Thông tin tóm tắt về những đóng góp mới của luận án tiến sĩ: Nghiên cứu chế tạo và tính chất màng polyme chắn khí và thăm dò ứng dụng.

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AND TRAINING SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY 
---

NGUYEN TUAN NAM

STUDY ON THE MANUFACTURING AND PROPERTIES OF GAS 
BARRIER MULTILAYERS FILMS AND APPLICATIONS

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

DISSERTATION SUMMARY

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The dissertation was completed at:

Institute of Chemistry

Vietnam Academy of Science and Technology

Scientific Supervisors:
1. Dr. Nguyen Tien Dung

The Faculty of Chemistry – Hanoi National University of Education
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 …..2020.

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A. INTRODUCTION 
1. Background

Packaging plays an important role in the food supply chain. They are
not only used to store, preserve and transport products but also used as a
marketing tool to bring added value to the product. Packaging protects food
from environmental influences such as oxygen, moisture, light, dust, volatile
compounds and microorganisms [1], it acts as a barrier between the
atmosphere around food and the outside environment. Oxygen and steam are
the two main reasons leading to the deterioration of food quality. Therefore,
the development of the gas barrier packaging products with low air and water
vapor permeability is a research direction that has been interested recently.
According to Smithers Pira, in 2015, the world consumed about 1.4 million
tons of gas barrier packaging films, in 2016 it was 1.86 million tons, with the
growth rate of 4.7%/year. The regions using the most gas barrier packaging
films were Asia-Pacific with 30.9%, followed by Western Europe (27.6%)

and North America (26.8%).

Among the materials used for packaging, plastic in the form of thin
films has many outstanding advantages compared to other packaging types
such as: light, durable, elastic, transparent, resistant to air and vapor. High
water, and at the same time have good heat sealing and sealing ability.
Polyethylene (PE) is the most commonly used plastic for packaging thanks to
its good moisture barrier, low cost, but poor resistance to O2, aromas and
essential oils. Like PE, PA6 has good moisture barrier but poor O2 and CO2
barrier. Therefore, the recent trend that scientists are most interested in
developing is to combine these polymers with another polymer with high gas
barrier ability in the form of polymer blends or multilayer films. The most
widely used and highly gas barrier polymer is EVOH [2]. Combining EVOH
with PE or PA6 can create a material that has both highly mechanical and
good gas, solvent, and moisture resistance, suitable for applications requiring
high gas barrier such as food packaging or dry agricultural packaging ...

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2. Objectives of the dissertation

Researching and fabricating gas barrier multilayer films based on the
polyme blends and exploring the applicability of packaging to preserve dry
agricultural products.

3. Main contents of the thesis

- Study on fabrication and properties of some polymer blends based on
EVOH (PE/EVOH and PA6/EVOH polymer blends).

- Fabrication and study on properties of gas barrier multilayer polymeric
films based on polymer blends of EVOH.

- Study on application of gas barrier multilayer packaging to preserve
some dry agricultural products (maize, soybeans).

4. Cấu trúc của luận án

The dissertation has 111 pages, including the Preface, Chapter 1:
Overview, Chapter 2: Experiment, Chapter 3: Results and discussions,
Chapter 4: Conclusions, Pubblications, with 29 images, 21 tables and 90
references.

DISSERTATION CONTENTS 
CHAPTER 1. LITERATURE REVIEW

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Studies have shown that EVOH has good hydrocarbon barrier
properties and is considered an oxygen barrier in food packaging applications
where oxygen is essential due to its high oil resistance and gas barrier
properties. However, its moisture-absorbing properties, being relatively
brittle and expensive, diminish its advantages. In order to reduce costs while
maintaining good gas barrier properties, studies on polymer blends of EVOH
have attracted a lot of attention in recent years, especially polymer blends of
EVOH with PE and PA6.

In the gas barrier packaging technology, the multi-layer extrusion
technology proved to be effective in improving the poor gas barrier
properties of polyolefin packaging. This technique allows the desired
properties of polymers to be combined into one structure with enhanced
performance. In this way it is possible to take advantage of the inherent
barrier properties and protect the plastic layer from high relatively humidity.
In addition, this plastic layer is also protected from corrosion, avoiding

miscibility problems and improving transparency of film.

In Vietnam, there are no research projects on manufacturing gas-barrier
multilayer polymeric packaging for agricultural preservation applications,
especially dry agricultural products. Therefore, this dissertation chooses the
topic "Study on the manufacturing and properties of gas barrier multilayer
films and applications".

CHAPTER 2. EXPERIMENTS 
2.1. Materials and equipments

2.1.1. Materials

Linear low density polyethylene (LLDPE), ethylene-vinyl alcohol
copolymer (EVOH), low density polyethylene graft maleic anhydride
(PE-g-MAH, MAH content of 0,1%), polyamide 6 (PA6), corn seed HQ 2000,
soybean seed DT96.

2.1.2. Equipments

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2.2. Study methods

2.2.1. Preparation of polymer blends based on EVOH

2.2.1.1. Preparation of PE/EVOH polymer blends

LLDPE and EVOH resins, PE-g-MAH compatibilizer were melt-blended
in an internal mixer model Plastograph® EC (Germany) at 190 oC, rotor speed
of 45 rpm for 5 min. The PE/EVOH polymer blends were compression
moulded into 1 mm thick plates on a GoTech hot press at 190 oC at a pressure

of 20MPa for 5 min.

2.2.1.2. Preparation of PA6/EVOH polymer blends

PA6 and EVOH resins were melt-blended in an internal mixer model
Plastograph® EC (Germany) at 215 oC, rotor speed of 30 rpm for 5 min. The
PA6/EVOH polymer blends were compression moulded into 1 mm thick
plates on a GoTech hot press at 190 oC at a pressure of 20MPa for 5 min.

