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Progress in Rubber, Plastics and Recycling Technology, Vol. 30, No. 1, 2014

Evaluation of Recycled Polymers From CRT Monitor Frames of Different Years of Manufacture

©

Smithers Information Ltd., 2014

Evaluation of Recycled Polymers
From CRT Monitor Frames of
Different Years of Manufacture

Adjanara P. Gabriel

a*

, Ruth M. C. Santana

a

, and Hugo M. Veit

a

a

Universidade Federal do Rio Grande do Sul – UFRGS - Materials Engineering, Av.

Bento Gonçalves, 9500 – Setor 4 – Prédio 74 – Sala 103
Porto Alegre/RS – Brazil - CEP: 91501-970

Received: 30 January 2013, Accepted: 1 May 2013

SUMMARY

The recycling of polymeric waste has attracted considerable interest and many
efforts have been made to facilitate large scale recycling. The rapid evolution of
technology has generated large volumes of obsolete and unusable polymeric
products. One example is the CRT (cathode ray tubes) monitor that are rapidly
being replaced by monitor types such as LCD, LED and Plasma. The present
materials and routes for recycling this waste is not well known, which encourages
studies in this area. The main objective of this work is to identify the type of
polymer present in the CRT monitor frames and evaluate if the quality of the
recycled polymer is changed according to the monitor age (year of manufacture).
Monitors of different years of manufacture but the same brand were collected
and disassembled. Frames were separated into two groups (older and younger).
After, the frames were comminuted and samples were injected, according
to ASTM D638-08. The samples were characterized by infrared, density,
mechanical, MEV and TGA tests. The results obtained by infrared (FTIR) showed
that regardless of the year of manufacture the monitor frames are produced with
the same polymeric material, which was identified as copolymer ABS (acrylonitrile
butadiene styrene). The results of mechanical and thermal tests showed that,
in general, the recycled ABS polymers regardless of the year of manufacture
showed no significant losses in their properties. However, it was found, by the
TGA test, that there was a small variation in polymer composition.

Keywords: CRT monitor, Polymeric frames, Characterization, Recycling

Corresponding author: *[e-mail]

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Progress in Rubber, Plastics and Recycling Technology, Vol. 30, No. 1, 2014

Adjanara P. Gabriel, Ruth M. C. Santana, and Hugo M. Veit

INTRODUCTION

The steady growth in solid waste generation has encouraged studies of
recycling processes. Electronic scrap is part of the universe of obsolete and/
or defective materials that need to be disposed of more appropriate way or
recycled [1].

The amount of electronic waste in the world is growing rapidly; as they contain
hazardous materials, these scraps can cause environmental problems if they
are not properly pretreated. Furthermore, the use of recycled materials instead
of virgin materials allows significant saving of energy [2, 3].

The Monitor of CRT (cathode ray tube) type, also known as kinescopes, are
composed of polymeric, metals and ceramics materials, among which there are
materials of economic value and also some toxic materials. The replacement
of CRT technology (in use for many years) by new technologies such as LCD,
LED and Plasma has generated a large amount of waste [4].

In CRTs (

Figure 1), there are toxic materials such as the phosphor layer on the

cathode ray tube, high content of lead in the glass funnel, mercury in batteries
and capacitors. In addition to hazardous materials, there are also some valuable
materials such as metals (copper, gold and silver) and polymeric materials [5].

Figure 1. CRT Monitor

ABS (Acrylonitrile Butadiene Styrene copolymer) is a polymer that is most
often used as frames for electronic equipment such as monitor, keyboards,
printers and others [6].

ABS is an engineering thermoplastic that consists of an amorphous polymer
with good mechanical properties and high impact strength [7]. Thus, it’s
important to evaluate the destination after use, and its mechanical recycling
is an alternative solution [8].

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Evaluation of Recycled Polymers From CRT Monitor Frames of Different Years of Manufacture

Knowledge about the effects of degradation process, that occur during the
lifetime of a polymeric material and also during the process of mechanical
recycling, is one of the factors that need to be considered. From this, it is
possible to predict the lifetime of products made from recycled materials [9, 10].

