Polymer producers have responded to the changing tyre industry expectations, their innovations take into account a more reactive functionality within polymer architecture, and this is closely matched by increasingly greater degrees of filler surface chemistry. As a result, tyre compound properties may now be tailored to meet quite specific tyre performance targets.

Tyre processing methods also underwent progressive stages of modernisation in recent years, for example, more sophisticated reactive mixing technology together with high-speed extrusion systems allowing for direct extrusion onto the building drum become established as cost effective production routes for many of the major producers.

These advancements however bring about their own conflicts, processing pathways involving multiple stages, often with the ability to rework compound or adjust rheological properties by additional time or energy input during the process are no longer viable options for most tyre producers. It has thus become necessary to achieve processability through an increasingly narrow operating window.

Formulations optimised to achieve peak tyre performance in most cases also tend towards more challenging processing characteristics. This is to be expected; the use of high and narrow molecular weight reactive polymers alongside fillers having high surface area and chemistry, often in loadings above that of the polymer are the norm. The trend towards usage of high loading of plasticiser and resinous materials to adjust tyre tread grip and traction response all contribute to a less forgiving processing nature. Often those compounds that are highly reinforced appear the most fragile during processing and poor green strength with an easily tearing or crumbly compound appearance are often-discussed processability issues. By contrast, the use of high loadings of resins and plasticisers, for example in winter or high-performance tyre formulations, results in compounds that during processing can more resemble chewing gum than tyre treads!

The use of process additive chemicals in an attempt to overcome the processing limitations observed gives rise to further conflicts; Lubricant additives might improve compound surface appearance; however, green strength will probably further reduce due to the unwanted softening effect. The same is true for release additives where lower tack unfortunately remains at a higher value than the also lowered tensile strength of the compound. Filler dispersion is often targeted by additives, however higher loading of fillers mandate equally higher additive loadings, we should more accurately discuss loading as “parts per hundred of filler” not rubber, and under the appropriately higher additive loading, the risk of interference with vulcanisation properties or even additive migration leading to surface bloom become realistic concerns.

Conflicting performance characteristics

The development team at Schill + Seilacher has recognised the need to decouple conflicting performance characteristics found within conventional process additive chemistries. As a result, innovation within our Struktol® range offers tyre compounders opportunities to achieve processability without compromise.

Reduced viscosity leading to better extruder flow properties and improved surface appearance, whilst at the same time achieving an increased compound green strength can be realised by use of Struktol HT 300, a new generation of reactive process additive.

An extract of key processing and property influence in a typical highly silica filled sSBR tread compound are highlighted in the following data.

Significantly lowered Mooney viscosity as well as better mixer batch off with reduced sticking to the mixer rotor and gate with Struktol HT 300 are observed.

An increase in compound green strength was obtained by the addition of Struktol HT 300; this is the opposite of expectation for conventional process additive chemistry, where reduced viscosity is obtained. In addition, the filler dispersion as evidenced by a reduction in the so-called “Payne Effect” as tested in uncured compound by means of RPA strain sweep, is also improved.

Lab extrusion trials, using cold feed extruder demonstrate improved surface appearance and lower compound pressure achieved by use of Struktol HT 300, both desirable processing conditions.      

Physical properties are also acceptable, with a progressive increase in tensile strength an elongation and maintenance of stiffness with loading of 6 phr of process additive, only at higher loading of 12 phr would a balancing slight reduction in process oil be required.

Compound hardness remained unchanged alongside improved wear resistance, as measured by DIN abrasion loss testing, even when using higher loading of process additive, are important aspects.

The ability to decouple the relationship between lubrication, important for improved rheological behaviour, and the maintenance of strength and stiffness in both the uncured and vulcanised condition is only possible with such new and innovative class of process additive. This departure from conventional thinking offers the tyre compounder significant degree of freedom to retain the benefits in terms of easier processability without sacrifice of key tyre performance properties.

In this example, the use of Struktol HT 300 prioritised green strength alongside reduced viscosity. By contrast, our new Struktol HT 250 decouples release from other properties, especially effective for winter tyre tread; compound stickiness is resolved without compromise of viscoelasticity.

