Al-Qadisiya Journal For Engineering Sciences Vol. 1 No. 1 Year 2008 126 Experimental Study of the Effect of Zinc Borate on Flame Retardancy of Carbon- Kevlar Hybrid Fibers Reinforced Composite Materials Mushtaq T.Ali. AlBdiry Al-Qadisiya University College of Engineering Ali I. Al-Mosawi Technical Institute-Babylon Mechanical Department Dr. Abbas A. Al-Jeebory Al-Qadisiya University College of Engineering Abstract This study aims to investigate possibility to increase the flame retardancy for composite materials by addition of a flame retardant material which represent the zinc borate as a coating layer of (4mm) thickness on the surface of composite material consist of araldite resin reinforced by hybrid fibers from carbon and kevlar fibers as a consecutive layers which be as a woven roving )º 90 - º 0( . Then, this system (flame retardant material and composite material) was exposed to a direct flame which generated from oxyacetylene flame (up to 3000ºC) and gas flame (2000ºC) under different exposure distances (10,15, and 20mm), and study the range of resistance of flame retardant material layer to the flames and protected the substrate where we used the method of measuring the surface temperature opposite to the flame where we obtained the better results with large exposed distance and large percentage from protective layer which is zinc borate (30%) for both types of flames , as well as the flame resistance will be increased with decrease the flame temperature . Keywords: Hybrid Composite Material,, Flame Retardant Material, Zinc Borate. اد مرآبة مقواة بأليافوعلى إعاقة الّلهب لم خارصينتأثير بورات ال عملية لدراسة هجينةفالر الي آ-آاربون الخالصة بورات مثل توالتي مادة معيقة لّلهب مكانية زيادة إعاقة الّلهب للمواد المرآبة عن طريق إضافة ه الدراسة لبحث ا هذ تهدف من المكونة من راتنج اإلرلدايت المقوى بألياف هجينة على سطح المادة المرآبة (4mm) بسمك بشكل طبقة طالء الخارصين ض ربعدها ع . ) º 90 - º 0( ظفائر محاآة ثنائية اإلتجاه طبقات متتابعة والتي تكون بشكل ألياف الكاربون وألياف آيفالر بشكل ة لّلهب المادة ا(هذا النظام ةولمعيق ر ) المادة المرآب علة ُأوآسي أستيلينية إلى ّلهب مباش د من ُش ن بدرجة حرارة متول أآثر م (3000ºC) رارة ة ح ة بدرج علة غازي ن ُش د م ب متول ة (2000ºC) وله رض مختلف سافات تع (20mm,15mm,10mm) وبم طريقة حيث تم إعتماد ى حمايتها للمادة المرآبة الواقعة تحتها ومدتين ودراسة مدى مقاومة طبقة المادة المعيقة لّلهب لحرارة الُشعل حيث تم الحصول على أفضل النتائج درجة حرارة السطح المقابل للشعلة في قياس درجة الحرارة المنتقلة خالل هذا النظام قياس الشعلتين إضافة ولكال ) 30%سبة ن (خارصين والتي هي بورات ال لطبقة الحامية لنسبة أآبر مسافة التعرض آبيرة و عندما تكون إلى ذلك تزداد المقاومة لّلهب آلما قلت حرارة الُشعلة علي إبراهيم الموسوي بابل-المعهد التقني مشتاق طالب البديري جامعة القادسية عباس عليوي الجبوري.د جامعة القادسية Al-Qadisiya Journal For Engineering Sciences Vol. 1 No. 1 Year 2008 127 Introduction Fire safety is an integral part of precautions. Fire precautions have the objective to minimize the number of and damage from measuring hindering their initiation, limiting their propagation and if possible excluding flash-over. Preventing fires or delaying them makes escape possible over a longer period of time. As a result, life, health, and property are efficiently protected [1]. Since plastics are synthetic organic materials with carbon and often high hydrogen contents, they are combustible. For various applications in the building, electrical, transportation, mining, and other industries, plastics have to fulfill flame retardancy requirements laid down in mandatory regulation and voluntary specification. The objective in flame retarding polymers is to increase ignition resistance and reduce rate of flame spread [2]. One way to better protect combustible materials against initiating fires is the use of flame retardants , which are substances that can be chemically inserted into the polymer molecule or be physically blended in polymers after polymerization to suppress , reduce , delay or modify the propagation of a flame through a plastic materials. There are several classes of flame retardants; halogenated hydrocarbons (chlorine and bromine containing compounds and reactive flame retardants): inorganic flame retardants (boron compounds, antimony oxides, aluminum hydroxide, etc); phosphorus containing compounds; nitrogen containing flame retardants. Depending on their nature, flame retardants can act physically or chemically [3]. 