Journal of Thermal Analysis and Calorimetry
https://doi.org/10.1007/s10973-019-08883-5
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Thermoanalytical tests (TG–DTG–DSC, Py-GC/MS) of foundry binders
on the example of polymer composition of poly(acrylic acid)–sodium
carboxymethylcellulose
1 •
_
Beata Grabowska1 • Sylwia Zymankowska-Kumon
Sylwia Cukrowicz1 • Karolina Kaczmarska1
1 •
2
Artur Bobrowski Bo_zena Tyliszczak
•
Received: 19 November 2018 / Accepted: 1 October 2019
The Author(s) 2019
Abstract
The results of thermal analysis (TG–DTG–DSC) of a foundry binder from the BioCo group in the form of a polymer
composition of poly(acrylic acid)–sodium carboxymethylcellulose (PAA/CMC-Na) are presented in this article. The range
of temperature of degradation has been determined. It was found that as the temperature rises, physical and chemical
changes take place in the binder as a result of evaporation of solvent water, release of constitutional water, intermolecular
dehydration reactions and decomposition of polymer chains with the formation of gaseous decomposition products.
Pyrolysis gas chromatography mass spectrometry method (Py-GC/MS) was used to identify PAA/CMC-Na binder
degradation products in a predetermined temperature range based on the previously performed thermal analysis of TG–
DTG–DSC. Py-GC/MS tests were also carried out to determine the emission level of gaseous products of the polymeric
binder in the context of the processes occurring in the moulding (foundry) sand, in conditions of its contact with liquid
metal. In addition, Py-GC/MS tests were carried out for two commonly used foundry binders based on alkaline phenolic
resin cured with esters and based on urea-formaldehyde resin with furfuryl alcohol cured with sulphonic acids. The
obtained Py-GC/MS results for commercial binders were referred to the results obtained for the new PAA/CMC-Na binder.
It was found that the new polymer binder is characterized by the lowest emission level of gaseous products.
Keywords Polymer binders Foundry sands Thermal degradation TG–DTG–DSC Py-GC/MS
Introduction
At present, one of the largest groups of foundry sands used
for the production of moulds and cores is the moulding
sands based on the mineral matrix and bonded with
organic binders in the form of synthetic resins. Resins are
mixtures of synthetic monomers and polymers with a
relatively small degree of polymerization, linear or
& Beata Grabowska
beata.grabowska@agh.edu.pl
1
Faculty of Foundry Engineering, AGH University of Science
and Technology, Reymonta 23, 30 059 Kraków, Poland
2
Department of Chemistry and Technology of Polymers,
Faculty of Chemical Engineering and Technology, Cracow
University of Technology, Warszawska 24, 31-155 Kraków,
Poland
branched, in which the composition usually contains
phenyl (aromatic) groups. The most commonly used
foundry sands bonded with synthetic resins include
moulding sands with organic resins, among others phenolic, furfuryl, phenol-formaldehyde (generally mixture of
them) or alkyd resins [1, 2]. The process of cross-linking
organic binders in moulding sand is usually carried out at
room temperature. At the same time, this process is often
aided by the blowing through the binder system of gaseous
substances, including SO2 or CO2 and amines. This type of
cross-linking has a positive effect on many moulding sand
properties, including to increase the bonding rate in the
binder matrix system, as well as to reduce energy consumption. On the other hand, the use of synthetic resins is
associated with their negative impact on the environment
like the presence of harmful organic compounds in their
composition or using SO2 or toxic amines in the curing
process. In addition, during pouring the mould with a
123
B. Grabowska et al.
liquid metal, harmful products of thermal decomposition
of binders are emitted to the atmosphere [2–9].
In foundry process, as organic binders for moulding
sands and cores are mainly used polymer binders, which,
unlike synthetic resins, contain only synthetic, natural or
modified polymers dissolved in a suitably selected solvent.
Among the synthetic polymers used in foundries are,
among others, polystyrene, polyacrylates and polyurethanes. In the literature, one can find works focusing on
the development of adhesives and casting processes using
natural polymers, as well as polymers from the so-called
renewable sources (including from biomass) [9–13].
