Hongshen Liu

Thermal and Rheological Properties of Breadfruit Starch

The thermal and rheological properties of breadfruit starch were studied using DSC and 2 different rheometers. It was found that the gelatinization temperature of starch with excess moisture content (>70%) was at approximately 75 °C. A new endotherm was detected at about 173 °C when the moisture content was lower than required for full gelatinization of the starch. A detailed examination revealed that this endotherm represented the melting of amylose-lipid complexes. Breadfruit starch paste exhibited shear-thinning fluid characteristics, and good thermal and pH stability. The setback viscosity of the breadfruit starch was lower than that of potato and corn starches. The rheological properties of the breadfruit starch paste was well described by the Herschel-Bulkley model at a shear rate of 0 to 100 s(-1), where R(2) is greater than 0.95, and it behaved like a yield-pseudoplastic fluid. Both the storage modulus and loss modulus of the paste initially increased sharply, then dropped after reaching the gelatinization peak. Breadfruit starch gel showed both flexibility and viscosity. Suspension with 6% starch content exhibited very weak gel rigidity; however, this increased significantly at starch contents above 20%.

Thermal behaviour of high amylose cornstarch studied by DSC

The thermal behaviour of high amylose cornstarches (80% amylose content) was studied by DSC using high pressure stainless steel pans in the temperature range between 0-350 °C. The number of endotherms and the enthalpy of gelatinization were found to depend on moisture content. Up to four endotherms and one exotherm were determined when the moisture content was above 40%. The meaning of each endotherm has been discussed. The enthalpy of gelatinization was calculated based on the summation of all the gelatinization endotherms and found to increase with increasing water content.

Effect of Compatibilizer Distribution on Thermal and Rheological Properties of Gelatinized Starch/Biodegradable Polyesters Blends

Abstract Thermal and rheological properties of various blends of gelatinized starch and biodegradable polyester, polycaprolactone (PCL) or poly(butylene succinate adipate) (PBSA), were studied by DSC, TGA and rheometry. Methylenediphenyl diisocyanate (MDI) was used as a compatibilizer and was distributed in different phases through controlled processing. The addition of MDI showed a stronger effect on thermal and rheological properties when it was mainly distributed in the polyester phase prior to blending. Starch was shown to increase the shear viscosity of both types of polyesters. The two blends, starch/PCL and starch/PBSA, showed a similar pattern of a power law dependence of viscosity on shear rate. MDI was shown to enhance the effect of starch on the melting and decomposition temperatures, especially when distributed in the polyester phase.

Synthesis and Characteristics of Graft Copolymerization of Starch-G-PAM Using A Twin-Roll Mixer as Reactor for Cornstarch with Different Amylose/Amylopectin Ratios

Abstract Starch-based superabsorbent polymers (SAPs) were produced by graft copolymerization of starch-g-acrylamide using a twin-roll mixer as reactor. This work focused on the effect of starch microstructure (amylose/amylopectin contents) from the same source (corn starch) on the graft ratio (GR), graft efficiency (GE) and Add-on (AO), as well as water absorption capability (WAC) of the SAPs, which were investigated by FTIR, NMR, gravimetric and TGA. The torque variation represented all the processing in the reactor, including compress, gelatinization, graft reaction and crosslinking. Results showed that all the starches were successfully grafted with acrylamide then crosslinked by N.N′-methylene-bisacrylamide through this technology. Both AO and GR increased with increasing amylose content. But the GE decreased with increasing amylose content, which is different from the results in the solution reaction. The higher WAC of high amylose starch-based SAP corresponds with higher AO and GR, while the higher WAC of waxy-based SAP corresponds with higher GE.