Effect of Crystallinity on the Glass Transition Temperature of Starch

Abstract

The glass transition temperature (T(g)) of potato and wheat starches, stored for several periods after gelatinization, was measured by differential scanning calorimetry (DSC), and the relative crystallinity of the starches was measured by X-ray diffractometry. T(g) of stored starches was higher than that of starches without storage, and the T(g) increment of starches gelatinized at 120 degrees C was higher than that of starches gelatinized at 60 degrees C. The water content at which the glass transition of a starch occurs at 25 degrees C was estimated from DSC data, and it increased linearly with relative crystallinity in two groups that differed in the gelatinization method. These results also showed the quantitative relationship between T(g) and retrogradation. In addition, these results suggested that the glass transition of starch could be interpreted in the same way as the glass transition of cross-linked synthetic polymers.

Impact of the Crystallinity on the Physical Properties of Inulin during Water Sorption

“…This difference can be explained by the fact that the crystallization of the whole amorphous matrix could physically entrap an amorphous fraction and this part is too highly constrained to crystallize further. These kinds of results were previously reported by Mizuno et al (1998) Stored at 0-59% RH, the semi-crystalline inulins were characterized by a dual endothermic peak (labeled peak 1 and 1′) at T 1 =171-172°C and T 1′ =178-179°C, which corresponded to the melting of two populations of crystals which probably differed by their shape, size, perfection, and/or molecular weight and thus led to different thermal properties (Figure 4a,b). The thermal profile (in open pans) of fully amorphous inulins was characterized by a jump at around 150°C, which corresponded to the glass transition temperature (Figure 4c,d).…”

Thermal, Mechanical, and Surface Properties of Poly(2‐N‐alkyl‐2‐oxazoline)s

“…[9] On the other hand for the samples with a butyl or with longer side-chains, the effect of crystallinity on the glass transition temperatures starts to play a role. According to Struik [18] and Mizuno et al, [19] a larger crystalline volume fraction in a semi-crystalline polymer disturbs the amorphous phase, increasing the materials T g . This may be the reason for the deviation of the PentOx in the M/I ¼ 60 series from the general trend, since for the M/I ¼ 100 series, the overall crystalline volume fraction is lower due to the longer main chains.…”

Enthalpy relaxation of gelatin in the glassy state

“…T g, c 1/2 p ) of the partially crystalline gelatin was slightly higher than that of the amorphous structure. This phenomenon is typical for many semi-crystalline synthetic polymers [33,34] and some biopolymers [28,35,36] and is discussed in more details in the following section. As expected both the glass transition and the melting endotherm shifted to lower temperatures as the water content increased reflecting the plasticisation of the polymer by water.…”