Speciality Elastomers forIndustrial Applications presentation byD. J. BharuchaBhimrajka Exim LLP, MumbaiatETDS seminar, New Delhi on 5th March, 2014
Introduction Rubber is a common material which is used in almost every industrial application. The requirement of rubber products is constantly towards better quality standards and higher performance limits, and this is only possible by continuous improvement in materials, manufacturing process and management attitude. Automation and computerization play a great role in product improvement, so also developments in newer monomers, molecular architecture of polymers, and more efficient compounding ingredients. General purpose rubbers like NR and SBR have limited resistance to heat and environment, special rubbers have been developed where the thermal performance has been stretched from minus 100 C to over 300 C, and are serviceable in difficult environments like ozone, chemicals, oils and fuels.
Definitions Specialityelastomers: Can be defined as rubbers having higher performance limits in terms of thermal properties, or chemical resistance or environmental adaptibility or even in strength properties, when compared with general purpose rubbers like NR and SBRs. It is expected that the products made from these rubbers will perform better, last longer, and tolerate more difficult environments, save machine downtime and improve productivity, at the same time contributing to a safer, cleaner and healthier working conditions.
Types of rubbers General purpose; NR, BR, SBR, IR, Special rubbers: (mid performance) IIR, EPM/EPDM, CR, NBR, OT Specialityelastomers: CSM, CM, ECO, ACM, AEM, VMQ, (high performance) HNBR, FKM, FFKM, FVMQ Most of these rubbers have been developed and introduced in the middle of the last century (1930’s to 1980’s), and to the best of our knowledge, no new rubbers have been introduced, except for modifications of existing rubbers.
Performance properties RubberServiceTg,C Resistance Ozone Tensile temp. C to OIl #3 resistancestrength NR/IR 70 - 75poor poor v.high BR 70 - 85 poor poor med SBR 80 - 55 poor poor high IIR 100 - 65 poor med med EPDM 125 - 55 poor high med CR 100 - 50 med med high NBR 100 - 40 good poor med - high OT 70 -10 good high low HNBR 150 - 40 good high med - high
Performance properties RubberServiceTg,C resistance Ozone Tensile temp. C to Oil #3 resistancestrength CSM 140 - 40 med high med-high CM 150 - 30 med high med-high ECO 130 - 45 good high med ACM 160 - 30 good high med AEM 170 - 40 med high med VMQ 225 - 110 med high low FVMQ 200 - 65 good high low FKM 250 - 30 good high med FFKM 300 - 10 v.good high med HNBR 150 - 40 good high med - high
Application in fluids and chemicals Hydrocarbon rubbers, e.g. NR, BR, SBR, IIR, EPDM, have little or no resistance to petroleum based oils and fuels (very high swell in IRM903 oil). The introduction of polar groups (containing atoms like Cl, N, O, S, F ) imparts good to very good resistance to oils and fuels, depending on their polarity. FKM, FVMQ, HNBR/NBR, ECO, ACM have particularly good resistance to hydrocarbon oils and fuels. EPDM rubbers, Butyls, CSM and FKM (certain grades) have very good resistance to acids and aqueous chemicals. EPDM is particularly preferred for high temperature steam application. FKM on the other hand are not serviceable in strong bases and amines, for which special grades like TFE/P are required.
Special rubbers Apart from good thermal properties and fluid resistance, polar rubbers have other attributes as well. • They can conduct electrical charges, and therefore suitable for anti-static applications. (e.g. NBR types) • The polar molecules are excited by high frequency microwave energy, with the result that the compound gets uniformly heated and cured throughout its mass even in thick cross-sections. • Rubbers with halogenated molecules are inherently fire retardant or self-extinguishing.(e.g. CR, CM,CSM, FKM,)
Processing of special rubbers Processing involves various steps to convert raw rubber into the final product. These include compounding, mixing, shaping operations (e.g. extruding, calendering etc.), curing and finishing. Most important point in processing is to ensure proper dispersion of the fillers and compounding ingredients. All these operations are similar to that of general purpose rubbers, except that extra care has to be taken to control heat history. Temperature at each step has to carefully maintained to get maximum output with minimum input of heat energy. As speciality rubbers are relatively expensive, it makes good sense to aim for a zero defect production by following good manufacturing practices.
