Acrylate-terminated poly(lactic acid)(DPLA) was synthesized by polycondensation, using lactic acid, polyalcohol and acrylic acid as the raw materials. The prepolymer products in each process were characterized by FT-IR, 1 H-NMR, GPC and DSC. DPLAs were then formulated with reactive diluent and diphenyl ketone as photoinitiator and photopolymerized into film(FPLA). Thermal stability and degradation properties of the UV curing PLA film were studied. The results showed that the structures of prepolymer and the performances of the film could be adjusted by changing the types and content of the branching agent polyalcohol. After crosslinking modification, the degradation rate of FPLA was reduced and FPLA had better thermal stability than the pure PLA.
Slow positron beam was applied to study the depth profile structure of the virgin and the aged high-temperature vulcanized silicone rubber(HTV). Scanning electron microscope(SEM) images show that the surface of virgin sample is smooth, while the outdoor aged samples are all rough. According to the S(E) curves obtained by slow positron beam, in a depth of more than 1 μm, the S parameter of the sample aged at low-potential side keeps the same value with the virgin one;while the S values of the highpotential side aged sample remain rather low in a depth of about 5 μm. Thermo gravimetric analysis(TGA) results show that the sample in high potential side contains more inorganic constituents than that of other samples. The results are attributed to the strong electric field induced corona aging at high potential side of the composite insulator.
TiO2-based nanosheets (TiNSs), TiO2-based nanotubes (TiNTs) were prepared by hydrothermal processing, and polyurethane foams with TiO2 nanopowders (P25), TiNSs and TiNTs were synthesized by free-rising foaming method. The Fourier-transform infrared (FT-IR) spectra show that the addition of titanium dioxide does not affect the chemical structure of polyurethane foam. However, microscope observations show that PU/TiNSs composite foams have more uniform cells and the average aperture smaller than that of pure poly-urethane foams. According to the results of thermal analysis, the PU/TiNSs composite foams have better thermal stability, the temperature of decompostion occurring with a maximum weight loss rate is about 30 ℃ higher than that of pure PU foams. The decompostion temperatures are 167 ℃ and 148 ℃ for the PU/P25 composite foams and the PU/TiNTs composite foams respectively, which are lower than that of pure PU foams. Moreover, with the addition of the fillers, the sound absorption property also has changed; the addition of TiNSs improved the sound absorbing property efficiently. The better thermal stability and sound absorption of PU/TiNSs composite foams are mainly due to the uniform cells diffuse and smaller aperture.
We investigated the aging effect on the chemical structure of silicone rubber composite materials under outdoor environment. The variations of low molecular weight siloxanes in silicone rubber were probed by gas chromatography-mass spectrometry during the degradation process. The experimental results indicate that a series of cyclic siloxanes exist in both the virgin and aged silicone rubber samples, while the additional low molecular weight siloxanes(hexamethyl cyclotrisiloxane) only appear in the aged samples. Meanwhile, the total amounts of low molecular weight siloxanes in the aged samples are much less than those in the virgin ones. The loss of low molecular weight siloxanes is induced by the chain scission and depolymerization.
