In the 1930s, when rubber became one of the essential commodities, selection was never a problem because we had only Natural Rubber (NR) that time. Today, beyond 2010, there are number of elastomers are being used in the industry and the choice is typically important with respect to the competitive advantage of both, durability in the service and cost.

 

NR was called rubber because it could have rubbed out pencil mark. When other synthetic rubbers were produced, they had also similar property of rubbing out pencil mark, but were called elastomers because NR was then typically identified as Rubber. However, both NR and other synthetic rubber (SR) together are called elastomers, because they had typical elastic properties and interestingly, all rubber and elastomers are high polymers. From the time 1930 , industries have increased many folds of time. Engineering requirement in the manufacturing industries, with respect to temperature, pressure and durability have also simultaneously increased and our demand on the applications have also been increased.

CAPTION Fig.1: Asia Pacific Total Elastomers (54%), NR+SR

 

With very competitive demand in the market, all rubber properties cannot be achieved only by NR. Balancing critical demand for rubber applications, that we require in our day to day life, use of SR or blending with SR has become very common practice in the industry today.

 

For example, other than pneumatic tyre, there is hardly any uses of NR these days in automotive industries. Uses of various grades of EPDM, Silicone rubber (Q), Nitrile rubber(NBR), Fluoro Elastomers (FKM) , Perfluoro Elastomers (FFKM) , Hydrogeneted Nitrile rubber (HNBR), Chlorosulphonated Polyethylen (CSM), Polychloroprene(CR) , Polyurethane Rubber (AU/EU), Fluorosilicone Silicone Rubber (FQ) etc. have been increased due to typical automotive parts requirement. Since automobile spares are now mostly manufactured in Asia Pacific countries, they are the largest consumer of total elastomers (Fig.1).

 

CAPTION Fig.2: Only SBR is the highest (47%) synthetic rubber

 

After NR, the next high consuming elastomer is SBR (Fig.2) because of its higher filler and oil loading capability and higher abrasion resistant quality. After SBR, the next high quantity rubber used is BR, followed by IIR (BIIR,CIIR) and EPDM. Recently silicone rubber uses have increased many fold times in Western countries, China, Japan, Korea and in India. However, the total SR uses remains highest in Asia Pacific(Fig.3).

 

CAPTION Fig.3: Asia Pacific Highest Consumer of SR (48%)

 

In critical applications, it is therefore, advisable to give considerable thought, or take advice, on the formulation of the compound. As the potential for 'tailoring' compound to specific applications is essentially limitless, it is often advisable to carry out preliminary qualification tests to ensure that the compound chosen will perform as intended by customer need.

A considerable thought in critical applications, for the formulation of the specific compound need considerable experience with selecting raw materials and art of processing. Very common mistakes by rubber compounder is mostly related to incorrect selection of (1) ingredients, (2) their doses, (3) rubber blends and (4) correct machines. Rubber compounding is an art of developing rubber mixtures with suitable raw material and their doses, that will perform in desired services but with minimum cost possible such that product can be competitive in the market and can be processed well in machines without any difficulties faced by man and machines.

 

There are broadly two classes of Rubbers or elastomers, they are Natural Rubber (NR) and Synthetic Rubber (SR). NR occurs naturally in the plant and hence the name but all synthetic rubbers are man made rubbers and are produced by chemical synthesis. Among the Synthetic elastomers, there is again two category; one is general purpose rubbers (GPR),which can be used as equivalent to NR, e.g., Butadiene Rubber (PBR) and Styrene Butadiene Rubber (SBR) and the other category is specialty elastomers. Specialty elastomers are generally costlier than GPR and are only used in special purpose. Following are the list of specialty elastomers ,which are widely being used in rubber industry beyond 2000:

 

Butyl Rubber (IIR), Chlorobutyl Rubber (CIIR), Bromobutyl Rubber (BIIR), Chlorinated Polyethylene(CM), Chlorosulphonated Polyethylen (CSM), Ethylene Acrylic(EEA) , Ethylene Propylene Rubber(EPM) , Ethylene Propylene Diene Rubber(EPDM), Fluoro elastomers (FKM), Hydrogenated Nitrile Rubber (HNBR), Isoprene Rubber (IR), Nitrile Rubber(NBR) ,  Polyacrylic Rubber (ACM), Perfluoro Elastomers (FFKM), Polychloroprene (CR) , Polysulphide Rubber (TR) , Polyolefin Elastomer (POE),   Polyurethane Rubber (AU/EU) , Silicone Rubber(Q), Fluorosilicone   Silicone Rubber (FQ) etc.

