Silane-treated hollow glass microspheres offer additional performance improvements. A silane coupling agent acts at the interface between an inorganic substrate, like hollow glass microspheres, and an organic polymer to bond, or couple, the two dissimilar materials.
Very destructive to adhesion is migration of water to the hydrophilic surface of the inorganic glass filler. Water attacks the interface, destroying the bond between polymer and filler. But a true coupling agent creates a water-resistant bond at the organic/inorganic interface. Silane coupling agents not only enhance bond strength but also prevent de-bonding at the interface during composite aging and use.
Notched Izod impact, tensile and flexural strengths and elongation at break all show much better properties when a coupling agent is applied to the microsphere filler. In general, notched Izod and tensile strength improve by about 40% when comparing silane-treated and untreated hollow glass microspheres. In addition, silane treatment slightly enhances the density reduction obtainable with microspheres, because the silane provides a lubricious surface layer that reduces microsphere breakage during compounding.
Adding silane treatment further increases the advantages of the newest, strongest microspheres. The most significant property improvement is in elongation at break. Here, there is almost 300% improvement from 35% elongation at break for silane-treated S60HS microspheres to 100% for silane-treated iM30K additives.
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