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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The Association of Natural Rubber Producing Countries (ANRPC) has released its Monthly Natural Rubber Statistical Report for June 2026, documenting a period of price resilience within the sector. This stability persisted despite seasonal supply improvements and firm downstream demand, set against a backdrop of significant geopolitical friction and macroeconomic volatility. The month of July presented a starkly different energy landscape compared to June, as renewed regional conflicts and major shipping route disruptions replaced the brief period of stability following the provisional reopening of the Strait of Hormuz.

The escalation in Middle Eastern tensions exerted considerable upward pressure on global energy markets. Brent crude oil averaged approximately USD 83.76 per barrel in July, with the spot price surging to USD 96.95 per barrel by the end of the month. This sharp increase was primarily attributed to fears of potential restrictions on oil shipments through the strategic waterway, amplifying supply risks and embedding a higher risk premium within oil pricing structures.

Physical natural rubber prices exhibited divergent trends across major grades during the month. The Kuala Lumpur market saw SMR-20 average USD 2.22 per kilogramme, representing a month-on-month decline, while STR-20 in Bangkok followed a similar downward trajectory. RSS-3 also registered a decrease, contrasting with RSS-4, which posted a notable gain. Latex-in-bulk prices softened over the same period. Trade flows showed mixed results, as Chinese imports contracted, while significant import growth was recorded for India, Viet Nam and Malaysia. On the export front, shipments from Thailand, Viet Nam and Malaysia advanced, whereas Cambodia and Indonesia experienced moderate declines.

For the full year 2026, the ANRPC projects global production to expand by over two percent to reach 15.279 million tonnes, driven primarily by anticipated increases in Thailand, China, India and Malaysia. However, on a monthly comparative basis, July 2026 production is estimated to be over five percent lower than the same month in the previous year, though seasonal recovery is expected in key producer nations. Global demand is forecast to grow modestly by 0.4 percent for the year, with consumption in July rising year-on-year, supported by robust tyre manufacturing and electric vehicle-related demand, as well as a strong manufacturing performance and record auto sales in India.

Currency valuations saw the Malaysian ringgit and Thai baht trade within defined ranges against the US dollar. Futures markets reflected the mixed sentiment, with the SHFE September 2026 contract averaging 16,802.61 CNY per tonne, while the SGX September 2026 contract averaged USD 2.14 per kilogramme, both registering month-on-month declines. The overall data suggests a market navigating the complex interplay of supply recovery, shifting trade dynamics and persistent geopolitical uncertainty.

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Flexsys, a prominent entity in material science and advanced tyre additives, has announced two significant advancements in its quest to develop a substitute for the chemical 6PPD. The company is progressing towards a new era in tyre manufacturing, having identified two primary molecular candidates that will undergo extensive evaluation. This development follows a prior announcement in November 2025, where Flexsys revealed it had created the first viable alternative to the established antidegradant.

The two finalist molecules have successfully passed rigorous internal and external testing, meeting stringent safety, performance and environmental standards. Significantly, neither compound belongs to the PPD chemical family, and crucially, they do not produce a quinone transformation product during usage. With the initial screening phase complete, Flexsys is now concentrating on expanded testing for these candidates, with the ultimate goal of selecting a definitive replacement for 6PPD in tyre production.

In a parallel effort to ensure environmental safety, Flexsys has formalised a Cooperative Research and Development Agreement with the U.S. Geological Survey. This collaboration is designed to independently and thoroughly assess the potential effects of the two molecules on aquatic ecosystems. Building upon a previous CRADA with the U.S. Department of Agriculture, this new agreement with the USGS represents a critical phase in determining the complete aquatic toxicity profile. The research will employ novel testing methodologies that extend beyond standard chemical registration requirements.

Under the agreement, scientists from the USGS Western Fisheries Research Center, alongside other USGS divisions, will study the molecules and their breakdown products. The focus will be on the impact on Pacific salmon and other aquatic species, utilising innovative cell-line research to pioneer new testing methods. This approach aims to create alternative assessment tools applicable to a wide range of chemicals. The CRADA formalises and expands upon preliminary testing that had already commenced at the research centre.

Flexsys acknowledged the support from the Economic Development Administration’s Tech Hubs Program, as a member of the Akron Sustainable Polymers Tech Hub. Concurrently, the company is optimising the process chemistry for both candidates to facilitate efficient, large-scale production. Both molecules utilise intermediate chemistry similar to that used for 6PPD, allowing the industry to leverage existing manufacturing assets. This strategic approach is expected to promote faster adoption and reduce overall investment costs while Flexsys continues its engagement with global regulatory agencies for commercial approval.

