Dissertation Summary: Study on the biodegradability of Polyetylene in the presence of transition metal stearates (Mn, Fe, Co)

MINISTERY OF EDUCATION
AND TRAINING

VIETNAM ACADEMY OF
SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

-------------

PHAM THU TRANG

STUDY ON THE BIODEGRADABILITY OF POLYETYLENE IN
THE PRESENCE OF TRANSITION METAL STEARATES
(Mn, Fe, Co)

Scientific Field: Organic Chemistry
Classification Code: 62 44 01 14

DISSERTATION SUMMARY

HA NOI - 2018


The dissertation was completed at:
Institute of Chemistry
Vietnam Academy of Science and Technology

Scientific Supervisors:
1. Prof. Dr. Nguyen Van Khoi
Institute of Chemistry - Vietnam Academy of Science and Technology

2. Dr. Nguyen Thanh Tung
Institute of Chemistry - Vietnam Academy of Science and Technology
1st Reviewer: ...........................................................................
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2nd Reviewer: ..........................................................................
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3rd Reviewer: ...........................................................................
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The dissertation will be defended at Graduate University of Science And
Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc
Viet, Cau Giay District, Ha Noi City.
At ….. hour….. date….. month …..2018.
The dissertation can be found in National Library of Vietnam and the
library of Graduate University of Science And Technology, Vietnam
Academy of Science and Technology.


1

INTRODUCTION
1. Background
Plastics play an important role in the modern world. They have been
found to be extremely versatile materials with many useful uses for human
life since the 1950s. In 2015, 322 million tonnes of plastics were produced
throughout the world. Average plastic consumption per capita in 2015 is 69.7
kg/person in the world, 48.5 kg/person in Asia, 155 kg/person in USA, 146

kg/person in Europe, 128 kg/person in Japan, 41 kg/person in Vietnam (a
significant increase by 33 kg/person compared to 2010). Polyethylene is the
most widely used thermoplastic in the world, consumed more than 76 million
tons per year, accounting for 38% of total plastic consumption. Increased
demand for plastics causes increase in waste and global environment
pollution. In 2012, the amount of plastic waste dumped into the environment
was 25.2 million tons in Europe, 29 million tons in the United States.
According to environmental reports of the United Nations, around 22- 43%
of the world's waste is buried in the landfill and 35% of waste in ocean. In
Vietnam, the average annual volume of solid waste has increased by nearly
200% and will increase in the near future, estimated at 44 million tons per
annum. According to the Marine Conservation Organization and the
McKinsey Center for Business and Environment, plastic waste of Vietnam is
the world's fourth largest by volume (0.73 million tons/year, representing 6%
of the total in the world) in 2015. To solve this problem, in the past few
decades, scientists have focused on the development of plastic materials
which decompose easily. Adding pro-oxidant additives is the most interesting
method.
Prooxidant additves are usually transition metal ions introduced in the
form of stearates or complexes with other organic compounds. Transition
metals are used as prooxidant additves, including Ti, V, Cr, Mn, Fe, Co, Ni,
Cu, Zn, Ca ..., the most effective of which are the stearate of Co, Mn and Fe.
Under the influence of ultraviolet (UV) radiation, temperature or mechanical
impacts, prooxidant additives promote the oxidation of polymer chains to
form functional groups such as carbonyl, carboxyl, hydroxide, ester, etc...
which can be consumed by microorganisms. In the presence of prooxidant
additives, the degradation time of plastics from hundreds of years decreased
to several years or even several months.
For the above reasons, we propose the dissertation: “Study on the
biodegradability of polyetylene in the presence of transition metal

stearates (Mn, Fe, Co)”.


2

2. Objectives of the dissertation
Studied and evaluated the biodegradability (including the degradation
and the biodegradation in the soil environment) of polyethylene films
containing prooxidant additives which is stearate salts of Fe (III), Co ( II) and
Mn (II).
3. Main contents of the thesis
- Research on the degradation process of PE films containing prooxidant
additives under accelerated conditions (thermal oxidation and photooxidation) and natural weathering.
- Research on the biodegradation process and level of oxidized PE films
with prooxidant additives in soil.
4. Structure of the thesis
The dissertation has 119 pages, including the Preface, Chapter 1:
Overview, Chapter 2: Experiment, Chapter 3: Results and discussions,
Chapter 4: Conclusions, Pubblications, with 62 images, 20 tables and 130
references.
DISSERTATION CONTENTS
CHAPTER 1. LITERATURE REVIEW
The literature review provided an overview of plastic production and
consumption, introduced polyolefins, the degradation of polyolefin,
approaches to enhance the biodegradation of polyethylene (PE) and the
degradation of PE containing prooxidant additives. Polyolefin especially
polyethylene was widely used in plastic pakaging with 80%. However,
polyolefins are very difficult to degrade in the natural emvironment so they
causes global environment pollution. Combining polyethylene with
prooxidant additives, which are organic salts of transition metals is the most

effective and interesting method. In the presence of these additives the
polyolefin will decompose in two stages:
- The first stage: the reaction of oxygen in the air with the polymer.
Under the influence of solar ultraviolet radiation (UV), heat, mechanical
stresses, humidity... the polymer chains were cleaved into shorter chains to
form functional groups such as carbonyl, carboxyl, ester, aldehyde, alcohol ...
- The second stage: the biodegradation by microorganisms such as fungi,
bacteria ..., which decompose the oligomer to form CO2 and H2O.
The literature review showed that there were some research groups in
the country to increase the degradability of polyethylene, but these studies
focused on manufacture blend of polyethylene and starches. Thus enhancing
the biodegradability of polyethylene with transition metal stearates is a
promising new direction.


