A. de La Luz Ramos
A. de La Luz Ramos
A. de La Luz Ramos
Consorcio Nacional de Recursos de Informacion Científica y Tecnologica, on 13 Oct 2020 at 15:16:50, subject to the Cambridge Core terms of use, available at
1
Instituto Politécnico Nacional, Centro Mexicano para la Producción más Limpia
(CMPL), Av. Acueducto S/N, La Laguna Ticomán, C. P. 07340, Mexico City, Mexico.
2
Instituto Politécnico Nacional, ESIQIE, Departamento de Metalurgia, C.P 07300,
Ciudad de México, Mexico
ABSTRACT
https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2020.377
The environmental problems caused by the persistence and improper disposal of single
use plastics, have led the worldwide authorities to migrate into a sustainable production
of bio-based materials, whose components need to be studied for proving their nature and
to confirm their degradability. For this reason, the identification and monitoring
degradation of five single use straws were assessed through FT-IR, TGA/DTA and SEM
techniques which demonstrate that the straws tagged as biodegradable contain polymers
of fossil origin in their formulation. Degradation of them was found to be influenced by
polar groups, such as ester and glycosidic bonds of the biodegradable phase. The thermal
stability decreased and the morphological characteristics as cracks and holes were
detected after biodegradation.
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INTRODUCTION
The amount of plastic waste derived from long-lasting polymers has been
estimated to be c.a. 300 million Tons in the world provoking [1] serious environmental
problems caused by their improper disposal and persistence. For example, if they are
either burnt or dumped in landfills, can generate pollutants and to release toxic substances
in the ground and water reservoirs [2]. Similarly, it exists a great problem when plastics
are fragmented into microplastics in marine environments affecting the wildlife by
trapping, ingestion or habitat destruction and ecotoxicity [3]. This has led to the
worldwide authorities to implement several strategies such as either taxes and bans or
through of migration into a sustainable production to avoid those problems.
Mexico is reviewing its waste management laws and policies [4]. Now, it is
intending to implement the ban of single-use plastic for 2021, including bags, trays, coffee
capsules, balloons, cutlery, glasses and straws. As stated by O. H. Lara , it is necessary to
consider the plastics that are beneficial to a healthy society and those that are detrimental
as well as to consider the composition of polymers to be used to ensure the recyclability,
technical compatibility with closed loop systems [4]. In this context, it is of high
importance to have a state of the art of those products that are being commercialized in
the country.
Specifically, the fossil-based straws are considered as either single-use or
disposable and their improper disposal in conjunction with the slow degradation, which is
typically reported over 100 years, have made them a controversial product; they are
considered in the top 10 plastic items that are polluting the world´s seas and coasts. Then,
the industry has started to use and even to import several raw materials obtained
apparently from natural resources to produce ecofriendly products. The majority of straws
in the market are tagged as 100 % biodegradable and there are few studies confirming it.
For this reason, there is a need for carrying out the researcher to prove the nature of the
products, i.e. fossil, 100 % or partially biodegradable (bio-based), to confirm the
degradation time/percentage as well as to document under what conditions are
decomposed.
As known, two types of degradability can be considered in the plastic field.
The first is the ultimate degradability, which is associated to the degradation starting with
the action of the extracellular enzymes in the macromolecules obtaining oligomers
https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2020.377
(known as primary) and then these molecules are taken into the microbial cell and
decomposed into carbon dioxide and water [5]. The second is the weight-loss
degradability that does not consider the ultimate decomposition but so the sum of the
primary and the ultimate [6]. To determinate the extent of biodegradation, the structural,
thermal and morphological performance related to the physical and chemical changes in
the polymer backbone is required [7].
The aim of this work is to determinate if the nature of selected-commercial
straws is of renewable resources, as they are labeled, and to analyze the degradability to
known their features before being composted. Here, the study of five common and tagged-
biodegradable straws used in the market are taken into account to evaluate their nature,
their identification and the biodegradability features through aerobic conditions by the
weight loss method. Fourier Transform Infrared (FT-IR) spectroscopy,
thermogravimetric/differential thermal analysis (TGA/DTA) and visualization under
Scanning Electron Microscopy (SEM) are discussed in structural, thermal and
morphological terms related to the type of plastic straws.
