In addition to curing performance, several other performance aspects are also crucial for sealants:

1、Appearance:

    The appearance of sealants mainly depends on the dispersion of fillers in the base compound. Fillers are solid powders that, after dispersion through kneaders, grinders, or planetary mixers, are evenly distributed in the base compound to form a fine paste. Occasionally, depending on the nature of the fillers themselves, the presence of very small amounts of fine particles or sand-like material cannot be completely ruled out, and this is considered an acceptable normal occurrence. If the fillers are poorly dispersed, there will be many coarse particles. Besides filler dispersion, several other factors can affect the product's appearance, such as the presence of granular impurities or skin formation. These conditions are considered as rough appearance. The appearance is typically observed by removing the product from the packaging for direct inspection or by placing 1-2g of the product on white paper, folding the paper, flattening it, and then unfolding it for observation; this is referred to as "butterfly observation." When coarse particles are found, they should be assessed accordingly.

2、Hardness

    Hardness refers to the degree of resistance that a sealant exhibits after it has fully cured into a rubber-like substance. It is one of the physical mechanical properties of the product. Hardness represents a material's ability to resist indentation or penetration by an external object. There are various methods to measure hardness, including Brinell hardness, Rockwell hardness, and Shore hardness, among others. In the context of sealants, Shore A hardness is commonly used as per national standards. The standard hardness value is determined by testing using a hardness tester on specimens prepared according to the national standard method.

    For sealants, higher hardness indicates a stiffer surface with greater rigidity and reduced elasticity and flexibility. Conversely, lower hardness indicates better elasticity and flexibility with reduced rigidity. Therefore, the ideal hardness of a sealant depends on specific requirements, and it is neither the harder, the better, nor the softer, the better; rather, it should fall within a certain specified range based on practical needs.

 3、Tensile Strength

    Tensile strength, also known as tensile or pulling strength, is one of the mechanical properties of a sealant after it has fully cured. It represents the material's ability to resist being pulled apart when subjected to a tensile force. The value of tensile strength is determined using methods specified by national standards. Depending on the intended use, sealants may have specific strength requirements, especially for structural adhesives, where minimum strength values are often explicitly defined in national standards. Sealants with poor strength may not meet the performance requirements for their intended use. However, it's essential to strike a balance because excessively emphasizing strength in a sealant at the expense of elasticity can also be detrimental.

4、 Elongation at Break

Elongation or elongation at break is a measure of the elasticity of the sealant after it has fully cured, and it is one of the mechanical properties. It refers to the percentage ratio between the total elongation of the material under tension and its original length. Sealants with good elasticity exhibit higher elongation values. As a minimum requirement for elongation, sealants must meet the performance criteria specified in national standards.

5、Tensile Modulus and Displacement Capability
 
    Tensile modulus and displacement capability represent the comprehensive performance of the above-mentioned mechanical properties. The tensile modulus characterizes the strength of the sealant when stretched to a certain elongation. Therefore, the measurement is expressed in conjunction with elongation, such as a tensile modulus of 0.46 MPa at an elongation of 25%.

    Displacement capability indicates the ability of the sealant to accommodate displacements caused by thermal expansion and contraction of the substrate. For example, when we say a sealant has a ±25% displacement capability, it means that the sealant joint can withstand stretching and compression of up to 25% of its original width. For instance, if the original joint width is 12mm, it can compress down to 9mm or stretch up to 15mm. Displacement capability can be tested using methods such as tensile-compression cycling or thermal cycling.

 6、Adhesion to Substrate

    This is a crucial property in the actual use of sealants. Sealants must exhibit good adhesion to the substrate they are intended to be used on. A simple method to test adhesion is to clean the substrate with an appropriate solvent or detergent, let it dry, and then apply the sealant to it. After the sealant has cured (approximately 3-5 days), it can be manually peeled off, and the adhesion can be observed.

7、Extrusion Capability    

    This is one of the construction performance parameters of sealants, used to indicate the ease of extrusion during sealant application. A sealant that is too thick will have poor extrudability, making it challenging to apply. However, if the sealant is made too thin solely for the sake of extrudability, it can affect the thixotropy of the sealant. Extrudability can be measured using methods specified in national standards.

8、Thixotropy

    Thixotropy refers to the property of a material, including sealants, to become less viscous or flow more easily when subjected to shear forces, such as stirring, mixing, or application pressure. It is the ability of a material to change from a thicker, more gel-like consistency to a thinner, more fluid state when agitated or stressed. In the context of sealants, thixotropy is desirable because it allows the sealant to be easily applied and spread during installation while maintaining its sealing properties when at rest.