- Email: [email protected]
Temperature buffering capacity of silk hydrogel: A useful packaging material
Accepted Manuscript Temperature buffering capacity of silk hydrogel: A useful packaging material Liang Zhao, Yu Li, Hao Wang, Jie Luo, Guolin Song, Guoyi Tang PII: DOI: Reference:
S0167-577X(17)31434-9 https://doi.org/10.1016/j.matlet.2017.09.088 MLBLUE 23202
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
14 February 2017 15 September 2017 23 September 2017
Please cite this article as: L. Zhao, Y. Li, H. Wang, J. Luo, G. Song, G. Tang, Temperature buffering capacity of silk hydrogel: A useful packaging material, Materials Letters (2017), doi: https://doi.org/10.1016/j.matlet. 2017.09.088
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Temperature buffering capacity of silk hydrogel: A useful packaging material
Liang Zhao1, 2, Yu Li1, 2, Hao Wang1, 2, Jie Luo1, 3, Guolin Song1,*, Guoyi Tang1, * 1.
Advanced Materials Institute and Clearer Production Key Laboratory, Graduate School at Shenzhen, Tsinghua
University, Shenzhen 518055, China 2.
School of Materials Science and Engineering, Tsinghua University, Haidian District, Beijing 100084, China
3.
School of Materials Science and Energy Engineering, Foshan Univercity, Foshan 528000, China
Abstract: The n-octadecane incorporated silk hydrogel is developed by the gelation of an o/w emulsion made of
n-octadecane and the aqueous silk solution acting as the oil and water phases, respectively. SEM images show
that n-octadecane grains can be clearly observed in the pores of the lyophilized hydrogel, which indicates the
successful embedment of n-octadecane in the composite hydrogel. Furthermore, the composite hydrogel exhibits
good water absorption capability and thermal regulation capacity. Therefore the silk composite hydrogel can be a
promising candidate as the potential packaging structures for temperature sensitive materials.
Keywords: Biomaterials; Silk hydrogel; Phase change materials; Thermal properties; Packaging materials
1.
Introduction
Packaging with the efficient temperature buffering capacity for the preservation and transportation of
temperature sensitive materials (TSM) including beverages, pharmaceutical products, blood derivatives and
others has been highly desirable [1]. The incorporation of phase change materials (PCMs) into the packaging
*
Corresponding author Tel.: +86 0 755 26036752
E-mail addresses: [email protected] (G. Song); [email protected] (G. Tang). 1
structures, which have the capability to store heat and cold in a range of only several degrees through the phase
transition process, has been developed recently as a promising candidate to maintain TSM within the desired
temperature limits [2]. Meanwhile, the development of bio-based polymeric hydrogel as the novel packaging for
TSM has aroused considerable research interests due to the desirable properties of high water absorption capacity,
flexibility, biodegradability, etc [3]. The high water absorption capacity of hydrogel resulting from the
macromolecular three-dimensional (3D) networks is important for the absorption of the moisture released by
TSM, such as the fresh fruits, vegetables and the food stuffs, and this is helpful for preventing them from fast
decay [4]. However, the bio-based hydrogel lacks the capability to buffer the potential temperature fluctuations,
and therefore the embedment of PCMs into the bio-based hydrogel could endow it with the characteristic
properties of thermal regulation for the conservation of TSM safely and effectively.
Silk hydrogel has been recently received great attention in the biomedical engineering field due to its
distinctive properties of biodegradability, biocompatibility, 3D porous structure and minimal inflammatory
responses in vivo [5]. This work is accordingly dedicated to incorporate PCMs into the silk hydrogel for the
application as the novel packaging materials for TSM. Furthermore, n-octadecane has been chosen as PCMs
because of its distinctive features of high heat storage density, minute supercooling degree, non-toxicity and
non-corrosion [6]. It is noteworthy to mention that it is incompatible of n-octadecane with the aqueous silk
solution, leading to the difficulty of the direct incorporation of n-octadecane into the silk hydrogel. The gelation
2
of an o/w (oil-in-water) emulsion composed of n-octadecane and aqueous silk solution acting as the oil and water
phases, respectively, could be a feasible way to solve this problem. However, kinds of surfactants as the
emulsifiers to prepare the stable emulsion can usually stimulate the gelation of silk solution, resulting in the
separation of oil and water phases during the fabrication process of the emulsion [7]. Therefore it is reasonably
significant to choose the suitable surfactants to emulsify the blend of n-octadecane and the silk solution before
the fabrication of the n-octadecane incorporated silk hydrogel.
