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Characterization of bioplastics developed from
Kappaphycus alvarezii crosslinked with commercial
sodium alginate
Eunice Lua Hanry
Universiti Malaysia Sabah
Noumie Surugau ( lnoumie@ums.edu.my )
Universiti Malaysia Sabah
Research Article
Keywords: Kappaphycus alvarezii, crosslinked biopolymer, algae, alginate, sustainable bioplastics
Posted Date: March 31st, 2023
DOI: https://doi.org/10.21203/rs.3.rs-2754347/v1
License: This work is licensed under a Creative Commons Attribution 4.0 International License.
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Additional Declarations: No competing interests reported.
Characterization of bioplastics developed from Kappaphycus alvarezii crosslinked with
commercial sodium alginate
Eunice Lua Hanry & Noumie Surugau*
Seaweed Research Unit, Faculty of Science and Natural Resources, Universiti Malaysia Sabah,
Malaysia
*Corresponding author: lnoumie@ums.edu.my
ORCID ID: 0000-0002-5385-8946, 0000-0003-1271-1486
Abstract
Plastic pollution has become one of the most concerning problems globally due to excessive use
of one-time use plastics. However, bioplastics could be the answer to help combat this problem
as they are readily biodegradable. Development of bioplastics was done by mixing seaweed
biomass into distilled water at specific ratio, using glycerol as plasticizer. Bioplastics were
developed at the ratio of 100:0, 75:25, 50:50, 25:75, and 0:100 K. alvarezii to commercial
sodium alginate ratio. Characterization was done based on their appearance, mechanical, thermal
and permeability properties, and biodegradability. Resulted data for their appearance showed that
when more K. alvarezii was in the mixture there were more colour differences in comparison to
white background and the same trend for the opacity due to the natural colour of whole K.
alvarezii. As for their mechanical properties, tensile strength of the bioplastics decreased from
100:0 ratio to 0:100 ratio at 7.91 ± 0.45 MPa (100:0), 6.78 ± 0.31 MPa (75:25), 5.20 ± 0.37 MPa
(50:50), 4.13 ± 0.17 MPa (25:75) and 3.76 ± 0.14 MPa (0:100), respectively. Same goes for their
elastic modulus at 20.93 ± 0.61 MPa (100:0), 16.47 ± 0.99 MPa (75:25), 11.42 ± 0.53 MPa
(50:50), 8.78±0.45 MPa (25:75) and 6.65±0.32 MPa (0:100), respectively. This shows that the
addition of alginate enhances the elasticity but decreases tensile strength. As a conclusion,
developed seaweed-based bioplastics resulted different properties at different mixture ratio show
potential to be incorporated into the market as they are a greener option to fight single-use plastic
wrappings such as saran wrap, beverages and food additive packets.
Keywords: Kappaphycus alvarezii, crosslinked biopolymer, algae, alginate, sustainable
bioplastics
1.0 Introduction
Seaweeds are macroalgae that can grow wildly in the ocean or be commercially grown, each for
their own purpose according to their type and species (Phang et al., 2019). Seaweed has been
used in many industries, especially the food industry, either as a raw ingredient or as an additive.
It has also been used as a supplement in medicine, as it has been shown to have many health
benefits for its users (Buschmann et al., 2017). There are a lot of circumstances that affect the
growth of seaweeds, which at the same time can alter their properties when conditions are
changed (Sugumaran et al., 2022). Malaysia has a great sea environment for the growth of
seaweeds, which has led to concentrated seaweed availability (Hussin & Khoso, 2017). For that
reason, K. alvarezii is abundant even though it is in the group of commercialized seaweeds
(Hamid et al., 2020). Since the price of seaweed is not controlled, seaweed growers are
demotivated to continue and instead concentrate on other business sectors because the
government does not care about their welfare, which caused the price of seaweed to increase as a
result of imports from other ASEAN countries (Asri et al., 2021; Hussin & Khoso, 2017).
