Effect of Different Fumed Silica Additions on the Tensile Strength of Epoxy Adhesives
In modern polymer materials science, epoxy adhesives are widely used in aerospace, electronic packaging, automotive manufacturing, and structural construction for their excellent adhesive properties, superior heat resistance, and chemical stability. However, the pure epoxy resin system suffers from defects such as insufficient toughness and high internal stress, which limit its further expansion in high-performance applications. To improve these properties, researchers often optimize the mechanical performance of adhesives by incorporating functional fillers.
Among them, fumed silica, as a nanoscale inorganic filler, has become a crucial modifier for enhancing the overall performance of epoxy adhesives due to its high specific surface area, good dispersibility, and surface activity.
HIFULL analyzed the action patterns and explored the reinforcement mechanisms based on data regarding the influence of two types of fumed silica(HB-139 and a certain hydrophobic competitor) on the tensile strength of epoxy adhesives at different additions.
Figure 1
As shown in Figure 1, observing the performance of HB-139: when the addition was 0%, the tensile strength of the adhesive was only 15 MPa; as the addition increased to 1%, the tensile strength rose to 23.9 MPa; continuing to increase to 2%, it reached 32.1 MPa; at 3%, it peaked at 44.2 MPa, representing an increase of nearly 200% compared to the matrix strength.
Subsequently, when the addition rose to 4%, the strength dropped to 33.2 MPa; and further decreased to 25.9 MPa at 5%. The overall trend presents a typical parabolic pattern of “rising first and then falling,” indicating the existence of an optimal addition ratio.
Figure 2
As shown in Figure 2, in comparison, the performance of the hydrophobic competitor differed. At 0% addition, the tensile strength was also 15 MPa; at 1%, it increased to 23.2 MPa; at 2%, it reached the maximum value of 37.0 MPa.
Afterward, as the addition increased, the strength fluctuated slightly: it dropped to 28.1 MPa at 3%, rebounded to 31.0 MPa at 4%, and stabilized at 33.1 MPa at 5%. Although its maximum strength was lower than that of HB-139 (44.2 MPa), the overall curve was flatter, demonstrating strong resistance to over-filling.
The influence of fumed silica on the tensile strength of adhesives mainly depends on its dispersion state in the system, interface bonding strength, and the three-dimensional network structure formed. Hydrophobic fumed silica undergoes surface modification, where its silanol groups are replaced by organic groups, thereby reducing surface energy and improving compatibility with organic resins.
Furthermore, fumed silica can form a three-dimensional network structure in the adhesive via van der Waals forces or hydrogen bonds. This structure effectively restricts the movement of resin molecular chains and enhances strength.
However, because nano-fillers are prone to agglomeration due to their high specific surface area, especially at high additions, the tensile strength gradually declines. This aligns with the general rule that “appropriate addition significantly improves performance, while excess has the opposite effect.”
In summary, fumed silica, as a vital functional additive, can significantly enhance the tensile strength of epoxy adhesives. HB-139 exhibits optimal performance at a 3% addition, reaching a strength of 44.2 MPa, reflecting its excellent reinforcement capability.
Conversely, the hydrophobic competitor demonstrates good dispersion stability and overload resistance, making it suitable for applications requiring high filler content. The selection between the two materials should be weighed according to specific application scenarios: those pursuing extreme strength should choose HB-139 and control the dosage precisely, while those focusing on processing stability and long-term performance may prioritize the hydrophobic competitor.
About HB-139
HIFULL® HB-139 is hydrophobic fumed silica which is produced by hydrophilic fumed silica with a specific surface area of 200m2/g after chemical post-treatment with PDMS / Polydimethylsiloxane, also known as silicone oil.
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Hello, Customers
My name is Van, I’m the business manager of HIFULL, I have been in Fumed Silica Industry for more than 10 years. Feel free to contact me. I’m happy to provide you the best service and products.
