2021

Bonding thermoplastic elastomers to polar and non-polar substrates has been widely studied in the past few decades to create products that enhance ergonomic comfort and functionality. Overmolding a TPE compared to two-shot molding is a litmus test for bonding the material to the substrate. The TPE must wet the cold surface and must melt a few nanometers of the surface of the substrate that is being overmolded on to facilitate bonding.

Preformed membranes are primarily made from EPDM, PVC, TPO, HDPE, atactic PP, SBS and modified bitumin, etc. The focus of this article is TPO membranes, which are extensively used for exposed roof waterproofing and heat insulation. First introduced in Europe in the early 1990s, TPO membranes were developed as an alternative to PVC to overcome issues around plasticizer migration and membrane integrity breakdown, resulting in wash away and chemical contamination, as well as mold growth affected by weathering over the years; and finally culminating in cracking and leakages. TPOs have since become very popular due to their durability, UV and heat resistance, energy efficiency, as well as cost-effectiveness.

Fumed silica is widely used as a reinforcement additive in silicone elastomers with significant mechanical property benefits, namely increased tensile strength, elongation and tear strength, among others. However, the use of fumed silica in thermoplastics is limited because of the difficulty to effectively add them via melt compounding by an extruder. Fumed silicas are extremely light; they have a bulk density of about 50 to 100 g/l. Thus, feeding this low density powder into the extruder, as well as conveying and mixing it with a viscous polymer melt, presents a challenge in typical plastics compounding operations.