Polychloroprene (CR) DuPont’s Neoprene, the world’s first commercial synthetic elastomer, was introduced in 1931. It is truly the first multipurpose elastomer, thanks to its combination of useful properties. > Outstanding physical toughness > Good resistance to heat, oxidation, ozone and weathering > Good resistance to hydrocarbon oils and greases > Good flame resistance and self-extinguishing characteristics.
CR GRADES Gradation of Neoprene is based on: • Crystallization rate – slow , medium , fast. Slow - for items requiring long term stability, like bridge bearing pads, etc. Medium - for general goods, like hoses, molded items etc. Fast – specially for contact adhesives. 2. Viscosity – low to high, e.g. 20 to 140 ML4/100C. Low viscosity for ease of processing, good flow properties High viscosity for improved strength, high loading capability 3. Type of modifier – normal nercaptan grades, or sulfur modified grades (next slide) 4.Gel content (pre-crosslinked) – reduced ‘nerve’, smoother and faster extrusion and calendering.
CR grades Comparison of sulfur- and mercaptan modified grades sulfur- mercaptan- mixed (GW type) (Neoprene type ) ( G types) (W ) (GW ) Storage stability limited better good Mixing peptizable not peptizablepeptizable Tack very good goodmedium Cure rate fast medium fast to medium Accelerator not required requiredslight Tensile, tear properties very good goodgood Ageing, heat resistance good better better Compression set not so good goodmedium Dynamic flex very good acceptable good ( Neoprene GW combines the best of both)
Processing of Neoprene Neoprene or polychloroprene has been around for over 70 years, and compounders are well versed in handling the same. Nevertheless, a few points are worth mentioning again. 1. Check the shelf life, as it is limited, and control the heat history to a minimum. 3. Add high active MgO at the start of mixing, and ZnO at the end only. 4. Sulfur-modified grades are peptizable, and more prone to sticking. Vanax® 552 of R.T. Vanderbilt is an effective chemical peptizer for the sulfur modified types. 5. Polybutadiene rubber at 5 phr and stearic acid helps prevent mill sticking. 6. Other processing aids include zinc-free lubricants like Struktol® HT204 or WB 16 microbeads for superior dispersion, and improved flow and surface finish.
CR applications Adhesives: Highly crystalline grades, solid and latex. Wire and Cable: normal grades, low viscosity for smooth extrusion. Power transmission belts:S-modified grades, low to medium viscosity. Hose covers: normal grades, med. to high viscosity, for oil and hydraulic hose, LPG hoses, etc. Rollers : for printing machines, paper, textile, steel mills, etc. Sulfur grades, medium to high viscosity. Molded goods: bridge bearing pads, expansion joints, etc. (low crystallizing grades) Coated fabrics: S-modified grades for frictioning and calandering. Dipped goods, foams, etc: CR latex Automobile items: mainly normal grades and many more
CR rollers Printing machine roll ( Sh. A 25) High hardness, abrasion resistant (Sh A 85) Neoprene GRT 60 phr Neoprene GRT 100 phr Neoprene WHV 40 MgO 4 MgO 4 OCD 2 OCD 2 Stearic acid 1.5 Stearic acid 1.5 Low mw PE 2 Low mw PE 2 N330 HAF black 30 MT black 20 N990 MT black 20 Factice 50 Precipitated silica 20 Aromatic pr. oil 50 CI resin 5 ZnO 5 Aromatic pr oil 10 ZnO 5 TETD 1
Nitrile rubber (NBR) Acrylonitrile-butadiene copolymers, in short Nitrile rubbers are really the workhorse of the special rubber industry. They have the best oil resistance with fairly good heat resistance ,and therefore suitable for a number of applications in the auto and industrial products sectors. NBR, like SBR, has good stability, can be easily mixed and processed, and can be cured with similar sulfur accelerator systems. Physical properties and compression set is very good , ideally suited for many sealing applications. Being unsaturated, ozone and weathering resistance is missing. Electrical resistivity is low therefore suitable for antistatic products, but not for insulation.
Gradation of NBR Gradation of NBR is mainly based on the acrylonitrile content which ranges from a low of 18% to a high of 48%., higher the ACN, better is the oil resistance, but low temperature properties are affected. The viscosity of various grades can range from very low to high as with other rubbers. Oil extended grades are also available, usually with DOP or now with safer plasticizers. Powder grades are also available specially for plastic modification , or for continuous mixing operations. Modification of NBR by carboxylation (XNBR) confers improved strength properties, where as modification by hydrogenation (HNBR) improves thee ozone and weathering, as well as resistance to wear and tear, and oils containing aggressive additives.
