| Financially supported by the Key Technology R&D Program of China"The key technology of processing and application of bioadsorbent for mining wastewater"(No.2007BAB18808), to satisfy the environmentally friendly requirement and practical application, a series of novel thermoplastic copolymers based on soy protein isolate (SPI) were synthesized in this thesis. The novel thermoplastic materials which were grafted from SPI, methyl acrylate (MA) and methyl methacrylate (MMA) were prepared in urea aqueous solution with ammonium persulfate as an initiator, sodium sulfite as a denaturant. The obtained materials were characterized by means of modern analytical tools. Their thermal, mechanical, rheological and spectroscopy properties were analyzed respectively, and the results were shown as follows:(1) The grafting rate increased with the urea concentration, initiator concentration, reaction temperature and reaction time rising, and then decreased, until reaching a certain concentration in the graft copolymerization. The optimum conditions were obtained by orthogonal experiments. The optimum graft conditions for T-SPI (MA as initiator) were: reaction temperature 70℃, initiator concentration 70 mmol/L, reaction time 3 h, urea concentration 3.6 mol/L, monomer concentration of 2.64 mol/L. The optimum conditions for T-SPI (MMA as initiator) were: reaction temperature 70℃, initiator concentration 70 mmol/L, urea concentration of 2.4 mol/L, reaction time 4 h, monomer concentration of 2.66 mol/L; The optimum conditions of T-SPI (the mixture of MA and MMA as initiator, MA/MMA=1) were: reaction temperature 70℃, initiator concentration 105 mmol/L, urea concentration of 2.4 mol/L, reaction time 3 h, monomer concentration 2.66 mol/L. The corresponding grafting rates were 70 %, 79 % and 71 %, respectively.(2) FTIR spectrum analysis shown that graft copolymerization did occur between SPI and all kinds of monomers. There was an absorption peak around 1738 cm-1, which was belonged to the carboxyl of the monomers, and the peak intensity increased with the grafting rate rising. This could verify that the monomers were grafted onto the SPI. The same phenomena occurred again in the peaks of the methyl, methylene and ester bonds. The increase or decrease at 10.3°and 21.8°of XRD patterns of T-SPIs indicated that the molecular reaction destroyed the internal secondary structure and hydrogen bond of SPIs, making theαhelix,βsheet structure and hydrogen bond strengthened or weakened.(3) We could see that, T-SPIs modified by different monomers had different morphology from their SEM images, the T-SPI (MA as initiator) looked as slices, and the T-SPI (MMA as initiator) showed as flocculent, while the T-SPI (the mixture of MA and MMA as initiator, MA/MMA=1) presented as slices state (at high grafting rate) or flocculent state (at low grafting rate).(4) The thermal stability of T-SPIs significantly improved after grafting with different monomers, and their decomposition temperature increased. All thermoplastic materials could move molecularly at a lower temperature. The glass transition temperature of T-SPI (MA as initiator) was about 20-25℃, the glass transition temperature of T-SPI (MMA as initiator) was about 120-130℃, and the glass transition temperature of T-SPI (the mixture of MA and MMA as initiator, MA/MMA=1) was about 60-65℃. So it can be deduced that as-prepared materials had the potential to become the thermoplastic one. (5) The torque flow analysis of T-SPIs proved that the thermoplastic materials had good processing properties, several groups with high grafting rate were in good agreement with the high-density polyethylene (HDPE), indicating that the T-SPIs had a good thermoplastic performance.(6) The mechanical property measurements of T-SPIs verified that: the T-SPI (MA as initiator) could be used as flexible materials, while the T-SPI (MMA as initiator) could be used as rigid materials, and the usage of T-SPI (the mixture of MA and MMA as initiator, MA/MMA=1) could be changed by the grafting rate. |
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