In addition, it has been reported that the silk hydrogel with superior mechanical performance can be got by
the physical crosslinking of silk with cellulose [8], and accordingly the formation of silk hydrogel in the present
work is designed to be developed by this way.
2.
Experimental
The aqueous silk solution was fabricated from Bombyx mori silkworm cocoons according to the procedures
reported previously [9]. The silk solution was concentrated against the PEG solution to the concentration of 8
wt%. Then the hydroxypropyl methyl cellulose (HPMC) powders were dissolved in the deionized water to yield
the solution with the concentration of 5 wt%. The synthetic process for the fabrication of n-octadecane
incorporated silk hydrogel has been illustrated in Fig. 1 and the typical procedures can be described as follows:
firstly, the silk solution and HPMC solution were mixed with the weight ratio of 3:1 and a homogeneous and
transparent mixture solution was formed after the ultrasonic treatment to remove the bubbles. Subsequently,
3
n-octadecane and the mixture solution were mixed according the weight ratios listed in Table 1 and the blend
was emulsified at 40 °C with the aid of the compound emulsifier made of span-80 and hexadecyltrimethyl
ammonium bromide (CTAB). Then the stable o/w emulsion was sealed and incubated in an oven at the
temperature of 75 °C for 2 h to prepare the silk hydrogel. Finally, the silk hydrogel was freeze-dried at -60 °C for
24 h to obtain the silk sponges (dried hydrogel).
Then the morphologies and thermal behaviors of the lyophilized silk hydrogel were investigated by means
of field emission scanning electron microscope (FE-SEM) and differential scanning calorimeter (DSC),
respectively. The water uptake of the hydrogel was determined from Equation (1), where Wd and Ws are the mass
of the dry hydrogel and the swollen one after immersing it in the deionized water at 37 °C for 24 h [10].
Water uptake (%) = (Ws-Wd)*100/Ws
3.
(1)
Results and Discussion
SEM images in Fig.2a and 2b show that the freeze-dried pure silk hydrogel presents the laminar
microstructure with the pore size of about 60 µm. The composite silk hydrogel was subjected to the acetone
solvent to remove n-octadecane within it for the morphology comparison with the pure one. As shown in Fig 2c
and 2d, even though the overall morphology of n-octadecane incorporated hydrogel is similar with that of the
pure one, the pores are relatively smaller and the surrounded silk layers are prone to have some orientation. In
addition, the n-octadecane grains can be also observed in the pores of the original composite silk hydrogel (Fig.
4
2e and 2f), indicating the successful embedment of n-octadecane in the composite hydrogel.
The water absorption capability of the freeze-dried hydrogel is listed in Table 1, and it is observed that the
water uptake decreases from 91.0 to 87.4% when the amount of n-octadecane added into the mixture solution
increases from 0 to 0.4 g. The slight decrease of the water uptake capacity results from the fact that the
occupation of n-octadecane in the pores has limited the space to capture more water (as shown in Fig.2f). It can
be clearly seen that there is no significant difference of the water uptake between the composite hydrogel and the
pure one, which indicates that the n-octadecane incorporated silk hydrogel also exhibits good water absorption
capability.
Fig.3 shows the solidifying and melting curves of pristine n-octadecane and the freeze-dried composite
hydrogel prepared from different amount of n-octadecane during the cooling and heating process. There is an
intensive peak and a weak shoulder peak in the solidifying curve of pristine n-octadecane; whereas it is observed
two distinctive crystallization peaks for n-octadecane within the composite hydrogel. The crystallization peak at
higher temperature for the composite hydrogel can be attributed to the heterogeneous nucleation effect of
n-octadecane grains on the surrounded silk layers of the composite hydrogel. In addition, the phase-change
enthalpies of the composite hydrogel calculated from the DSC curves are listed in Table 1. It is readily seen that
the melting enthalpy of the composite hydrogel increases from 26.0 to 125.3 J/g when the amount of
n-octadecane added into the mixture solution increases from 0.2 to 0.4 g. Although this value is still lower than
5
that of pristine n-octadecane (189.1 J/g), the composite silk hydrogel exhibits the comparable latent heat capacity
compared with other thermal energy storage materials [11]. The composite silk hydrogel could absorb or release
thermal energy through the phase change of n-octadecane within it when the environmental temperature alters.