Processing of NBR and HNBR The most important point to remember is that sulfur is less soluble in NBR and difficult to disperse. It has to be added first in the mixing cycle. Sulphur preparations like Struktol® SU 95 or SU120 dustless powders, or polymer bound products give good dispersion. Semi-EV curing system-low sulfur high accelerators is advisable Whilst mill mixing is quite easy, high viscosity and high ACN grades may take a longer time to form a band. Processing aids help in dispersion of fillers and reducing nerve. Struktol WB 222 is particularly effective in NBR as well as in HNBR. Tackifiers for NBRs are polar resins like CI resins or PF resins, and other proprietary resinous tackifiers like Struktol TS 35, are also very effective. Plasticizers of the ester and ether types are needed for NBRs as they are easily compatible, and give improvement in low temperature flexibility, whilst polyethylene glycol ester (Struktol AW-1) improves the anti-static properties still further.
Applications of NBRs Main application of NBR is the automobile industry for oil seals, O-rings, gaskets and hoses in oil environments. In our country though the biggest use probably is in rice dehusking rollers due to its wear and tear properties in combination with phenolic resins and precipitated silicas. NBR finds use in antistatic products like safety footwear, and textile products like cots and aprons. Carboxylated NBR is also ideal for spinning cots where modified glue is still being used for good performance. Hydrogenated nitrile (HNBR) has a major application in poly-V belts and synchronous timing belts.
Typical roller compounds Printing roll Textile/Paper mill roll (non-black) OE-NBR 150 phr NBR 100 phr Sulfur 2 Sulfur 1.5 St. acid 1 Stearic acid 1 ZnO 5 ZnO 5 A/o TDQ 1 A/O TDQ 2 Factice 40 Pptd silica 45 DOP 15 PF resin + hardener 15 MT (N990) 10 TiO2 5 TMTMS 1 WB222 2 MBTS 1 Shore A : 40 80
Textile spinning cot Rice dehusking roll XNBR (X 1.46) 100 phr NBR/BR 80/20 phr Sulfur 10 Sulfur 2 ZnO 5 ZnO 5 TiO2 10 Stearic acid 1 Modified glue 75 Ppted silica 60 Antistatic plasticizer 10 PF resin + hardener 20 MBTS 1.5 A/o TDQ 1 DOP 5 Shore A: 78 CBS 1.2 (anti static) Shore A: 90
Chlorosulfonated polyethylene( CSM) CSM, often termed as Hypalon® of DuPont, is a special elastomer, akin to CR, but with better heat and fluid resistance, better weathering and ozone and improved physical properties. Various grades contain 28 to 43 % chlorine, but all have around 1% sulfur only, to help crosslinking by different curative systems. CSM is a versatile polymer having applications in the cured or uncured state also. It is the most colour-stable polymer, and has good storage stability also.
Processing of CSM Chlorosulfonated polyethylene (CSM) is, or rather was, a speciality of DuPont Performance Elastomers, now from other sources. This is also a sticky polymer, in spite of its high viscosity, and the following process aids are always recommended. • Low molecular weight polyethylene (2 phr) • Polyethylene glycol (2 – 4 phr) • Paraffin and microcrystalline waxes (2 -4 phr) • Stearic acid and stearates (not zinc), e.g. Struktol® WB222 • High cis-polybutadiene or high ethylene EPDM (3 to 5 phr) Caution; zinc oxide and zinc compounds to be avoided. Cold stocks of CSM are dry and tack-free for laminating and building operations; warming the sheets to 65 – 70°C is a better way of tackifying the compound prior to roll building. Proprietary tackifiers like Struktol TS35, coumarone resins, etc., and others are also useful, though they may aggravate mill sticking.
Curing of CSM The highly reactive sulfonyl chloride crosslinking site offers a wide choice of practical curing systems. The common acid acceptors used are high activity MgO with pentaerythritol, 4 + 3 phr, or 8 to 10 phrMgO alone. The common curatives are : - TMTD plus sulfur - Tetrone® A (tetraethyl thiuramtetrasulphide or – hexasulphide. - HVA-2® (n,n’-m-phenylenedimaleimde) - Peroxide +coagent and various combinations of the above.
