ACTA UNIVERSITATIS AGRICULTURAE ET SILVICULTURAE MENDELIANAE BRUNENSIS
Volume 66
37
Number 2, 2018
https://doi.org/10.11118/actaun201866020349
SEM ANALYSIS AND DEGRADATION
BEHAVIOR OF CONVENTIONAL AND
BIO-BASED PLASTICS DURING COMPOSTING
Dana Adamcová¹, Maja Radziemska², Jan Zloch¹, Helena Dvořáčková³,
Jakub Elbl³, Jindřich Kynický³, Martin Brtnický³, Magdalena Daria Vaverková1
¹Department of Applied and Landscape Ecology, Faculty of AgriSciences, Mendel University in Brno, Zemědělská
1, 613 00 Brno, Czech Republic
²Warsaw University of Life Sciences – SGGW, Faculty of Civil and Environmental Engineering, Department of
Environmental Improvement, Nowoursynowska 159, Warsaw, Poland
³Department of Geology and Pedology, Faculty of Forestry and Wood Technology, Mendel University in Brno,
Zemědělská 1, 613 00 Brno, Czech Republic
Abstract
ADAMCOVÁ DANA, RADZIEMSKA MAJA, ZLOCH JAN, DVOŘÁČKOVÁ HELENA, ELBL JAKUB,
KYNICKÝ JINDŘICH, BRTNICKY MARTIN, VAVERKOVÁ MAGDALENA DARIA. 2018. SEM
Analysis and Degradation Behavior of Conventional and Bio-Based Plastics During Composting. Acta
Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, 66(2): 349 – 356.
Recently, various materials have begun to be marketed that claim to be biodegradable or compostable.
Terms such as “degradable”, “oxo-biodegradable”, “biological”, “compostable” and “green” are often
used to describe and promote different plastics. Commercial bioplastics and a petrochemical plastic
(claim to be degradable) were used for this study. The research was carried out in real conditions in
the Central Composting Plant in Brno, Czech Republic. SEM analysis of the samples was done in
order to analyze microstructure and morphology of specimens, validating dispersion results. It can be
concluded that samples certified as compostable have degrade in real composting conditions. Samples
(4 – 7) showed significant erosion on surface when subjected to the SEM analysis. Samples labeled (by
their producers) as 100 % degradable (Samples 1 – 3) did not show any visual signs of degradation.
Keywords: bioplastics, biodegradation, real composting environment, SEM analysis
INTRODUCTION
Problems associated with an ever-increasing
amount of waste from packaging and disposable
products made from conventional durable plastics
have led to the search for new biodegradable
packaging and disposable products (Sikorska et al.,
2015).
Biodegradable
polymers
represent
a promising way to reduce the amount of plastic waste
disposed in landfills, with composting the preferred
alternative for their disposal (Adamcová et al.,
2017). Many biodegradable polymers have been
developed in the last two decades with the desired
performance properties (Castro-Aguirre et al., 2017).
Thus, along with the development of these
novel materials, evaluation and understanding
of their biodegradation performance and their
environmental impacts have become essential.
The European Waste Framework Directive
recommends composting as a method of recycling
post-consumer biodegradable waste. At present,
a challenge is to develop composting as a disposal
technology and the redirection from landfills to
composting facilities. In the Europe packaging
and packaging waste management, including a test
scheme and a procedure to assess the compostability,
is regulated by the European Norm BSI. 2000, which
defines the criteria for material to be recognized
as “compostable” (Sikorska et al., 2015; BSI., 2000).
Biodegradation of plastics depends on both
the environment in which they are placed and
the chemical nature of the polymer. Biodegradation
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D. Adamcová, M. Radziemska, J. Zloch, H. Dvořáčková, J. Elbl, J. Kynický, M. Brtnicky, M. D. Vaverková
is an enzymatic reaction; hence it is very specific to
the chemical structures and bonds of the polymer
(Vaverková et al., 2014).
There are different mechanisms of polymer
biodegradation. The biodegradation of polymers
consists
of
three
important
steps:
(1)
Biodeterioration, which is the modification of
mechanical, chemical, and physical properties of
the polymer due to the growth of microorganisms
on or inside the surface of the polymers. (2)
Biofragmentation, which is the conversion of
polymers to oligomers and monomers by the action
of microorganisms and (3) Assimilation where
microorganisms are supplied by necessary carbon,
energy and nutrient sources from the fragmentation
of polymers and convert carbon of plastic to CO2,
water and biomass (Emadian et al., 2017).