Seaweeds are also studied for their hydrocolloid extracts, especially alginate,
carrageenan, and agar, which are used in a wide range of fields (Qin, 2018). Other than being in
those mainstream industries, current studies have focused on trying to introduce seaweed as a
biomass source for bioplastics (Rajendran et al., 2012; Zhang et al., 2019). This is because
studies have shown that seaweed-based bioplastics have good protective qualities (Lomartire et
al., 2022). There are a few types of seaweed-based bioplastics that differ in terms of their source
of biomass, like using whole seaweed (Hanry & Surugau, 2020; Moey et al., 2018), agar (Hii et
al., 2016), alginate (Castro-Yobal et al., 2021; Yupa et al., 2021), and carrageenan (Farhan &
Hani, 2017; Nasution et al., 2019). However, the properties of seaweed-based bioplastics depend
on a few factors, starting from the source of biomass until the process of developing bioplastics
(Lomartire et al., 2022).
Before going deeper into this study, K. alvarezii- and alginate-based bioplastics were
studied to understand their properties individually. K. alvarezii-based bioplastics are closely
similar to semi-refined or refined carrageenan-based bioplastics but lack purity in terms of k-
carrageenan since K. alvarezii is the raw material for k-carrageenan production (Rudke et al.,
2020). According to research, bioplastics are frequently crosslinked. For instance, adding pectin
and mica flakes to increase barrier qualities (Alves et al., 2010) or crosslinking with essential oils
to improve antibacterial and antioxidant activities (Shojaee-Aliabadi et al., 2013, 2014). Previous
research on alginate-based biofilms concentrated on using them in medicine as pill capsules,
pads for treating wounds, and others (Zia et al., 2017). According to studies, the main reason
why other elements were added to alginate-based films was to improve their mechanical
characteristics (Abdullah et al., 2021).
The study focused on using both alginate and K. alvarezii to produce bioplastics in the
hopes of getting the good properties from both as their individual qualities were proven by
previous studies. It was concluded that both K. alvarezii- and alginate-based films individually
each have their own pros and cons. Hanry et al. (2022) and Hanry & Surugau (2020) studies
revealed that there was more room for the use of K. alvarezii- and alginate-based bioplastics with
the goal of replacing single-use packaging. This study is a follow-up that aims to serve as a
baseline reference for following research by comparing each characteristic to assess the effects
of combining commercial sodium alginate with K. alvarezii at various ratios to produce seaweed-
based bioplastics.
2.0 Materials and method
2.1 Materials
The raw materials used in this study were fresh Kappaphycus alvarezii from Semporna, Sabah
and commercial sodium alginate (SYSTERM). Chemicals used include glycerol with purity of
99% (SYSTERM), magnesium nitrate hexahydrate (SYSTERM), silica gel (SYSTERM).
2.2 Development of seaweed-based bioplastics
The method was adapted from a study by Rahmawati et al., (2019) with slight modification after
preliminary study. The biomass to water ratio was 1:60, where biomass used in this study is
whole seaweed (K. alvarezii) (from this point referred as WS) and commercial sodium alginate
(from this point referred as CA). The mixture ratio of WS to CA was at set at 100:0, 75:25,
50:50, 25:75, and 0:100 %(w/w), respectively. 2g of biomass was dissolved in 120mL of distilled
water while being heated and stirred continuously to 60°C. Solution was remained for 10
minutes once the temperature reached 60°C before adding 1% (v/v) glycerol. The mixture was
blended for 1 minute to homogenize the mixture before being heated to 80°C and remained for 1
minute. Mixture was taken off the heating plate. By slowly swirling the solution, any bubbles in
the solution were eliminated with a glass rod. Bioplastics were created using the casting method,
in which the solution was poured onto a petri dish and dried for 24 hours at 50°C in a vented
dryer. Samples were left to cool before removing them from the cast which resulted Figure 3.1.
2.3 Characterization
2.3.1 Functional Group Analysis
Functional groups of raw materials and samples were determined using ATR-FTIR (Agilent
Technologies). All the samples were tested to compare the differences and intensity in each
mixture, plus before any reaction (raw material).