CSM applications Automotive: power steering and oil cooler hose, fuel hose cover, emission and vacuum tubing ,etc. Industrial : Hydraulic hose covers, oil and fuel hose covers, rollers for paper and textile industry, tank linings. Electrical: wire and cable sheathings, appliance wires, etc. Solution applications: coatings on various substrates, structural adhesives, primers, collapsible storage tanks, etc. Uncured applications: magnetisablestrips, roofing membranes, pit liners, rainwater harvesting, etc. ( higher green strength due to higher ethylene content )
CSM –typical compounds Power steering hose:Textile mill roll CSM -40 100 phr CSM-40 100 phr MgO 5 MgO 5 Pentaerythritol 3 pentaerythritol 3 N762 black 60 Hard clay 60 DOP 15 CaCO3 30 Process aids 4 TiO2 15 NBC 1 Chlor paraffin 20 Tetrone A 1 PEG 2 MBTS 0.5 Par. Wax 2 Tetrone A 2 MBTS 0.5 161
CSM applications Magnetic strips CSM (24% Cl) 100 phr Ba or Strontium ferrite 900 PE wax 2 Polyethylene glycol 5 Unvulcanized, good green strength. Extruded strip passed thru a magnetizer.
EPDM Ethylene-propylene-dieneterpolymer is one of the fastest growing special rubber in the non-tyre industry. (Global production may touch a million tonnes by 2018.) The saturated main chain is responsible for the extremely good weather and ozone resistance, as well as good resistance to heat and oxidation. Being a non-polar rubber, it has resistance to polar oils and solvents, but not to hydrocarbon mineral oils. It is compatible with many chemicals including hot water and steam. At a specific gravity of 0.86 to 0.88, it is the lightest rubber available giving advantage in volume cost.
EPDM gradation Gradation is based on: • Diene content: from 0 to 10%. Low diene grades are cured with peroxides, whilst grades with 5 to 10% diene are termed as fast curing grades with sulfur-accelerator systems. 2. E :P ratio : Grades with ethylene content upto 60% are considered as amorphous , easier to mix on the mill, and having good set properties. 70 and above ethylene are semi-crystalline grades, having good green strength and extrusion properties, and can be highly loaded. • Mooney viscosity of various grades range from 20 to 85 and even higher in case of oil extended grades. • Other variables: Oil extended grades (20 to 100 phr paraffinic oil ) Molecular weight distribution – narrow, med, broad.
EPDM – properties and characteristics EPM and EPDM vulcanizates are characterizsed by their following good properties. 1, Highly resistant to oxidation, weathering and ozone due to its saturated backbone. 2. Good heat resistance upto 150C with peroxide cures. 3. Very good resistance to hot water and steam (220C, 250 psi). 4. Resistant to polar solvents, e.g. ketones, alcohols, glycols, phosphate esters, 5. Resistant to vegetable oils, various acids, alkalies, sodium hypochlorite, etc. 6. Good physical properties and compression set, low temp properties. 7. Good electrical properties ( insulation for low and medium voltage cables) 8. Can be loaded highly with fillers and plasticizers (for economy). 81
Applications of EPDM Main use of EPDM is in the automotive industry for profiles and weatherstrips, window channels, etc,. When properly compounded extruded profiles can be continuously cured in microwave tunnels, and other CV systems. EPDM is also the main polymer for radiator hoses, brake hoses and cups for automobiles. EPDM is also an ideal polymer for wire and cable insulations for low and medium voltage power cables. Pipe seals for potable and sewage water. Automotive FEAD belts for high temperature resistance. In other industrial applications, EPDM is the only polymer for high pressure steam and water hoses, and fire fighting hoses. Rubber rollers with EPDM are also used in certain applications like paper and textile processing and metal coating industry.