Ensuring that migration and ultimately bloom within rubber compounds is kept to the lowest level is important for final article aesthetics, for tyres additional considerations arise; they are composite structures, therefore it is imperative that chemicals do not migrate across boundary layers in an uncontrolled manner, which could result in changed behaviour or interfacial adhesion failure over time. In order to limit migration, the compatibility, solubility and concentration of chemicals are carefully considered. However, one method of ensuring long-term stability involves chemically binding the additive within the vulcanisation network.

At Schill + Seilacher, we have achieved this degree of crosslinking capability for a number of new-generation Struktol process additives. Their usage allows the compounder to avoid completely the risk of migration and bloom due to additive presence.

Photographs of two vulcanised rubber sheets based on the same formulation. On the left-hand side, evidence of typical surface bloom, which may occur due to migration of a conventional process additive, on the right, containing reactive additive Struktol HT 600 as replacement, it can be seen that bloom was eliminated.

This technology also opens tremendous opportunities to “fix” process additives in place within the respective component, the role of additives withinthe cross-linking mechanism may additionally lead to vulcanisate performance characteristics.

                                                                                  One interesting tyre related example involves the development of a superior tyre curing bladder performance, here we have developed new reactive plasticisers called Struktol HT 815 and Struktol HT 820, their use is directed towards resin-cured butyl rubber. This combination of polymer and curing system provides for superior heat resistance with excellent flex fatigue resistance and is used as the basis for tyre curing bladders. Here the replacement of widely used castor oil as plasticiser with new Struktol HT 800 series product leads to a significantly improved bladder performance life, with greater stability in viscoelastic properties. Reduced stiffening of the bladder, due to lower degree of plasticiser migration translated into a much lower flex-cracking rate, especially after high temperature steam ageing.

Reactive Struktol plasticisers, HT 815 and HT 820 exhibit a significantly reduced flex cracking rate when compared to the widely used castor oil, which readily migrates from the bladder; as a result, significant extension of bladder service life is possible.

New reactive process additives, with tailored functionality to closely match the specific chemistry of polymers, fillers and cure systems are actively developed. These innovative products under the Struktol brand offer tyre compounders a more comprehensive toolkit in order to tailor compound performance to meet tyre performance demands. The conflicts of property versus processability diminish and new possibilities emerge!

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Synthos, recognised as Europe’s foremost synthetic rubber producer and a global leader in solution styrene butadiene rubber, has secured the EcoVadis Gold Medal once again. The company, also a top European manufacturer of expanded polystyrene, continues to rank among the world’s most sustainable businesses.

The 2026 assessment placed Synthos in the 97th percentile, with its highest marks received in labour rights, human rights, ethics and environmental stewardship. This achievement underscores steady advancement across multiple sustainability fronts and highlights a sustained dedication to responsible expansion and continuous innovation.

EcoVadis operates as a premier global evaluator of corporate sustainability, judging firms on environmental impact, social responsibility, ethical conduct and supply chain management using international standards. The Gold Medal’s annual renewal demands that Synthos consistently remain within the top three percent of all rated companies worldwide.

This recognition affirms that Synthos’ sustainability measures are both persistent and methodical. The company supports its long-range climate and circular economy goals through participation in the UN Global Compact and reporting aligned with ESRS and GRI standards. Synthos will keep leveraging EcoVadis feedback to refine future priorities and advance its ongoing sustainability journey.

Agata Gładysz-Stańczyk, CEO, Synthos, said, “Receiving the EcoVadis Gold Medal again confirms the importance of sustainability within our strategy and the commitment of Synthos teams across all locations. While we are proud of this achievement, we also see sustainability as a continuous journey. It is embedded in how we innovate, how we operate, and how we create value for our customers, employees, partners and communities. This recognition encourages us to continue strengthening our ambitions and driving further progress.”

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The Rubber Board Statistics Consultative Panel reviewed the performance of India’s natural rubber sector during its 29th meeting at the Rubber Board Headquarters in Kottayam. The panel, which includes representatives from small and large growers, producers’ societies, dealers, processors and tyre manufacturers, examined key indicators such as production, consumption, imports and exports. India remains the sixth-largest natural rubber producer globally.

