Nghiên cứu sự biến đổi đặc trưng, tính chất và hình thái cấu trúc của polyethylene tỷ trọng cao trong quá trình thử nghiệm tự nhiên tại bắc trung bộ tt tiến anh

MINISTY OF EDUCATION ANH TRAINING VINH UNIVERSITY ********** LE DUC MINH STUDY ON THE CHANGE IN CHARACTERISTICS, PROPERTIES AND MORPHOLOGY OF HIGH DENSITY POLYETHYLENE EXPOSED NATURALLY IN NORTH CENTRAL SUMMARY OF CHEMISTRY DISSERTATION Sepcialization: Organic chemistry Code: 9.44.01.14 NGHE AN - 2018 The present study has been completed at: Department of Physico – Chemistry of non - metallic materials Institute for tropical technology – Vietnam Academy of Science and Technology and Specialized Lab Organic Chemistry - Faculty of Chemistry Vinh University Supervisors: Prof Dr Thai Hoang Assoc Prof Dr Le Duc Giang Reviewer 1: Reviewer 2: Reviewer 3: Thesis will be presented and protected at school-level thesis vealuating Council at: Vinh University, 182 Le Duan, Vinh City, Nghe An Province Dissertation is stored in: National libarary of Vietnam Nguyen Thuc Hao Library and Information Center of Vinh University PUBLISHED WORKS Le Duc Minh, Nguyen Thuy Chinh, Nguyen Thi Thu Trang, Nguyen Vu Giang, Tran Huu Trung, Mai Duc Huynh, Tran Thi Mai, Le Duc Giang, Thai Hoang (2016), Study on change of some characters and morphology of polyethylene compound exposed naturally in Dong Hoi-Quang Binh, Vietnam Journal of Chemistry, 54(2), 153-159 Le Duc Minh, Nguyen Thuy Chinh, Nguyen Vu Giang, Tong Cam Le, Dau Thi Kim Quyen, Le Duc Giang, Thai Hoang (2017), Study on change of color and some properties of high density polyethylene/organo-modified calcium carbonate composites exposed naturally at Dong Hoi-Quang Binh, Vietnam Journal of Chemistry, 55(4), 417-423 Le Duc Minh, Nguyen Thuy Chinh, Le Duc Giang, Tong Cam Le, Dau Thi Kim Quyen, Thai Hoang (2018), Prediction of service half-life time of high density polyethylene/organo-modified calcium carbonate composite exposed naturally at Dong Hoi – Quang Binh, Vietnam Journal of Chemistry 56(6), pp 767-772 Le Duc Minh, Nguyen Thuy Chinh, Nguyen Vu Giang, Le Duc Giang, Tong Thi Cam Le, Dau Thi Kim Quyen, Tran Huu Trung, Mai Duc Huynh, Thai Hoang (2017), Study on the change in characteristics and morphology of high density polyethylene/organo-modified calcium carbonate composites exposed naturally at Dong Hoi – Quang Binh, Asian Workshop on Polymer Processing 2017, Hanoi University of Science and Technology, Program & Proceedings book, 154-159 Le Duc Minh, Nguyen Thuy Chinh, Le Duc Giang, Tong Thi Cam Le, Dau Thi Kim Quyen, Thai Hoang (2019), Study on the change in characteristics and prediction of service half-life time of high density polyethylene/organo-modified calcium carbonate composite exposed naturally at Dong Hoi – Quang Binh, Journal Chemical industry (accepted) INTRODUCTION Preamble High density polyethylene (HDPE) is the typical polymer hydrocarbon of thermoplastic and is widely used in technical and life Under different methods, HDPE is applied in the manufacture of food containers, covers for electric wires and cables, communication cables, hard tubes, twisted pipes for construction, architecture, electricity, telecommunication, etc In the process of use, especially in the outdoors, polymers in general and HDPE, PE composites in particular are always affected by sunlight and other environmental factors Oxidation reactions occurring when polymer is illuminated play an important role in polymer aging and affect the lifetime of HDPE The results of research on the photo-oxidation process of HDPE under the influence of sunlight in some parts of the world show that the mobility of HDPE macromolecular is changed, HDPE circuit is broken, the mechanical properties are greatly reduced over time In Vietnam, the study on the changes in properties and morphology of PE, PVC and rubber under natural exposure has been conducted in Hanoi, Quang Ninh, Da Nang and Ho Chi Minh City following different times However, natural exposure of HDPE with additive CaCO3 modified with steatic acid has not been conducted in Dong Hoi (Quang Binh), which is one of the locations showing the typical climate of the North Central region With average rainfall and number of rainy days are small in the year, meanwhile, relative humidity and average annual temperature are large, Dong Hoi (Quang Binh) has quite a harsh natural conditions Therefore, the process of thermal oxidation degradation, photodegradation, photo-oxidation degradation, ozone degradation for polymer composites may occur more strongly than other parts in our country In addition, there has not been any study in Vietnam that conducts both natural exposure and accelerated weather testing for HDPE/m-CaCO3 composite to compare the change of characteristics (infrared spectra, ultraviolet-visible spectra, nuclear magnetic resonance, molecular weight of products formed when HDPE was degraded, crystallinity percentage, etc.), mechanical properties, thermal properties, durability heat and morphology of HDPE Thus, no correlation coefficient has been determined between natural exposure and accelerated weather testing of HDPE as well as the