Nghiên cứu biến tính xenlulo từ bột giấy gỗ keo sản xuất trong nước và ứng dụng chế tạo thuốc phóng tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF DEFENCE ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY DOAN MINH KHAI MODIFICATION OF ACACIA-WOOD PULP IN VIETNAM AND APPLICATION FOR THE PROPELLANT Specialization: Organic Chemistry Code: 44 01 14 SUMMARY OF DOCTORAL THESIS IN CHEMISTRY HANOI – 2019 THE WORK WAS COMPLETED AT ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY Scientific Supervisors: Assoc Prof., Dr Phan Duc Nhan Dr Trinh Dac Hoanh Reviewer 1: Prof., Dr Thai Hoang Vietnam Academy of Science and Technology Reviewer 2: Assoc Prof., Dr Nguyen Cong Hoe General Department of Defense Industry Reviewer 3: Assoc Prof., Dr Chu Chien Huu Military Academy of Science and Technology The thesis was defended in front of the doctoral admission Broad of Academy of Military Science and Technology at…… h… / / / 2019 The thesis can be found at: - Library of Academy of Military Science and Technology - Vietnam National Library INTRODUCTION Necessary of the thesis: Modifying pulps is very important to make cellulose that meets specifications of propellant production Firstly, cellulose is a material for producing nitrocellulose (NC) which is the main ingredient of nitrocellulose-based propellants (56÷95%) Therefore, the characteristics of cellulose affect properties of the propellants Secondly, the propellants in Vietnam are producing from import celluloses (such as Canada, America, China, Indonesia, and Brazil) To raise the sense of initiative and diversified about raws in Vietnam, it is necessary to find out new types of cellulose for manufacturing the propellants The cellulose raws in Vietnam have not met the technical specifications of cellulose for the propellant One of the cellulose raws is Acacia pulp This pulp is cooked and bleached from Acacia mangium wood and is used for making paper In addition, the properties of Acacia mangium cellulose can differ from used cellulose and affect the quality of obtained propellant Hence it is necessary for science and reality to modify Acacia mangium pulp in Vietnam and applicate it for the propellant Goals of the research: The Acacia mangium pulp is modified to satisfy the technical specifications of producing propellant Additionally, the effect of the Acacia cellulose characteristics on reaction conditions and quality of the obtained product are investigated Object and scope of the research: The thesis focusses on the Kraft pulps from An Hoa Paper JSC and Vietnam Paper Corporation, Bai Bang – Phu Tho, and improving properties of the pulps for producing the propellants in Vietnam Research methodology: A cold caustic solution was used for improving the characteristics of Acacia cellulose; the obtained cellulose was functionalized by nitric acid in the presence of sulfuric acid; the analytical methods of chemistry and modern physic-chemistry were used to investigate the characteristics of cellulose, nitrocellulose, and propellant Research contents of the thesis: Investigating the technical characteristics of acacia wood pulp for orientation as required to make propellant; modifying Acacia pulp by the cold caustic method to improve the required characteristics; nitrating Acacia cellulose and investigating the characteristics of obtained NC; application of the obtained NCs to manufacture 11/7 propellant and investigate the properties, chemical stability, and ballistic stability of this propellant Contribution for science and reality: The results of the thesis contribute to clarify technical characteristics and structural characteristics of Acacia cellulose before and after modification; explaining by the mechanism of chemical reactions on the change of physicochemical characteristics and structure of Acacia cellulose when modification; selecting the suitable conditions of modification for Acacia cellulose to produce propellant The results of the thesis are the basis to actively and diversify sources of raw materials to produce propellant in Vietnam Structure of the thesis: The thesis contains an introduction, three main chapters, conclusion, and references - Chapter The literature review showed the brief of cellulose, the review of domestic and international researches on the modification and application of cellulose - Chapter Materials and methods present the process of manufacturing and the brightness of Acacia pulps; the chemicals, materials, and equipments for experimental; the methods for modifying pulps and for analyzing characteristics of cellulose, NC, and the propellant - Chapter Results and discussion showed the technical characteristics of Acacia pulps according to a Military standard including a trend in improvement of some characteristics of the cellulose; results and explanation of the effects of reaction conditions on the characteristics of this cellulose when modifying cellulose by cold caustic medium and by nitric acid in the presence of sulfuric acid; investigation on properties of obtained cellulose and NCs; the chemical