VESTOPLAST® is an amorphous poly-alpha-olefin (APAO), used as a raw material for hot melt adhesives for various applications. APAOs have been well-known in the market for many years. Recent market developments have shown that it is not only new polymers with new properties that are important for new applications, but also that specific physical properties of established polymers and their effect on operating windows and machine parameters are important. This way, experience and knowledge from well-known applications can be transferred into new applications. In recent years, Evonik has been focusing on gaining a deeper understanding regarding the relation between the technical properties of VESTOPLAST® such as viscosity and crystallinity content and different application systems, for example foam or spray application. The effect of different polymers and formulations on machine settings and handling are significant for an efficient production process.
One of the topics which has been analysed in more detail is the foaming behaviour of various pure polymers to gain a better understanding of the effect of the polymer structure on the foaming. A design of experiment has been performed with several APAOs and metallocene poly-olefins (mPO) to check the application window. The typical temperature of 150°C was tested, as well as lower temperatures of 130°C for more sensitive substrates and resource-efficient product and material handling. The foaming process is started by adding nitrogen to a melt in a tank under pressure. After releasing the mixture from the applicator, the nitrogen will expand and form bubbles, thus creating the foam. Therefore, it is necessary that the polymer backbone provides enough flexibility to allow the volume expansion but also show enough cohesion and crystallinity to keep the bubbles inside until the foam is hardened. Test results have shown that a reduction of polymer amount down to 30% was possible, meaning 70% nitrogen could be added to increase the volume and decrease the amount of polymer. The ideal ratio must be considered based on the physical properties which are needed for the end application.