lifetime prediction of this polymer From the research results in the country as well as the world, we found the study on changes in characteristics, properties, morphology, determining the lifetime of composites based on HDPE natural exposure in Dong Hoi (Quang Binh) combined with accelerated weather testing is very necessary, with both scientific and practical meaning Therefore, researcher has chosen to implement the thesis with the topic: “Study on the change in characteristics, properties and morphology of high density polyethylene exposed naturally in North Central” 2 Objects The research object of the thesis is the high density polyethylene/organomodified calcium carbonate composites exposed naturally at Dong Hoi City, Quang Binh province Tasks - The natural exposure the HDPE/m-CaCO3 composites was conducted at Dong Hoi City, Quang Binh province; The accelerated weather testing the HDPE/m-CaCO3 composites was carried out in a UV condensation weather device - Study on the change in characteristics, properties and morphology of high density polyethylene/organo-modified calcium carbonate composites exposed naturally and accelerated weather testing - Determining the correlation coefficient between the accelerated weather testing and natural exposure for lifetime prediction of the HDPE/m-CaCO3 composites - Proposing solutions to improve weather durability and increase the lifetime of the HDPE/m-CaCO3 composites exposed naturally in North Central New contributions of the thesis - The natural exposure the HDPE/m-CaCO3 composites were the first studied at Dong Hoi City, Quang Binh province (Viet Nam) - is a typical climate location of the North Central region - The change in characteristics, properties and morphology of the HDPE/mCaCO3 composites is closely related to weather factors, especially solar radiation and temperature during natural exposure - The correlation coefficient between the accelerated weather testing and natural exposure were determined for lifetime prediction of the HDPE/m-CaCO3 composites when studying the remained percentage of tensile strength, the remained percentage of elongation at break and the molecular weight of HDPE in HDPE/mCaCO3 composites Structure of the thesis It is displayed in a total of 133 pages with 21 tables, 58 figures, diagrams and 136 references Its major sections include: Introduction (3 pages), overview (45 pages), methods and experiment (12 pages), results and discussion (52 pages), conclusion (2 pages), published works (1 page) and references (17 pages) Morever, there is an appendix with 49 spectra, tables, figures and diagrams of the high density polyethylene/organo-modified calcium carbonate composites CHAPTER 1: OVERVIEW The thesis has conducted a literature review content: Basic information about polyethylene: introdution about polyethylene; photodegradation reaction and photo-oxidation degradation reaction of polyethylene High density polyethylene (HDPE): introdution about HDPE; structure, characteristics and properties of HDPE High density polyethylene/organo-modified calcium carbonate composites Natural exposure and accelerated weather testing of polymer Lifetime of polymer: effect of temperature; effect of humidity, steam; effect of weather Research situation natural exposure, accelerated weather testing and lifetime prediction of polymer CHAPTER 2: METHODS AND EXPERIMENT 2.1 Chemicals and equipment 2.1.1 Chemicals: High density polyethylene, calcium carbonate, acid stearic 2.1.2 Equipment: Preparation of the HDPE/m-CaCO3 composites samples (Haake internal mixer); measuring instrument IR, UV-Vis, 13C-NMR, XRD, DSC, TGA, SEM; instrument used for the accelerated weather testing (Atlas UVCON); measuring instrument the tensile properties (Zwich Z2.5), the color parameters (ColourTec PCM), electric properties (TR-10C) and viscosity (Ubbelohde) 2.2 Methods for polymer composite preparation Composites containing high density polyethylene, 30 wt.% calcium carbonate and wt.% acid stearic were prepared by melt mixing in a Haake internal mixer at 160oC for minutes Immediately after melt mixing, the composites were hot-pressed in melting state at 160oC with the pressure of about MPa into about 1-1.2 mmthickness sheets 2.3 Natural exposure and accelerated weather testing - Natural exposure: The HDPE/m-CaCO3 composites were exposed on outdoor testing shelves at the Natural Weathering Station of the Institute for Tropical Technology in Dong Hoi sea atmosphere region (Quang Binh) The inclining angle of shelves in comparison with the ground was 450 Total exposure time of the samples was 36 months - Accelerated weather testing: The instrument used for accelerated weather testing was the UV-CON 327 (USA) Test conditions were set according to the ASTM D 4329-99 Each cycle of the accelerated weathering test included hours of UV irradiation at 60oC and hours of condensation (with evaporation) at 50oC Total testing time was 720 hours (60 cycles) The UV-CON 327 was set on the automatic irradiance control mode with an irradiance level of 0.8 w/m2 at 313 nm After every six cycles, the samples were withdrawn and stored under standard