Tóm tắt Luận án Study on preparation and properties of rubber nanocomposite materials based on some kinds of rubber and its blends with carbon nanotubes

There should be further studies on the reinforcement possibility of CNT- Vast to the rubber nanocomposite material, especially the chemical denatured reaction CNT- Vast to improve its dispersion possibility in the polymer substrate. Also, there should be researches on the use of dispersion auxiliraries, compatible vegetable oil in manufacturing rubber nanocomposite materials reinforced CNT

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VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY ...*** CHU ANH VAN STUDY ON PREPARATION AND PROPERTIES OF RUBBER NANOCOMPOSITE MATERIALS BASED ON SOME KINDS OF RUBBER AND ITS BLENDS WITH CARBON NANOTUBES Major: Organic chemistry Code: 62.44.01.14 SUMMARY OF CHEMICAL DOCTORAL THESIS Ha Noi – 2016 1 A: Overview of the thesis 1. Problem statement Since having been discovered, carbon nanotube (CNT) is always a hot topic attracting many researches and practical applications by its outstanding mechanical-physical-chemical properties. CNT is known for its high flexibility, low density and high specific surface. Therefore, many real experiments have shown that this material has high modular and durability, and the results of thermal conductivity, electrical conductivity of polymer nanocomposite manufactured on the basis of CNT are also very noticable. However, CNT requires an appropriate dispersion method to avoid being rolled and sticked together. To increase the ability to link between the CNT and the polymer substrate, researchers have offered some measures such as changing the fabrication method or using a combination of auxiliary materials, but the additional functional groups attached to the surface of CNT is more popular. This means that generating the functional groups which react or physically interact with the polymer substrate; thus, it can improve interfacial interaction between the CNT and the substrate, as well as enhance thermodynamic capacity of the nanotube with the polymer substrate. Currently, that nanotechnology has become a develpoment strategy on which researches of different science fields focus like materials, electronics and biomedical attracts large investments. In our country, the studies on the applications of CNT to nanocomposite technology as well as to rubber and plastics industries have already implemented at the level of exploration. So far, no research on this field is applied to real production, but only one research result has been published in journals and conferences. Vietnam has an abundant human resourses and rational treatment policies so that many large electronic firms like Samsung and Canon have built pretty many manufacturing and assembly companies in many industrial areas. The development of electronic industry leads to the demand for anti-static mats spread on the assembly-tables in order to avoid conflicts of unwanted currents with IC, boards in particular and electronic products in general. Besides, textile industry and atomic explosive industry also have a high demand for anti-static. Therefore, the study of fabrication and application of rubber material CNT/nanocomposite that has not only mechanical durability, abrasion resistance but also 2 anti-static ability is necessary because it brings about high scientific and practical values. Derived from these reasons, the thesis aims to the issue: “Study on preparation and properties of rubber nanocomposites material based on some kinds of rubber and its blend with carbon nanotubes” as the subject of research. 2. Objectives of research and its content The objective of the research is to assess the reinforcement possibility of CNT in the rubber substrate and blend rubber in order to create rubber nanocomposite materials with a high mechanical properties, sustainability in the solvent, and suitable electrical conductivity. The content of the research: - Study on the denatured surfaced CNT by various methods. - Study on the reinforcement possibility of CNT and dispersion auxiliaries, compatible origin of vegetable oils with natural rubber (NR). - Study on manufacturing rubber nanocomposite and its properties based on the blend of NR/NBR with CNT. - Study on manufacturing rubber nanocomposite and its properties based on the blend of NR/CR with CNT. - Study on the possibility of manufacturing anti-static mats made from rubber/CNT nanocomposite. 3. Contributions of research - The carbon nanotubes were denatured by using some organic factors such as: 24,85 phr bis-(3-triethoxysilylpropyl) tetrasulfide; 3,29phr polyethylene glycol, 23 phr polyvinyl chloride, which was a basis of creating rubber nanocomposite. - Sucessfully manufactured NR/ NBR materials reinforced 4% CNT or 3% modified CNT, in which CNT-PVC was well compatible with the NBR substrate. - Sucessfully manufactured NR/ NBR materials reinforced 4% CNT or 3,5% modified CNT, in which CNT-TESPT dispersed best in the NR/CR substrate. - By the semi-dry method, CNT (CNT-Nanocyl và CNT-Vast) was dispersed in the substrate of rubber blend based on NR/CR regularly and isotropously. Besides, applying experimental planning and building a regression equation to identify the optimal levels of reinforcement of CNT in the NR/CR substrate quite fitted the results obtained. 