Applications of EPDM Applications in the rubber roll industry are for steel mills, metal coating rolls, and plastic processing rolls. Sulfur cured Peroxide cured Nordel™ IP4640 100 phrNordel™ IP 4640 100 phr Ppted silica 20 N774 black 50 Si 69 1 ZnO 5 N774 black 50 Struktol WB 16 2 Zn0 5 A/0 TDQ 1 St acid 1 A/O ZMTI 1 Low mw butyl 10 Paraffinic oil 5 A/o TDQ / ZMTI 1/1 Peroxide DBPH-50 HP 8 Sulfur 0.5 (TAIC ) 1 Accelerator package 5.0
Silicone rubbers Silicone rubbers, or polysiloxanes, are the only rubbers having an inorganic main chain, --O—Si—O—Si—O—Si—O– , with organic side chains. All other rubbers have a carbon-hydrogen organic main chain, -CH—CH—CH—CH—CH—CH--
Silicone rubbers All silicone rubber have predominantly methyl side groups, i.e. - CH3 However, a few vinyl side groups are always added to help crosslinking. --CH=CH2. Most of the commercial grades are VMQ type. Phenyl groups, - C6 H5 are added to improve the low temperature properties, and radiation resistance. These are the PVMQ types. Addition of fluoro groups greatly improves oil and fuel resistance, closer to Viton, but costlier than FKM. These are the FVMQ types Heat resistance: VMQ =PVMQ >FVMQ Oil resistance : FVMQ >> VMQ =PVMQ Low temp properties: PVMQ >>VMQ>FVMQ
Processing of silicone rubbers(VMQ) Properties:soft, low viscosity rubbers .Very good low temperature flexibility. Excellent heat resistance, Good electrical properties. Medium oil resistance. Curatives: peroxides only. No coagents required. 0R Addition (platinum) curing system also possible for fast cures. Postcuring 4 hrs at 200C recommended. No post cure grades also available. Problems faced: Crepe hardening, mill sticking, low green strength, low TS and tear except for some hi-strength grades. Processing additives: Proprietary masterbatches, for example Dow Corning’s Xiameter RBM 9001 to retard crepe hardening,(for overaged stocks). Xiameter RBM 9004 to improve green strength, Xiameter RBM 9003 to improve extrusion and calandering. Xiameter RMB 9010 for better mold release. Preventive measures; mix on absolutely clean and cold mill. No contamination from oils and grease from mill guides. Can be blended with other silicone grades to get intermediate properties. Addition of color pigments, flame retardants, etc should be in masterbatch form only. Mill freshening before curing or extruding is helpful.
Properties of Si Rubbers Thermal properties: Resistant to high and low temperature, - 110 to 250C. Widest service temperature range among all rubbers. Maintains physical properties even at high temperature. Electrical Properties: Very good insulation and dielectric properties, high dielectric strength, excellent arc and tracking resistance. Physical Properties: medium to low tensile and tear properties, poor abrasion resistance, very good compression set resistance. Environmental Properties: Very good resistance to oxidation, ozone and weathering, high radiation resistance, medium to good resistance to chemicals and oils, Other properties: water repellant, good flame resistance with non-toxic combustion products, high gas permeability.
Applications of silicone rubbers Automotive: seals, gaskets, spark plug boots, turbo hoses, exhaust pipe hangers, air bags, etc. Wire & Cable: Ignition cable, fire safety cables, furnace leads, Industrial: extruded and molded parts, rollers, technical textile coatings, key pads, office automation parts, etc. Food and medical: cathetors, tubings, feeding botle nipples, pacifiers, medical instruments, bake ware, household machines, cake molds, freezer gaskets, oven door profiles, etc. Sports and life style: swim caps, goggle frames, diving masks, etc Power T & D : High voltage insulators, surge arrestors, cable accessories,
Silicone rubber roll for office automation(Dow Corning grades RBB -66xx- 30 and 80)
Ethylene/acrylateelastomer(AEM) Polyacrylate rubbers ACM and AEM are specialityelastomers which fill in the gap between the high heat resistant rubbers of 200C plus, and medium heat of 150C. Vamac® AEM of DuPont is claimed to have an advantage over ACM in terms of processing ease, heat resistance, low temperature and damping characteristics, although the oil resistance is not as good as in ACM. Latest developments in Vamac® have increased the Mooney viscosity as well as thermal limits to 180C for high temperature applications.
AEM Whilst compounding of AEM is similar to other rubbers, it is important to add proper processing additives and aminiccrosslinking agents. Although one grade Vamac DP is peroxide curable, the other popular G types require a combination of Diak no.1 (hexamethylenediaminecarbamate) with a guanidine, DPG or DOTG Other safer substitutes are also available, e.g. Vulcofac ACT55, a tertiary amine complex (DBU)* of Safic Alcan in place of DPG,DOTG. As an antioxidant, Naugard 445 ( diphenylamine) is most suitable. Amine cured Vamac needs a post cure for 4 hrs/177 C, Peroxide cured moldings do not require post curing. * 1,8-diazabicyclo undec-7-en.
