Yekaterinburg, Ekaterinburg, Russian Federation
Yekaterinburg, Ekaterinburg, Russian Federation
Yekaterinburg, Ekaterinburg, Russian Federation
Yekaterinburg, Ekaterinburg, Russian Federation
Yekaterinburg, Ekaterinburg, Russian Federation
Introduction. Agriculture produces a lot of plant and food waste that is highly biodegradable. In order to recycle this waste and use it in the production of new materials, we need to find effective ways to increase their resistance to biodegradation. We aimed to study the biostability of binder-free wood and plant plastics, as well as to find an optimal method of their antiseptic protection. Study objects and methods. Our objects of study were binder-free plastics based on sawdust, wheat and millet husks. To determine their biostability, we exposed them in active soil for 21 days and analyzed their physical and mechanical properties. Also, we examined the effects of several methods of antiseptic treatment on the samples’ strength, water resistance, and biodegradation. Results and discussion. All the wood- and plant-based samples showed low biostability. Exposure in active soil caused significant morphological and structural changes, as well as impaired the samples’ physical and mechanical properties, especially those of the plant-based plastics. Their resistance to biodegradation was significantly determined by the type of filler or antiseptic, as well as by the method of antiseptic administration. Whether added to the press mixture or applied to the surface, the antiseptics changed the samples’ physical and mechanical properties. Among the antiseptics used, copper sulfate showed the best effect when introduced directly into the sawdust press mixture. It ensured the lowest decrease in flexural strength, but increased hardness, water absorption, and swelling. The wheat- and millet-based plastics protected with copper sulfate showed an increase in strength indicators, but lower water resistance. Conclusion. The antiseptic protection of binder-free wood and plant plastics affects a number of their physical and mechanical properties and therefore should take into account the expected conditions for their performance.
Binder-free plant plastics, binder-free wood plastics, bioplastics, wheat husks, millet husks, biostability, biodegradation, antiseptic protection
INTRODUCTION
In the spotlight of current research and development
are new formulations and technologies for producing
plastics based on plant fibers and fillers, polymer
composites combining products of traditional petrochemistry
and biotechnology, biodegradable plastics,
and biopolymers [1]. We can see new trends in the
development of these technologies. Many of them
become commercialized and acquire a wide applied
significance in addition to their scientific value [2].
Recent years have witnessed a growing interest in
biocomposites and bioplastics filled and reinforced with
natural fibers and plant components, as well as in plant
bioplastics that do not contain any products of largescale
petrochemistry [3–5]. Over the last few years, the
global market of biodiversity-based plastics has had an
average annual growth of 40% [3]. Largely stimulated
by consumer demand, the development of bioplastics
aims to improve the performance, availability, and
environmental sustainability of materials and products
[6]. The problem of microplastic pollution has also
attracted a lot of attention recently.
The requirements for biodegradable polymers are
changing: the decomposition of a polymer matrix
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Foods and Raw Materials, 2022, vol. 10, no. 1
E-ISSN 2310-9599
ISSN 2308-4057
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Buryndin V.G. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 148–154
into macro- and microscopic particles is no longer
an indicator of satisfactory destruction [7]. Although
actively developing abroad for several decades,
bioplastic technologies are a relatively new field of
research in Russia. Its President, Vladimir Putin,
declared 2017 the year of ecology, which stimulated
a search for low-waste and less resource-intensive
production methods, as well as for recycling and waste
disposal technologies to make industrial enterprises
more environmentally friendly [8]. In line with this
concept is the processing of wood and plant waste such
as sawdust and husks of wheat, oats, buckwheat, and
other crops into environmentally friendly and practical
materials. Quite promising is the production of wood
and plant plastics without binders [9].
Russia yearly produces significant amounts of waste
suitable for recycling and processing, such as husks,
oilcakes, fibers, etc. However, this waste is not widely
used to produce new materials. The reasons are a lack
of effective processing technologies and equipment,
financial and economic aspects, and a low market
interest [10].
To produce binder-free composite bioplastics based
on polymers and plant fillers, wood and plant bioplastics,
we need to prove their high performance properties. For
example, materials with a high rate of biodegradation
can be used for mulching or to make agrotechnical
films, as well as disposable containers for seedlings and
soil [11]. However, structural and finishing products,
or reusable packaging, need to be highly resistant to
various environmental factors.
For this, composites are often used whose matrix
contains recycled polyethylene or polypropylene with the
addition of plant components (fibers, husks, and flour).
The properties of such composites are well studied [12].
For example, the resistance of wood and plant plastics
is known to be determined by the biostability of the
press material (its main components) and the absence
of molecules that are a substrate or nutrient for soil,
saprophytic micro- and macroorganisms [13, 14].
