Utilization of Magnesium Hydroxide Produced by Magnesia Hydration as Fire Retardant for Nylon 6-6,6

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1 C O M U N I C A Ç Ã O Utiliztion of Mgnesium Hydroxide Produced y Mgnesi Hydrtion s Fire Retrdnt for Nylon 6-6,6 Sôni D.F. Roch Deprtmento de Engenhri Químic, UFMG Virgíni S.T. Ciminelli Deprtmento de Engenhri Metlúrgic e de Mteriis, UFMG Astrct: The present work investigtes the use of mgnesium hydroxide, produced y mgnesi hydrtion, s fire retrdnt in polymers. The hydrtion ws crried out in n utoclve, t temperture of 13 C for 1 hour, nd the product ws further sumitted to cominution in jet mill. The solids were chrcterized with regrd to their chemicl composition, prticle size distriution, surfce re nd morphology. The performnce evlution of the hydroxide s flme retrdnt for copolymer of nylon 6-6,6 ws crried out ccording to the UL94 specifictions for verticl urning tests. V- flmmility rting t 1.6 mm (6% mgnesium hydroxide-filled nylon composite) nd t 3. mm (4% mgnesium hydroxide filled nylon composite) were chieved. Mechnicl properties were mintined t the desired vlues. These results indicte tht the hydroxide otined from mgnesi hydrtion cn e successfully employed s fire retrdnt for nylon 6-6,6. Keywords: Fire retrdnt, mgnesium hydroxide, nylon 6-6,6. Introduction The use of ruer nd plstic mterils in the mnufcture of domestic nd industril products hs grown sustntilly in the lst decdes. Some pplictions of these products require the utiliztion of flme retrdnts, the hlogented (romides nd chlorides) nd phosphorous compounds eing the most widely used [1,]. Nevertheless, these compounds generte toxic nd highly corrosive fumes in fire, which mke the dmge even higher. Interest in using metl hydroxides s fire retrdnts hs grown, since these compounds do not produce fumes nd present low corrosiveness [3-5]. Metl hydroxides retrd comustion y soring het nd y cooling the sustrte through dehydrtion rection [5-7]. The metl hydroxide most commonly used s fire retrdnt is luminum hydroxide. Aluminum hydroxide hs een used s fire retrdnt in mny mterils including thermosets, elstomers nd thermoplstics. However, its low temperture of decomposition (pproximtely 18 C) limits its ppliction. Mny polymers must e processed t higher tempertures, which hinders the utiliztion of this compound. It is exctly in these cses tht the use of mgnesium hydroxide ecomes ttrctive, owing to its higher temperture of decomposition (pproximtely 33 o C). The min pplictions of mgnesium hydroxide re in polymers such s polypropylene nd nylon, which should e processed t high tempertures, nd in elstomeric cle cotings, which require high tempertures for rpid processing [8]. Mgnesium hydroxide, s well s lumin trihydrte, is commonly used t high concentrtions, such s 4% to 7%. Due to cost considertions, mgnesium hydroxide does not fully replce luminum hydroxide. Rther, it rodens the utiliztion of metl hydroxides s flme retrdnts in wy tht the dmges s well s the environmentl pollution re minimized. Mgnesium hydroxide-sed products re ville in the mrket. These re minly otined y precipittion of mgnesium hydroxide from rines Autor pr correspondênci: Sôni D. F. Roch, Deprtmento de Engenhri Químic, UFMG, Ru Espírito Snto, 35 6 o ndr,belo Horizonte, MG, CEP: E-mil:sdroch@deq.ufmg.r 116 Polímeros: Ciênci e Tecnologi, vol. 11, nº 3, p , 1

