How to Stabilize Polyurethane Foam Production Against Seasonal Temperature Changes?

The successful manufacture of flexible PU foam depends on strict control of initial conditions. Even slight fluctuations in ambient temperature can trigger chain reactions, becoming a fundamental challenge to product quality and process stability. In the foaming system, controlling raw-material temperature is considered the decisive factor governing chemical reaction activity.

I. Initial Settings of Reaction Kinetics: Baseline and Accumulative Effects

The final performance of polymerization strongly depends on the initial temperature and concentration of raw materials. These parameters define the “baseline” for the entire process.

Foaming is a complex, multi-stage, interactive progression. Any small deviation in the initial reaction rate will be amplified through dozens or even hundreds of reaction cycles. This accumulative chain effect means that differences in basic conditions eventually evolve into major fluctuations in product properties. Hence the widely accepted industry principle: “Foaming is fundamentally about heat—heat determines the reaction potential of the system.” Raising raw-material temperature essentially provides the reaction with a higher energy starting point.

The Overlooked “Small” Players

Even auxiliary components added in small amounts have crucial temperature requirements:

Water (chemical blowing agent):
Although the mass added is small, the number of water molecules is large, and its reaction with isocyanates dominates the overall polymerization progress. Therefore, water temperature must be considered in process control, as it directly influences the initial rate of foaming.

Additives (e.g., MC):
Some additives not only adjust density but also work as regulators of the overall reaction speed. Neglecting their temperature is one of the hidden causes of unstable winter production.

II. Physical Impact of Seasonal Temperature Changes on Raw-Material Conditions

Seasonal variations directly alter the physical properties of raw materials, affecting the metering accuracy and mixing efficiency of A and B components.

Winter: Stagnation and Performance Decline

When raw-material temperatures drop to colder ambient levels, their physical behavior becomes viscous and sluggish:

Isocyanate (A-side):
The main component, MDI, crystallizes below certain temperature thresholds, which may block pipes and reduce the amount of active material available for reaction.

Polyether polyol blend (B-side):
Although it does not crystallize, its viscosity increases significantly. This causes pumping difficulties, unstable metering flow, and severe damage to mixing uniformity with the A-side.

Low temperatures slow reaction speed and weaken polymerization strength. Insufficient gas generation leads to higher-than-intended foam density. Meanwhile, reaction heat is quickly absorbed by the cold environment, preventing full curing. Finished products may show shrinkage and cracking. Low-density foams may also exhibit reduced strength, bottom white lines, and more pronounced top surface patterns.

Summer: Dilution and Heat-Runaway Risk

High temperatures push raw materials to the opposite extreme:

General material behavior:
Viscosity drops significantly, increasing flowability. This may cause leakage inside metering pumps and disrupt the accurate A/B ratio.

A-side inherent risks:
Prolonged high-temperature exposure may trigger self-polymerization, producing insoluble solids or releasing gas, which increases tank pressure.

High temperatures accelerate reaction speed dramatically. Rapid gas expansion may cause overly low density and internal voids. More critically, combined heat from reaction and hot weather may push the foam core temperature beyond the decomposition threshold, causing charring or “burnt core.” Fast curing also limits raw-material flow, leading to poor fill or surface collapse.

III. Response Strategies: Process Control for Constant Production Stability

The key to overcoming seasonal foaming issues is maintaining raw materials at ideal reaction conditions through process adjustments.

Winter Heating and Reaction Activation

To counter low temperatures, operators must actively add energy to the system:

Preheating management:
Raw materials should be preheated in a temperature-controlled storage room. Crystallized MDI must be heated until fully melted.

Equipment assurance:
Equipment heating systems must be activated to bring all raw materials to designated process temperatures. Molds or substrates should also be preheated to reduce heat loss during early foaming.

Formula adjustments:
Besides raising the temperature of major materials, small or moderate increases in amine catalysts help boost overall reaction activity.

Summer Cooling and Reaction Suppression

Under high temperatures, the priority is lowering system temperature and slowing reaction speed:

Cool-storage:
Raw materials should be kept in shaded environments. Cooling-water circulation in storage tanks should be used to reduce material temperature.

Formula adjustments:
Catalyst dosage can be reduced to effectively slow reaction speed.

Pouring optimization:
For large-volume pours, multi-layer pouring is recommended to disperse heat load and prevent internal heat accumulation.

Conclusion

In the foaming process of flexible PU foam, temperature is the primary determinant of success. Only by precisely managing initial raw-material temperatures and applying temperature-control and activation strategies according to seasonal changes can manufacturers overcome environmental disturbance and consistently achieve the desired product performance and quality.