If your factory production line is running at full capacity, yet when you cut open the panel, what you see is not uniform off-white or light yellow foam, but striking dark red, brown or even charred black foam

This is what we commonly refer to as "Core burning"in the polyurethane industry

We will dive deep into the six causes of "core burning" and offer corresponding solutions.

Part 1: What Causes Core Burning?

It is essential to understand that polyurethane foaming is a strongly exothermic reaction. Heat dissipates rapidly from the panel surface; however, the foam core boasts excellent thermal insulation, trapping heat just like under a thick quilt. Once the internal temperature exceeds the tolerance limit of 160–180°C, polyurethane molecular chains undergo oxidative degradation and form chromogenic groups, turning white foam into a "black core". Simply put: Heat generation rate > Heat dissipation rate = Core burning.

Part 2: Six Causes and Remedies

1. Excessive Catalyst Dosage

· Root cause: To achieve faster demolding, many factories over-add catalysts, especially strong metal catalysts or highly reactive foaming catalysts. This accelerates the reaction sharply, generating explosive heat in the material within seconds, leaving no time for heat release from the core.

· Solution: Adopt a composite system of delayed-action catalysts or weak trimerization catalysts.

2. Improper Panel Dimensions

· Root cause: Overlarge or overly thick panels mean a larger pouring volume. A bigger foam core has a smaller specific surface area, making heat dissipation much harder.

· Solution: For ultra-thick panels (20 cm and above), adopt the layered pouring process. For continuous panel lines, slow down the reaction profile to match line speed, or use raw material systems with a lower exothermic peak temperature.

1. High Ambient and Mold Temperature

· Root cause: Core burning occurs most frequently in summer. High ambient temperature (>30°C) and high mold temperature raise the initial material temperature, speeding up the reaction and reducing the temperature difference available for heat removal.

· Solution: Cool the MDI component appropriately in summer, or adjust the formulation to reduce catalyst activity.

2. Impact of Flame Retardants

· Root cause: Certain additive flame retardants (e.g. TCPP) absorb part of the heat when heated and act as a heat sink. Removing flame retardants to cut costs leaves the pure organic system with no outlet for reaction heat.

· Solution: Even for low-cost Class B3 panels, retain basic flame-retardant fillers. They function not only for flame resistance but also as a physical cooling skeleton.

3. Uneven Density Distribution

· Root cause: Local high density. Regions with higher density contain a higher concentration of reactive groups, producing more heat per unit volume and creating local hotspots that trigger a chain reaction.

· Solution: Optimize the location and pattern of material injection to ensure a uniform foam flow front and avoid local accumulation of liquid resin.

4. Excessive Internal Mold Release Agent

· Root cause: Some internal release agents contain long-chain fatty acids, which catalyze the oligomerization reaction of isocyanates at high temperatures and generate extra heat.

· Solution: Minimize dosage while maintaining satisfactory demolding performance.

Qichen has been deeply engaged in the polyurethane industry for nearly 15 years. We select premium raw materials and provide one-stop supporting solutions. Our quality is well-controlled with reliable after-sales support, bringing you peace of mind for cooperation and product application.