubes was prepared for carbon fiber reinforced unsaturated polyester composite applications. The formation of chemical bonds among vinyl-functionalized carbon nanotubes, vinyl-functionalized carbon fibers, and unsaturated polyester in the coating was due to the radial polymerization process. Scanning electron microscopy images showed that a thin layer of unsaturated polyester coating containing carbon nanotubes was grafted on the surface of carbon fiber uniformly. Dynamic contact angle measurements, before and after sizing treatment, demonstrated an improvement in the surface energy and wettability that related to the increase of the polarity of sized fiber surface. X-ray photoelectron spectroscopy was used for surface functional group analysis of carbon fibers. Force modulation atomic force microscope (AFM) images indicated that an interface with local stiffness softer than that of carbon fiber and harder than that of matrix was gained. Results of the mechanical property tests showed that interlaminar shear strength increased from 46.7 to 64.5 MPa by 38% without sacrificing base fiber strength, and the impact resistance was increased simultaneously.

The Experimental Research on Recycling of Aramid Fibers by Solvent Method

Chemical degradation of aramid/epoxy composites to the recycle of aramid fibers is presented in this article. 1,2,3,4-Tetrahydronaphthalene served as the main solvent decomposes the epoxy matrix and the virgin fibers are released under different decomposition conditions. The influence of reaction time, temperature, and feedstock ratio on the decomposition rate is investigated to ascertain the optimum condition of this recycle process. Gas chromatography mass spectrometry (GC-MS), single fiber tensile strength, and scanning electron microscope (SEM) are used to characterize the recycled fibers respectively, illustrating that aramid/epoxy composites can be decomposed successfully with this chemical method on the experimental condition. The hydrogenative mechanism of epoxy resin is also discussed tentatively according to the experimental result.

Method of Recovering the Fibrous Fraction of Glass/Epoxy Composites

This study reports the method of recovery of glass fibers from glass/epoxy composites through the solvent method. It is possible to decompose epoxy resin with a yield of more than 99 wt% soluble products in a nitric acid solution (8 M) at 90 C for 5 h. The decomposition rate of epoxy resin increases with an increase in temperature and concentration of acid solution. The glass fibers can be recovered with very little contamination and they have a tensile strength reduction of 3.5% under decomposition conditions of T = 70°C, t = 250 h, C = 6 M and α= 6 g/100 mL. These fibers can be used as reinforcement to prepare new composites. The interlaminar shear strength (ILSS) of recovered short fiber-reinforced composites produce strength reductions of only 2.5% compared with pristine composites.