3

CHAPTER 2. EXPERIMENTS
2.1. Materials and equipments
2.1.1. Materials
High density polyethylene (HDPE), linear low density polyethylene
(LLDPE), low density polyethylene (LDPE), pro-oxidant additives Mn(II)
stearate, Fe(III) stearate and Co(II) stearate, calcium carbonate filler
(CaCO3).
2.1.2. Equipments
Plastic SJ-35 Single Screw Extruder, twin screw extruder Bao Pin,
INSTRON 5980 mechanical measuring device, UV-260 accelerated
weathering tester, Thermo Nicolet Nexus 670 Fourier Transform Infrared
Spectroscopy, differential scanning calorimeter (DSC 204 F1 Phoenix) and a
thermogravimetry analysis system (TGA 209 F1 Libra), SM-6510LV and

JEOL 6490 scanning electron microscope, thickness measuring íntrument
Mitutoyo IP67, Scientech scales, readability 0,001 (g), oven and laboratory
equipments.
2.2. Film preparation
These films were made by extrusion blowing using a SJ-35 extruder
with a 35 mm screw of L/D 28:1. The SJ-35 extruder is shown in Figure 2.2.

Figure 2.2. Image of the SJ-35 extruder
2.3. Methods
2.3.1. Effect of ratio of prooxidant additives on the degradation of polyethylene
films (PE)

Fomulas of LLDPE films containing prooxidant additives were shown
in Table 2.1.


4

Table 2.1. Fomulas of LLDPE films containing prooxidant additives (w/w)
Prooxidant additives
Samples LLDPE
M1
M2
M3
M4

99.7
99.7
99.7
99.7

MnSt2
0.0750
0.2455
0.2348
0.2400

Ratio of prooxidant
additives MnSt2:
FeSt3 CoSt2
FeSt3: CoSt2
0.2250
0
1:3:0
0.0540
0
9:2:0
0.0522 0.0130
18:4:1
0.0533 0.0067
18:4:0.5

The LLDPE films with various pro-oxidant additive mixtures were made
by extrusion blowing. Thermo- and photo-oxidative degradations were
carried out to evaluate the degradability of LLDPE films.
2.3.2. Effect of prooxidant additive mixture content on the degradation of
polyethylene films (PE)

HDPE and LLDPE films with a thickness of 30 μm were blown. The
pro-oxidant additves were incorporated into the film formulation at a

concentration of 0.1, 0.2 and 0.3 %. The sample labeling of PE films were
listed in Table 2.3.
Table 2.3. Sample labeling of PE films
Pro-oxidant
PE
PE
Pro-oxidant
Sample
additives
Sample
resin
resin
additives (%)
(%)
HD0
0%
LLD0
0%
HD1
0.1%
LLD1
0.1%
HDPE
LLDPE
HD2
0.2%
LLD2
0.2%
HD3
0.3%

LLD3
0.3%
The PE films were carried out thermo- and photo-oxidatives and
natural weathering process to evaluate the degradation degree.
2.3.3. The degradation of PE films containing CaCO3 and prooxidant
additives
HDPE films with a thickness of 30 μm containing 0,3% prooxidant
additives (equivalent to 3% prooxidant masterbatch) and different CaCO3
filler contents (5, 10 and 20% - symbol HD53, HD103, HD203 respectively)
were blown. The films were carried out photo-oxidative degradation.
2.3.4. The biodegradability of PE films in natural conditions
- Buried in the soil
- Determined the degree of mineralization


5

CHAPTER 3. RESULTS AND DISCUSSIONS
3.1. Effect of ratio of prooxidant additives on the degradation of polyethylene
films (PE)

3.1.1. The mechanical properties of oxidized LLDPE films
The mechanical properties of films after thermo- and photo-oxidative
degradation are shown in Figures 3.1a and 3.1 b, respectively.
1000
§é d·n dµi khi ®øt (%)

§é bÒn kÐo ®øt (MPa)

27

18

9

0

Ban ®Çu
Sau 5 ngµy oxy hãa nhiÖt
Sau 96 giê oxy hãa quang, nhiÖt, Èm

Ban ®Çu
Sau 5 ngµy oxy hãa nhiÖt
Sau 96 giê oxy hãa quang, nhiÖt, Èm

M1

M2

M3

MÉu

M4

800
600
400
200
0

M1

M2

MÉu

M3

M4

Figure 3.1 a. The tensile strength of Figure 3.1 b. The elongation at break
oxidized LLDPE films with
of oxidized LLDPE films with
prooxidant additive mixtures
prooxidant additive mixtures
The results showed that the thermo-oxidative degradation of LLDPE
films without CoSt2 increased with increasing MnSt2/FeSt3 ratio. The
mechanical strength of the M2 sample decreased more than that of the M1
sample after 5 days of thermal oxidation. But photo-oxidative degradation of
films decreased, the mechanical strength of the M1 sample decreased more
than that of the M2 sample after 96 hours of photo-oxidation.
The mechanical properties of oxidized LLDPE films with CoSt2 are
lower than those of films without CoSt2 on both the thermo- and photooxidation. The results also showed that the higher CoSt2 content increase, the
faster the deagradation is.
3.1.2. FTIR-spectroscopy of oxidized LLDPE films
The changes in the peak intensity at 1700 cm-1 of LLDPE films after 96
hours of photo-oxidation are shown in Figure 3.2.