1- The physical action occurs by: a. Cooling: the additives cool the substrate to a temperature below the combustion temperature. b. Formation of protective layer: a solid or gaseous protective layer, which excludes the oxygen necessary for the combustion process (e.g. phosphorus compounds). c. Dilution: the inert gases from the additive dilute the fuel in the solid and gaseous phase (e.g. aluminum hydroxide). 2- The chemical action occurs by: a. Reaction in gas phase : the radical mechanism of combustion is interrupted and exothermic reaction are stopped . System cools down (e.g. halogenated flame retardants). b. Reaction in solid phase: by forming carbonaceous layer on the polymer surface (e.g. phosphorus compounds). Flame Retardant Materials Flame retardants are substances used in plastics, textiles, electronic circuitry and other materials to prevent fires. There are several types of flame retardants as mentioned above, one of these types is inorganic flame retardants. Few inorganic compounds are suitable for use as flame retardants in plastics, since such compounds must be effective in the range of decomposition temperature of the plastic, mainly (150ºC - 400ºC). Inorganic flame retardants don't evaporate under the influence of heat ; rather they decompose ; giving off non-flammable gases like water , carbon dioxide , sulphur dioxide , hydrogen chloride , etc. mostly endothermic reaction . in the gas phase , these act by diluting the mixture of flammable gases and by shielding the surface of the polymer against oxygen attack [4] . The inorganic flame retardants act simultaneously on the surface of the solid phase by cooling the polymer via endothermic breakdown process and reducing the formation of pyrolysis products. In addition , as in the case of inorganic boron compounds , a glassy protective layer can form on the substrate , fending off the effect of oxygen and heat[5] .As example to inorganic flame retardants is zinc borate , aluminum hydroxide , magnesium hydroxide , and antimony oxides . Zinc borate is used as a flame retardant and smoke suppressant for wide range of plastics, rubber, paper, and textiles. It can replace antimony oxide as synergist in plastics and rubber to enhance the activity of primary flame retardants by stepwise releasing the radicals in a wide variety of end – use products . It is also used in paints, adhesives, pigments and ceramic industries. Table 1 shows the characterizations and properties of zinc borate. Al-Qadisiya Journal For Engineering Sciences Vol. 1 No. 1 Year 2008 128 Table (1): Characterizations and properties of zinc borate [3] Mol WtPH Density g/cm3 Melting Point °C Appearance Property 434.62 7.6 3.64 980 White Crystalline Value Composite Materials Composite material is a material consisting of two or more physically and (or) chemically distinct phase, suitably arranged or distributed. A composite material usually has characteristics that are not depicted by any of its components in isolation [6]. Generally, the composite material contains two elements: 1- Matrix material: it is the continuous phase; it may be metal, ceramic or polymer matrix. The polymer matrix is considered the best because of its mechanical and thermal properties, and also it can reinforced by a large fiber volume fraction compared with metal and ceramic matrix. In addition to the low cost and easy fabrication, as example for this materials araldite resin, polyester, and epoxy resin. Araldite resin belong to epoxy group which has excellent thermal and physical properties, and usually used in composite materials for different applications, where it distinct by excellent adhesive capability especially to fibers, also it retain constant dimensions after dryness [7]. 