Laboratory parameters of sealant

The laboratory parameters of sealant are the core basis for evaluating its performance and quality, covering multiple aspects such as physical properties, mechanical properties, durability, and environmental friendliness. 

These parameters not only provide guidance for product development, but also offer scientific support for application selection. Major global standard systems such as ISO, ASTM, and GB have clear stipulations for the key parameters of sealants. 

01 Physical Performance Parameters: Influencing Construction Experience and Basic Characteristics
The physical performance parameters of sealant directly affect its construction experience and basic usage characteristics. The table drying time refers to the time it takes for the surface of the sealant to form a film. It is usually measured at 25℃ and 50% humidity. Industrial standards typically control this time within the range of 10 to 60 minutes to meet the needs of different construction paces. 

The extrusion property reflects the ease with which the product can be extruded from the packaging. According to the ASTM C1183 standard, at a pressure of 0.17 MPa and through a 3mm diameter, the extrusion speed should be no less than 100 mL/min to ensure smooth construction without causing operational fatigue. 

The rheological properties are characterized by parameters such as viscosity and thixotropy index, and are tested using a rotational rheometer within a shear rate range of 0.5 - 10 s⁻¹. High-quality sealants possess the characteristics of high viscosity during storage (to prevent settling) and low viscosity during application (for easy extrusion), with the thixotropy index typically controlled between 3.0 and 5.0. 

The density measurement is carried out in accordance with the ISO 1183 standard. The fluctuation range should be controlled within ±0.05 g/cm³, which is crucial for the calculation of dosage and cost control. The solid content directly affects the curing shrinkage rate. For single-component silicone sealant, the solid content is generally ≥ 98%, ensuring volume stability. 

Color stability is quantified using a colorimeter, with the ΔE value being less than 3.0 (in the CIELAB system) to ensure consistent appearance over the long term. These basic parameters form the fundamental characteristics of the sealant product and become the primary consideration for users when making a choice. 

02 Mechanical Performance Parameters: Core Indicators of Load-bearing and Deformation
Mechanical performance is the core value manifestation of sealants as functional materials. The tensile bonding strength is tested according to ISO 8339 standards. The sample is stretched at a speed of 500mm/min until failure. The strength requirement for structural sealants is ≥ 0.6 MPa, and for weather-resistant sealants, it is ≥ 0.2 MPa. This parameter directly relates to the load-bearing capacity of the sealing system. 

The elongation at break indicates the toughness of the material. High-quality polyurethane sealants can reach over 800%, while silicone sealants usually fall within the range of 400-600%. This ensures that no brittle failure occurs when the joint undergoes dynamic changes. 

The elastic recovery rate is tested according to ISO 7389. After being stretched by 25% and kept for 24 hours, the recovery degree is measured after 5 minutes. The elastic sealant is required to be ≥ 70%, the plastic elastomer is 20% - 70%, and the plastic material is < 20%. 

The modulus parameters include tensile modulus and compressive modulus, which respectively represent the stress-strain relationship of the material in the tensile and compressive states. Low modulus sealants (≤ 0.4 MPa) are suitable for large displacement joints, while high modulus products (≥ 0.6 MPa) are used for structural assemblies. 

The hardness is measured using a Shore A hardness tester. Building sealants usually fall within the range of 15-50 Shore A, while automotive sealants are slightly higher, approximately 30-70 Shore A. This affects the puncture resistance and wear resistance of the sealing system. 

03 Durability Performance Parameters: Key to Predicting Product Service Life
Durability parameters serve as the scientific basis for predicting the service life of sealants. The aging performance is tested using an X-ray lamp aging instrument, simulating full-spectrum solar radiation. After 1000 hours of aging, the strength and elongation retention rate must be ≥ 80%. 

The thermal aging performance is tested according to ISO 11431. After being subjected to 70℃ and 14-day thermal air aging, no defects such as bubbles or cracks should appear on the surface, and the mechanical performance retention rate should be ≥ 85%. 

The water resistance performance includes water immersion and wet heat aging tests. The water immersion condition is 23℃ for 7 days, and the wet heat aging is 50℃ with 98% humidity for 21 days. The area of adhesive failure after the test should be ≤ 25%. 

The permanent deformation was tested under the conditions of 70℃, 22 hours, and a compression rate of 25%. This test characterizes the material's ability to maintain elasticity in a long-term compressed state. High-quality sealants are controlled within a range of ≤25%. 

