Versatile Polypropylene Composite Containing Post-Printing Waste

Abstract

The paper presents the results of the research on the possibility of using waste after the printing process as a filler for polymeric materials. Remains of the label backing were used, consisting mainly of cellulose with glue and polymer label residue. The properly prepared filler (washed, dried, pressed and cut) was added to the polypropylene in a volume ratio of 2:1; 1:1; 1:2; and 1:3 which corresponded to approximately 10, 5, 2.5 and 2 wt % filler. The selected processing properties (mass flow rate), mechanical properties (tensile strength, impact strength, dynamic mechanical analysis) and thermal properties (thermogravimetric analysis, differential scanning calorimetry) were determined. The use of even the largest amount of filler did not cause disqualifying changes in the determined properties. The characteristics of the obtained materials allow them to be used in various applications while reducing costs due to the high content of cheap filler.

Full text

Citation: Moraczewski, K.;
Karasiewicz, T.; Suwała, A.;
Bolewski, B.; Szabli´nski, K.;
Zaborowska, M. Versatile
Polypropylene Composite
Containing Post-Printing Waste.
Polymers 2022,14, 5335. https://
doi.org/10.3390/polym14245335
Academic Editor: Kamila Sałasi´nska
Received: 14 November 2022
Accepted: 3 December 2022
Published: 7 December 2022
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Attribution (CC BY) license (https://
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4.0/).
polymers
Article
Versatile Polypropylene Composite Containing
Post-Printing Waste
Krzysztof Moraczewski 1, * , Tomasz Karasiewicz 1, Alicja Suwała 1, Bartosz Bolewski 1, Krzysztof Szabli´nski 1
and Magdalena Zaborowska 2
1
Faculty of Materials Engineering, Kazimierz Wielki University, Chodkiewicza 30 Str., 85-064 Bydgoszcz, Poland
2Blue System Sp. z o.o., Rynkowska 17D Str., 85-503 Bydgoszcz, Poland
*Correspondence: kmm@ukw.edu.pl; Tel.: +48-52-3419331
Abstract:
The paper presents the results of the research on the possibility of using waste after the
printing process as a filler for polymeric materials. Remains of the label backing were used, consisting
mainly of cellulose with glue and polymer label residue. The properly prepared filler (washed, dried,
pressed and cut) was added to the polypropylene in a volume ratio of 2:1; 1:1; 1:2; and 1:3 which
corresponded to approximately 10, 5, 2.5 and 2 wt % filler. The selected processing properties (mass
flow rate), mechanical properties (tensile strength, impact strength, dynamic mechanical analysis) and
thermal properties (thermogravimetric analysis, differential scanning calorimetry) were determined.
The use of even the largest amount of filler did not cause disqualifying changes in the determined
properties. The characteristics of the obtained materials allow them to be used in various applications
while reducing costs due to the high content of cheap filler.
Keywords: circular economy; polypropylene; post-printing waste
1. Introduction
Wastes are substances or objects resulting from human activity, as well as residues from
their production, which are intended for disposal. The proper management of waste and
by-products from industrial and natural production and activities (agriculture, horticulture
and others) is the key to sustainable development, reduction in pollution, increase in
storage space, minimization of landfill, reduction in energy consumption and facilitation of
the circular economy [1].
The circular economy is a regenerative economic system in which the consumption
of raw materials and the amount of waste as well as the emission and loss of energy are
minimized by creating a closed loop of processes in which waste from one process is used
as raw materials for others, which minimizes the amount of waste production [
2
,
3
]. Waste
management is a series of processes related to the collection, transport and processing,
including the supervision of this type of activity, as well as the subsequent handling of
waste disposal sites, as well as activities related to waste trading [4,5].
One of the possibilities of reusing post-production waste is its use for the production
of other materials, including the production of composite materials with various matrices.
In recent years, composites with a polymer matrix and post-production waste fillers or
reinforcements have attracted a lot of interest. Due to the characteristics of polymeric
materials, thermoplastics in particular, it is possible to easily add post-production wastes in
various forms to the polymer mass and subsequently easily process them through extrusion
and injection processes.
In the production of polymer composites, the post-production waste used can be
divided into two types. The first consists of organic wastes from the agricultural or food
industry. The second consists of inorganic wastes from heavy industry such as the steel
industry or petrochemical industry [1].
Polymers 2022,14, 5335. https://doi.org/10.3390/polym14245335 https://www.mdpi.com/journal/polymers

Polymers 2022,14, 5335 2 of 13
The most frequently used post-production waste materials in the production of poly-
mer composites are natural wastes. Natural wastes are cheap and easily renewable, and
their biodegradability is one of their most important features. Among the organic waste,
the most commonly used post-production wastes is wood obtained from the wood and
furniture industries. Post-production wastes in the form of flour or chips from the processes
of cutting, turning, milling, planing, etc. are used as fillers for the production of wood-
polymer composites (WPC), most often with polyolefin or poly(vinyl chloride) matrix, but
also biodegradable polymers such as polylactide [6–11].
Other organic post-production wastes used in the production of polymer composites
include: shells of nuts and seeds [
12
–
15
], bamboo [
16
–
19
], coconut shells [
20
–
24
], husk of
rice and cereals [
25
–
30
], fruit and vegetables pomace [
31
–
34
], as well as waste of animal
origin, such as egg shells or shells of crustaceans [35–38].
In most cases, these organic fillers can be easily integrated into thermoplastic or ther-
moset matrices to change their thermal, mechanical and tribological properties. However,
not always only favorable changes in properties are observed. It is very often necessary
to properly modify the waste in order to obtain materials with good performance param-
eters. Therefore, the deterioration of properties, especially mechanical properties, can
most often be observed after adding unmodified waste. However, this deterioration does
not have to be disqualifying for these composites, as very often, their properties are still
sufficient for many planned applications, and their great advantage is a much lower price
and environmental friendliness thanks to the use of cheap waste materials.
Printing houses, publishing houses and printing companies have to tackle the issue
of increasing amounts of post-production waste on a daily basis. In the printing industry,
the different types of waste vary significantly. The most important of the solid, liquid and
gaseous wastes produced in the printing industry before, during and after the printing
process are waste ink, ink sludge and solvents emerging after machine washing, wastewater
of water-based ink, plate and film developer and fixer solutions, cleaning solvents and
volatile organic compounds (VOCs) [
39
]. The printing industry generates large amounts of
scrap paper, catalogs, posters, cardboard boxes and plastic foil. The loose waste piles up and
is stored in warehouses, taking up space and making it difficult to move around [
40
]. Some
of the produced wastes even fall into the hazardous waste category due to their processing
characteristics during the production process. The effective and regular extermination
of these wastes is necessary to protect the environment. This can be provided only by
the application of waste management. Some wastes are recycled and reused at printing
industry, but in some cases, that recycling is impossible, and these wastes should be
eliminated without harming human health and the environment [
41
]. In particular, the
materials whose disposal is compulsory should be classified at the source and sent to
licensed disposal companies. One of the solutions may be the reuse of generated waste in
the production of other materials while being part of the circular economy.
The paper presents the results of research on the possibility of using unmodified
post-production waste from the food label printing process. In the product labeling process,
the liner is often overlooked by many brands as part of the waste stream. Despite the
various recycling programs available on the market, such as UPM Raflatac’s RafCycle
®
,
they can still be a major environmental problem. The process of cutting the underlay to the
production dimensions still produces from several dozen to several hundred kilograms of
cut waste, which does not qualify for the recycling program and requires proper disposal,
which is a problem for the company. Due to the lack of modification of the waste, it
was expected that the properties of the obtained composites would deteriorate in relation
to pure polymer. However, it is purposeful to check whether the properties of the new
composites will still be sufficient for the use of the obtained composites.