Therefore it is concluded that the composite silk hydrogel has been endowed with the temperature buffering
property by the incorporation of n-octadecane.
4.
Conclusions
In summary, the incorporation of n-octadecane into the silk hydrogel is fabricated by the gelation of the o/w
emulsion wherein n-octadecane and the aqueous silk solution serves as the oil and water phases, respectively.
The composite silk hydrogel presents the novel property of temperature buffering in addition to the high water
absorption capability. Therefore the composite silk hydrogel can be a great candidate for the application as
packaging structures for the conservation and transport of temperature sensitive materials safely and effectively.
References: [1] W. Chalco-Sandoval, J.F. Fabra, L. Amparo, J.M. Lagaron, Electrospun Heat Management Polymeric Materials of Interest in Food Refrigeration and Packaging, J. Appl. Polym. Sci. 131 (2014) 40661. [2] W. Chalco-Sandoval, M.J. Fabra, A. López-Rubio, J.M. Lagaron, Development of polystyrene-based films with temperature buffering capacity for smart food packaging, J. Food Eng. 164 (2015) 55-62. [3] N. Roy, N. Saha, T. Kitano, P. Saha, Biodegradation of PVP–CMC hydrogel film: A useful food packaging material, Carbohyd. Polym. 89 (2012) 346-353. [4] L. Wang, J. Rhim, Preparation and application of agar/alginate/collagen ternary blend functional food packaging films, Int. J. Biol. Macromol. 80 (2015) 460-468. [5] J. Ming, M. Li, Y. Han, Y. Chen, H. Li, B. Zuo, F. Pan, Novel two-step method to form silk fibroin fibrous hydrogel, Materials Science and Engineering: C 59 (2016) 185-192. [6] L. Zhao, H. Wang, J. Luo, Y. Liu, G. Song, G. Tang, Fabrication and properties of microencapsulated
6
n-octadecane with TiO2 shell as thermal energy storage materials, Sol. Energy 127 (2016) 28-35. [7] J.H. Park, M.H. Kim, L. Jeong, D. Cho, O.H. Kwon, W.H. Park, Effect of surfactants on sol–gel transition of silk fibroin, J. Sol-Gel Sci. Techn. 71 (2014) 364-371. [8] K. Luo, Y. Yang, Z. Shao, Physically Crosslinked Biocompatible Silk-Fibroin-Based Hydrogels with High Mechanical Performance, Adv. Funct. Mater. 26 (2016) 872-880. [9] L. Zhao, J. Luo, H. Wang, G. Song, G. Tang, Self-assembly fabrication of microencapsulated n-octadecane with natural silk fibroin shell for thermal-regulating textiles, Appl. Therm. Eng. 99 (2016) 495-501. [10] K. Naresh, H. Nicholas, P. Ognen, K. Dana, V. Fritz, Silk fibroin gelation via non-solvent induced phase separation, Biomater. Sci.-UK 4 (2016) 460-473. [11] Y. Ma, X. Chu, G. Tang, Y. Yao, Synthesis and thermal properties of acrylate-based polymer shell microcapsules with binary core as phase change materials, Mater. Lett. 91 (2013) 133-135.
7
Fig.1. Schematic fabrication of the silk composite hydrogel. Fig.2. SEM images of the freeze-dried pure hydrogel (a, b) and composite hydrogel of sample 2 (c, d, e, f). Fig. 3. The melting and solidifying DSC curves of (a) pristine n-octadecane, (b) sample 1, (c) sample 2 and (d) sample 3.
8
9
10
11
Table 1 Basic formulations and properties of the silk composite hydrogel The absorption
Thermal
capacity
properties
Basic formulations Sample Mixture
n-octadecane
CTAB a
Span-80
Water uptake
∆Hm b
∆Hc b
(g)
(g)
(g)
(g)
(%)
(J/g)
(J/g)
Pure gel
5.00
-
-
-
91.0
-
-
1
5.00
0.20
0.20
0.04
90.9
26.0
22.7
2
5.00
0.30
0.30
0.06
88.5
60.4
58.9
3
5.00
0.40
0.40
0.08
87.4
125.3
125.2
No.
a
The concentration of CTAB solution is 2 wt%.
b
The melting and crystallization enthalpies of the samples.
12
13
Highlights
The n-octadecane incorporated silk hydrogel has been successfully fabricated.