At present, in the country and around the world, research
is being carried out to obtain binders composed of materials derived from natural, often renewable sources, which
is associated with a reduction in production costs, while
maintaining good-quality castings. The activities are carried out to create new binders that are environmentally
friendly in their original form and do not generate harmful
substances in the technological process. It is important to
minimize the emission of gaseous products of thermal
decomposition during the pouring process of liquid metal
[14–18].
Thermal degradation of polymeric materials is a complicated process running in a heterophasic system. Therefore, the choice of the analytical method and determination
of measurement conditions is important in the context of
the analysis of gaseous products generated during the
thermal decomposition process. The control and identification of emissions of gaseous products is also important
for environmental reasons, as harmful substances are
released on an industrial scale, including CO, SO2, H2S,
aromatic hydrocarbons or dioxins. In order to determine the
emission level of gaseous products, numerous research
works are carried out using thermoanalytical methods,
including coupled methods that combine spectral (MS, IR,
Raman) with thermal (TG-DSC) methods. Thermoanalytical techniques enable the combination of thermal analysis
methods and analysis of evolved gaseous products using a
mass spectrometer (MS) or an infrared spectrometer (IR) in
a single measurement [19–23].
Synthetic resins, solvents and organic hardeners used in
moulding sands and cores constitute the main source of
harmful compounds emission. Emission may occur already
at the stage of moulding sand preparation, while volatile
organic components, mainly solvents, are released. However, the largest amount of gaseous substances is formed
during the contact of the moulding sand with the liquid
metal, when under the influence of high temperature thermal destruction of its organic components occurs [24].
The level of gas emissions from moulding sands
becomes important in respect of maintaining the safety of
work in the foundry, as well as having the final impact on
123
the quality of the casting. Foundry technologies using
organic components containing phenyl, amine or sulphur
groups in their structure are potentially harmful. The effect
on the human body of released amines during the hardening of moulding sands or aromatic hydrocarbons generated
during the destruction of the organic components is not
indifferent. In addition, the technological and economic
aspect should be taken into account, as the gases emitted
during the destruction may enter undesirable reactions at
the mould–cast interface, which is the reason for many
defects of castings, including deterioration of the quality of
their surface [25–29].
The research team has been carrying out analytical work
for several years, including qualitative and quantitative
analysis of gaseous products emitted during the technological process, including the process of pouring the mould
with a liquid metal. The measurement method developed in
this area using spectral techniques allows to determine the
quantity and kinetics of emission of gases emitted, as well
as qualitative and quantitative analysis of aromatic
hydrocarbons: benzene, toluene, ethylbenzene and xylenes
(BTEX) during the pouring process [30]. The research also
uses a pyrolysis gas chromatography coupled with mass
spectrometry (Py-GC/MS) method to determine the emission level of gaseous substances released in the technological process [31–34].
This paper presents the results of a thermoanalytic cycle
research using the thermal methods (TG–DTG–DSC) and
pyrolysis gas chromatography coupled with mass spectrometry (Py-GC/MS). The research was aimed at completing the knowledge of the thermal degradation process
of a new group of BioCo polymer binders in a given
temperature range and at the same time determine the
emission level of gaseous substances released during the
destruction process. A new polymeric binder from the
BioCo group [13, 34–38] was tested, which contained two
dissolved in water polymers: poly(acrylic acid) and sodium
carboxymethylcellulose. In addition, Py-GC/MS tests were
carried out for two popular and commercial binders used in
the foundry industry based on alkaline phenolic resin cured
with esters and urea-formaldehyde resin with furfuryl
alcohol cured with sulphonic acids. Before the binders
were sent for testing, they were subjected to a hardening
process, because in their hardened form they are degraded
in real conditions, i.e. in contact with liquid metal.