Polymers 2022,14, 5335 3 of 13
2. Materials and Methods
The matrix of the tested materials was polypropylene (PP) Moplen EP548U (Lyondell-
Basell, Rotterdam, The Netherlands). The basic properties of the polymer according to the
data sheet are:
•Melt Flow Rate (230 ◦C/2.16 kg): 70 g/10 min.
•Density: 0.90 g/cm3.
•Tensile Stress at Yield: 28 MPa.
•Tensile Strain at Break: 30%.
•Tensile Strain at Yield: 5%.
•Charpy Impact Strength (Notched): 4 kJ/m2.
•Tensile Modulus: 1450 MPa.
•Melt temperature: 160 ◦C.
The filler of new materials is post- production waste after the printing process in the
form of cut off yellow transparent glassine backing cellulose paper with the trade name
HONEY GLASSINE 65 (UPM Raflatac, Tempere, Finland) with possible residues of hotmelt
rubber permanent adhesive and a polymer (polypropylene or polyethylene) label. Glassine
is a smooth and glossy paper that is air, water, and grease resistant. It is usually available
in densities between 50 and 90 g/m
2
. It is translucent unless dyes are added to color it or
make it opaque. Product is designed for general purpose high-quality multicolor-printed
labels to packaged food and homecare applications in ambient conditions. It is intended for
all reelstock applications, and it is suitable for automatic dispensing. The basic properties
of the backing paper according to the data sheet are:
•Substance: 55 g/m2.
•Caliper: 49 µm.
•Tensile strength MD: 6.0 kN/m.
•Tensile strength CD: 2.3 kN/m.
•Transparency: 49%.
The input material from the production of the filler was in the form of long strands,
approx. 4 mm wide. Initially, the waste was soaked in water, and then, it was formed with
a hydraulic press into discs with a diameter of about 10 cm. Then, the discs were dried in a
laboratory dryer and comminuted using a laboratory grinder. Ultimately, the filler was in the
form of short fragments with a width and thickness similar to the original strips (Figure 1).
Polymers 2022, 14, x FOR PEER REVIEW 3 of 14
The matrix of the tested materials was polypropylene (PP) Moplen EP548U (Lyon-
dellBasell, Rotterdam, The Netherlands). The basic properties of the polymer according
to the data sheet are:
• Melt Flow Rate (230 °C/2.16 kg): 70 g/10 min.
• Density: 0.90 g/cm
3
.
• Tensile Stress at Yield: 28 MPa.
• Tensile Strain at Break: 30%.
• Tensile Strain at Yield: 5%.
• Charpy Impact Strength (Notched): 4 kJ/m
2
.
• Tensile Modulus: 1450 MPa.
• Melt temperature: 160 °C.
The filler of new materials is post- production waste after the printing process in the
form of cut off yellow transparent glassine backing cellulose paper with the trade name
HONEY GLASSINE 65 (UPM Raflatac, Tempere, Finland) with possible residues of hot-
melt rubber permanent adhesive and a polymer (polypropylene or polyethylene) label.
Glassine is a smooth and glossy paper that is air, water, and grease resistant. It is usually
available in densities between 50 and 90 g/m
2
. It is translucent unless dyes are added to
color it or make it opaque. Product is designed for general purpose high-quality multi-
color-printed labels to packaged food and homecare applications in ambient conditions.
It is intended for all reelstock applications, and it is suitable for automatic dispensing. The
basic properties of the backing paper according to the data sheet are:
• Substance: 55 g/m
2
.
• Caliper: 49 µm.
• Tensile strength MD: 6.0 kN/m.
• Tensile strength CD: 2.3 kN/m.
• Transparency: 49%.
The input material from the production of the filler was in the form of long strands,
approx. 4 mm wide. Initially, the waste was soaked in water, and then, it was formed with
a hydraulic press into discs with a diameter of about 10 cm. Then, the discs were dried in
a laboratory dryer and comminuted using a laboratory grinder. Ultimately, the filler was
in the form of short fragments with a width and thickness similar to the original strips
(Figure 1).
Figure 1. Initial and final form of the filler.
Figure 1. Initial and final form of the filler.