and ballistic stability of a propellant produced from the NCs MAIN CONTENTS OF THESIS Chapter LITERATURE REVIEW Cellulose is a known material and used to make paper, silk, cotton, and cloth for a thousand years In the range from the 18th century to 1980s, the researchers focused on making clear about the general structure of cellulose molecular, the base properties of physic-chemistry, the difference from structure between various types of cellulose raws followed by a change of physic-chemical properties Recently, the matters of phase-structure (crystallinity and amorphousness) have been focused on different types of cellulose Additionally, the modification and application of cellulose have been concentrated on various origins for many purposes The aims of the application are accompanied by trends of modification for improving suitable properties Along with the trends, the modification of Acacia cellulose and application for producing the propellants is a new topic with science and reality Chapter MATERIALS AND METHODS 2.1 Objects of the research - Seven samples of Kraft pulp, which were bleached by O2-Dht-EOP-D1 with 83 to 89 %ISO of brightness, were collected from An Hoa Paper JSC, An Hoa Tuyen Quang - Two samples of Kraft pulp, which were bleached by O2-C-EOP-H with 76 and 84 %ISO of brightness, were collected from Vietnam Paper Corporation, Bai Bang – Phu Tho 2.2 Chemicals, materials, and equipments * Chemicals and materials Two samples of pine softwood cellulose (Neucel N94) were purchased from Canada as follows: α-cellulose 98.3% (CND-1) and alpha-cellulose 93.1% (CND-2) A sample of hardwood cellulose with alpha-cellulose 94.5% (INDO) was bought from Indonesia A single-base propellant 11/7 was produced from the pine softwood cellulose (Neucel N94) by Z195 Company (TPP-Ca) The other chemicals were purchased from Vietnam, Germany, and China companies; and were prepared in our laboratory * Equipments for experimental The equipments were used for experimental of the thesis in Military Technical Academy laboratories and Institute of Chemistry-Materials laboratories origin of which was made in America, Germany, France, Czech, and Vietnam after 2009 2.3 Methods for modifying pulp and preparing the propellant 2.3.1 Modification of Acacia pulp in a caustic medium 10 grams of the pulp was immersed in 300 ml of a NaOH solution with reaction conditions as follows: to 20% of a NaOH solution, at a temperature to 45oC and 100oC, from 15 to 120 of time, and 350 rpm of the stirring speed The yield of the modification was calculated by equation (2.1): 𝑚𝐶𝑒𝑙 𝑌= × 100 (2.1) 𝑚𝑃 Where: Y – yield of the modification, %; mCel – the weight of the dry sample after modification, g; mp – the weight of dry pulp, g 2.3.2 Synthesis of NC - The synthesis of NC was carried out in the following conditions: at a reaction temperature from 20 to 30oC, the weight ratio of acidic mixture to cellulose about 60 ÷ 80 times, and for a ÷ 60 minutes of reaction time The reaction was stopped by diluting in large quantities of ice The obtained NC was boiled in hot water and the diluted solution of sodium carbonate The product was dried at 65oC, and for hours 2.3.3 Preparation of the propellant The 11/7 propellant from Acacia cellulose was prepared according to the process of Z195 factory 2.4 Methods for determining the characteristics of cellulose, NC and propellant 2.4.1 Fourier transform infrared spectroscopy FTIR spectra of the samples were recorded on a Perkin Elmer Spectrum 400 (USA) A total of 32 cumulative scans were taken, with a resolution of cm-1, in the frequency range from 4000 to 450 cm-1 The absorbance of the bands was determined from ACDLABS software 2.4.2 Determining the physicochemical characteristics of cellulose The technical specifications of cellulose were tested according to the TQSB 206:2005 standard of Vietnam and the GOST standard of Russia In addition, the content of lignin was tested by the hydrolysis of pulp in concentrated sulfuric acid at 20oC for hours 2.4.3 The average molecular weight of cellulose Average molecular weight (MW) of cellulose was analyzed by a solution of ZVNK according to the GOST 25.438-82 2.4.4 The molecular weight distribution of cellulose The MW distribution of cellulose was determined by the fractions in various solutions of phosphoric acid from 73.3 % to 83.0 % 2.4.5 Calculation of the structural parameters of cellulose by FTIR - Lateral order index (LOI): LOI is defined as a ratio of absorbance intensity of 1430 cm-1 (A1430) band to 896 cm-1 (A896) band - Total crystalline index (TCI): TCI is defined as a ratio of absorbance intensity of 1372 cm-1 (A1372) band to 2900 cm-1 (A2900) band - Hydrogen bonding intensity (HBI): HBI is defined as a ratio of absorbance intensity of 3350 cm-1 (A3350) band to 1318 cm-1 (A1318) band - Asymmetric index (a/b): The asymmetry index of cellulose is calculated as the ratio of width to ½ height of absorption band of the hydroxyl group in the 3000-3700 cm-1 region Asymmetry index (a/b) is calculated by ACD Specmanager software - Hydrogen bonding