Recently, various materials have begun to
be marketed that claim to be biodegradable
or compostable. Terms such as “degradable”,
“oxo-biodegradable”, “biological”, “compostable”
and “green” are often used to describe and
promote different plastics. These materials include
conventional plastics amended with additives meant
to enhance biodegradability as well as bio-based
plastics and natural fiber composites (Gómez and
Miche, 2013).
Our previous study was conducted to investigate
whether the plastics marked “biodegradable”,
100 % – degradable or certified as compostable are
really biodegradable in real composting conditions.
Original research was carried out in 2011 and 2012.
The major goal of this study was to verify information
obtained by repeated research and repeatedly
examine the texture of the original samples and
samples that underwent composting process.
The rate of biodegradation has been analyzed by
investigating the morphological properties using
scanning electron microscopy (SEM).
MATERIALS AND METHODS
Commercial bioplastics and a petrochemical
plastic (claim to be degradable) were used for this
study. The research of biodegradability was carried
out in real conditions in the Central Composting
Plant in Brno, Czech Republic. The company operates
a regionally important (South Moravia) facility
processing biological wastes. The composting plant
is used for the conversion of biologically degradable
waste (bio-waste) from the city of Brno and its
surroundings (Vaverková et al., 2014). The compost
(three-month-old mature compost, which was
provided by a full-scale aerobic composting) was
the following physicochemical properties: moisture
30 ÷ 65 (%), combustibles min. 20 (%), total nitrogen
min. 0.6 (% DM), pH 6.0 ÷ 8.5, undecomposable
ingredients max. 2.0 (%), C : N max. 30, cadmium
2.0 (mg/kg), lead 100 (mg/kg), mercury 1.0 (mg/kg),
arsenic 20 (mg/kg), chromium 100 (mg/kg),
molybdenum 20 (mg/kg), nickel 50 (mg/kg), copper
150 (mg/kg), zinc 600 (mg/kg).
The investigated materials were single-use
plastic bags available in various networks of
shops on the European market, advertised as
100 % – degradable (Sample 1 – 3) or certified as
compostable (Sample 4 – 7). The thickness of each
sample was 0.2 mm. The material composition of
the samples is presented in Tab. I.
The samples were made of high density
polyethylene (HDPE) with the Totally Degradable
Plastic Additives (TDPA) (Sample 2) and made of
polyethylene (PE) with an addition of pro-oxidants
(d2w) (Sample 1 and 3). The eighth, control sample
was cellulose paper (CP) (with dimensions 0.3 mm
thickness) (Sample 8). CP was to check the potential
of biological decomposition in the tested
environment (positive control). Samples (1 – 8) were
placed into frames. The frames were designed and
made by the authors themselves of wooden slats
as follows: width = 280 mm, length = 340 mm and
height = 50 mm. A 1 × 1 mm polyethylene mesh was
fixed onto the frames. The frames were designed
so that they would facilitate the placement and
identification of the samples in the compost pile.
The frames with the samples were properly marked
and photographed to document future visual
comparison (Vaverková et al., 2014). All 8 samples
were inserted into one clamp within the compost
pile (Fig. 1). The samples were installed at a height
of 1m from the upper side of the compost pile and
at 1.5 m from the lower side of the pile. In these
conditions, the experimental period was estimated
to be 12 weeks. The samples were checked visually
at regular intervals of about 14 days. After the end
of the experiment, the samples were lifted from
I: Material composition of the samples.
Sample
Type
Description
1
N/A
BIO-D Plast
2
HDPE + TDPA
100 % degradabel
3
N/A
100 % degradabel
4
Starch
Compostable 7P0147
5
Starch and Plycaprolactone
OK Kompost AIB VINCOTTE
6
N/A
Compostable 7P0202
7
Natural material
Compostable 7P0073
8
Cellulose (blank)
–
Sem Analysis and Degradation Behavior of Conventional and Bio-Based Plastics During Composting
the compost pile and all samples were subsequently
photographed and assessed (Vaverková et al., 2014).
In addition, all original samples as well as samples
obtained after the end of the experiment were
submitted for SEM.