condition 2.4 Methods Infrared (IR), ultraviolet (UV), nuclear magnetic resonance spectroscopic 13C-NMR, X-ray diffraction (XRD), Scanning Electronic Microscopy (SEM), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), electric properties measurement, tensile properties measurement, color measurement, viscosity measurement CHAPTER 3: RESULTS AND DICUSSION % Transmittance 3.1 The change in morphology and structure of HDPE/m-CaCO3 composites exposed naturally 3.1.1 Infrared spectra (IR) IR spectra of M0, M12, M24, M36 samples of HDPE/m-CaCO3 composites presented in Fig 3.1 3370 1639 1380 725 1715 2921 2854 1465 Wavenumbers (cm-1) Figure 3.5 IR spectra of HDPE/m-CaCO3 composites versus natural exposure time In the IR spectrum of M0, M12, M24 and M36 samples, some peaks characterize for stretching and bending vibrations of CH groups in HDPE were found at 2921, 2854, 1465 and 1380 cm-1 Beside, a peak corresponding to out-of-plane bending vibration of CH group appears at 725 cm-1 The absorption peak around 1735 cm-1 characterizes for the stretching vibrations of carbonyl groups was seen clearly in IR spectra of the exposed samples In addition, photolysis of ketones results in the formation of vinyl-type unsaturations with absorption band appearing at 1639 cm-1 A small increase in the region of 3300-3500 cm-1 was attributed to hydroxyl groups This is caused by the formation of the carbonyl groups such as ketone, lactone carbonyl and aliphatic ester occurring in photodegradation process of HDPE according to the Norish and Norish reaction and mechanism has been well described in the scheme 3.1 Table 3.1 Peaks characterize of some groups in the HDPE/m-CaCO3 composites Pic (cm-1) Groups M0 M12 M24 M36 719 724 721 724 CH (bending vibration) 1376 1373 1376 1376 CH3 (bending vibration) 1463 1465 1463 1463 CH2 (bending vibration) 1639 1639 1639 C=C (stretching vibration) 1715 1716 1716 Carbonyl (stretching vibration) 2849 2852 2850 2850 CH3 (stretching vibration) 2918 2915 2920 2931 CH2 (stretching vibration) 3345 3370 3370 OH (stretching vibration) HDPE h CH2 CH2 CH CH2 CH2 O2, PE H CH2 CH2 C CH2 O CH2 OH h H CH2 CH2 C O CH2 CH2 OH H CH2 CH2 C CH2 CH2 CH2 CH2 OH CH2 CH2 C CH2 carboxylic acid ester lactone h CH2 CH2 CH2 O Norrish CHO + CH2 Norrish CH2 C CH3 + H2C CH CH2 O CH2 CH2 C + CH2 O CH2 hNorrish CH CH2 + CH3COCH3 P + CH2 CH CH2 C CH O CH CH2 h saturated ketone CH CH CH2 + P CH CH3 PE CH CH CH3 (vinylene) Scheme 3.1 Simplified photo-degradation mechanism of HDPE To quantify relatively the carbonyl group content existed in the exposed samples, carbonyl index (CI) was calculated using the following equation: CI  I1715 I1462 Carbonyl index (CI) Where, I1725 and I1465 are absorption peak intensity at 1715 cm-1 and 1462 cm-1 Figure 3.2 shows the change of CI index of natural exposure samples versus exposed time Time (months) Figure 3.2 CI value of HDPE/m-CaCO3 composites versus natural exposure time Absorbance Figure 3.2 exhibits a increase of CI index as increasing the natural exposure time After months of natural exposure, the CI index of composite sample increase 1.7 times compared with the initial value and increase 3.0 times after 36 months of natural exposure The significant increase of the CI was observed for the samples exposed from to months, from 12 to 18 months and from 24 to 30 months (hot season) while from to 12 months, from 18 to 24 months and from 30 to 36 months (cold season) the CI varies more slowly 3.1.2 UV-Vis spectra The UV-Vis spectra showed an increase of the absorption intensity of HDPE in the composites between 200 and 300 nm wavenumber In the UV-Vis spectrum of initial sample (M0 sample), there was one very strong absorption band at 226 nm The absorption at 226 nm must be associated with the π – π* transition of the ethylenic group of the α,β-unsaturated carbonyl of impurity chromophores of the enone type in photo-oxidation degraded HDPE Wavenumber, nm Figure 3.3 UV-Vis spectra of HDPE/m-CaCO3 composites versus natural exposure time 3.1.3 Nuclear magnetic resonance spectroscopic 13C-NMR Nuclear magnetic resonance spectroscopic 13C-NMR of HDPE sample (M0n), HDPE/m-CaCO3 composites samples before natural exposure (M0) and HDPE/mCaCO3 composites samples after 36 months natural exposure (M36) were performed in figures 3.4 - 3.6 Figure 3.4 13C-NMR spectra of HDPE sample (M0n) 10 3.1.5 Morphology (a) (b) (c) (d) (e) (g) (h) Figure 3.9 SEM images of M0 (a); M6 (b); M12 (c); M18 (d); M24 (e); M30 (g); M36 (h) samples versus natural exposure time Figure 3.9 demonstrates the surface images of the samples before and after natural exposure Before natural exposure, the sample surface was relatively smooth, only had some small cracks (M0 sample) After - 36 natural exposure months, there were more cracks found on the surface of the exposed samples The number and size of cracks were increased with increasing natural exposure time The cracks also became bigger and deeper 3.1.6 Color change Figure 3.10 The change of a*, b*, L* and E* value of HDPE/m-CaCO3 composites according to natural exposure time 11 The change in values for three color parameters (L*, a* and b*) as well as the total color change (E) of the composites as a function of natural exposure time was displayed in table 3.4 and figure 3.10 The surface of the samples of HDPE/m-CaCO3 composites was lightened continuously, the L* and E values were increased with increasing natural exposure time The changes in E values for the samples were found to be consistent with the change in L* values The results of color change indicated that the surface of the samples of HDPE /m-CaCO3 composites was faded continuously with increasing natural exposure time expressed by a constant increase in L* value and significant loss in both redness and yellowness This phenomenon may be due to the change in morphology and existence of double bonds inside the HDPE macromolecules during photodegradation HDPE/m-CaCO3 composites The mechanism of forming some double bonds of composite samples were presented in the schemes 3.2 – 3.5 H C H C H H C H O H h O H H C O P C H O O H C H + H H H O H P P Scheme 3.2 Schematic representation of the formation of trans-vinylene in HDPE chain H h CH2CH2CH2 - C O CH O C CH2 H2C CH3 - C CH=CH2 + CH2=C O OH Scheme 3.3 Schematic representation of Norrish type II reaction in HDPE chain C C C H2 C H2 + H2C CH2 CH2 CH2 Scheme 3.4 Schematic representation of beta scission in HDPE chain H O CH H C C C O h O H O O CH O H H H CH H Scheme 3.5 Schematic representation of the formation of carbonyl in HDPE chain Table 3.4 The a*, b*, L* and E value of HDPE/m-CaCO3 composites according to natural exposure time Samples a* b* L* E M3 3,27 1,04 2,99 4,03 M6 2,63 0,10 3,11 4,26 M9 2,33 -0,06 3,77 4,44 M12 2,05 -0,18 5,27 5,71 M15 1,71 -0,95 7,22 7,64 M18 1,41 -1,75 7,62 8,00 M21 1,21 -1,89 7,98 8,33 12 M24 M27 M30 M33 M36 1,11 1,027 0,957 0,902 0,836 -2,07 -2,71 -3,51 -3,75 -3,94 9,24 10,08 10,32 10,83 12,07 9,73 10,85 11,12 11,38 12,43 3.1.7 Average molecular weight The M v of the samples significantly was decreased during natural exposure time (figure 3.11) After 12 and 36 months of natural exposure, the Mv of M12 and M36 samples were 47.83 and 71.74% of its initial value of M0 sample, respectively The result can be explained by considerable influence of weather factors as solar irradiation, temperature and humidity on deterioration in average molecular weight of HDPE, especially in the starting progress of its natural exposure Table 3.5 Average molecular weight of HDPE/m-CaCO3 composites versus natural exposure time Samples M6 160000 M12 120000 M18 100000 M24 80000 M30 70000 M36 65000 Average molecular weight, đvC Mv M0 230000 Samples Figure 3.11 Average molecular weight of HDPE/m-CaCO3 composites versus natural exposure time 3.2 The change in tensile properties, thermal properties and electric properties of HDPE/m-CaCO3 composites versus natural exposure time 3.2.1 Tensile property The remained percent of tensile strength (σ), elongation at break (ε) of HDPE/m-CaCO3 composites were decreasing with increasing natural exposure time (figure 3.12) They were decreased significantly during the first months of natural exposure with 29,4 and 81,4%, respectively After first months of natural exposure, the tensile strength and elongation at break of HDPE/m-CaCO3 composites were decreased more slowly Table 3.6 The remained percent of tensile strength, elongation at break and Young modulus of HDPE/m-CaCO3 composites versus natural exposure time Times (months) σ (%) ε (%) E (%) 100 100 100 12 18 24 30 36 70,6 60,4 52,6 50,2 47,5 46,2 18,6 13,4 11,2 9,5 7,4 6,9 117,4 146,1 164,2 168,4 171,5 174,1 The remained percent of elongation at break, ε (%) The remained percent of tensile strength, σ (%) 13 (a) 12 18 24 30 (b) 36 12 18 24 30 36 Time (months) Time (months) The remained percent of Young modulus, E (%) Figure 3.12 The remained percent of tensile strength (a), elongation at break (b) of HDPE/m-CaCO3 composites versus natural exposure time 12 18 24 30 36 Time (months) Figure 3.13 The remained percent of Young modulus of HDPE/m-CaCO3 composites versus natural exposure time The Young modulus (E) of HDPE/m-CaCO3 composites was increased with increasing natural exposure time (figure 3.13) After 6, 12, 18, 24, 30 and 36 months of natural exposure, it was increased 17.4, 46.1, 64.2, 68.4, 71.5 and 74.1% compared with the unexposed HDPE/m-CaCO3 composites, respectively 3.2.2 Thermal properties The thermal datas and DSC curves of HDPE/m-CaCO3 composites before and after natural exposure was displayed in table 3.7 and figures 3.14 – 3.17 Table 3.7 Melting temperature (Tm), melting enthalpy (Hm) and relative degree crystalline (C) of HDPE compoundversus natural exposure time C (%) Samples Tm, PE (oC) Hm, PE (J) M0 144 168,5 57,4 M3 143 169,3 57,7 M6 144 169,3 57,7 M9 143 179,7 61,2 M12 145 179,1 61,2 M15 142 179,5 61,3 M18 142 179,8 61,6 M21 142 180,4 62,3 M24 144 180,3 62,1 M27 144 180,9 62,7 M30 143 181,4 62,6 M33 143 181,8 62,7 M36 144 181,7 63,4 14 Figure 3.14 DSC curve of M0 sample Figure 3.15 DSC curve of M12 sample 15 Figure 3.16 DSC curve of M24 sample Figure 3.17 DSC curve of M36 sample The melting temperature (Tm) of exposed and unexposed samples is almost