The fatigue durability simulation of the joint subjected to reciprocating motion under a ±25% strain range, after 5000 cycles, the sealant should have no internal cohesive failure and the strength retention rate should be ≥ 70%. These accelerated aging tests provide reliable data support for predicting the service behavior of the sealant in real environments. 

04 Environmental and Safety Parameters: Meeting increasingly strict regulatory requirements
As environmental regulations become more stringent, the environmental and safety parameters of sealants have become a key factor for market entry. The VOC content is measured according to ISO 11890, and for eco-label products, it is required to be ≤ 80g/L. The EU Ecological Design Regulations further limit the content of specific harmful substances such as formaldehyde and benzene derivatives. 

The heavy metal content must comply with the RoHS directive. All eight major heavy metals, including lead, mercury, cadmium, hexavalent chromium, etc., must be below the limit. Detection is carried out using ICP-MS, with a detection limit of 0.1mg/kg. 

The flammability grade is evaluated according to the UL 94 standard. The V-0 grade represents the highest flame retardant level. The requirement is that after two 10-second burning tests on the sample, the smoldering time should not exceed 10 seconds and the absorbent cotton should not be ignited. 

The toxicity index is for indoor sealants, tested in accordance with GB 18583. After the product cures, it should not cause pollution to indoor air, and the formaldehyde emission should be less than 0.1mg/m³. 

Biological stability is of great significance for mold-resistant sealants. According to the ASTM G21 test, after 28 days of cultivation, the mold resistance level should reach level 0 (no growth), ensuring that no microorganisms grow in humid environments. 

05 Chemical Composition Parameters: Revealing the Essential Characteristics of Materials
Chemical composition parameters are crucial for understanding the fundamental properties of sealants. The analysis of main components employs techniques such as FTIR and NMR to determine the type of base polymer and the main functional groups, such as the characteristic Si-O-Si peak (1000-1100 cm⁻¹) of silicone sealant and the N-H peak (3300 cm⁻¹) of polyurethane sealant. 

The crosslinking density is determined by the swelling method or DMA, and it affects the mechanical properties and durability of the sealant. The crosslinking density of silicone sealant is usually between 1×10⁻⁴ - 5×10⁻⁴ mol/cm³. 

The distribution of fillers was analyzed using a laser particle size analyzer. The particle size distribution (D50 value) and specific surface area of fillers such as calcium carbonate and silica directly affect the rheological properties and mechanical properties of the product. 

The thermal properties were characterized by DSC and TGA. The glass transition temperature (Tg) reflects the low-temperature elasticity of the material, while the thermal decomposition temperature (Td) indicates the high-temperature resistance limit. High-quality silicone sealant can have a Td of over 350℃. 

Chemical composition consistency is monitored through GC-MS to detect differences between batches, ensuring product quality stability. This is particularly important for automated construction. 

06 Application Performance Parameters: The Bridge Connecting Laboratory and Engineering Practice
Application performance parameters directly connect laboratory tests with engineering practice. Bonding performance is tested using the cross-tensile method, and a systematic evaluation is conducted on the bonding strength and failure mode (cohesive failure ≥ 75% is considered qualified) of common substrates such as concrete, glass, and aluminum. 

The displacement capacity is tested in accordance with ISO 9047. After undergoing temperature cycling from -20℃ to +70℃ or mechanical cycling, the maximum seam width variation rate at which the sealant maintains effective sealing is ±25% as the basic requirement, and ±50% as the high-performance grade. 

Pollution is particularly significant for porous materials such as stone and concrete. By accelerating the aging process to evaluate the contamination of the substrate caused by the migration of sealant components, neutral curing silicone sealant performs exceptionally well. 

The storage stability of the product, when stored at 40℃ for 30 days, is equivalent to being stored at room temperature for one year. After the test, the changes in extrudability, curing speed, etc. should not exceed 15% of the initial values, ensuring that the product maintains stable performance within the shelf life. 

The compatibility test assesses the interaction between the sealant and adjacent materials (such as spacers, backing adhesives), preventing performance degradation due to component migration. This is crucial for ensuring the long-term reliable operation of the sealing system. 

The laboratory parameter system for sealants is constantly being improved with the advancement of technology. Intelligent detection technologies such as AI-assisted data analysis and online monitoring systems are enhancing the efficiency of testing and the reliability of data. 

Characterization methods at the micro-nano scale, such as atomic force microscopy and micro-CT, have provided a new perspective for understanding the relationship between the microstructure and macroscopic properties of materials. 

In the future, with the application of digital twin technology in material research and development, laboratory parameters will be able to more accurately predict the performance of products in actual engineering, driving the sealant industry towards a more scientific and reliable direction.