2 nd se wter [3]. The production of the hydroxide for fire retrdnt filler ppliction vi hydrtion of mgnesium oxide hs een hindered y the process economics. Purity requirements for this ppliction result in the need for purifiction steps, which sustntilly increse the finl cost of the product. Direct hydrtion ecomes very interesting option where lrge deposits of pure mgnesite ( precursor of mgnesium oxide) re ville, s in Brzil [9,1 ]. Different processes led to products with different crystllite size, surfce re, prticle morphology nd chemicl composition. According to the literture [1], these properties ffect not only the fire retrdnt performnce ut lso the mechnicl properties of the finl composite. The present work is prt of n investigtion imed t estlishing the mechnism of mgnesi hydrtion nd t evluting the use of mgnesium hydroxide s fire retrdnt for polymers. The utiliztion of mgnesium hydroxide, produced y mgnesi hydrtion, s fire retrdnt for nylon 6-6,6, is evluted. The performnce of the filler otined y MgO hydrtion is compred with tht of commercil product otined y precipittion from rine. Experimentl High-grde mgnesium oxide (97%) supplied y Mgnesit S.A ws hydrted in Prr utoclve ( cm 3 ), t 13 C, during 1 hour. After drying, the solids were milled in jet mill nd were chrcterized with regrd to their chemicl composition (X-ry fluorescence in X-ry Spectrometer Phillips PW 1), prticle size distriution (Sedigrph 5ET), surfce re (BET in Quntchrome Nov 1), density (Quntchrome Stereopicnometer), presence of crystlline phses (Diffrtometer Phillips PW 1) nd morphology (Scnning Electron Microscope Jeol JSM 35C). Thermogrvimetric (TGA) nd thermodifferentil (DTA) nlyses determined the decomposition tempertures nd the dehydrtion het, respectively, in N tmosphere, t heting rte of C/min (Shimdzu 5 Thermoclorimeter). The copolymer of nylon 6-6,6, dditives (luricnt nd pigment) nd the mgnesium hydroxide were mixed t 55 C in Werner & Pfleiderer twin-screw extruder, model ZSK 3 of 3mm dimeter. The mixes were prepred ccording to the formultions shown in Tle 1. The mgnesium hydroxide produced y hydrtion Polímeros: Ciênci e Tecnologi, vol. 11, nº 3, p , 1 Tle 1. Mix formultions using products otined y mgnesi hydrtion (MH-H) nd precipittion (MH-P). Mgnesium hydroxide (g/kg mix) 15 g/kg mix of 5% w/w mixture of cron lck in polymide 6 ws used s pigment. will e further referred to s MH-H nd the product of precipittion will e denominted MH-P. Sheets of.6, 1.8 nd 3. mm thickness were molded t 48 o C nd t n injection pressure of 35 Br, in Bttenfeld Ferte injector. Flming tests were crried out ccording to UL94 specifictions for verticl urning test [11]. Tensile strength, elongtion t rek nd impct strength ccording to ISO/179/1d (Chrpy unnotched smple) nd ISO 18/3A (notched smple- IZOD) were determined. The mechnicl properties of the composites otined with oth mgnesium hydroxides re compred with those of polymide 6,6 filled with 4% tlc. Results nd Discussion Nylon 6-6,6 (g/kg mix) Luricnt 1(MH-P) (MH-P) 3(MH-P) g/kg mix of g/kg mix of 4(MH-H) 5(MH-H) 5 5 6(MH-H) 7(MH-H) 8(MH-H) g/kg mix of 1g/kg mix of 1:1mixture of zinc sterte nd teflon The chemicl nd physicl chrcteristics of mgnesium hydroxide fillers re shown in Tle. The MgO contents in oth smples re very similr. Among the minor constituents, the min differences re shown y iron nd mngnese oxides, with reltively higher content in the mteril produced y hydrtion. This mteril is lso chrcterized y lrger prticle sizes nd smller specific surfce res thn the solids produced y precipittion. According to Levesque [1], surfce res lower thn m /g, low rectivity with groups, high purity nd 1% of the prticle sizes elow 1 µm re the requirements for good performnce in polyolefins. Similr specifictions re required for ppliction 117

