Anal. Methods Environ. Chem. J. 5 (4) (2022) 43-54

Research Article, Issue 4

Analytical Methods in Environmental Chemi s try Journal

Journal home page: www.amecj.com/ir

AMECJ

Preparation of chitosan lms pla s ticized by lauric

and maleic acids

Sara Hikmet Mutasher a

and Hadi Salman Al-Lami a,*

a Department of Chemis try, College of Science, University of Basrah, Basrah, Iraq

AB S TRACT

The energy crisis and environmental concerns have increased

intere s t in natural polymers, and the bio-sourced materials eld is

experiencing rapid growth. A useful alternative to conventional pla s tic

packaging manufactured from fossil fuels is packaging con s tructed

of biodegradable polymers. Consideration has been given to the

in s trumental methods for examining modications to the chemical

composition and characteri s tics of modied chitosan. The molecular

weight and the kind of pla s ticizer present in these materials are the

two primary variables inuencing their usability and performance.

This s tudy set out to physically blend chitosan with two dierent

acids, lauric and maleic, to enhance chitosan ca s t lms’ physical

and mechanical properties. Dierent pla s ticizer ratios appeared to

have little eect on the various properties of the chitosan ca s t lms.

Examining the obtained lms by FTIR implies that chitosan’s native

s tructure was unchanged. The lms prepared had more exibility and

better solubility than those made with un-pla s ticized chitosan. It was

evident from an analysis of the mechanical properties of the lms

that both acid pla s ticizers enhanced the mechanical properties of the

chitosan.

Keywords:

Chitosan,

Lauric acid,

Maleic acid,

Films pla s ticizers,

Mechanical properties,

Solubility

ARTICLE INFO:

Received 5 Aug 2022

Revised form 14 Oct 2022

Accepted 25 Nov 2022

Available online 29 Dec 2022

*Corresponding Author: Hadi Salman Al-Lami

Email: hadi.abbas@uobasrah.edu.iq

https://doi.org/10.24200/amecj.v5.i04.209

------------------------

1. Introduction

The intere s t in natural polymers has grown as a

result of the energy crisis and environmental

concerns, and the eld of bio-sourced materials

is currently expanding quickly. In this situation,

the indu s try mu s t look for new sources of organic,

environmentally friendly, and biodegradable

polymers to replace those derived from petroleum.

Polysaccharides in this area have enormous potential

for use in active and intelligent packaging, smart

textiles and biomedical devices, environmental

remediation, and other applications. Chitosan is a

special cationic polysaccharide with an excellent

anity for various surfaces and out s tanding

cosmetic properties, even when left unaltered. It

is a naturally occurring cationic copolymer [1].

This biopolymer, which is abundant in nature

(the second one after cellulose), holds much

promise for various uses. It is a highly renewable,

biodegradable, environmentally friendly, and

non-toxic polymer. Indeed, chitosan has been

successfully used as a scaold for biomedical

applications, water engineering, treatment, the

food indu s try, lms, coatings, and con s truction

elds. The functionalization of its chemical

s tructure often enhances its characteri s tics until

it obtains properties equivalent to synthetic

products [1]. The development of chitosan-

based materials has attracted much attention

44 Anal. Methods Environ. Chem. J. 5 (4) (2022) 43-54

due to their great qualities, such as, nontoxicity,

biodegradability, biocompatibility, antibacterial

properties, and biofunctional characteri s tics, not

only in the biomedical sector but also in the eld

of food contact materials. The new or improved

properties of chitosan would be obtained through

the chemical modication of its s tructure via

the blending or attaching of various chemicals.

Therefore, chitosan does not present problems of

handling and disposal that may be encountered

with some of its synthetic counterparts [2].

