PMMABonding

Manufacturing of large-sized components made of PMMA

Aim of the development

The aim of this project was to produce large-format, microfluidic devices (DIN A3) consisting of the thermoplastic polymethyl methacrylate (PMMA). Various methods for processing and joining the plates were investigated for this purpose. The insertion of the cavities was realized on the one hand by laser ablation using an ultrashort pulse laser and on the other hand by forming. For joining, the methods of diffusion bonding, joining by means of an adhesion promoter and vibration friction welding were used.

Advantages and solutions

The aim of the project was to create a new knowledge base for joining large-format PMMA sheets to exploit microfluidic effects (resulting from the surface-to-volume ratio of channels). The insertion of cavities for large-area microfluidics consisting of PMMA is technically carried out using the stereolithography method. For this fully automated process, a three-dimensional model must first be constructed on the computer. By briefly immersing a carrier plate in a photopolymerizable resin/polymer and then curing it by laser irradiation, a very intricate 3D model can be built up layer by layer by repeating the process several times. Detail resolutions of up to 20 µm can be generated. However, as stereolithography is an expensive and time-consuming process, the USP laser ablation method tested here can be used to flexibly produce different cavity construction plans down to 2 µm. In the project, an approach to joining using adhesive systems was to be investigated: the selection of an adhesive that does not require high thermal stress for curing and a thin layer thickness. After the joining process, it should be possible to rinse out the excess adhesive due to its different solvent resistance compared to PMMA.

iffusion bonding on plastics is a state-of-the-art thermal joining process for PMMA. The challenge here was the uniform heating of large joining parts with previously inserted cavities without deformation of the channels due to the thermal load or the pressing pressure. Another interesting joining method for large-format microfluidics made of PMMA is vibration friction welding. This method has so far only been used for small thermoplastic parts. The challenges associated with this method relate to the dimensional accuracy of the cavities, maintaining the thickness of the apparatus and the tightness of the resulting microfluidic components. A combination of mechanical and chemical joining processes under milder processing conditions was also tested. The project demonstrated that ultrashort pulse laser ablation of the extruded PMMA with the diffusion bonding joining method is an optimal process for obtaining large-format (DIN A3 format) microfluidic plates with dimensionally stable cavities of various diameters. The machining and processing steps also ensured that the developed demonstrator retains the properties of the base material.

The project is therefore a good contribution to the use of large-format PMMA plates as microfluidic devices in various fields of application. The focus here is on "scaling up", which in microfluidics is referred to as "numbering up" or "equaling up". In technology, several separate microfluidic systems are operated side by side for this purpose.

Target market

To date, most microfluidic devices have been manufactured from rigid materials such as glass, silicone or the polymer PDMS. PMMA represents an economical alternative to existing materials due to its processing options and recyclability. Due to its lower weight and higher breaking strength, devices made of PMMA are also easier to handle. Microfluidic equipment is mainly used in the chemical industry. However, the know-how gained from the project also benefits other sectors. For example, manufacturers of the equipment can benefit from the new knowledge of PMMA processing. The project investigated and optimized processing methods that enable the resource-saving and therefore economical processing of PMMA products. This enables manufacturers to expand their portfolio and use PMMA as a new material for their production.