2.2.2. Preparation of gas barrier multilayer films based on EVOH

2.2.2.1. Preparation of PE/PE-EVOH/PE gas barrier multilayer films

The film blowing process was performed on a multi-layer film blowing
device Model 3SJ-G2000, with the following layer structure:
LLDPE/PE-g-MAH polymer blend (layer 1)/PE/EVOH polymer blend (layer 2)/LLDPE/
PE-g-MAH polymer blend (grade 3). The parameters of the 3 screws in the
film blowing device are as follows: screws 1 and 3 with a diameter of 65mm,
the ratio of L/D = 30, the temperature of the heating zones and die heads are
180, 190, 200, 210, 210oC, screw speed 20 rpm; screw 2 has a diameter of
70mm, the ratio L/D = 30, the temperature of the heating zones and the die
head is 210, 210, 220, 220, 220oC, screw speed 15 rpm.

2.2.2.2. Preparation of PE/PA-EVOH/PE gas barrier multilayer films

The film blowing process was performed on a multi-layer film blowing
device Model 3SJ-G2000, with the following layer structure:
LLDPE/PE-g-MAH polymer blend (layer 1)/ PA6/EVOH polymer blend (layer 2)/LLDPE/
PE-g-MAH polymer blend (grade 3). The parameters of the 3 screws in the
film blowing device are as follows: screws 1 and 3 with a diameter of 65mm,

the ratio of L/D = 30, the temperature of the heating zones and die heads are
180, 190, 200, 210, 210oC, screw speed 20 rpm; screw 2 has a diameter of
70mm, the ratio L/D = 30, the temperature of the heating zones and the die
head is 230, 230, 240, 240, 240oC, screw speed 15 rpm.

2.2.3. Application of gas barrier multilayer films in the preservation of 
some dry agricultural products

2.3.3.1. Application of gas barrier multilayer films in the preservation of 
maize grain

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indicators such as: moisture, protein, starch, lipid content and yeast-mold
infection degree every month.

2.3.3.2. Application of gas barrier multilayer films in the preservation of 
soybean

Soybean was selected according to standard TCVN 4849:1989, is
packed into bags with the size of 25x35cm, and thickness of 80 µm, weight 2
kg/bag, then vacuumed on the BZQ 500 machine (vacuum pressure
-0.08MPa). The packed samples are stored in the laboratory. Samples were
analyzed quality indicators such as: moisture, protein, lipid content, acidity in
extract oil and yeast-mold infection degree every month.

CHAPTER 3. RESULTS AND DISCUSSIONS 
3.1. Study on preparation of polymer blends based on EVOH

The dissertation has investigated two factors affecting the properties of
the material: compatibilizer content and the ratio of LLDPE/EVOH.

- The effect of the ratio of LLDPE / EVOH: content of LLDPE-g-MAH
compatibilizer 4%, weight ratio of PE/EVOH in polymer blends 90/10,
80/20, 70/30, 60/40, 50/50.

- The effect of the LLDPE-g-MAH compatibilizer content: the ratio of
LLDPE/EVOH 70/30, compatibilizer content of 0-10%.

3.1.1. Study on preparation of PE/EVOH polymer blends

3.1.1.1. Viscosity of PE/EVOH polymer blends

* Effect of the ratio PE/EVOH on the viscosity PE/EVOH polymer
blends

Curves of mixing torque versus time for PE/EVOH polymer blends
containing 4% LLDPE-g-MAH compatibilizer at different PE/EVOH ratios
were shown in fig. 3.1.

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Specifically, torque of PE/EVOH polymer blend in molten equilibrium with
the ratios of 90/10, 80/20, 70/30, 60/40 and 50/50 are 15.7; 17.8; 18.7; 19.4
and 19.9 N.m, respectively.

* The effect of the PE-g-MAH content on the viscosity of the
PE/EVOH polymer blend was shown in fig. 3.2.

Fig. 3.2. Curves of mixing torque versus time for PE/EVOH 70/30 polymer 
blend with different PE-g-MAH content

Fig. 3.2 showed that when the PE-g-MAH compatibilizer was present,
torque in the molten state of PE/EVOH polymer blends increased as

compared to when not using the compatibilizer even though PE-g-MAH has
low viscosity. The results also showed that when increasing the content of
PE-g-MAH compatibilizer, the torque of the polymer blend increased.

3.1.1.3. Mechanical properties of PE/EVOH polyme blends

Effects of PE/EVOH ratio on mechanical properties of PE/EVOH
polymer blends with and without PE-g-MAH compatibilizer were presented
in Table 3.1.

Table 3.1. Effect of the composition ratio on the mechanical properties
of PE/EVOH polymer blend

PE/EVOH 
ratio

PE-g-MAH 
compatibilizer (%)

Tensile 
strength (MPa)

Elongation at 
break (%) 
100/0

29.5 1005.4

90/10 19.6 765.7

80/20 15.8 420.3

70/30 12.4 256.2

60/40 10.1 148.5

50/50 7.6 89.6

0/100 25.2 17.1

90/10

24.5 359.2

80/20 26.4 389.3

70/30 28.3 404.9

60/40 27.1 367.5

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In samples without PE-g-MAH compatibilizer, both tensile strength
and elongation at break of the polyme blend samples decreased with
increasing EVOH content. This is because PE and EVOH have differences in
nature, chemical structure, polarity, surface interaction energy ... so the low
adhesion between PE and EVOH leads to agglomeration of a large EVOH
amount in the PE matrix.

In the presence of a compatibilizer, the mechanical properties of the
polymer blends were significantly improved. Tensile strength and elongation
at break increased because PE-g-MAH acted as an effective compatibilizer
between EVOH dispersion phase and PE matrix. Adding PE-g-MAH
increased the dispersion of EVOH and increases the adhesion between phases
to enhance the mechanical properties of polymer blends.

The results also showed that in the presence of 4% compatibilizer,
when the EVOH content increased from 10-30%, the tensile strength and
elongation at break increased. Tensile strength was significantly improved
when increasing EVOH content in polymer blends possibly due to high
tensile strength of EVOH. However, when the EVOH content was > 30%, the
mechanical properties of the polymer blends decrease because the tensile
strength was strongly influenced by the phase interaction between PE and
EVOH. This showed that when the EVOH content increased, the binding
capacity of PE and EVOH decreased.

