Green electrolyte host based on synthesized benzoyl kappa-carrageenan: Reduced hydrophilicity and improved conductivity

Norsyabila Shrgawi; Intan Juliana Shamsudin; Hussein Hanibah; Norherdawati Kasim; Siti Aminah Mohd Noor; Safura Taufik

doi:10.1016/j.arabjc.2023.104687

View/Download PDF

Buy Reprints

PDF

Translate this page into:

Original article

05 2023

:16;

104687

doi:

10.1016/j.arabjc.2023.104687

Green electrolyte host based on synthesized benzoyl kappa-carrageenan: Reduced hydrophilicity and improved conductivity

Norsyabila Shrgawi^{^a}, Intan Juliana Shamsudin^{^b,⁎}, Hussein Hanibah^{^c}, Norherdawati Kasim^{^b}, Siti Aminah Mohd Noor^{^b}, Safura Taufik^{^b}

aFaculty of Defence Science and Technology, National Defence University of Malaysia, Sungai Besi Camp, 57000 Kuala Lumpur, Malaysia

bCentre for Defence Foundation Studies, National Defence University of Malaysia, Sungai Besi Camp, 57000 Kuala Lumpur, Malaysia

cCentre of Foundation Studies, Universiti Teknologi MARA, Dengkil Campus, 43800 Dengkil, Selangor, Malaysia

⁎Corresponding author. intanjuliana@upnm.edu.my (Intan Juliana Shamsudin)

Received: 2022-12-1, Accepted: 2023-2-12,

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Newly synthesized benzoyl kappa carrageenan (Bz-ƙcar) was successfully produced by the Friedel Craft acylation method. The successful substitution of benzoyl molecule into kappa carrageenan (ƙcar) polymeric chain was confirmed by the FTIR analysis based on the formation of new carbonyl (C⚌O) and C⚌C bonds in Bz-ƙcar. ¹H NMR analysis further proved the benzoylation by the appearance of new multiple resonances peaks at δ = 6.6–9.50 ppm, which belonged to the characteristic signals of protons in the aromatic benzoate group. XRD analysis showed reduced crystallinity of the synthesised carrageenan, while elemental analyser analysis revealed the increased percentages of carbon in Bz-ƙcar upon the substitution. The highest degree of substitution obtained was 0.27. TGA showed lower degradation temperature in the synthesised carrageenan, while water contact angle analysis demonstrated that Bz-ƙcar was less hydrophilic as compared to the pristine ƙcar. Solubility tests showed that Bz-ƙcar was best dissolved in ethylene glycol. The benzoylation also improved the ionic conductivity of Bz-ƙcar to 3.10 × 10⁻⁴ Scm⁻¹ at ambient temperature.

Keywords

carrageenan

electrolyte

benzoyl

hydrophilic

conductivity

acylation

Show Related Articles from PubMed

1 Introduction

Kappa-carrageenan (ƙcar) is an anionic sulfated linear polysaccharide extracted from red seaweed with a linear backbone built of an alternating (1 → 3)-linked β-d-galactopyranose and (1 → 4)-linked α-d-galactopyranose (Campo et al., 2009). Eucheuma cottonii is known as the important species that yields ƙcar (Distantina and Fahrurrozi, 2011). This seaweed-based polysaccharide is categorized into six basic forms as Kappa (κ)-, Iota (ɩ)-, Lambda (λ)-, Mu (μ)-, Nu (ν)-, and Theta (θ). They differ in terms of the sulfate content, source of extraction, and solubility. Of these, κ, ɩ, and λ are of commercial importance due to their viscoelastic and gelling properties (Cunha and Grenha, 2016). Major applications of ƙcar include its uses as an additive in the foods industry (Hotchkiss et al., 2016; Walayat et al., 2022; Zhang et al., 2020 ), cosmetic and personal care products (Infante and Campos, 2021), and pharmaceutical industry (Pacheco-Quito et al., 2020). Meanwhile, special characteristics of ƙcar involve biocompatibility, biodegradability, high water retention capacity, and mechanical strength of its gel. Over the past decade, the use of ƙcar in electrochemistry field has been actively developed and progressed (Bella et al., 2015; Zainuddin and Samsudin, 2018; Nunes et al., 2019 ). Recent utilizations of ƙcar as propitious electrolytes in electrochemical devices were also reported (Serra et al., 2022; Huang et al., 2019; Wu et al., 2022 ).

However, similar to other polysaccharides, the main concern is the high polarity and hydrophilicity of ƙcar due to the large numbers of hydroxyl groups (OH) in its chemical structure (Tecante and Nunez Santiago, 2012). In this case, ƙcar has strong interactions with water molecules, as the hydroxyl groups are capable of forming hydrogen bonds with polar water molecules. Unfortunately, the presence of water/moisture in most of the electrochemical devices such as batteries and dye- sensitized solar cells is not favorable. The interaction of moisture with air/moisture sensitive metal/parts in the devices might have caused an explosion and risked the surrounding. Additionally, the exposure to moisture will lead to corrosion issues in the devices, thus deteriorating and affecting the devices performance. Chemical modifications on ƙcar to alter the hydrophilic properties of ƙcar were previously reported. Recently, hydrophobic modification of ƙcar microgel particles was performed to stabilize foams in food industry applications (Ellis et al., 2019). Previously, Tye and co-workers (2018) performed alkali modification on ƙcar (Tye et al., 2018). The results showed that the alkali-modified ƙcar exhibited better thermal stability, water vapor barrier properties and less hydrophilic as compared to the unmodified carrageenan film. Besides that, a study on the synthesis of acylated ƙcar was reported. Long alkyl chain, decanoyl chloride was used as an acylating agent in the synthesis (Mahmood et al., 2014). The hygroscopic nature of the acylated carrageenan was reduced as compared to pure carrageenan. However, no study on the potential of the modified ƙcar as electrolyte was reported, although all the investigations reported reduced hydrophilicity.

Another concern on ƙcar as a polymer host in electrolyte systems is that its thin-film conductivity (σ) is rather low (10⁻⁷ S cm⁻¹). Increment in σ is important to be applicable as an electrolyte in electrochemical devices. Therefore, studies of synthesized ƙcar in order to enhance the σ were previously reported. In the recent past, succinyl ƙcar was synthesized by mixing ƙcar with succinic anhydride (CH₂CO)₂O via a one-step modification reaction (Abu Bakar et al., 2020). The substitution of the succinic group into ƙcar backbone improved the σ and its interaction with ions compared to its pristine form. In another study, O-methylene phosphonic κ-carrageenan (OMPC) was chemically synthesized via phosphorylation reaction (Liew et al., 2017). Methylene phosphonic acid was introduced into carrageenan as a phosphoryl functional group in order to produce phosphorylated carrageenan. The σ of OMPC film was 1.54 × 10⁻⁵ S cm⁻¹, one order of magnitude higher than the pure carrageenan. The researchers concluded that the improvement in the σ was due to the oxygen-rich ionogenic group (-CH₂PO₃H₂) substituted into the side chain of ƙcar. Synthesis of carboxymethyl carrageenan was formerly reported (Mobarak et al., 2012). The substitution of polar group (CH₃COOH) brought more oxygens to the polymeric matrix, thus providing a vacancy for cations to coordinate with the polymer. As a result, the σ was reported to enhance by three orders of magnitude to 2.0 × 10⁻⁴ S cm⁻¹, as compared to the pure ƙcar film. Nonetheless, although all the synthesis successfully increased the σ, with the increasing number in the polar groups, the hydrophilic properties were also increased, thus affecting the electrolytes performance in electrochemical devices.

