Discussion on the Development of Polyurethane Flexible Foam

Polyurethane flexible foam, also known as sponge, usually undergoes a liquid-to-solid transformation process within two minutes. Compared to other fields of polyurethane, the short and intense reaction time of flexible foam increases the difficulty in achieving fine and orderly cell structure, as well as molecular arrangement.

Research and development (R&D) involve introducing new materials to give products new properties. New materials can be categorized into two types based on their reaction characteristics: one type consists of raw materials that conform to the chemical reactions of polyurethane, such as polyether, isocyanate, silicone oil, and catalysts with different properties and activities. These materials do not fundamentally disrupt the chemical reaction process. The other type includes raw materials (fillers) that do not conform to the chemical reactions of polyurethane, such as adding non-foaming substances like special metal powders, specially formulated inorganic or organic powders with unique properties, ultrafine inorganic powders (with a fineness of over 5000 mesh), special antibacterial agents, etc. These materials sometimes completely disrupt the reaction process, leading to new reaction patterns. Some fillers cause the original formula to collapse completely, while others cause a significant change in the density of the finished product by 30% to 50%. Some fillers drastically alter the rise time of the reaction in the formula, and some fillers cause severe damage to the foam structure after being added.

R&D usually keeps certain raw materials on hand to deal with common problems encountered during the process. These raw materials typically require a wide range of physical and chemical properties. For example, amines such as A33, A-1, A-210, A-230, A-260, 33-LV, CS-90, 9717, and 9727 are commonly used in production but may not all be kept on hand for R&D purposes because their reactivity does not have a fundamental difference. In extensive R&D, the above-mentioned amines can be classified as materials in the same category. For instance, if adding a particular substance causes significant collapse when using A33 for foaming, then the remaining eight types of amines might be deemed ineffective.

One common issue encountered in R&D is foam collapse, which is the least efficient result. It is often said that analyzing and adjusting can only be done effectively once the foam structure is stable. Many cases of foam collapse cannot be resolved by adjusting the formula alone; either the foam properties change drastically, rendering it impractical, or the foam remains unstable. To address this, crosslinking agents are introduced. Crosslinking agents, commonly used as additives in R&D, generally come in two types: linear structured agents, where 1,4-butanediol represents the raw material and urea formation occurs through linear chain growth, and bulk structured agents, such as diethanolamine and glycerol, which are closer to polyether chain growth patterns.

For example, in one R&D case, adjusting the formula could not prevent foam collapse. Experience revealed that strong amine activity caused imbalance. The amine content was reduced from 0.2 parts per hundred polyether to 0.05 parts, and the high cyanate content in the formula seemed odd. The overall reaction rate also slowed significantly with the reduction in amine content, but the collapse persisted. Later, switching to a weaker amine resolved the issue. Hence, sometimes the activity of an amine cannot be compensated for by its concentration alone. It should be noted that the addition of certain substances may result in significant differences in performance between small-scale and large-scale foam production. In such cases, the performance of the last large-scale foam produced should be the main reference point for adjustment.

Sunlight, air, and water—the most ordinary and often overlooked things—are the most precious. Mastering foam production, which seems simple and lacking content at first glance, is actually quite challenging. As a colleague in R&D often says, "I have too little knowledge (one regrets having too little knowledge when it's needed)" and "How long will we keep doing this? (There's pressure)." R&D and learning foam production involve using known points to understand unknown areas, while production and teaching foam production involve using known areas to operate unknown points. Although these two aspects seem similar, bridging the gap between them is quite difficult.