The effect of the PE-g-MAH content on the mechanical properties of
the PE/EVOH polymer blends was presented in Table 3.2.

Table 3.2. Effect of PE-g-MAH content on mechanical properties of
PE/EVOH 70/30 polymer blend

PE-g-MAH content
(%)

Tensile strength
(MPa)

Elongation at break
(%)

0 12.4 256.2

2 25.6 379.8

4 28.3 404.9

6 26.5 416.3

8 24.1 420.4

10 23.9 418.5

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3.1.1.4. Surface morphology of PE/EVOH polymer blends

SEM images of fracture surface of PE/EVOH polymer blends without
and with PE-g-MAH compatibilizer wre shown in Figure 3.6 and Figure 3.7.

a) PE/EVOH 90/10 b) PE/EVOH 80/20 c) PE/EVOH 70/30

d) PE/EVOH 60/40 e) PE/EVOH 50/50

Fig. 3.4. SEM images of fracture surface of PE/EVOH polymer blends 
without PE-g-MAH compatibilizer

a) PE/EVOH 90/10 b) PE/EVOH 80/20 c) PE/EVOH 70/30

d) PE/EVOH 60/40 e) PE/EVOH 50/50

Fig. 3.5. SEM images of fracture surface of PE/EVOH polymer blends with 
4% PE-g-MAH compatibilizer

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However, when increasing EVOH content in polymer blend from 40-50%,
the compatibility between EVOH and LLDPE phases becomes worse.

3.1.1.5. Differential scanning calorimetry (DSC) of PE/EVOH polymer blends 
DSC curves of PE/EVOH polymer blends with 4% PE-g-MAH
compatibilizer at different PE/EVOH ratios were summarized in Table 3.3.
Table 3.3. Effect of the LLDPE/EVOH ratio on thermal properties of 
polymer blends

LLDPE/EVOH 
ratio

Tg (oC) Tm (oC) Tc (oC) 
Polyme blend LLDPE EVOH LLDPE EVOH

100/0 -20.7 121.8 - 104.8 -

90/10 -14.5 121.3 182.1 104.7 161.9
80/20 -2.4 120.4 182.7 104.6 161.3
70/30 6.32 122.0 183.0 102.5 159.2
60/40 6.5 và 38.5 120.7 184.0 103.8 161.1
50/50 6.0 và 38.8 122.3 184.2 104.3 160.9

0/100 40 - 184.4 - 162.3

The results showed that at 4% PE-g-MAH compatibilizer, when

increasing the EVOH content from 0-30%, a Tg in the range Tg of EVOH
(Tg = 40oC) and Tg of LLDPE (Tg = -20.7oC). This proves that in the
presence of a PE-g-MAH compatibilizer, at 10-30% EVOH, the two
polymers had good compatibility with each other. When the EVOH content
continued to increase from 40-50%, two Tg values appeared in the range of
Tg of the two component polymers. However, there was a shift in Tg of
LLDPE to Tg of EVOH. This proves that at the EVOH content of 40–50%, in
the presence of a PE-g-MAH compatibilizer, there was partial compatibility
between the two polymers.

The results also showed that the melting temperature Tm of LLDPE in
polymer blends did not change much when the EVOH content increased.
However, when increasing the EVOH content, the Tm value of EVOH in the
polymer blends increased slightly but was smaller than the Tm value of
EVOH resin.

Crystallization temperature (Tc) of LLDPE in blends is almost
unchanged. Meanwhile, when increasing EVOH content, Tc value of EVOH
in polymer blend decreased slightly compared with Tc of EVOH resin.

3.1.2. Study on preparation of PA6/EVOH polyme blends

To study preparation of polymer blend PA6/EVOH, polymer blend
samples were prepared at different ratios of PA6/EVOH 100/0, 90/10, 80/20,
75/25, 50/50 and evaluate the properties of the polymer blend samples.

3.1.2.1. Viscosity of PA6/EVOH polyme blends

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Fig. 3.10. Curves of mixing torque versus time for PA6, EVOH, PA6/EVOH 
polyme blends

The results showed that the torque in the molten equilibrium of
PA6/EVOH polymer blends was lower than EVOH and higher than PA6. In
addition, when increasing the EVOH content in the polymer blend, the torque
in the molten equilibrium of the polymer blends increased. This may be due
to the interaction between the organizational groups in the polymer blend,
namely the amino groups of PA6 and the hydroxyl groups of EVOH. When
EVOH increased, the number of hydrogen bonds between hydroxyl groups
and amine groups increased, increased the intermolecular and intermolecular
bonds leading to an increase in torque.

3.1.2.2. Mechanical properties of PA6/EVOH polymer blends

Effects of the PA6/EVOH ratio on the mechanical properties of the
polymer blends wre presented in Table 3.5.

Table 3.5. Mechanical properties of PA6/EVOH polymer blends 
PA6/EVOH ratio

(%)

Tensile strength 
(MPa)

Elongation at break 
(%)

100/0 60.4 29.5

90/10 58.7 42.5

80/20 52.6 58.6

75/25 48.6 74.2

50/50 32.4 68.4

0/100 25.1 17.2

The results showed that the tensile strength of PA6/EVOH polymer
blends decreased when the EVOH content increased. However, the
elongation at break increased when the EVOH content increased from 0-25%,
when the EVOH content increased to higher than 25%, the elongation at
break decreased.

3.1.2.3. Surface morphology of PA6/EVOH polymer blends

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shown in figure 3.11.

PA6/EVOH 90/10 PA6/EVOH 80/20 PA6/EVOH 75/25
Fig. 3.11. SEM images of fracture surface of PA6/EVOH polymer blend

Observing the fracture surface SEM images of the PA6/EVOH polymer
blends, it was found that the fracture surface was relatively smooth, difficult
to distinguish the morphology of the two phases PA6 and EVOH after
mixing. This demonstrates a good dispersion of the two phases together.

