Mountains of discarded clothing are rising across the planet. So-called “fast fashion” encourages people to buy cheap clothes that are quickly discarded, leading to enormous waste and pollution. At the same time, synthetic fabrics such as polyester shed tiny plastic particles during washing. These microplastics enter seas, poison marine life and even contaminate the food humans eat.
Global fiber production is about 150 million metric tons per year, with two-thirds synthetic. Polyester alone (primarily, polyethylene terephthalate or PET) accounts for roughly half of all fiber production. Despite the scale of consumption, textile recycling rates remain extremely low; only about 1% of textiles are recycled or reused in the European Union, for example, leaving the rest for landfill or incineration.
Textiles that are recycled are typically subject to depolymerization or thermochemical conversion processes such as pyrolysis, hydrothermal liquefaction or monomer recycling. While these methods recover chemical value, they destroy the molecular architecture that originally required significant energy to create.
At this point, you may be wondering what this has to do with grease.
From a grease maker’s perspective, the properties that complicate textile waste management, including high molecular weight, crystallinity and fibrous morphology, are assets. Fibers readily form structured networks capable of generating yield stress, stabilizing oil and promoting shear-thinning behavior.
In this context, textile fibers may be considered as preformed thickeners. Instead of synthesizing a thickener through saponification or polymerization, the structure already exists and requires only dispersion within the oil.
Approaches that preserve polymer structure therefore offer a potentially more efficient pathway for circular material use by turning a waste into a feedstock.
Historically Speaking
Grease architecture has been defined by chemistries such as lithium complex, calcium sulfonate, aluminum complex, clay or polyurea. The introduction of NLGI’s High Performance Multiuse (HPM) specification shifts that framing: grease is now defined by performance — water resistance, mechanical stability, oil separation, corrosion protection and wear — not thickener identity, which paves the way for alternative thickeners.
The convergence of performance-driven grease design, polymeric thickener technology and a global waste stream dominated by durable synthetic textiles creates a sustainability opportunity not to be missed. Rather than landfilling or burning materials, the time and energy invested to make the fiber architecture can be redirected into grease where they function as novel grease thickener systems pushing us toward lithium-independence.
Using one industry’s problem to solve another’s creates a resilient circular economy where the persistent waste stream of one sector becomes a functional raw material for another. Waste textiles can be capitalized on without reinvesting more time and energy into complex monomer recycling or pyrolysis efforts.
Table 1. Screening and results of various strategies to incorporate PET fibers
| Strategy | Primary Mechanism | Stability While Milling | Yield Stress | Oil Bleed | Overall Outcome |
|---|---|---|---|---|---|
Rerefined base oil only (control) | Viscous suspension | Poor | None | High | Not viable |
Synthetic ester | Improved wetting | Moderate | None | Moderate | Marginal |
High viscosity ethylene-propylene oligomers | Viscosity increase | Good | Weak | Moderate | Failed |
High tackifier | Elastic cohesion | Good | Weak | Moderate | Processing aid only |
Aromatic esters (phthalate / trimellitate) | Increased polarity | Poor – Moderate | None | High | Failed |
Unsaturated estolide | Associative pseudo-network | Good | Weak | Low | Encouraging |
Co-thickened with polymer thickener | Continuous elastomer network | Excellent | Strong | None | Selected system |
Plastic Properties
PET is a highly crystalline polyester with strong dimensional stability, and PET derivatives such as terephthalic acid have previously been investigated in tribological systems. Polyamides already have precedent in tribological systems; oil-impregnated nylon bushings function as structured oil reservoirs capable of storing and releasing lubricant under load. The present question is whether fiberized recycled polymers can perform a similar structural role within grease. Prior attempts to incorporate polymer fibers or recycled polymer materials into lubricants and greases provided a useful foundation for this investigation.
Polymeric and ashless grease systems further support this architectural approach. Polyurea and polypropylene thickeners derive structure from polymer networks rather than metal soaps, offering low ash and strong thermal stability. Fiber reinforcement is common in anti-seize compounds and demonstrates that fibrous phases can enhance load distribution, resist squeeze-out, and stabilize solid dispersions.
Textile-derived fibers as a preformed thickener extend this logic where the fiber forms the grease matrix. Clay-thickened greases provide the closest historical analogue for dispersion-based grease. These systems perform well in open gear and high-temperature industrial service but can suffer from pumpability and shear recovery limitations.