Indian natural rubber production grew by 3.4 percent in the 2025-26 period, rising to 905,000 tonnes from 875,000 tonnes the previous year. Favourable weather across major rubber-growing regions increased tapping days and productivity. Board initiatives like rain guarding, self-tapping, scientific practices, skill programmes and disease control supported output, while Kerala’s Rubber Production Incentive Scheme also encouraged continued tapping.

Domestic natural rubber prices strengthened, renewing grower interest in tapping. Prices that rose sharply in 2024–25 showed relative stability in 2025–26, narrowing the gap with international rates. The trend continued into early 2026, with RSS-4 peaking at INR 262 per kg on 14 May. Meanwhile, total natural rubber demand rose 1.2 percent, though the auto tyre sector, accounting for nearly 64 percent of consumption, declined by 4.0 percent. The general rubber goods sector posted robust growth instead.

The panel noted a 16.7 percent decline in natural rubber imports, falling to 459,000 tonnes from 551,000 tonnes. However, imports of compounded rubber under HS Code 4005 increased significantly, reaching 349,000 tonnes from 245,000 tonnes in the previous year. Consumption of natural rubber rose 1.2 percent to 1,427,000 tonnes from 1,410,000 tonnes in 2024-25.

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Pyrum Innovations AG has secured unlimited delivery approval from Continental for its ThermoTireBlack (TTB), a recovered carbon black produced at the company’s new milling and pelletising facility in Dillingen/Saar. Following the approval, Continental officially commissioned all units tied to the plant expansion at Pyrum’s main site.

The milling and pelletising plant shifted to regular production in April 2026, operating at a capacity of 750 kilogrammes per hour. A short-term capability analysis conducted by Pyrum confirmed that ThermoTireBlack delivers consistent process conditions and stable, reproducible quality. After a subsequent audit, Continental granted full supply approval, specifically praising the new machine’s excellent short-term performance metric (Ppk).

This latest approval for TTB follows previous clearances granted in 2024 for the shredding plant and the TAD2 and TAD3 thermolysis reactors, giving Pyrum complete supply approval for its Dillingen/Saar facility. Through added improvement measures, the company expects to reach the target maximum TTB production volume after a planned modification in the third quarter of 2026, significantly expanding capacity and strengthening Pyrum’s role as an industrial raw material producer and pyrolysis technology leader.

Pascal Klein, CEO, Pyrum Innovations AG, said, “Continental’s unlimited delivery approval for our new milling and pelletising plant is a major milestone for Pyrum. It confirms not only the consistently high quality of our ThermoTireBlack but also the industrial maturity of our entire production chain. We are proud to meet the automotive industry’s high standards and to further expand our close and trusting partnership with Continental. With the approval of the new plant, we are laying the foundation for further growth and a significant increase in revenue in the current year.”

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The German Rubber Industry Association (wdk) has sounded an alarm over an exceptionally difficult economic situation facing the rubber sector. Soaring raw material prices and persistently high energy costs, exacerbated by the Iran war, are coinciding with weak industrial demand. wdk Chief economist Michael Berthel noted an almost unprecedented economic disparity, as raw material costs approach historical highs from 2011 and 2022 while a lack of demand prevents any offset for manufacturers.

Since the final quarter of 2025, prices for key inputs have risen sharply. Natural rubber has jumped more than 40 percent within months, while butadiene-based synthetic rubbers have increased over 30 percent. EPDM synthetic rubber, carbon black and oil-based plasticisers have all risen more than 20 percent, with some individual chemicals exceeding 40 percent cost growth in just a few weeks.

Energy prices remain a major burden, with Middle East developments fuelling market uncertainty. Risks to international transport and supply chains persist, and German rubber companies are closely watching potential impacts on raw material availability and global logistics flows.

Berthel warned that firms face mounting pressure from high costs, geopolitical instability and structural disadvantages in Germany, with no short-term relief in sight. The industry depends heavily on fair and reliable partnerships across the value chain, as processing companies alone cannot absorb the current strain. He called for fair solutions and a shared understanding of this exceptional situation.

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