Surface morphology of the polymer blends after soaking in dioxane
solution was shown in Figure 3.12.

PA6/EVOH 90/10 PA6/EVOH 80/20 PA6/EVOH 75/25
Fig.3.12. SEM images of PA6/EVOH polyme blends after soaking in

dioxane solution

The results showed that with samples containing low EVOH content
(Fig. 3.12a), there was no EVOH dispersion zone in the PA6 substrate. When
the EVOH content increased (Fig.3.12 (b), (c) and (d)), the corrosive EVOH
regions appear and the number of these eroded regions increases and the size
of the regions were larger as EVOH the content in polymer blends increased..
3.1.2.4. Differential scanning calorimetry (DSC) of PA6/EVOH polymer blends

Effect of PA6/EVOH ratio on thermal properties (crystallization
temperature Tc, melting temperature Tm and glass transition temperature Tg)
of PA6/EVOH polymer blends was presented in Table 3.6.

The results showed that the melting temperature of PA6 in the
PA6/EVOH polymer blends decreased from 226.3oC to 207.1oC when the
EVOH content increased from 0-50%, and the molten heat absorption
process of EVOH was not observed.

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intermolecular and intramolecular hydrogen bonds and chemical interactions
between two polymers that form block copolymers (consisting of EVOH
blocks and PA6 blocks).

Table 3.6. DSC analysis results of polymer PA6, EVOH and PA6/EVOH 
polymer blends

PA6/EVOH 
ratio

Thermal properties of polyme blends 
Tc (

o

C) Tm (

o
C)

100/0 193.0 226.3

90/10 189.2 218.1

80/20 185.0 214.8

75/25 181.1 213.3

50/50 170.4 207.1

0/100 162.3 184.4

3.2. Study on preparation of gas barrier multilayer films based on 
polyme blends of EVOH and evaluate the lifetime of films

3.2.1. Study on preparation of PE/PE-EVOH/PE gas barrier multilayer films

3.2.1.1. Effect of PE-g-MAH compatibilizer content on properties of 
PE/PE-EVOH/PE gas barrier multilayer films

To evaluate the effect of PE-g-MAH compatibilizer content in layer 1
and layer 3 on the properties of the EVOH/PE multilayer film,
PE/PE-EVOH/PE multilayer film with layer 2 (PE/EVOH polymer blend) accounted
for 15% in volume, layer 1 and layer 3 (LLDPE/PE-g-MAH polymer blend)
accounted for 85% in volume were prepared. The PE-g-MAH compatibilizer
contents in layer 1 and layer 3 were 0-8%.

3.2.1.1.1. Effect of PE-g-MAH compatibilizer content on surface morphology 
of PE/PE-EVOH/PE gas barrier multilayer films

SEM images of the fracture surface of the PE/PE-EVOH/PE 3-layer
films with the PE/EVOH polymer blend content of 15% with and without the
compatibilizer was shown in Figure 3.16.

Fig.3.16. SEM images of the fracture surface of the PE/PE-EVOH/PE films 
a) without PE-g-MAH; b) with 2% PE-g-MAH; c) with 4% PE-g-MAH

SEM image of the fracture surface of the PE/PE-EVOH/PE films
containing the PE-g-MAH compatibilizer showed that with 2% of the
compatibilizer, the phase separation between layers was still relatively clear,

(b)

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but when the content of compatibilizer increased to 4%, it was difficult to
observe the division between layers, showing good adhesion between the
layers. It can be explained that the EVOH layer requires sufficient amount of
PE-g-MAH to develop covalent bond through the reaction between the
anhydride group of PE-g-MAH and hydroxyl groups of EVOH on the
interphase surface between LLDPE and EVOH.

3.2.1.1.2. Effect of PE-g-MAH compatibilizer content on mechanical 
properties of PE/PE-EVOH/PE multuilayer films

Effect of PE-g-MAH content on the mechanical properties of
PE/PE-EVOH/PE multilayer films was shown in fig. 3.17.

Fig.3.17. Effect of PE-g-MAH content on the mechanical properties of 
PE/PE-EVOH/PE films

The results showed that when adding 2% PE-g-MAH, the tensile
strength of the multilayer films decreased slightly, then the tensile strength
increased slightly when the PE-g-MAH content reached 4% and was almost
unchanged if the content of PE-g-MAH continues to increase. Thus, it can be
seen that PE-g-MAH had unsinificantly affect on the mechanical properties
of the PE/PE-EVOH/PE multilayer films.

3.2.1.1.3. Effect of PE-g-MAH compatibilizer content on oxygen 
transmission rate (OTR), water vapor transmission rate (WVTR) of 
PE/PE-EVOH/PE multilayer films

The effect of the PE-g-MAH content on the permeability of the PE /
PE-EVOH / PE multilayer film is summarized in Table 3.8.

Table 3.8. The oxygen and water vapor tranmisison rate of the 
PE/PE-EVOH/PE multilayer films with different PE-g-MAH contents (15% of
PE/EVOH)

Transmission rate The content of PE-g-MAH (%)

0 2 4 6 8

Oxygen transmission rate

(ml/m2.ngày) 3.01 3.22 3.26 4.58 5.64
Water vapor transmission

rate (g/m2.ngày) 6.87 6.85 6.89 6.86 7.01
400

450
500
550
600
650

10
15
20
25
30
35

0 2 4 6 8 Elongation

break

(%)

ensile

strength

(MPa)

PE-g-MAH content
Độ bền kéo đứt
Độ dãn dài khi đứt
Tensile stength

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The results showed that when the PE-g-MAH content increased from 0
- 4%, the oxygen transmission rate of the PE/PE-EVOH/PE film was almost
unchanged. However, at the PE-g-MAH content> 6%, the oxygen
transmission rate increased. The results also showed that the water vapor
transmission rate of the films was not affected by the PE-g-MAH content. 
3.2.1.2. Effect of PE/EVOH polyme blend (layer 2) content on properties of 
PE/PE-EVOH/PE multilayer films

To evaluate the effect of PE/EVOH polyme blend layer content on the 
properties of the PE/PE-EVOH/PE multilayer film, PE/PE-EVOH/PE
multilayer film with PE-g-MAH compatibilizer content layer 1 and layer 3 of
4%, PE/EVOH polymer blend content of 5 – 20% were prepared.