2- Reinforcing material: The distributed phase is called reinforcement, many reinforcement materials are available in a variety of forms; continuous fibers; short fibers; whiskers, particles...etc. Reinforcements include organic fibers such as carbon and kevlar fibers, metallic fibers, ceramic fibers, and particles [8]. High strength, and high modulus carbon fibers are of about (7-8µm) in diameter and consist of small crystallites of turbostratic graphite, one of the allotropic forms of carbon[9]. Kevlar is an organic aramid fiber with (3100 MPa) tensile strength, and (131,000 MPa) elastic modulus. A density approximately one-half of aluminum, good toughness, in addition it is flame retardant [10]. Flame Retardancy Test This test is used for thermal isolators which exposed to elevated temperatures exceed (3000ºC) as in the fires case. The heat of this test generated from thermal torch (oxyacetylene and gas). There are two methods to measure the temperature of material in this test [10]: 1- Surface temperature; in this method, a thermocouple puts on the opposite surface to the torch for calculate the amount of heat transmitted through flame retardant material and composite material. This method used in this study . 2- Depth of damage; after exposition, the material to the flame at specific time, we will measure the depth of penetration leaves on material surface. Experimental Work 1- Materials: There are three types of materials employed in this study: a. Flame retardant material, Zinc Borate 2335 (2ZnO.3B2O3.5H2O) was used as a flame retardant, which supply from C-Tech corporation. Table 2 shows the chemical composition of zinc borate. Table (2): Chemical composition of zinc borate Compound Zinc Oxide Boric Anhydride Water of Hydration Impurities Symbol ZnO B2O3 H2O - Content(%) 37 47 14 2 Al-Qadisiya Journal For Engineering Sciences Vol. 1 No. 1 Year 2008 129 b. Matrix material, Araldite resin (CY223) with density of (1.15-1.2 g/cm3) which belong to epoxies group was used in this study. Figure (1) shows the chemical structure of Araldite resin. c. Reinforcing fibers: Two types of fibers were used : c.1- Carbon fibers, A woven roving fibers )º 90 - º 0( with density of (225 g/m3). c.2- Kevlar fibers, A woven roving fibers )º 90 - º 0( with density of (285 g/m3). These types of fibers used as consecutive layers in same matrix . Figure (2) shows the chemical structure of kevlar fibers. 2- Preparation Test Specimens: Specimens of flame retardancy test are a square shape, as shown in figure (3) with dimensions (100 ×100mm), and (10mm) thickness, which it consist of two layers: a- Flame retardant material layer with (4mm) thickness represented by zinc borate. b- Composite material layer with (6mm) thickness, it contains carbon and kevlar fibers which used as consecutive layers in araldite resin . 3- Flame Retardancy Test . Two types of torch flame were used, oxy-acetylene and butane-propane flame. The system (contains flame retardant material and composite material) was exposed to these flames under different exposure distances (10, 15, and 20mm). Figure (4) shows the mechanism of flame retardancy test, surface temperature method used here to calculate the amount of heat transmitted through flame retardant material and composite material. Table (3) shows the temperatures of flames used in this study . Table (3): Temperatures of flames Gas Symbol Temperature,ºC Oxyacetylene C2H2 3000-3300 Butane-Propane C3H8-C4H10 2000 Results and Discussion From the results obtained by flame retardancy test, we can see : Figure(5) represents the flame retardancy test for composite material with zinc borate as a surface layer at exposed distance (10mm) , the temperature of the opposite surface to the torch begins to increase with increasing the time of exposition to the flame . During this stage , zinc borate (10 %) has a water of hydration in its chemical structure , therefore , it released this water to extinguish the fire through cooling , in addition , zinc borate will formed glassy coating layer which protecting the substrate (composite material) and the fire spread will decrease[5] . This process of released water and formation of glassy coating layer will be increased as the zinc borate increased to (20 %, and 30 %). Figure (6) shows the behavior of zinc borate with exposed distance (15mm). When the amount of flame retardant layer is (10 %), and with this exposed distance the time of break down of the retardant layer will be increased, because of decomposition of zinc borate and release the water, which dilute the ignition zone and the formation of protected layer will stay to longer time[4]. This state will be increased with increasing zinc borate content to (20 %, and 30 %). As a result, when the exposed distance to flame increased to (20mm), the time necessary to break down of flame retardant layer will increase and