Microsphere-reinforced photoluminescent epoxy road markings: optimized formulations for durable, high-visibility performance

Purpose This study aims to design and characterise new photoluminescent (PL) coatings intended for road marking applications, comprising a mixture of a transparent epoxy resin, phosphorescent pigments (SrAl2O4:Eu²+, Dy³+ and ZnS:Cu) and glass microspheres. The aim is to improve road marking durability, visibility and overall safety performance, particularly under low lighting and harsh environmental conditions. Design/methodology/approach Hybrid epoxy coatings were prepared with 5% and 10% pigment contents and sizes of Types 1 and 2 glass beads (sizing ranges of 100–850 µm and 600–2000 µm, respectively). The requisite standardised American Society of Testing and Materials and Deutsches Institut für Normung tests were also performed to evaluate the coatings based on adhesion, abrasion, slip, ultraviolet (UV) stability, water and oil resistance, luminance, dry film thickness and time to dry. Findings Compositions with 8 Wt.% Type 1 glass beads and 5–10 Wt.% SrAl2O4:Eu²+, Dy³+ pigment provided optimal luminosity and strength. The coatings were characterised by an adhesion strength of over 1.5 MPa, an abrasion loss of less than 40 mg after 1,000 cycles and a slip resistance of up to 56 British Pendulum Number (BPN). SrAl2O4:Eu²+, Dy³+ has an average luminosity retention of over 80% (> 400 mcd/m²) after 180 min, which is superior to that of ZnS: Cu-containing compositions. All formulations provided high light-fastness and UV resistance, with an average film thickness of 420–480 µm and an average drying time of 132–207 min. Originality/value The prepared microsphere-strengthened PL epoxy coatings exhibited superior durability and self-illuminative capabilities compared to common retro-reflective materials. To the best of the authors’ knowledge, it is the first time when SrAl2O4:Eu²+, Dy³+-based pigment-epoxy microsphere composites are tuned to exhibit optimal mechanical and optical properties simultaneously, which will prove to be more sustainable and.