The effect of pro-oxidant additives (Iron, Cobalt and Manganese stearates) on the biodegradation of recycle polyethelene mulching films was studied in both accelerated weather and natural exposure conditions. The degradation degree of film was determined by measuring mechanical properties and scanning electronic microscope (SEM). The results showed that the mechanical properties of film samples with pro-oxirant additives decreased rapidly, and that surface film with additives was degraded clearly compared to the films without additives after 30 cycles of accelerated weather. Reliability in terms of acceleration are 28 - 30 cycles of exposure and in the natural conditions reached 10-12 months

Cong, Trinh Duc

Hoan, Đỗ Công

Khoi, Nguyen Van

Manh, Nguyen Van

Phuong, Hoang Thi

Thang, Tran Vu

Trang, Pham Thi Thu

Tuan, Le Quang

Vietnam Academy of Science and Technology: Journals Online

   
Tạp chí Khoa học và Công nghệ 53 (3) (2015) 365-371  
DOI: 10.15625/0866-708X/53/3/4990 
EFFECT OF PRO-OXIDANT ADDITIVES ON DEGRADATION OF 
MULCH FILM BASED ON RECYCLED POLYETHYLENE 
 Nguyen Van Khoi, Le Quang Tuan, Tran Vu Thang, Nguyen Van Manh,                 
Hoang Thị Phuong, Pham Thi Thu Trang, Do Cong Hoan, Trinh Duc Cong* 
Institute of Chemistry, VAST, 18 Hoang Quoc Viet, Cau Giay, Hanoi 
* Email: congvhh@gmail.com 
Received: 18 September 2014; Accepted for publication: 31 October 2014 
ABSTRACT 
The effect of pro-oxidant additives (Iron, Cobalt and Manganese stearates) on the 
biodegradation of recycle polyethelene mulching films was studied in both accelerated weather 
and natural exposure conditions. The degradation degree of film was determined by measuring 
mechanical properties and scanning electronic microscope (SEM). The results showed that the 
mechanical properties of film samples with pro-oxirant additives decreased rapidly, and that 
surface film with additives was degraded clearly compared to the films without additives after 
30 cycles of accelerated weather. Reliability in terms of acceleration are 28 - 30 cycles of 
exposure and in the natural conditions reached 10-12 months. 
Keywords: pro-oxidant additives; photodegradable mulching films, polyethylene with pro-
oxidants. 
1. INTRODUCTION 
Polyolefin film (plastic bags, mulch ....) has become familiar in everyday life activities. 
With the advantages of durable, convenient and low cost, polyolefin film was present in almost 
all field of daily life activities. However, these products are often very persistent when released 
into the environment, which is negative impact on the environment and human health. Plastic 
waste causes serious impact to soil and water because it would prevent oxygen ingress through 
the soil that causing soil erosion and making the soil not porous, less nutrients support, which 
makes plants grow slowly. More seriously, soil and water contaminated by polyolefin film will 
affect directly and indirectly to human health. When burned they produced emissions dioxin and 
furan toxicity, endocrine influence, caused cancer, reduced immunity, digestive disorders and 
birth defects in infants. Therefore, the research on the manufacture of the potentially degradable 
polyolefin films to replace the persistent products is now an urgent request to solve the current 
[1 - 3]. 
There are a number of methods to minimize the impact on the environment of polyolefin 
films as collected and recycled, biodegradable increase of film material by adding some 
additives to promote the degradation of the films after disposal, blend of polyolefin with natural 
  