 

Elastomers having carbon-carbon double bond on the elastomeric backbone could be cross-linked with sulphur and accelerators. Many of these elastomers are also could be cured with organic peroxides, examples are NR,SBR,BR, AU/EU, CM, CR,CSM,EPM,EPDM,FPM,NBR,HNBR,IR,POE,Q,FQ. Elastomers that cannot be cured with organic peroxides are; ACM,IIR,CIIR,BIIR,ECO.

 

Rubber compounding

 

Rubber compounding is an art of developing rubber mixtures with suitable raw material and their doses, that will perform in desired services but with minimum cost possible such that product can be competitive in the market and can be processed well in machines without any difficulties faced by man and machines. In all rubber industry today, the biggest challenge is cost reduction of a good quality product. During selecting raw materials, therefore, the cost of these will also play a vital role in compound designing.

 

A rubber product might require desired physical properties and ageing properties. For this one need to add particular reinforcing filler or a suitable combination of reinforcing fillers to have desired physical properties. The typical ageing resistant property may be achieved with only NR by adding suitable anti-degradants or, NR could also be blended with synthetic elastomers with better ageing resistant property. NR being cheaper and easily available it is the first choice having good strength, abrasion , tear strength and low heat development in dynamic condition. A synthetic rubber product might require good green strength , in that case either NR or blend of rubber is the choice. For example, for better green strength of CIIR, it is often blended with NR.

 

CAPTION Fig.4: Turn-up Bladders

 

A rubber product may require a specific need , say air retention property or oil resistance property. For the former case the choice is essentially butyl rubber (or, halobutyl rubber , CIIR,BIIR) and for the later it is usually, NBR/HNBR and for both oil resistance and air impermeability, the usual choice is NBR / HNBR rubber (Turn-up bladder for tyre building operation, Fig.4). For a typical product, if the property demands oil resistance at 200 ⁰C, then the choice is FKM (Fluoroelastomers) or Q. For resistance upto 328 ⁰C , it is FFKM.

CAPTION Fig.5: Typical Industrial Gaskets

 

Heat resistance property is typically related to product durability and sustainability at desired temperature and is very important for various industrial gaskets (Fig.5). For temperature resistant rubber compounding and following temperature resistance of the polymer is important, NR ~ 65 °C, SBR ~ 75 °C, NBR ~ 110 °C, HNBR ~ 180 °C, Q ~ 200 °C+, FKM ~ 240 °C, FFKM ~ 328 °C. The temperature ranges quoted are only a rough guide, because the temperature resistant property also depend on the typical compound design as well, depends upon the particular application, and may depend on detailed differences between alternative versions of the same rubber.

 

Rubber compound is always developed as per customer need. For any rubber article, the first choice is the selection of right rubber. Rubber is selected mostly on the basis of :

 

• Cost
• Heat and/or Oil Resistance
• Temperature Requirements
• Energy Absorption
• Seal Ability
• Flex Resistance
• Water Resistance
• Gas Impermeability
• Electrical Properties
• Abrasion Resistances
• Dynamic Properties
• Flame Resistance

 

Rubber compound related definitions

 