Chitosan is a promising material based on its

chemical modications as dye-removing agents

and metal ion adsorbents. Recently, the progress

on chemical modications of chitosan has been

quite rapid, and we are condent that a more

extensive range of applications of chitosan

derivatives could be expected shortly [3, 4]. In

the pla s tics sector, pla s ticizers have long been a

popular element [5]. Examples of its numerous

applications include packaging, consumer

goods, medicines, s tructures, and con s truction

[6]. However, the indu s try is moving away from

phthalate-based pla s ticizers and toward bio-based

pla s ticizers due to environmental and health

concerns [7]. Low co s t per volume, low volatility,

diusivity, low specic gravity, good miscibility,

and s trong intermolecular interactions between the

pla s ticizer and the polymer resin are all desired

properties of pla s ticizers. A well-pla s ticized

product should be exible at low temperatures,

have a low ela s tic modulus, a low glass transition

temperature, and have good tensile elongation

but low tensile s trength [8]. Physical blending

is a practical and important method for altering

chitosan to serve various applications. Chitosan-

based lms’ s tructural and physical characteri s tics

have been extensively researched for use in

biomedical and other applications [9,10]. When

polymer chains separate from one another,

pla s ticizers ll the intermolecular spaces between

them. This reduces chain retraction and increases

free volume, enabling polymer chains to move

more freely [11]. The chitosan and pla s ticizer

hydrogen bonding interaction [12,13] regulates

the mechanical and physical characteri s tics of

the lms. The physically blended pla s ticization

of extracted chitosan with lauric acid and maleic

was carried out in this work. It also focuses on

the possible changes in molecular s tructure and

mechanical and water solubility properties to see

if they can produce appropriate chitosan lms for

packaging, which is a potential application for

chitosan.

2. Experimental

2.1. Reagents and Materials

Chitosan was obtained by the deacetylation

process of chitin extracted from local shrimp shell

wa s te as described in the literature [14,15]. It had a

viscosity average molecular weight of 2.702x105 g

per mole as determined by the viscosity technique

and a deacetylation degree of 80%. The acetic acid

(CH3CO2H; pure ≥99%; CAS No.: 64-19-7), Lauric

acid (CH3(CH2)10COOH. CAS No.: 143-07-7) and

maleic acid (HO2CCH=CHCO2H, MDL Number:

MFCD00063177; PubChem ID: 24896549, CAS

No.: 99110-16-7) used as pla s ticizers and acetic

acid as a solvent were purchased from Sigma-

Aldrich Company and utilized without further

treatment. The tris-maleate buer and sodium

maleate buer make of maleic acid and can be

used for the pretreatment of poplar tracheid cell

walls for the spectroscopic analysis of lignin.

2.2. Ins truments

An FTIR-8101M Shimadzu spectrometer in the

4000–400 cm-1 range was used to inve s tigate

the chemical s tructures of the unpla s ticized

and chemically pla s ticized chitosan lms. The

mechanical properties (tensile s trength, Young’s

modulus, and %elongation at break) of the

unpla s ticized chitosan and their pla s ticizer blend

lms were measured in the tensile mode (speed 5

mm min-1) with a BTI-FR2.5TN.D14 (ZwickRoell,

Germany) mechanical te s ting machine.The

s tandard tes t method (AS tM D882-10) for tensile

properties of thin plas tic sheeting and lms was

used to determine the mechanical properties of the

pla s ticized and unpla s ticized chitosan lms in the

Modications Chitosan Films by Lauric and Maleic Acids Sara Hikmet Mutasher et al

form of s tripes of 20 x 2 mm. This te s t method

covers the determination of tensile properties of

pla s tics in the form of thin sheeting and lms (less

than 1.0 mm (0.04 in.) in thickness).

2.3. Preparation of the chitosan lms

The unpla s ticized chitosan lm was prepared by

the solvent evaporation method by dissolving 1.0

g of chitosan in 100 ml of 2% (v/v) acetic acid

solution under s tirring at ambient temperature for

24 h. Then, it was poured into a leveled Petri dish

of 50 mm in diameter. The lm was removed from

the dish, dried for 12 hours at 45°C, and then s tored

before determining its s tructural, physical, and

mechanical properties [16]. In the same procedure,

pla s ticized chitosan lms with dierent ratios of

various acid pla s ticizers were prepared, as shown

in Table 1.