3.2.1.2.1. Effect of PE/EVOH polyme blend content on mechanical properties 
of PE/PE-EVOH/PE multuilayer films

Effect of the content of PE/EVOH polyme blend on the mechanical
properties of PE/PE-EVOH/PE multilayer films was summarized in table 3.9.
Table 3.9. Mechanical properties of PE/PE-EVOH/PE multilayer films

The content of 
PE/EVOH layer (%)

Tensile strength 
(MPa)

Elongation at break 
(%)

5 32.3 680.3

10 31.4 661.7

15 30.5 624.8

20 29.8 605.5

Mechanical properties measurement results showed that tensile strength
and elongation at break of multilayer films decreased slightly when
increasing the content of PE/EVOH polymer blend. This was due to the
PE/EVOH polymer blend layer had much lower elongation at break than
LLDPE resin. Especially, EVOH is a copolymers with high crystallinity
(58-70%), so it is quite brittle and low elongation, so increasing their content lead
to reduce elongation at break of the multilayer film.

3.2.1.2.2. Effect of PE/EVOH polyme blend content on oxygen transmission

rate (OTR), water vapor transmission rate (WVTR) of PE/PE-EVOH/PE 
multilayer films

Results of measuring oxygen and water vapor transmission rate of
multilayer films with different PE/EVOH polymer blend contents were
presented in Table 3.10.

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increased with increasing content of PE/EVOH blend layer. This is explained
by EVOH having -OH groups leading to its hydrophilic properties.
Increasing concentration of blend layer PE/EVOH means an increase in
EVOH content leads to an increase in the number of OH groups, making
them more hydrophilic.

Table 3.10. The oxygen and water vapor transmission of the 
PE/PE-EVOH/PE multilayer films (4% PE-g-MAH)

Transmission rate The content of PE/EVOH polymer blend (%)

5 10 15 20

Oxygen transmission rate

(ml/m2.ngày) 20.60 12.13 3.26 2.34
Water vapor transmission

rate (g/m2.ngày) 4.78 5.34 6.89 9.58

3.2.2. Study on preparation of PE/PA-EVOH/PE gas barrier multilayer films

3.2.2.1. Effect of PE-g-MAH compatibilizer content on properties of

PE/PA-EVOH/PE gas barrier multilayer films

To evaluate the effect of PE-g-MAH compatibilizer content in layer 1
and layer 3 on the properties of the PE/PA-EVOH/PE multilayer film,
PE/PA-EVOH/PE multilayer film with layer 2 (PA6/EVOH polymer blend)
accounted for 10% in volume, layer 1 and layer 3 (LLDPE/PE-g-MAH
polymer blend) accounted for 90% in volume were prepared. The PE-g-MAH
compatibilizer contents in layer 1 and layer 3 were 0-10%.

3.2.2.1.1. Effect of PE-g-MAH compatibilizer content on surface morphology 
of PE/PA-EVOH/PE gas barrier multilayer films

SEM image of fracture surface of the PE/PA-EVOH/PE three layer 
films with the PA6/EVOH polymer blend content of 15% with compatibilizer
was shown in Figure 3.19.

(a) Fracture surface of
film

(b) Fracture surface of
LLDPE/PE-g-MAH
polymer blend layer

blend layer

Fig.3.19. SEM image of fracture surface of the PE/PA-EVOH/PE film with

4% PE-g-MAH compatibilizer

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membranes there is a covalent bond between the carbonyl group of MAH in
PE-g-MAH and the amino group in PA6 and the hydroxyl group in EVOH.
This strong interaction lead to increased adhesion between
LLDPE/PE-g-MAH polymer blend layer and PA6/EVOH polymer blend layer.

3.2.2.1.2. Effect of PE-g-MAH compatibilizer content on mechanical 
properties of PE/PA-EVOH/PE multuilayer films

Effect of the PE-g-MAH content on the mechanical properties of
PE/PA-EVOH/PE mulitayler films was shown in figure 3.20.

Fig.3.20. Effect of the PE-g-MAH content on the mechanical properties of

mulitayler films

The results showed that PE-g-MAH unsignificantly affected to the
tensile strength of the PE/PA-EVOH/PE multilayer films. The results also
showed that the elongation at break of the PE/PA-EVOH/PE multilayer films
increased slightly with the addition of PE-g-MAH and the elongation at break
increased when the PE-g-MAH content in film increased.

3.2.2.1.3. Effect of PE-g-MAH compatibilizer content on oxygen 
transmission rate (OTR), water vapor transmission rate (WVTR) of 
PE/PA-EVOH/PE multilayer films

The influence of the PE-g-MAH content on the permeability of the
PE/PA-EVOH/PE multilayer films is summarized in Table 3.11.

Table 3.11. The oxygen and water vapor tranmisison rate of the 
PE/PA-EVOH/PE multilayer films with different PE-g-MAH content (10% of
PA6/EVOH)

Transmission rate The content of PE-g-MAH (%)

0 2.5 5 7.5 10

Oxygen transmission rate

(ml/m2.ngày) 1.86 2.52 2.43 4.21 5.39
Water vapor transmission

rate (g/m2.ngày) 6.70 6.69 6.72 6.79 6.75
The results showed that the presence of PE-g-MAH increased oxygen
tranmisison rate. However, when the PE-g-MAH content increased from 2.5
to 5%, the oxygen tranmisison rate was almost unchanged. When the 
PE-g-MAH content was > 5%, the oxygen tranmisison rate increased. The results

400
450
500
550
600
650
700

10
15
20

25
30
35

0 2,5 5 7,5 10

Elongation

break

(%)

ensil

strength

(MPa)

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also showed a similar trend for the PE/PE-EVOH/PE multilayer films,
PE-g-MAH did not affect the water vapor tranmisison rate of the PE/PA-EVOH/PE
multilayer films.

