Insights into SEBS Modification and the Mechanism of Grafted SEBS in Nylon Enhancement

1. Main Applications of SEBS
Compared with SBS, SEBS exhibits a higher degree of main-chain saturation. After hydrogenation, the polybutadiene blocks become tightly entangled, providing SEBS with greater crosslinking effects per unit volume. This structural advantage gives SEBS high modulus and excellent resistance to degradation, making it a standout among styrene-based block copolymer elastomers.

The highly saturated main chain not only enhances SEBS’s stability relative to SBS, but also improves its heat resistance, oxidation resistance, weatherability, and solvent resistance. As a result, SEBS finds broad applications across adhesives, coatings, plastic modification, automotive components, wires and cables, food packaging, medical devices, and recreational products.

SEBS also demonstrates exceptional compatibility with other polymers, enabling efficient blending with polypropylene (PP), polystyrene (PS), high-density polyethylene (HDPE), polycarbonate (PC), polyamide (PA), and polyphenylene oxide (PPO), significantly enhancing their impact resistance. Notably, blending SEBS with paraffin oil, naphthenic oil, and PP can also greatly improve product transparency.

2. Mechanism of SEBS-g-MAH Modified PA/PP

The amide groups on the PA backbone are highly polar, forming hydrogen bonds that promote crystallization and impart excellent wear and solvent resistance. However, this polarity also increases PA’s moisture absorption and reduces dimensional stability. In dry or low-temperature conditions, PA exhibits lower impact resistance and reduced elastic modulus.

In PA/PP/SEBS and maleic anhydride-grafted SEBS (SEBS-g-MAH) systems, PP addition not only reduces cost but also improves the impact resistance of PA and lowers moisture uptake. Yet, PP is thermodynamically incompatible with highly polar PA, limiting blend performance. Fortunately, reactions between the PA amide groups and the MAH-grafted compatibilizer significantly enhance interfacial adhesion. Experiments show that rigid SEBS-g-MAH is more effective than softer EPDM-g-MAH as a compatibilizer, greatly improving the strength and toughness of PP/PA6 blends while maintaining hardness.

SEBS-g-MAH distributes at both the PA matrix and the PA/PP interface, providing a dual effect: it increases the volume fraction of the elastomer for toughening, and forms elastomer-PA graft copolymers that act like surfactants, enhancing PP/PA interfacial adhesion.

In PP/PA/SEBS-g-MAH blends, when the PP/PA mass ratio is 70:30, a PP-continuous core-shell structure forms, with rigid PA6 as the core and soft elastomer as the shell. At a 50:50 PP/PA6 ratio, increasing SEBS-g-MAH lowers tensile strength; conversely, at a 75:25 PA6/PP ratio, increasing SEBS-g-MAH improves tensile strength. This indicates that careful formulation allows SEBS-g-MAH to act as a volume enhancer, creating blends that balance rigidity and toughness.

Functionalized SEBS (e.g., maleic anhydride, sulfonation, chloromethylation, or hydroxymethylation) further improves compatibility with specific systems, expanding its application potential and demonstrating significant industrial value.