Polymer molecules can be destroyed physicochemically,
through hydrolysis, under the action of acidic
or alkaline media, or under the action of enzymes
from fungal and bacterial cultures. Both ways of
biodegradation are possible with binder-free plant and
wood plastics [10]. They are mainly damaged by fungi
and, to a lesser extent, by bacteria that cause rot and
destroy lignin [13].
The shelf-life of household products made of binderfree
wood bioplastics is estimated at 7.5 years if used
at room temperature and moderate humidity [15].
Antiseptic protection is needed to maintain and improve
their performance characteristics. However, materials
treated with antiseptic agents change their physical,
mechanical, and operational properties [16, 17]. Thus,
to fully use agricultural plant waste in recycling and
production of new materials, we need to find the
most effective methods to increase their resistance to
biodegradation.
In this regard, it seems relevant to study the
biostability of binder-free wood and plant plastics based
on sawdust, wheat and millet husks, as well as to find an
optimal way of their antiseptic protection. Our aim was
to study the biodegradation of wood (based on sawdust)
and plant (based on millet or wheat husks) plastics
produced without binders and treated with antiseptics.
For this, we analyzed the biostability of the samples
of binder-free wood plastics (BF-WP) and binder-free
plant plastics (BF-PP), assessed the effect of antiseptics
on their physical and mechanical characteristics, and
analyzed the biostability of the samples antiseptically
protected by different methods.
STUDY OBJECTS AND METHODS
Our study objects were the antiseptically treated
samples of binder-free wood plastic (BF-WP) based on
sawdust and binder-free plant plastic (BF-PP) based on
wheat and millet husks. The samples were 2–4-mmthick
discs, 90 mm in diameter, made by pressing from
raw materials containing the plant component (sawdust,
wheat or millet husks). The weight of the press material
was 10 g per disk. The pressing time was 10 min,
pressure 124 MPa, cooling time under pressure 10 min.
Some of the samples were treated with antiseptic
compounds by adding them to the press material or by
applying them to the finished sample after conditioning.
We used a water repellent (1 g/disc), 12% CuSO4
(0.6 kg/100 m2), and a Forwood antiseptic (Raduga
Coating Works, Novosibirsk) (2 g/disc). The amounts of
antiseptics were based on the previous studies.
Before assessing biostability, we analyzed the
physical and mechanical properties of the samples. In
particular, we determined the density, flexural strength,
hardness, elasticity number, compression modulus,
flexural modulus, breaking stress, yield stress, water
absorption, and swelling in thickness after 24 h. Then,
the samples were kept in active soil for 21 days to study
biostability.
The soil was prepared in accordance with State
Standard 9.060-75. At the beginning of the tests, the
soil extract had a pH of 7.0 and a biological activity
coefficient of 0.8. The soil’s microbiocenosis contained
native field strains of microorganisms. After the soil
exposure, the samples were analyzed for macro- and
microvisual signs of biodegradation (splitting, swelling,
loosening, cavities, morphological changes in the plant
particles, changes in color, colonies of microorganisms,
hyphae, fungal fruit bodies inside or on the surface of
the sample, sliming of the surface). Then, we examined
the physicomechanical parameters of those samples
which were not damaged by the exposure in active soil.
RESULTS AND DISCUSSION
First, we analyzed the key physical and mechanical
properties of the control samples, namely binder-free
wood plastic based on sawdust (BF-WP) and binderfree
plant plastics based on wheat husks (BF-PP-wheat)
and millet husks (BF-PP-millet). We found that the
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Buryndin V.G. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 148–154
exposure in active soil caused significant visual changes
in both wood and plant samples. On average, 60% of
BF-PP-millet, 58% of BF-PP-wheat, and 47% of BF-WP
samples showed pronounced longitudinal and transverse
splitting, edge swelling, and loosening in thickness.
They also had micro- and macrocavities, especially
along the edges and in the splitting areas. The defects
varied from 1.5 to 5.5 mm.
All the samples featured microscopic signs of
morphological changes in the plant particles: edge
fibrillation, fragmentation and destruction of individual
husk and sawdust particles, focal darkening, and
microcavities of different size between the particles.
Surface sliming and signs of mold growth were also
found in all of the samples. In particular, multiple
large colonies of mold fungi in different stages of
maturity were present in 74% of BF-PP-millet, 85%
of BF-PP-wheat, and 62% of BF-WP samples (Fig. 1).
On the whole, the visual signs of biological
degradation were more pronounced in the plant-based
samples. The sawdust-based samples had mainly edge
and surface changes that hardly affected the middle.
