Unexpected Rheological Behavior of a Hydrophobic Associative

Jun 7, 2018 - E-mail: [email protected]., *Telephone: +86-871-63860021. E-mail: [email protected]. Cite this:J. Agric. Food Chem. XXXX, XXX ...
1 downloads 0 Views 1MB Size
Subscriber access provided by Kaohsiung Medical University

Biofuels and Biobased Materials

Unexpected Rheological Behavior of Hydrophobic Associative Shellac-based Oligomeric Food Thickener Jianan Gao, Kun Li, Juan Xu, Wen-wen Zhang, Jinju Ma, Lanxiang Liu, Yanlin Sun, Hong Zhang, and Kai Li J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b01148 • Publication Date (Web): 07 Jun 2018 Downloaded from http://pubs.acs.org on June 7, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22

Journal of Agricultural and Food Chemistry

1

Unexpected Rheological Behavior of Hydrophobic Associative

2

Shellac-based Oligomeric Food Thickener

3 4

†‡

Jianan Gao,













Kun Li, Juan Xu , Wenwen Zhang , Jinju Ma , Lanxiang Liu , Yanlin Sun, Hong †



5

Zhang, * Kai Li *

6

†Research Institute of Resources Insects, Chinese Academy of Forestry, Kunming, 650224,

7

People’s Republic of China

8

‡Faculty of Chemical Engineering and Technology, Kunming University of Science and

9

Technology, 650224, People’s Republic of China

10 11 12 13 14 15 16 17 18 19 20 21



22

(E - mail: [email protected] Phone: +86-871-63860021)

Correspondence to Kai Li

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

1

Abstract

2

The sodium shellac constituted of “surfactant” monomer, which is sensitive to shear

3

stress, exhibits shear-thickening behavior at low concentration (5 wt%), and reacts

4

with H+ to retain the transient high viscosity under shear, is introduced in this study.

5

The steady-shear flow test proved that under high shear rate, sodium shellac

6

suspension could change from Newtonian fluid to continuous shear thickening

7

non-Newtonian fluid. Dynamic oscillation test suggested that the sodium shellac

8

solution at low concentration (0.1 and 1 wt%) under low shear rate behaved as the

9

viscous fluid (G´´>G´), and the solution at high concentration (5, 10 and 15 wt%)

10

behaved as the elastic fluid (G´´1, and also in this regime, the viscosity of the five curves increased

9

mildly with the shear rate27. This indicated that under high shear rate, the sodium

10

shellac suspension could change from Newtonian fluid to continuous shear thickening

11

non-Newtonian fluid28.

12 13

Figure 3. Shear stress ()versus shear rate ( ) for sodium shellac suspensions, plotted

14

on a log-log scale.

15

The relationship between shear rate ( ) and viscosity (η) was present in Figure 4.

16

When the concentration of sodium shellac suspension was higher than 0.1 wt%, the

17

shearing thickening could be detected. This finding was also in agreement of the

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

1

previous result18, which stated that when the concentration of sodium shellac was

2

higher than CMC (1.189 g/mL, 0.1189 wt%), it could aggregate into clusters or

3

micelle beads. Thus, relationship curves of sodium shellac suspension with high

4

concentration could be divided into three regimes. Firstly, with the increase in shear

5

rate, the viscosity of sodium shellac decreased. This was a consequence of the

6

organized motion of sodium shellac beads under shear flow. Then, the viscosity of the

7

suspension under medium shear rate did not alter considerably. Notably, at higher

8

shear rates, the viscosity was raised with shear rate. Under high shear rate, the sodium

9

shellac clusters could get close to form big scale hydroclusters. Under the critical

10

shear rate ( c ), the viscosity of the solution begin to gradually increase. Meanwhile,

11

the  c was related to the concentration of the solution. As shown in Figure 4 (b), the

12

 c of the sodium shellac suspensions with 5, 10 and 15 wt% was 131, 148 and 185 S-1

13

respectively. The critical shear rate rise with the increasing concentration of sodium

14

shellac (Figure 4b). On the contrary, the critical shear rate decrease with the growing

15

concentration of hard square particle solution25. The shear-thickening reason for the

16

hard square particle solution could be due to the large-scale transient hydroclusters

17

assembled of hard square particles under strong hydrodynamic coupling29. So, it was

18

accessible to formation of large-scale hydroclusters in the solution with more particles.