Carl Brech, Chief Executive Officer, Flexsys, said, “The tyre industry has been waiting for two things: a molecule that actually works and independent proof that it is safe. As of today, both are in hand or in motion. With tyre and environmental safety testing underway, the focus has shifted from finding a potential replacement to thorough validation, regulatory approval, scale-up and industry adoption.”

Neil Smith, Chief Technology and Sustainability Officer, said, “This marks a significant milestone for our team, and we’re pleased to announce we’ve narrowed our efforts to two final molecules that continue to meet our strict targets for in-rubber performance, scalability, toxicity profile and environmental sustainability. The selected alternative must be reliable and safe, not only today but for decades to come. USGS expertise provides independent evaluation with a level of rigour we could not execute on our own. We are proud to help pioneer novel toxicity-testing methods and eager to see the results.”

Michael Schmidt, Center Director, U.S. Geological Survey Western Fisheries Research Center, said, “USGS has spent the past five years studying the effects of 6PPD on aquatic species and developing innovative methods to screen the safety of potential alternatives. For nearly a century, the Western Fisheries Research Center has provided objective science to support management of aquatic species across the Western United States.”

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Aircraft tyre retreading may resemble truck tyre retreading on the factory floor, but the similarities end there. Stringent US Federal Aviation Administration (FAA) oversight, exhaustive inspection protocols and extensive documentation make it one of the most tightly regulated segments of the tyre industry. According to President of Central Marketing Inc., these rigorous requirements coupled with high upfront investment and the dominance of major tyre manufacturers have created a niche market where only a limited number of players can compete.

Tire Retread Information Bureau mentions that over 100,000 retreaded tyres are done annually in United States, while another report published by the United States International Trade Commission on retreaded tyres in 2012 stated approximately 80 percent of aircraft tyres in US are retreaded and that retreading saves commercial and military operators over USD 100 million annually.

Since publication of the report over a decade ago, the state of the tyre retreading industry remains quite optimistic. Market Research Future estimated that US aircraft tyre retreading market will reach USD 1.42 billion by 2035, up from USD 948.2 million in 2025.

However, aircraft tyre retreading demands for stricter regulatory oversight than conventional truck and bus tyre retreading.

According to President Central Marketing Inc Edd Burleson, “FAA certification, rigorous inspections, extensive documentation and high entry barriers define the sector, where major tyre manufacturers dominate and independent retreaders serve mainly private aircraft operators.”

In a tete-a-tete with Tyre Trends, he delves into the dynamics of the aircraft retreading industry of United States and North America as his company has been a supplier of retreading machinery in these markets for over four decades.

“Although aircraft tyre retreading follows the hot retreading process, with many of the same steps seen in truck and bus radial retreading, the level of oversight is substantially higher. The process is fundamentally similar but is much more tightly controlled,” contended Burleson.

Everything is Federal Aviation Administration (FAA) certified. The inspection procedures are much stricter, there are more process controls, much more record-keeping and the Federal Aviation Administration oversees the entire process. The basic manufacturing process is similar, but the level of control and inspection is significantly higher.

He added that the dominance of major tyre manufacturers and strict regulatory requirements make it difficult for independent companies to enter the sector. And that’s because the smaller independent retreaders mainly service the private aircraft market rather than the major commercial airlines.

“Not everyone has the inspection capabilities or qualifications required to obtain an FAA license to retread aircraft tyres. It’s a speciality market and different from commercial truck tyre or OTR retreading,” he added.

Obtaining regulatory approval requires substantial investment before any licence is granted. A company will have to establish a plant, demonstrate its entire retreading process, undergo inspections and prove that it has the capability to perform aircraft tyre retreading.

“It’s not simply a matter of applying for a license and getting approval. You take on the risk of investing in the facility and processes before knowing whether you’ll actually be approved,” Burleson said.

In addition, entering the market isn’t easy because new plants will compete against major players like Goodyear, Michelin, Dunlop and Bridgestone. Hence, as an independent company, it’s generally conducive to enter the private aircraft market.

Burleson said the industry’s structure further limits competition because manufacturers sell tyre services rather than tyres themselves.

“The major players manufacture the new tyres and they’re not selling tyres but the service, most which is charged per cycle,” he said.

MARKET DYNAMICS

Aircraft tyre retreading remains a stable and highly specialised market. “The market across North America is well developed because airlines routinely retread their tyres as part of their operating model,” said Burleson.

The airlines themselves are responsible for maintaining the tyres including tyre pressure and general maintenance. The tyre company is responsible for supplying the tyres to the airlines and get paid on a per cycle basis. A cycle here means an entire take-off to landing cycle.

The number of times an aircraft tyre can be retreaded depends on the tyre size and aircraft type. “Some aircraft tyres can be retreaded two or three times, while others can be retreaded five or six times,” Burleson said.

