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  • 1. Journal Basic Science And Technology, 1(2),5-9,2012 ISSN : 2089-8185 The Effect of Water Content Hydrogen Peroxide to The Structure of HTPB (Hydroxy Terminated Polybutadiene) Product as Radically Polymerization of Butadiene A Heri Budi Wibowo Pusat Teknologi Roket LAPAN Bogor, Indonesia heribw@gmail.com d Polymerization of butadiene can be proccess by free radical and ionic polymerization. The advantages of ionic polymerization is can produce HTPB with narrow molecule weight distribution and dominan cis-1,4 structure, but cost of production is expensive [2]. The special treatment must be applied to maintain vacuum process. The free radical polymerization is simple process and many cheap catalyst, but product HTPB is broad molecular weight distribution . For industry application, the free radical polymerization is the effective process because ease for process and cheap. HTPB can be made with catalyst hydrogen peroxide in alcohol solvent. The solvents are etanol, butanol, propanol, etc [8,9]. Abstract—HTPB is resin that used as the best fuel binder propellant. HTPB is strategic, expensive, and renewable. For this application, HTPB can be synthesis by radically polymerization of butadiene. One of catalyst than ussually can be used is hydrogen peroxide. The problem of the use of this catalyst is water content that can inhibit the polymerization process. This paper discuss the effect of water content of hydrogen peroxide on structur of HTPB base on polymerization of butadiene. The raw materials used were fresh butadiene 98%. The reactor used was a three neck flask 500 mL equipped with a thermocouple, a stirrer, a sample syringe, and a hot or cold water circulator. Catalyst is hydrogen peroxide with water content 30 – 50%. The reaction is conducted for 70 minutes at 180oC and 350 psig. The HTPB product is analyzed by FTIR spectrometer. The decreased of water content of hydrogen peroxide is increase efectivity of catalyst on polymerization. The cis-1,4 HTPB is increase and the vynil 1,2-structure of HTPB is decrease. One of the problem on butadiene polymerization is the water content of hydrogen peroxide. Butadiene is not soluble in water. Action of catalyst hydrogen peroxide is free radical hydroxyl forming by decomposition. The excess of water is inhibit the radical hydroxyl forming so decreased the effectivity of this catalyst. The excess of water may be affect on structure of HTPB by hydroxyl bonding on polymer growth [11]. Keywords- HTPB, polybutadiene, radical polymerization I. INTRODUCTION TThe investigation of HTPB as propellant fuel binder is very important in aerospace technology authority framework. The solid propellant is consists of ammonium perchlorate as oxydator, binder, and material additive. The most used of propellant binder is polyurethane based on HTPB (Hidroxy Terminated Polybutadiene). HTPB is an expensive, strategic, and unrenewable. HTPB is polymer base on butadiene monomer with the end functional groups is hydroxyl (OH) [3]. The aim of this investigation is to discover the efectivity of catalyst hydrogen peroxide on HTPB forming and their structures. Based on this parameters, we will to find out polymerization proccess condition are able to fullfill the term of suitable solid propellant binder. II. THEORY A. Structure of Polybutadiene The main characterization of polymer HTPB are molecular weight distribution and structure (configuration). The fexibility or hardness of polyurethane base on HTPB is affected by the molecular weight distribution and structure of HTPB. Increased of molecular weight distribution of HTPB can produce harder polyurethane. The increase of cis-1,4 structure of HTPB is contributed on flexibility of polyurethane, but the increase of trans-1,4 structure of HTPB is contributed on hardness of polyurethane [7]. Polybutadiene is a polymer or a series of butadiene monomer compounds. Butadiene is a compound that has the possibility to crosslinking reaction with other compounds at all owned by the C atom, the atom C coding as in figure 1. Butadiene polymerization reaction occurs with covalent bonding occurs between the CHCH group with others through adisi1 reaction [4,7]. 5