energy (EH): The energy of the hydrogen bonds EH for several OH stretching bands has been calculated by the equation νo -ν EH = × k νo (2.9) Where: νo is the standard frequency corresponding to free OH (3650 cm−1); ν is the frequency of the bonded OH; k is a constant (1/k = 2.625 × 102 kJ) 2.4.6 X-ray diffraction and calculation of crystalline parameters of cellulose X-ray diffractograms were collected using a sample holder mounted on a PANalytical X’pert pro with monochromatic CuKα radiation (λ = 0.15406 nm) The generator was utilized at 40 kV and 40 mA, and the intensities were measured in the range of 5° < 2θ < 40°, typically with scan steps of 0.1° at s/step (6° /min) Peak separations were carried out using Gaussian deconvolution - Crystalline Index: The surface method estimated the crystallinity index of the cellulose samples by the equation (2.6) 𝑆𝑐 𝐶𝑟 𝐼 (%) = × 100 (2.10) 𝑆𝑡 Where: Sc – area of the crystalline domain, St – area of the total domain - The size of crystalline domain: The crystalline size (L) was calculated by the Scherrer equation (2.7) 𝐾×𝜆 𝐿(𝑛𝑚) = (2.11) 𝛽 × 𝑐𝑜𝑠(𝜃) Where K is a constant of value 0.94; λ is the X-ray wavelength (0.15406 nm); β is the half-height width of the diffraction band (radian); and θ is the Bragg angle corresponding to the (101), (101̅) and (002) plane 2.4.7 Scanning Electron Microscope (SEM) The size and morphology of NC fibers were determined by SEM with 1000 times of magnification on JSM 6610LA-Jeol device 2.4.8 Methods to determine the technical characteristics of NC According to TQSB standard, the technical characteristics of NC were determined such as nitrogen content, ethanol solubility, ethanol-diethyl ether solubility, viscosity, stability, alkalinity, and ash content - Nitrogen content of NC was titrated by the reaction of iron (II) sulfate with nitric acid which was released by denitration of NC in cold concentrated sulfuric acid The excess of iron (II) sulfate reacted with nitrogen oxide to form a pink complex as the ending point of the titration process - Degree of substitution of NC (DS) was calculated from nitrogen content (N) by the equation (2.8): 3,6×N DS= (2.18) 31,11-N 2.4.9 The molecular weight distribution of NC: The NC fractions of MW were divided by the various mixtures of acetone-water with the water in the range from 14 to 19% The NC molecular weight of each fraction was determined by the dissolution of NC in acetone and calculated by equation (2.9): 𝜂𝑟 𝑀= (2.22) 𝐶 × 0.38 × 10−4 Where: C - a concentration of NC in acetone, w/v; 0.38.10-4 – a constant 2.4.10 The characteristics of propellant: The physicochemical and ballistic characteristics of single-base propellant 11/7 were determined according to the technical specifications 2.4.11 The chemical stability of propellant The TPP-VN sample was aged at 70oC with a time of 12 ÷ 73 days, 80oC with a time of 15 ÷ 45 days, and 90oC with a time of ÷ 18 days The TPP-Ca sample is also aged in the same conditions as the TPP-VN to compare the quality assessment of TPP-VN CHAPTER RESULTS AND DISCUSSION 3.1 The characteristics of Acacia-wood pulps 3.1.1 The technical characteristics As a basis for improving the technical properties in accordance with the requirements for the manufacture of propellant, the thesis investigated the characteristics of Acacia-wood pulps of different brightness required by TQSB 206:2005 (Table 3.1) Table 3.1 The technical characteristics of the Acacia-wood pulps α-cellulose, Viscosity, Lignin, Ash, Samples Absorption, g % cP % % AH-83 89.29 20.1 0.41 64.2 0.25 AH-85 89.12 18.8 0.34 66.3 0.28 AH-87 90.03 20.3 0.30 60.7 0.26 AH-89 90.86 20.0 0.29 65.7 0.24 BB-76 84.46 21.2 0.65 60.2 0.32 BB-84 86.53 20.8 0.36 63.2 0.30 Specifications ≥ 92 ≥ 20 ≤ 0.50 ≥ 100.0 ≤ 0.50 The technical characteristics of Acacia-wood pulps are the similar to together because they were produced according to the same technology Most of these samples have not met fully the technical specifications The characteristics need to be improved like that the α-cellulose, viscosity, and water absorption 3.1.2 The degree of polymerization and distribution of molecular weight In the process of producing pulp, cellulose is depolymerized to make a reduction of molecular weight in comparison with the original pulp The results of determining the MW of the samples with different brightness (83 ÷ 89% ISO) are shown in Table 3.2 Table 3.2 Average MW of the Acacia pulps ̅̅̅̅ 𝜂𝑠𝑝 No Samples MW 𝐷𝑃 AH-83 0.233 856 138,700 AH-85 0.251 875 141,700 AH-87 0.254 842 136,400 AH-89 0.267 878 142,200 The MW of Acacia pulp in the range of 136,400 ÷ 142,200 corresponding to the polymerization (DP) in the range of 842 ÷ 878 units The brightness of the sample did not affect significantly the MW For synthesizing NC, the high brightness cellulose is preferred The MW distribution of Acacia pulp is given in Figure 3.1 300 AH-89 AH-87 AH-85 AH-83 dw/dLogMw 250 200 150 100 50 0 200 400 600 800 1000 1200 DP Figure 3.1 MW distribution of the Acacia wood samples The DP of the Acacia pulps concentrate in the range of 600 to 