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.

The Recycling and Economic Development Initiative of South Africa (REDISA) called out the country’s waste tyre recycling system a ‘ticking time bomb’. The country with an estimated population of about 62 million has more than 13 million registered vehicles including roughly eight million passenger cars and generates an estimated 200,000–250,000 tonnes of waste tyres from road vehicles alone each year.

This has created a major environmental and waste-management challenge alongside rising vehicle ownership.

Commenting on the issue, Executive Director of Operations at REDISA Stacey Jansen told Tyre Trends, “Waste tyre management in South Africa has, in effect, collapsed since the Waste Management Bureau under the Department of Forestry, Fisheries and the Environment (DDFE) took over in 2017. The effect is overfull depots posing significant fire risks including the dumping and burning of tyres illegally causing harmful chemicals to seep into groundwater and causing severe air pollution.”

“Economically, a huge opportunity is being missed, in that a structured management programme geared towards recycling can not only create jobs but also contribute to the circular economy as a whole. This was precisely what REDISA did between 2013 and 2017,” she added.

She also stated that internal research has shown that a functional waste plan for just 13 waste streams could raise South Africa’s GDP growth by 1.5 percentage points. For a country struggling with unemployment and stagnation, this is an avenue that must be pursued.

REDISA alleges serious governance failures within the DFFE and the Waste Management Bureau. The first problem is that no dependable data exists.

“We all know that there is a problem, but we don’t know the extent of it. The department’s figures and reports are filled with inconsistencies and errors and this impacts any effective decision-making on how to fix the issue of waste tyre management,” said Jansen.

Secondly, she argues that there does not seem to be a realisation that the government cannot handle waste tyre management on its own as it does not have the expertise, technology or experience.

Thirdly, more headline-grabbing issues such as conservation and climate, which are important, of course, receive a lot of attention. But ground-level interventions such as waste management, while not as media-friendly, offer real and relatively immediate ways to address environmental and economic problems, she stated.

THE BOMBARDING

The Biesiesvlei depot fire in 2023 caused extensive environmental damage. Alluding to the lessons learned from the incident, Jansen said, “This is a question perhaps best posed to the DFFE. Since that disaster, we have not seen a country-wide response that puts the safety of citizens and the environment first. If something isn’t done on a national scale, more depots will burn, releasing extremely toxic pollutants into the air.”

Moreover, the auctioning of nearly R100 million (USD 5–5.5 million) worth of unused pre-processing equipment has been called an ‘admission of failure’ by REDISA. Commenting on this, Jansen said, “We wish the government could tell us how they ended up idle. Either they bought the wrong equipment or they were unable to deploy it. The right decisions were clearly not made by the leadership in the department.”

Moreover, the exclusion of small businesses and micro-collectors from the current system has also impacted tyre collection, illegal dumping and rural employment.

According to Jansen, from 2013 to 2017, REDISA managed waste tyres in South Africa. In a short space of time, it built 22 tyre collection centres, employed more than 3 000 people and created 226 small waste enterprises.

This was all funded by a management fee levied on plan subscribers (producers and importers) as part of the approved Industry Waste Tyre Plan. In February 2017, following a legislative change, the state imposed an environmental levy, which replaced the fee REDISA was collecting. The levy is still being collected today, but the producers and the citizens are not seeing their money channelled into effective waste tyre management.

In fact, more than half of the money collected is going into the general tax fund. The result has been job losses, mostly in urban areas.

REDISA also claimed that the government underspent on tyre transport due to lack of storage space. Answering how does this contradiction affect the integrity of the waste tyre management system, she said, “The department admits this underspend and gives the reason in its latest annual report. They are silent on the consequences, but it can only lead to illegal dumping and burning of tyres. If you drive by almost any informal settlement or urban fringe in South Africa, you will see dumped tyres. And this could be transformed into an asset under the right system.”

CLEAR VIEW

During her interaction, Jansen encouraged citizens and journalists to visit waste tyre depots in their communities and see if they adhere to safety standards viz-a-viz 6-metre fire breaks between heaps, 8-metre gaps to buildings and fences, maximum heap size of 10 metre x 20 metre and more.

Collectors and transporters regularly complain to REDISA that the situation at the overfull depots and dumps have worsened so much since 2017 and that they are deeply concerned.

Questioning the sustainability of the current approach, Jansen said that generating nearly 70,000 waste tyres every day makes an over-reliance on storage depots deeply flawed. “This is not sustainable at all. The only outcome will be increased air pollution, contaminated groundwater and heightened fire risks. It is an attempt to apply a band-aid to the problem without addressing its root cause,” she said.

Jansen was equally critical of the DFFE’s decision to issue tenders for 32 new depots covering close to one million square metres. According to her, the move signals more than a stop-gap response. “I would describe it as an acknowledgement of defeat and clear evidence of an inability to effectively address tyre recycling in South Africa,” she added.

Reflecting on South Africa’s earlier leadership in circular tyre waste management, Jansen said restoring that position would not require sweeping policy or structural reforms. “The DFFE does not need new frameworks or radical changes. What is required is leadership that acknowledges the scale of the crisis and a willingness to return to a model that has already proven its worth, the internationally recognised REDISA model,” she said.