Nguyen Van Khoi, et al.  
366 
or synthetic polymer as polylactic acid, polycaprolactam, or the research of environmentally 
friendly products. 
Currently, the biodegradable film based on PE or PP with pro-oxidant additives has been 
interested. Pro-oxidant additives will make the path to self-destruct polyolefin catalysts to break 
the chain length of the polyolefin into shorter chain molecules and the incorporation of oxygen 
into these molecules as organic functional groups (i.e.: carboxylic or hydrocarboxilic acids, 
esters as well as aldehydes and alcohols). The molecules of low molecular weight are easily 
degraded by microorganisms, temperature and humidity in the environment, making the 
biomass, CO2 and H2O [1 - 5]. 
In this report, biodegradable films with and without pro-oxidant additives were prepared 
based on recycle PE resin. The biodegradation was determined in accelerated weather and 
natural exposure. Film characteristics were determined by measuring the mechanical properties 
(tensile strength and tensile elongation at break and SEM image.   
2. EXPERIMENTAL 
2.1. Materials 
Low-density Polyethylene (LDPE) (Malaysia); recycled polyethylene (PE) (Vietnam); pro-
oxidant additives: Iron (II) stearate Fe(C17H35COO)2, cobalt(II) stearate Co(C17H35COO)2, 
manganese (II) stearate Mn(C17H35COO)2, (Merck), containing by weight 99 % was made under 
masterbatch form at polymeric Lab - Institute of Chemistry, additive process palmowax 
(Malaysia). 
2.2. Method 
The process of film blowing was done using plastic mixture (including mLDPE 4%, 
recycle polyetylene plastic 67,2 % and polyetylene plastic 22,8 %). The plastic mixture was 
mixed with the amount of masterbatch containing additives such that each type of additive 
concetration in the film is 1 % w/w. 
- Film blowing: thin films (50 µm) were blowed from recycled polyethylene and 
masterbatch as mentioned above so that the concentration of additive in the film is 1 % w/w.  
- The film samples were noted as follows: film without additive (PE), film with Iron (II) 
stearate (PE-Fe), film with manganese (II) stearate (PE-Mn), film with cobalt(II) stearate (PE-
Co). 
- The film samples with or without pro-oxidant additives were tested in accelerated weather 
and natural exporuse  after that mechanical properties and surface morphology of the films were 
determined. 
 -  Accelerated weathering: PE films with and without additives were accelerated weather 
tested on equipment UVCON (Ultra Violet / Condensation Screening Device) Model UC-327-2. 
Samples were cut into rectangular dimensions of 7 × 14 (cm × cm) and mounted on aluminum 
panels. 30 cycles accelerated weather (UV 8-hour day, 4 hour stop / 1 cycle) were performed to 
evaluate weather durability and longevity. Samples were taken periodically and after every 4 
cycles samples were undertaken to measure the durability and longevity (ASTM G154). 
  
Effect of pro-oxidant additives on degradation of mulch film based on recycled polyethylene 
367 
- Natural exposure: Samples were cut into rectangular dimensions of 10 × 14 (cm × cm), 
hanging on the rack model. Film samples were exposed in period from July 2013 to July 2014. 
In that period, the samples were taken periodically to determine the properties. 
2.3. Methods of analysis and testing 
- Testing of critical mechanical properties: Samples of the films were tested accordingly to 
determine the tensile properties. Tensile tests were performed at room controlled conditions                   
(25 0C and 50 % humidity) and at 5 mm/min rate by AGS-J 10 kN (Shimadzu) equipment. Each 
sample was measured 5 times and then taking the average of the measurements. 
- Morphology of the film surface is determined on the scanning electron microscope 
Hitachi S4800 FESEM at Institute of Materials Science - Academy of Science and Technology 
Vietnam). 
3. RESULTS AND DISCUSSION 
3.1. Effect of additives on the properties of film in accelerated weathering 
Tensile strength and elongation at break of the film samples with and without pro-oxidant 
additives were measured. The results are presented in Figure 1 and Figure 2. 
 
 
Figure 1. Decrease in the tensile strength due to accelerated weather testing. 
The results showed that the value of t1/2TS (the time at which the tensile strength decrease 
by 50 % compared to the initial value, when the t1/2TS < 50 % of the initial value, the film as 
broken and film containing additives decreases faster than that without additives. The PE-Fe 
film has the fastest decreases, the value of  t1/2TS is about 24 cycles. Value t1/2TS of the PE-Mn 
film is about 27 cycles, 3 cycles higher than that of PE-Fe; while the value of PE-Co film is of 
about 29 cycles, which is  of 5 cycles more than that of additive iron stearate. On the other hand, 
PE films containing pro-oxidants exhibited a significant decrease in tensile strength.  
  
