We will elaborate on three aspects:
Material Structure
Reaction Mechanism
Formulation
Formulation is a result of combining material structure and reaction principles. Several factors influence tear strength:
The raw materials themselves: For instance, polyester groups significantly enhance tear strength, and their inclusion in the formula yields noticeable improvements.
TDI (Toluene Diisocyanate): Its benzene ring is highly stable, promoting cross-linking reactions. This stability contributes to a considerable increase in tear strength when added to the formula.
Cross-linking materials: These have a triangular structure, providing strong tear resistance. Furthermore, the formation of diamond-shaped side chains in these structures enhances both tear resistance and thermal stability.
Analyzing Adjustments to Formulations to Optimize Tear Strength
Below is a base formulation, followed by analysis of how adjustments affect sponge tear strength:
Addition of 15 parts of halogen flame retardant (R):
Halogen flame retardants are acidic, suppressing reactions between TDI and urethane, as well as TDI and urea, while promoting reactions between TDI and water or TDI and amino acids. However, excessive halogen flame retardants often lead to a reddish core in the sponge due to reaction imbalances. Although the increased heat from reactions with water and amino acids theoretically enhances the TDI-urethane and TDI-urea reactions, actual tests show that adding halogen flame retardants reduces tear strength compared to the original formula. This suggests that halogen flame retardants strongly inhibit the key reactions responsible for higher tear strength.
Adding POP (Polymer Polyol):
POP has long molecular chains that impact tear strength. Additionally, its branched chains influence molecular integrity. The net effect on tear strength depends on the balance between these opposing forces. For instance, modifying the formulation to include 70 parts PPG and 30 parts POP results in an open-cell sponge without major formula adjustments. The higher reaction temperature increases the sponge’s hardness and strengthens TDI-urethane and TDI-urea reactions. POP’s branched chains also support these reactions. Based on experience, rigid groups like TDI generally synergize well with urea, likely enhancing tear strength.
Effect of Powder Additives (CaCO₃, BaSO₄, Melamine):
Adding these powders significantly decreases tear strength. This occurs because the powders strongly inhibit TDI-urethane and TDI-urea reactions, resulting in internal cracks within the sponge. Consequently, the sponge’s tear strength is drastically reduced.
This analysis provides insights into the intricate relationships between formulation components and their impact on tear strength, guiding further optimization for improved sponge performance.