RESULTS
Visual assessment of the samples
Upon the end of the experiment in composting
plant the samples were taken to laboratories of
the Department of Applied and Landscape Ecology
at Mendel University in Brno where they were
subjected to detailed evaluation. In all samples,
a visual comparison was made of their initial and
final states. Samples 1, 2 and 3 did not show any
significant visual changes or signs of decomposition,
the test material remained completely intact. No
breakthrough in disintegration was observed after
12 weeks of composting. The surface was smooth,
and there were no pinholes observed on the surface
after the test. However, Sample 3 exhibited some
changes in pigmentation.
The biodegradation of the certified compostable
plastic bags (Samples 4 – 7) proceeded very
well. In terms of visual assessment, Samples
4 and 5 exhibited the highest degree and rate
of decomposition (70 %). Samples 6 and 7 were
decomposed to about 80 % of their initial condition.
The CP (Sample 8) completely degrade implying
that the conditions required for biodegradation
to occur in sampling environment were present
(Vaverková et al., 2014).
351
The evaluation of the samples by means of
Electron Microscopy
SEM analysis technique allows examining
of changes in the morphology of materials at
the micro scale. In order to perceive monitoring
and the changes in the structure of the samples,
images from the SEM were used. All samples
were subsequently submitted for SEM. Surface
morphology by scanning electron microscopy was
determined on a FEG Quanta 200 (ESEM, USA)
in Analytical Centre of Warsaw University of Life
Sciences – SGGW.
The experiment involved images of both
the original samples and samples that underwent
composting process. Each sample was depicted at
50 ×, 100 × and 500 × magnification. The illustrations
are presented in Figs. 2 – 8. Via SEM images analysis,
is was possible to verify the considerable quality of
the samples.
The figures from SEM (Figs. 2 – 4) illustrate that
the structure of surface of the original samples
(defined as A) compared to the composted samples
(defined as B) show the smallest difference in case of
Sample 1 – 3. For the samples amended with additives
that were supposed to enhance biodegradability,
almost no biodegradation was observed after 12
weeks of composting. SEM images did not reveal
qualitative changes in the appearance of Sample
1 and 3. Only slight changes can be observed at
Sample 2 (Fig. 3 B). Sample 2 shows certain erosion
of surface.
SEM analysis exhibited the microbial activity of
degradation on the bioplastic Samples 4 – 7 (Fig. 5 – 8).
The surface structure of the material had lost its
smoothness, and cracks were evident. The samples
showed a significant change in the structure. SEM
images confirmed the biodegradation process
1: Location of the Central Composting Plant in Brno
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D. Adamcová, M. Radziemska, J. Zloch, H. Dvořáčková, J. Elbl, J. Kynický, M. Brtnicky, M. D. Vaverková
2: Sample 1 - Surface of the original sample (A) compared to the composted sample (B)
3: Sample 2 - Surface of the original sample (A) compared to the composted sample (B)
4: Sample 3 - Surface of the original sample (A) compared to the composted sample (B)
Sem Analysis and Degradation Behavior of Conventional and Bio-Based Plastics During Composting
5: Sample 4 - Surface of the original sample (A) compared to the composted sample
6: Sample 5 - Surface of the original sample (A) compared to the composted sample (B)
7: Sample 6 - Surface of the original sample (A) compared to the composted sample (B)
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D. Adamcová, M. Radziemska, J. Zloch, H. Dvořáčková, J. Elbl, J. Kynický, M. Brtnicky, M. D. Vaverková
8: Sample 7 - Surface of the original sample (A) compared to the composted sample (B)
that happened over the bioplastic film with
the presence of cracks and loss of filmy nature.
After the termination of the testing process in real
conditions, the bioplastic sample showed visual
modifications, and broke into pieces when touched
upon. Sample 6 and 7 significantly degraded
as apparent by visual detection. This fact was
additionally confirmed by the figures from the SEM
analysis (Sample 6 B and Sample 7 B see Fig. 7 and
8). The reduction on mechanical properties is one of
the main consequences of the degradation process
occurring during composting, this process also
favored the microorganism’s action. This effect could
be explained since the loss in mechanical properties
after 12 composting weeks produced a brittle
material consisting in broken pieces with a high
defects density, such as cracks and porous structure,
permitting the easy access of microorganisms to
the polymer bulk. The optical inspection of Samples
4 – 7 (Fig. 5 – 8) revealed these defects. SEM images
of bioplastics before and after composting showed
substantial changes in the surface of the material.