2.4. Film solubility

The amount of dry matter in the lm that dissolves

in water is used to calculate the solubility of the

lm. The solubility of the lms was evaluated

using previously described techniques with some

changes [17]. In a nutshell, the lms were divided

into 2 cm × 2 cm squares and entirely dried before

being s tored. The lms were weighed repeatedly

until a s table weight that matched the fully dried

lms was attained; this weight was then used as

the initial dry weight. The lms were s tirred at 25

°C for 24 hours while submerged in a glass beaker

in 50 ml of deionized water. After being taken

out of the beakers, the lms were dried at 105 °C

until they attained a con s tant weight. This quantity

served as the nal dry weight. The solubility

percentage was calculated using equation 1 [18].

(Eq: 1)

Table 1. Pla s ticizers used and their ratio to Chitosan

3. Results and Discussion

3.1. Cas t lm formation and appearance

The lms were easy to peel from the ca s t Petra

dish and simple to handle and treat further. The

ca s t lms were transparent, uniform, thin, exible,

and manageable.

3.2. FTIR characterization of unplas ticized

Chitosan lms

Figure 1(black) displays the spectrum of the

unpla s ticized chitosan lm produced by ca s ting a

2% acetic acid solution after it was removed from

the Petri plate and before s torage. The di s tinctive

features of the chitosan spectrum in this s tudy are

analogous to those in other inve s tigations [19,20].

Pure Cs exhibit characteri s tic polymer base-

s tate peaks, including those at 1037 cm–1 from

the vibration of C-O groups, 1562 cm–1 from NH

bending, and 1654 cm–1 from C=O s tretching (amide

I) O=C-NHR. The s tretching vibration of free

hydroxyl and the asymmetrical and symmetrical

s tretching of the N-H bonds in the amino groups

are correlated with the peaks between 3610 and

3000 cm–1 that are present in all of the lms under

examination [21]. The bands at 2912 and 2843 cm–1

indicate the vibrations of the aliphatic C-H [22].

3.3. FTIR inves tigation of Cs-lauric acid blended

lms

Figures 1 illu s trate the usual lauric acid peak,

which occurs between 2928 and 2844 cm–1 [23].

The amide II band for the C-O s tretch of the acetyl

group is represented by the band at 1654 cm–1,

while the band represents the N-H s tretch by the

band at 1597 cm–1. The linked C-O s tretch of the

glucosamine residue is represented by the skeletal

vibration at 1072 cm–1, and the asymmetric C-H

bending of the CH2 group is indicated by the band

at 1377 cm–1 [24]. The bands at 2916 cm–1 and 2850

cm–1, respectively, reect the s tretching vibrations

of CH2 and CH3, whereas the band at 1753 cm–1

represents the s tretching vibrations of C=O [25,26].

The band between 1750 and 1700 cm–1 represents

the carbonyl C=O s tretching.

4000 3500 3000 2500 2000 1500 1000 500

T (%)

Wavenumber (cm

-1

)

Cs-Lauric acid (1:1)

Cs-Lauric acid (1:3)

Cs-Lauric acid (2:1)

Fig. 1. FTIR spectra of Cs-lauric acid lms

Anal. Methods Environ. Chem. J. 5 (4) (2022) 43-54

3.4. FTIR examination of Cs-maleic acid

blended lms

The FTIR spectra of the physical blend of chitosan

with maleic acid lms are shown in Figure 2.

The spectra exhibited a peak in the 3500-2500

cm–1, which widened due to the OH groups of

both diacids combining chitosan with each diacid

individually. This sugge s ts that integrating the two

materials raised the proportion of hydroxyl groups

rather than changing the type of functional groups

in the backbone complex [27,28]. The outcome

demon s trated that maleic acid successfully

interacted with chitosan’s amine group.

Additionally, the diacid C=O band at 1701 cm–1

[29] is present. Similar to this, the contributions

of both diacid C-O bonds led to a wider chitosan

C-O absorption at 1180 cm–1. Creating an amide

link between maleic acid and the chitosan amine

group is responsible for the remaining spectrum

alterations.