Therefore, the aim of this study was to modify hydrophilic and low σ ƙcar into less hydrophilic and conductive benzoyl ƙcar (Bz-ƙcar). ƙcar was synthesized to undergo acylation reaction, while benzoyl chloride (BC) acts as the acylating agent. To the best of our knowledge, the investigation on the synthesis of Bz-ƙcar and its application as polymer host in an electrolyte system has never been reported elsewhere. Thus, this study is expected to give a new idea to improve the ƙcar-based electrolyte properties specifically and polysaccharide-ride-based electrolytes generally.

2 Materials and methods

2.1

2.1 Materials

ƙappa-carrageenan (ƙcar) powder (molecular weight: 788.7 g/mol) and benzoyl chloride (BC) (purity: 99 %) liquid were purchased from Sigma Aldrich, Malaysia. Pyridine (purity: ≥99 %) was purchased from Merck, Malaysia, while ethanol used was from HmbG Chemicals (purity: >95 %). Deuterated water (D₂O) (purity: 99.9 %) and hexadeuterodimethyl sulfoxide (DMSO‑d₆) (purity: 99.9 %) and dimethyl sulfoxide (DMSO) (purity: ≥99 %) were purchased from Sigma Aldrich. Tetrahydrofuran (purity: ≥99.5 %) and acetic acid (purity: ≥99.5 %) were purchased from SYSTERM ChemAR, Malaysia. Acetonitrile (purity: ≥99.9 %) and ethylene glycol (purity: ≥99.5 %) were purchased from Merck, Malaysia. All chemicals were of analytical grade and used without further purification.

2.2

2.2 Synthesis of benzoyl ƙ-carrageenan

Bz-ƙcar was prepared with a new synthesis route. Series of ƙcar: BC mass ratios were prepared (1:0, 1:1, 1:3, 1:5, 1:7 and 1:9). Some modification parts were similar to a previously reported acylated chitosan method (Zong et al., 2000). 3.0 g of ƙcar powder was soaked and stirred in 250 ml pyridine for 24 hr at 50 °C for good dispersion. Then, liquid BC was soaked and stirred in pyridine until dissolved at 60 °C. The mixture of pyridine and BC was added dropwise into the ƙcar mixture for 2 hr while being stirred continuously at 60 °C. Then, the mixed solution was heated to 60 °C under reflux and a heterogeneous product aggregation was observed in the final solution. Pale yellow solution was filtered by a vacuum pump and washed thoroughly with ethanol to remove excess pyridine. Light yellow powder sample was obtained and dried overnight in the oven. Then, the powder sample was stored in airtight container until further use.

The synthetic procedure of benzoyl carrageenan synthesis is shown in Fig. 1. Herein, the hydrogen atom in the hydrophilic hydroxyl group (–OH) is suggested to be substituted with benzoyl molecule (C₆H₅CO-), through an electrophilic substitution (acylation) reaction.

In this synthesis, benzoyl chloride acted as an electrophile and acylating agent that delivered benzoyl molecule into ƙcar polymeric chain. Pyridine served as a nucleophile for carbonyl groups and catalyst in this acylation reaction. The nitrogen atom in pyridine was nucleophilic as the lone pair of electrons on nitrogen could not be delocalized around the ring. The reaction initiated with pyridine performed nucleophilic attack on the carbonyl group to form benzoyl pyridinium salt. The carbonyl groups were then activated towards nucleophilic attack by the hydroxyl group in ƙcar. Then followed by the deprotonation by pyridine and removal of pyridine as good leaving group. Finally, Bz-ƙcar was produced as the final product. The complete proposed mechanism is shown in Scheme 1.

Proposed reaction mechanism for the benzoylation of ƙcar.

2.3

2.3 Preparation of ƙcar and Bz-ƙcar gels

Both ƙcar and Bz-ƙcar soft gel samples were prepared by dissolving each sample powder in ethylene glycol at the concentration of 3.3 % w/v at ambient temperature. The thick gels were stirred overnight in order to obtain complete dissolution. The dissolved gel then kept in air tight container to prevent any moisture contact.

3 Characterization

3.1

3.1 Fourier transform Infra-Red analysis (FTIR)

The analysis was performed using Perkin- Elmer Spectrum 2000, USA in the range of 4000–650 cm⁻¹ equipped with a diamond-attenuated total reflection accessory with scanning resolution 1 cm⁻¹ (Abu Bakar et al., 2020). The analyses were carried out to investigate any peak shifts and changes on the spectra due to the chemical interaction between polymer ƙcar and BC salt.

3.2

3.2 Elemental analyzer

The percentage of carbon (C), and sulfur (S) for ƙcar and Bz-ƙcar powders were analyzed using Vario el III, ELEMTAR, Hanau, Germany. The degree of substitution was calculated based on Eq. (1) (Abu Bakar et al., 2020):

(1)

Degree of substitution = \frac{ratio carbon : s u l p h u r_{Bz - κ c a r} - ratio c arbon : s u l p h u r_{κ c a r}}{number of new added carbon}

3.3

3.3 ¹H NMR spectroscopy

¹H NMR spectra were recorded on a Bruker Advance III HD 400 MHz spectrophotometer. Intact samples of ƙcar powder was dissolved in D₂O and Bz-ƙcar was dissolved in deuterated dimethylsulfoxide (DMSO‑d₆). Samples were transferred into a static magnetic field to excite the nuclei and measure the emitted frequencies.

3.4

3.4 X-ray diffraction (XRD)

A Bruker D8 Advance X-ray diffractometer was used to analyze the degree of crystallinity of ƙcar and Bz-ƙcar powders. The data were collected from a range of diffraction angle 2θ from 3° to 60° at the rate 0.05° s⁻¹. The crystallinity index (X_CI) has been calculated using peak separation software EVA. Amorphous subtraction method has been used in calculating the X_CI of the biopolymer electrolytes (Park et al., 2010). The amorphous contribution of ƙcar has been subtracted from the diffraction spectra. Then, X_CI was calculated from the ratio of the remaining diffractogram area due to crystalline ƙcar and the total area of the original diffractogram. The determination of X_CI is shown in Eq. (2):

(2)

X_{CI} = \frac{A_{c}}{A_{t}}

where X_CI referring to the crystallinity index of the biopolymer, A_c represents the crystalline area and A_t represents the total area of the diffractogram.

3.5

3.5 Thermogravimetric analysis (TGA)

A Simultaneous Thermal Analyzer (STA) brand NETZSCH model STA 449 F3 Jupiter was used to investigate the thermal behavior of the polymers. Both ƙcar and Bz-ƙcar powder samples with a mass of (3–5 mg) were tested under nitrogen gas atmosphere at a heating rate of 10 °C/ min at a temperature range from 30 °C−600 °C.

