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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WACKER has earned a distinguished ‘A’ rating in the 2025 CDP sustainability assessment for its climate protection management. This is Wacker’s third time in a row on the A list by the global environmental non-profit organisation. Beyond the climate category, WACKER maintained its strong standing in water security, again achieving an A- leadership rating. In the forests category, the company secured a B management-level score. These consistent results highlight WACKER’s ongoing commitment to holistic environmental responsibility and transparent reporting across all key sustainability areas.

The CDP, a globally respected non-profit formerly known as the Carbon Disclosure Project, conducts the world’s premier environmental disclosure system. It annually evaluates thousands of organisations on behalf of investors, using a detailed questionnaire that spans climate change, water security and forests. Scores follow an A-to-F scale, with an A denoting exemplary performance and disclosure.

Among over 22,100 companies evaluated worldwide, WACKER’s top climate score places it in the premier tier. According to CDP, such a rating reflects comprehensive, high-quality data disclosure and robust transformation strategies.

Peter Gigler, Head of ESG at WACKER, said, “We have our sustainability performance independently audited by CDP every year, so we’re very pleased that we were able to maintain our top rating for the third time in a row.”

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Midas, Asia’s largest manufacturer of tyre retreading materials, has launched O-rings designed for off-the-road (OTR) tyres, aimed at delivering reliable sealing performance in demanding operating conditions.

The O-rings are manufactured using high-quality natural rubber and are formulated to improve physical properties and ensure dimensional stability. According to the company, the product has been tested over many years in harsh environments and is intended to provide consistent, trouble-free performance in OTR tyre applications.

Midas said only REACH-compliant raw materials are used in the manufacture of the O-rings, underscoring its adherence to safety, quality and international regulatory standards.

Founded 56 years ago, Midas supplies tyre retreading materials to customers in more than 60 countries. The company said the launch reflects its continued focus on developing performance-oriented solutions for the global tyre and retreading industry.

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Toyoda Gosei has successfully commercialised automotive weatherstrips using recycled rubber, starting with the new Toyota RAV4. This marks a significant breakthrough in a field where rubber has historically been difficult to reuse, often ending up incinerated instead of truly recycled. Unlike steel or plastic, rubber recycling requires devulcanisation, a complex process that traditionally weakens the material and leaves behind unpleasant odours.

Through dedicated refinement of its proprietary devulcanisation technology, the company has overcome these longstanding quality hurdles. The advancements have dramatically increased the usable proportion of recycled material in automotive parts from under five percent to 20 percent, an achievement honoured by a Toyota Motor Project Award.

Looking ahead, Toyoda Gosei aims to extend this technology beyond synthetic rubber to include natural rubber, which is used in far greater volumes. The broader corporate ambition is to collaborate with automakers and partners to establish a full circular system. This system would collect and regenerate rubber from end-of-life vehicles, positioning the company as an industry leader in enabling both decarbonisation and sustainable resource circulation.

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Pursuing its strategic goals for 2030, Michelin is actively extending its technological leadership into adjacent, high-value sectors. This expansion is being accelerated through two key acquisitions announced in recent months: Cooley Group and Tex Tech Industries. Both US-based companies are leaders in advanced materials, specialising in high-performance fabrics and coatings, and align strongly with Michelin’s own focus on innovation and quality while bringing complementary geographic and technical strengths.

Cooley Group, marking its centennial in 2026, excels in creating engineered polymer-coated fabrics. Its fully integrated production enables custom solutions for critical applications in healthcare, industrial containment and waterproofing. Similarly, Tex Tech Industries, with over a century of operation, designs and manufactures specialised textiles for extreme demands, including thermal protection systems for aerospace, fire-blocking aircraft interiors and advanced composite materials.

These strategic moves significantly bolster Michelin’s existing position in coated fabrics, notably through its European brand Orca. By integrating Cooley and Tex Tech, Michelin anticipates accelerating its global market reach and increasing the revenue of its Polymer Composite Solutions division by approximately 20 percent, equating to roughly USD 280 million. Given the growing scale of this business, Michelin intends to establish it as a dedicated reporting segment starting in 2026.

The acquisitions, slated for completion in the first half of 2026 pending regulatory approvals, will be transacted in cash, with financial terms currently undisclosed.

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