Studies On The Structure And Properties Of Protein Modified With Waterborne Polyurethane

With petroleum resources gradually exhausted and environment pollution seriously caused by non-degradable synthetic polymer, the development and utilization of renewable resources and environmental friendly materials as one of the frontiers in polymer science has attracted more and more attention. Both casein and soy protein are abundant resources, and also biodegradable materials in the earth, which can be modified easily because of containing various functional groups. They will become one of the main chemical materials in the future. However, the wide utilization is restricted as a result of their water-sensitivity and brittle property. Blend is an important way to exploit new material for the polymers. The blending of the protein containing peptide with polyurethane containing amide groups can not only improve the pliability and the water-resistivity, but also keep biodegradability. The objective of this thesis is to modify protein by using blend and graft technology, developing their applications in the fields of material, food, medicine and agriculture and so on.In this thesis, several novel water-resistivity materials were prepared by blending waterborne polyurethane (WPU) with casein or soy protein isolate (SPI), and the structures and properties of the materials were characterized by employing advanced apparatus and methods. The creative achievements of this thesis are as follows: (1) the novel cross-linked casein/WPU materials were prepared successfully in water system, which exhibited good compatibility, mechanical properties and water-resistivity. (2) It has been revealed that the average particle size of WPU in dispersions plays an important role in the improvement of the mechanical properties for the composite materials of casein/WPU prepared by grafting and mixing. The lower average particle size resulted in better mechanical properties. (3) For the first time, the soy protein plastics plasticized with WPU were prepared successfully, and its toughness and water-resistivity were improved significantly. (4) The cross-linked composite materials of WPU/SPI were prepared successfully by using ethylene glycol diglycidyl ether (EGDE) as across-linker, and the mechanical properties were improved significantly both in wet and in dry states. (5) For the first time, novel nano-composite plastics of WPU/SPI were prepared by introducing (SiO2)n mH2O, and their toughness was improved obviously.The main research contents and conclusions are divided into the following parts.Waterborne polyurethane (WPU) and casein (1 : 1 by weight) were blended at 90 C for 30 min, and then were cross-linked by adding 1-10 wt% ethanedial to prepare a series of sheets. Their structures and properties were characterized by using infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and tensile testing. The results indicated that the cross-linked blend sheets exhibited a certain degree of miscibility, and much higher tensile strength and water-resistivity than the WPU, casein and uncross-linked blend from WPU and casein. When the ethanedial content was 2 wt%, the tensile strength( o b) and elongation( b) at break of cross-linked sheets achieved 19.5 MPa and 148% in dry state, and 5.0 MPa and 175% in wet state, respectively. 2 wt% ethanedial plays an important role in the enhancement of mechanical properties, thermal stability and water-resistivity of the blends of WPU and casein as a result of intermolecular cross-linking. This work provided a new protein plastic with good mechanical properties and water-resistivity.Two kinds of aqueous dispersions were prepared from WPU (10 wt%) by mixing (M) and grafting (G) with 10 wt% casein aqueous solution, respectively. The resulting dispersions were characterized by using rotary viscometer and particle size distribution meter, indicating that the viscosity, Z-average size and polydispersity of the dispersions increased with an increase of casein content, and the average particle size of the M dispersions (...