Figure 3.2. Changes in the peak intensity at 1700 cm-1 of oxidized LLDPE films

6

The results showed that the peak at 1700 cm-1 of M3 film was the
strongest intensity after photo-oxidation. The change in absorption intensity
of carbonyl group is consistent with the change in mechanical properties as
described in 3.1.1.
Therefore, the additive mixture of MnSt2/FeSt3/CoSt2 with ratio 18:4:1
is used for further studies in this thesis .
3.2. . Effect of prooxidant additive mixture content on the degradation of
polyethylene films (PE)
3.2.1. Thermo-oxidation of PE films
3.2.1.1. Mechanical properties of PE films after thermo-oxidation
Elongation at break is commonly used to monitor degradation process
rather than other mechanical properties. The film is considered to be capable
of degradation when the elongation at break is ≤ 5% according to ASTM
D5510 và ASTM D 3826 standard. Elongation at break of PE films with anh
without prooxidation additives during thermal oxidation is shown in Figure 3.5
and 3.6.
LLD0
LLD2

1200

Elongation at break (%)

Elongation at break (%)

1000

LLD1
LLD3

1000

800
600
400

HD0
HD1
HD2
HD3

200
0

0

3

6
9
Time (days)

12

Figure 3.5. Changes in elongation at
break of HDPE films after 12 days of
thermal oxidation

800

600
400
200
0

0

1

2 3 4
Time (days)

5

6

7

Figure 3.6. Changes in elongation at
break of LLDPE films after 7 days of
thermal oxidation

As shown in Figure 1, the additive-free HDPE and LLDPE polymer films
were slowly oxidized to a low extent. HD0, and LLD0 exhibit only about
9.4%, 20.1% loss while HD1, HD3 films lost about 48.4%, 52.8% of their
elongation at break in 7 days, respectively. On the other hand LLD1, LLD3
experiences almost 100% loss in 7 days. Thus, HDPE films are oxidized

more slowly than LLDPE films in both with and without prooxidant
additives.
These results show clearly that the pro-oxidant in PE has played a
significant role in inducing oxidation in PE leading to their embrittlement.
3.2.1.2. FTIR-spectroscopy of PE films after thermal oxidation
FTIR spectras of PE films before and after thermal treatment were
shown in Figure 3.7 a and 3.7 b.


7

Figure 3.7a. FTIR spectra of HDPE
films after thermal oxidation

Figure 3.7b. FTIR spectra of LLDPE
films after thermal oxidation

Figure 3.7 a and b showed that an increase in absorption in the carbonyl
region was recorded with time in the samples thermally aged containing prooxidants. The plot of 1640 - 1850 cm-1 range of carbonyl groups, as
determined by the overlapping bands corresponding to acids (1710 - 1715
cm-1), ketones (1714 cm-1), aldehydes (1725 cm-1), ethers (1735 cm-1) and
lactones (1780 cm-1) was observed, thus indicating the presence of different
oxidized products. The absorption maxima can be assigned to carboxylic acid
and ketones as the major components followed by esters in agreement with
the results obtained by Chiellini et al.
3.2.1.3. Carbonyl index (CI) of PE films after thermal oxidation
Figure 3.10 and 3.11 show changes in the carbonyl index of HDPE and
LLDPE films with and without pro-oxidant additives during thermal oxidation.
HD0
HD1

HD2
HD3

5

0

0

3
6
Time (days)

LLD0
LLD1
LLD2
LLD3

20

Carbonyl index (CI)

Carbonyl index (CI)

10

9

12

Figure 3.10. Carbonyl index of HDPE
films after 12 days of thermal oxidation

15

10
5
0

0

1
3
Time (days)

5

7

Hình 3.11. Carbonyl index of LLDPE
films after 7 days of thermal oxidation

Oxidation of PE films leads to the accumulation of carbonyl groups. As
the oxidation time increases, the oxygen absorption level and the rate of
intermediate products formation increases resulting in rapidly increasing
carbonyl group concentration. At the same time increasing the prooxidant
additive content, the carbonyl index also increased. So the presence of
prooxidant additive probably accelerated the oxidation degradation of films.
3.2.1.4. Different Scanning Calorimetry (DSC) of PE films after thermal
oxidation

Melting temperature (Tm), heat of fusion (ΔHf), degree of crystallinity


8

(IC) of HDPE and LLDPE films before and after 12 days of thermal
oxidation were listed in Table 3.1.
Table 3.1. Melting temperature (Tm), heat of fusion (ΔHf), degree of
crystallinity (IC) of HDPE and LLDPE films before and after 12 days of
thermal oxidation
Samples
HD0
HD1
HD2
HD3
LLD0
LLD1
LLD2
LLD3

o

Tm ( C)
135.3
134.8
134.9
134.6
121.8
121.5
121.3

121.0

Original
ΔHf (J/g)
172.3
170.3
170.7
170.5
73.61
73.67
73.74
73.86

IC (%)
58.8
58.1
58.3
58.2
25.1
25.1
25.2
25.2

12 days of thermal oxidation
Tm (oC)
ΔHf (J/g) IC (%)
135.1
175.0
59.7
133.7

186.3
63.6
133.5
190.9
65.2
133.0
195.2
66.6
121.5
86.8
29.6
120.6
124.5
42.5
120.3
130.6
44.6
120.0
139.6
47.7

The crystalline percentage (IC) which obtained from DSC scans shows that
IC of films increases after thermal oxidation. The crystalline percentage of
films containing prooxidant additives increases more strongly than that of
control (HD0, LLD0). With the same prooxidant additive concentration, ΔIC of
LLDPE films (17.4 – 22.4%) were significantly higher than that of HDPE (5.5
– 8.4%). This confirm that LLDPE films are oxidized more faster than HDPE
films in both with and without prooxidant additives.
3.2.1.5. Thermal gravimetric analysis (TGA) of PE films after thermal
oxidation

Thermal gravimetric analysis (TGA) traces of PE films after thermal
oxidation are shown in Figure 3.13.

HD0 – 12 days

LLD0 – 12 days

HD3 – 12 days

LLD3 – 12 days

Figure 3.13. TGA traces of PE films after thermal oxidation


9

The results showed that the degradation of original and thermally
degraded for 12 days PE films were only one stage. Degradation temperature
of HD3, LLD3 films after 12 days thermal oxidation is lower than that of
HD0 and LLD0. It is due to lower molecular weight products of chain
scissions by thermal oxidation.
3.2.1.6. Surface morphology of PE films after thermal oxidation
The changes in the surface morphology of thermally degraded for 12 days
HDPE films and thermally degraded for 7 days LLDPE films are shown in
Fig. 3.14 and 3.15.

