




































Highlights in BioScience
ISSN:2682-4043
DOI:10.36462/H.BioSci.20246

Research Article

Open Access

1 Department of chemistry, Faculty of Education,

University of Khartoum, Sudan.

* To whom correspondence should be
addressed: nawal.mahgoub@uofk.edu

Editor: Alsamman M. Alsamman, International
Center for Agricultural Research in the Dry Areas
(ICARDA), Cairo, Egypt.

Reviewer(s):
Khaled H. Radwan, National Biotechnology
Network of Expertise, ASRT, Cairo, Egypt..

Tamer Ahmed Elakkad, Faculty of Agriculture at
Moshtohor, Benha University, Benha, Egypt.

Received: May 3, 2024

Accepted: November 20, 2024

Published: December 27, 2024

Citation: Suleman NM, Eltyeb EM. The
effectiveness of bentonite and esterified plant
fibers on the biodegradability of 24 polypropylene
biocomposites . 2024 Dec. 27;7:bs20246

Copyright: © 2024 Nawal et al.. This is an
open access article distributed under the terms
of the Creative Commons Attribution License,
which permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper and supplementary materials.
Funding: The authors have no support or funding to
report.
Competing interests: The authors declare that they
have no competing interests.

The effectiveness of bentonite and esterified plant fibers on the
biodegradability of 24 polypropylene biocomposites

Nawal M. Suleman 1
>< �, Eiman M. Eltyeb1

>< �

Abstract

This study aims to evaluate the biodegradability of 24 bio-composites synthesized
from polypropylene and esterified plant fibers, with bentonite serving as a filler. The
biodegradation process was conducted using Aspergillus niger. The study utilized
standard laboratory equipment and the melt flow indexer. After three months of
biodegradation, all biocomposites under investigation showed a significant loss in
their weights. This is a logical observation because Aspergillus niger consumed parts of
biocomposites as food during the biodegradation. The study also evaluated properties
including density, melting point, melt flow rate (MFR), melt viscosity, molecular
weight, and water absorption capacity. Densities, melting range temperature, and
molecular weights were decreased (decreasing in molecular weights). The values of
biodegraded composites after the biodegradation process for three months are in good
agreement with the fact that the molecular chain breaks and the chain length shortens
after any degradation process. Water absorption capacities were significantly increased
(due to the holes resulting from the Aspergillus niger attack) for all biocomposites
under study; this is considered very good evidence for biodegradation.

Keywords: Bio-composite, biodegradation, Aspergillus niger, bentonite, polypropylene

Introduction
Biodegradable materials decompose within a year in their usual disposal environments, convert-

ing into non-toxic substances through the activities of living organisms [1]. The biodegradability of

polymers is influenced by two main factors. The environmental conditions are exposed to (biotic or

abiotic) and the polymer’s characteristics (such as mobility, crystallinity, density, molecular weight,

functional groups, and additives). Abiotic factors (e.g., pH, temperature, light, and moisture) can

change the hydrolysis reaction rates. Biotic factors, such as extracellular enzymes produced by distinct

microorganisms, can biodegrade certain polymers. For instance, Aspergillus niger and Aspergillus

flavus fungi produce enzymes that more easily break down aliphatic polyesters composed of 6 - 12

carbon di-acid monomers than those produced from other monomers [2]. Most conventional plastics

(polypropylene) are non-biodegradable, and their accumulation in the environment has endangered

the planet. To resolve all these challenges, several strategies have been utilized. Firstly, it involves the

degradation of some petrochemical-based plastics by biological processes. Secondly, the production

of plastics with a high degree of degradability. The aliphatic polyesters are regular plastic polymers

that show high potential for use as biodegradable plastics [3]. Polypropylene is a challenging substrate

for biodegradation by microorganisms due to its high molar mass and inability to pass through mi-

croorganisms cell membranes [4]. Biodegradation of polypropylene/starch or polypropylene/cellulose

composites has been observed, where organisms easily degrade starch or cellulose, producing polymer

waste. These carbohydrates or fillers increase the adhesion of organisms to the surface of the polymer

[5]. Protocols such as surface changes and changes in the mechanical and physical properties of the

polymer were utilized to characterize the biodegradability of composites [6]. This study aims to test

the biodegradability of 24 composites previously synthesized from polypropylene and esterified fibers

extracted from Khimp (Leptadenia pyrotechnica) and date palm tree (Phoenix dactylifera L.) and

esterified using citric and adipic acid (AAD).

Highlights in BioScience Page 1 of 4 December 2024|Volume 7

https://doi.org/10.36462/H.BioSci.20246
https://creativecommons.org/licenses/by/4.0/
mailto:nawal.mahgoub@uofk.edu
https://orcid.org/0000-0002-6909-7512
mailto:eimanmubarak@uofk.edu
https://orcid.org/0000-0003-0606-9634
http://bioscience.highlightsin.org/


Nawal et al., 2024 The effectiveness of bentonite and esterified plant fibers

Materials and Methods
The analytical chemicals used were polypropylene (9003-07-

0, Sigma-Aldrich), bentonite clay (from India Mart), adipic acid,
citric acid, sulfuric acid, acetic anhydride, sodium hydroxide,
peptone, glucose, ethanol, agar, and hydrochloric acid (from
BDH, India). Toluene (108-88-3, Sigma-Aldrich), xylene (1330-
20-7, Sigma-Aldrich), and deionized water (the bio-composites
of polypropylene were prepared previously) [7]. A computerized,
fully automated melt flow rate (MFR) tester was sourced from
India Mart.