• Elastomer, a polymeric material that recovers substantially to its original shape after significant deformation at room temperature.
• Compound, a mixture of elastomer and other materials that is intended to process (mold) satisfactorily and meet end-use specifications.
• Filler, a particulate material added to an elastomer that modifies both the workability and the end-use behavior of the resulting composition.
• Plasticizer, a material added to an elastomer to improve its workability.
• Resins are added to improve rubber tack.
• Waxes also used as plasticizer , are also added for smooth finish of rubber articles.
• Antioxidant, a chemical added to a compound to slow or prevent oxygen attack on the compound.
• Antiozonant, a chemical added to a compound to prevent ozone attack.
• Cross linking agent, a chemical added to a compound to link the long molecules in a polymer together, or to assist in the cross-linking process.
• Accelerator, a chemical added to a compound to increase the rate of cross-linking in the compound.
• For example, sulfur links the long molecules, while an accelerator increases the cross-linking rate.
• Retarder, a material added to an elastomer compound to delay the onset of cross linking (scorch).
• Vulcanization is same as cross-linking but with sulphur.
• Peroxide also helps in cross-linking process.

 

 

Elastomer blends

 

Elastomer blends often creates problem when two different types of unsaturated rubbers are mixed and vulcanized together. For example, NR and IIR have two different unsaturation level and hence both sulphur , ZnO and black flows more towards polar rubber, on NR phase, and results undercure in IIR phase and the resultant blend vulcanizate becomes spongy and cannot be used.

 

GPR (NR,SBR,BR) rubber could be blended to any proportion. For higher synthetic rubber level (BR,SBR) , accelerators dose is often adjusted to higher side and sulpur level is adjusted to lower side, because for equivalent curing, BR, SBR requires more accelerators as compared to NR. Stearic acid is added 2-3 phr with only synthetic elastomer and for NR, stearic acid dose of 0.5 phr is enough.

 

CAPTION Fig.6 : Micro Dispersion of Rubber Blends

 

Practically most of the polymers are not miscible to 100%, polymer blends usually consist of micro-dispersion of one rubber into the other rubber and this results after intensive mixing of these two different polymers. These micro dispersed rubber often has dimensions around 0.1-1.5 nm(Fig.6). When fillers are also mixed into such blends, a situation may develop in which the filler unevenly distributed between two phases. Such uneven distribution of fillers, naturally effects the uniformity of compound physical properties. In most blends the effect on the properties of blended elastomers depend on:

 

1. The polymer compatibility
2.  Distribution of fillers in different phases and
3. The degree of cross-links between rubber phases

 

Though NR,SBR,BR could be blended to any proportion , yet the blended phases are not compatible to hundred percent and there is also phase separation, where, on proper identification one can witness that there is phase separation with NR & SBR, NR & BR, BR & SBR. However, upon proper mixing these phase differences could be minimized (Fig.7) such that the resultant blend gets cured almost homogeneously . That is why very highly dispersed NR (5 to 10 parts) could also be co-cured with IIR.

 

 

CAPTION Fig.7 : Well Dispersed Rubber Blends

 

 IIR cannot be blended with GPR but can be blended with EPDM (having ENB diene content between 2-3 mole%) to any proportion. Higher diene content EPDM rubber (ENB, >9.0% mole) could be well blended with GPR. If high diene content EPDM is blended with IIR, filler, sulphur, accelerator and zinc oxide flows more towards EPDM than IIR. IIR could be blended with CIIR and BIIR to any proportion. Such blend is often used in making tyre inner-tubes and hose jacket compounds. When CIIR and BIIR doses are on the higher side with IIR (>60phr) it is worthwhile that zinc oxide is added in the final batch since zinc oxide is curative for CIIR & BIIR.

 

Besides zinc oxides, CIIR and BIIR can also be cured with sulphur/accelerator system as well. However, for very good heat resistant property, they are often cured with ZnO. Highly dispersed plastic (LDPE) could also be blended with CIIR/BIIR with no detrimental effect but with improvement on air permeability.

 

CIIR and BIIR could be blended to any proportion with GPR. Such blend is often used in tyre inner liner. When CIIR and BIIR doses are on the higher side (>60phr) both zinc oxide and amine type anioxidant/antioxonates are added in final batches as these are curatives in CIIR and BIIR.CIIR blend with GPR and EPDM is used in PC sidewall for glossy finish sidewall and addition of CIIR also help to reduce the curing time of PC tyre. Blend of EPDM/NR/SBR and EPDM/NR/SBR/CIIR are often used in tyre side wall compound for better look.