Polymers 2022,14, 5335 4 of 13
The prepared filler was added to the polymer matrix in a 1:3; 1:2; 1:1 and 2:1 volume
ratio, which corresponded to mass concentrations at the level of 1.9; 2.5; 5.1 and
10.3 wt %
.
The test samples are marked with the symbols P_x, where x is the volume ratio of the
filler. All test results were compared to the results of a pure polypropylene sample, which
was abbreviated as PP. Sample designations with corresponding volume ratio of filler and
calculated mass concentration are presented in Table 1.
Table 1. Samples designations.
Sample Filler: Matrix Volume Ratio Mass Concentration of Filler [wt.%]
PP - -
P_1_3 1:3 1.9
P_1_2 1:2 2.5
P_1_1 1:1 5.1
P_2_1 2:1 10.3
The granules of individual composites were obtained from the prepared composite
masterbatches by extrusion. Extrusion was carried out on a W25-30D single screw extruder
(Metalchem, Toru´n, Poland). In order to obtain a very thorough mixing of both components,
intensive mixing screws were used for this purpose, which additionally included kneading
and retracting segments. The rotational speed of the screw was constant at 200 rpm. The
temperatures of individual zones of the extruder were: 175, 185, 195 and 195
◦
C, and the
temperature of the head was 120 ◦C. The material coming out of the head was cooled in a
bath with water and then cut with a knife granulator.
From the obtained granulate by injection method, test specimens were obtained in
the form of standardized bone-shaped samples (Figure 2) and bars. Injection molding
was carried out on a TRX 80 Eco (Tederic, Zhejiang, China) injection molding machine.
The injection molding process for all compositions was conducted under the following
conditions: 170
◦
C, 170
◦
C and 175
◦
C with head temperature—180
◦
C. Other parameters
follow: mold temperature—35 ◦C, injection pressure—35 bar, cooling time—30 s.
Polymers 2022, 14, x FOR PEER REVIEW 4 of 14
The prepared filler was added to the polymer matrix in a 1:3; 1:2; 1:1 and 2:1 volume
ratio, which corresponded to mass concentrations at the level of 1.9; 2.5; 5.1 and 10.3 wt
%. The test samples are marked with the symbols P_x, where x is the volume ratio of the
filler. All test results were compared to the results of a pure polypropylene sample, which
was abbreviated as PP. Sample designations with corresponding volume ratio of filler and
calculated mass concentration are presented in Table 1.
Table 1. Samples designations.
Sample Filler: Matrix Volume Ratio Mass Concentration of Filler [wt.%]
PP - -
P_1_3 1:3 1.9
P_1_2 1:2 2.5
P_1_1 1:1 5.1
P_2_1 2:1 10.3
The granules of individual composites were obtained from the prepared composite
masterbatches by extrusion. Extrusion was carried out on a W25-30D single screw ex-
truder (Metalchem, Toruń, Poland). In order to obtain a very thorough mixing of both
components, intensive mixing screws were used for this purpose, which additionally in-
cluded kneading and retracting segments. The rotational speed of the screw was constant
at 200 rpm. The temperatures of individual zones of the extruder were: 175, 185, 195 and
195 °C, and the temperature of the head was 120 °C. The material coming out of the head
was cooled in a bath with water and then cut with a knife granulator.
From the obtained granulate by injection method, test specimens were obtained in
the form of standardized bone-shaped samples (Figure 2) and bars. Injection molding was
carried out on a TRX 80 Eco (Tederic, Zhejiang, China) injection molding machine. The
injection molding process for all compositions was conducted under the following condi-
tions: 170 °C, 170 °C and 175 °C with head temperature—180 °C. Other parameters follow:
mold temperature—35 °C, injection pressure—35 bar, cooling time—30 s.
Figure 2. Test specimens obtained by injection method.
Figure 2. Test specimens obtained by injection method.

Polymers 2022,14, 5335 5 of 13
Melt flow rate (MFR) studies were performed using an MP600 plastometer (Tinius
Olsen, Horsham, PA, USA). The tests were carried out at a temperature of 190
◦
C with a
piston load of 2.16 kg. For each tested material, 12 measurement sections were obtained of
which 10 values were taken for the calculations (two extreme ones were rejected).
The mechanical properties of the tested materials were determined by the tensile
strength test and the un-notch impact test. For the mechanical tests, twelve samples of each
composition were used for each test. The result of mechanical tests are the values obtained
as the arithmetic mean of individual parameters together with the calculated values of the
standard deviation.
Static tensile tests on PP and filler-containing polymer samples were performed on an
Instron 3367 (Instron, Norwood, MA, USA) universal testing machine. The tensile speed
was 50 mm/min. As part of the test, the tensile strength (
σM
), stress at break (
σB
), strain at
maximum stress (εM) and strain at break (εB) were determined.
Charpy impact tests were carried out with an XJ 5Z impact hammer (Liangong,
Shandong, China) using a 2 J hammer with a fall velocity of 2.9 m/s. Samples in the
form of bars with dimensions of 80 mm
×
10 mm
×
4 mm were tested. As part of the study,
the value of the impact strength without notch (ua) was determined.
Thermomechanical (DMA) tests were carried out using a Q800 (TA Instruments,
New Castle, DE, USA) dynamic mechanical analyzer. The tests were carried out in the
temperature range from 30 to 150
◦
C with a heating rate of 3
◦
C/min. The samples were
bars with dimensions of 80 mm
×
10 mm
×
4 mm. The strain was 15
µ
m, and the strain
frequency was 1 Hz.
The Q200 (TA Instruments, New Castle, DE, USA) calorimeter was used in the differen-
tial scanning calorimetry (DSC) studies. Samples weighing about 4 mg were heated in the
temperature range from 0 to 700
◦
C with the temperature change rate of
10 ◦C min−1
. The
test was conducted in a nitrogen atmosphere. Based on the cooling and heating curves, the
glass transition temperature (T
g
), the cold crystallization temperature (T
cc
), the change of
the cold crystallization enthalpy (
∆
H
cc
), the melting point (T
m
), the change of the melting
enthalpy (
∆
H
cc
) and the degree of crystallinity (X
c
) were determined. X
c
values were
calculated from equation:
Xc=∆Hm−∆Hcc
∆Hm100%·(1−x)·100% (1)
where
∆
H
m100%
—enthalpy change of 100% crystalline PP; 207 J/g [
42
]. x—share of post-
printing waste.
Thermogravimetric analysis (TGA) studies were performed under nitrogen atmo-
sphere using a Q500 thermobalance (TA Instruments, New Castle, DE, USA). The samples
weighing about 21 mg were tested in the temperature range from 25 to 700
◦
C with the
temperature change rate of 10
◦
C/min. Based on the thermogravimetric curves, the values
of T
5%
, T
50%
and T
95%
were determined, corresponding to the loss temperature of 5%, 50%
and 95% of the initial mass of the sample. The value of T
5%
was adopted as the parameter
defining the thermal resistance of the material. From the differential thermogravimetric
curve (DTG) (the first derivative of the TG curve), the T
max
values were also determined,
defining the temperatures of the fastest mass loss in the individual degradation stages.
3. Results
The determined melt flow rate (MFR) of pure PP was 11.2 g/10 min and was consistent
with the literature data (Figure 3). The addition of the filler into the polymer matrix did not
cause major changes in the MFR values. Although the applied post-print waste limited the
flow of the polymer, which is typical for this type of filler, the obtained decrease in MFR
was acceptable. At lower filler contents, i.e., samples P_1_3 and P_1_2, the MFR decreased
to the value of about 10 g/10 min. Even a further increase in the amount of filler did not
cause a large decrease in MFR, and the recorded values for the samples P_1_1 and P_2_1
were 9.0 g/10 min. Thus, the total decrease in MFR after adding the greatest amount of

