Starch crystallization, kinetics

Ke, T. and Sun, X. (2003) Melting behavior and crystallization kinetics of starch tmd poly(lactic add) composites. Journal of Applied Polymer Science, 89, 1203-1210. 

Ke T, Sun X (2003a), Melting behavior and crystallization kinetics of starch and poly(lactic acid) composites , J. Appl. Polym. Sci., 89(5) 1203-1210. 

Figure 49.2 shows the rate of NEB as a function of RH for lactose and lactose-gelatinized starch (3 1) systems incubated at 70°C. Since lactose is a reducing sugar, NEB rate values were higher in the lactose systems than in the lactose-starch ones as a result of a dilution effect of the reactants. As previously indicated the purpose was to compare the shape of the curves and the location of the maximum in the RH scale. The maximum NEB rate for the lactose system was observed at 43% RH, in which the sample was completely crystalline. The kinetics of lactose crystallization was delayed by the incorporation of starch. However, the RH value at which crystallization started was the same as the lactose system, and the rate of NEB decreased only slighly above 52% RH (Figure 49.2). Several other studies have also indicated that the addition of a polymer to an amorphous matrix delayed the crystallization of the sugar (Roos and Karel, 1991 O Brien, 1996 Gabarra and Hartel, 1998 Mazzobre et al., 2001 Biliaderis et al., 2002). At higher RH, the NEB rate dramatically decreased for lactose, which was completely crystalline and where water had an inhibitory effect on the reaction. In the...

The detailed thermal behaviours of the starch/PLA blends have been studied by DSC [204]. The experimental data was evaluated using the well-known Avrami kinetic model. Starch effectively increased the crystallization rate of PLA, even at a 1 % content, but the effect was less than that of talc. The crystallization rate of PLA increased slightly as the starch content in the blend was increased from 1 to 40 %. An additional crystallization of PLA was observed, and it affected the melting point and degree of crystalhnity of PLA. 

Kose and Kondo studied tbe size effects of cellulose nanofibres on the crystallization behaviour of PLA. They discovered that the smaller size of cellulose nanofibres on tbe nanoscale does not necessarily make a better nucleating agent for PLA. Table 9.1 summarizes the Avrami kinetic parameters for the isothermal crystallization of the PLA and PLA biocomposites with different types of nanocelluloses as compared to PLA composites with talc and nanoclay. With the addition of unmodified and silylated CNCs as nucleating agents, the t 2 value increases with increasing T similar to that of nanoclay and com starch, but opposite to that of talc. Comparing the... 

---