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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Birla Carbon, a leading global manufacturer and supplier of high-quality carbon materials, has been awarded the prestigious Platinum sustainability rating by EcoVadis, ranking it within the top one percent of all assessed companies globally. This honour recognises the firm’s enterprise-wide leadership in integrating sustainability across its operations, innovation and value chain.

The evaluation specifically commended its strong performance across four key areas: Environment, Labor & Human Rights, Ethics and Sustainable Procurement. This achievement is further validated by extensive third-party certifications, with over 75 percent of operations certified to international standards including ISO 14001, ISO 50001, ISO 45001, SA8000 and ISO 27001, underscoring the consistency and strength of its sustainability management systems.

John Loudermilk, President and CEO, Birla Carbon, said, “This Platinum rating reflects the steady progress we are making in embedding sustainability at the core of our business. Our growth strategy is geared towards delivering sustainability through innovation, operational excellence and responsible practices across our global footprint. We continually invest in sustainability and circularity-driven processes, keeping our operations sustainably efficient while creating long-term value for our customers, partners, communities and employees. Our sustainability strategy, Share the Future, serves as a roadmap to a sustainable future and guides our actions towards our aspiration of reaching net zero carbon emissions over the next 25 years. Being recognised among the top one percent of companies globally is a testament to the commitment of our teams worldwide.”

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The Yokohama Rubber Co., Ltd. recently conducted an educational seminar for local natural rubber farmers in partnership with the Surat Thani branch of the Rubber Authority of Thailand (RAOT). This marked the 10th such event since the programme's inception in 2020, involving 50 local farm households. Attendees received complimentary fertiliser, developed with RAOT's expertise, as part of the ongoing support.

The seminar curriculum covered essential agricultural topics, including soil and plant nutrition, correct fertiliser application and methods to prevent contamination in natural rubber. To commemorate the 10th seminar, the programme was expanded to include guest speakers from local government, police and healthcare. These guests addressed broader community and safety issues, such as human rights for foreign and minority workers, road safety and occupational health. A particular focus was placed on practical well-being, with the local hospital director offering guidance on preventing injuries during tree tapping and managing encounters with poisonous insects.

Post-event feedback from participants was overwhelmingly positive. Many expressed that they gained new, systematic knowledge about cultivation practices, despite years of experience. Several noted that hearing directly from a rubber manufacturer reinforced the critical importance of purity in their product. Others found the health and safety advice immediately useful. The engaging delivery of the seminar was also highlighted, with one farmer mentioning a desire to recommend the valuable and enjoyable experience to peers.

This initiative is a direct implementation of a memorandum of understanding (MoU) signed between Yokohama Rubber and RAOT in January 2020. The MoU focuses on economic support for farmers and improving supply chain traceability, aligning with the company's Procurement Policy for Sustainable Natural Rubber. Hosted in the region where Yokohama’s Thai natural rubber processing subsidiary, Y.T. Rubber Co., Ltd. (YTRC), operates, the seminar exemplifies the policy's guideline to support small-scale farmers within the supply chain.

As a founding member of the Global Platform for Sustainable Natural Rubber (GPSNR), Yokohama Rubber is committed to advancing these principles. The company views such efforts as integral to creating shared value under its sustainability slogan, ‘Caring for the Future’, and contributes to broader United Nations Sustainable Development Goals through the promotion of sustainable raw material procurement.

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In a significant event for India’s rubber sector, Minister for Ports, Co-operation & Devaswoms V N Vasavan inaugurated a ceremony for the transfer of innovative latex-based paint technology. This eco-friendly paint, a product derived from natural rubber, was developed by the Rubber Products Incubation Centre of the Rubber Research Institute of India. The technology was formally handed over to Kerala Paints Industries Private Ltd., with the Minister highlighting the event's historic nature for launching a sustainable product and stressing the importance of increasing domestic natural rubber consumption to improve grower returns.

Rubber Board Executive Director M Vasanthagesan outlined the centre's role in converting research into market-ready goods, reaffirming the Board's dedication to creating innovative, value-added rubber products. The gathering also heard remarks from several key figures, including Mahatma Gandhi University's K V Dayal, RRII Director Dr Debabrata Ray, RRII Senior Scientist Dr Shera Mathew and Kerala Paints' Managing Director Midhun P Pullumettel.

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The Association of Natural Rubber Producing Countries (ANRPC) has released its Monthly NR Statistical Report for November 2025, providing an overview of key developments in the global natural rubber sector.

While a modest rise in global production of 1.3 percent is anticipated for the year, this follows a revised, lower output forecast for Indonesia. Concurrently, worldwide demand is projected to grow by a more subdued 0.8 percent, bolstered by an upward adjustment in Indonesia's own consumption figures.

Recent price pressures have emerged due to this combination of uncertain supply, influenced by unpredictable weather patterns and generally muted demand. However, there are sporadic positive indicators, including noticeable recoveries within the tyre sector across some regional markets.

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