3 - The rubber nanocomposite materials on the basis of NR/CR reinforced CNT had electrical conductivity that was suitable to creating anti-static mats. 4. The thesis structure The research includes 140 pages with 23 tables, 53 figures, 120 references. The thesis structure:  Introduction (2 pages)  Chapter 1: Overview (38 pages)  Chapter 2: Materials and research methodology (11 pages)  Chapter 3: Results and discussion (72 pages)  Chapter 4: Conclusion (2 pages)  The publications relating to the thesis (1 page)  References (14 pages) B: Content of the thesis Introduction The introduction mentions the scientific and practical meaning, then set targets and research content of the thesis. Chapter 1: Overview The overview sythesizes materials inside and outside the country relating to the topic of the thesis such as:  Nanocomposite materials, nanocomposite rubber with its classification, its specific advantages and disadvantages.  Carbon nanotubes and four methods of surface denaturation, which also indicate that the denaturation method for packaging the molecular is not applied in nanocomposite rubber manufacturing technology.  The situation of CNT applications in nanocomposite rubber technology. Some points left open are also the thesis objectives. Chapter 2: Materials and research methods 2.1. Raw materials and chemicals  Carbon nanotubes multi wall: NC7000 Nanocyl S.A. ( Kingdom of Belgium), 95% purity, size 10- 15 nm.  Bis- (3- trietoxysilylpropyl) tetrasunfide (Si 69. TESPT), China: the transparent yellow liquid, fat-soluble and aromatic as alcohol, ether, keton. Boiling point: 250°C, density: 1.08. 4  Polyetylenglicol: PEG 6000 (BDH Chemicals Ltd company Poole-UK), the melting temperature of 61°C.  Polyvinylclorua: 710 SG Vietnam, a white powder, size: 20-150 micrometers, specific mass: 0,46- 0,48g / cm 3 .  D01: refined tung-tree oil, yellow liquid, the proportion (at 20°C): 1.500 to 1.520, acid index: 1.4; iodine index: 149.5 to 170.58; soap index: 193.38 to 196.73.  Cetyl trimetylamoni bromua (CTAB): Merck (Germany), M = 364.46g / mol, purity & gt; 97%.  Pure AlCl3: Merck (Germany).  Natural Rubber (NR): SVR- 3L, Viet Trung rubber company, Quang Binh.  Natural Rubber Latex: type pH & gt; 7; Dry content 60%, Phuoc Hoa Rubber Company, Vietnam.  Nitrile rubber (NBR): Kosyn- KNB35, Korea, containing acrylonitril 34%.  Clopren Rubber (CR): Baypren® 110 MV 49 ± 5, Lanxess.  Vulcanizing additives include: + Sulfur, Sae Kwang Chemical Ind firm. Co. Ltd. (South Korea) + Indian Zinc Oxide Zincollied + Stearic acid, PT. Orindo Fine Chemical (Indonesia) + Accelerators DM (Dibenzothiazolil disunfit), China + Accelerators D (N, N-diphenyl guanidine), China + Aging antioxidants D (Phenyl β-naphtylamin), China  Other chemicals Hydrochloric acid, toluene, KOH, iso-octane, ethanol 96%, acid acetic, DMF, petroleum ether, SOCl2, H2O2, NH3, tetrahydrofuran (THF), chloroform (CHCl3), CaCl2, acetone, petroleum ether of China. 2.2. Process of denaturing CNT surface and manufacturing rubber nanocomposite material reinforced-CNT 2.2.1. Denaturing CNT surface by Fischer esterification reaction The residual metal is removed from CNT by being soaked with special HCl and stirred for 2 hours at 50° C under a normal condition, washed several times with distilled water until pH = 7, dried for 12 hours, signed p-CNT. Disperse 0,3g p-CNT in 25ml mixture of NH4OH and H2O2 (1: 1). Stir the mixture for 5 hours at 80°C under normal pressure. Mixed product is filtered by a PTFE membrane (capillary size: 0.2 micron), washed with distilled water in neutral 5 environment and cleaned by acetone several times. The denatured product (CNT-COOH) is dried for 48 hours at 80°C. - Chlorinated CNT Put 0,5gam CNT-COOH into a flask 100ml with 20ml SOCl2 and 10ml DMF available inside, and stir under a normal pressure for 24 hours at 70°C. By the end of the reaction will be a dark brown mixture CNT-COCl, filter and wash with THF and dry at normal temperature. - Synthesis of CNT-PEG Melt 1g PEG at 90°C, then put into a flask containing 0,1g CNT- COCl, stir for 10 minutes, then add the 40ml mixture of benzene/THF (3:1). Conduct the reaction at 80°C in 40 hours. When the reaction ends, put the mixed product in ultrasonic vibration for 30 minutes at 60°C, speed 3000 rpm, then filter it through the PTFE membrane, the mixed black solid is washed with acetone and petroleum ether 3 times, dry at 90°C for 12 hours. - Synthesis of CNT-TESPT 5ml TESPT hydrolyzed in 20ml C2H5OH 96°, 10ml distilled water and 5ml NaOH 10% at 50°C for 2 hours, conduct to remove the solvent, then the yellow solid TESPT-OH is dried at 50°C for 4 hours [106]. Put 0.1g CNT-COCl and 1g TESPT-OH into a flask 100ml with 30ml anhydrous C2H5OH available inside, start to stir for 5 hours at 60°C, the mixed product is put in ultrasonic vibration for 60 minutes at 60°C, speed 6000 rpm, then filtered by the PTFE membrane, washed many times with hot water to remove residual silane components, dried and washed with acetone. The last product is vacuum-dried at 60°C in 5 hours. 