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Hydrophobic thermoplastic starches modified with polyester-based polyurethane
microparticles: Effects of various diisocyanates
Yamei Leng, Yu Zhang, Xiaoxia Chen, Chao Yi, Bingbing Fan, Qiangxian Wu*
Green Polymer Lab, Polymer Science Dept., College of Chemistry, Huazhong Normal
University, Wuhan 430079, China
ABSTRACT: It is critical to prepare ductile and hydrophobic modified starch material
in an effective and environmentally friendly way. In this work, polyurethane
prepolymers (PUPs) with various isocyanates were synthesized and mixed reactively
with thermoplastic starches (TPS) in an intensive mixer to prepare modified TPS. The
effects of the isocyanates on the structure and properties of the modified TPS were then
investigated by using scanning electron microscope (ESEM), tensile tester and contact
angle meter. Results showed that mechanical properties of the modified TPS were
improved with the isocyanate’s hydrophobicity increased. 4,4’-methylenedi-p-phenyl
diisocyanate ( MDI ) was hydrophobic, the NCO groups in PUPs were not easily
consumed by water when preparing modified starch, leading to a significantly increased
reaction of the NCO groups with starch. As the amount of urethane bonds between
starch and PUP increased, the compatibility between the two polymers was also
improved resulting in the improvement of tensile properties. Isocyanates played an
important role in improving the compatibility between the starch and PUP and the
properties of the modified TPS.
Supporting Information
Photos of 5wt % corn starch (CS) and CPT2 aqueous solution are shown in figure 1, and the
image was taken immediately after cooked at 906 for 30 min. CS was swelled into water
and turbid solution was formed due to its hydrophilcity. However, CPT settled towards the
bottom and not swelled in water, which indicated that hydrophobic polyurethane
cross-linked with starch, and decreased the interaction between starch and water, the
hydrophobicity of obtained modified starch was improved. Figure 2 showed that PUTDI1
powder + CS and CPT were independently mixed with two immiscible solvents
(water-butyl acetate) with different polarities, to observe with which solvent they were the
best wetted. The NCO groups of PUTDI were consumed in preparing PUTDI powder, the
PUTDI powder had no interaction with starch, and therefore the CS and PUTDI powder
were remained in the water layer and in butyl acetate layer, respectively. However, all CPT
remained in water layer and there were nothing in butyl layer, indicating that the PUTDI
effectively linked to starch in modification procedure and the obtained modified starch was
stabilized. These results indicated PU effectively linked to starch and the hydrophobicity of
obtained modified starch was improved by our method.
Annotation: 1. Polyurethane prepolymer prepared with 2, 4-toluene diisocyanate was
designated as PUTDI.
2. Starch modified with the PUTDI was designated as CPT.
Figure Captions
Figure S1. Photos of 5wt % CS and CPT aqueous solution
Figure S2. Photos of PUTDI powder + CS and CPT were independently mixed with
water-butyl acetate
Figure S1. Photos of 5wt % CS and CPT aqueous solution
Figure S2. Photos of PUTDI powder + CS and CPT were independently mixed with
water-butyl acetate
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