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Factors affecting the performance of foam plastics
Time:2021/10/11 11:39:42    

1. Processing factors

The performance of foam plastics is affected by processing factors, mainly including equipment, process control and operating experience of processing personnel. In the process of processing, especially in the process of foaming and expansion, the foamed plastic is affected by the control factors and the generated bubbles are deformed from round to elliptical or slender. In this way, the foam wall elongates in the expansion direction, resulting in anisotropy of the foam. As a result, the mechanical properties along the tensile direction increase (longitudinal strength increases), while the strength perpendicular to the orientation direction decreases. Experiments on polyurethane foam have shown that the greater the stretch of the cell, the greater the compression stress ratio and the modulus ratio and the greater the degree of anisotropy of the foam. As foam plastics, anisotropy should be avoided as much as possible.

2. Cell size

Cell size is one of the important factors affecting the compressive strength of foam. Compression experiments on two foam samples with different cell sizes using a spectrum microscope show that when the foam samples with large cells (0.51.5mm) are compressed by 10%, the outer cell ribs begin to bend. When compressed to 25%, the outer cells collapse, the inner cells begin to bend, and the cells in the center of the foam begin to deform. For small cell (0.0250.075mm) foam samples, when compressed, the cells are compressed in equal amounts, that is, the inner and outer cells of the foam can uniformly absorb the applied compression energy. It is generally considered that the small cell foam has good compression performance For large-cell foam.

3. Cell structure

   The performance of the same foam with open cells and closed cells is different. The experimental results show that the compressive strength decreases significantly with the increase of the open porosity. Compressive strength is one of the main indicators of foam plastics. To produce high-compression foams, the closed-cell ratio should be increased, and vice versa, the open-cell ratio should be increased. In addition, the size of the cell will also affect its water absorption, that is, the larger the cell diameter, the higher the water absorption will soon be.

4. Foaming ratio

The performance of foamed plastics also depends on factors such as resin performance, foaming agent dosage, foam density and other factors which are directly related to molding conditions. As the expansion ratio increases, the tensile strength, bending strength, and thermal deformation temperature of the foam will decrease while the molding shrinkage rate of the product will increase.

The main technical problems of polyurethane foam and products include: the storage stability of MDI, TDI and additive mixtures, the product's resistance to damp and heat aging, and product cavitation and cracking due to the instability of the foaming process.

The development needs of polyurethane foam and products mainly include: lightweight, multiple hardness, low odor, low haze, aging resistance, storage stability, environmental protection, such as the replacement of foaming agents.

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