2.2.2. Alkylize CNT surface Put 0.2g CNT and 0.5g PVC into a 3-neck flask with 30ml anhydrous CHCl3 available inside, the flask is connected to a canister of anhydrous CaCl2 and another pipe embedded in NaOH liquid 10% to remove HCl released during the reaction. Add 0.5 g AlCl3, and mix in nitrogen environment at 60°C for 30 hours. After cooling the mixture down to the normal temperature, the CNT-PVC product is stirred in ultrasonic vibration in the tetrahydrofuran solvent (THF) for 10 minutes, filtered and washed several times with petroleum ether and acetone, dried at 60°C in 10 hours. 2.2.3. Denatured by surfactants 6 Fuse 0.1g CTAB, then absorb 1g CNT, place in a warm cabinet at 60°C for 72 hours. Put 0.1g CTAB into 50ml distilled water and stir for 1 hour at normal temperature, add more 1g CNT and continue to stir for 1 hour. Add 50ml distilled water, and put the mixture in ultrasonic vibration at 60°C for 2 hours. Dry the last mixture at 60°C in 12 hours. 2.2.4. Method of creating a rubber nanocomposite sample 2.2.4.1. Sample NR/CNT CNT and NR components are presented in the following table: Table 2.1. CNT and NR components of researched samples Ingredients Content (%) NR 100 Zinc oxide 4,5 Aging antioxidants A 0,6 Aging antioxidants D 0,6 Stearic acid 1 Accelerators D 0,2 Accelerators DM 0,4 Sulfur 2,0 D01 1-4% CNT 1-5% 2.2.4.2. Rubber blend sample based on NR Based on the mixing from NR, the thesis surveyed the effects of CNT content (denatured or not denatured) on the properties of blend system NR/NBR 80/20 and NR/CR 70/30 with the following process: (the sign CNT in this process for both CNT that is denatured and not denatured) 7 natural rubber NR or CR mixer mixed CNT or CNT/ethanol produc 1 8 minutes, 75 0C, 50 rpm ZnO, acid, Antioxidant produc 2 S, accelerator semi-produc sheet nanocomposite 20-25 minutes, 1450Cvulcanization 10 minutes mixer 3 minutes, 500C, 50 rpm Figure 2.2. The chart of creating nanocomposite / CNT rubber To study the possibility of dispersing CNT in a polymer substrate, the thesis uses 3 different methods such as mixing the solution, using surfactants or compatible auxiliaries (the additive content, closed mixing conditions as well as vulcanization are constant) follow the process: NR, CR CNT/toluen mixer 3 hours, 500C mixer Toluen, 96 hours ultrasonic, 2 hours masterbatch (a) D01 CNT mixer 3 hours, 500C mixer 600C, 72 hours CNT/D01 NR CR (b) 8 CTAB/H2O CNT mixer mixer, 3hours, 500C mixer, 1 hour ultrasonic, 2 hours masterbatch CNT/CTAB CR latex natual rubber (c) Figure 2.3. Optimizing the CNT dispersion conditions in NR / CR substrate: the solution method(a), using dispersion auxiliaries (b), using cationic surfactant (c) 2.2.5. Research methods of structure and properties of denatured CNT The structure and properties of denatured CNT are determined by means of Infrared Radiation (IR) on the FTS-6000 P (Biorad, USA), Raman radiation method with a HR LabRAM 800 (France), UV -vis on SP3000 nano (Japan) and Thermal Gravimetric Analysis method on Setaram (France), heating rate is 10°C/ minute in the atmosphere, the temperature range from 25°C to 800°C. The image of a denatured CNT is researched on its morphological structure by means of Transmitting Electron Microscope (TEM) on JEOL 1010 (Japan). 2.2.6. The method of determining the structure and properties of materials Determination of tensile strength, elongation of the blend rubber material sample follows the standard TCVN 4509 – 2006. Determination of hardness (Shore A hardness) of the blend rubber materials follows TCVN 1595-1 : 2007. Determination of abrasion (Acron) of materials follows TCVN 1594 – 87. Determination of aging factor follows TCVN 2229-2007. Determination of the swell of the blend rubber materials in toluene solvent: iso-octane follows TCVN 2752 - 2008. Studying morphological structure of materials by means of Field Emisson Scanning Electron Microscope (FESEM) and thermal stability of materials by Thermal Gravimetric Analysis (TGA). 9 Chapter 3 - RESULTS AND DISCUSSION 3.1. Denature carbon nanotubes surface 3.1.1. The study on the process of the carbon nanotubes oxidation Raman radiation results: Figure 3.3. CNT and CNT Raman oxidation The increase in intensity ratio ID / IG proved that there was a change in the CNT structure corresponding with the process of transforming Csp 2 into Csp 3 by oxidation to successfully attach COOH group to the CNT edge. Attaching this functional group increases CNT’s size significantly. a Figure 3.5. TEM of CNT (a) and CNT- oxidation (b) TGA result showed that about 27.85% COOH and NH2 are attached successfully during oxidation process. 3.1.2. Fischer esterification reaction with TESPT and PEG On the Raman spectrum, it can be seen that the ratio ID/IG increased from 1.7 to 2.05 (CNT-PEG) and to 2.0 (CNT-TESPT), which means that increased the degree of chaos of the graphite during denaturation. The TEM image showed that the sizes of CNT-TESPT and CNT- PEG increased to about 25 and 30nm, respectively. The content of the Ester functional group is determined by means of TGA, the results are shown in Table 3.1 below: 10 (CH2 CH) Cl AlCl3 CHCl3 AlCl4 n (CH2 CH)n AlCl4 (CH2 CH)n CHCl3 CH CH2 Cl + + Table 3.1. TGA analysis results of the CNT-PEG and CNT- TESPT Material samples The starting temperature of decomposition The maximum temperature of decomposition 1 The maximum temperature of decomposition 2 Weight loss to 750 o C CNT 500 0 C 577 0 C - 53,67% CNT-PEG 400 0 C 443 0 C 607 0 