The exposure in active soil had a negative effect
on the physical and mechanical properties of the
control samples, which were not treated with antiseptic
compounds. The sawdust-based samples showed a
decrease in hardness by 66%, elasticity number by 43%,
compression elasticity modulus by 76%, breaking stress
by 64%, and yield stress by 64% (Fig. 2).
The plant plastics based on wheat and millet husks
had similar changes, namely a decrease in hardness
by 62 and 70%, elasticity number by 46 and 47%,
compression elasticity modulus by 73 and 80%, breaking
stress by 60 and 68%, and yield stress by 60 and 68%,
respectively.
The highest average of flexural strength was in the
sawdust BF-WP samples (4 MPa) and the lowest was
in the wheat BF-PP samples (1 MPa). Water absorption
and swelling had the lowest values in the millet BF-PP
samples (85%) and the highest values in the BF-WP and
wheat BF-PP samples (94 and 96%, respectively).
Biostability tests showed a high biodegradability
potential of all the samples. Biostability can be
increased by changing the process parameters (pressing
temperature, pressure, and time) [18]. However,
antiseptic treatment is the main way to reduce
biodegradation. An antiseptic component can be either
added to the raw mixture or applied to the finished
product. Thus, antiseptic treatment is a prerequisite
for using binder-free wood and plant plastics in highly
bioactive conditions, i.e., in an aggressive microbial
destructive environment.
At the next stage, we treated the experimental
plastics with antiseptics by adding them to the press
material or applying to the surface to protect the
Figure 1 Pigmented colonies of microorganisms
in binder-free wheat-based plant plastic after 21 days
of exposure in active soil
Figure 2 Changes in physical and mechanical properties of binder-free wood and plant plastics before and after biodegradation
in active soil
39
12
37
9
28
9
77
43
74
38
74
39
45
10
42
6
31
6
26
9
25
7
20
10 7
4
10
3 8 3
0
20
40
60
80
100
BF-WP before
biodegradation
BF-WP after
biodegradation
BF-PP-wheat
before
BF-PP-wheat after
biodegradation
BF-PP-millet
before
biodegradation
BF-PP-millet after
biodegradation
biodegradation
Hardness, MPa
Compression elasticity modulus, MPa X 10–1
Elasticity number, %
Breaking stress, MPa
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Buryndin V.G. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 148–154
material from biodegradation, improve its biostability,
and reduce its biodegradation potential. The samples’
physical and mechanical properties were analyzed
before and after biostability tests. We found that these
properties were affected by the type and method of
antiseptic administration.
The BF-WP samples had the worst indicators
when a water repellent was introduced directly into
the press material. In particular, there was an average
decrease in flexural strength by 49%, hardness by 14%,
water absorption by 30% (after 24 h), and swelling
in thickness by 1.5% (after 24 h).
This might be explained by the disturbed formation
of supramolecular bonds between the mixture particles
during pressing. Lignin was present in the liquid phase
of the mixture and the water repellent distributed it
on the surface of the particles, providing them with
hydrophobic properties. Thus, this modification became
a structural and mechanical factor that interfered into
the formation of bonds between the particles. However,
when applied to the surface of the BF-WP samples, the
water repellent improved their physical and mechanical
properties by an average of 1–10%.
The best indicators were found in those BF-WP
samples which were protected with copper sulfate
introduced into the press material. They had the highest
values of hardness, compression elasticity modulus, and
breaking stress compared to all the other experimental
(protected) and control (unprotected) samples.
A similar picture was observed in the binderfree
plant plastics. Introduced into the press mixture,
the water repellant caused a sharp deterioration in
flexural strength and water absorption (by 10 and 11%,
respectively). When applied to the surface, it improved
these properties by 10 and 14%, respectively. Copper
sulfate that was introduced directly into the press
mixture increased the strength indicators (flexural
strength by 14%, hardness by 49%), but reduced water
resistance (water absorption rose by 23% and swelling
by 28%). These effects must be taken into account when
formulating binder-free, antiseptically protected plastics
based on wood and plant materials.
The experimental BF-WP and BF-PP samples
were exposed in active soil for 21 days and then tested
for biostability. Our analysis of the physical and
mechanical properties of the control (unprotected) and
experimental BF-WP samples showed a significant
decrease in strength indicators. The greatest decrease
in flexural strength (by 39%) was found in the controls.