The n-octadecane grains have been observed in the pores of the hydrogel.
The hydrogel shows high water uptake capacity and thermal regulation property.
14
S0167-577X(17)31434-9 https://doi.org/10.1016/j.matlet.2017.09.088 MLBLUE 23202
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
14 February 2017 15 September 2017 23 September 2017
Please cite this article as: L. Zhao, Y. Li, H. Wang, J. Luo, G. Song, G. Tang, Temperature buffering capacity of silk hydrogel: A useful packaging material, Materials Letters (2017), doi: https://doi.org/10.1016/j.matlet. 2017.09.088
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Temperature buffering capacity of silk hydrogel: A useful packaging material
Liang Zhao1, 2, Yu Li1, 2, Hao Wang1, 2, Jie Luo1, 3, Guolin Song1,*, Guoyi Tang1, * 1.
Advanced Materials Institute and Clearer Production Key Laboratory, Graduate School at Shenzhen, Tsinghua
University, Shenzhen 518055, China 2.
School of Materials Science and Engineering, Tsinghua University, Haidian District, Beijing 100084, China
3.
School of Materials Science and Energy Engineering, Foshan Univercity, Foshan 528000, China
Abstract: The n-octadecane incorporated silk hydrogel is developed by the gelation of an o/w emulsion made of
n-octadecane and the aqueous silk solution acting as the oil and water phases, respectively. SEM images show
that n-octadecane grains can be clearly observed in the pores of the lyophilized hydrogel, which indicates the
successful embedment of n-octadecane in the composite hydrogel. Furthermore, the composite hydrogel exhibits
good water absorption capability and thermal regulation capacity. Therefore the silk composite hydrogel can be a
promising candidate as the potential packaging structures for temperature sensitive materials.
Keywords: Biomaterials; Silk hydrogel; Phase change materials; Thermal properties; Packaging materials
1.
Introduction
Packaging with the efficient temperature buffering capacity for the preservation and transportation of
temperature sensitive materials (TSM) including beverages, pharmaceutical products, blood derivatives and
others has been highly desirable [1]. The incorporation of phase change materials (PCMs) into the packaging
*
Corresponding author Tel.: +86 0 755 26036752
E-mail addresses: [email protected] (G. Song); [email protected] (G. Tang). 1
structures, which have the capability to store heat and cold in a range of only several degrees through the phase
transition process, has been developed recently as a promising candidate to maintain TSM within the desired
temperature limits [2]. Meanwhile, the development of bio-based polymeric hydrogel as the novel packaging for
TSM has aroused considerable research interests due to the desirable properties of high water absorption capacity,
flexibility, biodegradability, etc [3]. The high water absorption capacity of hydrogel resulting from the
macromolecular three-dimensional (3D) networks is important for the absorption of the moisture released by
TSM, such as the fresh fruits, vegetables and the food stuffs, and this is helpful for preventing them from fast
decay [4]. However, the bio-based hydrogel lacks the capability to buffer the potential temperature fluctuations,
and therefore the embedment of PCMs into the bio-based hydrogel could endow it with the characteristic
properties of thermal regulation for the conservation of TSM safely and effectively.
Silk hydrogel has been recently received great attention in the biomedical engineering field due to its
distinctive properties of biodegradability, biocompatibility, 3D porous structure and minimal inflammatory
responses in vivo [5]. This work is accordingly dedicated to incorporate PCMs into the silk hydrogel for the
application as the novel packaging materials for TSM. Furthermore, n-octadecane has been chosen as PCMs
because of its distinctive features of high heat storage density, minute supercooling degree, non-toxicity and
non-corrosion [6]. It is noteworthy to mention that it is incompatible of n-octadecane with the aqueous silk
solution, leading to the difficulty of the direct incorporation of n-octadecane into the silk hydrogel. The gelation
2
of an o/w (oil-in-water) emulsion composed of n-octadecane and aqueous silk solution acting as the oil and water
phases, respectively, could be a feasible way to solve this problem. However, kinds of surfactants as the
emulsifiers to prepare the stable emulsion can usually stimulate the gelation of silk solution, resulting in the
separation of oil and water phases during the fabrication process of the emulsion [7]. Therefore it is reasonably
significant to choose the suitable surfactants to emulsify the blend of n-octadecane and the silk solution before
the fabrication of the n-octadecane incorporated silk hydrogel.