Experimental
Materials
For the research were used three different binders used in
foundry process (with one of innovative and
Thermoanalytical tests (TG–DTG–DSC, Py-GC/MS) of foundry binders on the example of polymer…
Fig. 1 Samples used in this study: a PAA/CMC-Na, b ARR, c UFR
Table 1 Characteristics of compositions and their cross-linking
parameters
Table 2 Characterization of components of binders alkaline resol
resin and urea-formaldehyde resin
Composition components
Hardening conditions
Parameters
60% aqueous solution of poly(acrylic
acid) (PAA, 100 000 g mol-1,
BASF) and cellulose (CMC-Na,
modified cellulose), in a mass ratio
7:8, pH 2
Microwave device: RM 2001
Pc, Plazmatronica
R
ARR
UFR
Density in 20 C/g cm-3
1.55–1.65
1.20–1.30
Microwave power of 800 W
Viscosity/CST
15–25
50–150
Frequency of 2.45 GHz
Microwave action time: 60 s
Formaldehyde/%
0.12–0.14
\ 0.2
Nitrogen/%
3–4
–
Temperature inside the
device: 100 C
Gelation time in 20 C/min
7–12
11–14
H
Density in 20 C/g cm-3
1.22–1.24
1.09–1.28
environmentally friendly). The samples were prepared in
accordance with the manufacturer/inventor’s guidelines
and according to the appropriate proportions:
1. Polymer composition of poly(acrylic acid)–sodium
carboxymethylcellulose (PAA/CMC-Na) (Fig. 1a).
Their characterization and cross-linking condition
PAA/CMC-Na is provided in Table 1.
2. Alkaline resol resin (ARR)—alkaline resol type phenolic resin ‘‘R’’ (33–50% of phenol), liquid binder
cured with esters; hardener (activator) ‘‘H’’—mixture
of organic esters, liquid with a slight characteristic
odour and medium curing time (Fig. 1b); proportion of
mixture H:R = 1:5.
3. Urea-formaldehyde resin (UFR)—urea-formaldehyde
resin ‘‘R’’ modified by furfuryl alcohol (content of a
furfuryl alcohol is about 80%); hardened by mixture of
sulphonic acid and inorganic acid (Fig. 1c); proportion
of mixture H:R = 1:2.
The most important parameters of binders alkaline resol
resin and urea-formaldehyde resin are presented in Table 2.
Thermal examinations
The thermal examinations were carried out using a Netzsch
STA 449 F3 Jupiter thermal analyser which supports
simultaneous TG and DSC measurements, thus providing
two independent signals recorded in the same measurement
conditions, namely at/in the same temperature increase rate
(10 C min-1) and atmosphere and gas flow rate
(50 mL min-1). The measurements for the sample were
taken in an oxygen-free one (nitrogen). The sample submitted to the TG-DSC thermal analysis weighed approximately 15 mg. Crucibles with Al2O3 were used, as they
allowed measurements up to 1000 C.
Pyrolysis gas chromatography coupled with mass
spectrometry
The pyrolysis gas chromatography mass spectrometry (PyGC/MS) method is based on transforming a solid sample
(4 mg) into gas by heating in an atmosphere of inert gas
(helium) in a pyrolyzer ‘‘Py’’ (Pyroprobe 5000, CDS
Analytical Inc., USA), which is accompanied by thermal
decomposition. It has a platinum ribbon, which enables
heating of a sample to any temperature within the range
240–1300 C at a rate of up to 10,000 C s-1. The
obtained mixture of compounds (pyrolysate) is separated
on a chromatographic column (Rxi-5Sil MS columns,
fused silica with low-polarity phase: Crossbond 1,4bis(dimethylsiloxy)phenylene dimethyl polysiloxane,
123
B. Grabowska et al.
As the temperature rises, physical and chemical changes
occur due to evaporation of the solvent water (20–100 C)
and then of the structural water, and then intermolecular
dehydration reactions (100–260 C). Within this temperature range, mainly reversible processes occur. In the temperature range of 260–360 C, polymer chains decompose,
including the disintegration of side groups and glycoside
bonds (from CMC-Na). In the temperature range of
360–700 C, the polymer compositions decompose with
the formation of gaseous products of destruction. The part
of moulding sand which has not decomposed to about
900 C may contain carbonized carbon. Based on the
thermal analysis of TG–DTG–DSC for PAA/CMC-Na, the
temperature range (450 C, 700 C, 800 C) for Py-GC/
MS method was determined for all tested binders.
