Porous Starch Materials via Supercritical- and Freeze-Drying

Abstract

The production of porous materials based on starch has been explored with supercritical drying—yielding aerogel—and freeze-drying. The two drying procedures were applied on the same gelling solution of amylomaize starch pasted at 140 °C and for two concentrations (5 and 10 wt.%). After gelation and retrogradation, water from the samples to be supercritically dried was exchanged to ethanol. The resulting starch aerogel presented high specific surface area (197 m2/g). Freeze-drying was assessed by investigating the effect of the gelation, retrogradation, freezing temperature, and sublimation pressure. The resulting starch materials were macroporous, with limited specific surface area and limited mechanical integrity. Cohesive open cell foam with pore size of ~20 µm was produced by quenching the hot starch melt in liquid nitrogen. The highest specific surface area obtained with freeze-drying was 7.7 m2/g for the hot starch melt frozen at −20 °C.

Production of starch aerogel in form of monoliths and microparticles

“…These fibrils are composed of amylose crystal presenting a characteristic B-type Xray diffraction pattern corresponding to their double helix structure. Garcia-Gonzalez et al observed the same characteristic Xray diffraction pattern for starch aerogel [19] along with our results indicating a similar fibril structure in starch aerogel SEM pictures [36]. Lu et al studied the retrogradation of potato amylose at different temperatures and showed that after 24 h, only 13% of amylose retrograded at 25°C compared with 60% at 5°C [37].…”

Starch-Based Aerogels Obtained via Solvent-Induced Gelation

“…This important biopolymer is largely applied as thickening and gelling agent in food and non-food products [ 1 , 2 ]. Moreover, owing to its biodegradability and biocompatibility, starch has been widely associated with the development of new versatile eco-friendly porous materials, in particular, aerogels [ 3 , 4 , 5 , 6 ].…”

“…Starch-derived aerogels, low-density mesoporous solids with high specific surface area, are commonly prepared in three steps: hydrogel formation, solvent exchange using ethanol, and supercritical drying with carbon dioxide (CO 2 ) [ 3 , 7 ]. Aerogel properties are highly dependent on the source of starch and its concentration, degree of gelatinization, and retrogradation [ 3 , 8 ].…”

“…Starch-derived aerogels, low-density mesoporous solids with high specific surface area, are commonly prepared in three steps: hydrogel formation, solvent exchange using ethanol, and supercritical drying with carbon dioxide (CO 2 ) [ 3 , 7 ]. Aerogel properties are highly dependent on the source of starch and its concentration, degree of gelatinization, and retrogradation [ 3 , 8 ]. Starch-derived aerogels are suggested for many applications such as carriers for active compounds [ 8 , 9 , 10 , 11 ], thermal insulators [ 12 , 13 , 14 ], tissue engineering [ 15 , 16 ], as templates for making novel materials [ 17 ], and adsorbents [ 18 ].…”

Cryogelation and Cryogels

“…In several studies, the impact of gel formation parameters on mechanical and physical properties were investigated. Bauldron and colleagues investigated the difference between freeze-drying and supercritical drying on the physical properties of amylomaize starch gels [4]. It was determined that freeze-drying resulted in macroporous gels with 20-100 µm pores, whereas supercritical drying led to gels with 1 µm pores.…”