the combustion gaseous will reduced and there will be a less plastic to burn due to water of hydration and protected glassy coating layer[5], and this protection will improves with increasing flame retardant percentage to (20 %, and 30 %). All that will rise the time of break down for zinc borate layer and substrate composite material as shown in Figure(7) which represents flame retardancy test for zinc borate layer with exposed distance(20mm) . From all figure we obtained the better results with large exposed distance and large percentage from protective layer which is zinc borate (30%) for both types of flames , as well Al-Qadisiya Journal For Engineering Sciences Vol. 1 No. 1 Year 2008 130 as the flame resistance will increase with decrease the flame temperature as illustrated in the diagrams between surface temperature and time of flame exposition . Conclusions From this study, we concluded that: 1- Increasing the flame retardancy as the zinc borate content increased . 2- The resistance to flame spread will increased with increasing of exposed distance , due to decreased of the heat transmitted to flame retardant material which will rise the stand of glassy coating layer against flame . 3- The flame retardancy is increased as the flame temperature is decreased. References 1- Jürgen H.Troitzsch “ Overview of Flame Retardants ” , Chimica Oggi/chemistry Today , Volume 16, January/February 1998 . 2- Huy K. Tran , Christine E. Johnson , Daniel J. Rasky , and Frank C.L Hui “ phenolic Impregnated Carbon Ablators (PICA) as Thermal protection Systems for Discovery Missions ”, NASA Technical Memorandum 110440 , April 1997. 3- Edward A.Myszak “ Use of Submicro Inorganic Flame Retardants in Polymeric Systemic ”, Nyacol Nano Technologies, Inc. 2000. 4- Ali Ibrahim Moslem “ Study Using of Antimony Trioxide Material as a Flame Retardant Material ” , M.Sc. Thesis , Engineering College , Babylon University , 2003 . 5- Heinrich Horacek and Stefan pieh “ The Importance of Intumescent Systems for Fire Protection of Plastic Materials ”, polymer International ,49,2000. 6- George Lubin “ Handbook of Fiberglass and Advanced Plastics Composite ”, First Edition , 1975. 7- D.Hull “ An Introduction to Composite Materials” , Cambridge university press, 1981 . 8- Phillip S.Waldrop “ Plastic Composite in the 21st Century”, NAIT Conference , 2000 , 1-8pp . 9- Marcus Langley “ Carbon Fibers in Engineering ”, McGraw-Hill Book Company Ltd,1973. 10- E.P.DeGarmo, J.T. Black, and R.A. kohser “ Materials and Processes in Manufacturing ” , Eighth Edition , john Wiley & Sons , 1999 . Al-Qadisiya Journal For Engineering Sciences Vol. 1 No. 1 Year 2008 131 CH3 CH3 CH3 CH3OH O O n Figure (1): Chemical structure of Araldite resin[10]. CH2-CH- CH2-O- -C- -O-CH2-CH-CH2-O- -C- -O-CH2-CH-CH2 CO - - CO – NH - - NH Figure (2): Chemical structure of kevlar fibers[10]. Figure (3): Specimen of thermal erosion test Composite material layer flame retardant material layer 4mm 6mm 00.0000 Specimen Holder Sliding Slotter Measuring temperature unit Flame Thermocouple Figure (4): Mechanism of Flame Retardancy Test Al-Qadisiya Journal For Engineering Sciences Vol. 1 No. 1 Year 2008 132 0 5 10 15 20 25 30 35 40 45 50 0 20 40 60 80 100 120 140 160 180 200 Butane - Propane Torch %10 Zinc Borate %20 Zinc Borate %30 Zinc Borate 0 1 2 3 4 5 6 7 8 9 10 0 20 40 60 80 100 120 140 160 180 200 Oxy-acetylene Torch %10 Zinc Borate %20 Zinc Borate %30 Zinc Borate Figure (5): Flame Retardancy Results for Zinc Borate Layer with Exposed Distance (10mm) Time, sec Su rf ac e T em pe ra tu re , º C Time, sec Su rf ac e T em pe ra tu re , º C 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 20 40 60 80 100 120 140 160 180 200 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 0 20 40 60 80 100 120 140 160 180 200 Figure (6): Flame Retardancy Results for Zinc Borate Layer with Exposed Distance (15mm) Su rf ac e T em pe ra tu re , º C Time, sec Time, sec Su rf ac e T em pe ra tu re , º C 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 0 20 40 60 80 100 120 140 160 180 200 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 0 20 40 60 80 100 120 140 160 180 200 Figure (7): Flame Retardancy Results for Zinc Borate Layer with Exposed Distance (20mm) Time, sec Su rf ac e T em pe ra tu re , º C Time, sec Su rf ac e T em pe ra tu re , º C