Application of Large Area Plasma Cathode Electron Beam for Natural Rubber Vulcanization

Transcription

1 Oal Session Application of Lage Aea Plasma Cathode Electon Beam fo Natual Rubbe Vulcanization P. Rahajo, K. Uemua, N.N. Koval*, V. Shuguov*, V. Denisov*, V. Jakovlev*, W. Setiawan**, and M. Utama*** ITAC Ltd., 8-2 Kamisuwa Tsubame City Niigata Niigata, Japan Phone: +81-(0) , Fax: +81-(0) , *Institute of High Cuent Electonics, 4, Akademichesky ave., Tomsk, , Russia **Indonesia National Nuclea Enegy Agency (PTAPB BATAN), Babasai, Yogyakata 55281, Indonesia ***Indonesia National Nuclea Enegy Agency (PATIR BATAN), Ps. Jumat, Jakata 12070, Indonesia Abstact In this study, iadiation of natual ubbe latex using pulsed plasma cathode electon beam system has been attempted. Fundamentally diffeent fom the conventional hot filament electon souces, the pesent pulsed plasma cathode electon beam can be used fo vulcanization pocess with lage aea of iadiation ( mm), low electical powe consumption (< 9 kw), and high efficiency. The evaluation esults show that afte electon beam iadiation at 150 kv 18 A on old natual ubbe latex with stiing method, an incease of the tensile stength up to 12.3 MPa can be achieved without any chemical additive o sensitize. Highe tensile stength until 18.0 MPa can be povided on fesh natual ubbe latex. It suggests that the pesent system can be applied as a new type of electon acceleato fo coss-linking of natual ubbe latex. 1. Intoduction Consideing envionmental issues in the futue, natual ubbe latex has been pedicted to be moe competitive against synthetic ubbe. Not only due to cuent ising pice of petoleum as aw mateial of the synthetic ubbe, but also poductions of goods such sugical gloves, cathetes, condoms, ties etc. fom natual ubbe latex (Hevea basiliensis) could be moe envionmental-fiendly compaed to the synthetic ubbe. Moeove, waste of the natual ubbe disposals can be easily decomposed by soil micooganisms, and plantation of the Hevea tees can contibute impotant oles fo educing the eath global waming. Unfotunately, thee ae still emaining poblems fo obtaining optimal application of the natual ubbe, i.e., the vulcanization poblem and the content of nitosamine o allegenic potein in the Hevea ubbe latex. Sulfu and othe chemical additives used in conventional vulcanization of the ubbe ae known as the main obstacle in the ecycling pocess of the ubbe tie wastes. Nitosamine, which may be fomed fom the ubbe pecuso additives, has been epoted to be esponsible fo cance diseases (cacinogen) in the human body [1]. In addition, natual ubbe latex itself inheently contains allegenic potein, which may lead to motality fo some allegic peoples. To solve the poblems, iadiation pocess on the natual latex has been aleady attempted in Indonesia National Nuclea Enegy Agency since 1979 by using gamma-ay 60 Co [2]. Howeve, iadiation pocess using the gamma-ay equies huge and thick shielding concete building fo iadiation potection of the opeatos, which may not be economically eliable fo in-situ fesh latex pocessing nea the Hevea plantation aea. Fo the latex teatment, consecutive pocess of fesh latex just afte havesting is stongly equied; othewise, the expected mechanical popeties of the vulcanized ubbe will be deteioated due to bacteial and/o oxidation duing the stoage [3]. Instead of gamma ay, iadiation with low enegy electon beam (EB) becomes a new altenative method fo poviding the in-situ fesh latex pocessing. Owing to low electic enegy consumption of compacted electon beam machines, mobile iadiation facilities in ual aea may be possible to be ealized in the futue. Makuuchi et al. have developed electon beam system with acceleating voltage about kv fo natual ubbe vulcanization iadiation [4]. The system applies stiing pocess with impelle to obtain homogenous beam iadiation. Howeve, as commonly used in conventional electon beam systems, the latex EB iadiation system uses a filament fo the electon souce, which will not be eliable fo poviding lage aea iadiation. Anothe disadvantage of the conventional EB system is in the maintenance of the electon beam souce as shot lifetime of the filament. In this study, iadiation of natual latex by using pulsed plasma cathode electon beam with low acceleating voltage less than 200 kv is intoduced. The electon souce is fundamentally diffeent fom conventional electon beams using hot filament electon souces. With the pulsed plasma cathode electon beam, it is possible to obtain lage aea of latex iadiation without beam scanning, to povide highly efficient vulcanization pocess of natual ubbe latex. 2. Expeimental pocedue Natual ubbe latex used fo the pesent electon beam iadiation test is high ammonia (HA) concen- 497