Formulation Challenges
Can waste synthetic textile fibers be structurally upcycled into functional grease architectures using low-energy processing methods and rerefined lubricant base oils? Can they directly serve as structural components within grease systems?
Two synthetic textile waste polymers — PET and nylon-66 — were selected because of their environmental persistence, high embedded greenhouse gas intensity and prevalence in global textile waste streams. The aim was to convert plastics in fiber-form into grease-like lubricating composites form through physical network formation rather than chemical transformation.
Greases were manufactured using a comparatively simple and energy-efficient process involving moderate-temperature mixing, fiber incorporation and three-roll milling. Importantly, the production route avoided the conventional soap grease manufacturing steps of saponification, dehydration and prolonged cook cycles. Instead, structure formation relied entirely on polymer gelation and mechanical incorporation of fibers. The experimental greases were manufactured in a rerefined API Group III base oil, chosen specifically to maximize the amount of “circular content.”
The first phase of the study focused on how to incorporate the PET fibers as the primary thickener. Simply dispersing PET fibers into rerefined or paraffinic base oils was insufficient to create stable grease structures. The use of tackifier and viscosity modifiers also failed to achieve persistent grease-like body or long-term oil retention. Similarly, no meaningful swelling or solvency effects were observed in a number of synthetic and aromatic esters. These findings demonstrated that polarity, solvency and viscosity modifications alone were inadequate for structurally arresting PET fibers in an oil matrix.
A significant breakthrough occurred when a styrene-based thermoplastic elastomer gel system was introduced and created a continuous structural network capable of immobilizing the textile fibers and entrapping the low-viscosity oil phase.
The second phase of the study expanded the approach to nylon-66 fibers and further optimized the balance between fiber loading and polymer gel concentration. Nylon systems generally produced softer textures than PET at equivalent loadings, necessitating evaluation of higher fiber concentrations to achieve NLGI-2 consistency.
Comparison
How well does this new grease system behave like conventional greases?
Comparison with historical grease datasets showed that the textile-fiber formulas exhibited the same levels of non-Newtonian thixotropic behavior as other lithium and polyurea greases. This confirmed that textile-fiber greases are expected to pump and behave similarly to industrial greases formulated with traditional thickeners. The fibers functioned as reinforcing elements within a gel-supported network analogous to the fiber-like architectures of lithium and polyurea greases.
Practical performance was evaluated using dropping point and four-ball extreme pressure (EP) testing. PET grease exhibited a dropping point of 278 degrees Fahrenheit (137 degrees Celsius), whereas nylon grease reached 418 degrees (214 Celsius). Nylon’s superior thermal stability was attributed to its lower crystallinity, amide functionality, and stronger oil affinity, which improved retention of the oil phase at elevated temperatures. Although the mechanism differs from soap-thickened greases, dropping point remained a useful indicator of structural collapse in these polymer-fiber systems. Technically, the industry is shifting away from dropping point claims, but this remains key to marketing toward end users.
In EP testing, textile-reinforced greases achieved a weld load of 126 kilogram force versus 100 kgf for the gelled-oil control, demonstrating that textile incorporation maintained and modestly improved boundary lubrication performance.
Future Work
The central finding is that preserved polymer fibers from textile waste can function as pre-formed grease thickeners in combination with the gel polymer strategy. Unlike conventional grease production, where thickener structure must be generated through saponification or polymerization, textile fibers already possess the cohesion and structure required to form a network. In this sense, textile fibers behave similarly to emerging preformed polymer thickener technologies based on polyamide or polyurea but originate from an existing waste stream rather than new polymer synthesis.
Rheological benchmarking against historical lithium and polyurea datasets confirms that textile scaffold greases form stable, pumpable networks similar in shear-thinning behavior to lithium or polyurea greases. Likewise, dropping points exhibited by PET and nylon fell in the range of calcium soap greases.
This concept reframes fast-fashion polymer waste from a disposal challenge into a potential structural feedstock for grease formulation. Rather than breaking polymer architecture down through chemical recycling, textile fibers can be repurposed directly as network-forming components that stabilize oil and generate grease-like rheology.
Future work should therefore focus on validating textile fibers as a practical preformed thickener platform, including systematic additive response studies, oxidation and water durability testing, mechanical stability evaluation, and pumpability assessment under application-specific conditions. Only through such benchmarking can textile greases transition from proof-of-concept materials to specification-capable formulations aligned with the NLGI HPM grease specification in industrial applications.
Erik Willett, PhD CLS, is president of Functional Products Inc. and specializes in polymer-based lubrication development.