  • 2. Journal Basic Science And Technology, 1(2),5-9,2012 ISSN : 2089-8185 polymerization in which initiation occurs via a free radical. Operating conditions include a reaction and the reaction media system operating conditions (temperature, press ure, inert,and reagent composition) [3]. Based on the polymerization reaction medium can occur with a bulk, solution, suspension, and emulsion systems. Polymer structures that occur can be predicted based on the reaction mechanism that occurs so it can be identified factors that influence the structure of the polybutadiene [3,5]. n (CH2-CH=CH-CH2 ) (CH2=CH-CH=CH2)n (1) Bond addition reactions can occur in two ways. The first way is the reaction between the C atom by C no 1 to C no 4 of the other compounds to form a bond butadiene adduct 1.4. Addition of 1.4 will lead to bond the two structures based on geometric shapes. If the group H at the position opposing the so-called bond in trans position. If the group H on the position side by side each other so called cis-bond at position 5 [4,8]. B. Radical Polymerization of Butadiene Free radical polymerization occurs through the formation of free radical. Free radicals can be generated from the redox reactions or reactions of radicalization. Redox reactions like the reaction of iron (III) sulfate with manganese oxide to form iron (II) sulfate and hydroxyl radicals (OH.) or pyrolysis of hydrogen peroxide to produce free radicals. Free radical then reacts with butadiene to form radicals (CH2CH2CH2CH2OH. or MOH.). Propagation reaction initiated by reaction with butadiene radical other to form a dimer radical. The polymer is growth. Radical reaction with butadiene will stop in several ways, namely the inter-radical termination, radical with the growing polymer, or in the presence of other compounds [9, 10]. Reaction mechanism can be shown on this equation. H2O2 2 HO. (4) 2 HO. (5) H2O2 (2) The second way occurs through the bond between the C atom No. 1 with butadiene number 2 on the other, the bond will be formed at a position 1.2 or called bonds at the vinyl position (equation 3). M + MOH. M + M2OH. M + MxOH. (3) M2OH. M3OH. Mx+1OH. (6) (7) (8) Polymer growth occurs through a random system, where the growth of radical reactions do not occur one on one, but occur simultaneously, and the reaction of butadiene with not only the polymer radicals are formed, but also the reaction between the growing polymer with another polymer that is growing. Known free radical polymerization reaction is very fast, so the reaction between polymer radicals occurs at random. Therefore, the radical polymerization will produce a polymer with a molecular weight distribution is not uniform. Polymer growth can be stopped by radical chain reactions bimolekuler pair through the coupling reaction or a combination (equation 9) and the disproportionate reaction by hydrogen atom transfer (equation 10). If equation 7 is the case, then the polymer is a polymer formed by a single hydroxyl end groups. MxOH. + MyOH. HOMxMyOH (9) MxOH. + MyOH. HOMx + MyOH (10) Configuration can be either cis, trans, and vynil. The existence of two double bonds in the polymerization process can give adduct 1.4- which can be either cis-1,4 and trans-1,4. The existence of a single bond to generate vinyl structure or 1.2 with the possibility of isotactic structure, sindiotaktik, and static. Structure of polybutadiene with cis-1, 4 - the higher is soft, good dynamic properties, low hysteresis and good abrasion, the glass transition temperature up to 102oC. Polybutadiene with the dominant structure of trans1,4 is a resilient elastomer, hard, glass transition temperature 107oC to 83oC. Polybutadiene with isotactic structure of the dominant 1.2 -sindiotaktic is a brittle, crystalline material that has a low solubility. Polybutadiene structure that occurs will depend on the operating conditions of the reaction and the mechanism through which the reaction. There are two mechanisms of polybutadiene reaction, the ionic polymerization in which initiation occurs through cation and anion, and radical Reaction rate equation is expressed by the reduced monomer per unit time, is a function of the monomer and the radical chain. Every time the value of the radical concentration is proportional to the initial initiator concentration. 6