constant, around 144 oC Table 3.7 exhibits a slight increase of melting enthalpy and relative degree crystalline during the first months of natural exposure with 169.3J and 57.7%, respectively The significant increase of melting enthalpy and relative degree crystalline was observed for the samples exposed from to months while 16 from to 36 months, the melting enthalpy and relative degree crystalline varies more slowly The thermo gravimetric (TG) data of HDPE/m-CaCO3 composites samples exposed naturally are listed in table 3.8 Table 3.8 Initial degradation temperature (Tini), maximum degradation temperature (Tmax) and remained weight at different temperature of HDPE/m-CaCO3 composites exposed naturally Samples Tini, oC Tmax, oC M0 M3 M6 M9 M12 M15 M18 M21 M24 M27 M30 M33 M36 463 462 455 453 451 450 449 449 448 447 446 445 445 467 465 459 461 460 460 458 457 457 456 453 454 453 Remained weight (%) at 400 (oC) 450 (oC) 500 (oC) 89,55 56,75 3,45 88,55 55,92 2,72 87,46 54,82 1,22 87,44 53,60 1,40 86,77 52,27 1,07 86,11 51,89 1,05 85,83 51,12 1,05 85,21 50,47 1,04 85,02 50,02 0,92 84,66 48,93 0,94 84,19 48,86 0,93 83,81 48,23 0,93 83,62 47,32 0,86 The TG curves demonstrate first weight loss stage of the samples observed at 300-465oC Then, the highest weight loss stage of the samples is at 465-500oC, and finally, small weight loss stage is at 500-600oC The results in table 3.8 show the initial thermo-degradation temperature, maximum thermo-degradation temperature, as well as remained weight of the samples to have a decrease trend versus natural exposure time and aging temperature This confirms the influence of natural exposure time on decrease of average molecular weight and chemical durability of HDPE macromolecules 3.2.3 Electric properties 3.2.3.1 Dielectric constant It can be seen that the effective dielectric constant of the M0 sample was very weakly dependent on frequency, which is the typical characteristic of non-polar polymers The M0 sample contained non-dipolar units and there were not frequency characteristics in the range of 100 – 106 Hz For the exposed samples, the interfacial polarization can cause an increase of dielectric constant when compared with the M0 sample When the chains of HDPE in HDPE/m-CaCO3 composites were scissed, the free volumes could be decreased and may cause the increase of dielectric constant Additionally, it was caused by the formation of the carbonyl groups such as ketone, lactone carbonyl and aliphatic ester occurring in photo-degradation process of HDPE/m-CaCO3 composites Dielectric loss Dielectric constant 17 Frequency (Hz) Frequency (Hz) Figure 3.18 Frequency dependence of dielectric constant (a) and dielectric loss (b) of HDPE/m-CaCO3 composites according to natural exposure time 3.2.3.2 Dielectric loss The dielectric loss of HDPE/m-CaCO3 composites was decreased with increasing natural exposure time and frequency because a higher frequency voltage can yield higher electrical conductivity as shown in figure 3.18b Unlike the dependence of dielectric constant, the dielectric loss of the samples decrease when increasing natural exposure times There were two competitive factors that affect the dielectric loss of the samples such as hindrance in charge transport and the incorporation of charge 3.2.3.3 Electrical breakdown voltage The value of electrical breakdown voltage of the samples was decreased gradually with increasing natural exposure time This observation is of vital importance for engineering application because the dielectric rupture always occurs at the weakest points In other words, the real dielectric strength of the samples is determined by the weakest part of their insulation Firstly, when increasing natural exposure time, the relative crystalline degree of the samples was reduced This can be explained by the scission photo-degradation of HDPE macromolecules in HDPE/mCaCO3 composites leading to decrease crystalline regions of HDPE/m-CaCO3 composites In the result, the intrinsic strength of the samples was decreased Secondly, the mobility of charges in the HDPE/m-CaCO3 composite insulation is much higher with inreasing natural exposure time Therefore, the charges are wider distributed in the HDPE/m-CaCO3 composites and the screening effect is less pronounced The above reasons make decrease the electrical breakdown voltage of the composites according to natural exposure time Table 3.9 Electrical breakdown voltage data of HDPE/m-CaCO3 composites according to natural exposure time Samples E (kV/mm) Samples E (kV/mm) M0 24,17 M21 15,89 M3 21,89 M24 15,34 M6 21,55 M27 15,21 M9 18,33 M30 14,86 M12 17,54 M33 14,46 M15 M18 17,04 16,23 M36 14,23 3.2.4 Test and evaluation of fungal spores in HDPE/m-CaCO3 composite Figure 3.19 reflects incubation results of composite samples at 23°C, through 72 hours after months and 40 months of natural exposure Observation results of the composites with naked eye and a template on a microscope (x100) showed no development of mold on both samples in the same testing conditions This can be explained by the petroleum origin of HDPE, a thermoplastic resin which is quite 18 inert, resistant to