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

The thesis with the objective of researching to assess the biodegradability (including decomposition process and decomposition in soil environment) of polyethylene film containing additives promoting oxidation is Fe stearate salts (Fe). III), Co (II) and Mn (II).

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: Prof Dr Nguyen Van Khoi Institute of Chemistry - Vietnam Academy of Science and Technology 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 … 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 INTRODUCTION 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 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) 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 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 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 CHAPTER 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 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 1:3:0 0.0540 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 CHAPTER 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 Độ dãn dài đứt (%) Độ bền kéo đứt (MPa) 27 18 Ban đầu Sau ngµy oxy hãa nhiƯt Sau 96 giê oxy hãa quang, nhiệt, ẩm Ban đầu Sau ngày oxy hóa nhiÖt Sau 96 giê oxy hãa quang, nhiÖt, Èm M1 M2 M3 MÉu M4 800 600 400 200 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 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 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 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 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 Time (days) Figure 3.6 Changes in elongation at break of LLDPE films after 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 days, respectively On the other hand LLD1, LLD3 experiences almost 100% loss in 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 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 0 Time (days) LLD0 LLD1 LLD2 LLD3 20 Carbonyl index (CI) Carbonyl index (CI) 10 12 Figure 3.10 Carbonyl index of HDPE films after 12 days of thermal oxidation 15 10 0 Time (days) Hình 3.11 Carbonyl index of LLDPE films after 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 (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 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 Cacbonyl index (CI) Cacbonyl index (CI) 10 LLD0 LLD1 LLD2 LLD3 20 15 10 0 24 48 72 Time (hours) 96 Figure 3.21 Carbonyl index of HDPE films after 96 hours of photo-oxidation 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 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 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 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 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 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 – 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 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 month months months months months months HD0 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 month months months months months months LLD0 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 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 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 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 86.0 400 300 200 100 W av enu mber s ( c m- 1) Figure 3.41 FTIR of oxidized LLD3 after burying for months in soil 20 After 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 months HD3 after months LLD0 after months LLD3 after 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 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: 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 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 days, the LLDPE films with 0.1 and 0.2% prooxidant additives lost 100% of its initial mechanical properties after 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 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 weeks of aging, the LLD1, LLD2 films are considered to be capable of degradation after weeks of aging 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 The biodegradation of polyethylene films containing pro-oxidant additives in soil was evaluated by methods: buried in natural soil and incubated in soil - After 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% 24 NEW CONTRIBUTIONS OF THE DISSERTATION The mixture of Mn(II) stearate, Fe(III) stearate and Co(II) stearate which used as prooxidant additives promoted the degradation and biodegradation of PE films in both of natural condition and accelerated conditions (thermo-oxidation and photo-oxidation) The presence of CaCO3 fillers has effect of prolonging the induction phase of the degradation of HDPE films However, HDPE films with > 5% CaCO3 has lower stability than that with < 5% CaCO3 PUBLICATIONS Pham Thu Trang, Nguyen Quang Huy, Nguyen Van Khoi, Pham Thi Thu Ha, Nguyen Thanh Tung, “Comparison of the degradability of various polyethylene films containing pro-oxidant additive”, Vietnam Journal of Chemistry, 54(6), 683-687, 2016 Pham Thu Trang, Nguyen Quang Huy, Nguyen Thanh Tung, Nguyen Van Khoi, Trinh Đuc Cong, Le Van Duc, “Degradation of high density polyethylene (HDPE) films containing pro-oxidant additives in natural and accelerated weathering”, Vietnam Journal of Chemistry, 54(6E1), 11-16, 2016 Pham Thu Trang, Đang Van Cu, Nguyen Quang Huy, Pham Thi Thu Ha, Nguyen Van Khoi, Nguyen Thanh Tung, “Biodegradability of linear low density polyethylene (LLDPE) containing prooxidant additives”, Vietnam Journal of Chemistry, 54(6E1), 160-165, 2016 Nguyen Thanh Tung, Pham Thu Trang, Nguyen Quang Huy, Nguyen Lien Phuong, Pham Thi Thu Ha, Nguyen Van Khoi, “Accelerated weathering degradation of linear low density polyethylene films (LLDPE) containing prooxidant additives”, Vietnam Journal of Chemistry, 55(5e34), 240-244, 2017 Pham Thu Trang, Nguyen Thanh Tung, Nguyen Thu Huong, Nguyen Thi Mien, Nguyen Van Khoi, “The effect of CaCO3 filler contents on the properties of high density polyethylene (HDPE)”, pending review by the Journal of Chemistry Pham Thu Trang, Nguyen Thanh Tung, Nguyen Van Khoi, Nguyen Trung Duc, Pham Thi Thu Ha, “Study on degradation of oxidized high density polyethylene (HDPE) containing pro-oxidant additives in soil”, pending review by the Journal of Chemistry ... in the presence of transition metal stearates (Mn, Fe, Co) 2 Objectives of the dissertation Studied and evaluated the biodegradability (including the degradation and the biodegradation in the. .. 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. .. 322 days of incubation in soil, the mineralization level of HDPE films is > 24%, the mineralization level of LLDPE films is > 40% 24 NEW CONTRIBUTIONS OF THE DISSERTATION The mixture of Mn(II)