The Cross‐Linking of Polyurethane Incorporated with Starch Granules and their Rheological Properties: Influences of Starch Content and Reaction Conditions

Abstract

Abstract Two series of polyurethanes were synthesized using one‐ and two‐step reactions in a bulk phase at 175 °C with polycaprolactone diol, butane‐1,4‐diol, and 4,4‐diphenylmethane diisocyanate (MDI) in a suspension of starch granules to observe cross‐linking phenomena. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) analysis, and complex viscosity η *( ω ), storage G′ ( ω ), and loss‐modulus G″ ( ω ) as rheological measurements, were carried out to characterize the cross‐linking in the polyurethane incorporated with starch. SEM micrographs indicated that grafted polyurethane was cross‐linked between starch granules forming a three‐dimensional network. The plots of η * against ω , and log G′ against log G″ showed that the starch content increased cross‐linking, so as to induce gelation ( G′ ≥ G″ ). However, the cross‐linked networking was decreased over the higher range of starch contents (> 33 wt.‐% for the low hard‐segment series, psb2m3 and > 27 wt.‐% for the high hard‐segment series, psb4m5). Cross‐linking is also enhanced in the high hard‐segment series compared to the low hard‐segment series. Increasing the catalyst concentration also enhanced the cross‐linking inside of the polyurethane phase. Plots of η * against ω for p7s3b4m5(OSR C 0.01) and p7s3b4m5(TSR C 0.01). magnified image Plots of η * against ω for p7s3b4m5(OSR C 0.01) and p7s3b4m5(TSR C 0.01).