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EXPERIMENTAL PROCEDURE
The nature of polymers of each straw was related through the association of its
functional groups detected in FT-IR spectra. The assignments are recorded in Table I and
the FT-IR spectra are shown in Figure 1a-e. The following assignments were identified in
the straws spectra: hydroxyl stretching groups between 3600 and 3100 cm -1, OH bending
(in plane) at 1335 cm-1, CH asymmetric stretching at 2894 cm-1, CO stretching at 1640
cm-1, CH2 symmetric bending at 1430 cm-1, CH2 wagging at 1316 cm-1, COC asymmetric
stretching at 1160 cm-1, CO antisymmetric stretching at 1104 cm-1 , β-(1,4) glycosidic at
897 cm-1 and CH2 rocking at 712 cm-1 (1st straw, Figure 1a) [8]. CH3 symmetric stretching
at 2919 cm-1, CH asymmetric stretching at 2996 cm-1, C=O symmetric stretching at 1750
cm-1, CO stretching at 1180 cm-1, CH3 symmetric bending at 1383 cm-1, COO stretching at
1267 cm-1, COC symmetric stretching at 1207 cm-1, COC stretching at 871 cm-1 and CH3
rocking as well as stretching CC at 956 cm-1 (2nd straw, Figure 1b) [9]. OH stretching at
3335 cm-1, CH stretching at 2912 cm-1, C=O stretching at 1754 cm-1, CH symmetric
bending at 1383 cm-1,CO stretching at 1079 cm-1 and α-1-4 glycosidic bond at 930 cm-1
(3rd straw, Figure 1c) . OH stretching at 3325 cm-1, CH stretching at 2916 cm-1, C=O
stretching at 1645 cm-1, CH2 bending at 1471 cm-1, CO bond stretching at 1017 cm-1 and
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1-4 glycosidic at 930 cm-1 (4th straw, Figure 1d) [10]. CH3 asymmetric stretching at 2949
cm-1, CH2 symmetric bending at 1455 cm-1, CH3 symmetric bending at 1375 cm-1 and CH3
rocking at 1167 cm-1 (5th straw, Figure 1e) [11]. From these observations, straws were
recognized as 1) cellulose (biodegradable), 2) polylactic acid (PLA) (biodegradable), 3)
corn starch/polypropylene (PP) (partially biodegradable), starch/polyester (partially
biodegradable) and PP (fossil).
a)100 b)100 c)
100
Transmittance (%)
Transmittance (%)
Transmittance(%)
90
CH2
90
OH 90
OH
80 80 80
OH C=O
70 70 70
60
C=O 60 CH
60
50 50
50
Beginning
COC
40 Beginning 40 Beginning C=O
40 Week 12 COC Week 12
4000 3500 3000 2500 2000 1500 1000
30 Week 12 30 COC
4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000
Wavenumber (cm-1) Wavenumber (cm-1) Wavenumber (cm-1)
d)100 e)
100
Transmittance (%)
Transmittance (%)
90
C=O 90
80
70 OH CH2 80
60 70 CH3
50 CH 60
CH2
Beginning Beginning
40
CO 50 CH3 Week 12
30
Week 12
4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000
Wavenumber (cm-1) Wavenumber (cm-1)
Figure 1. FT-IR spectra of a-b) biodegradable, c-d) partially biodegradable and e) fossil straws before
and after being subjected to aerobic degradation by 12 weeks.