Several researches have been performed to determine routes for recycling materials
in electronics waste. The metal recovery is the aim of most [

11, 12, 13, 14].

Some authors have researched the recycling of polymers in electronics waste.
Brennan studied recycling ABS and HIPS (high impact polystyrene) from waste
computer equipment [6]. Chancerei studied recycling of polymers from small
waste electrical and electronic equipment [8]. Kasper evaluated the recycling
of polymeric frames from mobile phones [15]. However, none of the authors
evaluated if the polymer mixture (older and younger) modifies the quality of
the material recycled.

Thus, the main objective of this work is to identify the type of polymer present
in the monitor frames and evaluate if the quality of the recycled polymer is
changed according to the monitor age (year of manufacture).

MATERIALS AND METHODS

CRT monitor, damaged and obsolete, the same brand, but with different years
of manufacture and colors were collected in various technical support. Then,
they were divided by the year of manufacture and separated into two groups:
before and after the year 2002, as shown in

Table 1. For the group prior to the

year 2002, 3 monitor, all beige, were collected. For the group of Monitor after
the year 2002, 2 monitor, one beige and one gray, were collected. The monitor
were disassembled manually and separated into three parts: frames, printed
circuit boards and cathode ray tubes. This study aimed to characterize and
recycle only polymer frames. The other parts were stored in the laboratory
for use in other lines of research.

Table 1. Monitor collected divided by their
year of manufacture

Sample

Year of manufacture

< 2002

1998, 2002

> 2002

2005, 2006

The inner surface of the monitor had the symbol “ABS” etched on it, as shown
in

Figure 2, indicating that the composition was manufactured. However, to

check this, the composition was analyzed using infrared spectroscopy – FTIR.

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Progress in Rubber, Plastics and Recycling Technology, Vol. 30, No. 1, 2014

Adjanara P. Gabriel, Ruth M. C. Santana, and Hugo M. Veit

Figure 2. Front view of the inner wall of the CRT frame, with the ABS symbol

Then, the frames were ground in mill knives until particle sizes less than 8 mm
were obtained. These particles were used for the injection of samples, according
to ASTM 638-08. Samples were injected at a temperature of 200°C and a
pressure of 50 b in an injection molding machine, Battenfeld brand Plus 350.

The samples were characterized using physico mechanical and thermal
tests. Initially, the densities of the samples before and after injection were
determined by the pycnometer method (ISO 1183-1). The mechanical tests:
Impact (CEAST, model Impactor II, Izod method); Tensile (Instron, model
3369); Bending (Instron, model 3369) and Hardness (Sd Woltest 300) based
on ASTM D256-06, ASTM D-638, ASTM D-790 and ASTM D2240 standards,
respectively, were performed. The morphology of the fracture of the samples
after tensile testing was conducted via scanning electron microscopy (model
JSM 6060). The thermogravimetric analysis (TGA) of samples was performed
on TA Instruments, model TGA 2050 at an ambient temperature to 1000°C
and a heating rate of 20°C/min using nitrogen.

RESULTS AND DISCUSSION

FTIR

Figure 3 shows the FTIR spectra of the samples, where the bands of the
functional groups characteristic of ABS were found. The acrylonitrile group is
identified in the band 2230 to 2240 cm

-1

; the phases of butadiene are found

in the band 910 to 960 cm

-1

and the peaks near 700 and 760 cm

-1

, related

to the aromatic ring corresponding to styrene. The year of manufacture, as
well as a possible exposure of the polymers to sun and rain did not change
the shape of the spectra. These results also confirm that the symbol “ABS”

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Progress in Rubber, Plastics and Recycling Technology, Vol. 30, No. 1, 2014

Evaluation of Recycled Polymers From CRT Monitor Frames of Different Years of Manufacture

etched on the inner face of the frames is correct. Davis et al. [16] studied,
by FTIR analysis, the effect of weathering on ABS and concluded that no
changes in spectra occur.