 

CR rubber is not normally blended in the industry as it is mostly used in adhesive industry. However, they can be blended to any proportion with GPR. In adhesive industry crystallinity is important and CR gives the highest degree of crystallinity among all general-purpose rubber. CR could be blended with IIR , close to 5-15 phr, for bladder making and in general, only 5.0 phr is added in the beginning of the mixing cycle.

 

In bladder mixing, Zinc oxide could be mixed with CR in master batch. CR is premasticated in mixing mill for making bladder compound, before adding in Banbury.CR/BR blend is used in hose covers.CR could also be blended with GPR at any proportion like CIIR. Both zinc oxide and amine type antioxidant / antioxonates are added in final batches as these are curatives in CR and CIIR.

 

In general Silicone rubber (MQ,PMQ,VMQ) cannot be blended with any other rubber because of phase difference problem but highly dispersed EPDM could be blended with it upto 10 -15 phr. EPDM/Q blend is used in heat resistant cover roll compound.

 

EPDM, being a good elastomer as weather resistant and heat resistant is often blended with number of other elastomers to get the benefit of the vulcanisates.

EPDM/CR blend are very popular in making gaskets. EPDM/IR blend is widely used in car wiper rubber blades. EPDM/SBR blends are used in gaskets, sponges and hose stocks. EPDM/CSM blend is used in transmission belt, conveyor belt and in hose covers. EPDM/LDPE blend is very popular in making cable insulation compound.

 

NBR in general, is not blended with other elastomers as this rubber having higher degree of polarity , is exclusively used for oil resistance property. It may have acrylonitrile content ( ACN) ranging from 18-50%. Incase of higher oil resistance, the elastomeric grade is selected with higher ACN. For better abrasion however, 10-20 phr of BR could be added to NBR with the aid of good dispersing agents , used in shoe sole, high abrasion resistance rolls and in conveyer belts. Higher ACN content will have better abrasion property. NBR could be cured both by sulphur/accelerators or by peroxides. Hydrgenated NBR (HNBR) has emerged into market with better heat resistant property as compared to NBR. For intermediate heat resistant property NBR and HNBR could be blended.

 

NBR/SBR blends used in hydraulic hose tubes, high pressure hose, belt cover, idler roll compounds and in gasket compounds. NBR/PVC blend and NBR/PVC/BR blend are used for roll cover compound, very popular in electric cable insulation and in closed cell sponge applications in shoe industry. XNBR/PVC blend is used for heavy duty cable jackets, roller cover, belt cover, hose cover stocks etc. NBR/IR blend and NBR/TR blend is popular in colored or non-black roll covers. The later is mostly used in printing roll cover compound.

Orion Engineered Carbons, a specialty chemical company, started commercial sales in Italy from the first new reactor for carbon black production to be commissioned in the European Union in over 40 years. 

The new 25-kiloton line at the facility in Ravenna, in the northern region of Emilia-Romagna, produces both specialty and technical rubber carbon blacks, primarily for the European market, the company said in a release. 

Corning Painter, CEO, Orion, said, “The new line offers customers seeking long-term solutions a unique strategic opportunity to align with a dependable plant that has been operating for more than 60 years in Europe.” 

Additional investments at the plant include a new co-generation facility to convert waste heat into electricity, generating up to 120 MWh of electricity per year. Seventy percent of the electricity is supplied to the national grid, serving about 30,000 households. Orion is a net exporter of electricity in Europe and worldwide. (TT)  

Shin-Etsu Chemical, a leading chemical company, plans to invest $702 million in its silicone portfolio, a key component of its functional materials business segment.

This latest investment follows a plan announced in February 2022, worth $562 million, to meet the surging demand for advanced functional silicone products. However, due to the continuous growth in need, especially for eco-friendly options that align with the global goal of carbon neutrality, the company has decided to expand the applications of its silicone products. The company will also focus on enhancing the advanced functionality of its product lineup and further developing environmentally friendly silicones.