Restek Corporation, USA) in a chromatograph ‘‘GC’’
(Focus GC, Thermo Scientific, USA). A temperature programme was applied: an initial temperature of 40 C was
held for 3 min; ramped 3 C min-1 up to 100 C and held
for 3 min, and then 250 C with heating rate 20 C min-1
was maintained for 3 min. Carrier gas (helium) flow rate
was 1 mL min-1 and sample split ratio was 1:30. The
separated compounds are analysed in a mass spectrometer
‘‘MS’’ (ISQ Thermo Scientific, USA) in the full range m/z.
Electron ionization (70 eV) at a temperature of 250 C was
applied [36].
Results and discussion
TG–DTG–DSC analysis
Py-GC/MS analysis
Figure 2 depicts the temperature-dependent mass change
(TG), rate of mass change (DTG) and heat flow rate (DSC)
of the polymer mixture PAA/CMC-Na. In total, five mass
loss steps of 7.37%, 24.03%, 8.87%, 34.35% and 10.28%
were observed. The maximal mass loss rates were obtained
for the temperatures 138.8 C, 260.6 C, 360.8 C,
422.4 C and 726.2 C which can be seen from the DTG
signal. In correlation with the mass loss steps, different
energetic effects occurred in the DSC signal. Three overlapping endothermic effects with peak temperatures of
151.3 C, 253.0 C, 621.9 C and 729 C occurred. The
fourth mass loss step correlated with an exothermic peak at
413.7 C and 492.7 C.
160
3.5
exo
0
360.8 °C
140
726.2 °C
138.8 °C
DTG
3.0
120
–5
260.6 °C
TG/%
40
2.0
– 24.03%
80
60
422.4 °C
– 7.37%
– 8.87%
253.0 °C
151.3 °C
1.5
– 34.35%
20
– 10.28%
1.0
TG
0.5
621.9 °C
– 10
DSC/mW min–1
100
2.5
– 15
– 20
0
729.0 °C
492.7 °C
– 20
0.0
DSC
413.7 °C
– 25
– 0.5
– 40
– 30
150
300
450
600
Temperature/°C
123
750
900
DTG/% min–1
Fig. 2 TG–DTG–DSC curves
of PAA/CMC-Na composition
Compounds found after pyrolytic decomposition for all
studied samples: PAA/CMS-Na, ARR and UFR, are summarized in Tables 3–5. The comparison of the measured
mass spectra to the National Institute of Standards Technology database (NIST MS Search 2.0) and own patterns
(e.g. benzene, toluene) gave possible types for the released
compounds. For some peaks, structural similar compounds
(e.g. structural isomers) were found with high quality of
probability. Some pyrolysis products which occupy large
peak areas in the Py-GC/MS chromatograms (pyrogram,
replaceable name) cannot be identified clearly because of
the low matching quality in mass library. Resulting products are not decomposed under mild conditions of pyrolysis
Thermoanalytical tests (TG–DTG–DSC, Py-GC/MS) of foundry binders on the example of polymer…
(from 250 to about 400 C); therefore, exemplary chromatograms (pyrograms) in the selected temperature range:
450 C, 700 C and 800 C, are shown in Figs. 3–5.
Table 3 Compounds in the
pyrogram of sample PAA/
CMC-Na for selected
temperature points/areas
Peak no.
Name of compound
The strongest signal in the pyrogram of all tested samples is that corresponding to carbon dioxide emission (full
range of temperature, Figs. 3–5). Sample ARR at 700 C
No. CAS
Mass weight/u
Retention time RT/min
250–650 C
700 C
750 C
800 C
1.
Carbon dioxide
124-38-9
44
2–5
2.13
2.14
2.14
2.
3-Methylfuran
930-27-8
82
–
–
3.50
3.46
3.
Butan-2-one
78-93-3
72
–
3.81
3.83
3.75
4.
Benzene
71-43-2
78
–
–
4.60
4.60
5.
Toluene
108-88-3
92
–
–
7.53
7.46
Table 4 Compounds in the pyrogram of sample ARR for selected temperature points/areas
Peak no.
Name of compound
No. CAS
Retention time RT/min
Mass weight/u
250–450 C
500–600 C
650–700 C
750 C
800 C
1.