At 1708 cm–1, the carbonyl C=O s tretching

absorption became visible. The literature claims

that pure diacid has two C=O peaks around 1700

cm–1 and 1750 cm–1, respectively, and s tands for free

and hydrogen-bonded carboxylic acid groups [30].

The peak at 1750 cm–1 vanished after the chitosan

reaction, and there were no additional peaks in

the 1735 cm–1 region, indicating that e s terication

did not occur. According to a literature review

on maleic acid amides, the cyclic amide analog

emerged around 1770 cm–1, but the acyclic amide

displayed classic C=O absorption near 1620 cm–1

[31]. The cyclic s tructure cannot exi s t since there

are no peaks in the 1770 cm–1 area of the chitosantric

acid spectra. Examining peaks in the 563–675 cm–1

range proves that chitosan’s native s tructure was

unchanged. According to Mima et al. [32], these

peaks are sharpe s t for 99 percent deacetylated

chitosan and gradually fade away as acetylation

increases (amide production), and this is the case

here because the extracted chitosan used had about

81% degree of deacetylation.

4000 3500 3000 2500 2000 1500 1000 500

T (%)

Wavenumber (cm

-1

)

Cs-maleic acid (1:1)

Cs-maleic acid (1:2)

Cs-maleic acid (2:1)

Fig. 2. FTIR spectra of Cs-maleic acid lms.

Modications Chitosan Films by Lauric and Maleic Acids Sara Hikmet Mutasher et al

3.5. Tensile properties of Chitosan lms

Especially for single-use packaging when

the material is s tretched during use owing

to continuous wear and tear, flexibility is an

important property of pla s tics. The mechanical

properties of synthetic biopla s tics mu s t be

precisely s tudied to define their range of uses.

Polymer films’ s trength and ela s ticity can be

determined through mechanical te s ting. The

amount to which the film subjected to the applied

pull force reacts is defined by tensile s trength

measurements. A pla s ticizer is a sub s tance that,

when added to polymer materials, increases

their ela s ticity. This pla s ticizer is necessary

to get around the s tiffness of films made with

chitosan. The inter-polymer bond between

chitosan polymer chains and pla s ticizers may

become brittle and break. The pla s ticized and

unpla s ticized chitosan films were te s ted in dry

s tates according to AS tM D882-2010 “S tandard

Te s t Methods for tensile properties of thin plas tic

sheeting and films,”

3.6. Tensile properties of plas ticized Cs: lauric

acid lms

The eect of the addition of lauric acid pla s ticizer

resulted in a decrease of the tensile s trength,

Young modulus, and % elongation at break with an

increasing amount of lauric acid, which was shown in

Figures 3, 4, and 5. This leads to the indication that a

level of interfacial adhesion may be lacking between

chitosan and lauric acid. Adorna et al [33] obtained

the same line of results. This happened because too

many lauric acid pla s ticizer molecules were in a

separate phase outside the phase of the pla s ticized

blend. This sugge s ts that there may not be enough

interfacial adhesion between chitosan and lauric

acid. The intermolecular force between the chains is

reduced because of the conditions. It is concluded that

the decrease in the measured mechanical properties

of chitosan pla s ticized with increasing lauric acid

pla s ticizer amount is in good accord with other reported

results [34,35]. Their results were explained due to the

pla s ticizer’s eect on the promotion of intermolecular

forces, thus lowering the high intramolecular forces

inside the pla s ticized polymer mix chains.

Fig. 3. The eect of Cs: Lauric acid ratios on the tensile s trength of pla s ticized chitosan.

Anal. Methods Environ. Chem. J. 5 (4) (2022) 43-54

3.7. Tensile properties of plas ticized Cs: maleic

acid lms

Figures 6, 7, and 8 showed the eect of dierent

ratios of chitosan: maleic acid pla s ticizer on

the mechanical properties of the chitosan-

based blended lms, i.e., tensile s trength,

Young modulus, and %elengotion at the break,

respectively. It can be observed that Cs: maleic

acid lms with a ratio of 2:1 showed higher

s tress at maximum load and Young’s modulus

than those by (1:2) cross-linked by maleic acid,

accompanied by an increase in the %elongation at

break as well. This is because there is an excess

of cross-linking bridges, resulting in lower chain

s tiness and higher extendibility.

