Product performance stability remains one of the biggest challenges in the adhesives and sealants industry. These performance variations are often closely related to the formation and stability of the internal gel network structure within the material. However, these structures cannot be observed with the naked eye, manufacturers typically use gel strength analysis to evaluate the internal network structure of the gel during gelation and curing. They assess the material’s gel strength, elasticity, cohesion, deformation recovery, and adhesion to ensure its structural integrity, stability, and suitability for application.
Application of Gel Strength Testing
- Polyurethane (PU) Structural Sealants: Automotive windshield sealants, rail transit body joint fillers, and container structural sealants.
- Hot-Melt Adhesives: High-speed carton sealing adhesives, perfect binding adhesives for books, and automotive headliner adhesives
- Acrylate Pressure-Sensitive Adhesives: Highly breathable medical tapes, automotive scratch-resistant protective films, and high-end industrial double-sided labels.
- Epoxy Structural Adhesives: Structural adhesives for aerospace carbon fiber honeycomb panels, wind turbine blade main spar bonding, and electronic component potting compounds.
- Silicone Sealants: Weather-resistant sealants for building curtain walls, secondary structural sealants for insulated glass units, and moisture-proof RTV sealants for electronic modules.
- Modified Polyether/Silane-Modified Polymer (MS Polymer) Adhesives: Structural adhesives for rail transit car frames, structural adhesives for new energy bus roofs, and joint sealants for prefabricated buildings.
- Water-based Polyvinyl Alcohol/Vinyl Acetate (PVA/VAE) Emulsion Adhesives: Water-based wood finger-joint adhesives, paper product laminating emulsions, and eco-friendly construction white glue.
- Cyanoacrylate Instant Adhesives (CA / Quick-drying Adhesives): Quick-drying adhesives for securing electronic wire harnesses, adhesives for toy and precision plastic assembly, and medical skin suture adhesives.
Why Gel Strength Testing Matters in the Adhesives & Sealants Industry?
Building sealants exposed to the elements, automotive adhesives subjected to vibration, and industrial assembly adhesives used on high-speed production lines all rely on the stability of their gel structure.
A stable gel structure ensures that products deliver their intended performance and remain safe throughout their entire lifecycle.
Maintaining Stability
During the assembly of vehicle components, insufficient gel strength can cause uncured material to flow downward under its own weight. This sagging can compromise the integrity of the seal and its waterproofing performance. Gel strength testing allows for precise evaluation of a material’s yield stress and initial storage modulus, ensuring that the gel structure remains stable and delivers reliable results.
Ensuring Reliable Bonding in Harsh Environments
During use, adhesives are subjected to various extreme and unpredictable environmental conditions, such as extreme temperature fluctuations, continuous mechanical vibration, high humidity, and chemical corrosion. Common automotive windshield adhesives must perform reliably under continuous mechanical vibration and varying temperatures. Gel strength testing evaluates the linear viscoelastic range and cohesive energy density to assess the adhesive’s resistance to deformation, ensuring excellent viscoelastic recovery properties and guaranteeing reliable bonding performance.
Enhancing Formulation Stability During Storage
Adhesives and sealants undergo prolonged transportation and storage. If the gel’s structural stability is insufficient, phenomena such as filler settling, phase separation, and changes in consistency may occur. Gel strength testing measures the long-term stability of the static storage modulus, static complex viscosity, and linear viscoelastic range, ensuring that the static storage modulus is significantly greater than the loss modulus and thereby achieving product stability during long-distance transportation and throughout the shelf life.
Optimizing Manufacturing Processes
On high-frequency, high-speed automated production lines, unstable gel strength can easily lead to issues such as bead collapse and stringing. Gel strength testing evaluates the recovery rate of the thixotropic structure, enabling precise control over the gel’s ability to rapidly lock its geometric shape after exposure to high shear forces, thereby facilitating high-speed automated production.
Reducing the Risk of Product Failure in the Market
If adhesives and seals leak or crack during use, it not only results in high recall costs but also damages brand reputation. Gel strength testing enables precise control over the uniformity of the cross-linked network, ensuring the smooth release of internal stress and reducing the risk of failure.
Common Testing Methods for Evaluating Gel Strength
Dynamic Oscillatory Strain Testing
Primarily measures the storage modulus and loss modulus to predict stability during long-distance shipping and extended storage.
Three-Step Shear Thixotropic Recovery Testing
Primarily measures the thixotropic recovery rate, simulating the adhesive’s full lifecycle within a dispensing valve to ensure dispensing does not result in trailing, stringing, or edge collapse.
Dynamic Time-Scanning Method
Monitors the curing curve of the adhesive in real time to identify the gel point. Helps manufacturers accurately determine the effective application window for two-component adhesives and sealants before gelation affects processing and bonding performance.
Texturometer Analysis
Primarily measures gel rupture strength and gel hardness, reflecting the adhesive’s ability to resist mechanical puncture both on the surface and internally.
Cross-Blade Probe Test Method
Primarily measures the static yield force of adhesives and sealants. It serves as a critical benchmark for evaluating whether high-viscosity products will experience self-weight slippage (sagging) on vertical application surfaces.
Gel Time Tester Method
Measures gel time under standard process conditions. Primarily used for re-inspection of catalytic activity and polymerization stability in factory batches of high-volume epoxy molding compounds and electronic insulation potting compounds.
Five Key Factors Affecting the Accuracy of Gel Strength Testing
- Consistency in sample preparation: Affects the formation of the gel network, leading to variations in local structure.
- Curing process and timing of testing: Testing too early may underestimate structural strength, while testing too late may occur during the fully cured stage, resulting in data that does not accurately reflect the material’s gel state.
- Temperature and environmental conditions: Affect the rate of polymerization and the formation of the network structure.
- Test parameter settings: Improper parameter settings may disrupt the gel structure or fail to accurately capture the material’s true mechanical response, thereby affecting the accuracy of the results.
- Material formulation and storage conditions: Affect the uniformity and stability of the gel structure.
Conclusion
In the adhesives and sealants industry, a precise understanding of the stability of gel network structures is essential not only for quality control but also for meeting global compliance requirements. Quantifiable gel strength data helps prevent product failure and the resulting damage to brand reputation.
For laboratories and manufacturers seeking precise, repeatable gel strength analysis, the Saicheng TA-3000 Texture Analyzer offers a reliable solution for evaluating the mechanical properties of adhesive and sealant gels, making it a trusted choice. The instrument not only supports versatile measurements but also comes equipped with a variety of test fixtures, facilitating formulation optimization and quality control to help ensure stable and reliable product performance.
Applications of Gel Strength Testing in Various Industries:
Gel Strength Testing in Food Manufacturing
Gel Strength Testing for Pharmaceutical & Medical Devices
Gel Strength Testing in Biotechnology & Biomedical Materials