Structure and mechanical properties of hydroxypropylated starch films.
Films of acid-hydrolyzed hydroxypropylated pea starch with average molecular weight M w ranging from 3.3 x 10 (4) g/mol to 1.6 x 10 (6) g/mol were prepared from 25% (w/w) solution by casting. The structure of the films was investigated by means X-ray diffraction and calorimetry, evidencing a B-type crystalline structure. In similar drying conditions, 25 degrees C and 40% of relative humidity, the crystallinity varied from 24% for the low molecular weight (A5) to almost none for the highest molecular weight (A160). The influence of the drying temperature was also investigated. A reduction of the crystallinity from 16% to almost none was found when increasing temperature from 25 to 65 degrees C. The glass transition temperature ( T g) at different water contents was determined. The difference of T g between the first and the second scan was interpreted by changes in the water distribution between phases into the B-type crystalline structure. Mechanical properties of the films determined by tensile tests and by DMTA in the glassy state showed no effect of the average molecular weight or of crystallinity. In contrast, thermomechanical experiments by DMTA showed that the average molecular weight of the sample influenced the mechanical relaxation and the moduli in the rubbery state.
INRA, UR1268 Unité Biopolymères Interactions et Assemblage, rue de la Géraudière, F-44000 Nantes, France.
David
D
Lafargue
Bruno
B
Pontoire
Alain
A
Buléon
Jean Louis
JL
Doublier
Denis
D
Lourdin
D006868:Hydrolysis; D015394:Molecular Structure; D018532:Pisum sativum; D013213:Starch / Q000032:analysis* / Q000737:chemistry*; D013314:Stress, Mechanical; D013329:Structure-Activity Relationship
D013213:Starch