Effects Of Processing Condition And Polyurethane Structure On The Structure/Properties Of A Novel Starch Thermoplastic

Polyurethanes polymer (PUP) that contain high amounts of isocyanates has been used to toughen starch, because its isocyanate groups have high reactivity with the hydroxyl groups of starch. Thus, starches modified with PUP have attracted increasing attention. Organic solvents were also used in preparing modified starch, however, caused serious environmental pollution. It is therefore necessary to use an environmentally friendly method for preparing ductile thermoplastic starch (TPS). In our previous works, starch, water and PUPs natural castor oil based were mixed reactively in a mixer or extruder to prepare modified TPS. Genarally, material processing, structure and properties influence and restrict each other in polymer science. Therefore, this thesis study effects of processing condition and polyurethane structure on the structure/properties of modified starch.First, study the effect of processing condition on the structure/properties of modified starch. Results showed as compared with pure starch material, modified TPS processed at different temperatures (60-90℃) showed similar morphologies, thermal behaviors and tensile properties. The reaction ratio of PUP cross-linked to the starch matrix was 98.83±0.01%. The toughness and hydrophobicity of the modified TPS were significantly improved.Second, study the effect of polyurethane structure on the structure/properties of modified starch. (1). PUP with anion hydrophilic components of 2,2-dimethylol propionic acid (DMPA) was synthesized, and then was used to modify starch. The results showed that the elongation at break of the modified TPS increased from 5.4 to 9.8% with the content of PUP in modified TPS increasing from 10% to 20%. The reaction ratio of PUP used for preparing the modified TPS was 98.5±0.03%. Compared to oil-based PUP modified starch, the modified TPS showed increasing viscosity and decreasing contact angle. (2) PUP with nonion hydrophilic components of polyethylene glycol (PEG) was synthesized, and then was used to modify starch. The results showed the mechanical properties of modified starch decreased compared to pure starch. However, the modified TPS showed increasing viscosity and decreasing contact angle.In summary, the effect of processing temperature on the structure/properties of a novel starch thermoplastic was not obvious. This was because the formation of microparticles with a high amount of NCO groups and high reaction activity of each NCO group played important roles to improve the reaction efficiency. Further, compared to oil-based PUP, PUP containing hydrophilic components caused the increase of hydrophilicity of modified starch, which broadened application value of modified starch. Therefore, the modified method was feasible, effective and green.