Density

The density test was performed on samples before and after reprocessing,
as shown in

Figure 4. The results of the density test of the ground material

showed no significant variation. The results of the density test of the injected
samples showed minor variations, with a small decrease in younger samples

Figure 4. Results of the density of the samples before and after injection molding

Figure 3. FTIR spectra of the samples < 2002 and > 2002

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Progress in Rubber, Plastics and Recycling Technology, Vol. 30, No. 1, 2014

Adjanara P. Gabriel, Ruth M. C. Santana, and Hugo M. Veit

(> 2002). Tiganis et al. [17] studied that the thermo-oxidative degradation on
the surface of the polybutadiene phase may cause an increase in the density
of the polymer, however, in the samples tested, this trend, didn’t occur.

Impact

The results of impact testing are shown in

Table 2. The sample < 2002 had a

mean value of 130 J/m and the sample > 2002 had a value close to 140 J/m.
There was a small increase in the value obtained, however insignificant.
However, the study by Tiganis et al. [12] showed that the impact strength
of ABS decreased rapidly after heat aging; the faults on impact are critically
dependent on the condition of the surface layer in ABS. However, in the samples
tested none of these situations occur, which could indicate that the samples
do not exhibit degradation, and the increased ability to absorb impact can
be due to the fact that frames (>2002) contain smaller filler content.

Regarding the hardness tests results, the sample < 2002 obtained a value
slightly higher than the sample > 2002, which is in agreement with the impact
test results. Although these variations of energy of the impact and hardness
tests, between the analyzed samples, are small, this may indicate that there
was a small change in the composition of the filler content of the frames,
also confirmed by the density results of samples injected. Rahiman et al. [18]
studied the mechanical properties of ABS and their blends and concluded
that a considerable variation in hardness tests is related to the variation of
composition of the material, which probably did not occur in the samples
tested in this study.

Table 2. Results obtained in the impact and hardness tests

Sample

Impact Strength (J/m)

Hardness

< 2002

127.9 +/-7.3

62.4 +/-2.1

> 2002

137.5 +/-9.0

59.1 +/-1.8

Tensile Test

Table 3 shows the results of tensile strength obtained from the tensile test.
Samples <2002 and > 2002 had very close values. A decrease in tensile
strength and the rupture properties can be explained by considering that the
mechanical properties of ABS are influenced by the amount of butadiene in
the copolymer phase [19]. Another factor that can influence the mechanical
properties is the process of “fusion” that occurs during the injection of the test

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Evaluation of Recycled Polymers From CRT Monitor Frames of Different Years of Manufacture

samples. In this case, the main molecular chains of the polymer can break,
thereby increasing the number of shorter chains of the respective polymer.
Thus, fewer entanglements and a decrease in tensile strength [20] occur.
Degradation of the polymer can also involve changing tensile properties,
resulting in loss of quality of material [21]. But, it can be seen from the results
that, independently of the lifetime of recycled polymers and injection process,
the tensile properties were not significant changes.

The results of the modulus of elasticity obtained by the tensile test show that
the sample < 2002 obtained a value slightly above the sample > 2002, which
may occur due to the presence of a higher amount of fillers and additives
in the formulation. Scaffaro et al. [14] studied the recycling of virgin ABS
and compared the results with recycled ABS blends. They observed that,
the modulus of elasticity, for the reduction of properties at break, during the
reprocessing cycles, is most relevant to the virgin ABS blends compared
with, for example, PC-ABS.