biological agents, including mold attack Although HDPE matrix was photo-oxidation degraded forming the products are low-molecular compounds with oxygen-containing groups, including ester, hydroperoxide groups, etc HDPE still has a relatively high average molecular weight, so it cannot be a nutrient source for fungal spores in the air to localize and develop in three dimensions of the sample, first of all on the sample surface Figure 3.19 The samples tested for fungal spores Where, well 1,4: M1 sample; well 2,5: M2 sample; well 3,6: for control 3.3 Lifetime rediction of the HDPE/m-CaCO3 composites exposed naturally in North Central 3.3.1 Prediction of service half-life time of HDPE/m-CaCO3 composite 3.3.1.1 Prediction of service half-life time based on remained percentage of tensile strength The change in remained percent of tensile strength (σ) of HDPE/m-CaCO3 composites exposed naturally condition was described by the trend types including to linear, exponential and polynomial types were applied for points of σ at the different testing times in figure 3.20 The equations and regression coefficients obtained from fitting these types were listed in table in which, y is the remained percentage of tensile strength; x is the natural exposure time Among the different orders of polynomial functions, the 6th order polynomial function exhibited a highest regression coefficient (R2 = 1) It means that the tendency of decrease in tensile strength of the HDPE/m-CaCO3 composite vs exposure time complied with 6th orderpolynomial function This was a complex process and combined multi-effects From figure 3.20, it can be observed the service half–life time of HDPE/mCaCO3 composite according to the tensile strength was 25.6 months Table 3.10 Trend type, equation and regression coefficient (R2) of variation of tensile strength during 36 months of natural exposure No Trend type Equation R2 Linear Exponential Polynomial Polynomial Polynomial Polynomial Polynomial y = -1.2964x + 84.407 y = 83.886e-0.02x y = 0.0624x2 – 3.544x + 95.645 y = -0.0026x3 + 0.2048x2 – 5.4422x + 99.062 y = 0.0001x4 – 0.0107x3 + 0.3829x2 - 6,.6586x + 99.804 y = -7.10-6x5 + 0.0007x4 – 0.0294x3 + 0.6197x2 – 7.6485x + 99.952 y = 10-6x6 – 0.0002x5 + 0.0065x4 – 0.1389x3 + 1.5534x2 – 10.447x + 100 0.7694 0.8476 0.9621 0.9939 0.9982 0.999 19 Figure 3.20 Remained percentage of tensile strength (σ) of the HDPE/m-CaCO3 composite vs exposure time 3.3.1.2 Prediction of service half-life time based on remained percentage average molecular weight of HDPE in the composite Table 3.11 Trend type, equation and regression coefficient (R2) of variation of average molecular weight during 36 months of natural exposure No Trend type Equation R2 Linear Exponential Polynomial Polynomial Polynomial 0,8713 0,9645 0,9826 0,9945 0,9984 Polynomial Polynomial y = -4279,8x + 197036 y = 203983e-0,035x y = 147,16x2 – 9577,4x + 223524 y = -5,0154x3 + 417,99x2 - 13188x + 230024 y = 0,3303x4 – 28,795x3 + 946,23x2 - 16796x + 232225 y = 0,0016x5 + 0,1856x4 – 24,262x3 + 888,94x2 16557x + 232189 y = -0,0052x6 + 0,5642x5 – 22,661x4 + 405,38x3 – 2774,7x2 - 5575x + 232000 0,9984 Table 3.21 Variation of average molecular weight of HDPE chains in HDPE/m-CaCO3 composite vs natural exposure time The equations and regression coefficients obtained from fitting these types were listed in table 3.11 (y is the average molecular weight of HDPE in HDPE/m-CaCO3 20 composite, x is the natural exposure time) Accordingly, the variation trend of average molecular weight of HDPE chains in HDPE/m-CaCO3 composite was also fitted to the 6th order polynomial function like the variation trend of tensile strength as above discussed However, from figure 3.21, the service half-life time of HDPE/mCaCO3 composite based on average molecular weight of HDPE in the composite was only 11.2 months This value was much different from that value obtained owing to remained percentage of tensile strength 3.3.2 Lifetime prediction based on correlation between the natural exposure and accelerated weather testing 3.3.2.1 Correlation between the natural exposure and accelerated weather testing in tensile strength The remained percent of tensile strength (σ) of HDPE/m-CaCO3 composite natural exposure and accelerated weather testing were demonstrated in table 3.12 Table 3.12 The remained percent of tensile strength of HDPE/m-CaCO3 composite natural exposure and accelerated weather testing Natural Artificial Days σ (%) Hours σ (%) 180 360 540 720 900 1080 100 70.6 60.4 52.6 50.2 47.5 46.2 72 144 216 288 360 432 504 576 648 720 100 83.5 70.2 62.5 56.4 52.7 49.8 48.2 46.1 45.2 45.1 The equations and regression coefficients for the remained percentage of tensile strength of HDPE/m-CaCO3 composite in both testing conditions were given as follows: r2 = 0.9939 YN  99.06  0.1814X N  2.275 *10 4 X 2N  0.9764 *107 X 3N YA  99 54  0.2504 X A  4.159 * 10 4 X 2A  2.424 * 10 7 X 3A r2 = 0.9987 Remained percent of tensile strength (%) Natural Artificial Times (natural: days; arfiticial: hours) Figure 3.22 Correlation coefficient between natural exposure and accelerated weather testing based on remained percentage