2.3.2 Moisture Content
Moisture content was calculated using equation 2.1 after heating the sample in an oven at 105°C
for 3 hours.
Moisture Content (%) =
(2.1)
2.3.3 Appearances
Prior to any testing, the thickness of samples was measured using a digital caliper. For their
opacity, they were scanned at 660nm using UV-Visible spectrophotometer (Agilent
Technologies). Calculation for opacity was done using equation 2.2 with the absorbance resulted
from the scans.
Opacity (O) =
(2.2)
For their colour determination, each of them was scanned using colour reader (Konika Minolta),
which gave L* (brightness), a* (+ redness, - greenness), b* (+ yellowness, - blueness) readings
for each sample. The resulted data was calculated using equation 2.3, L = 83.8 , a = 12.4 , b = -
3.0. to determine the colour difference in comparison to the white background
Colour Difference (ΔE) = ) (2.3)
2.3.4 Thermal Stability
Thermal stability of samples was determined using a Thermal Gravimetric Analyzer (TGA)
(Mettler Toledo) with a temperature range of 25 - 700°C, a ramp speed of 20°C/min, and a gas
flow rate of 30mL/min. The TGA/DTG graph was obtained from the scan.
2.3.5 Mechanical Properties and Water Vapour Permeability
according to ASTM D-618 (ASTM, 2002), samples were subjected to initial conditioning for 72
hours at 53% RH using magnesium nitrate hexahydrate (Mg(NO3)2.6H2O) before undergoing
mechanical and water vapour permeability testing. For determination of mechanical properties,
samples were cut into dumbbell shape in strips of 90mm x 15mm and fixed on using Universal
Tensile Machine (GoTech Instruments) at 5mm/min with 50mm gauge.
For water vapour permeability tests, silica served as the 0% RH medium while water
served as the 100% RH medium. Each sample was placed in a desiccator on a permeation cup,
and the weight of the sample was measured hourly for 6 hours. The permeability result was
calculated using equation 2.4. Note that the silica was heated at 100°C for 3 hours prior to use.
WVP =
(2.4)
2.3.6 Biodegradability
The soil burial method was modified in relation to the method proposed by Chuensangjun et al.
(2013) for sample biodegradability. Samples were cut into 5cm × 5cm squares and buried in the
ground 10cm deep at 40% RH. Samples were monitored, and the number of days required for
samples to decay completely was recorded.
2.4 Statistical Analysis
All samples were developed and tested in 3 replicates. The statistical analysis, Analysis of
Variance (ANOVA) with Tukey HSD multiple comparison as post-hoc analysis was done using
IBM SPSS Statistics 29.
3.0 Results
(a) 100 TO 0
(b) 75 TO 25
(c) 50 TO 50
(d) 25 TO 75
(e) 0 TO 100
Figure 3.1: Bioplastics at different WS to CA mixture ratio
Figure 3.2: FTIR spectrum of K. alvarezii, sodium alginate, glycerol, and bioplastics at different
WS to CA mixture ratio
Table 3.1: Moisture content, thickness, and opacity of bioplastics at different WS to CA mixture
ratio
Sample
Characterization
MC (%)
T (mm)
O (cm-1)
100 TO 0
23.4 ± 0.6a
0.054 ± 0.05a
2.757 ± 0.001a
75 TO 25
23.4 ± 0.4a
0.052 ± 0.04a
2.468 ± 0.001b
50 TO 50
23.3 ± 0.3a
0.050 ± 0.04a
1.844 ± 0.008c
25 TO 75
23.3 ± 0.4a
0.053 ± 0.01a
1.057 ± 0.001d
0 TO 100
23.5 ± 0.5a
0.052 ± 0.04a
0.653 ± 0.001e
MC: Moisture content, T: Thickness, O: Opacity; Data reported are mean ± standard deviation
(n = 3), and values of different letters a-e of the same column are significantly different (P<0.05)
from each other.
