HNBR - CHARACTERISTICS & GENERAL COMPOUNDING - AN OVERVIEW - Ramcharan
Volume : 4 Issue No: 3 Month : June 2016 HNBR – CHARACTERISTICS & GENERAL COMPOUNDING – AN OVERVIEW HNBR – HYDROGENATED ACRYLONITRILE BUTADIENE RUBBER Modern automotive engineering demands elastomers that can withstand high temperatures and aggressive substances and can meet the particular requirements of fuel-saving engine and car body designs. The demands in the oil exploration industry are just as stringent. Here, elastomers must weather aggressive environments and high mechanical stresses. Standards were set in these fields over 25 years ago with the invention of HNBR (Hydrogenated Acrylonitrile-Butadiene Rubber). metal catalyst at a designated temperature and pressure, brings about a selective hydrogenation to produce HNBR. The nitrile groups are unaffected during the process, but the carbon-carbon double bonds in nitrile rubber are converted into more stable single bonds. Different grades can be made by precise control of the proportion of unconverted double bonds in the material - 10% is considered to be an upper limit, but grades containing 4-8% (partially hydrogenated) or virtually no double bonds (fully hydrogenated) are used in most cases. HNBR polymers are high temperature and oil The nitrile groups are unaffected during the process, but the carbon- ‐carbon double resistant elastomers. HNBR compounds are Partially bonds in nitrile rubber are converted into more stable single bonds. Different grades hydrogenated materials can be crossHNBR – HYDROGENATED ACRYLONITRILE BUTADIENE RUBBER can be made by precise control of the proportion of unconverted double bonds in the formulated to meet demanding applications linked material - ‐ using 10% is considered e an upper limit, but grades containing 4- ‐8% (partially bothto bsulphur and peroxide cure Modern and automotive engineering demands can withstand high hydrogenated) or virtually no double bonds (fully hydrogenated) are used in most environments with elastomers a widethat operational systems, and the fully hydrogenated grades can temperatures and aggressive substances and can meet the particular requirements of cases. temperature fuel- ‐saving engine and car range. body designs. The demands in the oil exploration industry be cross-linked with peroxides only. This further are just as stringent. Here, elastomers must weather aggressive environments and high Partially hydrogenated materials can be cross- ‐linked using both sulphur and peroxide cure systems, and the fully hydrogenated grades can be cross- ‐linked peroxides expands the range of grades and opens upwith more mechanical stresses. Standards were set in these fields over 25 years ago with the only. This further expands the range of grades and opens up more applications for invention of HNBR (Hydrogenated Acrylonitrile- ‐Butadiene Rubber). applications for these HNBR materials. these HNBR materials. HNBR polymers are high temperature and oil resistant elastomers. HNBR compounds The material itself is a derivative of nitrile rubber, are formulated to meet demanding applications and environments with a wide which is hydrogenated in solution using precious operational temperature range. metal catalysts. The basic structure of an HNBR CHEMISTRY AND MANUFACTURING PROCESS elastomer is provided in Figure 1. As outlined The material itself is a derivative of nitrile rubber, which is hydrogenated in solution below, the process begins with the production of using precious metal catalysts. The basic structure of an HNBR elastomer is provided in an emulsion-polymerized NBR. This polymer is Figure 1. As outlined below, the process begins with the production of an emulsion- ‐ polymerized NBR. This polymer is then dissolved in an appropriate solvent. After the then dissolved in an appropriate solvent. After dissolution process is complete, the addition of hydrogen gas, in conjunction with a precious the metal catalyst at a designated and pressure, brings about a dissolution process temperature is complete, the addition selective hydrogenation to produce HNBR. Properties of HNBR CHEMISTRY AND MANUFACTURING PROCESS of hydrogen gas, in conjunction with a precious Properties HNBR High mechanical sof trength (up to 30 MPa) at RT. Good mechanical properties even at elevated temperature Excellent resistance to lubricants with extremely additives engine High mechanical strength (up toaggressive 30 MPa) at in RT. oils, ATF, power steering fluid and coolants Very gmechanical ood hot air and steam Resistance. Good properties even at elevated Very good low temperature flexibility. Excellent resistance to many modern fuels including biodiesel temperature Low permeability to volatiles and gases Figure 1 Excellent resistance to lubricants with extremely aggressive additives in engine oils, ATF, power steering fluid and coolants