1050 units In addition, the MW and molecular weight distribution of the samples are almost equal 3.1.3 The structural characteristics of the pulps according to FTIR Based on the results of the FTIR spectra, the structural characteristics of the samples and comparative samples were determined (Table 3.5) Table 3.5 Total crystalline index (TCI), lateral order index (LOI), hydrogen bonding intensity (HBI), and asymmetric index (a/b) of the pulps TCI LOI HBI a/b Samples 1.114 2.006 2.318 0.29 AH-83 1.124 1.907 2.252 0.29 AH-84 1.103 2.013 2.300 0.26 AH-85 1.119 2.060 2.174 0.25 AH-86 1.143 2.071 2.333 0.30 AH-87 1.131 1.994 2.352 0.31 AH-88 1.140 2.008 2.491 0.31 AH-89 1.155 2.532 2.202 0.24 INDO 1.205 2.906 2.112 0.21 CND-1 The structural parameters of Acacia-pulp samples are quite different from the pine wood pulp However, the structural parameters of Acacia-pulp samples are quite equal So, it can select samples that represent the research process later 3.2 Modification and characteristics of obtained cellulose from Acacia pulps With the characteristics of locally produced acacia-wood pulp, the modified method needs to achieve the main objectives: - purify cellulose to increase α-cellulose; 2- modify cellulose structure to increase viscosity and increase water absorption As analyzed in the overview of methods of modified cellulose structure, the thesis selected modification of Acacia cellulose by a cold caustic method 3.2.1 Effect of brightness and production technology To study the effect of brightness and the technology of production, the An Hoa samples have a brightness of 83 ÷ 89% ISO and two samples of Bai Bang pulp with a brightness of 76 ÷ 84% ISO was modified and then the results were compared with the quality of a CND-1 sample The modified process was carried out in a solution of 10% NaOH, at a temperature of 20 oC, the concentration of 3.3% pulp, and for 120 minutes (Table 3.6) 12 Table 3.8 The amount of hydrogen bonds of some cellulose samples The intermolecular bonds, % The intramolecular bonds, % Samples O(6)H…O’(3) O(2)H…O’(2) O(3)H…O(5) O(6)H…O(2) AH-NL 15,85 53,70 30,45 AH-7.5 19,63 49,12 31,25 AH-15 24,65 35,87 39,48 INDO 24,43 39,85 35,72 CND-2 24,23 40,47 35,30 The amount of O(6)H…O’(3), O(2)H…O’(2) bonds and O(6)H…O(2) bond increased after modifying The amount of O(3)H…O(5) decreased Thus, obtained cellulose with the orientation of OH groups has changed The energy calculation of the hydrogen bonds is shown in Table 3.9 Table 3.9 The energy of hydrogen bonds in cellulose samples The energy of hydrogen bonds EH, kJ Samples O(2)H…O(6) O(3)H…O(5) O(6)H…O’(3) O(2)H…O’(2) AH-NL 10.143 20.247 30.035 AH-7.5 8.702 19.777 30.565 AH-15 8.990 19.777 28.605 36.752 CND-2 9.565 20.137 30.565 INDO 9.579 20.325 30.807 The energy of intramolecular hydrogen bonds is smaller than intermolecular hydrogen bonds After modifying, the energy of the hydrogen bonds decreases 3.2.3.3 The crystalline characteristics of Acacia cellulose according to XRD To examine the crystallinity and crystal parameters of the cellulose, the Xray diffraction of the samples is resolved by Gaussian distribution to separate the spectral regions interspersed with each other Based on the results of spectral resolution, crystallinity (Cr.I) and crystal parameters of the samples are calculated and given in Table 3.10 Table 3.10 Crystalline parameters of samples Crystalline domain size, nm Samples Cr.I, % Angle βo L(101) L(101̅) L(002) AH-NL 57.40 85.2 3.71 6.54 4.67 AH-7.5 60.28 84.0 4.33 8.58 4.80 AH-15 60.67 60.2 4.04 3.55 2.99 INDO 55.20 84.4 3.88 6.54 4.48 CND-2 57.70 84.1 3.68 6.55 4.44 13 The results (Table 3.10) show the crystallinity and crystalline domain size of Acacia cellulose has significant differences by modification as well as in comparison with the cellulose from CND-2 and INDO The angle of crystal is different between cellulose I (84-85o) and cellulose II (60.2o) Compared with the imported cellulose samples (INDO and CND-2), XRD crystal parameters of acacia wood pulp and obtained cellulose after modifying were significantly different Because the cellulose heterogeneous reaction when preparing nitrocellulose, the difference of this structural parameter will be very strong in the reaction and quality of the product 3.3 Synthesis and characteristics of NC from the modified cellulose 3.3.1 The nitrated reactivity of the Acacia cellulose According to Titov and et al, the reagent (ion NO2+) is released by the mixture of nitric acid in the presence of sulfuric acid as follow: Nitroni ion (NO2+) is electrophilic reagent The formation of this reagent depends on the mass ratio of HNO3: H2SO4: H2O The thesis selected two nitration mixtures with different activities to investigate the nitrated reactivity of Acacia cellulose as follows: - A strong reactive acid mixture of nitration: 25.6% HNO3, 65.8% H2SO4, and 8.6% H2O; - A weak reactive acid mixture of nitration: 21.5% HNO3, 62.1% H2SO4, and 16.4% H2O The results of nitration of the AH7.5, AH-15, and CND-2 are shown in Figure 3.12 3.0 2.4 2.8 2.6 Degree of subsitution