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