C 78,52% CNT- TESPT 400 0 C 441 0 C 687 0 C 56,96% 3.1.3. CNT denatured by polyvinylclorua CNT’s structure composed of many atoms C 2sp linked together to form an equilateral hexagon which are nearly like the benzene circle. Therefore, the implementation of a reaction between polyvinylclorua and CNT with anhydrous AlCl3 as a catalyst is determined by the mechanism of the alkylized Fridel- Craft reaction as follows: From the result of Thermal Gravimetric Analysis, we could identify the content of PVC attached to CNT surface is about 23% by weight (at 400°C). That PVC was attached to CNT edge successfully increased its size to about 25nm. 3.1.4. CNT denatured by surfactants As we know, CNT was completely insoluble in water despite under the ultra-sound condition for a long time, so it can not obtain the signals in the visible light area . Conversely CNT/CTAB can be fully dispersed in water, so the signal UV-vis can be obtained in the 200- 800nm waveband. Two characteristic absorption peaks in the area of 240- 265 cm -1 are corresponding to the shift of the electron π π * of conjugate atom Csp2. 11 TGA results of CNT- CTAB sample is shown in Figure 3.18. Figure 3.18. TGA schema of CNT-CTAB Thus, it is possible to estimate that about 17% CTAB are absorbed at 300°C 3.2. Research on manufacturing and material properties of NR/CNT by means of melting mixing. The thesis surveyed CNT content and dispersion auxiliraries, D01. The results are presented in Table 3.2 and 3.3 below: Table 3.2. Effects of CNT content on the mechanical properties of the material on the basis of NR and additives CNT content (%) Tensile strength (MPa) Elongation (%) Abrasion (cm 3 /1,61km) Hardness (Shore A) 0 14,14 920 0,93 42 1 15,25 900 0,85 44 3 16,03 860 0,81 45 5 17,92 860 0,75 46 7 16,94 820 0,79 47 10 15,96 600 0,86 50 Table 3.3. Effects of D01 content on the mechanical properties of NR / 5% CNT Content D01 (%) Tensile strength (MPa) Elongation (%) Abrasion (cm 3 /1,61km) Hardness (Shore A) 0 17,92 860 0,75 46 1 18,89 870 0,70 45,9 12 2 20,13 890 0,63 45,5 3 19,24 915 0,60 44,6 4 17,03 940 0,58 43 - Optimal content of CNT that are reinforced for NR is 5% by weight (compared to NR). In this denaturation ratio, materials have superior mechanical properties rather than control samples such as tensile strength increased by 27%, the starting temperature of decompositon increased by 7°C, the maximum temperature of decomposition increased 5,4°C, the aging factor of the material in the environment also increased significantly. - With 2% more dispersion auxiliaries, compatibility (D01) made materials structure tighter and steadier, increased mechanical properties, thermal durability as well as environmental durability of the material. 3.3. Research on manufacturing and material properties of NR / NBR / CNT samples by means of wet mixing 3.3.1. Influences of CNT content on mechanical - thermal properties of NR / NBR. Based on the research results of Ngo Ke The and his colleagues on creating the NR / NBR blend system, the ratio of 80/20 was chosen to study the reinforement possibility of CNT. Mechanical properties of NR / NBR reached the maximum value with 4% CNT content or 3% denatured CNT content. At these levels, the CNT (not denatured and denatured) has significantly improved thermal durability of the materials. CNT- PVC interacted well with the NR / NBR substrate rather than CNT-PEG. Therefore, NR / NBR / CTN-PVC sample had mechanical properties and thermal stability that were higher than NR / NBR / CNT- PEG sample. Figure 3:24. Effects of reinforcing substances content on the elongation of the materials NR/NBR/CNT 13 That denatured CNT was easily compatible with the polymer substrate improved mechanical properties of the materials more clearly than non-denatured CNT. CNT-PEG had hydrogen-bonded with the rubber substrate as the following model [93]: Despite not having too much differences, CNT- PVC had higher mechanical properties than CNT- PEG. This could be explained by the well compatibility between PVC and NB so that the presence of PVC on the surface (as well as partially absorbed in the process of denaturation) made CNT-PVC be compatible with the rubber substrate better. Therefore, the mechanical properties of the material were improved better. Denatured CNT made the structure of the material tighter and steadier, which increased the environmental durability: the aging factor in the air and salt water was high, the solvent durability was improved. Figure 3:29. Morphological structure of reinforced materials NR/NBR: CNT (a), CNT-PVC (b), CNT- PEG (c) 14 Table 3.9. Aging factor of NR/NBR/CNT materials at 70°C during 72 hours Samples Aging factor in the air Aging factor in salt water NR/NBR 0,82 0,8 NR/NBR/4%CNT 0,89 0,87 NR/NBR/3%CNT-PVC 0,91 0,89 NR/NBR/3%CNT-PEG 0,9 0,88 0 20 40 60 80 100 120 140 160 180 200 220 240 0 8 16 24 32 40 48 56 64 72 Thời gian (giờ) Đ ộ t rư ơ n g CSTN/NBR/CNT CSTN/NBR/CNT-PVC CSTN/NBR/CNT-PEG CSTN/NBR Figure 3:30. The swell levels of NR/NBR reinforced CNT solvent 3.3.2. Influences of carbon nanotubes on vulcanization of the NR/NBR materials Mechanical properties of the materials are also presented in the perspective of vulcanization. Selecting right vulcanization conditions would increase the durability of technical rubber. The