This result was also in agreement with Reddy and

Yang [36] and Thessrimuang and Prachayawarakorn

[37]. They reported using an acid pla s ticizer caused

by excess cross-linking, which led to an increase in

tensile s trength, and this was the case here.

Fig. 4. The eect of Cs: Lauric acid ratios on the Young modulus of pla s ticized chitosan.

Fig. 5. The eect of Cs: Lauric acid ratios on the % elongation at break

of pla s ticized chitosan.

Modications Chitosan Films by Lauric and Maleic Acids Sara Hikmet Mutasher et al

Fig. 6. The eect of Cs: Maleic acid ratios on the tensile s trength of pla s ticized chitosan.

Fig. 7. The eect of Cs: Maleic acid ratios on the Young modulus of pla s ticized chitosan.

Anal. Methods Environ. Chem. J. 5 (4) (2022) 43-54

Fig. 8. The eect of Cs: Maleic acid ratios on the % elongation at break

of pla s ticized chitosan.

3.8. Solubility of plas ticized and un-plas ticized

Chitosan lms

As measured by the lm water solubility of chitosan

lms with various chitosan: pla s ticizers ratios

(w/w), the impact of various pla s ticizers on the

water barrier qualities of the materials was s tudied.

The solubility of lms in water was measured in

triplicate. According to the type of pla s ticizer and its

relative ratio, the lms’ water solubility increased,

as shown in Table 2. This might be explained by the

pla s ticizers’ higher hydrophilicity than chitosan. By

adju s ting the kind and proportion of each pla s ticizer

used in the production of those lms, the solubility

of chitosan/pla s ticizer lms and blends may be

controlled, opening up a wide range of indu s trial

applications. While it may be necessary for certain

materials to be insoluble in specic applications

to ensure the dependability and durability of

the implemented product, lm solubility may

occasionally be desired before consumption. It will

therefore rely on how each pla s ticizer is used when

preparing the sample [38,39].

It may be worth mentioning here that the chitosan

lms always turned rubbery when submerged

in water, but they never retained their s tructural

integrity because the soluble pla s ticized portion

of the lm interfered with the s tructure. However,

the type and concentration of the pla s ticizer can

be adju s ted to modify the solubility of the lm,

making it necessary for more potential applications.

Table 2. Solubility of some pla s ticized chitosan

Cs-Pla s ticizer Ratio SW 1 (%) SW 2 (%) SW 3 (%) SW 4 (%)

Cs 0:0 2.1 2.8 3.3 3.9

Cs-Lauric acid 1:3 10.25 12.8 16.2 26.5

Cs-Maleic acid 2.1 2:1 48.7 53 55

Modications Chitosan Films by Lauric and Maleic Acids Sara Hikmet Mutasher et al

The soluble pla s ticized part of the chitosan lms

interferes with the s tructure, which may be worth

highlighting here. Despite usually turning rubbery

when submerged in water, they never maintained

their s tructural integrity. However, the kind and

amount of the pla s ticizer can be altered to change

how soluble the lm is, necessitating it for more

applications.

4. Conclusions

The purpose of this research was to examine how

the types of mono and di-acid pla s ticizers aected

the molecular s tructure, solubility, and mechanical

characteri s tics of chitosan ca s t lms. To improve

some of the physical and mechanical qualities of the

resulting pla s ticized ca s t pla s ticized chitosan lms,

the characteri s tics of the original chitosan lm were

evaluated in conjunction with those of the other

lms. The in s trumental techniques used to s tudy

changes in the chemical s tructure and properties

of modied chitosan have been considered. Every

pla s ticizer te s ted showed enhanced mechanical

performance, and regardless of the kind or quantity

utilized, they all demon s trated the typical pla s ticizer

action of increasing elongation and decreasing

lm s tiness. Data demon s trating the possibility

of using modied chitosan in food packaging as

su s tainably as possible have been presented.

5. Acknowledgement

The authors wish to thank the Department of

Chemi s try, College of Science, University of

Basrah for supporting this work.

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