3.6

3.6 Solubility test

The solubility test was performed according to a previous published method (Yusharani et al., 2019). Solubilities of ƙcar and Bz-ƙcar powders were evaluated in multiple solvents: pure water, acetonitrile, tetrahydrofuran, pyridine, dimethyl sulfoxide and acetic acid. All samples were prepared at the concentration of 1.0 % w/v and stirred overnight at 25 ^οC. The solution was filtered and dried to determine the amount of undissolved sample left. The test was repeated three times. Solubility percentage and the standard error (SE) were calculated based on Eqs. (3) and (4) respectively.

(3)

Solubility (%) = \frac{mass of sample after dissolution (g)}{mass of sample before dissolution (g)} \times 100 %

(4)

SE = \frac{solubility standard deviation}{\sqrt n u m b e r o f s a m p l e s}

3.7

3.7 Water contact angle

The water contact angle of the ƙcar and Bz-ƙcar gel samples were measured using The Ossila Contact Angle Geniometer (model L2004A1) with angle range of 5^ο to 180^ο. A thin layer of gels was spread on a slide glass (75 mm × 25 mm) and fixed on the horizontal movable stage (50 mm × 50 mm). The WCA was measured soon after dropping an ultra-pure water drop (10 μL) using Eppendorf micropipette.

3.8

3.8 Impedance spectroscopy

Impedance spectra was measured using a high-frequency response analyzer (HFRA: Solartron 1296) with frequency ranging from 100 Hz to 1 MHz with 100 mV amplitude. A dip-cell probe for gel sample was used to measure the conductivity of ƙcar and Bz-ƙcar gel samples. The cell constant was determined with a solution of 0.01 M KCl at ambient temperature (298 K).

4 Results and discussion

The FTIR spectra of ƙcar and synthesized ƙcar powders with different ratios of BC (ƙcar:BC − 1:0, 1:1, 1:3, 1:5, 1:7 and 1:9) are shown in Fig. 2. The characteristic peaks at 922 cm⁻¹ were attributed to C—O—C vibration of the 3,6-anhydro-d-galactose residue, while the intense peak at 1037 cm⁻¹ represented the C—O stretching mode in ƙcar. Peaks at 1231 cm⁻¹ and 844 cm⁻¹ were assigned to O⚌S⚌O symmetric vibration and to –O–SO₃ stretching vibration at the C-4 position of galactose in the ƙcar polymer chain, respectively (Pereira et al., 2009).

FTIR spectra of different ratios ƙcar: BC (1:0, 1:1, 1:3, 1:5, 1:7 and 1:9) at (a) 4000–2800 cm−1 and (b) 2000–650 cm−1.

In order to confirm the benzoyl molecule (C₆H₅CO-) substitution into ƙcar chains, changes in the FTIR signals were observed. Based on Fig. 2(a), a broad stretching vibration of hydroxyl group (OH band) in ƙcar powder (ratio 1:0) is detected at around 3200 – 3600 cm⁻¹. As the ratio of benzoyl chloride increases (ratio 1:1–1:9), the intensity of the broad OH band is reduced, thus indicating the decrement of hydroxyl bond in the ƙcar structure. This observation might be related to the electrophilic substitution of hydrogen atoms in the –OH group with C₆H₅CO-molecule leading to disruption of hydrogen bonds in the polymer matrix, thus signifying the reduction of hydrophilic nature in the synthesized ƙcar.

The further confirmation of benzoyl substitution is shown in Fig. 2b by the appearance of several new bands in the synthesized ratio 1:3, 1:5, 1:7 and 1:9. New carbonyl (C⚌O) stretch peak appeared at 1716 cm⁻¹ (Abu Bakar et al., 2020). The intensity of the C⚌O signal was enhanced with a higher ratio of BC salt, indicating successful substitution of C₆H₅CO- occurred. A pair of new peaks was also detected at 1451 and 1605 cm⁻¹ bands belonging to the aromatic C⚌C stretch (Bardakçı and Bahçeli, 2005), thus confirming the successful substitution of C₆H₅CO- into the ƙcar matrix. Noticeably, a new C–Cl peak was formed at 710 cm⁻¹ in higher ratios; (1:5, 1:7 and 1:9), which might be due to the excess of BC salt in the synthesized ƙcar.

Significant shifts in the wavenumbers in pure ƙcar (ratio 1:0) and ƙcar with increasing ratios of BC salt (ratio 1:1 – 1:9) were observed. Stretching modes in C—O—C and C—O in the synthesized ƙcar were shifted slightly to higher and lower wavenumbers respectively. The O⚌S = O symmetric vibration band also showed significant changes as the band shifted to higher wavenumbers. The shifts of the characteristic bands might be caused by the coordination interaction of oxygen atoms as electron rich species in the polymer matrix with the hydrogen ion (H⁺) that was detached from the hydroxyl bond as a result of the acylation reaction. Hence, these changes suggested the successful substitution of benzoyl molecule in the ƙcar matrix. The summarized shifts and assignments of the individual characteristic bands are shown in Table 1. Based on all these IR peak changes, we concluded that Bz-ƙcar was produced.

Table 1 The assigned bands and wavelength of the synthesized ƙcar powders.

Assignments of bands	ƙcar: BC ratio Wavelength (cm⁻¹)
Assignments of bands	1:0	1:1	1:3	1:5	1:7	1:9
O—H	3384	3381	3374	3368	3327	3378
C⚌O	None	None	1718	1716	1716	1716
C⚌C	None	None	1452,1602	1451,1602	1451,1602	1451,1602
O⚌S⚌O	1231	1224	1267	1267	1267	1268
C—O	1037	1036	1036	1028	1027	1027
C—O—C	921	926	927	929	933	933
C—Cl	None	None	711	710	710	708

The elemental analysis of C and S for series of ƙcar: BC ratios are tabulated in Table 2. The analysis displayed a higher percentage of C as the ratios of BC salt increased. This suggested that the synthesized ƙcar reacted with BC salt and benzoylation took place in ƙcar matrix. The utmost percentage of C was observed in the ratio 1:5 of ƙcar: BC, an increase of 35 % as compared to the pristine ƙcar (ratio 1:0). The degree of substitutions (DS) were calculated based on equation (1) by comparing the C and S ratio obtained from element analysis in each ratio. Notably, Bz-ƙcar with the ratio 1:5 showed the highest degree of substitution (DS) at 0.27, suggesting ratio 1:5 of ƙcar: BC contained the highest benzoyl substitution in ƙcar matrix and implied as the most ideal ratio for the synthesis. The DS started to decrease as a higher amount of BC salt was included (ratio 1:7 and 1:9), which could be caused by the saturation or agglomeration of BC salt in the polymer matrix, thus hindering the substitution.

Table 2 Elemental analysis and DS of synthesized ƙcar.