Degree of subsitution 2.2 NC from AH-7.5 NC from AH-15 NC from CND-2 2.0 1.8 1.6 1.4 2.4 2.2 NC from CND-2 NC from AH-7.5 NC from AH-15 2.0 1.8 1.6 1.2 1.4 1.0 10 20 Time, 30 40 1.2 10 20 30 40 50 60 Time, (a) (b) Figure 3.12 The substitution degree of Acacia cellulose with a weak active acid mixture (a) and a strong active acid mixture (b) The reactive ability of Acacia cellulose in the weak active acid mixture is similar to that of CND-2 at the end and better than CND-2 in the first few minutes In the strong reactive acid mixture, the nitration of Acacia cellulose reaches its limit (DS ~ 2.65) This Acacia cellulose has a lower reactivity than CND-2 (DS = 2.72) 14 3.3.2 The effect of reaction conditions on preparing NC from Acacia cellulose 3.3.2.1 The dependence of DS on the water content in the acid mixture The thesis carried out nitration of Acacia cellulose by the acid mixtures with water content from to 17%, at the temperature of 30oC, for 30 minutes and at a module of 70 (Table 3.13) Table 3.13 The effect of the acid mixture on NC characteristics Composition of acid mixture,% NC characteristics H2SO4 HNO3 H2O Qv, kcal/kg %N DS 70.91 20.86 8.23 1047 13.21 2.66 67.44 20.61 11.95 1023 13.03 2.59 64.13 20.79 15.08 950 12.47 2.41 63.37 20.78 15.85 925 12.27 2.35 62.80 20.68 16.52 875 11.89 2.23 62.13 20.76 17.11 837 11.59 2.14 In the nitration process, the reaction of the hydroxyl groups with the nitrated reagent (NO2+) is in the following order: - The first hydroxyl group in position C6 has the strongest ability of reaction to form mononitrate cellulose: - Then, the second hydroxyl group in position C2 is preferred to the next reaction to form dinitrate cellulose: - Finally, the second hydroxyl group in position C3 has the hardest ability of reaction to form trinitro cellulose, according to the following reaction scheme: 15 Table 3.13 shows that the water content of the acid mixtures is a basic factor that regulates cellulose esterification The nitrogen content of the obtained NC was reduced when the water content of the acid mixtures increased In order to prepare NC products with high nitrogen content (pyroxylin), it is necessary to use the acid mixture of to 9% water; In addition, to produce NCs with low nitrogen content (colocxilin), it is necessary to use the acid mixture of 15 to 17% water 3.3.2.2 The effect of nitrated time at different temperatures In order to investigate the effect of nitration time on DS of NC at different temperatures, the thesis conducted nitration of modified Acacia cellulose at a temperature of 20oC and 30oC with different times (Table 3.14) Table 3.14 Effect of nitration time at different temperatures on the DS of NC Temperature, Time of nitration o C 10 20 30 40 50 20 2.03 2.16 2.22 2.28 2.32 30 2.23 2.29 2.34 2.35 2.36 Table 3.14 shows that the higher temperatures will accelerate the rate of nitration, but not affect the final esterification level of the NC 3.3.2.3 Effect of stable conditions on the viscosity and stability of NC The thesis carried out hydrolysis of NC with a nitrogen content of 12.34% in a 0.3% solution of dilute sulfuric acid, 2% of NC suspension for 10 to 40 hours respectively at a temperature 100 to 120oC (Table 3.15) Table 3.15 The effect of time on the viscosity of NC t, hours 10 20 30 40 1000 C η, E0 8.37 6.44 5.51 4.06 t, hours 10 1100 C η, E0 8.37 5.87 5.08 4.41 3.72 3.31 t, hours 10 1200 C η, E 8.37 4.42 2.87 1.93 1.27 0.99 From the results in Table 3.15, when the hydrolysis time increases the NC viscosity decreases and decreases sharply at higher hydrolysis temperatures The rate of viscosity reduction also shows the hydrolysis - depolarization rate of NC The depolymerization reaction at the position of glycoside bonds occurs according to the following reaction: 16 Table 3.16 Effect of temperature and time on the stability of NC Stability of NC (ml NO/gr.) Temperature, oC hour hours hours hours hours 4.13 3.65 2.76 2.17 1.35 100 (6 hr.) (9 hr.) (20 hr.) (30 hr.) (40 hr.) 110 3.71 2.66 1.82 1.65 1.32 120 3.37 2.24 1.51 1.32 1.3 The stability of the NC was significantly improved after stabilization because the residual acid in NC fibers was released and the sulfoesters was decomposed The samples with acceptable stability are less than 2.5 ml NO/gr The high temperatures allow to reduce the time of stabilization 3.3.3 Characteristics of NC from the Acacia cellulose 3.3.3.1 Morphology and fiber size of NC from the Acacia cellulose The morphology and size of NC fibers from Acacia cellulose were investigated by high-resolution SEM images (1000 times) and compared with NC fibers from pine cellulose (Figure 3.14) (b) NC-2 of Pine cellulose (a) NC-2 of the Acacia cellulose Figure 3.14 SEM image of NC-2 from Acacia cellulose (a) and Pine cellulose (b) 17 The SEM image showed that NC fiber from Acacia cellulose was about times smaller and smooth than NC fiber from pine cellulose It can lead to a longer dissolution and swelling time of NC from Acacia cellulose 3.3.3.2 Spectral characteristics of the NCs The FTIR spectrum characteristics