TABLE OF CONTENTS FPF starts as a mixture of liquid chemicals and within a few minutes becomes a matrix of solid polymer with a uniform, flexible, cellular structure. There are five discrete stages to the foaming process: raw material conditioning, mixing, growth, cell opening and cure. Distinctly different chemical and physical changes occur in each stage, and all affect the final product.
A polyurethane foam manufacturer controls many of the chemical and mechanical inputs to the process, but once the liquid leaves the mix head, chemistry and physics determine the fate of the foaming mass. The only way to produce consistent foam is to start with consistent raw materials. The ingredients arriving at the mix head must be at the right temperature and should also have a certain amount of dissolved gas. If these properties vary outside the normal range, defects may result.
The main reason for controlling temperature is that some chemical reactions are more thermosensitive than others. The temperature affects the overall rate of reaction, and even the relative rates. This can lead to an imbalance that changes the properties of the final product. Viscosity also changes with temperature, and this affects flowability and mixing.
Gas molecules dissolve in polyol and isocyanate as it comes in contact with air during transportation and storage. Dissolved gas is essential for cell nucleation in the mix head. If raw materials are too fresh (not enough dissolved gas) insufficient nucleation can result in a cell structure that...
