Q & A Ralated with Alkane Plasticizers
Chinese National Standard 14683-2017 requires sealants not to contain detectable alkane plasticizers, as this agent is the real cause of cracking, is this correct?
Answer by Feng He:
Proper application of alkane plasticizers is beneficial to the bonding of certain non-polar materials, as alkane plasticizers are non-polar solvents that facilitate the spreading and wetting of the sealant on the surface of non-polar materials. Nevertheless, too much alkane plasticizer can affect the bonding performance between the sealant and the substrate, since excessive plasticizers form a barrier layer between them, affecting the generation of chemical bonds between the sealant and the substrate. Additionally, excessive addition will also result in excessive external release per unit of time. When the concentration is too high, the plasticizers will migrate to areas of lower concentration, potentially causing contamination of other bonding materials.
It is similar to using oil for stir-frying, experienced chef will use the right amount to avoid creating a paste in the pan and not spoiling the flavor of the ingredients.
Why GW sealant requires zero alkane plasticizers?
Answer by Feng He:
The reason GW sealants (Sealants designed for Glass and Curtain Wall) requires 0% alkane plasticizers is to prevent them from migrating to contaminate other bonding materials and compromising bonding performance. Since GW weather-resistant sealants are often in direct contact or very close proximity to structural adhesives, the main concern is the effect on structural adhesive bonding. If a GW sealant contains white oil, it can migrate into the structural adhesive and may result in degraded bonding properties.
WD Sealants’s structural sealants WD-986 and WD-981 are widely used in concealed frame curtain walling where bonding properties are critical. If the bond strength of the structural adhesive falls below 0.6 MPa, it must be replaced. The bond strength of structural adhesives is gradually reduced by climatic factors. Studies have shown that 25 years of exposure to the elements reduces the performance of structural adhesives to about 85% of their original performance, which is still within safe limits.