Table 3.2: Colour of bioplastics at different WS to CA mixture ratio
Sample
Colour
L*
a*
b*
ΔE
100 TO 0
75.57 ± 0.12a
15.57 ± 0.25a
5.53 ± 0.15a
12.3 ± 0.1a
75 TO 25
77.60 ± 0.10b
20.53 ± 0.21b
1.13 ± 0.06b
11.0 ± 0.2b
50 TO 50
78.63 ± 0.25c
19.43 ± 0.06c
0.87 ± 0.06c
9.5 ± 0.1c
25 TO 75
80.20 ± 0.10d
18.03 ± 0.06d
0.63 ± 0.06d
7.6 ± 0.1d
0 TO 100
82.43 ± 0.12e
17.17 ± 0.06e
0.27 ± 0.06e
5.9 ± 0.1e
L*: Lightness (100)/ darkness (0), a*: redness (+)/ greenness (-), b*: yellowness (+)/ blueness (-
), ΔE: Colour difference; Data reported are mean ± standard deviation (n = 3), and values of
different letters a-e of the same column are significantly different (P<0.05) from each other.
Table 3.3: Mechanical properties, water vapour permeability, and biodegradability of bioplastics
at different WS to CA mixture ratio
Characterization
TS
(MPa)
EM
(MPa)
WVP
(Kgs-1m-1Pa-1)
Biodegradability
(days)
100 TO 0
7.91 ± 0.45a
20.93 ± 0.61a
4.69E-14 ± 1.46E-15a
15 ± 1
75 TO 25
6.78 ± 0.31b
16.47 ± 0.99b
3.80E-14 ± 7.82E-16b
15 ± 1
50 TO 50
5.20 ± 0.37c
11.42 ± 0.53c
3.33E-14 ± 1.00E-15c
15 ± 1
25 TO 75
4.13 ± 0.17d
8.78 ± 0.45d
2.64E-14 ± 1.21E-15d
15 ± 1
0 TO 100
3.76 ± 0.14d
6.65 ± 0.32e
2.22E-14 ± 6.57E-16e
15 ± 1
TS: Tensile strength, EM: Elastic Modulus, WVP: water vapour permeability; Data reported are
mean ± standard deviation (n = 3), and values of different letters a-e of the same column are
significantly different (P<0.05) from each other.
Figure 3.3: TGA/DTG graph of bioplastics at different WS to CA mixture ratio
4.0 Discussion
For the crosslinking of whole seaweed, K. alvarezii (WS), with commercial sodium alginate
(CA), the ratio of WS to CA was set at 100:0, 75:25, 50:50, 25:75, and 0:100, respectively, in
which bioplastics developed as shown in Figure 3.1, respectively. The biomass was dissolved in
distilled water and glycerol was used as plasticizer. The bioplastics were developed using casting
method.
4.1 Functional group
Functional groups of bioplastics and raw materials are important to identify changes before and
after reactions and differences at varying WS/CA ratios, as shown in Figure 3.2. This is
important as the addition of glycerol will cause plasticization, which will alter the peaks (Vieira
et al., 2011). Figure 3.2 was analyzed and divided into a few sections with explanations after
referring to multiple previous studies (Arzani et al., 2020; Dewi et al., 2015; Distantina et al.,
2011; Naseri et al., 2019; Paula et al., 2015; L. Pereira et al., 2009).
Firstly, section (a) ranged between 3255.02 – 3369.12 is the hydroxyl (-OH) stretching,
which was present for all the samples. Next, at section (b) is the -CH stretching which was
present for glycerol at 2932.94 and 2880.50 but not intense in WS and CA. For the bioplastics,
since all of them were added at the same concentration of glycerol, they each have the -CH
stretching peaks which ranged between 2933.93 – 2939.17. At section (c), it shows peaks for
COOH bonding, where it also showed that the intensity was more for CA and weaker for WS and
no peak found on FTIR spectrum of glycerol. Bioplastics also showed that as more CA ratio, the
more intense the peak.