3.2.2.2. Effect of PA6/EVOH polyme blend (layer 2) content on properties of 
PE/PE-EVOH/PE multilayer films

To evaluate the effect of PA6/EVOH polyme blend layer content on the

properties of the PE/PA-EVOH/PE multilayer film, PE/PA-EVOH/PE
multilayer film with PE-g-MAH compatibilizer content layer 1 and layer 3 of
5%, PA6/EVOH polymer blend content of 5 – 20% were prepared.

3.2.2.2.1. Effect of PA6/EVOH polyme blend content on mechanical 
properties of PE/PE-EVOH/PE multuilayer films

Effect of the content of PA6/EVOH polymer blend layer on the
mechanical properties of mulayer films was presented in table 3.11.

Table 3.11. The mechanical properties of multilayer films with different 
PA6/EVOH polymer blend layer contents

The content of 
PA6/EVOH layer (%)

Tensile strength 
(MPa)

Elongation at break 
(%)

5 30.7 560.4

10 34.1 520.8

15 35.2 512.7

20 35.7 508.6

The results in table 3.11 showed that the tensile strength of films
increased slightly when the polymer blend layer content increased from
10-15%. When continuing to increase the content of polymer blend layer to
20%, the tensile strength is almost unchanged.

3.2.2.2.2. Effect of PA6/EVOH polyme blend content on oxygen transmission 
rate (OTR), water vapor transmission rate (WVTR) of PE/PA-EVOH/PE 
multilayer films

Results of measuring oxygen and water vapor transmission rate of
multilayer films with different PA6/EVOH polymer blend contents were
presented in table 3.13.

Table 3.13 The oxygen and water vapor transmission of the 
PE/PA-EVOH/PE multilayer films (5% PE-g-MAH)

Transmission rate The content of PA6/EVOH blend layer (%)

5 10 15 20

Oxygen transmission rate

(ml/m2.ngày) 4.54 2.43 1.69 1.32

Water vapor transmission

rate (g/m2.ngày) 5.6 6.72 8.1 11.1

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layer increased, the WVTR increased slightly.

Compared with the PE/PE-EVOH/PE multilayer membrane with the
same middle layer content, it was found that the oxygen barrier ability of the
PE/PA-EVOH/PE films was better, or the oxygen transmission rate was
lower. This can be explained by the fact that PA6 has a much higher barrier
to oxygen than PE but less than EVOH. In contrast, the water vapor barrier
ability of PE/PA-EVOH/PE multi-layer films was less than that of
PE/PE-EVOH/PE films with the same middle layer content, because PA6 contains
polar amide groups, which are hydrophilic so its water vapor transmission
rate was higher.

General comment: it can be seen that with the same content of the
middle layer, the PE/PE-EVOH/PE multi-layer film has lower WVTR but
higher OTR as compared with PE/PA-EVOH/PE multilayer film. So,
depending on the purpose of use, choose the right film. According to some
studies, to make the gas barrier film, the OTR of the film must be ≤ 5
ml/m2.day and the WVTR of the film must be ≤ 8 g/m2.day. The results
showed that the PE/PE-EVOH/PE multilayer film with the PE/EVOH polymer
blend content of 15% and the PE/EVOH/PE multilayer film with the
PA-EVOH polymer blend content of 5, 10 and 15% (signed PAEV-5, PAEV-10,
and PAEV-15, respectively) were unsatisfactory as gas barrier film.

3.3. Study on application of gas barrier multilayer films in the preservation 
of some dry agricultural products

3.3.1. Study on application of gas barrier multilayer films in the preservation of 
maize grain

Corn at 10.98% moisture content is packed into PAEV-10 bags, then
vacuumed on BZQ 500 machine (Maize-CK) (vacuum pressure -0.08MPa).
The control samples (without vacuum, Maize-T) were similarly conducted.

3.3.1.1. Effect of packaging conditions on maize quality

The changes in quality of maize grain under packaging conditions were
summarized in Table 3.15.

Table 3.15. The quality of maize grain under packaging condition during 
storage

Quality

indicators Samples

Time (months)

0 2 4 6 8

Moisture
content (%)

Maize-CK 10.98 10.96 11.04 11.09 11.18
Maize -T 10.98 11.30 11.64 11.95 12.05
Starch content

(%)

Maize -CK 74.58 74.49 74.32 74.26 73.02
Maize -T 74.58 74.33 73.06 71.93 70.14
Protein content

(%)

Maize -CK 9.07 9.06 8.97 8.81 8.60
Maize -T 9.07 9.04 8.89 8.12 6.93
Lipid content

(%)

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The results showed that the preservation maize grain by gas barrier
packaging with vacuum gave better efficiency when not vacuuming, so this
method is selected for the next study.

3.3.1.2. Effect of moisture content of maize grain on storage capacity

Corn at different moisture contents 10.98; 12.04 and 13.10% are
packed in PAEV-10 bags and vacuumed to a vacuum pressure of -0.08MPa.

The moisture content of the grain is an important parameter that
determines the shelf life of the seeds because it greatly affects the growth of
microorganisms and fungi. The degree of yeast and fungal contamination of
maize with different moisture of maize were summarized in Table 3.16.

Table 3.16. The degree of fungal contamination of maize during storage 
(CFU/ml)

Moisture content of

maize 10.98% 12.04% 13.10%

0 0 0 0

2 months 0 0 0

4 months 0 0 86

6 months 0 68 125

8 months 0 140 650

10 months 0 725 950

12 months 25 1.2 x 103 1.5 x 103

The results in Table 3.16 showed that with the moisture content of
maize of 10.98%, in the first 10 months, the sample was not contaminated
with yeast, mold; after 12 months of storage, the level of yeast and mold
infection was 25 CFU/ml. With higher maize moisture content (12.04% and
13.10%), it can be seen that the level of yeast and mold infections increased
with storage time. After 10 months, the level of yeast and mold infections of
these 2 maize samples were 725 and 950 CFU/ml, respectively. After 12
months of preservation, the levels of yeast and mold infections were > 103
CFU/ml. According to the Decision No. 46/2007/QĐ-BYT, the allowable
limit of the total number of yeast and mold spores in the food sample was 103
CFU/ml. Thus, at the moisture content of 12.04% and 13.10%, maize can
only be preserved for 10 months, with the moisture content of 10.98%, maize
can be preserved for over 12 months. Therefore, the material moisture
content of 10.98% was selected for the next study.