3 Tle. Chemicl nd physicl properties of mgnesium hydroxides otined y hydrtion (MH-H) nd precipittion (MH-P) P rmeter Content (%) MH-H MH-P MgO CO SiO.. Fe O Al O 3.. MnO. 1 Loss y ignition (weight %) Specific surfce re, BET, (m / g) Medin prticle size, µm Specific grvity, (g/cm 3 ) () 5% finer s mesured y Sedigrph of mgnesium hydroxide in polymides []. Figure 1 depicts the prticle size distriution curves for oth products. It is oserved tht only 9% nd 88% of MH-P nd MH-H prticles, respectively, re smller thn 1 µm nd thus, oth mterils do not fully comply with the reported specifictions. Exmintion under SEM (Figure ) showed tht the MH-H prticles were constituted y ggregtes of irregulr nd tiny crystls. The predominnt crystlline phse in oth MH-H nd MH-P is Mg(OH) ; smll mounts of MgO were detected in MH-H due to the fct tht hydrtion ws not 1% complete (MH-H loss of ignition=3.%). According to the thermogrvimetric nlysis, MH-H dehydrtion egins t 33 o C while MH-P dehydrtes t 35 o C. Endothermic hets of 1. kj/g for MH-H nd 1.4 kj/g for MH-P were mesured. Figure 1. Prticle size distriution of fillers - mgnesium hydroxide otined y hydrtion (MH-H) nd precipittion (MH-P). () Figure. SEM Microgrphs of fillers - mgnesium hydroxide otined y () hydrtion (MH-H) nd () precipittion (MH-P). Hornsy nd Wng [] studied the ppliction of mgnesium hydroxide of vrious origins s fire retrdnt in polymide 6 nd polymide 6,6. The uthors oserved tht the decomposition tempertures nd lso the mgnitude of the endotherm peks could e mrkedly ffected y the experimentl conditions employed during the nlysis. This fct could explin the low vlue of the het decomposition oserved in the present work when compred to the reported vlue of out 1.4kJ/g. The results of the flmmility tests re shown in Tle 3. A mteril clssed 94V- shll [11] : i) Not hve ny specimens tht urn with flming comustion for more thn 1 seconds fter either ppliction of the test flme; ii) Not hve totl flming comustion time exceeding 5 seconds for the 1 flme ppliction for ech set of five specimens; iii) Not hve ny specimens tht urn with flming 118 Polímeros: Ciênci e Tecnologi, vol. 11, nº 3, p , 1

4 Tle 3. Flmmility rting of nylon 6-6,6 copolymer contining mgnesium hydroxides otined y hydrtion (MH-H) nd precipittion (MH-P) s fillers. 3 Finl composite 4% MH-P 6% MH-P Flmmility - UL94.8mm 1.6mm 3.mm V-/V- V-/V- V-/V- V -/V- 4 4% MH-H V-/V- V -/V % MH-H 4% MH-H 4% MH-H + zinc sterte nd teflon V-/V- V-/V- V-/V- V-/V- V-/V- V -/V- 48 h conditioning t 3± o C nd 5±5% reltive humidity/ fter 168 h t 7±1 o C without conditioning. or glowing comustion up to the holding clmp; iv) Not hve ny specimens tht drip flming prticles tht ignite the dry sorent surgicl cotton locted 35 mm elow the test specimen; v) Not hve specimens with glowing comustion tht persists for more thn 3 seconds fter the second removl of the test flme. The requirements tht must e reched y mteril clssed s 94V-1 nd 94-V- re less restrictive. The results indicte V- flmmility rting t.8 nd 1.6 mm for 4% mgnesium hydroxide (MH-H) filled nylon composite, in the presence nd sence of the dditives. Better flmmility rting (V-) either t 1.6 mm (6% MH-H) nd t 3. mm (4% MH-H) ws chieved. Hornsy et l [13] otined V- flmmility rting t 3. mm for 6% mgnesium hydroxide-filled nylon 6 composite. In the present work, V- flmmility rting t 1.6 mm ws lso reched for 6% mgnesium-hydroxide-filled nylon 6-6,6 composite. Similr results were otined using the product (MH-P) produced from mgnesium hydroxide precipittion from rine. According to Hornsy et lli [13], the origin of the product my strongly influence the flmmility chrcteristics of polymide 6 nd polymide 6,6. Despite the different origins, prticle sizes nd surfce res of the fillers used in the present study, no significnt differences in flmmility rting were oserved. The finl compounds otined with oth fillers (MH-H nd MH-P) presented similr mechnicl properties (Tle 4). The properties of polymide filled with 4% tlc re lso included [14]. The impct strength (unnotched chrpy) ws higher when the oth mgnesium hydroxides (MH-H nd MH-P) ssocited with were used. Despite the fct tht high percentge of filler leds to etter flmmility clss, the mechnicl properties were ffected in deleterious mnner y n increse in the mgnesium hydroxide dosge. The increse in the mgnesium hydroxide Tle 4. Mechnicl properties of nylon 6-6,6 copolymer filled with mgnesium hydroxide otined y hydrtion (MH-H) nd precipittion (MH-P). Composite Tensile strength (MP) Elongtion t rek (%) Impct strength (Chrpy unnotched smple) kj/m Impct strength (Izod notched smple) kj/m Polimide 6,6 ith 4% tlc [ 1] 6 w % MH-P + 68,9,98 43,, 9 4 4% MH-H 78,,8 3, 3, 5 5% MH-H 78, 1,7, 3, 7 4% MH-H + 66,9,84 5, 1, 9 Polímeros: Ciênci e Tecnologi, vol. 11, nº 3, p , 1 119

