Positron annihilation study of biopolymer inulin for understanding its structural organization

•Positron annihilation study of the edible polymer inulin as a non-destructive, in-situ probe is reported for the first time.•It reveals important structural characteristics of Inulin.•Non-monotonous temperature variations of the structure are important for shelf food storage.•Temperature dependent free volume analysis depicts a thermotropic transition ∼320-330 K, and loss of structure beyond 330 K.

Inulins are nano-meter size semi-crystalline particles, composed of oligomeric fructose units. This bio-macromolecular material has been subjected to fine micro-structural analysis under temperature variations using mainly positron annihilation spectroscopy for the first time. The results show a non-monotonous temperature sensitive behavior of the positron parameters that help to understand the molecular stacking pattern. Considerable variation of its free volume size has been observed through the ortho-positronium pick-off component annihilation results. The material shows a major thermotropic transition at ∼320 K and further a structure loss due to glass transition. Differential Scanning Calorimetry confirms the onset of the major molecular transition around the same temperature with an enthalpy change of ΔH ∼379 J/gm and thermo-gravimetric analysis shows a ∼7.5% mass loss in the said transition.

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