ƙcar: BC sample	C (%)	S (%)	C/S	DS
1:0	28.00	4.70	5.96	–
1:1	28.30	4.60	6.15	0.03
1:3	32.50	5.00	6.50	0.08
1:5	37.90	4.75	7.98	0.27
1:7	37.20	4.90	7.59	0.23
1:9	37.80	5.20	7.27	0.19

Further evidence of benzoyl substitution into ƙcar matrix was supported by ¹H NMR spectroscopy. ¹H NMR spectroscopy has the advantage of high selectivity and suitable for quantitative approximation for different types of carrageenan (Lankhorst and Chang, 2018). The ¹H NMR spectra of ƙcar and Bz-ƙcar (ratio 1:5) samples are shown in Fig. 3 (chemical shift ranging between δ = 2.0 and 10.0 ppm). Proton signals of ƙcar backbone appeared at range 3.45–5.38 ppm and the chemical shifts could be assigned as follows: ¹H NMR (D₂O): δ = 5.37(H1), δ = 3.52 (H2), δ = 3.63–3.69(H3), δ = 3.98 (H4), δ = 3.50–3.53 (H5), δ = 4.01 (H6), δ = 5.36 (H7), δ = 4.81 (H8) δ = 4.03 (H9), δ = 4.18 (H10) δ = 4.16 (H11) and δ = 3.77 (H12), comparable with previous studies (Tye and HPS, A. K., Kok, C. Y., & Saurabh, C. K. , (2018, June).; Abu Bakar et al., 2020). The chemical shifts spectrum of Bz-ƙcar showed similar characteristic to ƙcar proton signals with the appearance of new multiple resonances peaks (δ = 6.6–9.50 ppm), belongs to the characteristic signals of protons in aromatic benzoate group (C₆H₅CO-). Similar proton signals of benzoylated derivatives were published (Chen et al., 2015; Namyslo et al., 2021). These findings proved the electrophilic substitution of benzoyl group into ƙcar matrix and supported the FTIR analysis. Therefore, this has also confirmed that the synthesis was successfully accomplished.

Fig. 4 shows the X-ray diffraction pattern of pure ƙcar and Bz-ƙcar powders (ratio 1:5). Observably, the nature of pure ƙcar film is semicrystalline, with a small hump at 2θ = 2.0–10.0° and a broad hump at around 2θ = 12.0–41.0°. Sharp peaks were shown at 2θ = 29.0° and 41.0° similar to the conventional characteristic diffraction peaks of ƙcar reported (Zainuddin et al., 2018).

XRD pattern of ƙcar and Bz-ƙcar powders.

Modification of ƙcar had exhibited significant changes in the structural phase of the biopolymer as displayed in the diffractogram of Bz-ƙcar. Noticeably, there were multiple formation of new peaks ranging at 2θ = 9.0–37.0° with accentuated peaks at 2θ = 12°, 14°, 19°, 25°, 32° and 37°. The appearance of these new peaks is probably due to the engagement of crystalline benzoyl molecule in the biopolymer backbone, which leads to the formation of polymer–benzoyl complexes as the optimum amount of benzoyl chloride was included. The residue of benzoyl molecule might have also been the cause. A comparable trend was observed in the synthetization of acylated chitosan derivatives (Ma et al., 2009).

Observably, the small hump at 2θ = 6.0–12.0° was not significantly changed upon modification. However, the reduced intensity with disordered structure of the synthesized Bz-ƙcar as compared to the pristine ƙcar was observed at 2θ = 10.0–40.0°. This observation might be related to the electrophilic substitution of the hydroxyl (OH) group with aromatic benzoyl (C₆H₅-CO-) molecule in the ƙcar matrix (Scheme 1). Consequently, there were disruption of inter and intramolecular hydrogen bonding in the biopolymer matrix thus resulted in the disordered arrangement in the synthesized benzoyl ƙcar chain. The disordered structural arrangement then affected the crystallinity of the biopolymer as the crystallinity index (X_Cl) of benzoyl ƙcar was found to lessen at 24.3 % as opposed to the pure ƙcar, 26.7 %. Thus, this has also shown that the modification of ƙcar has arranged the polymer chain structure whereby the new arrangement has enhanced the formation of amorphous phase. Table 3 shows the percentages of X_Cl and amorphous in ƙcar and Bz-ƙcar.

Table 3 Crystallinity index and amorphous percentages of ƙcar and Bz-ƙcar.

Sample	Crystallinity index, X_CI (%)	Amorphous (%)
ƙcar	26.7	73.3
Bz-ƙcar	24.3	75.7

The TGA and DTG curves of ƙcar and Bz-ƙcar are shown in Fig. 5. Based on the figure, three distinct stages of weight loss were observed in ƙcar, while Bz-ƙcar showed two stages of weight loss. The information on the start, end and maximum degradation temperatures of each stage were clearly showed in the DTG curves. The first weight loss stage in ƙcar was about 5.2 % at temperatures ranging from 40 to 140 °C. Bz-ƙcar showed lower weight loss of approximately 4.8 %, at a similar temperature range. These initial weight losses were due to the presence of moisture in the samples and related to the characteristic of polysaccharides that had a strong affinity for water (Tecante and Nunez Santiago, 2012). Reduced moisture weight loss in Bz-ƙcar was related to its less hydrophilicity characteristic due to the acylation of benzoyl molecule and disruption of hydrogen bonding in the polymer chain thus reducing polar interactions with water molecules.

The second degradation peak of ƙcar was found at a temperature peak 222.9 °C with a small weight loss of about 6.1 %, followed by the third degradation stage started at 231.0 °C and reached a maximum at 251.8 °C. The synthesized polymer, Bz-ƙcar exhibited lower degradation temperature, which a maximum degradation peak appearing at 205.9 °C with 58 % weight loss. This degradation step was identified as devolatilization where the main pyrolytic process occurred and various volatile components might release gradually. According to a previous study, this degradation step was attributed to the loss of –SO₃ - group from the pendant chains attached to the polymeric backbone and also may be due to the polysaccharide backbone fragmentation (Mishra et al., 2008; Mishra et al., 2010). Noticeably, the second degradation temperature of the acylated ƙcar was lower as compared to the original biopolymer. This might be due to the effect of disruption of hydrogen bonding in the molecule chains, thus leading to disordered structure and the reduced crystallinity of Bz-ƙcar as discussed in the structural analysis part. Therefore, less energy was needed for Bz-ƙcar to degrade. Nevertheless, the degradation temperature of the Bz-ƙcar is still favorable and suitable to be applied for industrial applications.

To examine the effects of the benzoyl substitution on ƙcar’s hydrophilicity, solubility test on ƙcar and Bz-ƙcar powders in several solvents with various range polarity indices were performed. Solubility is regarded as the ability of solute to form solution with solvent. Table 4 displays solubility percentages of ƙcar and Bz-ƙcar in seven different solvents and the standard errors. Generally, the higher the polarity index, the more polar the solvent is, as a result of the strong hydrogen bonds in the molecule (Marcus and Migron, 1991). The low standard errors observed in the overall test signify the reliability of the data.

Table 4 Solubility percentages of ƙcar and Bz-ƙcar in different solvents, and the standard errors.