of NCs synthesized from Acacia cellulose and AH-7.5 cellulose are shown in Figure 3.15 AH-7.5 100 % Transmittance NC-3 80 NC-2 NC-1 60 40 -OH 20 -ONO2 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1 Hình 3.15 FTIR spectra of the NCs and AH-7.5 The NCs from Acacia cellulose have bands for characteristic groups of pure NC The impurity groups in these NCs is not detected Crystalline properties affect the solubility, swelling, and plasticity of NC The crystal structure of the NC was examined by XRD diffraction (Figure 3.16) 22.26 6000 NC-3 AH-7.5 Intensity [counts] 5000 4000 3000 14.66 16.36 2000 34.06 1000 0 10 20 30 Angle[o2Theta] 40 50 60 Figure 3.16 X-ray diffraction of the NC from the Acacia cellulose 18 The result (Figure 3.16) shows that the NC-3 diffraction signal is much weaker than the Acacia cellulose The diffraction signals are unclear It can be explained by incomplete esterification of the OH groups (DS ~ 2.24) It leads to the disorder of NC-3 chains 3.3.3.3 The technical characteristics of NC For producing propellant in Vietnam, the types of NC prepared from wood cellulose are NC-1, NC-2, and NC-3 In particular, the NC-1 and NC-2 are often used to make single-based propellant and the NC-3 is often used to make doublebased propellant The thesis has selected the conditions for preparing some types of these NCs including NC-1, NC-2 (table 3.17) and NC-3 (table 3.18) as well as compared with the characteristics of NCs made from pine cellulose Table 3.17 The technical specifications of NC-1 and NC-2 Characteristics Nitrogen content, % Viscosity of 2% NC solution, Eo Solubility in ethanol, % Solubility in ethanol-diethyl ether, % Thermal stability, cm3/g Ash, % NC from AH-7.5 NC-1 NC-2 13.22 12.35 7.85 4.12 2.26 3.15 6.85 95.55 2.03 1.82 0.23 0.20 NC from CND-2 NC-1 NC-2 13.38 12.32 8.02 3.91 1.15 2.16 5.22 96.61 2.15 1.76 0.22 0.21 The results show the important technical characteristics of these NCs meet fully the technical requirements used for the production of a single-based propellant The nitrogen content of NC-1 from Acacia cellulose is much smaller than that of NC-1 from CND-2 Table 3.18 The characteristics of the NC-3 Characteristics Nitrogen content, % Solubility in ethanol, % Solubility in ethanol-diethyl ether, % Insoluble substance in acetone, % Viscosity of 2% NC solution in acetone, Eo Thermal stability at 132oC, cm3/gr Ash, % NC-3 11.93 2.16 99.2 0.06 2.24 2.1 0.2 Specifications 11.75÷12.09 ≤ 12.0 ≥ 98.0 1.9÷2.6 ≤ 2.5 ≤ 0.5 19 The technical characteristics of NC-3 from acacia cellulose satisfy the requirements of NC-3 according to Vietnamese standards and the requirement of E-grade pyro-cellulose according to MIL-DTL-244C 3.3.3.4 Molecular weight and molecular weight distribution of the NCs The MW fraction of NCs from Acacia cellulose was made by dissolving in various mixtures of acetone and water The results of NC-1 and NC-2 fractions are shown in Figure 3.17 2.5 Integation curve derivative curve 1.5 0.6 1.0 0.4 0.2 0.5 0.0 0.0 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 Integation (m), g 0.8 Derivation dm/dlog(Mw) Integation (m), g 1.2 1.0 2.0 Integation curve Derivation curve 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0.0 3.6 5.4 1.0 0.8 Derivation dm/dlog(Mw) 1.0 3.8 4.0 Log(Mw) 4.2 4.4 4.6 4.8 5.0 0.0 5.2 Log(Mw) (a) (b) Figure 3.17 Molecular weight distribution of the NCs: (a): NC-1; (b): NC-2 The graph in Figure 3.17 shows that the MW of NC-1 ranges from 4,500 to 160,000 and focuses on 58,000 The MW of NC-2 ranges from 5,000 to 110,000 and concentrates on 31,000 For NC-3, MW fraction results are given in in Figure 3.18 30 Percent of fraction, % 24.76 20 16.14 14.44 14.9 13.93 10 8.72 6.15 0.96 0.0 5.0x10 1.0x10 1.5x10 2.0x10 2.5x10 3.0x105 Molecular weight, g/mol Hình 3.18 The molecular weight fraction of NC-3 from Acacia cellulose The molecular weight of NC-3 ranges from 24,000 ÷ 300,000 In particular, about 70% of the weight is distributed in the range of 24,000 ÷ 75,000 20 3.3.3.5 Distribution of nitrogen content of the NCs Investigation on the above structural characteristics confirmed that the crystallinity and fiber sizes of Acacia cellulose differ significantly from those of other cellulose In this work, the nitrogen content distribution of NCs from Acacia cellulose was investigated by fractionating with a mixture of ethanol and diethyl ether in different proportions The results are shown in Figure 3.19 100 NC-1 from AH-7.5 NC-1 from CND % weight %N % weight %N 100 93.63 90.89 96.61 95.55 % weight %N % weight %N NC-2 from AH-7.5 NC-2 from CND 50 50 10.21 9.62 2.26 12.66 12.41 6.85 13.37 13.46 3.15 1.15 10.13 9.81 5.22 Fraction 12.42 2.16 13.31 12.36 1.3 Fraction 13.25 1.23 (a) (b) Figure 3.19 The nitrogen content distribution of NCs: (a) - NC-1 of AH-7.5 (13.22 %N), NC-1 of CND-2 (13.38 %N) and (b) - NC-2 of AH-7.5 (12.35 %N), NC-2 of CND-2 (12.32 %N) The obtained NC after nitration may have a different degree of substitution in each unit (1 to OH groups) The position of nitrate groups may vary as follows: With DS = 1, mono-nitrate