Water vapor sorption and glass transition temperatures of phase-separated amorphous blends of hydrophobically-modified starch and sucrose.

This article contains water vapor sorption data obtained on amorphous blends of octenyl succinic acid-modified (denoted as hydrophobically modified starch; HMS) and sucrose (S) in the anhydrous weight HMS/S ratios between 100/0 and 27/75. The water vapor sorption data was obtained gravimetrically. The amorphous state of the blends was confirmed by X-ray diffraction. The glass transition temperatures of the phase-separated blends are listed; the blends show phase separation into a sucrose-rich phase and a HMS-rich phase, the composition of which varies with the blend ratios. The sucrose-rich phase is characterized by a glass transition temperature T g,lower that is 40 to 90 K lower than the glass transition temperature T g,upper of the HMS-rich phase.

Specifications table

Value of the data

We present a broad set of water vapor data on blends of hydrophobically modified starch and sucrose with a systematic variation in composition. The water vapor data are obtained in the range between 0.11 and 0.75 at T = 298 K.

Data on the glass transition temperatures of the phase-separated blends is valuable in the context of the understanding of the phase behavior of amorphous phase-separated systems.

These data allow the exploration of the effect of composition on water vapor sorption behavior in the glass transition range.

Data

Spray-dried blends of hydrophobically-modified starch and sucrose were water activity-equilibrated at water activities 0.11, 0.22, 0.33, 0.43, 0.54, 0.68 and 0.75 (T = 298 K). Water vapor sorption was determined gravimetrically until equilibrium was achieved (1200 h); the data is reported in Table 1. Water activity-equilibrated samples were analyzed for eventual crystallinity by X-ray diffraction (Fig. 1) and for the glass transitions of the phase separated blends (sucrose-rich and modified starch-rich phases) by Differential Scanning Calorimetry (Tables 3 and 4).

Table 1

Equilibrium water content of water activity equilibrated HMS-S blends at T = 298 K.

aw(T = 298 K)	Water content on wet basis [wt.%]
	100/0	90/10	80/20	60/40	45/55	25/75
0.11	6.1	4.7	3.3	2.4	2.3	2.3
0.22	7.7	6.0	4.6	3.9	4.4	4.6
0.33	9.1	7.1	5.7	5.5	6.4	6.8
0.43	10.4	8.3	7.4	7.9	9.2	10.1
0.54	11.7	9.7	9.2	10.5	12.0	13.6
0.75	15.9	15.1	16.9	19.6	22.9	29.8

Fig. 1

Normalized powder X-ray diffraction profiles of spray-dried HMS/S blends equilibrated at selected water activities. Q׳s is the weight fraction of sucrose in the HMS/S blends on anhydrous basis.

Table 3

Water content and parameters associated with the glass transition fitting, as described in Section 2.4 of [2], for water activity equilibrated HMS-S blends. Q׳s is the weight fraction of sucrose in the HMS-S blends (on anhydrous basis), Qw is the weight fraction of water in the matrices, ∆Cp,lower and ∆Cp,upper are the changes in heat capacity associated with the lower and upper glass transitions, Tg,lower and Tg,upper are the glass transition temperatures and of the sucrose-rich and the HMS-rich phases, respectively, and ∆Tg,lower and ∆Tg,lower are the widths of the two glass transitions.