This indicator fell by 29% in the samples treated with
Table 1 Physical and mechanical properties of binder-free wood plastics protected with antiseptic coating (biostability tests)
Physical and mechanical properties Control Antiseptic coating
Water repellent Copper sulfate Forwood antiseptic
Week Week Week Week
1 2 3 1 2 3 1 2 3 1 2 3
Flexural strength, MPа 3.4 2.6 2.0 3.5 2.8 2.6 3.2 2.8 2.7 3.2 2.3 2.2
Hardness, МPа 8.6 8.6 8.6 17.2 9.1 9.0 9.0 8.8 8.9 9.2 9.0 8.9
Elasticity number, % 40 39 39 65 38 37 41 41 41 51 42 37
Compression elasticity modulus, МPа 62 58 58 156 64 63 63 61 61 64 62 62
Breaking stress, МPа 6.4 6.4 6.4 12.3 6.8 6.7 6.7 6.6 6.7 6.8 6.7 6.7
Yield stress, МPа 2.6 2.6 2.6 4.9 2.7 2.7 2.7 2.6 2.7 2.7 2.7 2.7
Water absorption in 24 h, % 82 82 95 49 55 56 67 72 71 54 76 84
Swelling in thickness in 24 h, % 6.1 6.8 8.4 3.7 6.5 7.5 5.5 7.0 7.4 5.6 7.6 8.1
Table 2 Physical and mechanical properties of binder-free wood plastics protected with an antiseptic introduced into the press
mixture (biostability tests)
Physical and mechanical properties Control Antiseptic introduced into the press mixture
Water repellent Copper sulfate
Week Week Week
1 2 3 1 2 3 1 2 3
Flexural strength, MPа 3.4 2.6 2.0 1.1 1.1 0.8 4.7 3.9 3.7
Hardness, МPа 8.6 8.6 8.6 8.9 8.4 8.4 16.2 14.1 10.3
Elasticity number, % 40 39 39 50 45 41 48 34 33
Compression elasticity modulus, МPа 62 58 58 61 57 57 146 121 76
Breaking stress, МPа 6.4 6.4 6.4 6.6 6.3 6.3 11.5 10.1 7.6
Yield stress, МPа 2.6 2.6 2.6 2.7 2.5 2.5 4.6 4.1 3.1
Water absorption in 24 h, % 82 82 95 110 115 115 44 47 51
Swelling in thickness in 24 h, % 6.1 6.8 8.4 7.5 7.7 9.8 4.2 4.5 4.5
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the Forwood antiseptic and by 26% in the samples with
a water repellent introduced into the press mixture
(Tables 1 and 2).
Flexural strength had the smallest losses in the
samples protected with copper sulfate, namely 15%
for the coated sample and 21% for the sample with a
modified press mixture.
Hardness was the highest in the wood plastics
treated with the water repellent and those with the
copper sulfate-modified press mixture, namely 17.2 and
16.2 MPa, respectively, on the eighth day of exposure in
active soil. However, it was these samples that had the
greatest loss of hardness by the end of the biostability
test, by 48 and 36%, respectively. Yet, this indicator
remained the highest in the samples with added copper
sulfate (10.3 MPa).
Water absorption had the highest values in the
samples with an added water repellant, averaging 115%
after three weeks of exposure. The lowest values were in
the samples with added copper sulfate, namely 51% by
the end of the tests (a loss of 16%).
The plant plastics also showed changes in their
physical and mechanical parameters. The smallest loss
(24%) of flexural strength over three weeks of exposure
in active soil was found in the samples with an added
water repellent, although they had one of the lowest
values (0.4 MPa) in the first week. On the eighth day,
this indicator was the highest in the samples coated
with a water repellent (2.5 MPa), decreasing by 53% to
1.1 MPa by the end of the test (Table 3). The hardness
indicator decreased in all the plant samples within three
weeks of exposure in the range of 1–6%.
Daily water absorption was the highest in the
samples with an added water repellent, amounting to
228% after three weeks of exposure in active soil, with
a 42% decrease of water absorption. By the end of the
biostability tests, the lowest water absorption was in the
samples coated with the Forwood antiseptic (122%).
CONCLUSION
Our study showed high biodegradation and
low biostability of the binder-free wood and plant
plastics based on sawdust, and wheat and millet
husks. Therefore, antiseptic protection is required
to improve their performance. Their exposure in a
bioactive environment caused some morphological and
structural changes, as well as affected their physical and
mechanical properties.
