Interactions of hydrophilic plasticizer molecules with amorphous starch biopolymer—an investigation into the glass transition and the water activity behavior

Abstract

In this article, we demonstrated that within a hydrophilic biopolymer–plasticizer system, the molecular “activity” of the plasticizer also influenced the extent of these interactions. We demonstrated through an analysis of crystallinity and calorimetry results that the equilibrium moisture content within the starch matrix can preferentially interact with the hydrophilic plasticizers and modify the polymer recrystallization process to an extent that the commonly acknowledged relationship between the crystallinity and the glass transition behavior is disrupted. Two plasticizers, glycerol (three OH groups) and xylitol (five OH groups), were selected. The water sorption isotherm of polymer samples with 5–20 wt % (dry basis) plasticizers were examined across a water activity range from ∼0.11 to ∼0.95 and using Guggenheim‐Anderson‐de Boer analysis, we compared the molar sorption enthalpies of various starch–plasticizer mixtures. Finally, the competitive plasticization between water and plasticizer molecules at different water activities was also discussed using known glass transition models. The analyses validated the antiplasticization limit for glycerol to be ∼10–15 wt %, but for xylitol, its antiplasticization behavior did not manifest till 20 wt %. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Behavior of biodegradable composites based on starch reinforced with modified cellulosic fibers

“…The GAB model (Guggenheim–Anderson–de Boer) has many advantages over the others, such as having a viable theoretical background because it is refinement of Langmuir and BET theories of physical adsorption, showing a good description of nearly all isotherms from 0 to 0.9 water activity, being mathematically simple, and being easy to interpret because parameters have a physical meaning …”

Advanced Nano-biocomposites Based on Starch

“…Thus, unstable processing or undesirable foaming may be caused due to the evaporation of the water. Furthermore, the final products based on starch containing only water usually have poor mechanical properties especially due to the brittleness, because of its final temperature usually lower than its glass transition temperature (T g ) Enrione et al 2010;Forssell et al 1997;Liu et al 2011bLiu et al , 2009bLiu et al , 2010aLourdin et al 1997) and/or resulting from the densification (happening below T g ) or retrogradation (also known as recrystallization, happening above T g ) (Atwell et al 1988;Bulkin et al 1987;Gudmundsson 1994;Liu and Thompson 1998). To overcome these issues, nonvolatile (at the processing temperature) plasticizers such as polyols (glycerol, sorbitol, glycol, etc.…”

Thermoplastic Starch

“…Competitive plasticisation has been assessed using glass transition temperature models. The study validated the anti-plasticization limit for glycerol to be ∼10-15 %·w/w, however for xylitol, its anti-plasticization limit did not manifest until 20 %·w/w (Liu, Chaudhary, Ingram, John, 2011). A new hydrogen bonding highly polar plasticizer, N,N-bis(2-hydroxyethyl)formamide, has been synthesized and used to prepare TPS from corn starch (Dai, Chang, Yu, Ma, 2008).…”