Qs[dimensionless]	aw[dimensionless]	Qw[dimensionless]	∆Cp,lower[J g−1K−1]	Tg,lower[K]	∆Tg,lower[K]	∆Cp,upper[J g−1K−1]	Tg,upper[K]	∆Tg,upper[K]
0	0.11	6	–	–	–	0.16 ± 0.01	405 ± 1	13 ± 1
	0.22	7.7	–	–	–	0.16 ± 0.01	388 ± 1	16 ± 1
	0.33	9.1	–	–	–	0.17 ± 0.01	377 ± 1	15 ± 1
	0.43	10.4	–	–	–	0.17 ± 0.01	366 ± 1	16 ± 1
	0.54	11.7	–	–	–	0.17 ± 0.01	357 ± 1	14 ± 1
	0.68	14.1	–	–	–	0.19 ± 0.01	337 ± 1	17 ± 1
	0.75	15.9	–	–	–	0.19 ± 0.01	325 ± 1	18 ± 1
0.1	0.11	4.7	0.41 ± 0.04	330 ± 2	84 ± 6	0.16 ± 0.01	378 ± 1	20 ± 1
	0.22	6	0.44 ± 0.03	322 ± 2	80 ± 5	0.16 ± 0.01	366 ± 1	20 ± 1
	0.33	7.1	0.43 ± 0.03	312 ± 2	76 ± 5	0.19 ± 0.01	356 ± 1	22 ± 1
	0.43	8.3	0.42 ± 0.03	305 ± 2	70 ± 5	0.20 ± 0.02	347 ± 1	22 ± 1
	0.54	9.7	0.44 ± 0.03	295 ± 2	70 ± 4	0.22 ± 0.02	337 ± 1	22 ± 1
	0.75	15.1	0.54 ± 0.03	270 ± 1	69 ± 3	0.18 ± 0.01	307 ± 1	22 ± 1
0.2	0.11	3.3	0.51 ± 0.03	327 ± 1	65 ± 3	0.12 ± 0.02	365 ± 1	23 ± 2
	0.22	4.6	0.50 ± 0.03	313 ± 1	59 ± 3	0.17 ± 0.02	350 ± 1	24 ± 2
	0.33	5.7	0.50 ± 0.02	303 ± 1	54 ± 2	0.19 ± 0.02	341 ± 1	22 ± 1
	0.43	7.4	0.49 ± 0.01	291 ± 1	48 ± 1	0.19 ± 0.01	330 ± 1	21 ± 1
	0.54	9.2	0.51 ± 0.01	284 ± 1	47 ± 1	0.18 ± 0.01	323 ± 1	22 ± 1
	0.75	17	0.53 ± 0.01	245 ± 1	37 ± 1	0.21 ± 0.01	281 ± 1	26 ± 1
						(0.04 ± 0.01	323 ± 1	17 ± 3)a
0.4	0.11	2.4	0.52 ± 0.01	320 ± 1	28 ± 1	0.11 ± 0.01	348 ± 1	16 ± 1
	0.22	3.9	0.55 ± 0.01	304 ± 1	25 ± 1	0.13 ± 0.01	336 ± 1	20 ± 1
	0.33	5.5	0.55 ± 0.01	290 ± 1	22 ± 1	0.16 ± 0.01	324 ± 1	30 ± 2
	0.43	7.9	0.81 ± 0.02	278 ± 1	17 ± 1	0.03 ± 0.01	336 ± 1	25 ± 3
	0.54	10.5	0.70 ± 0.02	262 ± 1	15 ± 1	0.06 ± 0.01	332 ± 1	23 ± 3
	0.75	19.6	0.85 ± 0.02	232 ± 1	15 ± 1	0.09 ± 0.01	323 ± 1	22 ± 2
0.55	0.11	2.3	0.58 ± 0.01	302 ± 1	16 ± 1	0.13 ± 0.01	342 ± 1	23 ± 2
	0.22	4.4	0.68 ± 0.01	286 ± 1	11 ± 1	0.13 ± 0.01	341 ± 1	19 ± 1
	0.33	6.4	0.72 ± 0.02	269 ± 1	11 ± 1	0.10 ± 0.01	335 ± 1	18 ± 1
	0.43	9.2	0.75 ± 0.02	259 ± 1	11 ± 1	0.12 ± 0.01	333 ± 1	21 ± 1
	0.54	12	0.81 ± 0.02	247 ± 1	11 ± 1	0.12 ± 0.01	328 ± 1	20 ± 1
	0.75	22.9	0.68 ± 0.03	216 ± 1	9 ± 1	0.09 ± 0.01	315 ± 1	21 ± 2
0.75	0.11	1.9	0.72 ± 0.02	301 ± 1	9 ± 1	0.09 ± 0.01	350 ± 1	19 ± 2
	0.22	4.2	0.72 ± 0.02	286 ± 1	8 ± 1	0.09 ± 0.01	345 ± 1	19 ± 2
	0.33	6.2	0.72 ± 0.03	273 ± 1	7 ± 1	0.09 ± 0.01	340 ± 1	19 ± 1
	0.43	7.6	0.85 ± 0.02	258 ± 1	9 ± 1	0.12 ± 0.01	334 ± 1	23 ± 1
	0.54	11.8	0.61 ± 0.07	246 ± 1	8 ± 1	0.09 ± 0.01	331 ± 1	20 ± 2
	0.75	24.2	0.80 ± 0.04	214 ± 1	7 ± 1	0.18 ± 0.01	325 ± 1	25 ± 2

Parameters of a third resolved glass transition in the Q′S = 0.2, aw = 0.75 HMS-S blend.

Table 4

Water activity and parameters associated with the glass transition fitting, as described in Section 2.4 of [2], for the oven-dried HMS-S blends. Q׳s is the weight fraction of sucrose in the HMS-S blends (on anhydrous basis), aw is the water activity of the matrices, ∆Cp,lower and ∆Cp,upper are the changes in heat capacity associated with the lower and upper glass transitions, Tg,lower and Tg,upper are the glass transition temperatures and of the sucrose-rich and the HMS-rich phases, respectively, and ∆Tg,lower and ∆Tg,lower are the widths of the two glass transitions.