PE (origin)
HD0
HD2
HD3

Figure 3.14. SEM micrographs of HDPE films after 12 days of thermal oxidation

LLD0
LLD1
LLD2
LLD3
Figure 3.15. SEM micrographs of LLDPE films after 7 days of thermo-oxidation

LLD0
LLD1
LLD2
LLD3

1000

Độ dãn dài khi đứt
(%)

Độ dãn dài khi đứt
(%)

As seen from the figure 3.14 and 15, original HD0, LLD0 films and
degraded these films present a smooth surface free of defects. In contrast, the
surfaces of PE films with pro-oxidant after thermal aging showed a
pronounced roughness with craters/grooves by effect of prooxidant additoves
and thermal.
3.2.2. Photo-oxidation of PE films
3.2.2.1. Mechanical properties of PE films after photo-oxidation
A decrease in elongation at break of PE films during photo-oxidative
degradation is shown in Figure 3.18 and 3.19.

800
600
HD0
HD1
HD2
HD3

400
200

0
0

24
48
72
Thời gian (giờ)

96

Figure 3.18. Changes of elongation at
break of HDPE films after 96 hours of
photo-oxidation

800
600
400
200
0
0

24

48
72
96
Thời gian (giờ)

120

Hình 3.19. Changes of elongation at

break of LLDPE films after 120 hours of
photo-oxidation


10

Elongation at break decreases with increasing time of photo-oxidative
degradation and decreasing as UV radiation. The results showed that
elongation at break of HD1, HD2, HD3 is 4.7 %, 2.5 %, and 0.2 %,
respectively after 96 hours accelerated aging, while that of HD0 is 478.4%.
Elongation at break of LLD1, LLD2, LLD3 is 3.2%, 2.1%, and 0.2%, that of
LLD0 is 365.9%.
Comparison of thermo-oxidative and photo-oxidative degradation of
PE films showed that:
- In both case, the HDPE films degraded more slowly than LLDPE
films. This is due to the difference in the amorphous content, the chain
scission occours only in the amorphous region. LLDPE is a low crystalline
polymer (~25%) so oxygen easily penetrates the polymer matrix to oxidizing

LLDPE chain to form oxidation products while HDPE is a higher crystalline
polymer (~58%)
- The mechanical properties of both LLDPE and HDPE films of
photo-oxidation decrease more rapidly than that of thermo-oxidation due to
prooxidation additive mixture that used in this dissertation is Mn (II) stearate,
Co (II) stearate and Fe (III) stearate. Co and Mn stearate promote thermal and
photo oxidation while Fe only promotes photo oxidation so Fe stearate
doesn’t promote thermo-oxidative degradation.
- The difference in the mechanical properties of HDPE and LLDPE
films of photo-oxidation is less than that of thermo-oxidation due to UV light
is the main agent that affects HDPE degradation.
3.2.2.2. FTIR-spectroscopy of PE films after photo-oxidation
FTIR spectras of PE films before and after aging were shown in Figure
3.20 a and b.

Figure 3.20a. FTIR spectra of HDPE

Figure 3.20b. FTIR spectra of LLDPE

films after 96 hours of photo-oxidation

films after 96 hours of photo-oxidation

After photo-oxidation, FTIR spectras of PE films occur peak in the
range of 1700 – 1800 cm-1 for carbonyl groups. That shows the presence of
various oxidation products such as aldehyde or ester (1733 cm-1), acid
carboxylic (1700 cm-1), γ-lacton (1780 cm-1). Also, a slight increase in the


11

peak area of 3300 – 3500 cm-1 region which is attibuted to the hydroxyl
group is observed.
3.2.2.3. Carbonyl index (CI) of PE films after photo-oxidation
Carbonyl index is a parameter which used to evaluate the level of
degradation. CI values of original and oxidized PE films are shown in Figure
3.21 and 3.22.
25

HD0
HD1
HD2
HD3

8
6

Cacbonyl index (CI)

Cacbonyl index (CI)

10

4

2

LLD0
LLD1
LLD2

LLD3

20
15
10
5
0

0
0

24

48
72
Time (hours)

96

Figure 3.21. Carbonyl index of HDPE
films after 96 hours of photo-oxidation

0

24

48
72
Time (hours)

96

120

Figure 3.22. Carbonyl index of
LLDPE films after 120 hours of photooxidation

The results showed that carbonyl indexs increase with increasing the
content of pro-oxidant additives at any time. With the same amount of prooxidant additives, LLDPE films are oxidized strongly than HDPE films that
is similar to the decrease in mechanical properties.
3.2.2.4. Different Scanning Calorimetry (DSC) of PE films after photooxidation
Melting temperature (Tm), heat of fusion (ΔHf), degree of crystallinity
(IC) of HDPE films before and after photo-oxidation were listed in Table 3.3.
Table 3.3. Melting temperature (Tm), heat of fusion (ΔHf), degree of
crystallinity (IC) of HDPE films after 96 hours of photo-oxidation
Samples
HD0
HD1
HD2
HD3

o

Tm ( C)
135.3
134.8
134.9
134.6

Original

ΔHf (J/g)
172.3
170.3
170.7
170.5

IC (%)
58.8
58.1
58.3
58.2

96 hours of photo-oxidation
Tm (oC) ΔHf (J/g)
IC (%)
133.4
176.1
60.1
132.0
193.8
66.1
130.6
197.2
67.3
129.0
205.1
70.0

After 96 hours of photo-oxidation, melting temperature decreases with
increasing content of pro-oxidant additives. Degree of crystallinity (IC) of

control film (HD0) increases by 1.3% while films with pro-oxidant additives
HD1, HD2, HD3 increase by 8.0, 9.0 and 11.8%. The greater the amount of
pro-oxidant additives is, the higher the crystalline content of films after
oxidant is and the more strongly the degradation process occurs.
Melting temperature (Tm), heat of fusion (ΔHf), degree of crystallinity
(IC) of LLDPE films before and after photo-oxidation were listed in Table
3.4.