The warning signs are no longer theoretical. Idle equipment, expanding depots and rising illegal dumping point to a system drifting further from circularity. Without decisive leadership and a return to proven, accountable models, South Africa risks compounding environmental damage, economic loss and public health threats, allowing a ticking time bomb to keep counting down.

Ecolomondo Corporation, a leading Canadian innovator in sustainable scrap tyre recycling technology, has engaged August Brown, LLC as an independent risk advisor. This appointment supports the planning stages for a new facility in Shamrock, Texas. The firm will conduct a validation of the project's business plan and risk management approach, a step taken in preparation for marketing the green bond that will finance the development.

The proposed Texas site will feature a six-reactor plant, replicating the company’s proprietary, modular Thermal Decomposition Process (TDP) technology currently operating at its Hawkesbury, Ontario, facility but with triple capacity. This expansion follows the successful commercialisation of Ecolomondo’s proprietary TDP technology. Local support has been secured through the Shamrock Economic Development Corporation, along with a 136-acre industrial site and long-term feedstock agreements intended to supply ongoing operations.

August Brown's role will begin with a comprehensive feasibility study examining business, market and financial risks. A subsequent phase will focus on engineering, technology validation and project execution risks. This independent review process aims to improve transparency and strengthen confidence among potential bondholders and project partners. The project represents the next phase in the company's growth strategy, replicating its proven modular technology on a larger scale.

Eliot Sorella, Executive Chairman, Ecolomondo, said, “Independent validation of our technology, projected operations and financial model for our planned Shamrock Facility is an essential step that resonates strongly with investors, lenders and potential joint-venture partners.”

The Wacker Group is showcasing two new silicone-based impact modifiers, GENIOPERL W37 and GENIOPERL W38, at the JEC World composites exhibition. These additives are engineered to enhance the mechanical properties of thermosetting resins such as epoxies and vinyl esters. Their specialised molecular structure, built on functional silicone, facilitates a distinct phase separation within the resin matrix. This process creates tiny elastomeric domains that increase toughness and help prevent composite materials from fracturing under stress. Sustainability was a key consideration in their design, leading to a notably reduced cyclics content. Both modifiers disperse readily with simple mixing equipment, maintain their effectiveness even at low concentrations and do not compromise the material’s inherent strength, viscosity or thermal resistance. The company is located at booth 5N142 at JEC World, taking place in Paris from 10 to 12 March 2026.

GENIOPERL W37 is specifically formulated to boost impact resistance in low-temperature environments. It is recommended for use at concentrations between two and eight percent by weight, a level at which it has minimal impact on the resin’s viscosity or the cured product’s glass transition temperature. Achieving optimal dispersion requires processing temperatures of at least 50 degrees Celsius. Similarly, GENIOPERL W38 also improves impact strength at very low temperatures when used within the same dosage range. It offers the added benefit of containing anti-foaming agents, making it particularly suitable for casting processes conducted under reduced pressure.

A third major highlight at the Wacker booth will be POWERSIL Resin 710, a silicone compound developed for components that must endure extreme heat. This material can be processed using compression moulding, pressure gelation or injection moulding. Parts manufactured from it meet the criteria for thermal class R, signifying their ability to withstand prolonged exposure to temperatures reaching 220 degrees Celsius. As an alternative to high-performance polymers like PTFE and PEEK, POWERSIL Resin 710 provides excellent electrical insulation, mechanical strength and UV stability. It is solvent-free, has a low viscosity for easier processing and is available in both peroxide-curing and catalyst-curing versions.

Wacker’s exhibition will also feature a range of other specialised products for the composites industry. These include SILRES silicone resins for enhancing electrical insulation and flame retardancy, HDK pyrogenic silica for precise rheology control, VINNAPAS low-profile additives to reduce shrinkage and GENIOSIL organofunctional silanes for promoting adhesion and treating fillers and fibres.

Sri Trang Agro-Industry Public Company Limited (STA) has formally committed to the Science Based Target Initiative for Industrial Greenhouse Gas Reduction towards Net Zero (Phase 3), organised by Thailand Greenhouse Gas Management Organization (TGO) in collaboration with the Center of Excellence in Eco-Energy, Faculty of Engineering, Thammasat University. This declaration positions the company among 16 leading Thai organisations committed to embedding scientifically validated climate targets throughout their operations and supply networks.

STA has established a target to cut Scope 1 and 2 emissions by 23 percent by 2030, using 2024 as its reference point, with the ultimate ambition of reaching net zero by 2050. These goals directly support the international objective of capping global warming at 1.5 degrees Celsius. Beyond direct emissions, the company is enhancing its rubber and teak plantations to function as carbon sinks, generating certified credits while supplying raw materials. This strategy aligns with its net zero pathway and responds to the European Union’s Corporate Sustainability Due Diligence Directive, which promotes heightened corporate environmental accountability.

By embracing this initiative, STA underscores its vision of evolving into a low-carbon, fully integrated natural rubber enterprise. The company aims to reconcile commercial growth with ecological and social stewardship, thereby aiding Thailand’s wider shift towards a sustainable, low-carbon future.