Nguyen Van Khoi, et al.  
368 
 
Figure 2. Decrease in tensile elongation at break due to accelerated weather testing.  
Similarly to broken tensile, the tensile elongation at break of PE-Fe film occurs much faster 
than that of the film without additives and it is the fastest of the PE-Mn and PE-Co films. Value 
t1/2EB (time at which the elongation at break decrease by 50 % compared to the initial values) 
of PE-Fe is about 26 cycles. Thus it suggests that the effective degradation of the PE-Fe film is 
higher compared with the manganese and cobalt based PE films. This may be due to differences 
in chemical structure of pro-oxidant additives. 
- The surface morphology of the film samples before and after accelerated weather is 
presented in Figure 3. 
  
 
Original PE film after 30 
cycles 
PE-Fe film after 30 
cycles  
PE-Mn film after 30 
cycles 
 PE-Co film after 30 
cycles 
Figure 3. The surface morphology of the film samples before and after accelerated weather. 
The surface morphology investigation of the films showed that after weather accelaration 
the films with additives exhibited cracks appearing on the surface. The cracks density on the 
surface of the PE film is reduced in comparison with those in the other additives added samples. 
This indicates an important role of pro-oxidant additives, namely under the impact of high 
energy radiation, the additive is capable of promoting the disconnected chain macromolecules 
into shorter chain molecules and the incorporation of oxygen into these molecules as organic 
functional groups (i.e: carboxylic or hydro-carboxilic acids, esters as well as aldehydes and 
alcohols). The photo-oxidative behavior was found to depend upon the type of metal present in 
the matrix and follows the order: Fe>Co>Mn. 
3.2. Effect of pro-oxidant additives on the properties of film in natural exposure 
  
Effect of pro-oxidant additives on degradation of mulch film based on recycled polyethylene 
369 
Tensile strength and elongation at break of the film samples with and without pro-oxidant 
additives were determined. The results are presented in Figure 4 and Figure 5. 
 
Figure 4. Decrease in the tensile strength due to natural weather testing. 
It can be noted that tensile strength of PE film mitigated after 12 months of outdoor 
weather exposure. Conversely, tensile strength of PE films containing additives significantly 
decreased after 12 months of outdoor weather exposure. This is due to that the ability of the 
metal stearate in catalyzing the degradation process has been reported to arise from its ability to 
intra-molecularly cleave into radicals, which can abstract hydrogen from the polymer chain, 
thereby generating free radicals. Products are hydrophilic oligomer, the double bond and the 
ester group susceptible to hydrolysis to form smaller molecules, a source of food for 
microorganisms and bacteria. After about 10-12 months of exposure, tensile strength of the film 
samples containing additives are reduced to less than 50% of the initial value. 
 
Figure 5. Decrease in tensile elongation at break due to natural weather testing. 
Tensile elongation at break of the film sample containing additives in samples exposed to 
natural conditions also decreased over time. The combined influence of such factors as 
temperature, UV radiation, humidity etc plays a role of an agent to promote the process of free 
radicals, and cause hydrocarbons disconections in the molecular structure of polyethylene. The 
interruption and oxidation of macromolecules circuit result in forming hydrophilic molecules 
such as esters, ketones, alcohol, which in turn, lead to deterioration of physical properties, 
  