12

Table 3.4. Melting temperature (Tm), heat of fusion (ΔHf), degree of
crystallinity (IC) of HDPE films after 120 hours of photo-oxidation
Samples
LLD0
LLD1
LLD2
LLD3

o

Tm ( C)
121.8
121.5
121.3
121.0

Original
ΔHf (J/g)
73.6

73.7
73.7
73.9

IC (%)
25.1
25.2
25.2
25.2

120 hours of photo-oxidation
Tm (oC) ΔHf (J/g)
IC (%)
121.4
88.5
30.2
120.6
126.3
43.1
119.6
141.3
48.2
118.5
156.2
53.3

Melting temperatute of LLDPE films also decreases after photooxidation. After 120 hours of photo-oxidation, degree of crystallinity (IC) of
control film (LLD0) increases by 5.1% while films with pro-oxidant additives
LLD1, LLD2, LLD3 increase by 17.9, 23.0 and 28.1%. The greater the
amount of pro-oxidant additives is, the higher the crystalline content of films

after oxidant is and the more strongly the degradation process occurs.
3.2.2.5. Thermal gravimetric analysis (TGA) of PE films after photo-oxidation
Thermal gravimetric analysis (TGA) traces of PE films after 96 hours of
photo-oxidation are shown in Figure 3.24.

HD0 – 96 hours

LLD0 – 96 hours

HD3 – 96 hours
LLD3 – 96 hours
Figure 3.24. TGA traces of PE films after photo-oxidation
The results showed that TGA of films after photo-oxidation is the same
as thermo-oxidation. The degradation of original and photo-oxidised PE films
for 96 hours were only one stage. Degradation temperature of HD3, LLD3
films after 96 hours photo-oxidation is lower than that of HD0 and LLD0 and
of original films. This is showing that PE films degraded to shorter chains.


13

3.2.2.6. Surface morphology of PE films after photo-oxidation
The SEM photographs of PE films after photo-oxidation, are shown in
Fig. 3.25 and 3.26.

HD0

HD1

HD2

HD3

Figure 3.25. SEM micrographs of HDPE films after 96 hours of photooxidation

LLD0

LLD1

LLD2

LLD3

Figure 3.26. SEM micrographs of LLDPE films after 120 hours of photooxidation
The results showed that the surfaces of photo-oxidised PE films
showed a pronounced roughness with craters/grooves. However, the surface
of control films was less damaged than that of films containing pro-oxidant
additives. The results also that the level of damage increased significantly by
increasing amount of pro-oxidant additives in the films.
3.2.3. Natural weathering process
3.2.3.1. Mechanical properties of PE films after natural aging
For films containing pro-oxidation additives, tensile strength and
elongation at break are reduced by prolonging natural aging time and
mechanical properties are reduced by increasing amount of pro-oxidant
additives. After 12 weeks of natural exposure, elongation at break of HD1,
HD2 and HD3 films is 4.9%, 2.8% and 0.6%, respectively, while that of HD0
film is 637.6%. After 8 weeks of natural exposure, elongation at break of
LLD1 and LLD2 films increased to 4.5% and 1.8%, respectively, LLD3 film
is no longer measurable. This confirm that pro-oxidant additives have
promoted scission reaction of polymer chain to form shorter chains under

effect of environment factors.
3.2.3.2. FTIR-spectroscopy of PE films after natural aging
FTIR spectras of PE films before and after natural aging were shown in
Figure 3.27 and 3.28.


14

Figure 3.27. FTIR spectra of original
HDPE (a) and after 12 weeks of natural
aging: HD0 (b). HD1 (c). HD2 (d). HD3
(e)

Figure 3.28. FTIR spectra of original
LLDPE (a) and after 8 weeks of natural
aging: LLD0 (b). LLD1 (c). LLD2 (d).
LLD3 (e)

After natural aging, FTIR spectras of PE films occur peak in the range
of 1700 – 1800 cm-1 for carbonyl groups. It is possible to observe a wide
absorption band of 3400 cm-1 region which is attibuted to the hydroxyl group.
It can also observed the weak intensity peak at 1641 cm-1 which is attibuted
to the hydroxyl vinyl group (C=C).
3.2.3.3. Carbonyl index (CI) of PE films after natural aging
Carbonyl index is a parameter which used to evaluate the level of
degradation. CI values of original and natural aged PE films are shown in
Figure 3.29 and 3.30.

Figure 3.29. Carbonyl index of HDPE
films after 12 weeks of natural aging

Figure 3.30. Carbonyl index of LLDPE
films after 8 weeks of natural aging

It can be seen that the CI of control films changes insignificantly in the
early stage of aging as well as after 12 weeks of natural aging for HD0 film
and after 8 weeks of natural aging for LLD0 film. The CI of LLDPE films
containing increase slowly in the early stage and then CI values incease by
increasing natural aging time. At the same time if the pro-oxidant additives
content increases, carbonyl index of films also increases.
3.2.3.4. Different Scanning Calorimetry (DSC) of PE films after natural
aging
Melting temperature (Tm), heat of fusion (ΔHf), degree of crystallinity
(IC) of HDPE and LLDPE films before and after natural aging were listed in
Table 3.8.