survey result of the CNT’s influence on the process of vulcanization NR/NBR blend is shown in Table 3.8. Table 3.8. Effects of CNT on the process of NR/NBR blend vulcanization Samples Mmin (kgf.cm ) Mmax (kgf.cm ) Ts1 (min:sec) Tc90 (min:sec) NR/NBR/CNT 0,2 4,75 02:19 7:57 NR/NBR/CNT-PVC 0,17 5,26 02:42 8:55 NR/NBR/CNT-PEG 0,16 4,83 02:26 7:51 15 The minimum value of torque presented softness or flexibility of rubber in soft initial state. The results showed that in which sample containing CNT, Mmin was highest. This was appropriate because CNT had no strong polarized groups, so the possibility to mix with the blend system containing polar rubber NBR decreased. Meanwhile, samples containing PVC and PEG, the occurrence of polar functional groups like Cl, NH2, OH will increased the ability to blend. The maximum value of torque was often related to chemical bonding or crosslinking density. This value of the samples containing CNT-PVC was higher, corresponding to the hardness of the samples containing CNT-PVC was also higher. By that time, S-S bonding of sulfur reached the highest point. Vulcanization time Tc90 of the samples containing PEG was lowest because CNT-PEG contains a NH2 group which was an agent to boost the process of vulcanization. The pretty high Tc90 value of the samples containing CNT-PVC was also an obstacle to the process of manufacturing products. 3.4. Research on manufacturing and material properties of NR / CR / CNT by means of wet mixing 3.4.1. Effects of CNT on the NR / CR vulcanization Based on the research results of Do Quang Khang and his colleagues on creating the NR / CR blend system, the ratio of 70/30 was selected to study the reinforcement possibility of CNT by means of wet mixing with CNT/ ethanol. They have studied of the possibility of vulcanization of the material samples containing CNT and denatured CNT. The maximum and munimum values of torque, vulcanization time 90% (Tc90) are presented as below: Table 3.11. Effects of CNT on the possibility of vulcanization of blend NR / CR Samples Mmin (kgf.cm) Mmax (kgf.cm) Ts1 (min:sec) Tc90 (min:sec) CSTN/CR/CNT 2,35 20,58 01: 32 14:54 CSTN/CR/CNT-PVC 1,6 18,63 01: 27 14:44 CSTN/CR/CNT-PEG 1,96 20,03 01:28 14:24 CSTN/CR/CNT-TESPT 1,31 21,71 01:21 12:48 16 Vulcanization time Tc90 of the samples containing TESPT was lowest (12 minutes 48 seconds). This could be explained that CNT- TESPT contained a NH2 as an accelerator and the appearance of S-S formed by slightly decomposition under high temperature (Figure 3.37), which directly participated in the crosslinking and coupling system in rubber. This caused a premature vulcanized phenomenon (ts1 value is lowest) and reduced the vulcanization time. Tc90 short vulcanization time has an economic value in the process of manufacturing products so that CNT- TESPT is very noteworthy. 3.4.2. Effects of CNT content on the mechanical properties of materials NR / CR From the results above, it can be seen that only 1% CNT (not denatured and denatured) has significantly increased the mechanical properties of the blend NR / CR. When the CNT and CNT- TESPT content increased, the mechanical properties (tensile strength, elongation) of the materials also increased and reached the maximum value with 4% CNT by content or 3.5% CNT-TESPT. Mechanical properties of materials NR/CR/CNT- TESPT were higher than CSTN/CR/CNT. This was explained that CNT- TESPT had better interaction than CNT. Also, they created a link with rubber vessel, because the thermal decomposition process of silane did appear S-S bond which not only directly involved in vulcanizing a tight network, but also created a chemical bond with the rubber substrate. Releasing HCl molecule increased the thermodynamic durability and created a direct link Si-O-C to consolidate the durability of nanocomposite. Assuming the links in the nanocomposite network as the following model 3:37. Figure 3:33. Effects of reinforced substances content on the elongation of the materials NR / CR / CNT 17 Figure 3:37. Description of surfaced link between the CNT-TESPT and CSTN / CR The structure of materials NR / CR / CNT- TESPT was tight and had a steady distribution, so it influenced the thermal durability, the aging factor as well as the swell in the solvent. Figure 3:38. Morphological structure of materials NR / CR reinforced- CNT (a) and CNT- TESPT (b) NH2 OOC Si HO (CH2)3 S4 (CH2)3Si(OH)3HO NH2 OOC Si HO CH2CH2CH2 S SHHO t0 H3C C H 2 C = C H C H 2 Cl C H 2 C = C H C H 2 OOC Si OH(CH2)3 HO COO Si HO (CH2)3 S SHO S S NH2CH2 CH2 C CH2 CH3 COO Si HO (CH2)3 S4HO (CH2)3Si(OH)3 COO Si HO (CH2)3 S SHHO CH2 CH2 C CH2 Cl t0 -HCl OOC Si OH(CH2)3 HO COO Si (CH2)3 S SHO S S NH2CH2 CH2 C CH2 CH3 CH2 CH2 C CH2 ClO- H OOC Si OH(CH2)3 HO COO Si (CH2)3 S SHO S S NH2CH2 CH2 C CH2 CH3 CH2 CH2 C CH2 O 18 Table 3.13. TGA analysis results of of some material samples on the basis of NR / CR 3.5. Research on optimizing the possibility of CNT dispersion in the rubber blend substrate NR / CR From the research results presented above, it can be seen that NR / CR system has higher properties than NR / NBR when using CNT and denatured CNT. To further enhance the properties of this blend system, the thesis also mentions the optimal conditions to disperse CNT by using 3 methods of dispersion as follow: - Method of