Carbon dioxide
124-38-9
44
1.7–2.14
2.10
2.09
2.11
2.10
2.
2-Methylfuran
534-22-5
82
–
–
3.38
3.38
3.34
3.
Benzene
71-43-2
78
–
4.55
4.55
4.52
–
4.
Toluene
108-88-3
92
–
7.46
7.40
7.43
7.32
5.
Ethylbenzene
100-41-4
106
–
11.49
11.49
11.49
–
6.
m-Xylene
108-38-3
106
–
11.63
11.66
11.64
–
7.
8.
Phenol
Styrene
108-95-2
100-42-5
94
104
–
–
13.45
13.62
13.51
13.68
13.51
13.66
–
–
9.
Indene
95-13-6
116
–
22.53
22.60
–
–
10.
Naphthalene
91-20-3
128
–
28.99
29.03
–
–
11.
Benzo[c]thiophene
270-82-6
134
–
29,42
29.45
–
–
Table 5 Compounds in the pyrogram of sample UFR for selected temperature points/areas
Peak no.
Name of compound
No. CAS
Mass weight/u
Retention time RT/min
250–400 C
450 C
500–600 C
650–700 C
750 C
800 C
1.
Carbon dioxide
124-38-9
44
1.5–2.5
2.11
2.10
2.10
2.09
2.11
2.
Hydrogen sulphide
7783-06-4
34
–
–
2.19
2.17
2.18
–
3.
Carbon disulphide
75-15-0
76
–
–
2.89
2.90
2.92
–
4.
2-Methylfuran
534-22-5
82
–
3.39
3.38
3.38
3.38
3.34
5.
Benzene
71-43-2
78
–
–
4.55
4.54
4.52
–
6.
Toluene
108-88-3
92
–
7.41
7.45
7.44
7.43
7.32
7.
8.
Ethylbenzene
m-Xylene
100-41-4
108-38-3
106
106
–
–
–
–
11.46
11.63
11.50
11.65
11.49
11.64
–
11.59
9.
Phenylethyne
536-74-3
102
–
–
13.45
13.52
–
–
10.
Styrene
100-42-5
104
–
–
13.61
13.67
13.64
–
11.
Indene
95-13-6
116
–
–
22.53
22.60
–
–
12.
Naphthalene
91-20-3
128
–
–
28.98
29.05
–
–
13.
Benzo[c]thiophene
270-82-6
134
–
–
29.42
29.45
–
–
14.
Biphenyl
92-52-4
154
–
–
31.60
–
–
–
15.
Acenaphthylene
208-96-8
152
–
–
32.47
–
–
–
16.
Bibenzyl
103-29-7
182
–
–
–
32.70
32.69
–
Thermal degradation products of chromatographic column
123
B. Grabowska et al.
44
1 100
100
Carbon dioxide
450 °C
Intensity/%
1
80
60
80
60
40
20
0
40
0
100
2 100
Intensity/%
20
0
700 °C
1
100
40
0
8
3
6
100
3 100
200
300
Mass/m z–1
0
–2
–4
3
4
5
6
Retention time/min
7
8
Butan-2-one
80
60
40
72
20
20
0
0
100
0
200
300
Mass/m z–1
800 °C
Intensity/%
4 100
100
10
8
60
Intensity/%
80
1
6
2 3
4
5
60
20
0
0
5
6
Retention time/min
7
0
3
4
5
6
Retention time/min
7
0
100
200
300
Mass/m z–1
8
400
Toluene
5 100
8
Intensity/%
4
20
2
78
40
2
3
1
Benzene
4
–4
0
400
80
–2
40
400
4
Intensity/%
Intensity/%
Intensity/%
82
60
0
2
40
3-Methylfuran
80
10
60
400
20
14
12
80
200
300
Mass/m z–1
80
60
40
92
20
0
0
100
300
200
Mass/m z–1
400
Fig. 3 Pyrograms of sample PAA/CMC-Na in full range of temperature: 450 C, 700 C, 800 C
observed new small signal from butan-2-one. At the temperature range of 750–800 C, other new signals correspond to 3-methylfuran, benzene and toluene (Fig. 3).