Solvent	Polarity index (Barwick, 1997; Gupta et al., 1997)	Solubility (%)		Standard error (SE)
Solvent	Polarity index (Barwick, 1997; Gupta et al., 1997)	ƙcar	Bz-ƙcar	ƙcar	Bz-ƙcar
H₂O	10.2	100	62	0	0.3
DMSO	7.2	100	85	0	0.3
Ethylene glycol	6.9	75	100	0.4	0.3
Acetic acid	6.0	24	18	0.5	0.6
Acetonitrile	5.8	5	20	0.6	0.5
Pyridine	5.3	23	27	0.5	0.6
THF	4.0	6	13	0.6	0.6

Noticeably, the original polymer, ƙcar, showed complete dissolution in both highly polar solvents; water and dimethyl sulfoxide (DMSO). On the other hand, Bz-ƙcar showed a reduced solubility percentage in both water and DMSO. A decrease of ∼ 38 % solubility was observed in water, while ∼ 85 % Bz-ƙcar dissolution was observed in DMSO, signifying the reduced polarity of Bz-ƙcar as compared to the original ƙcar. These findings might be due to the interrupted hydrogen bonds in Bz-ƙcar resulted in reduced polar groups in the polymer chain, thus limiting the interactions with the polar solvents. Complete dissolution of Bz-ƙcar was observed in ethylene glycol (EG), suggesting EG as the most ideal solvent for Bz-ƙcar. The high solubility of Bz-ƙcar in EG is most likely related to the semi-polar characteristic of Bz-ƙcar, as the strong inter and intramolecular hydrogen bonds in the polymer chains were not entirely destroyed. This explained the relatively low degree of substitution (DS) in Bz-ƙcar as discussed in the elemental analysis part.

Low percentages in solubility were detected in the less polar solvents for both ƙcar and Bz-ƙcar. Better dissolution in acetic acid was observed in ƙcar, as opposed to Bz-ƙcar. Whereas, the synthesized Bz-ƙcar portrayed an improved solubility percentage trend in solvents with low polarity values (acetonitrile, pyridine and THF), indicating its less polar behavior compared to ƙcar. These findings have proven that the acylation of benzoyl molecules into the polymer chains has altered its physical characteristic. Reduced solubility in highly polar solvents and better dissolutions in less polar solvents were achieved as a result of the reduced polarity and hydrophilicity in Bz-ƙcar.

The WCA of ƙcar and Bz-ƙcar gels are shown in Fig. 6 while the WCA data analysis is shown in Table 5. The polynomial fit of the unmodified gel, ƙcar, showed a very low average angle of 15.31°, signifying its highly hydrophilic properties as WCA smaller than 90° generally signifies a surface having an affinity toward the liquid (Hebbar et al., 2017). However, the average WCA of synthesized Bz-ƙcar gel increased to 26.52° indicating reduced hydrophilicity of Bz-ƙcar gel. The reduced hydrophilicity of Bz-ƙcar was mainly due to its reduced interaction with water molecules as a result of the interrupted inter and intramolecular hydrogen bonds in its polymer matrix. The substitution of hydrophobic benzoyl group in Bz-ƙcar matrix might have also hindered the polymer interaction with water molecules.

Water contact angles of ƙcar and Bz-ƙcar.

Table 5 WCA analysis of ƙcar and Bz-ƙcar.

Gel	Left Angle (°)	Right Angle (°)	Average Angle (°)	Left RMSE	Right RMSE
ƙcar	13.06	17.57	15.31	0.47	0.58
Bz-ƙcar	26.55	26.48	26.52	0.38	0.38

The low WCA value in the modified polymer (Bz-ƙcar) are in agreement with the relatively low DS value of Bz-ƙcar discussed in the elemental analysis part. The solubility tests that revealed low solubility of Bz-ƙcar in the less polar solvents, implying that the benzoylation was not completely taken place in the polymeric chain and the inter and intramolecular hydrogen bonds were not entirely diminished. Nevertheless, the hydrophilicity of Bz-ƙcar was proven to be reduced. The left and right root mean square error (RMSE) values for both polymer gels were below than 1.0, indicating the simulated angle values were in good fits.

Electrochemical impedance spectroscopy is an analysis to determine the ionic conductivity (σ). The Nyquist plots of ƙcar and Bz-ƙcar gels are shown in Fig. 7. The bulk resistance (R_b) was determined from the interception of the tilted spike at the real impedance axis (Z′). Bz-ƙcar gel displayed a smaller R_b value as compared to ƙcar gel indicating a higher value of σ. Fig. 8 illustrates the conductivity of both pristine and synthesized polymers at ambient temperature (298 K). It was observed that the σ of synthesized Bz-ƙcar was higher than its pristine ƙcar. The σ of ƙcar achieved was 8.20 × 10⁻⁵ Scm⁻¹, while the σ of Bz-ƙcar showed an increment close to 1 magnitude to 3.10 × 10⁻⁴ Scm⁻¹. This has proven that the acylation of benzoyl molecule into ƙcar matrix has improved its σ. This might be related to the disruption of strong hydrogen bonding and reduced crystallinity of Bz-ƙcar as shown in the FTIR and structural analyses. As the crystallinity decreased, the increase in the amorphous phase had softened the polymer backbone and enhanced the flexibility and segmental motion of the polymer chains (Zhu et al., 2019; Shamsudin et al., 2016). The gel form of Bz-ƙcar also contributed to the flexibility of the polymer chain. As a result, the enhancement in the ionic conductivity was perceived. The high σ of Bz-ƙcar achieved, even though measured at ambient temperature and without any charge carrier or cation salt, indicated the high potential of Bz-ƙcar as a gel polymer host in electrolyte system.

Ionic conductivity of ƙcar and Bz-ƙcar gels.

5 Conclusions

Benzoyl kappa carrageenan (Bz-ƙcar), a new ƙcar derivative with less hydrophilic and improved conductivity has been successfully produced via electrophilic substitution in acylation reaction. Benzoyl chloride was employed as the acylating agent. Meanwhile, pyridine was used as the catalyst and nucleophile source in the reaction. The substitution of aromatic benzoyl molecules into the polymer chain has led to less hydrogen bonding and polar interactions with water molecules, thus reducing the hydrophilicity of Bz-ƙcar. The chain flexibility of Bz-ƙcar gel was improved, thus increasing the ionic conductivity. Bz-ƙcar has a high potential to be applied as a green electrolyte in electrochemical devices. Better performance of Bz-ƙcar with the incorporation of charge carrier such as lithium or sodium salts is anticipated in the next study.

Funding

This research was funded by the Ministry of Higher Education Malaysia (M.O.H.E.) and National Defence University of Malaysia (NDUM) (Grant No: RACER/1/2019/STG01/UPNM//2 and UPNM/2021/GPPP/SG/2).