5 concentrtion from 4% to 5% led to composite with lower impct strength (unnotched Chrpy) nd the elongtion t rek ws reduced in 4%, fr elow the desired vlue of 4%. The utiliztion of s luricnt led to higher elongtion t rek nd higher impct strength. However, mteril with lower tensile strength ws otined. The impct strength (Izod notched smple) ws not ltered y the presence of this dditive. A comprison etween the mechnicl properties of the finl composite nd the vlues which re specified y polymides producers for polymer contining 4% of minerl filler (tlc) [14] indictes tht formultions re still not optimized. It is importnt to mention tht it ws eyond the scope of this study to optimize the formultions, nd lso to evlute other dditives such s silnes, which could improve the flmmility rtings s well s the mechnicl properties of the finl composite. These results demonstrte the potentil ppliction of mgnesium hydroxide otined y mgnesi hydrtion s fire retrdnt for copolymer of nylon 6,6-6. Conclusions The potentil utiliztion of mgnesium hydroxide otined y mgnesi hydrtion s fire retrdnt in copolymer of polymide 6-6,6 ws demonstrted, since the flmmility rtings s well s the mechnicl properties required in mny industril pplictions were chieved. Despite the different origin, the performnce of the mteril produced y hydrtion of MgO ws similr to tht otined y commercil product through precipittion of the hydroxide from rine. Acknowledgements The uthors would like to thnk CAPES, CNPq, Rhodi S.A nd Mgnesit S.A. nd, especilly, Cláudio Brros nd Rento Ciminelli for their importnt contriutions. References 1. Lwson, D.F.- Ruer Chem. Technol., 59, p.455 (1986).. Hornsy, P. R & Wng, J. - Prog. Ruer Plstics nd Technol., 1 (3), p.4 (1994). 3. Rothon, R. N. - Production of Crontes nd Hydrtes nd Their Use s Flme Retrdnt Fillers, in: Proceedings of the EUROFILLERS-95, p.73, Mulhouse -Frnce, (1995). 4. Hollowy, L. R. - Ruer Chem Technol., 61, p.186 (1987). 5. Soolev, I. & Woycheshin, E. A. - Alumin Trihydrte, in: Hndook of Fillers for Plstics, chp.6, Ktz, H.S. & Milewsky, J.(ed), (1987). 6. Lwson, D. F.; Ky, E. L. & Roerts Jr., D.T. - Ruer Chemistry nd Technology, 48, p.14 (1974). 7. Shermn, L. - Plstics Technol., July, 56 (199). 8. Ashley, R. J. & Rothon, R. N. - Use of mgnesium hydroxide s flme retrdnt filler in: Proceedings of the Minerl nd Orgnic Functionl Fillers in Polymers - Interntionl Symposium Moffis, p.87, Le Mns, (1991). 9. Coope, B. M. - Industril Minerls, August, p.57 (1983). 1. Kessler, C. - Outlook for mgnesi products, in: Conference Report of the Industril Minerls 97, Toronto-Cnd, (1997). 11. UNDERWRITERS LABORATORIES INC. Tests for flmmility of plstics mterils - UL94, 3 rd.ed (1989). 1. Levesque, J. - Mgnesium-sed fillers s flme retrdnt / smoke suppressnt. Recent dvnces in flme retrdncy of polymeric mterils. Business Communictions Compny, Stmford, Connecticut, USA, Morton Interntionl Corp., 13 (199). 13. Hornsy,P. R.; Jckson, V. V.; Rothon, R. N, & Wng, J. - Use of mgnesium hydroxide s flme retrdnt in polymides, in: Proceedings of the Minerl nd Orgnic Functionl Fillers in Polymers-Interntionl Symposium Moffis-93; p.161, Nmur-Belgium, (1993). 14. Rhodi - Technyl- proprieddes ds principis formulções- APE/CT, versão, Aril Receido: 8/6/1 Aprovdo: 7/9/1 1 Polímeros: Ciênci e Tecnologi, vol. 11, nº 3, p , 1