Observed signals (except carbon dioxide) are quite weak,
and as a result of pyrolysis, very few compounds are
released from the sample (Table 3).
123
In the pyrograms (Figs. 4, 5) of samples, ARR and UFR
are more expanded. Among those identified pyrolysis
compounds of samples ARR and UFR, the main signals
correspond to large group of aromatic hydrocarbons from
groups BTEX and PAH (polycyclic aromatic
hydrocarbons).
Thermoanalytical tests (TG–DTG–DSC, Py-GC/MS) of foundry binders on the example of polymer…
450 °C
*
100
44
1 100
Intensity/%
80
60
40
1
Carbon dioxide
80
60
40
20
20
0
0
100
0
92
4100
25
80
*
11
20
1
Intensity/%
Intensity/%
100
Intensity/%
700 °C
10
15
10
80
60
40
0
100
0
100
10100
40
Intensity/%
21 22 23 24 25 26 27 28 29 30 31
Retention time/min
20
0
80
60
40
20
800 °C
6
0
*
1
4
2
0
–2
6.0
20
6.5
8.0
7.0
7.5
Retention time/min
5
10
15
20
200
300
Mass/m z–1
400
Benzo[c]thiophene
80
60
40
20
8.5
0
0
0
134
11100
Intensity/%
Intensity/%
4
40
400
200
300
Mass/m z–1
128
Naphthalene
0
–5
60
Toluene
20
0
80
400
5
60
100
200
300
Mass/m z–1
25
0
100
200
300
Mass/m z–1
400
30
Retention time/min
Fig. 4 Pyrograms of sample ARR in full range of temperature: 450 C, 700 C, 800 C
The decomposition of sample ARR released mainly
aromatic hydrocarbons like benzene, phenol and their
derivatives and the low-volatile compounds (Table 4). In
the temperature range from 250 to 450 C, no significant
changes are observed. The temperature range 500–700 C
observed a lot of signals from aromatic hydrocarbons group
(Fig. 4). The highest signal is from benzene and toluene.
Other signals correspond to 2-methylfuran, ethylbenzene,
m-xylene, phenol (main compound of sample ARR), styrene, indene, naphthalene and benzo[c]thiophene. At
800 C, most of signals disappeared. (It may be related to
their total degradation.) The compounds identified in this
sample are connected to chemical composition of thermal
decomposition of resole resin [32].
The comparison of the pyrograms samples ARR and
UFR did not give significant difference in aromatic
123
B. Grabowska et al.
44
*
100
80
Intensity/%
1 100
450 °C
Carbon dioxide
80
60
40
20
60
0
40
100
200
300
Mass/m z–1
8 100
Intensity/%
1
20
0
1
60
20
15
8 9
60
106
40
10
11
0
40
12
15
18
21
24
27
30
102
Intensity/%
800 °C
Intensity/%
10
5
8
40
0
100
116
10
11
12
Retention time/min
13
Intensity/%
9
20
0
400
Indane
60
40
0
100
15
100
1
200
300
Mass/m z–1
80
0
–5
40
Phenylethyne
20
*
0
60
400
60
11
100
80
200
300
Mass/m z–1
80
0
0
100
100
20
33
Retention time/min
20
0
9 100
Intensity/%
Intensity/%
*
80
m-Xylene
80
0
30
100
400
20
700 °C
Intensity/%
0
200
300
Mass/m z–1
400
Bibenzyl
80
60
40
182
20
0
5
10
15
20
25
30
Retention time/min
0
0
100
200
300
Mass/m z–1
400
Fig. 5 Pyrograms of sample UFR in full range of temperature: 450 C, 700 C, 800 C
hydrocarbons area, probably only in concentration of
released compound (Table 5). The temperature range
500–700 C observed a lot of signals from aromatic
hydrocarbons group (Fig. 5) and also compounds like
hydrogen sulphide carbon disulphide (component of sample UFR, hardener for resin). The highest signal is from
benzene and toluene like in sample ARR. Other signals
correspond to similar compounds from sample ARR
123
2-methylfuran, ethylbenzene, m-xylene, styrene, indene,
naphthalene and benzo[c]thiophene. A few new ones are
also identificated—phenylethyne, biphenyl, acenaphtylene
and bibenzyl. At 750 C and 800 C, most of signals disappeared. Only toluene, 2-methylfuran, m-xylene are
visible.