2 Pulsed Powe Applications tated latex fom Jalupang Rubbe Plantation PTPN VIII Subang Bandung, Indonesia havested on May 14, This latex is indicated as old latex in this study, due to its 2-yea stoage peiod befoe the iadiation. Fesh latex, with stoage peiod less than 6 months, is also iadiated fo compaison. The natual ubbe latex samples ae iadiated without any chemical additive o sensitize, using DUET electon beam system available at Institute of High Cuent Electonics, Tomsk Russia. Figue 1 shows the pictue and schematic illustation of the electon beam system A, 40µm, 50 Hz kV DC Fig. 1. Photo and schematic illustation of the electon beam system. The intense gas plasma is geneated by pulsed lowpessue ac dischages and a hollow electode. Fom the plasma, electons ae extacted and acceleated to pefom pulsed lage aea electon beam iadiation in the atmosphee The system can be opeated at elatively low acceleating voltage of kv with beam cuent up to 100 A. The beam is pulse type with beam duation and fequency ae 40 mks and Hz, espectively. The above paametes ae independently adjustable which allow vaious applications. The beam outlet window is made of Al Be foil with thickness of 40 mkm and size of mm. Unlike conventional electon beam systems, in the pesent system thee is no use of hot filament, and lage iadiation aea is possible to be attained. As shown in Fig. 1, the acceleato of the EB system consists of a cylindical vacuum chambe with diamete of 700 mm and length of 1300 mm. In the acceleato, thee is a plasma emitte box in the fom of a hollow ectangula paallelepiped with sizes of mm. Two coaxial ac plasmageneatos ae installed on lateal side of the emitte box. The plasma-geneato consists of Mg cathode, tiggeing electode, and dielectic insulato between the cathode and the electode. At the bottom side of the emitte box, thee is a hoizontal extaction window fom whee electons ae extacted out. The mm window is coveed with a stainless steel emission gid having cell sizes of mm. The plasma emitte box is mounted to a bushing insulato made fom polythene by using tubula od though which the input cables fom the plasmageneato powe supply ae connected. To affod electical stength fo the voltage up to 200 kv, the uppe pat of the bushing insulato is suounded by insulating gas in a pessuized tank (nitogen at pessue 0.6 MPa). The electon souce in DUET acceleato is lowtempeatue volumetic plasma geneated by vacuum ac dischage, which can pefom high beam cuent density (up to 1 A/cm 2 ) with high beam homogeneity (± 15%) and lage iadiation aea (about 10 3 cm 2 ) at compaatively low enegy consumption (less than 2 kw). Once an ac dischage is initiated due to the beakdown of dielectic in the plasma-geneatos, a dischage between the plasma-geneato cathodes and hollow anode will be ignited [5]. The hollow anode function is fulfilled by intenal walls of the plasma emitte box. Modulation of beam cuent in this system can be caied out by paamete adjustments of the pulse ac dischage. High DC voltage kv is applied between the plasma emitte and the vacuum chambe to extact and acceleate electons passing though the emission gid. The DC acceleating voltage has benefit to avoid electon enegy loss duing penetation into atmosphee o highe pessue gas though the thin foil of the outlet window. It also allows fo obtaining almost mono-enegetic beam, due to the absence of electon acceleation in font of the window and no decay of high voltage impulse, which usually takes places in taditional pulse acceleatos. 498