Acknowledgments

The authors extend their appreciation to the Ministry of Higher Education Malaysia (M.O.H.E.) and National Defence University of Malaysia (NDUM) (Grant No: RACER/1/2019/STG01/UPNM//2 and UPNM/2021/GPPP/SG/2). The technical support regarding the use of the provided analytical instruments throughout this research from Research Centre for Chemical Defence (CHEMDEF), National Defence University of Malaysia, is also greatly appreciated.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

Abu Bakar M.H., Azeman N.H., Mobarak N.N., Mokhtar M.H.H., Bakar A.A., . Effect of active site modification towards performance enhancement in biopolymer κ-Carrageenan derivatives. Polymers. 2020;12(9):2040.
[Google Scholar]
Bardakçı B., Bahçeli S., . An IR study of benzoyl chloride adsorbed on KA, NaA, and CaA zeolites. Zeitschrift für Naturforschung A. 2005;60(8–9):637-640.
[Google Scholar]
Barwick V.J., . Strategies for solvent selection—a literature review. TrAC Trends Anal. Chem.. 1997;16(6):293-309.
[Google Scholar]
Bella F., Mobarak N.N., Jumaah F.N., Ahmad A., . From seaweeds to biopolymeric electrolytes for third generation solar cells: an intriguing approach. Electrochim. Acta. 2015;151:306-311.
[Google Scholar]
Campo V.L., Kawano D.F., da Silva Jr D.B., Carvalho I., . Carrageenans: Biological properties, chemical modifications and structural analysis–A review. Carbohydr. Polym.. 2009;77(2):167-180.
[Google Scholar]
Chen W., Feng Y., Zhang M., Wu J., Zhang J., Gao X., He J., Zhang J., . Homogeneous benzoylation of cellulose in 1-allyl-3-methylimidazolium chloride: Hammett correlation, mechanism and regioselectivity. RSC Adv.. 2015;5(72):58536-58542.
[Google Scholar]
Cunha L., Grenha A., . Sulfated seaweed polysaccharides as multifunctional materials in drug delivery applications. Mar. Drugs. 2016;14(3):42.
[Google Scholar]
Distantina S., Fahrurrozi M., . Carrageenan properties extracted from Eucheuma cottonii, Indonesia. Int. J. Chem. Mol. Eng.. 2011;5(6):501-505.
[Google Scholar]
Ellis A.L., Mills T.B., Norton I.T., Norton-Welch A.B., . The hydrophobic modification of kappa carrageenan microgel particles for the stabilisation of foams. J. Colloid Interface Sci.. 2019;538:165-173.
[Google Scholar]
Gupta M.N., Batra R., Tyagi R., Sharma A., . Polarity index: the guiding solvent parameter for enzyme stability in aqueous-organic cosolvent mixtures. Biotechnol. Prog.. 1997;13(3):284-288.
[Google Scholar]
Hebbar R.S., Isloor A.M., Ismail A.F., . Contact angle measurements. In: Membrane Characterization. Elsevier; 2017. p. :219-255.
[Google Scholar]
Hotchkiss, S., Brooks, M., Campbell, R., Philp, K., Trius, A., 2016. The use of carrageenan in food. Carrageenans: sources and extraction methods, molecular structure, bioactive properties and health effects, 229-243.
Huang Y., Liu J., Zhang J., Jin S., Jiang Y., Zhang S., Li Z., Zhi C., Du G., Zhou H., . Flexible quasi-solid-state zinc ion batteries enabled by highly conductive carrageenan bio-polymer electrolyte. RSC Adv.. 2019;9(29):16313-16319.
[Google Scholar]
Infante V.H.P., Campos P.M.M., . Application of factorial design in the development of cosmetic formulations with carrageenan and argan oil. Int. J. Phytocosmetics Natural Ingredients. 2021;8(1):4.
[Google Scholar]
Lankhorst P.P., Chang A.N., . The application of NMR in compositional and quantitative analysis of oils and lipids. Cham, Switzerland: Springer International Publishing AG; 2018. p. :1743-1764.
Liew J.W.Y., Loh K.S., Ahmad A., Lim K.L., Wan Daud W.R., . Synthesis and characterization of modified κ-carrageenan for enhanced proton conductivity as polymer electrolyte membrane. PLoS One. 2017;12(9):e0185313.
[Google Scholar]
Ma G., Yang D., Kennedy J.F., Nie J., . Synthesize and characterization of organic-soluble acylated chitosan. Carbohydr. Polym.. 2009;75(3):390-394.
[Google Scholar]
Mahmood W.A.K., Khan M.M.R., Yee T.C., . Effects of reaction temperature on the synthesis and thermal properties of carrageenan ester. J. Phys. Sci.. 2014;25(1):123.
[Google Scholar]
Marcus Y., Migron Y., . Polarity, hydrogen bonding, and structure of mixtures of water and cyanomethane. J. Phys. Chem.. 1991;95(1):400-406.
[Google Scholar]
Mishra D.K., Tripathy J., Behari K., . Synthesis of graft copolymer (k-carrageenan-gN, N-dimethylacrylamide) and studies of metal ion uptake, swelling capacity and flocculation properties. Carbohydr. Polym.. 2008;71(4):524-534.
[Google Scholar]
Mishra M.M., Yadav M., Sand A., Tripathy J., Behari K., . Water soluble graft copolymer (κ-carrageenan-gN-vinyl formamide): Preparation, characterization and application. Carbohydr. Polym.. 2010;80(1):235-241.
[Google Scholar]
Mobarak N.N., Ramli N., Ahmad A., Rahman M.Y.A., . Chemical interaction and conductivity of carboxymethyl κ-carrageenan based green polymer electrolyte. Solid State Ion.. 2012;224:51-57.
[Google Scholar]
Namyslo J.C., Drafz M.H., Kaufmann D.E., . Durable Modification of Wood by Benzoylation—Proof of Covalent Bonding by Solution State NMR and DOSY NMR Quick-Test. Polymers. 2021;13(13):2164.
[Google Scholar]
Nunes S.C., Saraiva S.M., Pereira R.F.P., Silva M.M., Carlos L.D., Almeida P., Gonçalves M.C., Ferreira R.A.S., de Zea Bermudez V., . Luminescent κ-Carrageenan-Based Electrolytes Containing Neodymium Triflate. Molecules. 2019;24(6):1020.
[Google Scholar]
Pacheco-Quito E.M., Ruiz-Caro R., Veiga M.D., . Carrageenan: drug delivery systems and other biomedical applications. Mar. Drugs. 2020;18(11):583.
[Google Scholar]
Park S., Baker J.O., Himmel M.E., Parilla P.A., Johnson D.K., . Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance. Biotechnol. Biofuels. 2010;3(1):1-10.
[Google Scholar]
Pereira L., Amado A.M., Critchley A.T., Van de Velde F., Ribeiro-Claro P.J., . Identification of selected seaweed polysaccharides (phycocolloids) by vibrational spectroscopy (FTIR-ATR and FT-Raman) Food Hydrocoll.. 2009;23(7):1903-1909.
[Google Scholar]
Serra J.P., Fidalgo-Marijuan A., Teixeira J., Hilliou L., Gonçalves R., Urtiaga K., Gutiérrez-Pardo A., Aguesse F., Lanceros-Mendez S., Costa C.M., . Sustainable lithium-ion battery separator membranes based on carrageenan biopolymer. Adv. Sustain. Syst. 2022:2200279.
[Google Scholar]
Shamsudin I.J., Ahmad A., Hassan N.H., Kaddami H., . Biopolymer electrolytes based on carboxymethyl k-carrageenan and imidazolium ionic liquid. Ionics. 2016;22(6):841-851.
[Google Scholar]
Tecante A., Nunez Santiago M.C., . Solution properties of κ-carrageenan and its interaction with other polysaccharides in aqueous media. Rheology. 2012;1:241-264.
[Google Scholar]
Tye, Y. Y., HPS, A. K., Kok, C. Y., & Saurabh, C. K. (2018). Preparation and characterization of modified and unmodified carrageenan based films. In IOP Conference Series: Materials Science and Engineering (Vol. 368, No. 1). IOP Publishing, p. 012020.
Walayat N., Wang X., Liu J., Nawaz A., Zhang Z., Khalifa I., Cervera M.A.R., Pateiro M., Lorenzo J.M., Nikoo M., Siddiqui S.A., . Kappa-carrageenan as an effective cryoprotectant on water mobility and functional properties of grass carp myofibrillar protein gel during frozen storage. Lwt. 2022;154:112675
[Google Scholar]
Wu S., Lou D., Wang H., Jiang D., Fang X., Meng J., Sun X., Li J., . One-pot synthesis of anti-freezing carrageenan/polyacrylamide double-network hydrogel electrolyte for low-temperature flexible supercapacitors. Chem. Eng. J.. 2022;435:135057
[Google Scholar]
Yusharani, M. S., Ulfin, I., & Ni’mah, Y. L. (2019). Synthesis of water-soluble chitosan from squid pens waste as raw material for capsule shell: temperature deacetylation and reaction time. In: IOP Conference Series: Materials Science and Engineering (Vol. 509, No. 1). IOP Publishing, p. 012070.
Zainuddin N.K., Saadiah M.A., Abdul Majeed A.P.P., Samsudin A.S., . Characterization on conduction properties of carboxymethyl cellulose/kappa carrageenan blend-based polymer electrolyte system. Int. J. Polym. Anal. Charact.. 2018;23(4):321-330.
[Google Scholar]
Zainuddin N.K., Samsudin A.S., . Investigation on the effect of NH4Br at transport properties in k–carrageenan based biopolymer electrolytes via structural and electrical analysis. Mater. Today Commun.. 2018;14:199-209.
[Google Scholar]
Zhang B., Yan H.B., Su L.J., Chen X.N., . Kappa-carrageenan oligosaccharides retard the progression of protein and lipid oxidation in mackerel (Scomber japonicus) fillets during frozen storage. RSC Adv.. 2020;10(35):20827-20836.
[Google Scholar]
Zhu M., Wu J., Wang Y., Song M., Long L., Siyal S.H., Yang X., Sui G., . Recent advances in gel polymer electrolyte for high-performance lithium batteries. J. Energy Chem.. 2019;37:126-142.
[Google Scholar]
Zong Z., Kimura Y., Takahashi M., Yamane H., . Characterization of chemical and solid state structures of acylated chitosans. Polymer. 2000;41(3):899-906.
[Google Scholar]