of tensile strength of the HDPE/m-CaCO3 composite according to natural exposure and accelerated weather testing time As presented in figure 3.22, 412.6 hours of accelerated weather testing was corresponded to 710 days of natural exposure for the remained percentage of tensile strength 50% 3.3.2.2 Correlation between the natural exposure and accelerated weather testing in elongation at break The remained percent of elongation at break (ε) of HDPE/m-CaCO3 composite natural exposure and accelerated weather testing were demonstrated in table 3.13 21 Table 3.13 The remained percent of elongation at break of HDPE/m-CaCO3 composite natural exposure and accelerated weather testing Natural Artificial Days σ (%) Hours σ (%) 180 360 540 720 100 18.6 13.4 11.2 9.5 72 144 216 288 100 45.5 22.7 13.5 10.7 900 7.4 360 8.5 1080 6.9 432 6.6 504 5.4 576 4.6 648 4.1 720 3.2 The equations and regression coefficients for the remained percentage of elongation at break of HDPE/m-CaCO3 composite in both testing conditions were given as follows: YN  99 93  0.8944 X N  3.404 * 10 3 X 2N  6.016 * 10 6 X 3N  4.95 * 10 9 X 4N  1.535 * 10 12 X 5N r2 = 0.9993 YA  98 99  1.393 X A  8.314 * 10 3 X 2A  2.299 * 10 5 X 3A  2.933 * 10 8 X 4A  1.397 * 10 11 X 5A r2 = 0.9949 Remained percent of elongation at break (%) Natural Artificial Times (natural: days; arfiticial: hours) Figure 3.23 Correlation coefficient between natural exposure and accelerated weather testing based on remained percent of elongation at break of the HDPE/m-CaCO3 composite according to natural exposure and accelerated weather testing time From the figure 3.23, the correlation factor determined by the elongation at break that for 46.52 hours accelerated weather testing was as the same as the case tested for 74.19 days in natural exposure condition 3.3.2.3 Correlation between the natural exposure and accelerated weather testing in average molecular weight of HDPE in the composite The average molecular weight of HDPE in the composite natural exposure and accelerated weather testing were demonstrated in table 3.14 Table 3.14 Average molecular weight of HDPE in the composite natural exposure and accelerated weather testing Natural Artificial Days M v (đvC, 103) Hours M v (đvC, 103) 180 230 160 360 120 540 100 720 80 900 70 1080 65 72 230 185 144 150 216 125 288 110 360 96 432 85 504 73 576 61 648 57 720 51 22 The equations and regression coefficients for remained percent of average molecular weight of HDPE in HDPE/m-CaCO3 composite in both testing conditions were given as follows: YN  100.2  0.2136X N  0.2595 *103 X 2N  1.134 *107 X 3N ; R2 = 0.992 Remained percent of average molecular weight (%) YA  99.11  0.2821X A  0.4201*10 3 X 2A  2.48 *10 7 X 3A ; R2 = 0.9978 Natural Artificial Times (natural: days; arfiticial: hours) Figure 3.24 Correlation coefficient between natural exposure and accelerated weather testing based on remained percent of average molecular weight of HDPE according to natural exposure and accelerated weather testing time The analysable results of average molecular weight of HDPE in HDPE/mCaCO3 composites showed that for 258.3 hours accelerated weather testing was as the same as the case tested for 384.3 days in natural exposure condition 3.4 Proposing solutions to improve weather durability of the HDPE/m-CaCO3 composites exposed naturally in North Central To improve weather durability, lifetime of HDPE/m-CaCO3 composites for outdoor applications such as hard tubes, twisted tubes, communication cables, panels, flooring, partitions, railing, fence, etc the researcher proposed to supplement some other additives with m-CaCO3 into HDPE, which are: - Ultraviolet ray absorbers, optical stabilizers based on hydroxybenzophenone, o-hydroxyphenylsulfoxide derivatives, hydroxyphenyl benzotriazole, cyanoacrylate, hydroxyphenyl triazine, hindered amine light stabilizers (HALS) and piperidine derivatives obstructing space, etc Ultraviolet ray absorbers, optical stabilizers allow HDPE to keep color unchanged, limit the deterioration of mechanical properties, extend the lifetime - The anti-oxidant for HDPE has the effect of eliminating free radicals R, RO, and ROO during the polymer is photo-oxidation degraded The effect of anti-oxidants depends on the amount of hydroxyl groups in the molecular Typical commercial anti-oxidants are alkylphenol derivatives and aromatic amines obstructing space such as 2,6-bis(1,1-dimethylethyl)-4-methylphenol (BHT), 2,6-di-tert-butyl-4phenylphenol, 4,4’-(propane-2,2-diyl)diphenol (BPA), 2,2’-methylenebis-(4-methyl6-tert-butylphenol), 2,2’-di-thio-bis(4,6-di-tert-butylphenol), [3-(3,5-di-tert-butyl-4hydroxyphenyl)- propionate] (Irganox 1010), 2-(2’-hydroxy-5’- methyl-phenyl)benzotriazole (Tinuvin P), 2-(2’-hydroxy-3’-tert-butyl-5’-methylphenyl)-5   23 chlorobenzotriazole (Tinuvin 326), etc Anti-oxidants limit the chain breakdown of the HDPE macromolecular, deteriorating mechanical properties, extending the lifetime of products from HDPE - The hydroperoxide groups exist in HDPE and form during the photo-oxidation degradation of polymer are the agents promoting the subsequent polymer