Polymers 2022,14, 5335 6 of 13
filler, i.e., twice the volume excess of filler, was 2.2 g/10 min, which is 20% of the value
of pure PP.
Polymers 2022, 14, x FOR PEER REVIEW 6 of 14
P_1_1 and P_2_1 were 9.0 g/10 min. Thus, the total decrease in MFR after adding the great-
est amount of filler, i.e., twice the volume excess of filler, was 2.2 g/10 min, which is 20%
of the value of pure PP.
Figure 3. Melt flow rate (MFR) of individual samples.
The determined tensile strength (σ
M
) and tensile stress (ε
B
) of pure PP samples were
slightly lower than the values given in the data sheet for the tested polymer but in line
with the literature data for PP. The addition of post-printing waste to the matrix resulted
in a slight decrease in the strength of the tested materials (Figure 4) as well as equating
the values of σ
M
and ε
B
, which is related to the change in the elasticity of PP after intro-
ducing the filler particles (stress aggregation sites). As for MFR, one observes a clear two-
stage decrease in the tensile strength of the tested materials. A smaller drop in strength by
approx. 2.5 MPa compared to pure PP was observed for P_1_3 and P_1_2 materials, i.e.,
materials with a predominance of polymer in the composition. A greater decrease in
strength by about 4.5 MPa in relation to pure PP was observed for higher waste content,
i.e., P_1_1 and P_2_1 materials, where the initial volume fraction of waste was equal to or
higher than the polymer fraction. The overall decrease in the tensile strength of PP after
adding the post-printing waste was 4.5 MPa, which is approx. 19% of the value of pure
polymer.
Figure 3. Melt flow rate (MFR) of individual samples.
The determined tensile strength (
σM
) and tensile stress (
εB
) of pure PP samples were
slightly lower than the values given in the data sheet for the tested polymer but in line
with the literature data for PP. The addition of post-printing waste to the matrix resulted in
a slight decrease in the strength of the tested materials (Figure 4) as well as equating the
values of
σM
and
εB
, which is related to the change in the elasticity of PP after introducing
the filler particles (stress aggregation sites). As for MFR, one observes a clear two-stage
decrease in the tensile strength of the tested materials. A smaller drop in strength by approx.
2.5 MPa compared to pure PP was observed for P_1_3 and P_1_2 materials, i.e., materials
with a predominance of polymer in the composition. A greater decrease in strength by
about 4.5 MPa in relation to pure PP was observed for higher waste content, i.e., P_1_1 and
P_2_1 materials, where the initial volume fraction of waste was equal to or higher than
the polymer fraction. The overall decrease in the tensile strength of PP after adding the
post-printing waste was 4.5 MPa, which is approx. 19% of the value of pure polymer.
The introduction of the printing waste into the PP matrix was also accompanied by
a large decrease in elongation at break (
εB
), which was additionally equal to the values
of elongation at maximum stress (
εM
) (Figure 5). Due to the characteristics of PP and the
occurrence of the phenomenon of necking during the tensile test, where the stretching and
ordering of macromolecules occurs, this polymer is characterized by high
εB
values, which
significantly exceed the
εM
values. The applied printing waste reduces the values of
εM
and
εB
to the level of approx. 5%, while the values for pure PP were, respectively, 8.1 and
35.9%. The obtained strain drop was the same regardless of the volumetric content of the
filler in the matrix. The lack of differences in the deformation between individual materials
is probably because, regardless of the amount of waste in the cross-section of the sample,
there will always be a filler particle, on which stress aggregation and sample rupture will
occur before the necking phenomenon occurs.

Polymers 2022,14, 5335 7 of 13
Polymers 2022, 14, x FOR PEER REVIEW 7 of 14
Figure 4. Tensile strength (σ
M
) and stress at break (σ
B
) of individual samples.
The introduction of the printing waste into the PP matrix was also accompanied by
a large decrease in elongation at break (ε
B
), which was additionally equal to the values of
elongation at maximum stress (ε
M
) (Figure 5). Due to the characteristics of PP and the
occurrence of the phenomenon of necking during the tensile test, where the stretching and
ordering of macromolecules occurs, this polymer is characterized by high ε
B
values, which
significantly exceed the ε
M
values. The applied printing waste reduces the values of ε
M
and ε
B
to the level of approx. 5%, while the values for pure PP were, respectively, 8.1 and
35.9%. The obtained strain drop was the same regardless of the volumetric content of the
filler in the matrix. The lack of differences in the deformation between individual materi-
als is probably because, regardless of the amount of waste in the cross-section of the sam-
ple, there will always be a filler particle, on which stress aggregation and sample rupture
will occur before the necking phenomenon occurs.
Figure 4. Tensile strength (σM) and stress at break (σB) of individual samples.
Polymers 2022, 14, x FOR PEER REVIEW 8 of 14
Figure 5. Elongation at maximum stress (ε
M
) and elongation at break (ε
B
) of individual samples.
The PP sample subjected to impact tests does not break, which is often observed for
pure polypropylene due to its high flexibility and hence high impact resistance. Even the
lowest content of post-printing waste in the material caused the samples to break as a
result of the impact, and the value of the impact strength was recorded (u
a
) (Figure 6).
Figure 6. The impact strength (u
a
) of individual samples.
Figure 5. Elongation at maximum stress (εM) and elongation at break (εB) of individual samples.
The PP sample subjected to impact tests does not break, which is often observed for
pure polypropylene due to its high flexibility and hence high impact resistance. Even the
lowest content of post-printing waste in the material caused the samples to break as a result
of the impact, and the value of the impact strength was recorded (ua) (Figure 6).
The obtained u
a
value for the P_1_3 sample was 28.3 kJ/m
2
. With an increase in the
filler content, the impact strength decreased, reaching the lowest value of 21.9 kJ/m
2
for the
P_2_1 sample, i.e., a material with a waste content twice as high as PP. The total decrease in

