In 2025, the coating industry is accelerating toward the dual goals of “green transformation” and “performance upgrading.” In high-end coating fields such as automotive and rail transit, waterborne coatings have evolved from “alternative options” to “mainstream choices” thanks to their low VOC emissions, safety, and non-toxicity. However, to meet the demands of harsh application scenarios (e.g., high humidity and strong corrosion) and users’ higher requirements for coating durability and functionality, technological breakthroughs in waterborne polyurethane (WPU) coatings continue apace. In 2025, industry innovations in formula optimization, chemical modification, and functional design have injected new vitality into this sector.
Deepening the Basic System: From “Ratio Tuning” to “Performance Balance”
As the “performance leader” among current waterborne coatings, two-component waterborne polyurethane (WB 2K-PUR) faces a core challenge: balancing the ratio and performance of polyol systems. This year, research teams conducted in-depth exploration into the synergistic effects of polyether polyol (PTMEG) and polyester polyol (P1012).
Traditionally, polyester polyol enhances coating mechanical strength and density due to dense intermolecular hydrogen bonds, but excessive addition reduces water resistance due to the strong hydrophilicity of ester groups. Experiments verified that when P1012 accounts for 40% (g/g) of the polyol system, a “golden balance” is achieved: hydrogen bonds increase the physical crosslink density without excessive hydrophilicity, optimizing the coating’s comprehensive performance—including salt spray resistance, water resistance, and tensile strength. This conclusion provides clear guidance for WB 2K-PUR basic formula design, especially for scenarios like automotive chassis and rail vehicle metal parts that require both mechanical performance and corrosion resistance.
“Combining Rigidity and Flexibility”: Chemical Modification Unlocks New Functional Boundaries
While basic ratio optimization is a “fine adjustment,” chemical modification represents a “qualitative leap” for waterborne polyurethane. Two modification paths stood out this year:
Path 1: Synergistic Enhancement with Polysiloxane and Terpene Derivatives
The combination of low-surface-energy polysiloxane (PMMS) and hydrophobic terpene derivatives endows WPU with dual properties of “superhydrophobicity + high rigidity.” Researchers prepared hydroxyl-terminated polysiloxane (PMMS) using 3-mercaptopropylmethyldimethoxysilane and octamethylcyclotetrasiloxane, then grafted isobornyl acrylate (a derivative of biomass-derived camphene) onto PMMS side chains via UV-initiated thiol-ene click reaction to form terpene-based polysiloxane (PMMS-I).
The modified WPU showed remarkable improvements: static water contact angle jumped from 70.7° to 101.2° (approaching lotus leaf-like superhydrophobicity), water absorption dropped from 16.0% to 6.9%, and tensile strength surged from 4.70MPa to 8.82MPa due to the rigid terpene ring structure. Thermogravimetric analysis also revealed enhanced thermal stability. This technology offers an integrated “anti-fouling + weather-resistant” solution for rail transit exterior parts such as roof panels and side skirts.
Path 2: Polyimine Crosslinking Enables “Self-Healing” Technology
Self-healing has emerged as a popular technology in coatings, and this year’s research combined it with WPU’s mechanical performance to achieve dual breakthroughs in “high performance + self-healing ability.” Crosslinked WPU prepared with polybutylene glycol (PTMG), isophorone diisocyanate (IPDI), and polyimine (PEI) as crosslinker exhibited impressive mechanical properties: tensile strength of 17.12MPa and elongation at break of 512.25% (close to rubber flexibility).
Crucially, it achieves full self-healing in 24 hours at 30°C—recovering to 3.26MPa tensile strength and 450.94% elongation after repair. This makes it highly suitable for scratch-prone parts like automotive bumpers and rail transit interiors, significantly reducing maintenance costs.
“Nanoscale Intelligent Control”: A “Surface Revolution” for Anti-Fouling Coatings
Anti-graffiti and easy-cleaning are key demands for high-end coatings. This year, a fouling-resistant coating (NP-GLIDE) based on “liquid-like PDMS nanopools” attracted attention. Its core principle involves grafting polydimethylsiloxane (PDMS) side chains onto a water-dispersible polyol backbone via the graft copolymer polyol-g-PDMS, forming “nanopools” smaller than 30nm in diameter.
PDMS enrichment in these nanopools gives the coating a “liquid-like” surface—all test liquids with surface tension above 23mN/m (e.g., coffee, oil stains) slide off without leaving marks. Despite a hardness of 3H (close to ordinary glass), the coating maintains excellent anti-fouling performance.
Additionally, a “physical barrier + mild cleaning” anti-graffiti strategy was proposed: introducing IPDI trimer into HDT-based polyisocyanate to enhance film density and prevent graffiti penetration, while controlling the migration of silicone/fluorine segments to ensure long-lasting low surface energy. Combined with DMA (Dynamic Mechanical Analysis) for precise crosslink density control and XPS (X-ray Photoelectron Spectroscopy) for interface migration characterization, this technology is ready for industrialization and is expected to become a new benchmark for anti-fouling in automotive paint and 3C product casings.
Conclusion
In 2025, WPU coating technology is moving from “single-performance improvement” to “multi-functional integration.” Whether through basic formula optimization, chemical modification breakthroughs, or functional design innovations, the core logic revolves around synergizing “environmental friendliness” and “high performance.” For industries like automotive and rail transit, these technological advances not only extend coating lifespan and reduce maintenance costs but also drive dual upgrades in “green manufacturing” and “high-end user experience.”
Post time: Nov-14-2025