Py-GC/MS was found to be appropriate method for
assessment of changes taking place during pyrolysis of
Thermoanalytical tests (TG–DTG–DSC, Py-GC/MS) of foundry binders on the example of polymer…
tested samples of foundry binders. Results indicate that
during the pyrolysis process only one of these samples is
friendly to environment (PAA/CMC-Na). The changes in
type and emission of these compounds in samples ARR
and UFR are small. The presented results of the Py-GC/MS
measurements show that the applied analytic methods are
feasible to perform only a qualitative characterization of
the binder samples (due to the construction of pyrolyzer).
In the temperature range up to 450–500 C, mainly carbon
dioxide emissions are observed, related to the decomposition of carbonates (components of tested samples). At the
temperature above 500 C, secreted compounds are mainly
volatile aromatics from BTEX and PAH groups or phenol
(component of sample ARR). Most of these compounds
belongs to group of high risk and pose a threat to humans
and the environment. The highest concentration of hazardous and dangerous substances in gas form occurs during
the mould pouring with liquid metal (mainly cast iron).
Gases emitted to the atmosphere should be neutralized (e.g.
scrubbers, filters with active carbon). In addition, it can be
concluded that the PAA/CMC-Na polymeric binder is
characterized by the lowest emission level of gaseous
products in a given temperature range.
Conclusions
The sample of a foundry binder in the form of a poly(acrylic acid)–sodium carboxymethylcellulose polymer
composition has been subjected to thermal analysis of TG–
DTG–DSC in order to determine the course of its thermal
destruction taking into account temperature ranges in
which mass losses and gaseous decomposition products
occur. It was found that with the temperature rise, there are
physical and chemical changes associated with the evaporation of solvent water, release of constitutional water,
intermolecular dehydration, and then decomposition of
polymer chains with the formation of gaseous products of
destruction. On the basis of the thermal analysis for the
PAA/CMC-Na polymer composition, the temperature ranges (450 C, 700 C, 800 C) in which the pyrolysis gas
chromatography with mass spectrometry will be performed. In addition, commercial samples of two foundry
binders (alkaline resol resin and urea-formaldehyde resin)
were included in the study, which allowed to compare their
emission levels and the type of gaseous decomposition
products.
It was found that the course of degradation with the
release of gaseous hydrocarbon products, including BTEX
and their derivatives for commercial binders based on ARR
and UFR resins, is similar in a given temperature range,
with the most signals on pyrograms observed in the
500–700 C temperature range. The highest signal comes
from benzene and toluene for the ARR sample. In the
temperature range of 750–800 C, most of the signals
disappear; however, the signal from toluene, 2-methylfuran
and m-xylene is still visible.
Based on the conducted research, it can be concluded
that pyrolysis gas chromatography mass spectrometry
method is suitable for assessing the changes occurring
during the pyrolysis of foundry binders. In combination
with thermal analysis, TG–DTG–DSC gives the possibility
of full assessment of emission levels and gaseous products
released.
The results obtained indicate that only one of these
samples is environmentally friendly during the pyrolysis
process. It is a sample of a new polymer binder from the
BioCo group (PAA/CMC-Na). The type and emission of
gaseous products is small compared to the observed
emission level in ARR and UFR samples. The presented
results of Py-GC/MS measurements confirm that the
applied analytical methods are only able to perform the
qualitative characteristics of binder samples. In the lower
temperature range of 250–500 C, mainly CO2 emissions
are observed. Above 500 C, the observed compounds are
mainly volatile aromatics from the BTEX and PAH groups,
and phenol, which is the main component of the ARR
sample.
It is important to note that most of the emitted compounds belong to the high-risk group and pose a threat to
people and the environment, with the highest concentration
of hazardous and dangerous gaseous substances occurring
during casting process. In this context, the obtained
knowledge can be the basis for undertaking work on
reducing and optimizing the process of neutralizing the
gases emitted during casting process, when the mould has
the contact with liquid metal.
Open Access This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License (http://creative
commons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
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