Effect of annealing on morphologies and performances of hydroxypropyl methylcellulose/hydroxypropyl starch blends

Abstract

The morphologies and performances of the blends of hydroxypropyl methylcellulose (HPMC), which is a thermal gel, and hydroxypropyl starch (HPS), which is a cooling gel, provides a scientific model to understand the relationship between the microstructure and performance of the unique thermal/cooling gel system. The films based on these blends have been developed for various applications, such as food packaging and medicine capsules, mainly for improving processibility. The morphologies and performance of the blends strongly depend on annealing or storage conditions and time since they are neither miscible nor compatible. This work focuses on the effects of storage conditions and time on the morphologies and performance of the blend films. It was found that the morphologies of the blend system depend on temperature, moisture, and annealing time. Correspondently, the gas permeability and mechanical properties of the film were also environmentally and time dependent. When HPS is continuous phase, the annealing results in starch recrystallization, which increases rigidity. When HPMC is the continuous phase, the materials showed less moisture sensitivity. Starch recrystallization and phase separation, which resulted in microcracks on the surface of the films, are the main reasons for the reduction in gas barrier and elongation. This work will study these issues using scanning electron microscope, X‐ray diffraction, mechanical testing and establish their relationship.

Influence of Ulluco Starch Modified by Annealing on the Physicochemical Properties of Biodegradable Films

“…These defects may be due to shrinkage of the starch phase after drying and may negatively affect material properties such as water vapor permeability and mechanical properties. A similar phenomenon was observed in hydroxypropyl methylcellulose/hydroxypropyl starch films [ 18 ]; the authors related the presence of the micro and macrocracks on the films’ surface with the decrease in elongation and increase of gas permeability. These micro and macro fractures may also be associated with the high degree of ordering of the modified starch compared to the native starch.…”

“…The differences in permeability in the analyzed samples can be related to the defects (macrocracks) in the morphologies of the films obtained with ANN starch. An increase in permeability related to defects in morphology was also observed in films prepared using a mixture of hydroxypropyl methylcellulose/hydroxypropyl starch [ 18 ]. In addition to the presence of macrocracks, the microcracks produced by the recrystallization of the modified starch could also influence the increase in permeability [ 21 ].…”

“…Generally, films with high crystallinity degrees presented high TS and YM values [ 28 , 29 , 30 ]. Another determining factor is the presence or absence of macro and microcracks in the morphology of starch annealed films which can influence the mechanical properties reducing its elasticity and others, such as barrier properties [ 18 ].…”