Q׳S[dimensionless]	aw[dimensionless]	∆Cp,lower[J g−1K−1]	Tg,lower[K]	∆Tg,lower[K]	∆Cp,upper[J g−1K−1]	Tg,upper[K]	∆Tg,upper[K]
0	0.014	–	–	–	0.16 ± 0.01	449 ± 4	15 ± 1
0.1	0.01	0.31 ± 0.05	390 ± 7	140 ± 20	0.08 ± 0.01	430 ± 1	15 ± 1
0.2	0.013	0.40 ± 0.02	361 ± 1	74 ± 3	0.09 ± 0.01	396 ± 1	16 ± 1
0.4	0.031	0.46 ± 0.01	331 ± 1	33 ± 1	0.08 ± 0.01	357 ± 1	19 ± 1
0.55	0.112	0.53 ± 0.01	310 ± 1	20 ± 1	0.11 ± 0.01	342 ± 8	27 ± 3
0.75	0.163	0.60 ± 0.01	301 ± 1	13 ± 1	0.07 ± 0.01	350 ± 1	20 ± 2

The water vapor sorption data in Fig. 2 are fitted by the GAB equation (Fig. 2):where K, C and Wm are fitting coefficients [3].

Fig. 2

Water vapor sorption isotherms of the HMS-S blends at T = 298 K fitted with the GAB equation. The fitting coefficients are collected in Table 2.

Table 2

GAB fitting coefficients for the water vapor sorption isotherms of the HMS-S blends.

GAB coefficient	HMS-S blend
	100/0	90/10	80/20	60/40	45/55	25/75
K	0.767	0.91	1.03	0.99	1.00	1.06
C	27.2	33.5	12.8	3.06	2.58	2.50
Wm	8.25	5.67	4.77	6.99	8.45	7.25

Experimental design, materials, and method

HMS-S blends were prepared by spray drying aqueous dispersions with well-defined ratios of HMS and S [2]. The blends were then equilibrated at a range of water activities (aw) at T = 298 K in desiccators containing saturated salt solutions (aw (salt) = 0.11 (LiCl), 0.22 (CH3COOK), 0.33 (MgCl2), 0.43 (K2CO3), 0.54 (Mg(NO3)2), 0.75 (NaCl). The pure spray-dried HMS (Q′S = 0.0) was also equilibrated at aw = 0.68 (KI)). The water activities are given by Greenspan [1]. Water sorption was followed gravimetrically for 1200 h. In this time, all samples reached their equilibrium water content. The water content of the blends was determined from the weight loss/gain upon water activity equilibration and the initial water content of the blends. These initial water contents were Initial water contents of the HMS-S blends were determined by dehydration in a laboratory oven for 27 h at 253 K at a pressure below 25 mbar and under a slight flow of dry nitrogen. Powder diffraction patterns were collected using a Phillips X׳pert Pro diffractometer (Panalytical) operating at 40 kV and 30 mA utilizing Cu Kα radiation (λ = 0.154 nm). Scans were performed at 298 K under local atmospheric humidity over the 2θ range 5–35° with a step size of 0.02° and a data acquisition time of 2 s at each step. Glass transition temperatures were determined from the 2nd heating ramp of experiments carried out by Differential Scanning Calorimetry (DSC) as described by [2]. The midpoint glass transitions were extracted from the thermograms by deconvolution assuming the presence of multiple glass transitions each characterized by a Gaussian line shape of the first derivative of the heat flow curve [2].

Subject area	Physical chemistry
More specific subject area	Hydrocolloids, carbohydrate polymers, phase transitions
Type of data	Table (Water vapor sorption, glass transition data), figure (X-ray diffraction, Water vapor sorption isotherms
How data was acquired	Water vapor sorption data (gravimetric analysis); X-ray diffraction data (Phillips X’pert Pro diffractometer (Panalytical)); Differential Scanning Calorimetry (Discovery DSC, TA Instruments)
Data format	Analyzed data
Experimental factors	Spray-dried blends of Octenyl succinic acid-modified starch and sucrose in the anhydrous weight ratios 100/0, 90/10, 80/20, 60/40, 45/55 and 25/75.
Experimental features	Spray-dried blends were water activity-equilibrated at water activities 0.11, 0.22, 0.33, 0.43, 0.54, 0.68 and 0.75 (T = 298 K). Water vapor sorption was determined gravimetrically until equilibrium was achieved (1200 hours). Water activity-equilibrated samples were analyzed for eventual crystallinity by X-ray diffraction and for the glass transitions of the phase separated blends (sucrose-rich and modified starch-rich phases) by Differential Scanning Calorimetry.
Data source location	NA
Data accessibility	NA
Related research article	D. J. Hughes, G. Badolato Bönisch, T. Zwick, C. Schäfer, C. Tedeschi, B. Leuenberger, F. Martini, G. Mencarini, M. Geppi, M. A. Alam, J. Ubbink, Phase separation in amorphous hydrophobically-modified starch - sucrose blends: Glass transition, matrix dynamics and phase behavior, Carbohydrate Polymers (in press)