3.3.1.3. Effect of packaging materials on maize storage capacity

Corn at 10.98% moisture content is packed in PE, PAEV-5, PAEV-10,
PAEV-15 bags and vacuumed to a vacuum pressure of -0.08MPa.

* The change in quality indicators of maize grain

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Fig.3.24. The change in moisture 
content of maize when stored with

different materials

Fig.3.25. The change in starch 
content of maize when stored with

different materials

Fig.3.26. The change in protein 
content of maize when stored with

different materials

Fig.3.27. The change in lipid 
content of maize when stored with

different materials

The results showed that the moisture content of maize grain when
stored in PE packaging increased slowly in the early stage and increased
rapidly after 5 months of storage, while the moisture content of maize stored
in gas barrier multilayer packaging (PAEV-5 , PAEV-10, PAEV-15) were
almost unchanged. After 12 months of storage, the moisture content of maize

grain preserved in PE, PAEV-5, PAEV-10 and PAEV-15 packaging was
13.58; 11.04; 11.38 and 11.63%, respectively. Figure 3.25-3.27 also showed
that after 12 months of storage in gas barrier packaging, the starch, protein
and lipid content almost unchanged, only decreased by 1.39-4.36; 0.9-0.95
and 0.49 - 0.71%, respectively. Meanwhile, maize stored in PE bags only
maintains its quality in the first 2 months. When comparing 3 types of gas
barrier packaging PAEV-5, PAEV-10, PAEV-15 together, it was found that
the starch content of maize grain preserved in the PAEV-5 packaging
decreased the least (1.39%), in the bag. PAEV-15 decreased the most
(4.36%). Meanwhile, the lipid content tended to change in reverse, this value
decreased the most when maize was stored in PAEV-5 bags, the least

0
2
4
6
8
10
12
14

0 2 4 6 8 10 12

Moisture
content
(%)
Time (months)
PE
PAEV-5
PAEV-10

PAEV-15
50
55
60
65
70
75
80

0 2 4 6 8 10 12

Starch
content
(%)
Time (months)
PE
PAEV-5
PAEV-10
PAEV-15
0
2
4
6
8
10

0 2 4 6 8 10 12

Protein
content

(%)
Time (months)
PE
PAEV-5
PAEV-10
PAEV-15
0
1
2
3
4
5

0 2 4 6 8 10 12

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decrease when stored in PAEV-15 bags, but not much. Thus, it can be seen
that PAEV-5 multilayer film gives better maize preservation efficiency.

3.3.2. Study on application of gas barrier multilayer films in the 
preservation of soybean

3.3.2.1. Effect of packaging conditions on soybean quality

Soybean at 10.07% moisture content is packed into PAEV-10 bags,
then vacuumed on BZQ 500 machine (S-CK) (vacuum pressure -0.08MPa).
The control samples (without vacuum, S-T) were similarly conducted.

The changes in quality of maize grain under packaging conditions were
summarized in Table 3.18.

Table 3.18. The quality of soybean under packaging condition during storage

Quality

indicators Samples

Time (months)

0 2 4 6 8 10 12

Moisture
content (%)

S-CK 10.07 10.08 10.07 10.11 10.15 10.18 10.23
S -T 10.07 10.14 10.47 10.62 11.27 11.86 12.49
Protein

content (%)

S-CK 36.87 36.81 36.69 36.33 35.85 35.41 35.01
S -T 36.87 36.44 35.97 35.15 34.67 34.01 33.21
Lipid content

(%)

S-CK 19.65 19.53 19.21 18.84 18.47 18.08 17.62
S -T 19.65 19.41 18.82 18.21 17.63 17.08 15.89
The results showed that soybean stored in vacuum gas barrier
packaging had better quality than in packaging without vacuum.

3.3.2.2. Effect of moisture content of soybean on storage capacity

Soybean at different moisture contents 10.07; 11,02 and 12,04% are
packed in PAEV-10 bags and vacuumed to a vacuum pressure of -0.08MPa.

The degree of yeast and fungal contamination of soybean with different
moisture of maize were summarized in Table 3.19.

Table 3.19. The degree of fungal contamination of soybean during storage 
(CFU/ml)

Moisture content of soybean 10.07 % 11.02 % 12.04 %

0 0 0 0

2 months 0 0 0

4 months 0 0 0

6 months 0 0 128

8 months 0 76 831

10 months 0 2.5 x102 1.1 x103

12 months 0 1.0 x103 13 x103

Moisture content of 10.07% was selected for the next studies.
3.3.2.3. Effect of packaging materials on soybean storage capacity

Soybean at 10.07% moisture content is packed in PE, 5,
PAEV-10, PAEV-15 bags and vacuumed to a vacuum pressure of -0.08MPa.

- The change in quality indicators of soybean grain

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content and acidity in extract oil of soybean during storage were summarized
in Table 3.20.