Next at section (d), CA showed a peak at 1407.35 for the C-O-H bond, while glycerol
also showed the same peak but with less intensity at 1412.05. Since WS showed no peak in that
section, the 100:0 C-O-H peak was less intense than the rest but had a peak due to glycerol
addition. Plus, as more alginate content was added, the peak also intensified, ranging from
1409.09 – 1415.97. For section (e), WS showed a peak at 1224.16 that represented the S=O
bond, which was also present in glycerol at 1210.74 but not in CA. The peak was most intense at
100:0, which decreased with the addition of alginate which ranged from 1219.88 – 1227.66, and
finally showed no peak at 25:75 and 0:100. Following that, the peaks in section (f) represent
merging peaks of the C-O-C bond and mannuronic acid group for CA and the glycosidic bond
for WS and glycerol. The presence of these groups was also found in the bioplastics’ spectrum,
which ranged from 1027.88 to 1033.84. Next, sections (g) and (h) represented the OH
deformation and sulphate groups of the samples, respectively.
4.2 Moisture content, Thickness, Opacity and Colour
Data resulted from the study are tabulated in Table 3.1, which showed there were no significant
differences on the moisture content and thickness of the bioplastics developed, which ranged
between 23.3 ± 0.4% – 23.5 ± 0.5% and 0.050 ± 0.04mm – 0.054 ± 0.05mm, respectively, but
their opacity was significantly different from each other. For their opacity, their trend is 100:0 >
75:25 > 50:50 > 25:75 > 0:100, their opacity decreases and becomes more transparent as they are
lower in WS concentration and have higher CA content. The increase in transparency as more
alginate is added is directly linked to the homogeneity of the mixture (Paula et al., 2015). On the
other hand, since whole seaweed of K. alvarezii was used, there were more impurities, such as,
fibers, minerals, and others (Farah Nurshahida et al., 2020), which were directly linked to the
opaqueness of the bioplastics with higher WS content.
Next, their colour can be described numerically according to CIE L*a*b* colour
coordinate space, in which their coordinates can be translated to colour, where L represents
lightness (100) and darkness (0), a* represents redness (+) and greenness (-), and b* represents
yellowness (+) and blueness (-). To simplify, the bioplastics trend for L* and b* was 100:0 >
75:25 > 50:50 > 25:75 > 0:100, which means that going down the trend, the bioplastics were
brighter and less yellow. Meanwhile, a* showed the trend of 75:25 > 50:50 > 25:75 > 0:100 >
100:0, meaning that 100:0 was less red compared to the rest, and as more alginate was added, the
redness also decreased closer to 0. The colour difference in this study was in comparison to a
white background, which had L*a*b* values of 83.8, 12.4, and -3.0, respectively.
For the colour difference (ΔE), the purpose was to compare if there were major
differences compared to the white background, where the trend was similar as to their opacity.
However, due to the transparency of the bioplastics, the colour difference resulted in the
alteration of the white background colour when the respective bioplastics were placed on top of
it. The mixing of biomass in the bioplastics’ mixture causes deformity in the crystallization in the
polymer matrix, which allowed more light penetration through the bioplastic and consequently
resulted in lower opacity and colour difference (Farhan & Hani, 2017).
4.3 Mechanical, Water Vapour Barrier, Thermal and Biodegradability Properties
The outcome of the study on their mechanical, barrier, and biodegradability properties is
tabulated in Table 3.3. The trends for tensile strength (TS), elastic modulus (EM), water vapour
permeability (WVP), and thermal stability were 100:0 > 75:25 > 50:50 > 25:75 > 0:100. Their
biodegradability properties, on the other hand showed no difference among them.
