Today's KNOWLEDGE Share : Selection of Epoxy Resin Systems for Type 3/4 Composite CNG/H2 Cylinders

Today's KNOWLEDGE Share

Selection of Epoxy Resin Systems for Type 3/4 Composite CNG and Hydrogen Cylinders

✅Epoxy resin systems are fundamental to the structural performance of composite overwrapped pressure vessels (COPVs) used in Type III and Type IV CNG and hydrogen cylinders. The resin system must be carefully engineered to deliver optimal mechanical properties, processing stability, and long-term durability. Multi-component epoxy formulations are typically optimized for low viscosity and high wettability to ensure effective fiber impregnation during filament winding.

✅Key thermomechanical parameters including viscosity, pot life, glass transition temperature (Tg), and curing kinetics—must be precisely matched to the manufacturing cycle. Elevated resin viscosity compromises fiber wet-out and interfacial adhesion with carbon fibers, resulting in voids, air entrapment, and interlaminar delamination, all of which significantly degrade laminate integrity and mechanical performance.

✅Role of Low-Viscosity Epoxy Systems

Low-viscosity epoxy systems are essential for achieving uniform resin distribution and consistent fiber infiltration across all winding layers. Strict control of resin-to-hardener ratios and resin content throughout the process is critical, as variations promote void formation and delamination. Robust fiber–matrix interfacial bonding ensures efficient load transfer; insufficient impregnation leads to localized stress concentrations and premature structural failure.

✅Curing Time and Process Control

Curing schedules must strictly follow manufacturer specifications, as they are governed by the polymerization and crosslinking reactions between epoxy, hardener, and accelerators. Prior to winding, critical resin properties such as viscosity, pot life, and Tg should be verified, as contamination, moisture uptake, or improper storage can alter curing behavior. Impurities may retard polymerization, producing weak regions within the laminate.

To ensure consistent crosslink density and laminate quality, Type IV cylinder manufacturers employ controlled thermal curing cycles, typically maintaining prescribed temperatures for 2, 4, or 6 hours. Purpose-built curing ovens with accurate temperature uniformity and programmable multi-stage profiles are essential for process optimization.

✅ Importance of Curing Integrity

Improvised or inadequately controlled curing ovens during early plant setup pose a high risk of product nonconformance. Temperature overshoot or extended exposure beyond recommended limits can induce thermal degradation or resin embrittlement. The curing cycle must be continuous and uninterrupted, as any thermal discontinuity can compromise crosslink formation and final mechanical performance.

Muthuramalingam Krishnan

Photo : Hexagon Composites ASA