19

But the solution of sodium shellac at the high concentration (> 5 wt%) behave as an

20

elastic solution (G´ > G´´) like a virtual gel (Figure 6) . So, before the

21

Shear-thickening, the solution should be changed from “elastic” to “viscous” state30.

22

As we know, there was some interaction between the sodium shellac particles14, 18. So,

ACS Paragon Plus Environment

Page 10 of 22

Page 11 of 22

Journal of Agricultural and Food Chemistry

1

more shear force was needed to disrupt the interactions among more particles.

2 3

Figure 4 Dependence of the steady shear viscosity ( ) on the shear rate ( ) for

4

sodium shellac suspensions with different concentrations at 25 oC (b).

5

Dynamic oscillation behavior

6

To our knowledge, the rheological property of sodium shellac in aqueous mode has

7

not yet been studied. Thus, several parameters of this solution need to be detected, for

8

example, the linear viscoelasticity region. Figure 5 showed that the linear-viscoelastic

9

regime decreased as the increase in sodium shellac content. When strain was higher

10

than 1.57%, the G´ of the sodium shellac suspension with 15 wt% had already begun

11

to reduce. Conversely, linear viscoelasticity region of 0.1 wt% sodium shellac almost

12

covers the whole shear rate region. Thus, it also could be suggested that the sodium

13

shellac with high content was more unstable under high strain than that under low

14

strain. As the Figure 5 showed, in the non-linear region of dynamic oscillation test

15

sodium shellac at low concentration (0.1 wt%) could be assumed as “viscous”

16

solution. Meanwhile, both viscoelastic modulus of the solution were nearly

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

1

independent of strain amplitude. It could be noted that sodium solution at low

2

concentration should be a true molecular solution in which there are no more

3

interactions. At high concentration (1 wt% and 5 wt% ), the sodium shellac solutions

4

also behave as viscous solutions under large strain amplitude, and G´´ was also

5

independent of strain amplitude. But G´ decreased with the increase of the strain

6

amplitude. So tan δ of the solution should also rise with the increasing of the strain

7

amplitude. It meant that under large strain amplitude the viscous solution does not

8

have enough time to respond to the stress. At higher concentration (10 wt% and 15

9

wt% ), with increase strain amplitude the shellac solution changed from elastic fluid

10

to viscous fluid. There was a “gel-sol” crosslinking point between the G´´ and G´. It

11

could be interpreted that there were strong interactions between particles of sodium

12

shellac solution at high concentration by which the solution behave like an elastic

13

three dimension gel. But this virtual gel network could be destroyed under larger

14

strain amplitude leading to make the solution act like a viscous dispersion solution.

15 16

Figure 5 Dynamic strain sweep for sodium shellac with different concentration. (solid

ACS Paragon Plus Environment

Page 12 of 22

Page 13 of 22

Journal of Agricultural and Food Chemistry

1

symbol represented G´ and hollow symbol represented G´´).

2 3

Figure 6. Strain sweep for sodium shellac with different concentration. (solid symbol

4

represented G´ and hollow symbol represented G´´).

5

The Figure 6 revealed that the sodium shellac solution at low concentration (0.1 and 1

6

wt%) and low shear rate regime represented classic viscous fluid behavior (G´´>G´),

7

and the solution at the high concentration (5, 10 and 15 wt%) represented the elastic

8

gel behavior (G´´G´), and the solution at the high

12

concentration (5, 10 and 15 wt%), represented the elastic gel behavior (G´´