Introduction

Materials and methods

Materials
Synthesis of benzoyl ƙ-carrageenan
Preparation of ƙcar and Bz-ƙcar gels

Characterization

Fourier transform Infra-Red analysis (FTIR)
Elemental analyzer
1H NMR spectroscopy
X-ray diffraction (XRD)
Thermogravimetric analysis (TGA)
Solubility test
Water contact angle
Impedance spectroscopy

Results and discussion

Conclusions

Funding

Fulltext Views
857

PDF downloads
774

View/Download PDF
Download Citations

BibTeX
RIS

Show Sections

[1] Abu Bakar M.H., Azeman N.H., Mobarak N.N., Mokhtar M.H.H., Bakar A.A., . Effect of active site modification towards performance enhancement in biopolymer κ-Carrageenan derivatives. Polymers. 2020;12(9):2040.
[Google Scholar]

[2] Bardakçı B., Bahçeli S., . An IR study of benzoyl chloride adsorbed on KA, NaA, and CaA zeolites. Zeitschrift für Naturforschung A. 2005;60(8–9):637-640.
[Google Scholar]

[3] Barwick V.J., . Strategies for solvent selection—a literature review. TrAC Trends Anal. Chem.. 1997;16(6):293-309.
[Google Scholar]

[4] Bella F., Mobarak N.N., Jumaah F.N., Ahmad A., . From seaweeds to biopolymeric electrolytes for third generation solar cells: an intriguing approach. Electrochim. Acta. 2015;151:306-311.
[Google Scholar]

[5] Campo V.L., Kawano D.F., da Silva Jr D.B., Carvalho I., . Carrageenans: Biological properties, chemical modifications and structural analysis–A review. Carbohydr. Polym.. 2009;77(2):167-180.
[Google Scholar]

[6] Chen W., Feng Y., Zhang M., Wu J., Zhang J., Gao X., He J., Zhang J., . Homogeneous benzoylation of cellulose in 1-allyl-3-methylimidazolium chloride: Hammett correlation, mechanism and regioselectivity. RSC Adv.. 2015;5(72):58536-58542.
[Google Scholar]

[7] Cunha L., Grenha A., . Sulfated seaweed polysaccharides as multifunctional materials in drug delivery applications. Mar. Drugs. 2016;14(3):42.
[Google Scholar]

[8] Distantina S., Fahrurrozi M., . Carrageenan properties extracted from Eucheuma cottonii, Indonesia. Int. J. Chem. Mol. Eng.. 2011;5(6):501-505.
[Google Scholar]

[9] Ellis A.L., Mills T.B., Norton I.T., Norton-Welch A.B., . The hydrophobic modification of kappa carrageenan microgel particles for the stabilisation of foams. J. Colloid Interface Sci.. 2019;538:165-173.
[Google Scholar]

[10] Gupta M.N., Batra R., Tyagi R., Sharma A., . Polarity index: the guiding solvent parameter for enzyme stability in aqueous-organic cosolvent mixtures. Biotechnol. Prog.. 1997;13(3):284-288.
[Google Scholar]

[11] Hebbar R.S., Isloor A.M., Ismail A.F., . Contact angle measurements. In: Membrane Characterization. Elsevier; 2017. p. :219-255.
[Google Scholar]

[12] Hotchkiss, S., Brooks, M., Campbell, R., Philp, K., Trius, A., 2016. The use of carrageenan in food. Carrageenans: sources and extraction methods, molecular structure, bioactive properties and health effects, 229-243.

[13] Huang Y., Liu J., Zhang J., Jin S., Jiang Y., Zhang S., Li Z., Zhi C., Du G., Zhou H., . Flexible quasi-solid-state zinc ion batteries enabled by highly conductive carrageenan bio-polymer electrolyte. RSC Adv.. 2019;9(29):16313-16319.
[Google Scholar]

[14] Infante V.H.P., Campos P.M.M., . Application of factorial design in the development of cosmetic formulations with carrageenan and argan oil. Int. J. Phytocosmetics Natural Ingredients. 2021;8(1):4.
[Google Scholar]

[15] Lankhorst P.P., Chang A.N., . The application of NMR in compositional and quantitative analysis of oils and lipids. Cham, Switzerland: Springer International Publishing AG; 2018. p. :1743-1764.