cellulose: With DS = 2, di-nitrate cellulose: With DS = 3, tri-nitrate cellulose: 21 A NC chain may have units with DS = 1, DS = and DS = At the same time, the various macromolecules of NC also differ in the degree of substitution Figure 3.19 results show that the dispersion of nitrogen content of NC from Acacia wood is much larger than that of pine cellulose 3.4 Preparation and characterization of the propellant from acacia cellulose 3.4.1 Preparation, physicochemical and ballistic characteristics of the propellant The 11/7 single-based propellant (TPP-VN) was prepared by plasticization of NC mixture (NC-1 and NC-2) with ethanol/diethyl ether (1:2) to form a slurry Then, the slurry was pressed through a mold at 320 to 500 bars and cut to pieces The results are given in Table 3.21 Table 3.21 Physical and chemical characteristics of TPP-VN propellant TT Characteristics Value Specifications Outside evaporation, % 1.38 1.00÷1.80 Inside evaporation, % 1.11 ≥ 0.90 DPA content, % 1.74 1.00÷2.00 Specific density, g/cm3 1.61 ≥ 1.54 Bulk density, g/cm 0.80 ≥ 0.75 Heat of combustion, cal/g 905.5 ≥ 850 Vielle stability at 106,5oC, hours 67.5 ≥ 60 The results show that although it is necessary to adjust some of the conditions in the production, the physicochemical properties of the propellant made of acacia cellulose meet the technical requirements of the 11/7 propellant Table 3.22 Ballistic characteristics of TPP-VN propellant No Characteristics Value Specifications The sample was kept at 19oC, 48 hours Velocity of ammunition, m/s 1,004 1,000±7 Standard deviation of velocity, m/s 0.66 ≤ 2.8 Average maximun pressure PmaxTB, kG/cm 2,942 ≤ 3,100 Maximun pressure PmaxTB, kG/cm 3,032 ≤ 3,320 The sample was kept at 40oC, 48 hours Average maximun pressure PmaxTB, kG/cm2 3,346 ≤ 3,565 Maximun pressure PmaxTB, kG/cm2 3,411 ≤ 3,814 The results show that the propellant complied with the combat requirements of the 57 mm ammunition and fit well to the harsh conditions of the shot The 22 results of the newly developed propellant initially confirmed the applicability of Acacia cellulose in the production of single-based propellant 3.4.2 Chemical stability of TPP-VN propellant In order to speed up the process of decomposing propellant for the study of chemical stability, the thesis carried out aging TPP-VN, TPP-Ca samples at temperatures of 70, 80, and 90oC with different periods of time (Table 3.23) Table 3.23 The content of DPA in aged samples TPP-VN sample TPP-Ca sample 70oC 80oC 90oC 70oC 80oC 90oC Day DPA, % Day DPA, % Day DPA, % Day DPA, % Day DPA, % Day DPA, % 12 22 40 73 1.44 1.23 1.07 0.93 0.64 15 27 37 45 1.44 1.01 0.81 0.68 0.53 12 15 18 1.44 0.86 0.69 0.52 0.41 12 22 40 73 1.54 1.35 1.21 1.04 0.80 15 27 37 45 1.54 1.19 0.95 0.83 0.74 12 15 18 1.54 1.03 0.81 0.70 0.62 The results show that the decline in the content of stabilizers of TPP-VN seems to be faster than TPP-Ca Chemical stability is further clarified in the calculation of kinetic parameters and estimation of propellant storage time (Table 3.24) Table 3.24 Kinetic parameters and life-time of TPP-VN and TPP-Ca propellant Samples Kinetic parameters and life-time TPP-VN TPP-Ca Standard deviation,% 15.6 16.3 Optimal n-value 1.2 1.4 Activated energy, kJ/mol 91.42 89.24 Constant A, s-1 11.10x106 4.41x106 Life-time of 50% stabilizer depletion at 25oC, years 22.46 25.26 Table 3.24 shows that the activation energy of TPP-VN propellant is equivalent to TPP-Ca The life-time of 50% stabilizer depletion of TPP-VN is lower than TPP-Ca about years Therefore, this result suggests that the quality decline of TPP-VN propellant is faster than that of TPP-Ca 3.4.3 Stability of the ballistic characteristics of the propellants In order to investigate the decrease in the ballistic properties of the propellant after aging, the thesis has determined the ballistic parameters of TPP-VN and TPPCa samples before and after aging (Table 3.25) 23 Table 3.25 Ballistic characteristics of TPP 11/7 (gas pressure pmax, force of propellant f, and coefficient of burning rate u1) Time of f, u1, mm / s Samples T,oC m, gr pmax, bar KG / cm aging, day KG.m/kg 10 497.9 0.0569 0 920,020 20 1111.0 0.0573 10 483.3 0.0636 TPP-Ca 70 73 864,804 20 1123.6 0.0623 10 530.5 0.0645 90 18 1,031,338 20 1115.7 0.0591 10 511.9 0.0549 0 985,237 20 1088.7 0.0538 10 505.9 0.0679 TPP-VN 70 73 922,435 20 1147.8 0.0645 10 516.4 0.0654 90 18 977,971 20 1118.9 0.0617 850.000 ÷ 0.0508 ÷ The technical specifications of 11/7 propellant 1.100.000 0.1108 The results showed that the single-based propellant from the Acacia mangium cellulose ensured the stability of ballistic characteristics before and after aging as well as was equivalent to the propellant from the currently used material CONCLUSION Main results of the thesis: - The Acacia mangium pulps are relatively equal in composition and structure but not meet the technical requirements As a result, it is necessary to improve α-cellulose, viscosity, and water absorption as required by the propellant production - The An-Hoa pulp is modified by a cold alkaline