degradation process For that reason, they must be thoroughly deoxidated while it's important to ensure that no or very few free radicals are formed Effective hydroperoxide deoxidations are thiobisphenol, dilaurylthiodipropionate (DLTDP), dialkylsulphide, trialkylphosphite (typically Irgafos 168) Sulfur-containing tin compounds such as (C4H9)2Sn(SC12H25)2 are also a very effective hydroperoxide deoxidation for HDPE - To limit the effects of thunderstorms, lightning, ozone to HDPE-based products, antiozonants is necessary Typical antiozonants for polyolefins such as HDPE are p-phenylenediamine derivatives such as N,N,N’,N’-tetramethyl-pphenylenediamine (TMPPD), N,N’-dimethyl-butyl-p-phenylenediamine (6PPD), N,N’-diaryl-p-phenylenediamine (DPPD); tris-(N-dimethylpentyl-pphenylenediamine)-N’,N’,N’-1,3,5-triazine (6PPDTZ), hydroquinoline derivatives such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline; 6-dodecyl-2,2,4-trimethyl1,2-dihydroquinolin, etc Anti-ozonants limit color change and reduce crack formation on HDPE-based products - When being used separately, ultraviolet ray absorbers, optical stabilizers, antioxidants, hydroperoxide deoxidization, anti-ozonants significantly reduce the photooxidation degradation polymer used outside However, HDPE protection performance of them is limited because each substance only exhibits one or several functions in the process of inhibiting and preventing photo-oxidation degradation polymer which occurs very complexly with some degradation products capable of accelerating photo-oxidation degradation polymer subsequently Therefore, in order to improve the stability, anti-photo-oxidation polymer and improve the lifetime of products from HDPE, it is necessary to combine the above additives in one system In this system, each compound exhibits its own function (inhibiting and preventing photo-oxidation degradation polymer) In addition, they can support the regeneration of the original active compounds or synergism The effective synergistic additive mixture is an anti-oxidant 2,6-di-tert-butyl-4-methyl-phenol/dilaurylthiodipropionate (DLTDP) and a mixture of anti-oxidants is the interfering phenol derivatives production and the ultraviolet absorber compounds are benzotriazole derivatives as mentioned above 24 CONCLUSION HDPE/m-CaCO3 composites were photo-oxidation degraded so the carbonyl and vinyl groups were formed when HDPE/m-CaCO3 composites exposed naturally at Dong Hoi (Quang Binh) Carbonyl functional groups are formed via Norrish type I reaction and Norrish type II reaction The characteristics, properties of the HDPE/m-CaCO3 composites samples as tensile strength, elongation at break, initial thermo-degradation temperature, maximum thermo-degradation temperature and remained weight of the samples have a decrease trend as increasing the natural exposure time The decrease of characteristics, properties of the HDPE/m-CaCO3 composites is closely related to solar radiation temperature, humidity,… They were significant decreased in the summer and were decreased more slowly in the winter Results of the XRD, DSC and SEM analysis of the HDPE/m-CaCO3 composites exposed naturally showed that, the photo-oxidation degradation of HDPE macromolecules began to first happen in the amorphous region, then in the crystalline region, from the surface and then grow according to the depth of the composite materials Crystallinity percentage and crystallite size were increased when increasing natural exposure time The increase of total color and dielectric constant as well as the decrease of dielectric loss and electrical breakdown voltage showed that, the HDPE/m-CaCO3 composites have color change and reduced insulation capacity during natural exposure No fungal spores exist and develop in the HDPE/m-CaCO3 composites exposed naturally Combining between the natural exposure and accelerated weather testing for lifetime prediction of the HDPE/m-CaCO3 composites showed that, the tensile strength of composite tested in accelerated weather testing condition for 412.6 hours was as the same as the case tested for 710 days in natural exposure condition The correlation factor determined by the elongation at break that for 46.52 hours accelerated weather testing was as the same as the case tested for 74.19 days in natural exposure condition The analysable results of average molecular weight of HDPE in HDPE/m-CaCO3 composites showed that for 258.3 hours accelerated weather testing was as the same as the case tested for 384.3 days in natural exposure condition ... information about polyethylene: introdution about polyethylene; photodegradation reaction and photo-oxidation degradation reaction of polyethylene High density polyethylene (HDPE): introdution about HDPE;... The XRD patterns of HDPE/m-CaCO3 composites before and after 36 months natural exposure were demonstrated in figures 3.7 and 3.8 Figure 3.7 XRD patterns of M0 sample Figure 3.8 XRD patterns of... density polyethylene/ organo-modified calcium carbonate composite exposed naturally at Dong Hoi – Quang Binh, Journal Chemical industry (accepted) INTRODUCTION Preamble High density polyethylene