Unique photoinitiator combinations for UV curing composites
UV and UV LED curing has become a viable alternative to traditional peroxide-based cold and thermal curing in composite manufacturing, offering significant reductions in processing time, emissions, and energy consumption. Over the past 12 months, IGM has investigated the curing mechanisms, as well as the effects of various photoinitiator combinations on mechanical performance and industrial applicability for composite applications. Results show that with optimized photoinitiator systems, UV and UV LED curing can deliver equivalent material properties in a fraction of the cycle time—making it not only suitable but also an economically viable alternative for a wide range of composite production methods.
Introduction
Ultraviolet (UV) curing is rapidly emerging as an effective alternative to traditional cold and thermal curing methods in the production of fiber-reinforced polymer composites. By replacing peroxide curing with UV-initiated photopolymerization, manufacturers can significantly reduce processing time, control the exact timing of cure, and—where thermal curing is used—lower energy consumption and emissions, all while maintaining the mechanical performance of finished parts.
Advantages of UV curing in composite applications
UV curing involves initiating a polymerization reaction in a resin system by exposing it to ultraviolet radiation. This process can be integrated into several composite manufacturing techniques, including:
- Wet lay-up
- Vacuum infusion with UV-transparent membranes
- Filament winding
- Prepreg processing
- Pultrusion
- Hand lay-up and open mold processes
- Cured-in-Place Pipe (CIPP)
A critical requirement is that UV radiation must reach the resin—either directly or through a transparent barrier. Common UV sources include mercury arc lamps and LED arrays. Due to their longer wavelengths, LED lamps are particularly well-suited for curing thicker, reinforced composite layers.
| Cold cure | Hot cure | UV cure | |
|---|---|---|---|
| Cure time | Hours | Minutes to hours | ✓ Seconds to minutes |
| Cure on Demand | Not possible | Limited | ✓ Full control |
| Potlife | Hours | Hours | ✓ Unlimited potlife |
| Resin waste | Approx. 5–10% | < 5% | ✓ Re-use possible |
| Styrene emission in open mould | High | Medium | ✓ Low (fast cure) |
| Sandwich construction | Possible | Limited (temp) | ✓ Possible with hybrid cure |
| Curing equipment | None or limited equipment required | Heating chamber, oven, heated mould | ✓ UV/LED equipment |
| Investment required | Low | High | ✓ Medium |
| Energy consumption | Low | High | ✓ Medium |
Objective and methodology
UV-curable systems rely on photoinitiators that absorb UV light and produce reactive species to initiate polymerization. The two main curing mechanisms are:
- Radical polymerization (e.g. vinyl ester/acrylate-based systems, unsaturated polyester + styrene based systems)
- Cationic polymerization (e.g. epoxies)
The common challenges in UV curing composite radical polymerization are:
- Through cure into thick reinforced laminates
- Mechanical performance that is identical to peroxide cured composites
- Oxygen inhibition of the surface
- Light distribution across the 3 dimensional shapes
The objective of IGM’s study has been, to use the expertise of Printing & Packaging and Industrial coatings to explore the effects of using different photoinitiators combinations on the through cure, mechanical performance and oxygen inhibition for radically cured systems.
The resins that were selected for testing as industrial reference were:
- ISO NPG resin
- Vinylester resin
- Styrene-free VE resin
The test used were:
- Neat resin castings (4mm) for mechanical property confirmation and Barcol hardness
- Laminate (ca 4 mm produced under vacuum infusion) to determine ILSS values
- Depth of cure tests up to 15mm
Results & conclusions
As long as sufficient light energy is reaching the surface, it is possible to replace peroxides such as MEKP or BPO for with (a combination of) photoinitiators and achieve mechanical properties with UV LED curing that are in line with the mechanical properties of peroxide cured composites.
It is also confirmed that hybrid curing (so a combination of UV curing with hot or cold curing) is also possible and achieving similar mechanical properties as achieved with only peroxide curing. Adding photoinitiators, peroxides and accelerators to the formulation is to be carefully tested up front, as especially some accelerators might interfere with the photoinitiator performance.
IGM can support you in selecting the right photoinitiators for your resin system and application process with our dedicated laboratory services.
The benefits confirmed for UV LED curing:
- Speed of cure (neat resin ca 40 seconds vs 20 minutes)
- Cure on demand enabling a flexible and yet controlled production process
- UV cure is compatible with various unsaturated polyester (UP) resins
- Mechanical performance is comparable to peroxide-cured systems with the right selection of photoinitiators and light source.
IGM Resins: Driving Innovation in UV Curing
As a leading expert in UV curing technologies, IGM Resins has a dedicated team and laboratory capabilities focused on composite applications. Our teams are dedicated to optimizing photoinitiator systems for full-depth curing and ensuring mechanical performance—enabling manufacturers to harness the speed and efficiency of UV curing without sacrificing on mechanical performance.
With a strong global support network and a continuous commitment to innovation, IGM is advancing next-generation, energy-curable solutions tailored to meet the evolving needs of the composites industry.
Interested in learning more? Download our composite leaflet to explore the benefits of UV curing technologies in detail.