15

Table 3.8. Melting temperature (Tm), heat of fusion (ΔHf), degree of crystallinity
(IC) of HDPE after 12 weeks and LLDPE after 8 weeks of natural aging
Original
Natural aging
Samples
o
o
Tm ( C) ΔHf (J/g) IC (%)
Tm ( C) ΔHf (J/g) IC (%)
HD0
135.3

172.3
58.8
134.7
173.5
59.2
HD1
134.8
170.3
58.1
132.1
184.4
62.9
HD2
134.9
170.7
58.3
130.5
192.2
65.7
HD3
134.6
170.5
58.2
129.8
197.8
67.5
LLD0
121.8
73.6
25.1

121.7
77.73
26.5
LLD1
121.5
73.7
25.1
121.1
92.0
31.4
LLD2
121.3
73.7
25.2
120.7
107.8
36.8
LLD3
121.0
73.9
25.2
120.3
117.9
40.2
The crystalline percentage (IC) which obtained from DSC scans shows
that IC of films increases after natural aging. Similarly in the case of
accelerated aging, the crystalline percentage of LLDPE films increase more
strongly than that of HDPE after natural aging.
3.2.3.5. Thermal gravimetric analysis (TGA) of PE films after natural aging
Thermal gravimetric analysis (TGA) traces of PE films after natural

aging are shown in Figure 3.32.

HD3 – 12 weeks

LLD3 – 8 weeks

Hình 3.32. TGA traces of PE films after natural aging
Degradation temperature of HD3, LLD3 films after natural aging is
lower than that of control films and degradation temperature of natural aged
films is lower than that of original films. This is showing that PE films
degraded to shorter chains.
3.2.3.6. Surface morphology of PE films after natural aging
Changes in the surface morphology of natural aged PE are shown in
Figure 3.33 and 3.34.
(a)

(b)

(c)

(d)

Figure 3.32. SEM micrographs of HDPE films after 12 weeks of natural
aging: HD0 (a), HD1 (b), HD2 (c), HD3 (d)


16
(a)

(b)

(c)

(d)

Figure 3.33. SEM micrographs of LLDPE films after 8 weeks of natural
aging: LLD0 (a), LLD1 (b), LLD2 (c), LLD3 (d)
The results showed that the surfaces of natural aged PE films showed a
pronounced roughness with craters/grooves. However, the surface of control
films was less damaged than that of films containing pro-oxidant additives.
3.3. The degradation of PE films containing CaCO3 and prooxidant
additives
3.3.1. Mechanical properties of HDPE films containing CaCO3 and
prooxidant additives
Tensile stength and elongation at break of original and photo-oxidised
HDPE films containing CaCO3 and prooxidant additives are presented in
Table 3.12.
Table 3.12. Changes in mechanical properties of HDPE films containing
CaCO3 and prooxidant additives
Time
(hours)
Origin
24 hours
48 hours
72 hours
96 hours

Tensile strenth (MPa)
HD3 HD53 HD103 HD203

Elongation at break (%)
HD3
HD53 HD103 HD203

30.3 24.7
21.1
19.1
867.5 536.0 450.4 352.9
24.6 24.4
21.0
14.8
632.9 536.1 454.3 320.9
16.9 24.7
19.8
12.8
267.2 535.3 326.1 156.8
6.4
24.4
18.1
10.1
3.5
503.1 201.3 103.7
2.5
24.6
10.5
499.8
17.8
The mechanical properties of the original HDPE films containing CaCO3
decreased compared with the HD3 film and decreased with increasing amount
of CaCO3. This can be explained by the intermingling of inorganic additives

with different elastictity to the substrate, which reduces the mechanical
properties of films. After photo-oxidation, all HDPE films containing CaCO3
were degraded more slowly than HD3 film because CaCO3 acted as a
stabilizer. In their studies, Rosu et al found that CaCO3 could reflect nearly all
the ultraviolet light and protected HDPE from photo-degradation.
However, when increasing amount of CaCO3, the stabilization effect is
reduced. It is possible that at low concentrations, the CaCO3 filler dispersed
in the polyethylene matrix better than at high concentrations. At high
concentrations, the CaCO3 filler dispersed not well in PE matrix caused
defects on the films. At the same time, CaCO3 increases the gas permeability
of films so oxygen which causes oxidation reaction, easily penetrated. Yang
et al also found that inorganic fillers such as diatomite damade the film
surface when added to the film, that results in faster degradation of HDPE.


17

3.3.2. FTIR-spectroscopy of HDPE films containing CaCO3 and prooxidant
additives
FTIR spectras of original and photo-oxidised films were shown in
Figure 3.35 a. b. c and d.

Figure 3.35. FTIR-spectroscopy of HDPE films containing CaCO3 and
prooxidant additives after 96 hours of photo-oxidation
After 96 hours of photo-oxidation, FTIR spectras of HD103, HD203
films occur peak in the range of 1700 – 1800 cm-1 for carbonyl groups which
is attributed to various oxidation products such as aldehyde or ester (1733
cm-1), acid carboxylic (1700 cm-1), γ-lacton (1780 cm-1). This is confirm that
CaCO3 change the degradation rate, but it don’t change the degradation
mechanism of HDPE film.

The results also showed that, FTIR spectra of original and photooxidised HD53 film were not different. This is a proof that HD53 is not
oxidized after 96 hours.
3.3.3. Different Scanning Calorimetry (DSC) of HDPE films containing
CaCO3 and prooxidant additives
Analysis data from the DSC scans of HDPE films containing CaCO and
prooxidant additives before and after photo-oxidation is listed in Table 3.11.
Table 3.11. Different Scanning Calorimetry data of HDPE films containing
CaCO3 and prooxidant additives
Samples

HD3
HD53
HD103
HD203

Original
o

Tm ( C)
134.6
134.6
135.2
135.6

ΔHf (J/g)
170.5
151.0
146.4
119.7

96 hours of photo-oxidation

Tm (oC)
129.0
133.7
133.1
132.4

ΔHf (J/g)
205.1
126.7
141.4
110.9


18

DSC data of original films showed that when the CaCO3 was added, the
melting temperature of the HDPE films was higher than that of the HD3 film
and it increased with increasing amount of CaCO3. However, a reverse trend
is observed with heat of fusion. The heat of fusion of HDPE films containing
prooxidant additives decreases with the addition of CaCO3 and decreases
with increasing the amount of CaCO3. This means that when the CaCO3
content increases, the crystallinity of the HDPE films decreases. So CaCO3
filler changed the crystalline phase of the polymer. This explains why adding
more CaCO3 filler to the HDPE film makes the film more flexible and less
embrittle.
After 96 hours of photo-oxidation, similar to film without CaCO3
melting temperature of HD103, HD203 films is lower than that of original
film, while these values in HD53 are almost unchanged. However, heat of

fusion of HDPE film without CaCO3 increases but heat of fusion of HDPE
films with CaCO3 decrease.
3.3.5. Surface morphology of HDPE films containing CaCO3 and
prooxidant additives
Figure 3.37. 3.38 showed the surface morphology of HDPE films containing
CaCO3 and prooxidant additives before and after photo-oxidation.