3 Oal Session Anothe advantage of DUET acceleato is its possibility of independent paamete adjustment (fo beam cuent, acceleated electons enegy, pulse duation, pulse epetition fequency), which can allow us to vay the iadiation conditions on gases, liquids o othe poducts ove wide-ange egimes of paametes. Also, the plasma cathode can povide an electon acceleato with high efficiency and longe lifetime, compaed to conventional hot-filament cathodes. In this expeiment, the EB iadiation is subjected on 360g natual ubbe latex placed inside a special stiing vessel with iadiation paamete conditions shown in Table 1. Total iadiation dose of 183 kgy has been achieved by using 150 kv acceleating voltage and 18 A beam cuent in pulses. Since the plasma is geneated by pulse ac dischage, the beam duation can be defined indiectly fom the duation of ac dischage paamete, which is 40 mks in the pesent expeiment. With pulse epetition at 10 Hz, the teatment can be conducted in seveal minutes. Table 1. EB iadiation EB iadiation paamete Values Acceleating voltage (kv) 150 Electon beam cuent (A) 18 Pulse duation (µs) 40 Enegy density pe pulse (J/cm 2 ) 0.06 Total dose (kgy) 183 Pulse numbe Sample mass (g) 360 The stiing system shown in Fig. 2 has been specially fabicated to pefom homogenous iadiation on the natual ubbe latex. A otating stie is installed in the axes of double cylindical vessels having 86 mm opening diamete fo beam iadiation. Due to low enegy electon beam (less than 200 kev) in the cuent pocess, penetation depth of electon in the sample will be vey small (not moe than 1 mm). Only the uppe laye will be modified by the EB iadiation. Fig. 2. Electon beam iadiation condition with special stie fo latex mixing duing the iadiation pocess The stiing system is designed to flow down the iadiated uppe laye of latex suface into the oute cylinde to make continuous iadiation fo the next laye beneath the uppe laye. Afte the iadiation, the ubbe latex liquid is solidified and fomed into flat ubbe films using coagulant dipping method fo test pieces of the mechanical evaluation. The latex fome is fist coated with a laye of CaNO 3 as coagulant agent befoe dipped into the iadiated natual ubbe latex [6]. In this method, the coagulant convets the liquid latex film into a wetgel on the fome. The ubbe thin film is then cleaned in wam wate, died in ai, and died at 90 C fo 15 min in an oven. Fo the compaison, with the same method, the simila samples ae also pepaed fom initial and gamma ay iadiated natual ubbe latex. The gamma ay iadiation on fesh natual ubbe latex was conducted in Febuay, 2008 at PT. REL- ION (Bekasi, Indonesia) with iadiation dose of 25 kgy and nomal butyl acylate (n-ba) additives. To veify the vulcanization pocess as the effect of the iadiations, mechanical popeties such as tensile stength, swelling atio in toluene fo 24 hous, and pemanent set of the ubbe thin film ae evaluated accoding to ASTM standad [7]. 3. Results and discussion Coss-linking in natual ubbe is defined as the linking of two o moe molecula chains of the polymes (cis-1, 4-polyisopene) by means of covalent bonds. This ceates a thee dimensional netwok with an infinite molecula mass. Histoically, the vulcanization means coss-linking of ubbe molecules with sulfu. Now, howeve, coss-linking without sulfu is also called as vulcanization. As the coss-linking occus, mechanical popeties of the polyme will be changed. Table 2 shows the esults of mechanical popety evaluation on the films of latex iadiated with the plasma cathode electode beam, in compaison with initial and gamma ay iadiation. As shown in the table, the pemanent set of natual ubbe pepaed by EB has significantly deceased compaed to the initial sample. The pemanent set is defined as the defomation emaining afte a specimen has been stessed in tension fo a definite peiod, and eleased fo a definite peiod. Decease of pemanent set in the EBiadiated sample means that the vulcanization (cosslinking) of natual ubbe latex has occued due to the EB iadiation. Existence of coss-linking afte EB iadiation can be veified also by the incease of modulus and the decease of elongation at beak of the samples. Modulus is an indicato to the stiffness of ubbe films which is diectly dependent to coss-linking density [8]. Accoding to Allige, the elongation at beak is also educed by excessive coss-linking. Hence, the incease of modulus and decease of elongation at beak afte the iadiation in Table 2 indicate that the 499