Retreading significantly lowers operating costs for airlines by extending tyre life, he added. As a result, the cost per cycle comes down substantially. If airlines charged the same cost per cycle while using only new tyres, it would be three to four times more expensive.

The company supplies shearography inspection systems, repair machines, buffing machines, rubber extruders, laser engraving systems and curing presses. Its clientele includes Michelin, Bridgestone, Goodyear, Dunlop and one independent aircraft retreader, Wilkerson, in United States.

Besides, Central Marketing has been a servicing supplier to the tyre retreading industry as well as off-the-road, light truck, aircraft and the new tyre industries for 49 years. Its top-of-the-line computerised products have varying degrees of automation. Its base of operations is in Colonial Heights with a staff of 24 people.

Burleson described aircraft retreading as a stable market with limited growth because of the relatively small number of retreaders.

“The market is limited by the number of retreaders so it’s more of a stable market. Growth is typically around 3–5 percent annually. There’s no major boom like you’d see in an emerging market,” he said.

Unlike commercial truck tyre retreading, the aircraft sector in North America has not been affected by imports from Asian manufacturers.

“Bridgestone has one plant in US, Michelin has one, Goodyear has two and the total number of aircraft retreading plants isn’t very large,” Burleson said.

Outside United States, the market is even smaller.

“There’s a small aircraft retreader in Mexico and there isn’t any aircraft tyre retreading in Canada,” he said.

MAKING THE RETREADS

Aircraft retreading equipment differs from machinery used in commercial tyre retreading because aircraft tyres require greater precision during processing. The tyres are much more difficult to handle and buff.

Repairs are limited to very specific tolerances. Companies have to ensure their process doesn’t damage the body plies during buffing. There may be need to replace breaker belts and perform other specialised repairs.

Each stage of production must comply with tightly controlled specifications. Every step of the process has to meet a specific specification.

“If the temperature drops by more than a set number of degrees during curing, then the tyre may no longer be acceptable. Aircraft retreading is governed by much stricter rules and regulations because of the nature of the application. You’re transporting people, so there can be absolutely no compromise on safety,” Burleson said.

Burleson identified shearography as the most significant technological advancement in aircraft tyre retreading.

“I would say the biggest advancement has been shearography. Another important development is laser engraving. Each time an aircraft tyre is retreaded, it’s assigned an ‘R level’ to ascertain the exact retread generation,” he said.

Laser engraving the sidewall makes record-keeping much more accurate compared with using stencils. Considerable progress has been made in buffing technology through computerised profiles too.

Automation is increasing in selected areas, although regulations limit the use of artificial intelligence as a trained human inspector must still verify and confirm the results.

SUSTAINABLE OPERATIONS

Aircraft retreading makes a significant contribution to sustainability by extending tyre life as each tyre is retreaded between three to six times.

The economics of cost savings and inexistence of Asian imports have also written an optimistic future for aircraft tyre retreading in US till now, but challenges are present for retreading machinery suppliers.

“We don’t make the machines ourselves but procure it from different countries for the US market. The challenge is providing equipment that meets our customers’ requirements and being able to service that equipment when it’s installed in their plants,” said Burleson.

However, he said that the broader retreading industry is undergoing consolidation. “In US, the East Coast is probably the largest market, followed by the West Coast, where the major population centres are,” he said.

Retreading plants are becoming larger in the TBR segment, processing higher volumes and adopting more automation. At the same time, smaller retreaders are finding it increasingly difficult to compete and many are going out of business.

Aircraft retreading is insulated from those market trends because of its unique business model.

Summing up the sector, Burleson reiterated that aircraft tyre retreading should not be viewed in the same way as commercial tyre retreading.

“The main thing people need to understand is that aircraft retreading is a speciality market. Although the process follows many of the same basic steps as commercial tyre retreading, it’s performed under much stricter controls because of the critical nature of its application. It’s not something that anyone can simply enter. It’s a highly specialised industry. Even though it’s still retreading, it shouldn’t be viewed in the same way as the normal commercial TBR market,” he noted.

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The Government of Kerala has approved the twelfth phase of the Rubber Production Incentive Scheme, extending support to natural rubber growers through a guaranteed price mechanism.

The scheme is designed to ensure a price of INR 250 per kilogram for RSS 4 grade sheet rubber. Growers who are not yet enrolled may register for the programme until 23 October 2026, according to an official statement issued on 6 August in Kottayam.

Applicants seeking new registration must submit an Aadhaar card, bank passbook copy, current year land tax receipt and a photograph to their respective Rubber Producers’ Societies. Existing participants are required to renew their registration by providing land tax receipts for the 2026–27 period.

The release added that sale invoices or purchase bills submitted under the scheme must originate from licensed dealers who comply with statutory return requirements. Further details are available through the nearest Rubber Board office.

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