Compounding Technique

Rubber compounding What is rubber compounding? Why we are doing? How can we do it successfully?

Definition of Rubber Compounding is the art and science of selecting and combining elastomers and additives to obtain an intimate mixing that will develop the necessary physical and chemical properties for a finished product.

Objective of Rubber Compounding 1. To secure certain properties in the finished product to satisfy service requirements. 2. To attain processing characteristics necessary for efficient utilization of available equipment. 3. To achieve the desirable properties and processability at lowest possible cost.

To be Sucessful in Compounding Must understand the properties and function of hundreds of elastomers and rubber chemicals Must also have intimate knowledge of the equipment used for mixing, extrusion, calendering, molding and vulcanization.

Procedure for Compound Development 1. Set specific objectives (properties, price, etc.). 2. Select base elastomer(s). 3. Study test data of existing compounds. 4. Survey compound formulations and properties data presented by material suppliers in their literature . 5. Choose a starting formulation.

To be continued 6. Develop compounds in laboratory to meet objectives. 7. Estimate cost of compound selected for further evaluation. 8. Evaluate processability of compound in factory. 9. Use compound to make a product sample 10. Test product sample against performance specification.

Classification of Compounding Ingredients 1. Elastomers 2. Vulcanizing Agents (Curatives) 3. Accelerators 4. Activators and Retarders 5. Antidegradants(Antioxidants, Antiozonants, Protective Waxes) 6. Processing Aids(Peptizers, Lubricants, Release Agents)

To be continued 7. Fillers (Carbon Blacks, Non-black Materials) 8. Plasticizers, Softeners, and Tackifiers 9. Color Pigments 10. Special Purpose Materials(Blowing Agents, Reodorants, etc,)

Requirements of Rubber Compound for Good Processing 1. Uniform plasticity and recovery. 2. Uniform scorch rate. 3. Uniform rate of cure.

Vulcanizing Agents To cause chemical reaction resulting in crosslinking of elastomer molecules. Sulfur is by far the most widely used.

VULCANIZING AGENTS TYPE COMMON USE Sulfur or Sulfur- Natural Rubber, bearing Materials Isoprene, SBR, Buty1, Butadiene, EPDM, Nitrile,Norsorex Organic Peroxides Urethane, Silicone, Chlorinated Polyethylene, Crosslinked Polyethylene, Vamac, Vynathene, PVC/ Nitrile

To be continued TYPE COMMON USE Metallic Oxides Neoprene, Hypalon,Thiokol Organic Amines Acrylic, Fluorocarbon, Epichlorohydrin, Vamac Phenolic Resins Butyl

ACCELERATORS Use to reduce vulcanization time, or cure time by increasing the speed of vulcanization Most are organic substance containing both nitrogen and sulfur(Today) Inorganic accelerator was widelyused years ago (litharge, lime, and magnesia)

ORGANIC ACCELERATORS TYPE EXAMPLE TYPICAL USE Aldehyde-amine Reaction product of Fast curing butyral dehyde and accelerator for aniline reclaim,hard rubber and self- curing cements Amines Hexamethylene Delayed action tetramine slow accelerator for natural rubber

To be continued TYPE EXAMPLE TYPICAL USE Guanidines Diphenyl guanidine Secondary accelerator (DPG) to activate thiazole type accelerator Thioureas Ethylene thiourea Fast curing accelerator (ETU) for Neoprene,Hypalon and Epichlorohydrin

To be continued TYPE EXAMPLE TYPICAL USE Thiazoles Benzothiazyldisulfide Safe-processing (MBTS) moderately fast curing accelerator for natural rubber, Isoprene,SBR, Nitrile,Butyl and EPDM Thiurams Tetramethylthiuram Fast curing sulfur- disulfide (TMTD) bearing accelerator for SBR, Nitrile, Butyl and EPDM

To be continued TYPE EXAMPLE TYPICAL USE Sulfenamides N-cyclohexyl-2- Safe-processing, benzothiazyl- delayed action sulfenamide accelerator for (CBS) natural rubber, SBR and Nitrile Dithiocarbamates Zinc dimethyl Fast curing accelerator Xanthates Dibutylxanthogen Fast curing, low disulfide temperature accelerator for natural rubber and SBR