  • 3. Journal Basic Science And Technology, 1(2),5-9,2012 ISSN : 2089-8185 -d[M]/dt = kp[M.][M] (11) vynil configuration at wavelength 710 cm-1, 970 cm-1, and 910 cm-1. Effect of the reaction temperature follow the type operation follow Arhenius equation [4,7]. Effect of catalyst efectivity (water content) is decrease the activation energy. So effect of temperature (T) and water content of hydrogen peroxide (w) to reaction rate constant of cis polymerization (kpc), trans polymerization (kpt), and vynil polymerization (kpv) are expressed like eq. 12, 13, and 14. The symbol of Ec, Ac, and R are represented of activation energy, collision frequency factor, and ideal gas constant. (12) (13) (14) Fig 1. Spectra of HTPB. III. METODOLOGY AND RESULTS The kinetic of polymerization is identified by decrease of pressure of reactor as representated of monomer concentration (M). Initial pressure is 350 psig, and at the end of reaction, pressure is 14,7 psig. The decrease of reactor pressure every time is shown at fig 2. Trend of the line is exponential so the reaction is first order follow the equation (11). The value of total reaction rate constant (kpc+kpt+kpv) is the slope of curve ln [M] vs t. A. Material The raw materials used were fresh distilled butadiene 98%. The solvent is ethanol 96,5% withaout pretreatment. The catalyst is solution hydrogen peroxide 30 %, 32 %, 35 %, and 50%. B. Experiment The reactor used was a three neck flask 500 mL equipped with a thermocouple, a stirrer, a sample syringe, and a hot or cold water circulator. The reaction is conducted for 70 minutes at 180oC and 350 psig. The HTPB structure is analyzed by FTIR spectrometer. Cis 1,4-, trans 1,4- and vynil structure are shown by absorbtion at wave length 710 cm-1, 970 cm-1, and 910 cm-1. To study the kinetic of polymerization, data record is decrease of butadiene pressure as function of time. C. Discuss To prove the statement, the trial has been carried out by radical polymerization of butadiene using hydrogen peroxide initiator with ethanol as solvent. With the operating conditions of 170-210oC reaction temperature and initial pressure 350 psi, HTPB product is identified by FTIR spectra shown in figure 1. The product is wash by aquadest and benzen, then dried with vacuum oven at 60oC over 1 hour, and analyzed. The HTPB is represented by absorbstion at 1735cm-1 and spesific structure of cis, trans, and Fig 2. Decreasing of pressure as function of time For study of kinetic of polymerization include cis, tans, and vynil structure formation, the increase of each structure form is identified by area of absorbtion at wavelength 710 cm1 , 970 cm-1, and 910 cm-1. The area of spectra at wavelength 7
  • 4. Journal Basic Science And Technology, 1(2),5-9,2012 ISSN : 2089-8185 710 cm-1, 970 cm-1, and 910 cm-1 follow the table 1 as dominant. The cis structure can be optimized by change the represented of persen composition polymer HTPB. The reaction temperature. kinetic of formation of cis, trans, and vynil structure is Effect of temperature on reaction rate constant is measure expressed by eq. 15, 16, and 17. by extrapolation of ln k vs 1/T so the Arhenius constant A and -d[M]c/dt = (kpc) [M] (15) -d[M]t/dt = (kpc) [M] (16) -d[M]v/dt = (kpc) [M] E can be find by their slope. To study effect water content of hydrogen peroxide to reaction rate constant, curve reaction rate constant versus water content is power type extrapolation. By trendline analysis, the power index can be predicted (figure 4). (17) TABLE I. Time (min) COMPOSITION OF