HD3
HD53
HD103
H203
Figure 3.37. SEM micrographs of original HDPE films

HD3

HD53

HD103

HD203

Figure 3.38. SEM micrographs of HDPE films after 96 hours of photooxidation
SEM images showed that CaCO3 fillers were dispersed well in HDPE
matrices. Moreover, the fillers remained intact within the matrix. In contrast,
the agglomeration of fillers can be observed for HD203 which cause a loss in
the mechanical strength of film.
Due to roughness surface of original film containing CaCO3, it is much
more difficult to observe the changes of film surface after the oxidation.
Surface morphologies of HD53 and HD103 films were almost no change
while HD203 surface has more craters.

19

3.4. The biodegradability of PE films containing prooxidant additives in
natural conditions
3.4.1. The biodegradability of PE films containing prooxidant additives in
soil
3.4.1.2. The percentage weight loss after burying in soil
When buried in the soil the oxidized films continue to further divided
into shorter chains or converted into nutrients for microorganisms under the
action of enzymes produced by microorganisms. The percentage weight loss
of oxidized HDPE and LLDPE films containing pro-oxidant additives after
burying in soil is shown in Table 3.13 and 3.14.
Table 3.13. Weight loss of HDPE films after burying in soil (%)
Time 1 month 2 months 3 months 4 months 5 months 6 months
HD0
0
0
0.03
0.09
0.12
0.28
HD1
1.62
4.76
9.17
14.32
20.65
27.54

HD2
4.33
7.48
12.59
19.64
26.92
36.76
HD3
6.36
11.65
18.58
27.66
46.83
60.87
Bảng 3.14. Weight loss of LLDPE films after burying in soil (%)
Time 1 month 2 months 3 months 4 months 5 months 6 months
LLD0
0
0.04
0.08
0.15
0.28
0.43
LLD1
4.72
8.39
14.14
21.43
29.18
39.15

LLD2
7.01
12.12
20.48
31.21
48.44
63.76
LLD3
13.45
36.72
78.56
99.23
100
100
The weight loss of PE films containing pro-oxidant additives was much
more than the control film. After 6 months, the weight loss of HD0, HD1,
HD2, HD3 films were 0.28; 27.54; 36.76 and 60.87%, respectively and the
weight loss of LLD1, LLD2 films were 39.15 % and 63.76 %. Particularly
LLD3 film after 4 months buried in the soil has decreased by 99.23% of
weight and after five months, no pieces of this film were recovered in the
soil.
3.4.1.3. FTIR-spectroscopy of PE films after burying in soil
The FTIR spectra of LLD3 film after burying for 3 months in soil is
shown in Figure 3.41.
95.5

795.97

95.0
94.5

94.0

877.04

93.0

%T

91.5
91.0
90.5

533.70
464.66
415.33

1712.79

92.0

1627.37

92.5

717.92

93.5

90.0
89.5

89.0

1030.50

2850.13
2921.32

87.5

3430.00

88.0

1425.28

88.5

87.0
86.5
86.0
400 0

300 0

200 0

100 0

W av enu mber s ( c m- 1)

Figure 3.41. FTIR of oxidized LLD3 after burying for 3 months in soil


20

After 3 months of soil burial, the band of absorption between 1700 and
1740 cm-1 was significantly decreased due to ester, carbonyl group which
formed during degradation was assimilated by microorganisms in the soil. It
is also possible to see peak intensity at 1627 cm-1 that characterizes C=C
bond was significantly increased. The results also show that the band of
absorption between 950 and 1300 cm-1, which can be attributed to the
formation of smaller molecular weight pieces was strongly increased.
3.4.1.4. Surface morphological of PE films after burying in soil
SEM images of samples after burying in soil are shown in Figure 3.42.

HD0 after 6
months

HD3 after 6
months

LLD0 after 3
months

LLD3 after 3
months

Figure 3.42. SEM image of oxidized film surface after soil burial
SEM image shows that the surface of control film has changed
unsignificantly after soil burial, while the surface of HD3 and LLD3 films

have changed strongly, appeared holes and craters. The surface of the
polymer after biological attack was physically weak and readly disintegrated
under mild pressure.
In addition, the presence of microorganisms was observed on the HD3,
LLD3 film surfaces while wasn’t observed on the HD0, LLD0 film surfaces.
This can be explained by degradation of plastic polymer can cleave polymer
chains and lead to low molecular weight polymer fragments with hydrophilic
functional groups. That leads to more hydrophilic surface, creates good
conditions for microorganisms accessible to break down oligomer chains into
CO2 and H2O. Thus, the degraded HDPE films with pro-oxidant additices are
suitable substrates for the development of microorganisms due to abundant
nutrients (low molecular weight pieces) and hydrophilic surface. Several
other studies have also shown that microorganisms can grow on the surface
of PE and consume low molecular weight fragments which formed by abiotic
oxidation.
3.4.2. Determine the degree of mineralization
In addition to evaluating the degradation of polyethylene films,
assessing the level of biodegradability is an important step to predicting the
final decomposition of materials in the environment. In methods, determining
the degree of biodegradation is based on the amount of CO 2 generated from
the samples provided a more in-depth view. Celluloso or starch is often used
as a reference material for many biodegradable polymers to test the


21

reliability. The amount of CO2 evolved from the PE films, celluloso, blank is
shown in Figure 3.43 and 3.44.