In alignment with its newly announced silicones investment plan, Shin-Etsu Chemical will make investments not only in its central production hub in Japan, the Gunma Complex in Gunma Prefecture, but also in its Naoetsu Plant in Niigata Prefecture, Takefu Plant in Fukui Prefecture, and the Group company plant in Thailand, where silicone monomer and polymer production is conducted. The company will also invest further in existing silicone plants across other Asian countries, the United States, and Hungary. Simultaneously, Shin-Etsu Chemical will accelerate efforts to achieve carbon neutrality by embracing greener manufacturing processes.

Klean Industries Inc has announced that its partner Pyrolysis Hellas SA has completed Phase II of the Detailed Feasibility Study to design and build a tyre pyrolysis plant in Greece. Greek Authorities gave permits to its final Phase, the company said in a release. The company, while terming it as a significant milestone for the PHS project, claimed that it was the first tyre pyrolysis and carbon upgrading project in Greece to receive full authorizations.

Klean Industries Inc has announced that its partner Pyrolysis Hellas SA has completed Phase II of the Detailed Feasibility Study to design and build a tyre pyrolysis plant in Greece. Greek Authorities gave permits to its final Phase, the company said in a release. The company, while terming it as a significant milestone for the PHS project, claimed that it was the first tyre pyrolysis and carbon upgrading project in Greece to receive full authorizations.

Klean Industries Inc has announced that its partner Pyrolysis Hellas SA has completed Phase II of the Detailed Feasibility Study to design and build a tyre pyrolysis plant in Greece. Greek Authorities gave permits to its final Phase, the company said in a release. The company, while terming it as a significant milestone for the PHS project, claimed that it was the first tyre pyrolysis and carbon upgrading project in Greece to receive full authorizations.Klean Industries Inc has announced that its partner Pyrolysis Hellas SA has completed Phase II of the Detailed Feasibility Study to design and build a tyre pyrolysis plant in Greece. Greek Authorities gave permits to its final Phase, the company said in a release. The company, while terming it as a significant milestone for the PHS project, claimed that it was the first tyre pyrolysis and carbon upgrading project in Greece to receive full authorizations.

Each year, over 1.5 billion tyres are sold worldwide, representing more than 26 million metric tonnes, and just as many tyres each year also fall into the category of end-of-life tyres providing a large and partially untapped potential for resource and material recovery. Today, most traditional ELT treatment processes are not circular and do not result in any production of raw materials that are suitable to be reused in the tyre manufacturing industry. Without such ELT solutions in the EU, more than half of the EU end-of-life tyres and secondhand tyres are landfilled or are exported as tyre derived fuels for use into furnaces as an industrial fuel. The PHS project intends to reverse these trends and create a vibrant addition to advancements being made in the tyre recycling sector, the release said.

The PHS project is co-owned by Karabas European Hellenic Recycling. Currently, KEHR collects and recycles all types of scrap vehicle tyres and recycles them through traditional methods by shredding tyres into rubber granules, rubber powder & shock-absorbent surfacing slabs.

PHS has partnered with Klean Industries to build a modern tyre recycling facility that encompasses a state-of-the-art scrap tyre pyrolysis plant to recycle 20,000 TPA of waste tyres into valuable chemical products.

PHS proposes to construct and operate the Waste Tyre Pyrolysis Plant in Moulkia, a seaside town near Skala, Greece. It is located at an existing industrial site that is owned by KEHR, the release added. (TT)

ResiCare, an adhesive manufacturing subsidiary of Michelin, has found commercial use in Allin's plywood manufacturing unit, R'PLY. Allin and Michelin have been in collaboration since 2018.

The company claims that R'Ply is the first responsible plywood made using certified Poplar wood and integrating a ResiCare resin that is kinder to human health as well as the environment. The R’Ply is a high-performance plywood which can be used for multiple applications, according to the company. The plywood can be used for boat-building or in the building trade and will be available at certain DIY stores soon.

Michelin had set up a mobile ResiCare production unit at its Olsztyn site in May 2021. The company hopes to replace more than 80 percent of the usual adhesive used in its tyre textile reinforcement with the new ResiCare adhesive, which is free from any substances of very high concern for health (SVHC), by 2025. The company further plans to set up mobile production units similar to the one in Europe and Asia in the coming months. (TT)