How Does Temperature Affect Flexible PU Foam Production?

Flexible polyurethane foam is a crucial polymer material whose production involves complex physical and chemical transformation processes. Environmental temperature fluctuations directly affect the kinetics of the reaction system, resulting in significant changes in pore structure, mechanical properties, and thermal stability.

This article systematically analyzes the effects of temperature field variations on the foam molding process from three perspectives: molecular segment motion, foaming kinetics, and foam thermodynamics.

Regulatory Effect of Ambient Temperature on Polyurethane Foaming Kinetics

In the addition reaction between TDI/MDI and polyols, every 10°C increase in ambient temperature results in a 1.8–2.2 times increase in the reaction rate constant between isocyanate groups and hydroxyl groups. When the temperature rises from 20°C to 30°C, cream time shortens by 32–38%, and fiber time occurs 22–26% earlier.

Current mainstream cyclopentane foaming systems (global warming potential GWP < 5) show high sensitivity to temperature changes. When the temperature fluctuates ±5°C, the evaporation rate changes by 15–18% (measured via gas chromatography, Agilent 7890B). Data show that under 25°C, the standard deviation of cell diameter increases by 12–14% compared to 20°C.

The viscosity temperature coefficient of polyether polyols is approximately -2.3%/°C. Under identical stirring conditions (2000 rpm, paddle mixer), foam open-cell rate at 30°C is 7–11 percentage points higher than at 25°C.

Effect of Temperature Gradient on Foam Structure Formation

Heat transfer during foam curing is greatly influenced by ambient temperature. When the ambient temperature is below 25°C, a 7–11°C temperature gradient develops between the foam surface and core, leading to a 0.06–0.09 mm increase in skin thickness. This structural difference increases surface hardness by 14–18% but reduces elongation at break by 28–38%.

Microphase separation is highly sensitive to temperature variation. DSC testing (TA Q20 instrument, heating rate 5°C/min) reveals that ambient temperature fluctuations of ±5°C shift the glass transition temperature (Tg) of soft segments by 1.8–2.8°C and increase the standard deviation of hard segment microdomain size distribution by 16–18%.

Nonlinear Effect of Temperature Field on Crosslinking Density of 3D Network Structure

When ambient temperature exceeds 28°C, competitive reactions between urethane and urea groups intensify, increasing the crosslinking point distance by 0.18–0.28 nm. This reduces network regularity, resulting in a 7–9% decrease in foam resilience.

Mechanism of Temperature Cycling on Product Durability

Accelerated aging tests (GB/T 3512-2014) show that under -20°C to 60°C temperature cycling (4 hours per cycle), the compression set of flexible PU foam increases by 0.7–1.1% weekly. FTIR spectroscopy (Nicolet iS50, ATR mode) shows a 10–12% decrease in urethane characteristic peak intensity (1720 cm⁻¹) after 100 cycles.

Dynamic mechanical analysis (DMA, TA Q800, 1 Hz, 0.1% strain) shows that temperature cycling shifts the tanδ peak 5–7°C toward lower temperatures and increases the temperature dependence of the storage modulus by 22–28%.

SEM observations (Hitachi SU8010, 20 kV, 10⁻³ Pa) reveal that after 50 cycles, cell wall crack density increases by 3.2–4.5 times, and crack propagation rate reaches (0.80±0.05) μm/cycle (95% confidence interval).

Conclusion and Outlook

This study established a quantitative model linking temperature, structure, and performance (R² > 0.92), offering precise process control guidance for flexible PU foam production. Results indicate that maintaining the production environment at 23±1.5°C achieves optimal product performance stability (coefficient of variation < 5%). Future research should focus on:

*Synergistic mechanisms between intelligent temperature-controlled systems and adaptive catalysts

*Industrial application of multi-scale simulation technologies

*Mechanisms of coupled temperature-humidity effects