In engineering sealing, qualitative descriptions require quantitative data for support to enable the most accurate decision-making. Having previously discussed the concept of "modulus" in polyurethane sealants, let us now assign concrete numerical values to give "soft" and "hard" a defined character.
I. Core Distinguishing Criterion: A Quantitative Definition of Modulus
In materials science, one of the most common metrics for measuring sealant modulus is Tensile Modulus, typically referring to the stress generated when a specimen is elongated to 100% strain, measured in Megapascals (MPa). This value directly and objectively reflects the material's softness or hardness.
High Modulus: When stretched to 100%, it generates high stress (>0.6 MPa), demonstrating a strong ability to resist deformation.
Low Modulus: When stretched to 100%, it generates low stress (<0.4 MPa), demonstrating flexible characteristics and easy deformation.
Medium Modulus: Falls between high and low modulus, representing a zone of balanced performance.
II. Data-Based Modulus Classification and Comparison
The table below combines specific modulus values, movement capability, and applications to provide a clear decision-making map.
| Characteristic Dimension | Low Modulus Sealant | Medium Modulus Sealant | High Modulus Sealant |
|---|---|---|---|
| Quantitative Core Metric | 100% Modulus typically ≤ 0.4 MPa | 100% Modulus typically between 0.4 - 0.6 MPa | 100% Modulus typically ≥ 0.6 MPa |
| Core Characteristics | Soft texture, high flexibility | Medium hardness, good balance | Hard texture, high rigidity |
| Movement Capability | Very High (Typically ≥ ±50%) | High (Typically ±25% to ±40%) | Medium to Low (Typically ≤ ±25%) |
| Main Advantages | • Very low stress on substrates • Accommodates very large joint movement | • Balances flexibility and strength • Wide range of applications | • High adhesion strength, structural capacity • Good abrasion resistance, high mechanical strength |
| Main Disadvantages | • Relatively lower mechanical strength • Surface may be tackier | • Performance limited under extreme deformation | • High stress on substrates, risk of damaging fragile materials • Not suitable for large movements |
| Typical Applications | • Precast concrete panel joints (large movement) • Curtain wall joints (large movement) • Highway, airport runway expansion joints | • Perimeters of windows/doors • General building facade joints • Residential expansion joints | • Auto body structural sealing (requires high strength) • Industrial flooring joints (high load-bearing) • Sealing in high-traffic areas |
The Meaning Behind the Data:
When you see "100% Modulus ≤ 0.4 MPa", you can be confident this is a genuine low modulus sealant. It can act like a gentle dancer, protecting fragile substrates like concrete while effortlessly accommodating joint width changes exceeding 50%.
When you see "100% Modulus ≥ 0.6 MPa", this signifies a robust guardian. It provides structural capacity akin to welding, but it must be used in applications with minimal movement (≤25%) and on strong substrates; otherwise, its powerful "grip" could crack stone or old concrete.
III. How to Use Data for Precise Selection
Consult the Technical Data Sheet (TDS): This is the most critical step. Any responsible sealant manufacturer will clearly state the "Modulus @ 100% Elongation" or "100% Modulus" value in the product's TDS. Let this be the final basis for your selection.
Cross-Reference: Correlate the modulus data with the Movement Capability data. For a quality product, the modulus and movement capability are matched. For instance, a product claiming ±50% movement capability must have a 100% Modulus in the low modulus range.
Deduce from Application Scenario:
Scenario: Concrete curtain wall joints in a high-rise building.
Requirement: Large movement (likely >±25%), substrate is concrete (fragile).
Data Indicates: Must look for a low modulus product in the TDS with a 100% Modulus ≤ 0.4 MPa and Movement Capability ≥ ±50%.
Conclusion
In the field of engineering, data is the most precise language of communication. By translating the abstract concept of "modulus" into specific, verifiable metrics like "100% Modulus ≤ 0.4 MPa", we move beyond the perceptual descriptions of "soft" and "hard" into a realm of accurate and reliable, data-driven selection.