For their tensile strength, the outcome of this study of 7.91 ± 0.45 MPa for 100:0 was
higher than the previous study on K. alvarezii films by Siah et al. (2014) at 6.82 MPa but lower
than the studies by Sudhakar et al. (2020) and Ili Balqis et al. (2017) at 13.78 MPa and 69.69
MPa, respectively. However, the 0:100 resulted at 3.76 ± 0.14 MPa was much weaker than past
studies that develop alginate-based bioplastics due to lack of additives, where with calcium
chloride resulted 31 MPa (Paşcalau et al., 2012), with addition of pectin at 22.5 – 42.3 MPa
(Galus & Lenart, 2013), and others. The 100:0 were the strongest in terms of load bearing
strength, and as alginate was added, the tensile strength decreased. This addition of alginate into
the K. alvarezii mixture disrupted the homogeneity, which led to the decrease in tensile strength
following the trend (Ching et al., 2017). There were some previous studies that proved alginate-
based films themselves are very homogenous and strong, but only with the addition of calcium
chloride or with other enhancer (Abdullah et al., 2021), in which this study did not add any.
As for the elastic modulus (EM), higher value of the elastic modulus means higher
rigidity. The most elastic among the bioplastics was 0:100 which resulted at 6.65 ± 0.32 MPa
and the least was 100:0 at 20.93 ± 0.61 MPa. As for the rest, with more alginate into the film,
their elasticity was indeed improved which is due to the disrupted homogeneity in the polymer
matrix from the different type of biomass that reduces the rigidity among the particles (Paşcalau
et al., 2012)`. Next, their water vapour permeability also improved when more alginate
concentration was in the mixture. This is because although they are all hydrophilic by nature,
alginate is more hydrophobic compared to other hydrocolloids from seaweed (Castro-Yobal et
al., 2021). Hence, bioplastics with higher alginate content showed better protection from water
vapour.
For thermal stability, the resulting graph is shown in Figure 3.3. The first section dip at
25 – 120°C represents the loss in weight for evaporation of moisture absorbed, followed by the
next section, which represents the degradation of glycosidic bonds in cellulosic parts,
decarboxylation, decarbonylation, and hydration of alginate, which was around 170 - 400°C
(Azucena Castro-Yobal et al., 2021; R. Pereira et al., 2013). This shows that 100:0 is most stable
among them, with a degradation peak at 270°C, and 0:100 is the least stable at a lower
temperature degradation peak at 223°C. This resulted in that trend because the structure became
less compact as more alginate was added, which decreased the material’s stability (Paşcalau et
al., 2012). From Figure 3.3, there is a slight shift between the overlapping graphs, the graph
shifting towards the right indicates higher thermal stability (Doh & Whiteside, 2020). The
outcome of thermal stability helped supported the outcome of the mechanical and barrier
properties.
On the other hand, the biodegradability of the bioplastics showed no difference between them
as they were highly degradable. All the bioplastics were fully degraded between 14 -16 days
when buried in soil with 40% RH. This showed that although all the other properties, in terms of
mechanical, barrier, and thermal properties, were significantly different among them, their
biodegradability was not affected.
Conclusion
To conclude, this study focused on developing WS (K. alvarezii) to CA (commercial sodium
alginate) at different ratio at 100:0, 75:25, 50:50, 25:75, and 0:100. To summarize the outcome,
the opacity, colour difference, tensile strength, elastic modulus, water vapour permeability, and
thermal stability resulted in a trend of 100:0 > 75:25 > 50:50 > 25:75 > 0:100. The addition of
alginate to the mixture disrupted the stability of the K. alvarezii-based bioplastics and vice versa.
They still showed their potential to replace single-use plastic wrap at the right ratio. Low water
vapour permeability indicates improvement in its barrier properties, which are equivalent to its
protecting ability. The suggested future work from this point forward includes studying the
possibility of improving more on their barrier and mechanical properties as they will be applied
in the food industry, which will directly help extend the food preservation time.
Declaration
Funding
This study was funded by the Ministry of Higher Education of Malaysia (MoHE) through
FRGS0562-1/2021 (Project ID:20518; Reference code: FRGS/1/2021/STG04/UMS/02/2)
Authors Contribution
Eunice Lua Hanry is the postgraduate student, who conducted the research and wrote the first
draft. Noumie Surugau is the supervisor of this study, who was in charge of revising the draft
and approved the final version of the paper before it is submitted for publishing.
Acknowledgement
We would like to thank Universiti Malaysia Sabah for providing the laboratory facilities and
instruments to conduct this study.
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