Polymers 2022,14, 5335 8 of 13
u
a
between the lowest and the highest content of post-printing waste was 6.4 kJ/m
2
, i.e.,
approx. 22%. The observed decrease was caused by an increase in the amount of filler in
the matrix and thus also in the cross-section of the sample (Figure 7), which translated into
lower polymer content and lowered the impact strength of the entire system. The large
scatter of the obtained results suggests, however, that the distribution of the filler particles
was heterogeneous.
Polymers 2022, 14, x FOR PEER REVIEW 8 of 14
Figure 5. Elongation at maximum stress (ε
M
) and elongation at break (ε
B
) of individual samples.
The PP sample subjected to impact tests does not break, which is often observed for
pure polypropylene due to its high flexibility and hence high impact resistance. Even the
lowest content of post-printing waste in the material caused the samples to break as a
result of the impact, and the value of the impact strength was recorded (u
a
) (Figure 6).
Figure 6. The impact strength (u
a
) of individual samples.
Figure 6. The impact strength (ua) of individual samples.
Polymers 2022, 14, x FOR PEER REVIEW 9 of 14
The obtained u
a
value for the P_1_3 sample was 28.3 kJ/m
2
. With an increase in the
filler content, the impact strength decreased, reaching the lowest value of 21.9 kJ/m
2
for
the P_2_1 sample, i.e., a material with a waste content twice as high as PP. The total de-
crease in u
a
between the lowest and the highest content of post-printing waste was 6.4
kJ/m
2
, i.e., approx. 22%. The observed decrease was caused by an increase in the amount
of filler in the matrix and thus also in the cross-section of the sample (Figure 7), which
translated into lower polymer content and lowered the impact strength of the entire sys-
tem. The large scatter of the obtained results suggests, however, that the distribution of
the filler particles was heterogeneous.
Figure 7. Microscopic photos of the cross-sections of (a) P_1_3, (b) P_1_2, (c) P_1_1, (d) P_2_1 sam-
ple.
The post-printing waste did not change the thermomechanical characteristics of the
polymer. The PP modulus of elasticity at 30 °C (E’
30
) determined during the three-point
bending DMA test was 1225 MPa and decreased with increasing temperature, reaching
132 MPa at 150 °C, i.e., just before the material melting process. The thermomechanical
curves with the recorded E’ values for materials containing post-printing waste were sim-
ilar to the values of pure PP, regardless of the amount of filler in the polymer matrix. Thus,
the obtained materials retained the PP elasticity even with the highest content of post-
printing waste. All results of E’ measurements at different temperatures are presented in
Table 2.
Table 2. Results of dynamic mechanical analysis (DMA) tests of individual samples.
Sample E’
30
(MPa) E’
60
(MPa) E’
90
(MPa) E’
150
(MPa)
PP 1225 759 416 132
P_1_3 1207 782 432 142
P_1_2 1247 779 431 142
P_1_1 1326 791 443 143
P_2_1 1194 744 426 148
Figure 7.
Microscopic photos of the cross-sections of (
a
) P_1_3, (
b
) P_1_2, (
c
) P_1_1, (
d
) P_2_1 sample.

Polymers 2022,14, 5335 9 of 13
The post-printing waste did not change the thermomechanical characteristics of the
polymer. The PP modulus of elasticity at 30
◦
C (E’
30
) determined during the three-point
bending DMA test was 1225 MPa and decreased with increasing temperature, reaching
132 MPa at 150
◦
C, i.e., just before the material melting process. The thermomechanical
curves with the recorded E’ values for materials containing post-printing waste were similar
to the values of pure PP, regardless of the amount of filler in the polymer matrix. Thus, the
obtained materials retained the PP elasticity even with the highest content of post-printing
waste. All results of E’ measurements at different temperatures are presented in Table 2.
Table 2. Results of dynamic mechanical analysis (DMA) tests of individual samples.
Sample E’30 (MPa) E’60 (MPa) E’90 (MPa) E’150 (MPa)
PP 1225 759 416 132
P_1_3 1207 782 432 142
P_1_2 1247 779 431 142
P_1_1 1326 791 443 143
P_2_1 1194 744 426 148
Post-printing waste influenced the course of phase transformations in the tested
materials, i.e., changed their temperatures and intensity (Figure 8). With the lowest waste
content, the thermal characteristics of the P_1_3 sample are still close to the thermal
characteristics of pure PP. Only a slight decrease in the intensity of the melting process by
8 J/g is visible, which suggests a slightly lower content of the crystalline phase, which
results in a reduction in the calculated degree of crystallinity by 4.7 units. On the other hand,
the introduction of a larger amount of filler caused a clear decrease in the crystallization
temperature (T
c
) by a maximum of approx. 6
◦
C for the P_2_1 sample, i.e., by approx. 5%
compared to the value obtained for the PP sample.
Polymers 2022, 14, x FOR PEER REVIEW 10 of 14
Post-printing waste influenced the course of phase transformations in the tested ma-
terials, i.e., changed their temperatures and intensity (Figure 8). With the lowest waste
content, the thermal characteristics of the P_1_3 sample are still close to the thermal char-
acteristics of pure PP. Only a slight decrease in the intensity of the melting process by 8
J/g is visible, which suggests a slightly lower content of the crystalline phase, which results
in a reduction in the calculated degree of crystallinity by 4.7 units. On the other hand, the
introduction of a larger amount of filler caused a clear decrease in the crystallization tem-
perature (Tc) by a maximum of approx. 6 °C for the P_2_1 sample, i.e., by approx. 5%
compared to the value obtained for the PP sample.
Figure 8. DSC curves of cooling (solid line) and heating (dashed line) of selected samples.
The nature of the crystallization process also changed. At lower waste contents, the
recorded peak of the crystallization process was much lower but wider than the peak rec-
orded at the highest filler content. The enthalpy change of the crystallization process (ΔHc)
was also higher. With the increase in the content of waste, the ΔHc value decreased by 14.3
J/g, from 95.1 J/g for the P_1_3 sample to 80.8 J/g for the P_2_1 sample. Thus, the waste
content affects the structure and amount of the crystalline phase formed in PP. With a
lower waste content, the formed crystallites are probably larger, and there are more of
them. Changes in the crystallization process are influencing the structure and quantity of
the crystalline phase and obviously translate into the recorded melting process and the
calculated degree of crystallinity. As the filler content increases, the melting point (Tm) of
the materials slightly decreases. The Tm decrease is approx. 2 °C when comparing the PP
sample and the P_2_1 sample. The decrease in the melting enthalpy (ΔHm), and thus the
degree of calculated crystallinity (Xc), was much more pronounced. The ΔHm value de-
creased by 15.6 J/g comparing the PP and P_2_1 sample. Thus, the degree of crystallinity
of the tested materials decreased from 47.7 to 36.2%. All results of DSC are presented in
Table 3.
Figure 8. DSC curves of cooling (solid line) and heating (dashed line) of selected samples.
The nature of the crystallization process also changed. At lower waste contents, the
recorded peak of the crystallization process was much lower but wider than the peak
recorded at the highest filler content. The enthalpy change of the crystallization process