Figure 3.43. Cumulative CO2

Figure 3.44. Cumulative CO2
emissions of flask containing
emissions of flask containing original
oxidized PE films
PE films
The results showed that the amount of CO2 evolved from flasks
containing oxidized PE films and celluloso is significantly higher than the
amount of CO2 evolved from blank. It is a clear indication that
microorganisms in soil used them as a carbon sources. The amount of CO2
from flasks containing HD3, LLD3 during the first 100 days of incubation is
almost no different with that from blank. When extending the incubation time
for more than 100 days, there is a difference. In particular, the amount of CO2
evolved from the flask containing LLD0 is almost no different from that from
blank.
The mineralizations of the samples over time of soil incubation are
shown in Figure 3.45 and 3.46.

Figure 3.45. Mineralization profiles
Figure 3.46. Mineralization profiles
of oxidised PE films
of original PE films
The results showed that mineralization level of celluloso increased
rapidly during the initial incubation and reached about 50% after 100 days


22

of incubation. After that, the mineralization was slower and reached 68.91%
after 322 days of incubation in the soil.
It can be observed that the level of biodegradatiobn of LLD3-8T,

LLD3-96h, HD3-170h films increased slowly in the first 20 days. This is the
adaptation phase, it may be time for microorganisms adapt to the new
environment and start attacking the polymer fragments. This stage of HD312T film lasts more than 80 days. After this period, amount of CO2 which
evolved from samples, increased rapidly. After 322 days of incubation in the
soil, mineralization levels of LLD3-8T, LLD3-96h, HD3-170h films are
43.2%; 53.0% and 39.2%, respectively. Figure 3.45 also shows that
biodegradation level of HD3-12T film increases rapidly for 200 days of
incubation and reaches about 24%, then biodegradation level slow.
In addition, it can be seen that the LLD3 film which was oxidized by
thermal and photo, had higher and faster biodegradation rate than oxidized
HD3. The biodegradability of both of them is lower than the control
(celluloso). This assures that the rate of conversion of carbon dioxide from
substrate depends on its chemical structure and oxidation. It can be seen that
the biodegradation rate of HD3 and LLD3 films is proportional to the degree
of oxidation.
The results also showed that LLD0 films was not nearly decomposed.
The mineralization level is only 0.018% after 322 days of incubation in the
soil. The biodegradation of LLD3 and HD3 films is unobserved for the first
120 days. However, after 120 days, the biodegradation of them increased
slowly and reached 4.1 and 3.7 % after 322 days of incubation, respectively.
Thus under the influence of prooxidant additives, LLD3 and HD3 films have
been degraded to facilitate microbiological consumption. Due to the short
time of testing, it is not possible to confirm the biodegradability of these
films. However, compared to the films without additives, it is possible to see
a satisfactory result in increasing the biodegradability of PE films.
So when buried in the soil, PE films with prooxidant additives have
formed biofilm. The PE films with 5% prooxidant additives which oxidized
by photo or natural weathering, have high level of mineralization.

23

CONCLUSIONS
After a period of study, the thesis has obtained the following results:
1. The mixture of Mn(II) stearate, Fe(III) stearate and Co(II) stearate
prooxidant additives with ratio of Mn(II) stearat : Fe(III) stearat : Co(II) stearat
= 18:4:1 is the best in studied ratios for promoting degradation of PE films.
2. The process, which estimates the degradation of polyethylene films
containing pro-oxidant additives mixture of Mn(II) stearate, Fe(III) stearate,
Co(II) stearate with ratio 18:4:1 by thermal oxidation method according to
ASTM D5510, photooxidation method according to ASTM G154-12a and
natural weathering were established. The mixture of prooxidant additives
promotes the degradation of PE films. Promotion effects in the oxidation
increase by increasing the concentration of the mixture of prooxidant
additives in films.
- In the thermal oxidation test, the LLDPE film with 0.3% prooxidant
additives lost 100% of its initial mechanical properties after 5 days, the
LLDPE films with 0.1 and 0.2% prooxidant additives lost 100% of its initial
mechanical properties after 7 days and the HDPE film with 0.3% prooxidant
additives lost 100% of its initial mechanical properties after 12 days.
- In the photo-oxidation test, the HDPE and LLDPE films with 0.3%
prooxidant additives are considered to be capable of degradation after 72
hours, the HDPE and LLDPE films with 0.1 and 0.2% prooxidant additives
are considered to be capable of degradation after 96 hours.
- In the natural weathering test, the HD3 film is considered to be
capable of degradation after 9 weeks of aging, the HD1, HD2 films are
considered to be capable of degradation after 12 weeks of aging, the LLD3
film is considered to be capable of degradation after 6 weeks of aging, the
LLD1, LLD2 films are considered to be capable of degradation after 8 weeks
of aging.

3. The degradation of HDPE films containing CaCO3 and prooxidant
additves has been evaluated. CaCO3 fillers reduces the mechanical porperties
but increases thermal stability of HDPE films. CaCO3 fillers retard the
degradation of HDPE films with prooxidant but they don’t affect to the
mechanisms of degradation.
4. The biodegradation of polyethylene films containing pro-oxidant
additives in soil was evaluated by 2 methods: buried in natural soil and
incubated in soil.
- After 6 months in soil, the buried LLDPE films with additives lost 32
– 100% by weight, the buried HDPE films with additives lost 25 –60% by
weight.
- After 322 days of incubation in soil, the mineralization level of HDPE
films is > 24%, the mineralization level of LLDPE films is > 40%.