In addition, it has been reported that the silk hydrogel with superior mechanical performance can be got by
the physical crosslinking of silk with cellulose [8], and accordingly the formation of silk hydrogel in the present
work is designed to be developed by this way.
2.
Experimental
The aqueous silk solution was fabricated from Bombyx mori silkworm cocoons according to the procedures
reported previously [9]. The silk solution was concentrated against the PEG solution to the concentration of 8
wt%. Then the hydroxypropyl methyl cellulose (HPMC) powders were dissolved in the deionized water to yield
the solution with the concentration of 5 wt%. The synthetic process for the fabrication of n-octadecane
incorporated silk hydrogel has been illustrated in Fig. 1 and the typical procedures can be described as follows:
firstly, the silk solution and HPMC solution were mixed with the weight ratio of 3:1 and a homogeneous and
transparent mixture solution was formed after the ultrasonic treatment to remove the bubbles. Subsequently,
3
n-octadecane and the mixture solution were mixed according the weight ratios listed in Table 1 and the blend
was emulsified at 40 °C with the aid of the compound emulsifier made of span-80 and hexadecyltrimethyl
ammonium bromide (CTAB). Then the stable o/w emulsion was sealed and incubated in an oven at the
temperature of 75 °C for 2 h to prepare the silk hydrogel. Finally, the silk hydrogel was freeze-dried at -60 °C for
24 h to obtain the silk sponges (dried hydrogel).
Then the morphologies and thermal behaviors of the lyophilized silk hydrogel were investigated by means
of field emission scanning electron microscope (FE-SEM) and differential scanning calorimeter (DSC),
respectively. The water uptake of the hydrogel was determined from Equation (1), where Wd and Ws are the mass
of the dry hydrogel and the swollen one after immersing it in the deionized water at 37 °C for 24 h [10].
Water uptake (%) = (Ws-Wd)*100/Ws
3.
(1)
Results and Discussion
SEM images in Fig.2a and 2b show that the freeze-dried pure silk hydrogel presents the laminar
microstructure with the pore size of about 60 µm. The composite silk hydrogel was subjected to the acetone
solvent to remove n-octadecane within it for the morphology comparison with the pure one. As shown in Fig 2c
and 2d, even though the overall morphology of n-octadecane incorporated hydrogel is similar with that of the
pure one, the pores are relatively smaller and the surrounded silk layers are prone to have some orientation. In
addition, the n-octadecane grains can be also observed in the pores of the original composite silk hydrogel (Fig.
4
2e and 2f), indicating the successful embedment of n-octadecane in the composite hydrogel.
The water absorption capability of the freeze-dried hydrogel is listed in Table 1, and it is observed that the
water uptake decreases from 91.0 to 87.4% when the amount of n-octadecane added into the mixture solution
increases from 0 to 0.4 g. The slight decrease of the water uptake capacity results from the fact that the
occupation of n-octadecane in the pores has limited the space to capture more water (as shown in Fig.2f). It can
be clearly seen that there is no significant difference of the water uptake between the composite hydrogel and the
pure one, which indicates that the n-octadecane incorporated silk hydrogel also exhibits good water absorption
capability.
Fig.3 shows the solidifying and melting curves of pristine n-octadecane and the freeze-dried composite
hydrogel prepared from different amount of n-octadecane during the cooling and heating process. There is an
intensive peak and a weak shoulder peak in the solidifying curve of pristine n-octadecane; whereas it is observed
two distinctive crystallization peaks for n-octadecane within the composite hydrogel. The crystallization peak at
higher temperature for the composite hydrogel can be attributed to the heterogeneous nucleation effect of
n-octadecane grains on the surrounded silk layers of the composite hydrogel. In addition, the phase-change
enthalpies of the composite hydrogel calculated from the DSC curves are listed in Table 1. It is readily seen that
the melting enthalpy of the composite hydrogel increases from 26.0 to 125.3 J/g when the amount of
n-octadecane added into the mixture solution increases from 0.2 to 0.4 g. Although this value is still lower than
5
that of pristine n-octadecane (189.1 J/g), the composite silk hydrogel exhibits the comparable latent heat capacity
compared with other thermal energy storage materials [11]. The composite silk hydrogel could absorb or release
thermal energy through the phase change of n-octadecane within it when the environmental temperature alters.
Therefore it is concluded that the composite silk hydrogel has been endowed with the temperature buffering
property by the incorporation of n-octadecane.