DISCUSSION
Composting seems to be the most promising
for waste management options for biodegradable
plastics because the composting process is designed
to degrade wastes. There are, however, obstacles
that make many communities reluctant to accept
plastic bags for composting. Various studies
have shown that new biodegradable polymers
do biodegrade under controlled composting
conditions (Gómez and Miche, 2013; Unmar and
Mohee, 2008; Leejarkpai et al., 2011; Vaverková et al.,
2012; Bahramian et al., 2016; Castellani et al., 2016).
However, the biodegradability of plastics is
a complex process and is influenced by the nature of
each plastic (Selke et al., 2015).
The results of Gómez and Miche (2013) study
indicate that conventional plastics containing
additives do not biodegrade any faster than
non-additive containing plastics. Manufacturers of
these additives claim that if at least 1 – 5 % (by weight)
of their additive is added to plastics products,
these will fully biodegrade when disposed of in
microbe-rich environments. These claims are
not supported by the findings of study by Gómez
and Miche (2013). Moreover, for conventional
plastics with additive no significant conversion was
observed over the entire period of study.
An experimental investigation was conducted
by Leejarkpai et al. (2011). It was observed
that the swelling at the starch granules occurs
throughout the surface of the PE / starch due to
water absorption by the granules. However, almost
all surface of the PE / starch remained relatively
unchanged suggesting that only a small degree
of swelling had occurred (Leejarkpai et al., 2011).
Additionally, in this study SEM examination,
confirmed the biodegradation of biodegradable
plastics material. The results also prove that both
PE and PE / starch are non-biodegradable plastics
whereas Polylactic acid is a biodegradable plastic.
In a different study, Selke et al. (2015) examined
the effect of biodegradation-promoting additives
on the biodegradation of PE and polyethylene
terephthalate (PET). Biodegradation was evaluated
in compost, anaerobic digestion, and soil burial
environments. None of the additives tested
significantly increased biodegradation in any of these
environments. Thus, no evidence was found that these
additives promote and/or enhance biodegradation of
PE or PET polymers. The finding provides evidence
that anaerobic and aerobic biodegradation are not
recommended as feasible disposal routes for plastics
containing any of the biodegradation-promoting
additives (Selke et al., 2015).
Sem Analysis and Degradation Behavior of Conventional and Bio-Based Plastics During Composting
355
CONCLUSION
The experimental samples were placed in the compost pile operated by the Central Composting
Plant in Brno, and were checked and visually assessed during the experiment which lasted 12
weeks. The goal of the experiment was to test the biodegradation of the above-described samples in
real composting conditions. After the expiration of the experimental period it was found out that
the samples with the additive (Samples 1 – 3) had not been decomposed, their color had not changed
and that no degradation neither physical changes had occurred. SEM analysis of the samples was
done in order to analyze microstructure and morphology of specimens, validating dispersion results.
SEM images showed the biodegradation indicators such as fractures, breaches, cavities, and holes on
the surface (Samples 4 – 7). It can be concluded that samples certified as compostable have degrade
in real composting conditions. Selected Samples (4 – 7) showed significant erosion on surface when
subjected to the SEM analysis. Samples labeled (by their producers) as 100 % degradable (Samples
1 – 3) did not show any visual signs of degradation.
Acknowledgements
The research was financially supported by the IGA FA MENDELU No. TP 5/ 2017.
We would like to express our great appreciation to Dr. Agnieszka Ostrowska (Analytical Centre of
Warsaw University of Life Sciences – SGGW) for her assistance and her willingness to provide her
time so generously in preparing SEM images.
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D. Adamcová, M. Radziemska, J. Zloch, H. Dvořáčková, J. Elbl, J. Kynický, M. Brtnicky, M. D. Vaverková
Contact information
Dana Adamcová: dana.adamcova@mendelu.cz
Maja Radziemska: maja_radziemska@sggw.pl
Jan Zloch: xzloch@mendelu.cz
Helena Dvořáčková: helena.dvorackova@mendelu.cz
Jakub Elbl: jakub.elbl@mendelu.cz
Jindřich Kynický: jindrich.kynicky@mendelu.cz
Martin Brtnický: martin.brtnicky@mendelu.cz
Magdalena Daria Vaverková: magda.vaverkova@uake.cz