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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Kraton Corporation, a leading global producer of speciality polymers and high-value biobased products derived from pine chemicals, has revealed a new strategic initiative for its Berre, France facility. The plan involves streamlining its polymer operations to concentrate exclusively on manufacturing USBC products, which will result in the cessation of HSBC production at that site.

This move is designed to bolster Kraton's long-term competitiveness by optimising its manufacturing footprint in reaction to a global overcapacity for HSBC. The company has formally started an information and consultation process with the local Works Councils, with a final decision expected following this mandatory period. The company has reaffirmed its commitment to supplying HSBC from its broader global network and to leveraging its worldwide presence to continue adapting to market demands.

Prakash Kolluri, President, Kraton Polymers, said, “Our aim with this plan is to strengthen Kraton’s long-term competitive position by optimising our manufacturing footprint in response to changing market dynamics associated with global overcapacity of HSBC production capability. With this step, we are preparing Kraton for a sustainable future by securing Kraton’s position as the leading global HSBC producer. Kraton is fully committed to supporting our customers through this transition with supply of HSBC products produced within our unmatched global manufacturing network. We recognise the impact of these actions, and are committed to a safe, respectful and supportive transition. The health, safety and well-being of the employees remain our top priorities.”

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Continental is accelerating its transition towards a circular economy by systematically increasing the use of renewable and recycled materials in its tyres. The company, which averaged a 26 percent sustainable material share in 2024, has set an ambitious target to raise this to at least 40 percent within five years. This strategy involves not only internal innovation but also actively encouraging its supply chain to develop and provide more sustainable raw materials.

A critical area of development is finding green alternatives for reinforcement materials like steel and textiles, which are essential for tyre safety, durability and performance. These materials can constitute over 18 percent of a passenger car tyre, and even more in commercial vehicle tyres. Continental is already integrating recycled steel and is pioneering the use of polyester yarn made from recycled PET bottles. Depending on the tyre size, the carcass of a single passenger car tyre can incorporate the equivalent of up to 15 bottles. This recycled polyester, developed with partner OTIZ, is verified to cut CO₂ emissions by approximately 28 percent compared to conventional materials and is already featured in production tyres like the UltraContact NXT.

The company's sustainable material portfolio extends beyond reinforcements. It includes synthetic rubber derived from used cooking oil, bio-based resins from waste streams and silica obtained from rice husk ash. Complementing these material advances is a commitment to greener manufacturing processes. Together with Kordsa, Continental has developed COKOON, an adhesion technology that bonds textiles to rubber without harmful chemicals. In a move to uplift the entire industry, this innovative solution has been made available to all tyre manufacturers as a free, open-source license, demonstrating Continental's broader commitment to fostering industry-wide sustainability.

Dr Matthias Haufe, Head of Material Development and Industrialization, Continental Tires, said, “We are not reinventing the wheel – but we are reinventing the tyre, with more sustainable materials and more environmentally compatible production processes. It’s not just about the rubber itself. We also focus on the materials that give the rubber its shape and make tyres stable and safe. Recycled steel and polyester yarn made from recycled PET bottles are important for more sustainable tyre production. Our goal is to use at least 40 percent renewable and recycled materials in our tyres within five years. Every alternative material brings us an important step closer to this goal. When it comes to sustainability, it’s not just the materials we switch to, but also those we deliberately do without.”

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Pyrum Innovations AG has officially announced that it will break ground on its next wholly-owned recycling facility in Perl-Besch on 14 November 2025. This new facility is a landmark project for the company, designed to be its largest to date and more than double its existing recycling capacity by processing in excess of 22,000 tonnes of used tyres each year.

The financial framework for this expansion is already taking shape. The project is supported by a diversified funding strategy that includes drawing on a EUR 25 million credit line from BASF and a committed debt financing term sheet from a major European bank. Finalising the package is contingent upon an agreement with Saarland authorities regarding land costs. Crucially, securing the Perl-Besch financing will unlock access to further substantial funding, including a second loan tranche from BASF, paving the way for additional projects in the company's rollout plan.

From a technical and logistical perspective, the Perl-Besch plant will be a state-of-the-art operation. It will be constructed on a 25,000-square-metre site in the strategically important border triangle of Germany, France and Luxembourg. The integrated facility will comprise a shredder plant, three next-generation Pyrum reactors, its own power plant and a grinding and pelletising plant. Insights gained from the existing plant in Dillingen are being directly applied to optimise construction and commissioning, aiming for a faster ramp-up to full production. The site was selected for its superior logistical advantages, offering direct connections to the Moselle River, railway lines and a nearby motorway to efficiently manage material flows from across Europe.

This new facility is central to Pyrum's financial roadmap, with the company projecting it will reach break-even upon its commissioning in 2027. Achieving this milestone is anticipated to create significant momentum and provide a solid foundation for the accelerated rollout of the company's broader project pipeline.

Pascal Klein, CEO, Pyrum Innovations AG, said, “Now that all the legal formalities have finally been clarified – development plan, planning permission and access to the site – we can hardly wait for things to visibly get underway. In the background, planning is already well advanced: The site has been prepared, numerous plant components with long delivery times – so-called long leads – have been ordered and the architect’s tenders for the ground work are underway. During construction, we will also benefit from the experience we have gained from the expansion of our main plant in Dillingen, so we are planning to start production in Perl-Besch in 2027.”

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Capital Carbon, a brand under India's Rathi Group, has successfully commissioned its new greenfield Recovered Carbon Black (rCB) facility in Gummidipoondi, Tamil Nadu. This development dramatically boosts the group's total rCB manufacturing capacity to 20,000 metric tonnes per year, a significant rise from its previous 5,000-tonne capacity.

The group distinguishes itself through complete vertical integration, handling the entire process from shredding end-of-life tyres to pyrolysis. This operation transforms waste into valuable materials, including rCB, fuel oil, steel wires and pyrolytic gas. The company utilises this gas for process heating, while the carbon char is either refined into rCB or supplied to cement plants as a sustainable energy source.

Ravi Rathi, Director, Rathi Group, said, "As Recovered Carbon Black gains wider acceptance, the industry continues to prioritise quality and consistency – and that's exactly what we've focused on addressing.”

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