Table 3.20. The change in quality of soybean during storage with different 
packaging materials

Quality indicators Time (months)

0 2 4 6 8 10 12

Moisture
(%)

PE 10.07 10.24 10.67 11.12 11.57 12.26 13.19
PAEV-5 10.07 10.07 10.06 10.10 10.13 10.16 10.21
PAEV-10 10.07 10.08 10.07 10.11 10.15 10.18 10.23
PAEV-15 10.07 10.07 10.08 10.10 10.15 10.19 10.24
Protein

(%)

PE 36.87 35.42 34.87 34.02 33.45 32.68 31.62
PAEV-5 36.87 36.84 36.72 36.34 35.84 35.39 35.03
PAEV-10 36.87 36.81 36.69 36.33 35.85 35.41 35.01
PAEV-15 36.87 36.83 36.70 36.35 35.86 35.40 35.04

Lipid (%)

PE 19.65 19.09 18.54 17.63 16.58 15.34 14.11
PAEV-5 19.65 19.51 19.13 18.72 18.26 17.59 16.93
PAEV-10 19.65 19.53 19.21 18.84 18.47 18.08 17.52
PAEV-15 19.65 19.61 19.45 19.36 18.91 18.53 17.95
Acidity in

extract oil
(%)

PE 0.37 0.48 0.62 0.89 1.33 1.94 2.73
PAEV-5 0.37 0.39 0.44 0.48 0.56 0.61 0.64
PAEV-10 0.37 0.36 0.39 0.43 0.51 0.58 0.62
PAEV-15 0.37 0.37 0.38 0.40 0.48 0.56 0.59
Results showed that there was a significant difference in moisture
content when soybeans were stored with gas barrier packagings and PE
packaging. The moisture content of soybeans preserved by PE packaging
increased significantly after 12 months of storage (3.12%) while the moisture
content of soybeans was kept almost unchanged.

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CONCLUSIONS

After a period of research, the thesis had obtained some results as
follows:

1. Study on successful preparation of PE/EVOH and PA6/EVOH
polymer blends:

- The presence of a 4% PE-g-MAH compatiblizer increased the

dispersion of EVOH resin into the PE matrix. A suitable PE/EVOH ratio for
preparing PE/EVOH polymer blend was 70/30.

- For PA6/EVOH polymer blend: when increasing the EVOH content,
torque increased, tensile strength decreased, elongation at break reached the
maximum value at 25% EVOH content. The ratio PA6/EVOH suitable for
preparing PA6/EVOH polymer blend was 75/25.

2. Study on successful preparation of gas barrier multilayer films with
thickness of 80µm while PE film used as 2 outer layers and PE/EVOH or
PA6/EVOH polymer blend used as middle layer.

- For PE/PE-EVOH/PE multilayer films: Appropriate compatibilizer
content was 4%. When the PE/EVOH polymer blend layer content increased,
the mechanical properties of the multilayer films decreased slightly, the
oxygen transmission rate decreased, the water vapor transmission rate
increased. With the content of PE/EVOH (70/30) polymer blend layer 5 -
20%: oxygen transmission rate of the films 20.60 - 2.34 ml/m2.day, the water
vapor transmission rate of the films 4.78 – 9.58 g/m2.day.

- For PE/PA-EVOH/PE multilayer films: Appropriate compatibilizer
content was 5%. When the content PA6/EVOH polymer blend layer content
increased, tensile strength increased, elongation at break decreased, oxygen
transmission rate decreased, water vapor transmission rate increased. With
the content of PA6/EVOH (75/25) polymer blend layer 5 - 20%, the oxygen
transmission rate of the films 4.54 - 1.32 ml/m2.day, the water vapor
transmission rate of the films 5.6 - 11.1 g/m2.day.

3. Evaluate the lifetime of two gas barrier multilayer films by weight
thermal analysis using Ozawa/Flynn/Wall method according to ASTM

E1641-16. At 30oC, the durability of PE/PE-EVOH/PE and
PE/PA-EVOH/PE films was 17.1 and 11.5 years, respectively.

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NEW CONTRIBUTIONS OF THE DISSERTATION

1. The thesis has successfully prepared 03 polymer material systems
including: LLDPE/EVOH/LLDPE-g-MAH polymer blend with the weight
proportion of constituent corresponding to 70/30/4, LLDPE/LLDPE-g-MAH
polymer blend (corresponding mass ratio 95/5) and PA6/EVOH polymer
blend (corresponding mass ratio 75/25) from available materials which have
technical requirements for fabrication of gas barrier multilayer films.

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PUBLICATIONS

1. Hoang Thi Phuong, Tran Vu Thang, Nguyen Tuan Nam, Nguyen Van 
Khoi, Nguyen Thanh Tung, Trinh Duc Cong (2016) Effect of compatibilizer
and LLDPE/EVOH ratio on mechanical properties and physico-chemical
characteristics of LLDPE/EVOH blends, Vietnam Journal Chemistry, 54 (6e1),
166 - 169.

2. Hoang Thi Phuong, Tran Vu Thang, Nguyen Tuan Nam, Nguyen Van 
Khoi, Nguyen Thanh Tung (2016) Effect of polymer blend content
PA6/EVOH on permeability, mechanical properties and structural
characteristics of coextruded three-layer blown fimls, Vietnam Journal
Chemistry, 54 (6e2), 156 - 159.

3. Nguyen Tuan Nam, Hoang Thi Phuong, Nguyen Thanh Tung, Nguyen 
Tien Dung, Tran Vu Thang, Nguyen Van Khoi, Ha Van Đat (2019)
Preparation and study on the properties of PA6/EVOH polymer blends,
Journal of Chemistry and Application, 1(45), 34-36, 79.

4. Nguyen Tuan Nam, Nguyen Thanh Tung, Nguyen Tien Dung, Pham Thu 
Trang, Nguyen Van Khoi, Nguyen Trung Duc, Pham Thi Thu Ha (2019)
Lifetime prediction of gas barrier multilayer films based on ethylene vinyl
alcohol (EVOH) by decomposition kinetics, Vietnam Journal Chemistry,
57(2E1,2), 233-237.

5. Nguyen Tuan Nam, Nguyen Thanh Tung, Nguyen Van Khoi, Pham Thu 
Trang (2019) Effect of PE-EVOH polymer blend layer and compatibilizer on
characterizations of PE/PE-EVOH/PE gas barrier multilayer films, Vietnam
Journal Chemistry, 57(4E3,4), 220-224.

</div>

Thông tin tóm tắt về những đóng góp mới của luận án tiến sĩ: Nghiên cứu chế tạo và tính chất màng polyme chắn khí và thăm dò ứng dụng.

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