Table 3. Results obtained by the tensile test

Sample

Yield

Stress (MPa)

Fracture

(MPa)

Modulus of

Elasticity (MPa)

Maximum Elastic

Deformation (%)

< 2002

36.14 ± 0.67

20.58 ± 0.89

1565.56 ± 16.01

2.79 ± 0.05

> 2002

35.64 ± 0.69

20.48 ± 0.79

1526.45 ± 16.1

2.88 ± 0.09

Flexion Test

In the bending test, it was possible to examine the elasticity modulus and yield
stress. At maximum stress, the sample < 2002 obtained a result greater than
the sample > 2002, as shown in

Figure 5a. These results confirm the results

obtained by other mechanical tests where the frames composition has great
influence. In

Figure 5b, it can be seen that the elastic modulus of sample

< 2002 obtained a value above that of sample > 2002. Similar to the tension,
this may be related to the higher content of fillers in the composition of the
frames. Brennan et al. [6] studied that the recycling of ABS can decrease its
average stress; this implies that the method of recycling causes mechanical
degradation of the polymer. But in this case, the samples were not degraded.
In this study, the decrease in the elongation properties of ABS coincided with a
slight increase in stiffness of the material, i.e., an increase in elasticity modulus.
In the samples tested in this work, it can be seen that both stress and the
module showed higher values for older samples. Thus, this behavior can be
explained considering that variations in the composition of the formulation
of the material may have been more significant than the actual degradation.

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Adjanara P. Gabriel, Ruth M. C. Santana, and Hugo M. Veit

Figure 5. Flexure stress maximum (a) and elasticity modulus (b) obtained in the
bending test

Morphology of the Fracture Surface

Figure 6 presents the morphological analysis of images of the fractured
surface during the tensile test. It is noticed that the sample < 2002 is less
compact than the sample > 2002 due to the presence of some voids, as
highlighted in

Figure 6. The sample > 2002 presents encrusted particles can

be pigmented or load, since this sample has a monitor with a gray frame.
The observation of the fracture surface by SEM also allows one to verify the
correlation between the type of fracture and the characteristics shown in the
images [22]. In the case of the images shown in

Figure 6, it can be seen that

the fracture is of ductile type.

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Progress in Rubber, Plastics and Recycling Technology, Vol. 30, No. 1, 2014

Evaluation of Recycled Polymers From CRT Monitor Frames of Different Years of Manufacture

Figure 6. Image of scanning electron microscopy performed on the fractured surface
after the tensile test. (a) < 2002, (b) > 2002

TGA

Figure 7a shows the thermogravimetric curves of samples < 2002 and > 2002;
where it is possible to be analyzed from approximately 300°C, the polymer
begins to decompose.

Figure 7b shows the DTG curves from the variation in

weight, using which it is possible to analyze the peaks at which the material
decomposes most rapidly [23].

Table 4 shows these differences.

(a)

(b)

Figure 7. TGA tests

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Progress in Rubber, Plastics and Recycling Technology, Vol. 30, No. 1, 2014

Adjanara P. Gabriel, Ruth M. C. Santana, and Hugo M. Veit

Yang et al. [24] studied that the degradation of ABS components starts at
340°C and 350°C for butadiene and styrene, respectively. This same behavior
was obtained for the samples assayed, as shown in

Figure 7b where the first

peak occurred at around 350°C. Candido [25] studied the degradation of ABS
compared with PC and found that butadiene and styrene are more thermally
sensitive, because the thermal degradation of ABS was initiated at the range
of 220°C to 235°C, and the degradation of PC started at 274°C.

Table 4. Summary of the properties found in the TGA test

Sample

Tg

DTg

% M1

%M2

Residue

T p1 (°C)

T p2 (°C)

< 2002

25.98

66.76

6.45

343.7

429.8

> 2002

24.09

69.14

6.75

332.5

429.8

CONCLUSIONS

From the results obtained by FTIR, it was possible to confirm the composition
present in the formulation of monitor frames as the ABS copolymer. Results of
physical and mechanical tests showed that the younger frames evaluated were
a little lighter than the older frames, with an increase in the impact absorptive
capacity and a small decrease in hardness and the modulus of traction and
flexion, indicating the possibility of higher filler content, which was confirmed
by thermal analysis and SEM compared to older samples.

In general, it can be concluded that the recycling of monitor frames is
technically feasible and that there is no need to separate old and young
frames, since there is no significant variation in the mechanical and thermal
properties analyzed in this study and the frames are demonstrably made
of the same material.

ACkNOWLEDgMENTS

Capes, CNPq, FINEP (Sibratec).

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