solution: NR / CR / CNT / toluene. - Method of using a combination of NR latex with surfactants: LNR / CR / CNT-CTAB. - Method of using compatible dispersion auxiliraries: NR / CR / CNT / D01. The most noticeable result is the ability of the CNT dispersion under the influence of CTAB within NR latex as the following mechanism: Samples The starting temperature of decomposition ( o C) The maximum temperature of decomposition 1 ( o C) The maximum temperature of decomposition 2 ( o C) Weight loss to 600 o C (%) NR/CR 268,7 349,7 434,5 91,02 NR /CR/4CNT 272,4 350,2 433,2 86,67 NR/CR/3,5CNT- TESPT 274,5 353,6 428,4 90,66 NR /CR/3,5CNT-PVC 273 344 438,8 91,14 NR /CR/3,5CNT-PEG 274 347,7 432,9 92 19 Figure 3.46: The CNT detached-connected mechanism of CTAB and the dispersed mechanism of CNT-CTAB in NR latex The natural rubber latex particles had high flexibility. In spite of a very small amount, only 1% CNT also significantly increased the tensile strength from 13,32 to 16,12 MPa for LNR / CR and from 14.32 to 17.02 MPa for NR/ CR. The levels of 3% CNT and 3% CNT- CTAB were optimal contents for rubber molecules and CNT to form a polymeric network – a closed filler. The polymeric network- filler as described in Figure 3:43 is stabilized by Van der Walls link, hydrogen link and ion link (generated by negative electrons in the latex molecule and positive electrons in nitrogen atoms of CTAB). This increased the tensile strength of the material samples. Figure 3:43. Interaction between the CNT / CTAB and the polymer substrate 3.5.1. Manufacturing of rubber nanocomposite material by using CNT-Vast Based on the processing of the materials LNR / CR / CNT- CTAB, the thesis also did a research on using CNT manufactured at the Institute of Material Science - Vietnam Academy of Science and 20 Technology Institute (CNT- Vast) to reinforce the properties of the blend NR / CR. CNT-Vast was ultrasonicly vibrated in ethanol or dispersed in water with CTAB before being mixed with natural rubber, rubber clopren as the preparation process in section 2.2. Here are the results of mechanical properties obtained: Table 3.17. Effect of CNT- Vast content on the mechanical properties of materials NR / CR Samples Tensile strength (MPa) Elongation (%) Hardness (Shore A) NR/CR 13,32 610 51,2 NR /CR/1%CNT- Vast/etanol 15,12 603 51,9 NR /CR/2%CNT- Vast/etanol 17,28 592 52,6 NR /CR/3%CNT- Vast/etanol 16,53 584 53,0 LNR/CR/4%CNT- Vast/etanol 15,76 578 53,8 NR /CR/1% CNT- Vast/CTAB 15,52 600 51,8 NR /CR/2% CNT- Vast/CTAB 18,14 593 52,3 NR /CR/3% CNT- Vast/CTAB 17,09 567 54,0 NR /CR/4% CNT- Vast/CTAB 16,76 579 54,4 Mechanical properties of the material samples NR / CR / CNT- Vast / CTAB were pretty better than that of NR / CR / CNT- Vast / eatnol. To explain this, the thesis used the research results of the authors [97]. When comparing the size of the CNT- Vast and CNT- Nanocyl (the kind used primarily in the thesis), it could be seen that CNT- Nanocyl had small diameter and the equal diametral distribution rather than CNT- Vast. On the other hand, purity of CNT- Nanocyl (95%) is also larger than that of CNT- Vast (about 90%). Thus, it was obviously suitable that the reinforcement ability of CNT- Vast also declined slightly, and the CNT- Vast content optimally reinforced (2%) was lower than CNT- Nanocyl (3%). 3.5.2. The regression equation describing the dependence of the mechanical properties of the material LNR / CR on CNT-CTAB When calculating by FORTRAN algorithmic language program and proceeding the data, a regression equation was obtained as follows: -Tensile strength: 2 1 ^ 693,0202,4024,13 xxy  , with θ = 0,958 21 Easily realize that 1y  reached the maximum value at: dx d y1  = -2. 0,693 x+ 4,202 =0, solving this equation and refer x = 3,03%, 1y  max = 19,394 Mpa. This result indicated that around the value x = 3,03%, the value of tensile strength was the highest - Elongation: xy 14,1186,6142 ^  with r = -0,973 That r had negative value was completely suitable with the sign of x - Abrasion: 23 ^ 032,0202,0836,0 xxy  with θ = 0,988 -Hardness: xy 82,067,514 ^  with r = 0,979 Thus: Proceeding data to find out the regression equations describing experimental correspondence with high precision, enable to evaluate the rules of the CNT-CTAB influences on the mechanical properties of the materials. From that, we can solve optimization problems, find out the domain of CNT-CTAB for the mechanical properties of the materials. 3.5.3. Assessment of thermal-mechanical properties of the material CO- NR / CR sample CNT reinforced by three different dispersal methods The curves showed 3 distinct regions: the high module (glass area), transition area (in which the value E' drops rapidly with temperature) and the "rubber". Rubber had large accrued modules at low temperatures, then plummetted at around -60°C (sample containing CNT/toluene: -66°C, sample containing CNT- CTAB: - 64°C, sample containing CNT/D01: -63°C). The strong decrease of E' at this temperature indicated the transition from glassy state to "rubber" state. All three material samples were a little bit different from each other under the effect of load. The value E' of the samples containing CNT/ toluene was slightly higher due to the even dispersion of CN. The surface- appearance of CNT became an absorbing agent. 