Next-Generation Photoinitiators: Unlocking High Performance in UV-Cured Composites

The composites industry is increasingly turning to UV curing as a transformative technology for automated and efficient production. Recent research conducted by IGM Resins demonstrates that UV-cured composites using new-generation photoinitiators and sensitizer combinations can match the mechanical performance of traditional cold-cure systems while offering significant process advantages.

The composites industry is increasingly turning to UV curing as a transformative technology for automated and efficient production. Recent research conducted by IGM demonstrates that UV-cured composites using new-generation photoinitiators and sensitizer combinations can match the mechanical performance of traditional cold-cure systems while offering significant process advantages.

Strategic Advantages of UV Technology 
UV curing replaces conventional peroxide initiators and metal accelerators with photoinitiators that absorb specific light wavelengths to generate free radicals and initiate polymer chain formation. This shift provides composite manufacturers with several critical advantages:

• Speed and Efficiency: In pure resin tests on 4 mm castings, standard MEKP (methyl ethyl ketone peroxide) / cobalt systems require 35–40 minutes to reach peak exotherm, while UV systems achieve peak exothermic temperatures of up to 120°C in as little as 17 seconds. This enables significant gains in mold utilization; for example, filament-wound parts can be removed from the mold minutes after winding.
• Cure on Demand: Unlike peroxide systems with a defined pot life, UV-curable resins remain workable indefinitely when protected from light. This gives manufacturers unlimited layup time and full control over when to initiate the curing process.
• Sustainability and Safety: Fast surface polymerization rapidly "seals" the laminate, resulting in lower styrene emissions compared to open-cure processes. Additionally, a UV station shorter than 1 meter can replace a heating oven longer than 10 meters (in cases where UV curing replaces thermal curing), significantly reducing both floor space and energy consumption.
• Versatility: UV curing is compatible with industry-standard resins, including unsaturated polyesters and vinyl esters, and can be applied across processes ranging from CIPP (cured-in-place pipe) to filament winding, pultrusion, and vacuum infusion.

Solving the Through-Cure Challenge
The primary obstacle to UV composites has been achieving full through-cure in thick (4–200 mm) and fiber-reinforced laminates. If photoinitiator concentration is too high, the surface cures too rapidly and effectively "blocks" light from reaching deeper layers; if too low, it results in incomplete cure.

To solve this, IGM employed 395 nm LED lamps. The selection of a longer wavelength provides deeper light penetration into the material. Moreover, since many photoinitiators that function under LED conditions also absorb UV light produced by mercury lamps, formulations optimized for LEDs are likely to work with broadspectrum mercury UV lamps as well.

Test Methodology and Results IGM's work in partnership with Parthian Composite Excellence focused on achieving mechanical equivalence between UV and peroxide systems using an industry-standard isophthalic unsaturated polyester resin.

1. Pure Resin Performance 
Initial tests on 4 mm pure resin castings compared Omnirad® 819, TPO-L, and BAPO-L with a peroxide reference. UV systems reached peak exotherm temperatures of up to 120°C in 17 seconds and produced Barcol hardness comparable to post-cured peroxide systems. However, BAPO-L, which showed the best performance, initially delivered stress-max results slightly below reference levels, requiring further optimization through sensitizers.

2. Breakthrough in Sensitizer Technology
IGM's work introduced Esacure® 563, a glyoxylate-based technology. When added in combination with Omnirad® 819, TPO-L, and IGM's new Liquid BAPO technology, Esacure® 563 functions to delay the initial reaction—extending the time to peak at a cure distance of 500 mm to 113 seconds. This delay is critical; it allows UV light to penetrate the full depth of the laminate before the matrix "locks up," resulting in more homogeneous through-cure.

3. Reinforced Laminate Testing (ILSS) 
The most critical test involved 4 mm vacuum-infused fiberglass laminates (50% glass content) subjected to Interlaminar Shear Strength (ILSS) testing (ISO 14130). The inclusion of the sensitizer substantially increased mechanical performance, effectively matching the reference level of peroxide-cured composites.

• Peroxide Reference: 48 MPa.
• Standard UV (Omnirad® 819 Only): ~30–37 MPa.
• Optimized UV (BAPO-L + Esacure® 563): 47 MPa.

Conclusion
The transition to UV-cured composites is no longer limited by mechanical trade-offs. By optimizing photoinitiator combinations—particularly through the use of BAPO-L and glyoxylate sensitizers—manufacturers can achieve high-performance structural properties alongside the additional benefits of on-demand, cure-on-demand curing. As energy costs rise and demand for automated production increases, UV technology offers European composites manufacturers a clear path toward a more competitive and sustainable future.

Interested in how UV curing can advance your composite processes? Contact IGM Resins to discuss your application, curing challenges, and the right photoinitiator approach for your specific needs.

About IGM Resins
IGM Resins specializes in the development, manufacture, and supply of products and technical services for the global energy-curable coatings and inks market. Supported by technical laboratories to help create next-generation energy-curable coatings and inks, IGM Resins develops, manufactures, and distributes a complete range of radiation-curable materials from production facilities in Europe and Asia, including photoinitiators, energy-curable oligomers and monomers, and additives. For additional information about IGM Resins, visit www.igmresins.com.