When the PE/EVOH polymer blend layer content increased, the mechanical properties of the multilayer films decreased slightly, the oxygen transmission rate decreased, the [r]
Trang 1AND 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
HA NOI - 2020
Trang 2The 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:
2nd Reviewer:
3rd Reviewer:
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
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
Trang 3A 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 CO2barrier 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
Agriculture plays an important role in Vietnam's economy with great developments However, post-harvest losses of agricultural products are still high, from 15-20% for foods, the main reason is that the research, application and deployment of post-harvest technologies have not timely responded and are full of requirements In the country, there are also studies on the use of gas barrier packaging to preserve dry food and agricultural products, but the gas barrier packaging products on the market today are all imported products with expensive prices Stemming from the above problems, the thesis focuses
on: "Study on the manufacturing and properties of gas barrier multilayer films and applications"
Trang 42 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
In Vietnam, although the share of the agricultural sector in the country's GDP has decreased in recent years, its contribution to growth has remained stable at 16-18% The agricultural still plays an important role when it creates more than 40% of total employment for the whole country According to the World Food and Agriculture Organization (FAO), postharvest losses in developing countries amount to 20-30% In our country, the statistics show that the loss of yield during and after harvest for rice of 11-13%, maize of 13-15%, concentrated in the stages of harvesting, drying, preserving and milling The main cause is due to harvesting, packaging, transport and storage On the basis of synthesizing domestic and foreign research documents, it can be seen that gas barrier storage is an advanced preservation method, widely applied in the world today Packaging materials capable barrier of gas, moisture and solvents are increasingly popular, especially in the field of food preservation and dry food However, non-polar hydrocarbon solvents and their mixtures (such as xylene, toluene, white oil, etc.) can easily seep through the conventional polymer packaging (PE and PP) to degrade and cause health and food safety issues Therefore, combining polymers with specific features into new polymer materials that have all the preeminent features of the component polymers, meeting the technical requirements of gas barrier packaging products are essential
Trang 5Studies 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
Supermix high-speed mixer, Brabender Plastograph®EC device (Germany), hydraulic press, LyssyL-100-5000 water vapor permeability tester, N500 gas permeability tester, plastic SD-35 single screw extruder, 3SJ-G2000 multilayer film blowing device, BP-1068 mechanical measuring device, 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, BZQ 500 vacuum device, Mitutoyo IP67 electronic film thickness measuring device, scientech scales,
readability 0,001 (g), oven and laboratory equipments
Trang 62.2 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
Corn was selected according to standard 10TCN 513: 2002, 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
Trang 7indicators 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
Fig 3.1 Curves of mixing torque versus time for PE/EVOH polymer blends
The results showed that the torque in the molten equilibrium of the PE/EVOH polymer blend increased as the EVOH content increased
Trang 8Specifically, 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 (%)
Trang 9In 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)
Trang 103.1.1.4 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 SEM images of fractured surface of the polymer blends showed that in the polyme blends without compatibilizer (Fig 3.4), the phases dispersed unevenly, forming distinct phase separation regions, the dispersion of EVOH
in PE matrix was quite large and coarse With polymer blends containing compatibilizer, when the EVOH content increased from 10-30%, the component polymers had good dispersion and compatibility with each other
Trang 11However, 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
T g ( o C) T m ( o C) T c ( o C) Polyme blend LLDPE EVOH LLDPE EVOH
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
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
The effect of the components rate on the torque of PA6/EVOH polymer blends were presented in Fig 3.10
Trang 12Fig 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)
3.1.2.3 Surface morphology of PA6/EVOH polymer blends
Morphology of fracture surface of PA6/EVOH polymer blends was
Trang 13shown 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
Crystallization temperature of PA6 decreased from 193oC to 170oC when the EVOH content increased to 50% This indicated the formation of