Very good hot air and steam Resistance. b. Effect of RDB Content Very good low temperature flexibility. Excellent resistance to many modern fuels including biodiesel Low permeability to volatiles and gases Good resistance to crude oil even in the presence of hydrogen sulfide, amines, alkaline corrosion inhibitors and Oxidizing media. Good ozone resistance very good abrasion resistance (DIN abrasion: 30 - 50 mm3) 1. By controlled hydrogenation of NBR a HNBR, with different amounts of RDB (residual double bond) contents can be produced. 1. HNBR with high RDB can be cross-linked using sulfur and Peroxide b. Effect of RDB Content 1. By controlled hydrogenation of NBR a HNBR with different amounts of RDB 1.(residual Highdouble RDBbond) increases crosslinking density contents can be produced. 2. HNBR with high RDB can be cross- ‐linked using sulfur and Peroxide 3. RDB increases rosslinking density 1.High High RDB cincreases the compression set and 4. High RDB increases the compression set and reduces the ageing stability of the reduces the ageing stability of the material material Excellent Chemical Resistance Low compression set even at high temperature Good resistance to high energy radiation Low noise/vibration transmission Selection Criteria for HNBR Comparison of HNBR with other Polymers in term of Heat and Oil resistance When selecting a HNBR polymer for a specific application, three criteria to consider Comparison of HNBR with other Polymers in term of Heat and Oil resistance 1. Acrylonitrile content: fluid resistance as well as low temperature properties 2. Hydrogenation level: influences heat, chemical and ozone resistance 3. Polymer Mooney Viscosity: influences the processing of the compound and also the physical properties of the final article. a. Effect of Acrylonitrile Content 1. The nitrile group, coming from incorporated BASIC Compounding and Processing acrylonitrile monomers (ACN) strongly BASIC Compounding and Processing a. Selection of Grade: There are a wide variety influences the oil resistance and low a. Selection Grade: There are (ACN) a wide variety of acrylonitrile (ACN) content of of acrylonitrile content polymers temperature flexibility. polymers available in the HNBR today. They range from approximately 17 to 50% available in the HNBR today. They range from 2. Higher ACN content means better oil resistance, ACN. The ACN content not only controls fluid resistance but also impacts the approximately 17 to 50% ACN. The ACN content low- ‐temperature performance. If the ACN content of the polymer is increased, fuel resistance and gas permeability. the volume swell of the associated compound will decrease the low- ‐ not only controls fluid resistance butwhile also temperature flexibility will become poorer. Alternatively, if one decreases the 3. Higher ACN content means poorer low impacts the low-temperature performance. If ACN level of the polymer, the associated compound will have higher volume temperature flexibility ACN content of the polymer is increased, swell the and improved low- ‐temperature flexibility. the as volume swell better of theis associated compound Likewise, RDB% lower, Heat resistance, Ozone resistance, Compression set and Chemical resistance where as higher RDB % will improve will decrease while the low-temperature Dynamic properties, Hardness, Modulus and Crosslinking density. flexibility will become poorer. Alternatively, if Lastly, the wide range of Mooney viscosities grades available permits the one decreases the ACN level of the polymer, compounder to choose a product which best suits their specific method of manufacturing (e.g., compression, transfer, or will injection molding vs. extrusion). the associated compound have higher Today, HNBRs range in Mooney viscosity from 50 to approximately 100 when volume swell andwith improved low-temperature measured at ML(1 4)@100 C., special grades having Mooney 40. flexibility.
Likewise, as RDB% lower, better is Heat resistance, Ozone resistance, Compression set and Chemical resistance where as higher RDB % will improve Dynamic properties, Hardness, Modulus and Crosslinking density. Lastly, the wide range of Mooney viscosities grades available permits the compounder to choose a product which best suits their specific method of manufacturing (e.g., compression, transfer, or injection molding vs. extrusion). Today, HNBRs range in Mooney viscosity from 50 to approximately 100 when measured at ML(1 4)@100 C., with special grades having Mooney around 40. A typical recipe of HNBR is listed in Table below Ingredients HNBR Metal oxides Antidegradents Process Aid Phr 100 0–5 1.5 – 3 0–3 Filler 40 – 100 Co-agents 0-5 Plasticizer Curatives 0 – 20 3 – 10 b. Metal Oxides: 2 – 10 Phr of ZnO/MgO recommended for Sulphur cure whereas 2 Phr of ZnO/MgO is recommended for Peroxide cure compounds, in combination with stearic acid. c. Antidegradents: Many antioxidants like Phenolic type interfere with peroxide crosslinking, affecting properties such as modulus and compression set resistance. A combination of 0.4 phr of zinc methylmercaptobenzimidazole and 1.1 phr substituted or styrenated diphenyl amine (SDPA) provides the best balance of protection together with minimum effect on vulcanizate properties, in the case of peroxide cure. For sulfur cure systems, levels of 1 phr zinc methylmercaptobenzimidazole and 2 phr SDPA are best. Antiozonants are not needed. d. Process Aids: Process improvement additives can be incorporated in high-viscosity formulations at nominal 2.0 phr levels, to facilitate mold flow and reduce cycle times. Generally Zinc salts of high molecular weight fatty acids are effective process aids, M C Wax like R A Wax 1080 also improves processing. e. Fillers – Carbon Black: The physical