4 Pulsed Powe Applications plasma cathode EB iadiation, as well as gamma-ay iadiation, can be used to vulcanize the natual ubbe latex. Table 2. Mechanical popeties of the natual ubbe latex afte the plasma cathode EB iadiation in compaison with initial and gamma-ay iadiation Mechanical popeties Pemanent set, % Elongation at beak, % Modulus 600%, MPa Tensile stength, MPa Swelling atio in toluene (immesed fo 24 hous), % Initial EB iadiation (old) EB iadiation (fesh) Gamma ay iadiation n.a completely diluted As shown in Fig. 3, the tensile stength of the EB iadiated natual ubbe emakably inceases fom 2.2 MPa in initial latex. The incease of the stength is also pesented by the gamma-ay iadiation. As indicated by Makuuchi, the highe tensile stength of the adiation vulcanization natual ubbe latex film can be attibuted by both intepaticle coss-linking and entanglement of the polyme chains [9]. Lowe tensile stength (12.3 MPa) in the old latex might be due to degadation of the latex afte the stoage fo about 2 yeas. The EB iadiation on fesh latex without any chemical additives, howeve, can povide highe tensile stength up to 18.0 MPa, which is almost simila to the gamma-ay iadiation with n-ba additives. Tensile stength, MPa Fig. 3. Tensile stength of natual ubbe latex befoe (a), and afte iadiation with electon beam and gamma ay (b, c, d). The tensile stength can be emakably inceased afte the EB iadiation. Compaed to the old latex (b), EB iadiation on fesh latex (c) exhibits highe tensile stength up to 18.0 MPa, which is almost simila to the gamma-ay iadiation (d) Swelling atio is also anothe indicato of the degee of coss-linking. In this study, swelling atio coesponds to the inceasing of film aea (in cm 2 ) afte and befoe immesed in toluene fo 24 hous. If volume faction of the ubbe netwok in the swollen gel can be expessed as the ecipocal swelling atio, then lowe swelling atio is indicating highe cosslink density, accoding to Floy-Rehne equation (1) [10]: ( ) 2 ln 1 υ +υ +μυ ν=, (1) 1/3 V o υ υ /2 whee v is the coss link density; υ is the volume faction of the ubbe netwok in the swollen gel; V o is the mola volume of the toluene (106.4 cm 3 /mol); μ is the ubbe toluene inteaction paamete (0.393 fo natual ubbe). Powe consumption of the EB system is estimated fom powe supply units of the acceleato and the vacuum system. The DUET EB system in the pesent expeiment contains acceleato and vacuum pumps (mechanical otay pump and diffusion pump), with electical powe consumption ae 7 kw and 1.8 kw at 10 Hz, espectively. Theefoe, it is possible to make teatment of latex sample with compaatively low powe consumption, i.e., less than 9 kw. 4. Conclusions In this study, iadiation of natual ubbe latex using pulsed plasma cathode electon beam system has been attempted. Fundamentally diffeent fom conventional hot filament electon souces, the pulsed plasma cathode electon beam can be used fo vulcanization pocess with lage aea of iadiation ( mm), low electical powe consumption (< 9 kw), and high efficiency. The evaluation esults eveal that afte electon beam iadiation at 150 kv 18 A on old natual ubbe latex with stiing method, an incease of the tensile stength up to 12.3 MPa can be achieved without any chemical additive/sensitize. The EB iadiation on fesh natual ubbe can povide highe tensile stength until 18.0 MPa. It suggests that the pesent system can be applied as a new type of electon acceleato fo coss-linking of natual ubbe latex. Refeences [1] J.J. Kabaa, J. Lopez, and C.F. Robet, Natue Rubbe 41, 1 3 (2006). [2] M. Ridwan, F.I. Sundadi, M. Utama, and S. Katowadojo, Radiation Physics and Chemisty 14, (1979). [3] K. Makuuchi, An Intoduction to iadiation vulcanization of Natual Rubbe Latex, Bangkok, T.R.I Global Co., Ltd., 2003, pp [4] K. Makuuchi et al., Japanese patent P , [5] N.N. Koval, Yu.E. Keindel, V.S. Tolkachev, and P.M. Schanin, IEEE Tans. Elect. Insul. 20, (1985). 500

5 Oal Session [6] M. Utama, Hewinani, M. Sumati, Siswanto, Suhayanto, and S. Ruslim, Tial poduction of sugical gloves fom iadiated natual ubbe latex on factoy scale, National Nuclea Enegy Agency Technical Repot, [7] ASTM, Standad Test Method fo Rubbe in Tension, ASTMM D [8] G. Allige and I.J. Sjothun, Vulcanization of elastomes, New Yok, Robet E. Kiege Publishing Company, [9] K. Makuuchi, An Intoduction to iadiation vulcanization of Natual Rubbe Latex, Bangkok, T.R.I Global Co., Ltd. (2003) 87. [10] P.J. Floy and J. Rehne, J. Chem. Phys. 11, (1943). 501