Polymers 2022,14, 5335 10 of 13
(∆Hc) was also higher. With the increase in the content of waste, the ∆Hcvalue decreased
by 14.3 J/g, from 95.1 J/g for the P_1_3 sample to 80.8 J/g for the P_2_1 sample. Thus, the
waste content affects the structure and amount of the crystalline phase formed in PP. With
a lower waste content, the formed crystallites are probably larger, and there are more of
them. Changes in the crystallization process are influencing the structure and quantity of
the crystalline phase and obviously translate into the recorded melting process and the
calculated degree of crystallinity. As the filler content increases, the melting point (T
m
) of
the materials slightly decreases. The Tm decrease is approx. 2
◦
C when comparing the
PP sample and the P_2_1 sample. The decrease in the melting enthalpy (
∆
H
m
), and thus
the degree of calculated crystallinity (X
c
), was much more pronounced. The
∆
H
m
value
decreased by 15.6 J/g comparing the PP and P_2_1 sample. Thus, the degree of crystallinity
of the tested materials decreased from 47.7 to 36.2%. All results of DSC are presented
in Table 3.
Table 3. The results of the differential scanning calorimetry (DSC) for individual samples.
Sample Cooling Heating
Tc[◦C] ∆Hc(J/g) Tm(◦C) ∆Hm(J/g) Xc(%)
PP 124.5 97.4 163.7 98.8 47.7
P_1_3 124.8 95.1 163.1 90.8 43.0
P_1_2 119.0 80.1 161.5 85.6 40.3
P_1_1 119.0 81.8 161.5 83.1 38.1
P_2_1 118.4 80.8 161.4 83.2 36.2
After introducing the post-printing waste into the polymer matrix, changes in the
thermal resistance of the obtained materials were observed. Figure 9shows the ther-
mogravimetric curves of selected samples, while Table 4summarizes the results of the
determined thermal parameters.
Polymers 2022, 14, x FOR PEER REVIEW 11 of 14
Table 3. The results of the differential scanning calorimetry (DSC) for individual samples.
Sample Cooling Heating
Tc [°C] ΔHc (J/g) Tm (°C) ΔHm (J/g) Xc (%)
PP 124.5 97.4 163.7 98.8 47.7
P_1_3 124.8 95.1 163.1 90.8 43.0
P_1_2 119.0 80.1 161.5 85.6 40.3
P_1_1 119.0 81.8 161.5 83.1 38.1
P_2_1 118.4 80.8 161.4 83.2 36.2
After introducing the post-printing waste into the polymer matrix, changes in the
thermal resistance of the obtained materials were observed. Figure 9 shows the thermo-
gravimetric curves of selected samples, while Table 4 summarizes the results of the deter-
mined thermal parameters.
Figure 9. TG (solid line) and DTG (dashed line) curves of selected samples.
Table 4. The results of the thermogravimetric analysis (TG) of individual samples.
Sample T5% (°C) T50% (°C) T95% (°C) Tmax1 (°C) Tmax2 (°C)
PP 347.5 409.1 434.8 - 423.9
P_1_3 344.8 440.5 465.4 353.6 450.1
P_1_2 343.9 450.1 473.6 354.0 455.4
P_1_1 340.0 440.7 467.9 356.5 450.8
P_2_1 330.6 451.5 476.6 353.2 458.3
As shown in Figure 9, the introduction of post-printing waste into the polymer matrix
changes the nature of the degradation process from a one-stage (PP sample) to a two-stage
(samples with waste). After introducing the filler, an additional degradation step appears
in the range from 320 to 380 °C with the maximum decomposition rate (Tmax1) at approx.
355 °C, which becomes more significant the higher the content of waste in the polymer
matrix.
Figure 9. TG (solid line) and DTG (dashed line) curves of selected samples.
As shown in Figure 9, the introduction of post-printing waste into the polymer matrix
changes the nature of the degradation process from a one-stage (PP sample) to a two-
stage (samples with waste). After introducing the filler, an additional degradation step
appears in the range from 320 to 380
◦
C with the maximum decomposition rate (T
max1
)

Polymers 2022,14, 5335 11 of 13
at approx.
355 ◦C
, which becomes more significant the higher the content of waste in the
polymer matrix.
Table 4. The results of the thermogravimetric analysis (TG) of individual samples.
Sample T5% (◦C) T50% (◦C) T95% (◦C) Tmax1 (◦C) Tmax2 (◦C)
PP 347.5 409.1 434.8 - 423.9
P_1_3 344.8 440.5 465.4 353.6 450.1
P_1_2 343.9 450.1 473.6 354.0 455.4
P_1_1 340.0 440.7 467.9 356.5 450.8
P_2_1 330.6 451.5 476.6 353.2 458.3
The occurrence of an additional degradation stage indirectly contributes to the reduc-
tion in the thermal resistance of materials containing waste, which is determined based
on the 5% loss temperature of the sample mass (T
5%
). The thermal resistance of materials
dropped from 347.5
◦
C for a PP sample to 344.8
◦
C for the P_1_3 sample and 330.6
◦
C for
the P_2_1 sample. Therefore, the decrease in thermal resistance depended on the amount
of filler in the polymer matrix. With the lowest post-printing waste content, the decrease in
thermal resistance was insignificant: less than 3
◦
C. Increasing the waste content causes
a significant reduction in thermal resistance, as the recorded value of T
5%
decreased by
17
◦
C in relation to the value of pure polymer. The reduction in the recorded T
5%
value
is caused by the overlapping of the maximum waste degradation rate at the beginning
of the matrix degradation, so the higher the content of the filler, the sooner the loss of 5%
of the sample weight was achieved and the contractual thermal resistance of the material
changed. Regardless of the thermal resistance of the tested materials, their degradation
temperature significantly exceeded the typical temperatures of the use of polymer materials,
and therefore, developed materials can be successfully used in most typical applications.
4. Conclusions
Based on the conducted research, the following can be concluded:
•
The total decrease in the melt flow rate after adding the greatest amount of
filler, i.e., twice
the volume excess of filler, was 2.2 g/10 min, which is 20% of the value of
pure polypropylene.
•
The greatest decrease in the tensile strength of polypropylene after adding the post-
printing waste was 4.5 MPa, i.e., approx. 19% of the value of pure polymer. This result
was obtained with the highest degree of filling of the composite.
•
The obtained deformation drop was the same regardless of the volumetric content
of the filler in the matrix. The applied post-printing waste reduces the elongation at
maximum stress and elongation at break values to the level of approx. 5%, while the
values for pure polypropylene were 8.1 and 35.9%, respectively.
•
The total decrease in unnotched impact strength between the lowest and the highest
content of post-printing waste was 6.4 kJ/m2, i.e., approx. 22%.
•
The introduction of post-printing waste into the polypropylene matrix did not change
the thermomechanical characteristics of the polymer.
•
The degree of crystallinity of the tested materials decreased from 47.7% for pure
polypropylene to 36.2% for the material containing a double excess of printing waste.
•
The introduction of the post-printing waste into the matrix causes a reduction in
thermal resistance, as the registered value of the 5% weight loss temperature decreased
by 17 ◦C in relation to the value of pure polypropylene.
Thus, the introduction of post-printing waste causes the deterioration of the character-
istics of the obtained materials, but the decrease is fully acceptable in terms of the planned
applications of the new composites. It should be remembered that the main purpose of the
research described in the article was to eliminate post-production waste generated during
the production of labels, which was achieved by using them as a filler for the polymer.
Better properties of composites containing printing waste could probably be obtained after
prior modification of the waste, so this will be the subject of further research.