properties of HNBR compounds reinforced with carbon black depend on the particle size and structure of the black. Mostly FEF black is generally recommended to get optimum properties. Highly reinforcing black increases stiffness of compound permitting low doses. By increasing particle size of carbon black (FEF, GPF and MT) Resistance to compression set and heat resistance improve whereas tensile strength, tear resistance, and abrasion resistance are reduced. f. Mineral fillers: Precipitated silica provides the highest level of reinforcement; however, it yields very stiff, high viscosity compounds. Precipitated silicas generally improve the heat resistance of HNBR vulcanizates. Silane coupling agent improves rubber filler interaction. French powder (talc) is much easier to incorporate and yields comparatively similar modulus and hardness values as with silica. Blends of silica and talc are often utilized for balancing vulcanizate properties with processing characteristics. g. Plasticizer: Selection of Plasticizer is most important criteria of HNBR compounds. Plasticizers used to improve low temperature flexibility, to optimize physical properties and processing characteristics with low volatility at approx. temperature 150 C (302 F) and also resistance to extraction in oils and fuels. Generally Trimellitate plasticizers Like TOTM, TIOTM is being used. Sebacates, adipates can also be utilized but affects slightly high temperature ageing. h. Vulcanization: HNBR with less than 1% residual double bonds must be vulcanized with peroxide or high-energy radiation, as there is insufficient unsaturation to obtain a practical state of cure with sulfur systems. EV (efficient vulcanization) and semi-EV
sulfur cure systems can be used effectively with partially saturated grades to achieve improved adhesion to reinforcing substrates and to obtain favorable properties in dynamic applications. HNBR elastomers are typically cured with either peroxide or sulfur/sulfur-donor cure systems. Comparisons of sulfur/sulfurdonor and peroxide cured HNBR compounds indicate that peroxide curing provides better compression set and heat resistance. Because HNBR has fewer highly reactive allyl position hydrogens versus other diene-based elastomers, it is necessary to add 50-100% more peroxide in order to produce excellent curing characteristics. Many kinds of peroxides are available for curing HNBR. However, it is important to select one that is the most suitable based on the process and cure temperature that will be utilized to produce the finished parts. i. j. approximately 140 C. This master batch is then run through the mixer a second time adding the cure chemicals and again dropped from the mixer at approximately 100-110 C. HNBR polymers generate more heat during compounding in internal mixers or on open mills than NBR polymers; however, this can improve processing due to the thermoplastic nature of the polymers. Subsequent processing steps (extrusion, preform, moulding) should be carried out at the highest practical temperature to take advantage of the thermoplastic characteristics of the compound. This aspect of HNBR polymers is of particular importance for high-hardness formulations. Extrusion and Calendaring requires higher temperature as compare to NBR. Application of HNBR 1 Automotive: Gaskets, Seals, Diaphragms, Since peroxides have different molecular Boots, Timing Belts, Shaft Seals. weights and decomposition temperatures, it With the continued trend to ever decreasing is imperative to select the correct one based characteristics compound. This aspect of HNBR polymers is of particular space of inthe the engine bay, temperatures on the criteria noted above or one can greatly importance for high- ‐hardness formulations. Extrusion and Calendaring requires continue to rise, placing ever more demanding affect the processability and cost-effectiveness higher temperature as compare to NBR. requirements on the components operating in of producing the finished goods in question. Application of HNBR this environment. One consequence of this is Coagents: Resistance to heat and compression 1. Automotive: Gaskets, Seals, Diaphragms, Boots, Timing Belts, Shaft Seals. the need for Elastomers capable of ever-greater set can be maximized by incorporating long-term high-temperature resistance. With the continued trend to ever decreasing space in the engine bay, selected coagents with peroxides to increase temperatures continue to rise, placing ever more demanding requirements on Today’s elastomer must withstand harsh the components operating in this environment. One consequence of this is the the state of cure. Triallyl isocyanurate environments in the engine compartment. need for Elastomers capable of ever- ‐greater long- ‐term high- ‐temperature improves compression set properties, resistance. Today’s elastomer must withstand harsh environments in the engine Higher operating temperatures have resulted compartment. Higher operating temperatures have resulted in the development liquid 1,2-polybutadiene, N,N’-m-phenylene in aggressive the development of lubricants, more further aggressive of more automotive fluids and necessitating the dimaleimide effective at low temperature, use automotive of specialty elastomers combining greater heat and fluid resistance. fluids