Processing of EAM (contd) Precautionary measures: Select high viscosity grades wherever possible, and use cold mill. Don’t mill excessively. Release package most important to prevent mill sticking – Stearic acid 1.0 – 2.0 phr Octadecyl amine 0.5 phr (Armeen® 18D) Vanfre® VAM 1.0 phr (or Struktol® WB222) Use low volatility, heat resistant plasticizer ,e.g. mixed polyether/ester like Struktol KW 759 or TP 759. Cure under sufficient pressure to prevent blistering. Do not use any metal oxides like ZnO or MgO.
Applications of EAM Mostly in the automotive industry for hoses and seals to withstand increasingly hot and chemically aggressive engine environments. Due to its excellent damping characteristics, better than butyl at high temperatures, AEM is used in torsional dampers, and in cam cover and oil pan gaskets. In non-tyre applications, AEM in covers for halogen-free, oil-resistant, low smoke cables, and also in roll covers due its damping properties.
Applications of AEM Industrial roll covers:Flooring, low fire hazard Vamac G 100 phrVamac DP 75 phr Naugard 445 2 Elvax 265 25 Stearic acid 1.5 Stearic acid 2 Octadecyl amine 0.5 Octadecyl amine 0.5 Vanfre VAM 1 Vanfre VAM 1 CaCO3 80 ATH 200 Silica fumed 35 Mg (OH)2 50 Plasticizer 10 Pigmentaion 3 Diak # 1 1.5 DCP-50 10 DPG 4 TAC 2.5 Shore A: 80 93
FLUOROELASTOMERS • General term for elastomers containing fluorine atoms. • The high heat stability and fluid resistance is due to: • High ratio of fluorine to hydrogen atoms • Strength of C-F bonds • Absence of unsaturation • Types of fluoroelastomers: fluorine,% • # fluorocarbon rubbers (FKM/FPM) 66 - 70 • #perfluoroelastomers (FFKM ) 72 -73 • #fluorosilicone rubbers (FVMQ) < 50 • #tetrafluoroethylene-propylene (TFE/P) ~ 55 • 90
Viton® FKM The uniqueness of Vitonfluoroelastomers is due to: - high ratio of fluorine to hydrogen. Bond energy, kcal/m - very strong carbon-fluorine bond C – F 105.4 - absence of unsaturation (double bonds) C – H 80 C – Cl 78.5 (High bond strength increases the thermal and chemical stability of elastomers) Heat resistance Hours of service, >10,000 indefinite at 205 C > 3,000 at 230 C > 1,000 at 250 C > 240 at 290 C > 48 at 315 C 93
eat Ress. FFKM >1000 h 325°C Kalrez® perfluoroelastomer parts [Depending on the compound] >10000 h >3000 h** 10000 >1000 h 1000 >240 h >48 h Hours of Service* 100 10 1 205°C 232°C 260°C 287°C 315°C Test Temperatures * Approximate number of hours at which typical vulcanizate of Viton® will retain 50% of its original elongation at break. Data based on a standard 66% fluorine type (A family). ** car:180’000 km at 60 km/hour. “normal car lifetime” 94
FKM Apart from its excellent thermal properties, FKM has very good resistance to a broad range of fluids - oils, fuels, solvents, hydrocarbons and chemicals. FKM has good resistance also to oxygenated fuel mixtures like gasohol, unlike other fuel resistant rubbers like NBR. However, FKM can be severely affected by the following : - Ketones ( e.g MEK used as solvents for uncured FKM) - Esters , e.g. ethyl acetate - Amines (cause embrittlement) - Strong bases, e.gNaOH ( special grades required) 95
Processing of fluorocarbon rubbers (FKM) Properties: Excellent resistance to heat, oils, fuels and chemicals (except bases). High specific gravity, tough elastomer. Curatives:Bis-phenols, diamines, peroxides (grade dependent). Magnesium oxide, calcium hydroxide, zinc oxide Post cure required in most cases @ 24hrs/230C Problems faced: sticking to mill rolls and molds, mold fouling, flow marks, rough extrusion. Processing additives: Struktol WS280, Struktol HT 290, DuPont’s VPA 2, Carnauba wax, PAT 777, (dosage 0.5 to 2.00 phr) Preventive measures: Mix on cool and clean equipment. No oils, resins, plasticizers, antioxidants to be added. Avoid sulfur contamination (use new brush). Refine compound on tight mill before molding. Use clean molds with semi-permanent mold release agent, e.g. Permalease 90. Post cure to start at below 100C, increasing to 230C gradually.