22 -120 -100 -80 -60 -40 -20 0 20 40 0,00E+000 5,00E+008 1,00E+009 1,50E+009 2,00E+009 2,50E+009 M o d u l E ' Nhiet do Figure 3:49. The chart of accrued modules change with temperature Figure 3:50. The chart of mechanical loss factor change with temperature The Figure 3:50 shows that Tg value of NR and CR is in range of -50°C and -27°C. Vitrification temperature of NR was lower than that of CR due to the presence of Cl polarized groups. These groups mutually interacted, which restricted the movement of molecular circuits. Samples containing CNT / D01 had Tg1 = -51,2°C with high pic intensity, Tg2 = -27,8°C. Meanwhile, samples containing CNT / CTAB had Tg1 = -49°C with lower intensity, Tg2 = -27,5°C but with slightly lower intensity. Tg1 and Tg2 of samples containing CNT / toluene slightly decreased to -48,8°C and -27°C respectively, but the decrease of pic intensity of Tg1 was the most significant one. The rise of the Tg1 algebraic values to samples containing CNTs/D01 was due to the appearance of a few bundles of CNT as a barrier to the movement of the polymer chains around the temperature Tg. These results showed that the blend of NR / CR reinforced CNT / D01 was less compatible with each other. However, when using surfactants or dispersing in toluene, the compatibility was increased. This result was CNT/D01 CNT/toluen CNT/CTAB 23 consistent with the assessment of the results of TGA analysis, mechanical properties and morphological structure above. Besides, the intensity and location of pic tgδ indicated interaction between rubber substrate and CNT. If pic tgδ is wider, the aggregation of nano particles into clouds would be greater, the connection between the CNT and the substrate would became worse. Conversely, if pic tgδ was narrower, the connection between the CNT and the substrate would be better, CNT was dispersed evenly and hard to conglomerate. By comparing 3 pic tgδ, it could be seen that CNT/toluene and CNT/CTAB samples had narrow pic, the peak of pic with Tg1 is sharp, which proved the better reinforcement effect. 3.5.4. Influence of the dispersion method on electrical properties of NR/CR/ CNT materials Many studies have shown that doing a research on the electrical properties is also an effective mediate method to study the structure of the polymer nanocomposite material, which allows to assess interaction and the dispersion ability of the phases. Below are the descriptions of the electrical conductivity of the material. Figure 3:51. Electrical conductivity and the electric absorbent threshold of the material sample by CNT weight It could be seen that the CNT dispersion method had a strong impact the electrical conductivity of the material. Only 2% used CNT has increased the electrical conductivity of NR / CR / CNT by 10 6 times and that of LNR / CR / CNT by 10 4 times. Generally, the electrical conductivity of polymer synthetic materials was explained by the mechanism of the conduction theory (form a continuous 24 conductive network) and the mechanism of jump (electromagnetic radiation) of the electrons overcoming very small distances. Simply understanding, the arrangement of the CNT particles into the pipelines created a continuous line. The dielectric loss was very small so that it could be ignored. Moreover, the specific structure with the presence of conjugated bonds in CNT supported electronic lines to move continuously. That the appearance of the positive electron on nitrogen atom of CTAB atoms became electron transit center of CNT continuous network made the electronic transportation process more advantageous; thus, resistivity decreased, which also means electrical conductivity increased. When the content of CNT reached at 3%, the electrical conductivity reached 10 -5 . It means that the network structure was stable, CNT particles had the shortest average distance, which led to the formation of a 3-D network of the conductive phase. By that time, it has reached an electrical absorbent threshold (as described in Figure 3:51). Therefore, increasing the level of CNT content also made an increase of connected density among CNTs without changing the electrical conductivity. Table 3:21. The influence of the dispersion methods on the vulcanization ability of the blend NR / CR Samples Mmin (kgf.cm) Mmax (kgf.cm) T90 (min:sec) LNR/CR/CNT-CTAB 2,17 19,5 10:55 NR/CR/CNT/Toluen 2,32 20,82 10:06 NR/CR/CNT/D01 2,18 19,63 10:18 Vulcanization time Tc90 of the sample containing D01 was lower due to D01 structure had the link C = C which directly involved in crosslinking process, accelerated the process of vulcanization. Although the starting time of the vulcanization and Tc90 of the mixing solution sample were lowest, the most interesting thing was that the Tc90 time of the sample using latex was relatively short, even lower than that of the sample NR / CR / CNT-TESPT (Table 3:11). This was quite an important orientation to apply CNT in industry. 