Polymers 2022,14, 5335 12 of 13
Author Contributions:
Conceptualization, K.M. and M.Z.; methodology, K.M. and T.K.; validation,
K.M.; formal analysis, K.M.; investigation, T.K., A.S., B.B. and K.S.; resources, K.M. and M.Z.; data
curation, K.M., T.K., A.S. and B.B.; writing—original draft preparation, K.M.; writing—review and
editing, K.M. and K.S.; visualization, K.M., A.S. and B.B.; supervision, K.M. All authors have read
and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Das, O.; Babu, K.; Shanmugam, V.; Sykam, K.; Tebyetekerwa, M.; Neisiany, R.E.; Försth, M.; Sas, G.; Gonzalez-Libreros, J.;
Capezza, A.J.; et al. Natural and Industrial Wastes for Sustainable and Renewable Polymer Composites. Renew. Sustain. Energy
Rev. 2022,158, 112054. [CrossRef]
2. Bilitewski, B. The Circular Economy and Its Risks. Waste Manag. 2012,32, 1–2. [CrossRef] [PubMed]
3.
Zhou, Y.; Stanchev, P.; Katsou, E.; Awad, S.; Fan, M. A Circular Economy Use of Recovered Sludge Cellulose in Wood Plastic
Composite Production: Recycling and Eco-Efficiency Assessment. Waste Manag. 2019,99, 42–48. [CrossRef]
4.
Demirbas, A. Waste Management, Waste Resource Facilities and Waste Conversion Processes. Energy Convers. Manag.
2011
,52,
1280–1287. [CrossRef]
5. Amasuomo, E.; Baird, J. The Concept of Waste and Waste Management. J. Manag. Sustain. 2016,6, 88. [CrossRef]
6.
Basalp, D.; Tihminlioglu, F.; Sofuoglu, S.C.; Inal, F.; Sofuoglu, A. Utilization of Municipal Plastic and Wood Waste in Industrial
Manufacturing of Wood Plastic Composites. Waste Biomass Valorization 2020,11, 5419–5430. [CrossRef]
7.
Quitadamo, A.; Massardier, V.; Valente, M. Eco-Friendly Approach and Potential Biodegradable Polymer Matrix for WPC
Composite Materials in Outdoor Application. Int. J. Polym. Sci. 2019,2019, 3894370. [CrossRef]
8.
Teuber, L.; Osburg, V.S.; Toporowski, W.; Militz, H.; Krause, A. Wood Polymer Composites and Their Contribution to Cascading
Utilisation. J. Clean. Prod. 2016,110, 9–15. [CrossRef]
9.
Lewandowski, K.; Piszczek, K.; Zajchowski, S.; Mirowski, J. Rheological Properties of Wood Polymer Composites at High Shear
Rates. Polym. Test. 2016,51, 58–62. [CrossRef]
10.
Wei, L.; McDonald, A.G.; Freitag, C.; Morrell, J.J. Effects of Wood Fiber Esterification on Properties, Weatherability and Biodura-
bility of Wood Plastic Composites. Polym. Degrad. Stab. 2013,98, 1348–1361. [CrossRef]
11.
Friedrich, D. Thermoplastic Moulding of Wood-Polymer Composites (WPC): A Review on Physical and Mechanical Behaviour
under Hot-Pressing Technique. Compos. Struct. 2021,262, 113649. [CrossRef]
12.
Essabir, H.; Hilali, E.; Elgharad, A.; El Minor, H.; Imad, A.; Elamraoui, A.; Al Gaoudi, O. Mechanical and Thermal Properties of
Bio-Composites Based on Polypropylene Reinforced with Nut-Shells of Argan Particles. Mater. Des.
2013
,49, 442–448. [CrossRef]
13.
Laaziz, S.A.; Raji, M.; Hilali, E.; Essabir, H.; Rodrigue, D.; Bouhfid, R.; Qaiss, A.E.K. Bio-Composites Based on Polylactic Acid and
Argan Nut Shell: Production and Properties. Int. J. Biol. Macromol. 2017,104, 30–42. [CrossRef] [PubMed]
14.
Leszczy´nska, M.; Ryszkowska, J.; Szczepkowski, L. Rigid Polyurethane Foam Composites with Nut Shells. Polimery
2020
,65,
728–737. [CrossRef]
15.
Okonkwo, E.G.; Anabaraonye, C.N.; Daniel-Mkpume, C.C.; Egoigwe, S.V.; Okeke, P.E.; Whyte, F.G.; Okoani, A.O. Mechanical
and Thermomechanical Properties of Clay-Bambara Nut Shell Polyester Bio-Composite. Int. J. Adv. Manuf. Technol.
2020
,108,
2483–2496. [CrossRef]
16.
Sun, X.; He, M.; Li, Z. Novel Engineered Wood and Bamboo Composites for Structural Applications: State-of-Art of Manufacturing
Technology and Mechanical Performance Evaluation. Constr. Build. Mater. 2020,249, 118751. [CrossRef]
17.
Lokesh, P.; Surya Kumari, T.S.A.; Gopi, R.; Loganathan, G.B. A Study on Mechanical Properties of Bamboo Fiber Reinforced
Polymer Composite. Mater. Today Proc. 2020,22, 897–903. [CrossRef]
18.
Adediran, A.A.; Akinwande, A.A.; Balogun, O.A.; Olasoju, O.S.; Adesina, O.S. Experimental Evaluation of Bamboo
Fiber/Particulate Coconut Shell Hybrid PVC Composite. Sci. Rep. 2021,11, 5465. [CrossRef]
19.
Mousavi, S.R.; Zamani, M.H.; Estaji, S.; Tayouri, M.I.; Arjmand, M.; Jafari, S.H.; Nouranian, S.; Khonakdar, H.A. Mechanical
Properties of Bamboo Fiber-Reinforced Polymer Composites: A Review of Recent Case Studies. J. Mater. Sci.
2022
,57, 3143–3167.
[CrossRef]
20.
Agunsoye, J.O.; Isaac, T.S.; Samuel, S.O. Study of Mechanical Behaviour of Coconut Shell Reinforced Polymer Matrix Composite.
J. Miner. Mater. Charact. Eng. 2012,11, 774–779.
21.
Agunsoye, J.O.; Odumosu, A.K.; Dada, O. Novel Epoxy-Carbonized Coconut Shell Nanoparticles Composites for Car Bumper
Application. Int. J. Adv. Manuf. Technol. 2019,102, 893–899. [CrossRef]
22.
Nadzri, S.N.I.H.A.; Sultan, M.T.H.; Shah, A.U.M.; Safri, S.N.A.; Talib, A.R.A.; Jawaid, M.; Basri, A.A. A Comprehensive Review
of Coconut Shell Powder Composites: Preparation, Processing, and Characterization. J. Thermoplast. Compos. Mater.
2020
,35,
2641–2664. [CrossRef]