[16] Liew J.W.Y., Loh K.S., Ahmad A., Lim K.L., Wan Daud W.R., . Synthesis and characterization of modified κ-carrageenan for enhanced proton conductivity as polymer electrolyte membrane. PLoS One. 2017;12(9):e0185313.
[Google Scholar]

[17] Ma G., Yang D., Kennedy J.F., Nie J., . Synthesize and characterization of organic-soluble acylated chitosan. Carbohydr. Polym.. 2009;75(3):390-394.
[Google Scholar]

[18] Mahmood W.A.K., Khan M.M.R., Yee T.C., . Effects of reaction temperature on the synthesis and thermal properties of carrageenan ester. J. Phys. Sci.. 2014;25(1):123.
[Google Scholar]

[19] Marcus Y., Migron Y., . Polarity, hydrogen bonding, and structure of mixtures of water and cyanomethane. J. Phys. Chem.. 1991;95(1):400-406.
[Google Scholar]

[20] Mishra D.K., Tripathy J., Behari K., . Synthesis of graft copolymer (k-carrageenan-gN, N-dimethylacrylamide) and studies of metal ion uptake, swelling capacity and flocculation properties. Carbohydr. Polym.. 2008;71(4):524-534.
[Google Scholar]

[21] Mishra M.M., Yadav M., Sand A., Tripathy J., Behari K., . Water soluble graft copolymer (κ-carrageenan-gN-vinyl formamide): Preparation, characterization and application. Carbohydr. Polym.. 2010;80(1):235-241.
[Google Scholar]

[22] Mobarak N.N., Ramli N., Ahmad A., Rahman M.Y.A., . Chemical interaction and conductivity of carboxymethyl κ-carrageenan based green polymer electrolyte. Solid State Ion.. 2012;224:51-57.
[Google Scholar]

[23] Namyslo J.C., Drafz M.H., Kaufmann D.E., . Durable Modification of Wood by Benzoylation—Proof of Covalent Bonding by Solution State NMR and DOSY NMR Quick-Test. Polymers. 2021;13(13):2164.
[Google Scholar]

[24] Nunes S.C., Saraiva S.M., Pereira R.F.P., Silva M.M., Carlos L.D., Almeida P., Gonçalves M.C., Ferreira R.A.S., de Zea Bermudez V., . Luminescent κ-Carrageenan-Based Electrolytes Containing Neodymium Triflate. Molecules. 2019;24(6):1020.
[Google Scholar]

[25] Pacheco-Quito E.M., Ruiz-Caro R., Veiga M.D., . Carrageenan: drug delivery systems and other biomedical applications. Mar. Drugs. 2020;18(11):583.
[Google Scholar]

[26] Park S., Baker J.O., Himmel M.E., Parilla P.A., Johnson D.K., . Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance. Biotechnol. Biofuels. 2010;3(1):1-10.
[Google Scholar]

[27] Pereira L., Amado A.M., Critchley A.T., Van de Velde F., Ribeiro-Claro P.J., . Identification of selected seaweed polysaccharides (phycocolloids) by vibrational spectroscopy (FTIR-ATR and FT-Raman) Food Hydrocoll.. 2009;23(7):1903-1909.
[Google Scholar]

[28] Serra J.P., Fidalgo-Marijuan A., Teixeira J., Hilliou L., Gonçalves R., Urtiaga K., Gutiérrez-Pardo A., Aguesse F., Lanceros-Mendez S., Costa C.M., . Sustainable lithium-ion battery separator membranes based on carrageenan biopolymer. Adv. Sustain. Syst. 2022:2200279.
[Google Scholar]

[29] Shamsudin I.J., Ahmad A., Hassan N.H., Kaddami H., . Biopolymer electrolytes based on carboxymethyl k-carrageenan and imidazolium ionic liquid. Ionics. 2016;22(6):841-851.
[Google Scholar]

[30] Tecante A., Nunez Santiago M.C., . Solution properties of κ-carrageenan and its interaction with other polysaccharides in aqueous media. Rheology. 2012;1:241-264.
[Google Scholar]

[31] Tye, Y. Y., HPS, A. K., Kok, C. Y., & Saurabh, C. K. (2018). Preparation and characterization of modified and unmodified carrageenan based films. In IOP Conference Series: Materials Science and Engineering (Vol. 368, No. 1). IOP Publishing, p. 012020.

[32] Walayat N., Wang X., Liu J., Nawaz A., Zhang Z., Khalifa I., Cervera M.A.R., Pateiro M., Lorenzo J.M., Nikoo M., Siddiqui S.A., . Kappa-carrageenan as an effective cryoprotectant on water mobility and functional properties of grass carp myofibrillar protein gel during frozen storage. Lwt. 2022;154:112675
[Google Scholar]

[33] Wu S., Lou D., Wang H., Jiang D., Fang X., Meng J., Sun X., Li J., . One-pot synthesis of anti-freezing carrageenan/polyacrylamide double-network hydrogel electrolyte for low-temperature flexible supercapacitors. Chem. Eng. J.. 2022;435:135057
[Google Scholar]

[34] Yusharani, M. S., Ulfin, I., & Ni’mah, Y. L. (2019). Synthesis of water-soluble chitosan from squid pens waste as raw material for capsule shell: temperature deacetylation and reaction time. In: IOP Conference Series: Materials Science and Engineering (Vol. 509, No. 1). IOP Publishing, p. 012070.

[35] Zainuddin N.K., Saadiah M.A., Abdul Majeed A.P.P., Samsudin A.S., . Characterization on conduction properties of carboxymethyl cellulose/kappa carrageenan blend-based polymer electrolyte system. Int. J. Polym. Anal. Charact.. 2018;23(4):321-330.
[Google Scholar]

[36] Zainuddin N.K., Samsudin A.S., . Investigation on the effect of NH4Br at transport properties in k–carrageenan based biopolymer electrolytes via structural and electrical analysis. Mater. Today Commun.. 2018;14:199-209.
[Google Scholar]

[37] Zhang B., Yan H.B., Su L.J., Chen X.N., . Kappa-carrageenan oligosaccharides retard the progression of protein and lipid oxidation in mackerel (Scomber japonicus) fillets during frozen storage. RSC Adv.. 2020;10(35):20827-20836.
[Google Scholar]

[38] Zhu M., Wu J., Wang Y., Song M., Long L., Siyal S.H., Yang X., Sui G., . Recent advances in gel polymer electrolyte for high-performance lithium batteries. J. Energy Chem.. 2019;37:126-142.
[Google Scholar]

[39] Zong Z., Kimura Y., Takahashi M., Yamane H., . Characterization of chemical and solid state structures of acylated chitosans. Polymer. 2000;41(3):899-906.
[Google Scholar]

Green electrolyte host based on synthesized benzoyl kappa-carrageenan: Reduced hydrophilicity and improved conductivity

Abstract

Keywords

carrageenan

electrolyte

benzoyl

hydrophilic

conductivity

acylation

1 Introduction

2 Materials and methods

2.1 Materials

2.2 Synthesis of benzoyl ƙ-carrageenan

2.3 Preparation of ƙcar and Bz-ƙcar gels

3 Characterization

3.1 Fourier transform Infra-Red analysis (FTIR)

3.2 Elemental analyzer

3.3 1H NMR spectroscopy

3.4 X-ray diffraction (XRD)

3.5 Thermogravimetric analysis (TGA)

3.6 Solubility test

3.7 Water contact angle

3.8 Impedance spectroscopy

4 Results and discussion

5 Conclusions

Funding

Acknowledgments

Declaration of Competing Interest

References

Suggested read for related articles:

3.3 ¹H NMR spectroscopy