Nguyen Van Khoi, et al.  
370 
especially elongation at break. Meanwhile the elongation at break of PE samples decreased 
slightly. 
4. CONCLUSIONS 
This study attempted to investigate the effects of pro-oxidant additives on mechanical 
strength and the surface morphology of films in two conditions, accelerated weather and natural 
weather. The results showed that for the film samples containing pro-oxidant additives, tensile 
strength and elongation at break decreased significantly during the trial period. Besides, tensile 
strength of the film samples containing additives was reduced to less than 50% after 12 months 
exposed under natural weather condition. Analysis results by morphological surface SEM 
images showed that after 30 cycles accelerated weather, the surface film containing additives 
were degraded compared with films containing no additives. 
Acknowledgements. The authors would like to thank Hanoi Science and Technology Service to sponsor 
this project. 
REFERENCES 
1. Abrusci C., Pablos J. L., Marín I., Espí E., Corrales T., Catalina F. - Comparative effect of 
metal stearates as pro-oxidant additives on bacterial biodegradation of thermal- and photo-
degraded low density polyethylene mulching films, International Biodeterioration & 
Biodegradation 83 (2013) 25-32.  
2. Abrusci C., Pablos J. L., Marín I., Espi E., Corrales T., Catalina F. - Photodegradation and 
biodegradation by bacteria of mulching films based on ethylene-vinyl acetate copolymer: 
effect of pro-oxidant additives, Journal of Applied Polymer Science 126 (2012) 1664-
1675. 
3. Chiellini E., Corti A., Swift G. - Biodegradation of thermallyoxidized, fragmented low- 
density polyethylenes, Polymer Degradation and Stability 81 (2003) 341-351. 
4. Ioanna Kyrikou, Demetres Briassoulis, Miltiadis Hiskakis, Epifaneia Babou - Analysis of 
photo-chemical degradation behaviour of polyethylene mulching film with pro-oxidants, 
Polymer Degradation and Stability 96 (2011) 2237-2252. 
5. Roy P. K., Titus S., Surekha P., Tulsi E., Deshmukh C., Rajagopal C. - Degradation of 
abiotically aged LDPE films containing pro-oxidant by bacterial consortium, Polym 
Degrad Stab 93 (2008) 1917-22. 
 
 
 
 
  
Effect of pro-oxidant additives on degradation of mulch film based on recycled polyethylene 
371 
TÓM TẮT 
ẢNH HƯỞNG CỦA PHỤ GIA XÚC TIẾN OXI HÓA ĐẾN KHẢ NĂNG TỰ HỦY CỦA 
MÀNG PHỦ TRÊN CƠ SỞ NHỰA POLYETYLEN PHẾ THẢI 
 Nguyễn Văn Khôi, Lê Quang Tuấn, Trần Vũ Thắng, Nguyễn Văn Mạnh, Hoàng Thị Phương, 
Phạm Thị Thu Trang, Đỗ Công Hoan, Trịnh Đức Công* 
Viện Hóa học, Viện Hàn lâm Khoa học và Công nghệ Việt Nam 
18 Hoàng Quốc Việt, Cầu Giấy, Hà Nội 
*Email: congvhh@gmail.com 
Ảnh hưởng của phụ gia xúc tiến oxi hóa (muối stearat của Fe, Mn, Co) đến khả năng phân 
hủy của màng phủ trên cơ sở nhựa polyetylen phế thải đã đươc đánh giá trong điều kiện gia tốc 
thời tiết và phơi mẫu tự nhiên. Mức độ phân hủy của màng được xác định bằng cách đo tính chất 
cơ lí và ảnh SEM chụp bề mặt màng sau khi gia tốc thời tiết. kết quả cho thấy tính chất cơ lí của 
màng chứa phụ gia giảm nhanh so với màng không chứa phụ gia. Cụ thể, độ bền kéo của màng 
chứa phụ gia giảm xuống còn dưới 50 % giá trị ban đầu sau 12 tháng phơi mẫu tự nhiên và 30 
chu kì gia tốc thời tiết. Kết quả chụp ảnh SEM cho thấy bề mặt các mẫu màng chứa phụ gia bị 
phá hủy so với mẫu màng không chứa phụ gia sau 30 chu kì gia tốc thời tiết. 
Từ khóa: màng phủ tự hủy; màng phủ nông nghiệp. 
 
 


EFFECT OF PRO-OXIDANT ADDITIVES ON DEGRADATION OF MULCH FILM BASED ON RECYCLED POLYETHYLENE

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EFFECT OF PRO-OXIDANT ADDITIVES ON DEGRADATION OF MULCH FILM BASED ON RECYCLED POLYETHYLENE

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