# Reversible Joining Technology for Polyolefins Using Electromagnetic Energy and Homologous Hot-Melt Adhesives Containing Metallic and Ferrite Additives

## TL;DR

This paper explores using hot-melt adhesives with metallic and ferrite additives to reversibly bond polyolefins using electromagnetic energy.

## Contribution

A novel reversible joining technology for polyolefins using electromagnetic energy and hot-melt adhesives with metallic/ferrite additives is developed and tested.

## Key findings

- Al-based composites showed higher mechanical strength and elongation compared to Fe and ferrite-based ones.
- Ferrite-based composites exhibited the lowest water absorption and better dispersion in the polymer matrix.
- The most cost-effective bonding was achieved using 850 × 10³ W/kg power with 1 min exposure.

## Abstract

This research examined the development and testing of hot-melt adhesives incorporating metallic (Al and Fe powders averaging 800 nm) and ferrite additives, designed for reversible bonding technology of polyolefins through electromagnetic energy. The experimental models with Al displayed smooth particles that were fairly evenly distributed within the polymer matrix. Experimental models with Fe suggested that Fe nanopowders are more difficult to disperse within the polymer matrix, frequently resulting in agglomeration. For ferrite powder, there were fewer agglomerations noticed, and the dispersion was more uniform compared to similar composites containing Fe particles. Regarding water absorption, the extent of swelling was greater in the composites that included Al. Because of toluene’s affinity for the matrices, the swelling measurements stayed elevated even with reduced exposure times, and the composites with ferrite showed the lowest swelling compared to those with metallic particles. A remarkable evolution of the dielectric loss factor peak shifting towards higher frequencies with rising temperatures was observed, which is particularly important when the materials are exposed to thermal activation through electromagnetic energy. The reversible bonding experiments were performed on polyolefin samples which were connected longitudinally by overlapping at the ends; specialized hot-melts were employed, using electromagnetic energy at 2.45 GHz, with power levels between 140 and 850 × 103 W/kg and an exposure duration of up to 2 min. The feasibility of bonding polyolefins using homologous hot-melts that include metallic/ferrite elements was verified. Composites with both matrices showed that the hot-melts with Al displayed the highest mechanical tensile strength values, but also had a relatively greater elongation. All created hot-melts were suitable for reversible adhesion of similar polyolefins, with the one based on HDPE and Fe considered the most efficient for bonding HDPE, and the one based on PP and Al for PP bonding. When bonding dissimilar polyolefins, it seems that the technique is only effective with hot-melts that include Al. According to the reversible bonding diagrams for specific substrates and hot-melt combinations, and considering the optimization of energy consumption in relation to productivity, the most cost-effective way is to utilize 850 × 103 W/kg power with a maximum exposure time of 1 min.