Silica powder, as an important reinforcing filler in the rubber industry, plays a decisive role in improving rubber properties through surface modification. Unmodified silica powder has a large number of hydroxyl groups on its surface. These polar groups easily form hydrogen bonds between particles, leading to severe agglomeration. When directly added to the rubber matrix, these agglomerates are difficult to disperse, forming stress concentration points and weakening the rubber's mechanical properties. Introducing non-polar groups through surface modification can effectively reduce particle surface energy, decrease agglomeration, and allow silica powder to form a uniformly dispersed three-dimensional network structure in the rubber. This structure forms a physical entanglement with the rubber molecular chains. When the rubber is subjected to external forces, the network structure absorbs energy through deformation, significantly improving tensile strength and tear strength.
Surface modification has a crucial impact on the interfacial bonding between silica powder and rubber. The interaction between the hydroxyl groups on the surface of unmodified particles and the rubber molecular chains is weak, resulting in limited reinforcing effects. After treatment with modifiers such as silane coupling agents, one end of the modifier molecule reacts with the hydroxyl groups on the silica surface to form chemical bonds, while the other end forms physical adsorption or chemical bonding with the rubber molecular chains. This dual effect significantly enhances the interfacial bonding strength, forming a "bridge-like" structure that effectively transfers stress. When rubber deforms, the modified silica powder better restricts the slippage of molecular chains, reducing crack propagation and thus enhancing wear resistance and fatigue resistance.
The optimization of silica powder dispersibility through modification directly affects the processing performance of rubber. Unmodified particles agglomerate, leading to increased viscosity and energy consumption during rubber compounding, and resulting in poor compound uniformity. After surface modification, the particle surface is coated with an organic layer, reducing the coefficient of friction with rubber and making the compounding process smoother. Modified silica powder can also adjust the Mooney viscosity of rubber, improve extrusion and calendering performance, and reduce surface defects in products. Furthermore, the uniformly dispersed particle network structure prevents the formation of bubbles during vulcanization, improving the density and surface smoothness of the finished product.
Surface modification has a significant effect on improving the dynamic mechanical properties of rubber. Under alternating stress, the interface between unmodified silica powder and rubber is prone to detachment, leading to increased internal friction and severe heat generation. Modified particles form a unified structure with rubber through strong interfacial bonding, reducing internal friction and dynamic heat generation. This property enables modified silica powder-reinforced rubber to exhibit superior wet skid resistance and lower rolling resistance in dynamic applications such as tires, while also extending service life. The modified particles also inhibit oxidative degradation of rubber at high temperatures, improving thermal stability.
Different types of surface modification methods have varying effects on rubber properties. Silane coupling agent modification achieves strong interfacial bonding through chemical bonding, suitable for high-performance rubber products; alcohol ester modification is less expensive and suitable for general industrial rubbers; polymer grafting modification can impart special functions to rubber, such as conductivity or flame retardancy. The selection of modifiers must be determined comprehensively based on the rubber type, processing technology, and final performance requirements. For example, in silicone rubber, hydrophobic fumed silica, through surface silanization treatment, can significantly improve its mechanical strength and weather resistance.
Surface modification also affects the filler content of silica powder in rubber. Unmodified particles, due to poor dispersibility, can easily lead to excessively high rubber hardness and decreased elasticity when filled at high levels. After modification, the particles are uniformly dispersed, allowing for increased filler content without significantly sacrificing the processing and physical properties of the rubber. This characteristic enables modified silica powder to reduce costs while enhancing the overall performance of rubber, meeting the demands of high-end applications.
Surface modification of silica powder significantly improves its performance in rubber reinforcement through multiple mechanisms, including improved dispersibility, enhanced interfacial bonding, optimized processing performance, improved dynamic mechanical properties, adaptability to different modification methods, and increased filler content. This modification technology has become an indispensable key element in the modern rubber industry, driving the development of rubber products towards high performance, multifunctionality, and environmental friendliness.