3.6. Orient to manufacturing experimental anti-static rubber mats Based on the above findings, they have created a prototype of anti-static mats. Below is the quality standard of the anti-static mats manufactured in factories of Technical Rubber Ltd Globe Company compared to imported samples delivered by The Bao Nguyen Co., Ltd, 25 Dong Nai ( dien/Tham-cao-su-chong-tinh-dien-Kt-1-2m-x-10m-x-2mm- 474.html). Table 3:23. The quality standards of anti-static mats The major quality standards of the product Units of measure The results Imported mats Tensile strength MPa 19 3,6 Elongation % 650 188 Hardness Shore A 60 - Abrasion cm 3 /1,61km 0,5 1,0 Electrical resistivity of upper surface  10 6 10 4 – 106 Electrical resistivity of lower surface  10 6 10 4 – 106 Bulk resistivity .cm 10 5 10 6 – 109 Other advantages of anti-static mat samples: - High mechanical durability - High environmental durability - Long time for use - Against grease and other common solvents - Not containing Pb, Hg and other heavy metals - The major material is natural rubber latex limiting the spread of nanodust while being mixed (limiting the biggest drawback of the material nanocomposite) - Suitable for the factories to manufacture semiconductors, computers, electronic components and for chemical laboratories Conclusion 1. Has gained a success of denaturing CNT by 3 different methods, when being oxidized by H2O2/NH3 approximately 27.85% of COOH and NH2 groups were attached to the CNT surface. Then, through Fischer esterification reaction, about 24.85% of PEG ester group and 3.29% of TESPT ester group were joined with the CNT surface. Fridel Craft alkylation reaction helped to attach approximately 23% of polyvinylclorua by weight to the CNT. That CTAB was absorbed up to the CNT edge by Van der Walls link also helped to attach about 5% of CTAB surrounding the CNT. 26 2. Has used 5% of CNT by weight to reinforce NR by means of melt- mixing. The characteristic of the NR/CNT material system was promoted by using 2% more of dispersion auxiliaries, compatible D01. 3. Has used the wet-mixing method to disperse about 4% CNT or 3% denatured CNT in the NR/NBR system. CNT- PVC was well compatible with NBR so that it was well compatible with the NR / NBR substrate rather than CNT-PEG (only formed a physical link). 4. The wet-mixing method also dispersed was 4% CNT and 3.5% denatured CNT into the NR/CR system. Materials had a steadier and tighter structure, which increased mechanical properties strongly (tensile strength increased by 46.5%, elongation increased by 12%); the starting temperature of decomposition rised by 6°C, aging factor of the material in the environment also increased. 5. Dispersion of CNT in toluene solution was good but had some disadvantages of solvent cost and environmental pollution when being applied to industrial scale. The dispersion of CNT/ CTAB in latex got high effects even when using powerful mechanical agitation without using ultrasonic waves. Vulcanization time of LNR/CR/ CNT samples were short, which had to be concerned about when manufacturing. CTAB remarkable production deployment. Planning c Experimental planning determined that the amount of 3.03% CNT reinforcement was optimal. This confirmed the accuracy of experiments. 6. Initially identified the CNT-Vast content reinforced the blend system NR/ CR (about 2%). This was consistent with CNT- Vast’s diameter of about 40 nm, larger than CNT-Nanocyl’s diameter. 7. Rubber materials on the basis of the latex NR/ CR 4% reinforced CNT-TESPT/ CTAB had high mechanical properties, positive grease durability and electrical conductivity 4.1 ESD standard. This meet the requirements of creating anti-static mats serving in the electronic and textile fields. Recommendations: There should be further studies on the reinforcement possibility of CNT- Vast to the rubber nanocomposite material, especially the chemical denatured reaction CNT- Vast to improve its dispersion possibility in the polymer substrate. Also, there should be researches on the use of dispersion auxiliraries, compatible vegetable oil in manufacturing rubber nanocomposite materials reinforced CNT. 27 LIST OF WORKS HAS BEEN PUBLISHED 1. Chu Anh Van, Hoang Thi Hoa, Luong Nhu Hai, Luu Duc Hung, Ho Thi Oanh, Do Quang Khang, Some research results, manufacturing and properties of natural rubber materials nanocomposite carbon tubes, Journal of Chemistry, 2014, T52 (6A), 64-68. 2. Chu Anh Van, Le Hong Hai, Ho Thi Oanh, Do Quang Khang, Research on denaturing carbon nanotubes’ surface by Fischer esterification reaction, Journal of Chemistry, 2015, T53 (4), 520-525. 3. Chu Anh Van, Ho Thi Oanh, Luong Nhu Hai, Do Quang Khang, Research preparation and properties of rubber nanocomposite material based on blend NR/NBR and carbon nanotubes, Journal of Chemistry, 2015, T53 ( 5E3), 122-126. 4. Chu Anh Van, Vuong Quang Viet, Luong Nhu Hai, Do Quang Khang, Research preparation and properties of rubber nanocomposite material based on the blend of natural rubber and chloroprene rubber with carbon nanotubes, Journal of Chemistry, 2015, T53 (5E1), 194- 198. 5. Chu Anh Van, Ngo Quang Hiep, Ho Thi Oanh, Luong Nhu Hai, Ngo Trinh Tung, Do Quang Khang, Study on preparation of rubber nanocoposites based on natural rubber/chloropene rubber blends reinforced with carbon nanotube by semi-dried method, Journal of Chemistry, 2016 (accepted for publication). 6. Do Quang Khang, Chu Anh Van, Ngo Trinh Tung, Do Trung Sy, The process of manufacturing rubber nanocomposites material, patent registration, application number 1-2016-00883, accept for the application by the decision 19619 / QD-IP date 04.11.2016.

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