Activators and Retarders Activators - used to activate the accelerator and improve its effectiveness (ZnO, stearic acid, litharge, magnesia, and amine) - attain good crosslink efficiency Retarders - used to reduce the scorchness (phthalic anhydride, salicylic acid and sodium acetate)

Antidegradants To retard the deterioration of rubber compounds initiated by - oxygen, ozone - heat, light - metal catalyst and - mechanical flexing

PROCESSING AIDS To facilitate processing operation such as - Mixing - Calendering - Extrusion and - Molding

PROCESSING AIDS Activated Dithio- Pepton 44 Peptizer for NR COMPOSITION EXAMPLE(Tradenames) FUNCTION Activated Dithio- Pepton 44 Peptizer for NR bisbenzanilide Poly- Polyac Chemical conditioner paradinitrosobenzene for IIR

To be continued COMPOSITION EXAMPLE(Tradenames) FUNCTION Xylyl mercaptans RPA3 Peptizer for NR, IR, SBR and NBR. Stabilizer for cement viscosity Low-molecular- A-C Polyethylene Release agent, weight 617 A lubricant polyethylene Calcium oxide DesiCal P Dessiccant

To be continued COMPOSITION EXAMPLE(Tradenames) FUNCTION Aliphatic- Strucktol 60NS Homogenizing naphthenic- agent for all aromatic resins elastomers Paraffin Wax Numerous Release agent, lubricant Polyethylene Carbowax PEG3350 Activator for glycol silica lubricant Petroleum Petrolatum Release agent, hydrocarbon lubricant

Fillers To reinforce physical properties To reduce cost Devided into two types(Reinforcing and Extending) Selection of reinforcing filler is the third most important task in compounding(next to elastomer and cure system)

Types of Fillers Reinforcing Type Carbon Black (listed in order N220 (ISAF) of increasing particle size) N330 (HAF) N550 (FEF) N762 (SRF-LM) N990 (MT) Non-Black - Silica - Zinc Oxide - Magnesium Carbonate - Aluminum Silicate - Sodium Aluminosilicate - Magnesium Silicate

Types of Fillers (continued) Extending Type - Calcium Carbonate - Barium Sulfate - Aluminum Trihydrate - Talc

Hardness NR has hardness itself (no filler) 35-40 IRHD ISAF 1.7 phr increases 1 IRHD HAF 1.9 phr increases 1 IRHD Hisil 233 2 phr increases 1 IRHD Hard clay 5 phr increases 1 IRHD Soft clay 7.7 phr increases 1 IRHD Whiting 6.4 phr increases 1 IRHD CaCO3 Oil 2 phr decreases 1 IRHD

Particles Size Play a major role in the tensile strength small particle size highest tensile strength at optimum loading Fine fillers is difficult to process (need more energy for their dispersion into the elastomer) Effects Mooney scorch small particle size the scorch resistance reduces

PLASTICIZERS,SOFTENERS, AND TACKIFIERS Objective for Using - Aid mixing, - Modify viscosity, - Produce tack, - Provide flexibility at low temperature

Selection of Plasticizers The important criteria are: Compatibility Efficiency Cost Example: - Aromatic type oil is not compatibe with NR, Isoprene, IIR, EPDM - Paraffinic type oil is not compatible with SBR, butadiene, NBR, CR

PLASTICIZERS,SOFTENERS, AND TACKIFIERS CATEGORY OF MATERIAL FUNCTION Petroleum Oils -Aromatic Plasticizer,Softener - Paraffinic - Naphthenic Ester Plasticizers - Dioctyl phthalate - Dioctyl sebacate - Tributoxyethyl phospate Low temperature - Di (butoxyethoxyethyl) formal plasticizers - Triglycol ester of vegetable oil

To be continued CATEGORY OF MATERIAL FUNCTION Vulcanized Vegetable Oils Extender, Plasticizer Asphaltic Hydrocarbon Extender, Plasticizer Pine Tar Plasticizer,Tackifier Resins -Coumarone-indene Tackifier,Plasticizer - Petroleum - Phenolic Polymeric esters Extender, Plasticizer Rosins - Hydrogenated rosin Tackifier

Special Purpose Materials Not require in the majority of rubber compound Used for specific purpose Example: - Blowing agents - Reodorants - Adhesion promotors - Flame retardant - Fungicide - UV light absorbers