Biodegradation method
Biodegradation takes place according to the following equa-

tions:

(A): Cplastic + O2 → CO2 + H2O +Cresidual + Biomass

(B): Cplastic → CH4 +CO2 + H2O +Cresidual + Biomass

A: Aerobic biodegradation, B: Anaerobic biodegradation.
The ingredients of Sabouraud dextrose agar (SDA) (10g pep-

tone + 40g glucose + 15g Agar) were combined in 900 ml of
deionized water, then the pH was adjusted to 5.6 with HCl, and
the final volume was adjusted to 1000 ml by adding deionized wa-
ter. The mixture was boiled to completely dissolve the medium,
sterilized at 121oC for 20 min by autoclave, then warmed to 50oC
and distributed into petri dishes. The ingredients of Sabouraud
dextrose broth (20g glucose and 10g peptone) were suspended
in 1000 ml of deionized water, heated to dissolve the medium
completely, and the mixture was sterilized by autoclave at 121oC
for 15 min. The sterilization of polymer samples was conducted
under UV light and transferred into the middle of petri dishes.
The culture broth was replaced with 50 ml of sterile nutrient
broth every 10 days to enhance healthy microbial growth. After
three months, biodegraded composites were washed, dried, and
weighed to determine the weight loss caused by microbial action
during biodegradation. The composites were then subjected to
characterization [8].

Characterization of the Biodegraded Composites
Biodegraded composites were characterized by the same in-

struments and methods described for characterization of the syn-
thetic composites and properties [7]. The measured properties
that were characterized include density, melting points, melt
flow rate (MFR), melt viscosity, molecular weight, and water
immersion test.

Results and Discussions
Biodegradation of Composites

Providing sustainable alternatives to conventional plastics
is indispensable. Therefore, researchers and manufacturers are
attempting to integrate sustainable and biodegradable polymers
into industrial processes [9]. Regarding the environmental con-
cerns, this study was conducted. Biodegradation was carried

Figure 1. Petri dishes showing microbial colony diversity during biodegradation.

Figure 2. Biodegraded composites showing structural changes.

out according to the literature review. (Aspergillus niger) were
cultivated in order to provide a good culture for biodegradation
(Figure 1) shows some petri dishes prepared for this purpose.
During biodegradation, microorganisms start utilizing the poly-
mer surface as a food source and grow on it. Various polymer
characteristics influence biodegradation, such as their tactility,
crystallinity, molecular weight, functional group types, the type
of microorganism, and the pre-treatment method [10]. This
clearly occurred for all samples under investigation. The es-
terified fibers used as reinforcement agents in the synthesis of
the target composites introduced new functional groups to the
polypropylene resin and hence enhanced the biodegradability in
an acceptable way because the availability of functional groups
like ester increases hydrophilicity. This ester group not only
increases the hydrophilicity of the synthetic composites, but it
is also an easily breakable bond compared to the carbon-carbon
bonds in polypropylene. Biodegradation occurred differentially
depending on the amount and type of esterified fiber.

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Nawal et al., 2024 The effectiveness of bentonite and esterified plant fibers

Table 1. Characteristics of 24 biodegraded composites under study

No. Composite entity code Density (g/cm3) Melting range (řC) Melt flow rate Melt viscosity M-W Water absorption capacity (%)

