How Do Temperature and Humidity Affect the Physical Properties of Flexible PU Foam During Foaming?

(1) Explanation

In the production of flexible polyurethane foam, the foam’s physical properties are highly influenced by the ambient gas medium due to the reactivity of isocyanates. Among these, moisture in the air plays a major role, especially in affecting foaming hardness and elongation. This article compares foaming results using the same formulation under summer and winter conditions.

(2) Foaming Conditions

A. Low-Pressure Foaming Machine

Number of components: 5

Discharge rate: 8.3–8.5 kg/min (Max 3016/min)

Rotation speed: 4000 rpm

B. Foaming Parameters

Foaming date and liquid temperatures:

Summer: One day in July (R/I – 24/24 °C)

Winter: One day in January (R/I – 22/20 °C)

C. Formulation

MN-3050: 100 parts

Silicone oil L-6202: 1.3 parts

H₂O: 4.5 parts

Hinico L-1020: 0.19 parts

Niax A-133: 0.03 parts

MC: 3 parts

S.O (Tin Catalyst): Variable

TDI-80/20 Index: 1.10

D. Foaming Results

The foaming formulation and resulting foam physical properties are shown in Table (1).

Table (1): Formulation and Physical Properties (Summer vs. Winter)

The relationship between foam properties and tin catalyst dosage is illustrated in Figures (1)–(6):

Based on Figures (1)–(6), the following points can be observed:

①Rise Time: Shorter in summer than in winter due to higher liquid and ambient temperatures.

②Foam Density: Lower in summer, also a result of higher temperatures.

③Foam Hardness: Higher in winter. Even after accounting for density, winter foams remain harder.

④Elongation: Foams made in summer show higher elongation than those made in winter.

⑤50% Compression Set: No significant issues, but summer foams show slightly poorer values.

These observations show that temperature and humidity differences between summer and winter influence foam hardness and elongation due to variations in moisture in the gas medium. Therefore, adjustments in the formulation—particularly in polyether, TDI, and foaming agents—are required to compensate for seasonal variations.