method with higher efficiency than Bai-Bang pulp As the NaOH concentration increased from 4% to 20%, the α-cellulose increased and then almost stabilized Besides, the temperature (2 to 45 oC) has little effect on α-cellulose but reduces viscosity Increasing of time (15 to 120 minutes) goes up the α-cellulose and the viscosity Suitable conditions: at the temperature from 10 to 45oC, 7.5% of NaOH concentration, and 60 minutes of time Structural characteristics differ significantly from pine cellulose 24 - Researching on functional modification by nitration of Acacia cellulose with nitric acid in the presence of sulfuric acid, and investigating the characteristics of the obtained NC The results point out that the reaction of cellulose of acacia wood is relatively low; interpret by reaction mechanism of cellulose with nitric acid and by structural characteristics of Acacia cellulose; indicates appropriate reaction conditions and confirms the ability to prepare NCs to meet the requirements for use in the manufacture of propellants Preparing and analyzing, testing the characteristics of the TPP-VN from Acacia cellulose; investigating the stability of the obtained propellant by accelerating aging The propellant meets the technical requirements used for 57mm ammunition, the stability of the propellant is almost equivalent to that of traditional materials New contribution of the thesis: - The characteristics of locally produced Acacia mangium pulps as a raw material for making propellant were investigated and evaluated, then the pulps were selected to modify; - The conditions of modified reaction and characteristic of Acacia mangium cellulose modified by the cold caustic method were researched, then the optimum conditions were chosen; - The conditions of nitration and characteristics of nitrocellulose from Acacia mangium cellulose were researched and selected to make single-based propellant 11/7; - The chemical stability, evaluating life-time and ballistic stability of the single-based propellant from Acacia mangium cellulose were investigated The trends for continuous development: The results of thesis have opened the following research directions as follows: - Focusing on researching and solving technological difficulties when producing propellants on an industrial scale for this material source - Study on modification and application of modified cellulose to manufacture paints and glues on NC basis for civil and military use - Expand this research direction with some other cellulose sources in Vietnam to continue searching for new sources of materials for the defense industry in Vietnam LIST OF ORIGINAL PUBLICATIONS Doan Minh Khai, Phan Duc Nhan, Trinh Dac Hoanh (2016), “The technical characteristics of modified cellulose from Vietnamese acacia pulp”, Journal of Science and Technology, No.179, – Military Technical Academy, p.236-241 Doan Minh Khai, Phan Duc Nhan, and Trinh Dac Hoanh (2017), “Average molecular weight and molecular weight distribution of the Vietnamese acacia pulps”, Vietnam Journal of Chemistry 55(2), p 135-139 Doan Minh Khai, Phan Duc Nhan, and Trinh Dac Hoanh (2017), “An investigation of the structural characteristics of modified cellulose from acacia pulp”, Vietnam Journal of Science and Technology 55(4), p 452-460 Doan Minh Khai, Phan Duc Nhan, Trinh Dac Hoanh and Nguyen Duy Tuan (2017), “An investigation of the structural characteristics of the Vietnamese acacia pulp”, Journal of Analytical Sciences 22(3), p 148-152 Doan Minh Khai, Phan Duc Nhan, Trinh Dac Hoanh, Le Quang Dien, Phan Dinh Phong, Vu Manh Hung (2017), “The chemical reactivity of modified acacia cellulose with nitric acid in the presence of sulphuric acid”, Proceeding in the 6th Asian Symposium on Advanced Materials: Chemistry, Physics & Biomedicine of Functional and Novel Materials, Hanoi, p 279-283 Doan Minh Khai, Phan Duc Nhan, Trinh Dac Hoanh (2018), “Synthesis and characteristics of the nitrate celluloses from acacia cellulose”, Proceedings in The 5th Academic Conference on Natural Sciences from Asean Countries, Da Lat, p 240-246 Doan Minh Khai, Phan Duc Nhan, Trinh Dac Hoanh (2018), “The synthesis and characteristics of a pyrocellulose from acacia cellulose”, Vietnam Journal of Chemistry 56(4e1), p 235-239 Doan Minh Khai, Phan Duc Nhan, Nguyen Manh Hao, Trinh Dac Hoanh (2018), “Thermal decomposition of a nitrocellulose-based propellant from acacia cellulose”, Journal of Military Science and Technology, FEE, p.333339 ... acid mixture (a) and a strong active acid mixture (b) The reactive ability of Acacia cellulose in the weak active acid mixture is similar to that of CND-2 at the end and better than CND-2 in the... Analytical Sciences 22(3), p 148-152 Doan Minh Khai, Phan Duc Nhan, Trinh Dac Hoanh, Le Quang Dien, Phan Dinh Phong, Vu Manh Hung (2017), “The chemical reactivity of modified acacia cellulose with... Trinh Dac Hoanh (2018), “The synthesis and characteristics of a pyrocellulose from acacia cellulose”, Vietnam Journal of Chemistry 56(4e1), p 235-239 Doan Minh Khai, Phan Duc Nhan, Nguyen Manh Hao,