The retrogradation and physical ageing of model starch systems with respect to their glass transition temperatures Tg have been investigated by Fourier transform infrared Spectroscopy and solid state NMR spectroscopy. Diffuse reflectance Fourier transform infrared (DRIFT) spectra demonstrate the commencing retrogradation of starch materials stored above their Tg by changes in peak lineshapes and intensities in the characteristic area between 995 cm−1 and 1020 cm−1. Solid state NMR proton relaxation times in the rotating frame (proton T1ρ) show a characteristic course in relation to the storage conditions (time, humidity), for which a distinction is made between physical ageing which occurs below the Tg, and recrystallisation (retrogradation) which takes place above Tg. The proton T1ρ's of materials stored below Tg increase asymptotically in time due to physical ageing, whereas the proton T1ρ's of materials stored above Tg increase until a moisture content is reached that rises them above Tg, decrease due to further water absorption and then increase due to recrystallisation (retrogradation).

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Ageing of gelatinised and partly gelatinised potato starch and wheat starch were investigated in the presence of plasticisers with increasing size and number of OH groups (ethylene glycol, glycerol, threitol, xylitol, glucose, and for potato starch also maltose). The influences of these plasticisers and of granular remnants (ghosts) on recrystallisation were determined by using X-ray diffraction. Recrystallisation of potato starch samples in the presence of plasticisers resulted in crystallinity indices of ,0.5. The largest reduction in potato starch recrystallisation is found for threitol (4 OH) and xylitol (5 OH). In the plasticiser range examined, the crystallisation inducing effect of granular potato starch remnants is reduced better when the plasticiser contains more OH groups. Wheat starch recrystallises to a lesser extent than potato starch, resulting in crystallinity indices of , 0.4. The results for wheat starch do not show clear trends for the influences of plasticiser size and of ghosts. The difference in behaviour of the two starches is probably caused by wheat starch having shorter amylopectin chains. Resulting from these shorter amylopectin chains, the remaining structure in wheat starch ghosts may resemble A-type crystallinity, making it more difficult to form B-type crystals. Alternatively, the trends as found for potato starch may occur, but are less manifest for wheat starch, due to the lower total extent of recrystallisation. Solid state CP/MAS NMR spectra of the wheat starch samples containing ethylene glycol were obtained, in order to compare completely and partly gelatinised systems. The spectra were identical, confirming that the ghost structures do not influence wheat starch recrystallisation. Apparently, wheat starch ghosts do not act as nuclei for crystallisation.Similarly, the influence of various malto-oligosaccharides in combination with granular remnants (ghosts) was investigated on wheat starch ageing. Gelatinised and partly gelatinised wheat starch were plasticised with maltose, maltotriose, maltotetraose, maltopentaose or maltohexaose. This resulted in crystallinity indices of , 0.2, with the largest reduction in recrystallisation for maltotriose and maltotetraose. No trend was found for the influence of ghosts. The presence of ghosts did not influence the 13 C solid state HP/DEC NMR spectra. Less recrystallisation took place than with the previously mentioned smaller plasticisers that resulted in crystallinity indices of ,0.4. The finding that maltose was able to reduce retrogradation better than glucose could be of practical importance. q

The effect of processing temperature and time on the Btype crystallinity of thermoplastic starch was studied by recording X-ray diffractograms of conditioned, compression molded starch systems containing glycerol and water as plasticizers at a ratio of 100 : 30 : 56 (w/w/w). Initial recrystallization, developed during molding, was investigated further on similar amorphous potato starch and potato amylopectin systems. The crystallinity prior to processing does not influence the recrystallization, though residual (granular) crystallinity, present due to incomplete melting, increases the total crystallinity. After molding at high temperatures (b160°C), amylose is mainly responsible for initial recrystallization in the Btype lattice. The observed degree of recrystallization, however, cannot be due to amylose crystallization alone. Amylose seems to serve as a nucleus for crystallization of amylopectin or amylose±amylopectin co-crystallization takes place. Thermally induced starch polysaccharide±glycerol interactions were investigated on mixtures of dried starch and glycerol using differential scanning calorimetry and solid-state nuclear magnetic resonance spectroscopy. An exothermal transition was observed after which the mobility of glycerol was decreased significantly. This indicated the development of a strong polysaccharide±glycerol interaction in the absence of water.

The interaction between amylopectin, a starch polysaccharide, and ethylene glycol (EG) was investigated using broad-band dielectric relaxation spectroscopy. Water-free amylopectin (AP) was mixed with 21 wt % ethylene glycol. This resulted in a continuous ethylene glycol phase, as well as a molecularly mixed AP/EG fraction. After storage at room temperature or annealing, the mixture shows dynamic properties typical of a polymer with weak intermolecular interactions, suggesting that EG binds preferentially to AP and forms intrachain H-bridges leading to increased chain stiffness and thus an increased glass transition temperature. This structure evolution is accompanied by a sharp reduction in the size of the ethylene glycol droplets to a few nanometers, as revealed by pronounced confinement effects in the R-relaxation of the dispersed EG.