4.
Conclusions
In summary, the incorporation of n-octadecane into the silk hydrogel is fabricated by the gelation of the o/w
emulsion wherein n-octadecane and the aqueous silk solution serves as the oil and water phases, respectively.
The composite silk hydrogel presents the novel property of temperature buffering in addition to the high water
absorption capability. Therefore the composite silk hydrogel can be a great candidate for the application as
packaging structures for the conservation and transport of temperature sensitive materials safely and effectively.
References: [1] W. Chalco-Sandoval, J.F. Fabra, L. Amparo, J.M. Lagaron, Electrospun Heat Management Polymeric Materials of Interest in Food Refrigeration and Packaging, J. Appl. Polym. Sci. 131 (2014) 40661. [2] W. Chalco-Sandoval, M.J. Fabra, A. López-Rubio, J.M. Lagaron, Development of polystyrene-based films with temperature buffering capacity for smart food packaging, J. Food Eng. 164 (2015) 55-62. [3] N. Roy, N. Saha, T. Kitano, P. Saha, Biodegradation of PVP–CMC hydrogel film: A useful food packaging material, Carbohyd. Polym. 89 (2012) 346-353. [4] L. Wang, J. Rhim, Preparation and application of agar/alginate/collagen ternary blend functional food packaging films, Int. J. Biol. Macromol. 80 (2015) 460-468. [5] J. Ming, M. Li, Y. Han, Y. Chen, H. Li, B. Zuo, F. Pan, Novel two-step method to form silk fibroin fibrous hydrogel, Materials Science and Engineering: C 59 (2016) 185-192. [6] L. Zhao, H. Wang, J. Luo, Y. Liu, G. Song, G. Tang, Fabrication and properties of microencapsulated
6
n-octadecane with TiO2 shell as thermal energy storage materials, Sol. Energy 127 (2016) 28-35. [7] J.H. Park, M.H. Kim, L. Jeong, D. Cho, O.H. Kwon, W.H. Park, Effect of surfactants on sol–gel transition of silk fibroin, J. Sol-Gel Sci. Techn. 71 (2014) 364-371. [8] K. Luo, Y. Yang, Z. Shao, Physically Crosslinked Biocompatible Silk-Fibroin-Based Hydrogels with High Mechanical Performance, Adv. Funct. Mater. 26 (2016) 872-880. [9] L. Zhao, J. Luo, H. Wang, G. Song, G. Tang, Self-assembly fabrication of microencapsulated n-octadecane with natural silk fibroin shell for thermal-regulating textiles, Appl. Therm. Eng. 99 (2016) 495-501. [10] K. Naresh, H. Nicholas, P. Ognen, K. Dana, V. Fritz, Silk fibroin gelation via non-solvent induced phase separation, Biomater. Sci.-UK 4 (2016) 460-473. [11] Y. Ma, X. Chu, G. Tang, Y. Yao, Synthesis and thermal properties of acrylate-based polymer shell microcapsules with binary core as phase change materials, Mater. Lett. 91 (2013) 133-135.
7
Fig.1. Schematic fabrication of the silk composite hydrogel. Fig.2. SEM images of the freeze-dried pure hydrogel (a, b) and composite hydrogel of sample 2 (c, d, e, f). Fig. 3. The melting and solidifying DSC curves of (a) pristine n-octadecane, (b) sample 1, (c) sample 2 and (d) sample 3.
8
9
10
11
Table 1 Basic formulations and properties of the silk composite hydrogel The absorption
Thermal
capacity
properties
Basic formulations Sample Mixture
n-octadecane
CTAB a
Span-80
Water uptake
∆Hm b
∆Hc b
(g)
(g)
(g)
(g)
(%)
(J/g)
(J/g)
Pure gel
5.00
-
-
-
91.0
-
-
1
5.00
0.20
0.20
0.04
90.9
26.0
22.7
2
5.00
0.30
0.30
0.06
88.5
60.4
58.9
3
5.00
0.40
0.40
0.08
87.4
125.3
125.2
No.
a
The concentration of CTAB solution is 2 wt%.
b
The melting and crystallization enthalpies of the samples.
12
13
Highlights
The n-octadecane incorporated silk hydrogel has been successfully fabricated.
The n-octadecane grains have been observed in the pores of the hydrogel.
The hydrogel shows high water uptake capacity and thermal regulation property.
14