STRUCTURE HTPB AS FUNCTION TIME Area spectra FTIR at point wave length 710 cm-1 910 cm-1 970cm-1 0 100 135 360 10 120 150 379 20 130 165 398 30 140 175 417 40 150 190 423 50 160 196 437 60 165 198 440 70 167 200 445 Figure 4. graph ln k vs (1/T) To measure the reaction rate constans of kpc, kpt, and kpv, then data concentration of polymer with cis, trans, and vynil structure every time is extrapolation in graph ln [M]c,t,v vs t. By trend analysis, the slope of graph ln [M]c,t,v vs t is kpc, kpt, and kpv. The increase of structure of cis, trans, and vynil formation is proporsional with concentration of cis, trans, and vynil. Fig 5. Effect water content to reaction rate constant Generally, increase water content is decrease the efectivity of catalyst, so reaction rate of polymerization is increase. In experiment, if water content of hydrogen peroxide is less than 30%, HTPB product is no formed because the hydroxyl radical is not produced. The effect of temperature and water content are combined in expression 18, 19, and 20. Figure 3. graph [M] vs t Based on figure 3, the rate of vynil structur formation is greater than cis or trans formation. It’s clearly that radical polymerization have tendency to form vynil structure (18) 8
  • 5. Journal Basic Science And Technology, 1(2),5-9,2012 ISSN : 2089-8185 (19) REFERENCES (20) [1] [2] Based on index power of w on equation 18, 19, 20 expressed that reaction rate of cis, trans, and vynil structure formation is affected by water content of hydrogen peroxide. The effect of water content on cis formaton less fast than trans and vynil formation. The effect of temperature to reaction rate is follow the Arhenius equation. The increase of temperature is contribute effect follow trans structure formation > vynil formation > cis structure formation. [3] [4] [5] IV. CONCLUSION [6] Generally, increase water content is decrease the efectivity of catalyst, so reaction rate of polymerization is increase. In experiment, if water content of hydrogen peroxide is less than 30%, HTPB product is no formed because the hydroxyl radical is not produced. Reaction rate of cis, trans, and vynil structure formation is affected by water content of hydrogen peroxide. The effect of water content on cis formaton less fast than trans and vynil formation. The effect of temperature to reaction rate is follow the Arhenius equation. The increase of temperature is contribute effect follow trans structure formation > vynil formation > cis structure formation. [7] [8] [9] [10] [11] 9 H.B. Wibowo, H. Sulistyo, Rochmadi, “Polimerisasi Butadien Secara Emulsi ,” Majalah LAPAN, Vol 2 No 3, ISSN 0126-0480 , Juli 2000. H.B. Wibowo, E. Rosman, “Kinetika Polimerisasi Butadien Secara Emulsi dengan katalis H2O2,” Proceeding JNK, ISSN 0854-6541, Januari 2000. H.B. Wibowo, G. Rosita, “Pengembangan Mekanisme Reaksi Polimerisasi ButadienSecara Moleculer,” Buku Ilmiah Teknologi Dirgantara, ISSN 1829-9032, Januari 2005. H.B. Wibowo, “Activity Concept Approach on Non Ideal Polymerization Mechanism of Butadiene,” Jurnal Iptek Material JIMAT, Vol 4 No 2, ISSN 1412-2898, Juni 2005. H.B. Wibowo, “Polimerisasi Anionik Butadien Secara Bulk untuk Mendapatkan HTPB dengan Distribusi Berat Molekul yang Lebih Sempit,” Proceeding JASAKIAI, ISSN 0854-4778, Desember 2004. H.B. Wibowo, Henny. S., “Polimerisasi Butadiena Secara Anionik Dengan Menggunakan Katalis Yang Didespersikan dalam Serbuk Karbon,” Proceeding JASAKIAI, ISSN 1410-8313, Juli 2004. H.B. Wibowo, “Polimerisasi Butadien dengan Katalis Hidrogen Peroksida Sistem Fasa Tunggal (Homogen),” Jurnal Ilimiah TEKNOLOGI, Vol III No 7, ISSN 18584993, oktober 2007. B.S. Bahl , “Advanced Organic Chemistry,” S. Chand and Co. Ltd, New Delhi, pp 23-34, 2003. J. Flory , “Polymer Chemistry,” Cornell University Press, London, 1979. J. Timnat, “Advanced Rocket Propulsion,” Interscience Publisher, London, 1992. H.B. Wibowo, “Pembuatan HTPB Spesifikasi Fuel Binder Propelan Padat dan Implementasi untuk Industri Polimer,” Seminar IPTEK Dirgantara, Januari 2004..