1 1-a 0.84 165-166 5.02 0.86 1.8 x 105 10.3

2 1-b 1.00 170-173 8.3 0.82 1 x 105 15.3

3 1-c 0.92 169-173 4.68 0.87 0.8 x 105 32

4 1-d 0.89 170-175 4.91 0.87 0.8 x 105 24

5 1-e 0.93 168-169 1.54 0.90 0.3 x 105 28.3

6 1-f 0.82 175-177 6.9 0.81 0.9 x 105 15.6

7 1-g 0.82 169-172 3.55 0.89 0.6 x 105 36.5

8 1-h 0.87 160-163 6.2 0.85 0.9 x 105 25.4

9 1-i 0.95 164-170 2.69 0.90 0.5 x 105 15.9

10 1-j 1.00 168-171 10.6 0.80 1.1 x 105 11

11 1-k 0.87 165-167 2.11 0.93 0.4 x 105 24.2

12 1-l 0.83 175-178 6.06 0.84 0.9 x 105 44

13 2-d 0.84 160-163 10.5 0.80 1.1 x 105 8.75

14 2-e 0.80 165-168 2.71 0.91 0.5 x 105 10

15 2-f 1.00 161-165 4.72 0.87 0.8 x 105 18.9

16 2-j 0.82 167-171 5.37 0.85 0.8 x 105 18.8

17 2-k 0.95 170-174 6.17 0.82 0.9 x 105 15

18 2-l 0.92 170-172 8.5 0.82 1 x 105 20

19 3-a 0.94 174-178 8.2 0.82 1 x 105 33

20 3-b 0.92 172-177 5.41 0.86 0.8 x 105 12.2

21 3-c 0.86 169-171 4.9 0.86 0.8 x 105 26

22 3-g 1.00 169-172 6.4 0.84 0.9 x 105 13.3

23 3-h 0.80 167-170 3.34 0.89 0.6 x 105 12.3

24 3-i 0.90 170-172 1.29 0.97 0.2 x 105 25

Additionally, using bentonite as a filler provides a good en-
vironment for microorganisms; all biodegraded samples showed
an amazing change in their surfaces (Figure 2). In addition to
the surface change, there are many physical properties that indi-
cate biodegradation occurrence, such as density, water absorption
capacity, molecular weight, melt flow rate, and melt viscosity.
These properties will be discussed in detail after the character-
ization step. The loss of weight in 24 biodegraded composites
is presented in (Tables S1 to S4), quantifying the level of com-
posite biodegradation after three months of Aspergillus niger
incubation. The weights of composites before and after three
months were measured. Weights lost percentages were calculated
according to the following equation:

Weight lost (%) =
(wo − w)

wo
× 100

wo =weight before biodegradation and w =weight after biodegra-
dation.

A crucial aspect of our experiment is the impact of clay
nanoparticles on biodegradation; the presence of clay increases
microorganisms' attack, thus enhancing the biodegradation pro-
cess due to microorganisms' preference for clay media for growth,

as reported in the literature. Weights lost were clearly observed
for all composites and increased with increasing ester content,
either in the presence or absence of clay, except for samples 1-i,
1-k, 2-f, 2-k, and 3-b. This may have occurred due to the disper-
sion of either esterified fibers or clay among polypropylene resin
during the injection molding process. Another important obser-
vation is that composites made from sample one, esterified by
citric acid, showed significant increases in weight loss compared
to their analogs made from the same sample esterified by adipic
acid.

Characterization of Biodegraded Composites
The densities of the biodegraded composites were determined

based on the guidelines provided in [11]. Densities of composites
decreased clearly after the biodegradation process because mi-
croorganisms consume a part of the composite for their growth;
this is very good evidence of biodegradation occurrence (Table
1), and the melting range temperature of the 24 biodegraded com-
posites was measured experimentally as described in [11]. The
resulting melts of all composites under study were thick liquids.
Biodegraded composites melted at lower melting ranges than
those of synthetic composites.

The melt flow rate is a characterization method used to eval-

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Nawal et al., 2024 The effectiveness of bentonite and esterified plant fibers

Figure 3. water absorption capacities for the biodegraded composites samples

uate the degradation process of biodegraded composites by cal-
culating the reduction in molecular weight for each composite.
(Table 1) represents the values of the melt flow rate for the 24
composites under investigation. For determining melt viscosities,
the same equation described for synthesized composites was used
as follows:

[η] = 0.996 − 0.189 log(MFR)

[η]: Intrinsic Viscosity, MFR: Molecular Flow Ratio or Melt
Flow Rate. The average molecular weight of each biodegraded
composite was determined using the same equation applied for
the average molecular weight of synthesized composites.

log[MFR]composite = [0.454 × 10−6]Mw − 0.1273

Values of the average molecular weight for the biodegraded
composites are shown in Table 5. According to the above table,
molecular weights of biodegraded composites were decreased
significantly. The water immersion test demonstrates that all
biodegraded composites absorbed some amount of water over
time; however, they were insoluble in water. Water absorption
capacity (WAC) was calculated according to the equation clarified
by [12].

WAC (%) =
(

(m − mo)
mo

)
× 100

WAC (%): Water absorption capacity, mo: weight of dry sample,
and m: weight of sample after 24-hour immersion in distilled
water. There is a strong correlation between molecular weight
and water absorption capacity of all biodegraded composites;
biodegraded composites with lower molecular weight have more
water absorption capacities than those with comparatively high
molecular weight. This is considered a reasonable correlation
because when microorganisms attack the composite surface in
the biodegradation process, many holes occur as a result of this
action, allowing water to penetrate. The decrease in molecular
weights and the increase in water absorption capacities provide
strong evidence for the occurrence of biodegradation (Figure 3).

Supplementary
Table S1: Weights lost for composites of Khimp fiber ester-

ified by adipic acid. Table S2: Weights lost for composites of
Khimp fiber esterified by citric acid. Table S3: Weights lost for
composites of date palm leave fiber esterified by citric acid. Table
S4: Weights lost for composites of date palm fiber esterified by
adipic acid.

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	Abstract
	Introduction
	Materials and Methods
	Biodegradation method
	Characterization of the Biodegraded Composites

	Results and Discussions
	Biodegradation of Composites
	Characterization of Biodegraded Composites

	Supplementary