Polymers 2022,14, 5335 13 of 13
23.
Obasi, H.C.; Mark, U.C.; Mark, U. Improving the Mechanical Properties of Polypropylene Composites with Coconut Shell
Particles. Compos. Adv. Mater. 2021,30, 263498332110074. [CrossRef]
24.
Sundarababu, J.; Anandan, S.S.; Griskevicius, P. Evaluation of Mechanical Properties of Biodegradable Coconut Shell/Rice Husk
Powder Polymer Composites for Light Weight Applications. Mater. Today Proc. 2021,39, 1241–1247. [CrossRef]
25.
Bledzki, A.K.; Mamun, A.A.; Volk, J. Physical, Chemical and Surface Properties of Wheat Husk, Rye Husk and Soft Wood and
Their Polypropylene Composites. Compos. Part A Appl. Sci. Manuf. 2010,41, 480–488. [CrossRef]
26.
Arjmandi, R.; Hassan, A.; Majeed, K.; Zakaria, Z. Rice Husk Filled Polymer Composites. Int. J. Polym. Sci.
2015
,2015, 501471.
[CrossRef]
27.
Muthuraj, R.; Lacoste, C.; Lacroix, P.; Bergeret, A. Sustainable Thermal Insulation Biocomposites from Rice Husk, Wheat Husk,
Wood Fibers and Textile Waste Fibers: Elaboration and Performances Evaluation. Ind. Crops Prod.
2019
,135, 238–245. [CrossRef]
28.
Bisht, N.; Gope, P.C.; Rani, N. Rice Husk as a Fibre in Composites: A Review. J. Mech. Behav. Mater.
2020
,29, 147–162. [CrossRef]
29.
Suhot, M.A.; Hassan, M.Z.; Aziz, S.A.; Md Daud, M.Y. Recent Progress of Rice Husk Reinforced Polymer Composites: A Review.
Polymer 2021,13, 2391. [CrossRef]
30.
Wilpiszewska, K.; Antosik, A.K. Effect of Grain Husk Microfibers on Physicochemical Properties of Carboxymethyl
Polysaccharides-Based Composite. J. Polym. Environ. 2022,30, 3129–3138. [CrossRef]
31.
Berger, C.; Mattos, B.D.; Amico, S.C.; de Farias, J.A.; Coldebella, R.; Gatto, D.A.; Missio, A.L. Production of Sustainable Polymeric
Composites Using Grape Pomace Biomass. Biomass Convers. Biorefinery 2020,12, 5869–5880. [CrossRef]
32.
Morinaga, H.; Haibara, S.; Ashizawa, S. Reinforcement of Bio-Based Network Polymer with Wine Pomace. Polym. Compos.
2021
,
42, 2973–2981. [CrossRef]
33.
Aljnaid, M.; Banat, R. Effect of Coupling Agents on the Olive Pomace-Filled Polypropylene Composite. E Polym.
2021
,21, 377–390.
[CrossRef]
34.
Mirowski, J.; Oliwa, R.; Oleksy, M.; Tomaszewska, J.; Ryszkowska, J.; Budzik, G. Poly(Vinyl Chloride) Composites with Raspberry
Pomace Filler. Polymer 2021,13, 1079. [CrossRef]
35.
Hiremath, P.; Shettar, M.; Shankar, M.C.G.; Mohan, N.S. Investigation on Effect of Egg Shell Powder on Mechanical Properties of
GFRP Composites. Mater. Today Proc. 2018,5, 3014–3018. [CrossRef]
36.
Owuamanam, S.; Cree, D. Progress of Bio-Calcium Carbonate Waste Eggshell and Seashell Fillers in Polymer Composites: A
Review. J. Compos. Sci. 2020,4, 70. [CrossRef]
37.
Sakthi Balan, G.; Santhosh Kumar, V.; Rajaram, S.; Ravichandran Ramakrishnan, M.K. Investigation on Water Absorption and
Wear Characteristics of Waste Plastics and Seashell Powder Reinforced Polymer Composite. J. Tribol. 2020,27, 57–70.
38.
Vasanthkumar, P.; Balasundaram, R.; Senthilkumar, N.; Palanikumar, K.; Lenin, K.; Deepanraj, B. Thermal and Thermo-Mechanical
Studies on Seashell Incorporated Nylon-6 Polymer Composites. J. Mater. Res. Technol. 2022,21, 3154–3168. [CrossRef]
39.
Hayta, P.; Oktav, M. The Importance of Waste and Environment Management in Printing Industry. Eur. J. Eng. Nat. Sci.
2019
,3, 18–26.
40.
Carlos Alberto, P.J.; Sonia Karina, P.J.; Francisca Irene, S.A.; Adrielly Nahomee, R.Á. Waste Reduction in Printing Process by
Implementing a Video Inspection System as a Human Machine Interface. Procedia Comput. Sci. 2021,180, 79–85. [CrossRef]
41.
Medeiros, D.L.; Braghirolli, F.L.; Ramlow, H.; Ferri, G.N.; Kiperstok, A. Environmental Improvement in the Printing Industry:
The Case Study of Self-Adhesive Labels. Environ. Sci. Pollut. Res. 2019,26, 13195–13209. [CrossRef] [PubMed]
42.
Lanyi, F.J.; Wenzke, N.; Kaschta, J.; Schubert, D.W. On the Determination of the Enthalpy of Fusion of
α
-Crystalline Isotactic
Polypropylene Using Differential Scanning Calorimetry, X-Ray Diffraction, and Fourier-Transform Infrared Spectroscopy: An
Old Story Revisited. Adv. Eng. Mater. 2020,22, 1900796. [CrossRef]