and both lubricants, further The automotive industry seeks a tough elastomer with improved resistance to and trimethylolpropane trimethacrylate necessitating theHNBR use polymers of specialty chemical, fuel and heat. offer a elastomers unique combination of (TMPTMA) can be used as effective Coagents. resistance to coolants, both fuels and greater oils used in today’s while providing combining heatautomobiles and fluid excellent compression set resistance. Processing of HNBR resistance. The automotive industry seeks a All of the commercially available HNBRs can be mixed either on a two-roll mill or with an internal mixer. Most HNBRs are mixed by the use of internal mixing equipment. This is done to improve the quality of the finished compound while also significantly reducing the typical mix times. Typically, HNBRs are two-pass mixed in an internal mixer where the first pass through the mixer without the cure chemicals and is typically dropped out of the mixer at
tough elastomer with improved resistance to chemical, fuel and heat. HNBR polymers offer a unique combination of resistance to coolants, fuels and oils used in today’s automobiles while providing excellent compression set resistance. 3 Industrial and other Application: Rollers for Printing, Textile, Heat Exchanger Gaskets, Expansion jointing’s, Pumps and Couplings, Textile applications like Spinning cots and Aprons etc. Due to the ethylene content of HNBR polymers, 2. Oil Industry: Stators, Packers, Drill Bit seals, they are resistant to many chemicals used in Blow out preventors the roll industry offering excellent heat and steam resistance, for plate heat exchanger HNBR compounds meet the extreme demands for Fat/Oil application, it provides high in oilfield applications which require excellent temperature resistance and low compression properties in the harsh conditions like set at high temperature including FDA. It is resistance to corrosion inhibitor, Hydrogen also used as sexpansion joint, Industrial and being low compression et at high temperature including FDA. It is a sulfide / Sour gas, Resistance to crude and resistance being used as expansion joint, Industrial pumps, Couplings etc for very go Couplings etc for very good dynamic drilling fluids, High Tear and Abrasion dynamic pumps, properties and heat resistance. properties and heat resistance. resistance, Low water swell. Low compression set and most importantly very good resistance to Extrusions and Explosive Decompression (Rapid Gas Decompression) seen with today’s oilfield industry. While HNBR polymer can withstand the harsh abuse encountered in 2. Oil Industry: Stators, Packers, Drill Bit seals, Blow out preventors drilling operations, these compounds are also HNBR compounds meet the extreme demands in oilfield applications which able to stand up to the high temperatures and require excellent properties in the harsh conditions like resistance to corrosion encountered in the well.and Coupled inhibitor, pressures Hydrogen sulfide / Sour gas, Resistance to crude drilling fluids, High Tear and Abrasion resistance, Low water swell. Low compression set and with the excellent resistance to the various most importantly very good resistance to Extrusions and Explosive fluids such as crude oil, gases, acids and alkalis Decompression (Rapid Gas Decompression) seen with today's oilfield industry. While HNBR polymer can withstand the harsh abuse encountered in drilling HNBR compounds can meet the demands operations, these compounds are also able to stand up to the high temperatures required for application in these harsh and pressures encountered in the well. Coupled with the excellent resistance to the various fluids such as crude oil, gases, acids and alkalis HNBR compounds can environments. meet the demands required for application in these harsh environments. Note: For the requirement of HNBR, kindly contact us. 3. Industrial and other Application: Rollers for Printing, Textile, Heat Exchanger Gaskets, Expansion jointing’s, Pumps and Couplings, Textile applications like Spinning cots and Aprons etc. Email : contact@ramcharan.org Due to the ethylene content of HNBR polymers, they are resistant to many B chemicals used in the roll industry offering excellent heat and steam resistance, for plate heat exchanger for Fat/Oil application, it provides high temperature Tamil Nadu Andhra Pradesh West Bengal Maharashtra : : : : Chennai, Hosur, Madurai, Coimbatore Hyderabad Kolkata Mumbai Contact : 044-43541200 022-40154487 s Kerala Karnataka NCR : : : Trissur, Ernakulam Bangalore, Belgaum Faridabad, Ghaziabad
acrylonitrile monomers (ACN) strongly influences the oil resistance and low temperature flexibility. 2. Higher ACN content means better oil resistance, fuel resistance and gas permeability. 3. Higher ACN content means poorer low temperature flexibility with different amounts of RDB (residual double bond) contents can be produced. 1.
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(ASTM 1418) ISO/DIN 1629 Other Trade names & Abbreviations ASTM D2000 Designations Nitrile Acrylonitrile-butadiene rubber NBR NBR Buna-N BF, BG, BK, CH Hydrogenated Nitrile Hydrogenated Acrylonitrile-butadiene rubber HNBR (HNBR) HNBR DH Ethylene-Propylene Ethylene propylene diene
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