We found that the plant-based plastics underwent
a more pronounced degradation in active soil than the
sawdust-based plastics. According to our results, the
samples’ resistance to biodegradation was determined
by such process parameters as the type of filler
Table 3 Physical and mechanical properties of binder-free plant plastics protected with antiseptic coating (biostability tests)
Physical and mechanical properties Control Antiseptic coating
Water repellent Copper sulfate Commercial antiseptic
Week Week Week Week
1 2 3 1 2 3 1 2 3 1 2 3
Flexural strength, MPа 2.0 1.8 1.3 2.5 1.7 1.1 2.1 2.0 1.6 1.6 1.2 1.0
Hardness, МPа 8.7 8.7 8.3 9.1 8.7 8.7 8.8 8.6 8.5 8.9 8.7 8.4
Elasticity number, % 36 36 41 33 38 39 39 40 40 36 38 40
Compression elasticity modulus, МPа 60 59 56 64 60 59 60 59 58 62 60 57
Breaking stress, МPа 6.5 6.4 6.2 6.8 6.5 6.5 6.6 6.4 6.4 6.7 6.5 6.3
Yield stress, МPа 2.6 2.6 2.5 2.7 2.6 2.6 2.6 2.6 2.6 2.7 2.6 2.5
Water absorption in 24 h, % 89 113 158 90 121 151 103 119 151 88 101 122
Swelling in thickness in 24 h, % 7.5 7.9 9.6 5.2 5.7 7.8 5.2 6.0 7.5 7.4 7.5 7.9
Table 4 Physical and mechanical properties of binder-free plant plastics protected with an antiseptic introduced into the press
mixture (biostability tests)
Physical and mechanical properties Control Antiseptic introduced into the press mixture
Water repellent Copper sulfate
Week Week Week
1 2 3 1 2 3 1 2 3
Flexural strength, MPа 2.0 1.8 1.3 0.4 0.3 0.3 2.0 0.6 0.3
Hardness, МPа 8.7 8.7 8.3 8.9 8.9 8.9 8.9 8.8 8.7
Elasticity number, % 36 36 41 37 38 38 34 38 38
Compression elasticity modulus, МPа 60 59 56 62 61 61 62 60 60
Breaking stress, МPа 6.5 6.4 6.2 6.7 6.6 6.6 6.7 6.6 6.5
Yield stress, МPа 2.6 2.6 2.5 2.7 2.7 2.7 2.7 2.6 2.6
Water absorption in 24 h, % 89 113 158 161 203 228 135 135 171
Swelling in thickness in 24 h, % 7.5 7.9 9.6 5.1 5.2 5.3 5.3 5.4 5.6
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and antiseptic, as well as the method of antiseptic
administration.
We treated the plastics with three types of antiseptic
(water repellent, copper sulfate, and Forwood) by
adding them to the press mixture or applying them to
the surface. Both methods changed the initial properties
of the samples. When used as a coating, the water
repellent improved the samples’ physical and mechanical
properties. When added to the press mixture, however,
it significantly impaired their strength and water
resistance.
Copper sulfate showed the best effect among
those antiseptics introduced into the press mixture. It
decreased the flexural strength of the sawdust-based
samples by 5% and increased their hardness, water
absorption, and swelling. The plant-based samples with
added copper sulfate showed better strength indicators,
but lower water resistance. Thus, the antiseptic treatment
of binder-free plastics based on wood or plants affects a
number of their key physical and mechanical properties
and should be administered with regard to expected
performance conditions.
CONTRIBUTION
All the authors were equally involved in developing
the research concept, obtaining and analyzing the data,
and writing the manuscript.
CONFLICT OF INTEREST
The authors declare that there is no conflict of
interest.
1. Mellelo E, Samuilova EO, Denisov TS, Martynova DM, Olekhnovich RO. Influence of the bentonite-containing acrylic humectant composite on the soil microflora. Agronomy Research. 2019;17(5):1960-1968. https://doi.org/10.15159/AR.19.156.
2. Liška V. The energy intensity of the briquetting process in terms of profitability of waste treatment. Agronomy Research. 2019;17(1):186-193. https://doi.org/10.15159/AR.19.021.
3. Shen L, Haufe J, Patel MK. Product overview and market projection of emerging bio-based plastics. Utrecht: Utrecht University; 2009. 243 p.
4. Faruk O, Bledzki AK, Fink H-P, Sain M. Biocomposites reinforced with natural fibers: 2000-2010. Progress in Polymer Science. 2012;37(11):1552-1596. https://doi.org/10.1016/j.progpolymsci.2012.04.003.
5. Alao PF, Kallakas H, Poltimäe T, Kers J. Effect of hemp fibre length on the properties of polypropylene composites. Agronomy Research. 2019;17(4):1517-1531. https://doi.org/10.15159/AR.19.146.
6. Satyanarayana KG, Arizaga GGC, Wypych F. Biodegradable composites based on lignocellulosic fibers - An overview. Progress in Polymer Science. 2009;34(9):982-1021. https://doi.org/10.1016/j.progpolymsci.2008.12.002.
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