Separation of Multi-Material Polymer Combinations Produced by Joining Using Pin-like Structures

Abstract

In industrial applications, multi-material joints are becoming increasingly important to achieve a sustainable and resource-saving production. Not only high mechanical properties during the component use have to be given, but also possibilities to separate the joint after end of life are crucial. The recycling and re-use of the materials plays an increasing role in the process chain. Conventional multi-material joints can be separated by cutting out the joining zone, solvents, or thermal degradation. However, these methods result in a loss of material, damage to the base material, or high energy consumption. Therefore, novel joining methods are desirable, such as the joining using pin-like structures. The potential of this novel method for joining adhesion incompatible materials has been demonstrated in previous studies. This paper studies the separability of these connections. Therefore, joints between polyamide 66 (PA66) and polypropylene (PP) as well as PA66 and polymethylmethacrylate (PMMA) are investigated by means of thermal separation and shredding with subsequent sorting using the density difference of the materials. The separated components were investigated by analytical methods (including dissolution tests, viscosity number analysis, and Fourier-transform infrared spectroscopy) with respect to varietal purity and possible degradation effects. It could be shown that shredding allows a complete separation of the multi-material joint into its individual components without material residues or material loss. For thermal separation, material residues of PP or PMMA could be detected in the pin gaps of the PA66. For both separation methods, an influence on the base materials due to degradation effects could be excluded. It can be stated that joining using pin-like structures in vibration welding technology offers a sustainable production of multi-material joints with high recyclability.

Filling Behavior in Joining Using Pin-like Structures

“…The main geometrical dimensions can be seen in Figure 2 b, and a detailed drawing of the trapezoidal tool can be seen in [ 17 ]. The structuring parameters were chosen analogues with previous investigations [ 17 , 18 , 19 ], with a frequency of 235 Hz, an amplitude of 0.7 mm, a structuring force of 600 N and a structuring path of 1.2 mm. Before both process steps, structuring and joining, the PA66 specimens were dried in a vacuum oven at 70 °C until weight constancy was achieved according to DIN EN 1110 [ 21 ].…”

“…The second process step, the joining, was carried out on the one hand using the vibration welding process with the same machine as in the structuring step. The process parameters were selected analog to previous investigations [ 17 , 18 , 19 ]: frequency 235 Hz, amplitude 0.7 mm, joining force 400 N, joining path 1.5 mm. The structured-partner had ambient temperature (approximately 25 °C) in the joining step.…”

“…The achievable bond strength, as well as the failure behavior of the joint, depends on the geometry, the dimensions of the pin-like structures and the material combination [ 17 , 18 ]. In addition to a high bond quality, joining using pin-like structures also enables simple and pure separability of the base materials after the product life cycle [ 19 ]. Due to the adhesion incompatibility of the materials and thus the absence of material interaction in the joining zone, this can be achieved by simple and material-friendly methods, such as shredding.…”