80 1.6
80 Beginning
Week 12 1.6
Delta T
1.2
60
60
0.8 1.2
40 40
0.4 0.8
20 20
Beginning 0.0 0.4
Week 12 0
0
0 100 200 300 400 500 600 0 100 200 300 400 500 600
Temperature (°C) Temperature (°C)
Starch/Polypropylene
c) 2.4 d)100 Starch/Polyester
100 2.4
Beginning 2.0
Weight loss (%)
80 2.0
Weight loss (%)
80
Week 12
1.6
1.6
Delta T
60 60
Delta T
1.2 1.2
40 40 Beginning
0.8 Week 12 0.8
20 20
0.4 0.4
0
https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2020.377
0
0.0 0.0
0 100 200 300 400 500 600 0 100 200 300 400 500 600
Temperature (°C) Temperature (°C)
e) Polypropylene
2.8
100
2.4
Beginning
Weight loss (%)
80 2.0
Week 12
60 1.6
Delta T
1.2
40
0.8
20
0.4
0 0.0
Figure 2. TGA/DTA curves spectra of straw before and after being subjected to aerobic degradation
by 12 weeks.
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Similarly, the TGA/DTA curves of PLA straw in Figure 2b show two main
decomposition stages in the 260-350 °C (DTA peak at 335 °C) and 355-470 °C (DTA
peak at 390 °C) ranges with a weight loss of 86.7 % and 8.05 %, respectively; these
signals have been previously reported and associated to the lactide and methyl ketene
compounds releasing before obtaining the CO2 [13]. On the other hand, partially
biodegradable based on corn starch/PP (Figure 2c) showed a decomposition with two
main stages, one from 237°C to 400 °C losing 76.96 % (DTA peak at 365 °C) and the
second with a weight loss of 19.52 % from 400 °C to 475 °C (DTA peak at 450 °C); two
DTA peaks are also evident at 150 °C and 210 °C which could be of some plasticizers.
The starch/polyester (Figure 2d) is also decomposed through two stages in the 150 °C-300
°C (18.33 %, DTA peak at 230 °C), 300-326 °C (10.47 %, DTA peak at 310 °C), 330-500
°C (37.49 %, DTA peak at 470 °C) ranges corresponding to simple polysaccharides,
larger size protein fractions and complex polysaccharides, respectively. Finally, the fossil
straw in Figure 2e displays the typical degradation behavior of PP starting at 300 °C and
ending at 460 °C with a weight loss of 99.92 % (DTA peak at 425 °C).
Once the polymer type and the thermal transitions were identified, the straws
were subjected to degradation under aerobic conditions after twelve weeks, then, the
functional groups and the thermal decomposition were once again analyzed by obtaining
the FT-IR spectra and TGA/DTA thermograms. Results are included in Figure 1 and 2.
The main changes in cellulose straw (biodegradable) were the decrease of intensity of
OH, CO, COC, CC, CH2 and β-(1,4) glycosidic link bands and the appearance of a new
band corresponding to C=O (ester stretching 1730 cm-1). The PLA straw (biodegradable)
had changes only in the intensity of the bands, the C=O and COC, and in the presence of a
new arising OH band. The starch/PP straw spectrum maintained almost intact its CH2
bands of the fossil polymer with no appearance of the OH groups. In this case, the main
damage due to degradation were done in the COC and C=O bands of the biodegradable
phase since there was a reduction in intensity of them. In the starch/polyester straw
spectrum the following features in intensity were observed: 1) decrease of OH bands, 2)
increase of C=O and 3) no changes in the CH which are related to the no degradation of
the fossil part. From these results is evident that the degradation straws are mainly in
either ester or glycosidic bond. If the straw is partially biodegradable, the fossil polymer
did not change significantly after twelve weeks. This is confirmed in the fully fossil PP
straw shown in Figure 1e, in which, there is almost no evidence of changes in its
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250
Cellulose
Starch/Polyester
200 PP
PLA
Weight loss (%) Starch/PP
150
100
50
0
0 4 8 12
Week
Figure 3. Weight loss (%) evolution at 4th, 8th and 12th weeks of anaerobic degradation
Figure 4. SEM micrographs of a-b) PLA, c-d) starch/PP and e-f) starch/ polyester before and after
being subjected to biodegradation
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CONCLUSIONS
ACKNOWLEDGEMENTS
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