Quality control over polymer nanocomposites

PNCs are formed by mixing melted polymers with nanoparticle additives in an extruder. The use of functional nanoparticles in polymers is one of the most promising applications of this new class of materials. At low quantities, nanoparticles improve the fire resistance, electrical conductivity, and optical as well as mechanical properties of PNCs.

EU-funded scientists have now developed a new technology enabling precise control of PNC properties during production. Developed within the project NANOONSPECT (Reliable integrated on-line characterisation tool for thermoplastic compound), the onBOX allows monitoring of dispersion, particle size and particle network formation at high resolution.

Newly developed online sensors are integrated into this device that analyses the melt properties during PNC production. The onBOX incorporates a capillary viscometer as well as sensors for thermal and electrical conductivity, temperature, density and pressure. Near-infrared and Raman spectrometers provide information about the dispersion process and microwave sensors monitor the agglomeration behaviour.

To ensure adequate dispersion of nanoparticles, many processing variables need to be monitored. To solve such a multivariate problem, project partners developed a sophisticated control system based on an artificial neural network (ANN). An ANN mimics the function of the human brain where connections between neurons determine the most appropriate response to sensory stimuli.

On the one hand, an ANN calculates offline material properties from properties measured online. On the other, an expert system suggests suitable process parameters to achieve the desired online-monitored property. Additionally a new compounding technology (Nexxus Channel) was adapted to the processing line, enabling an excellent dispersion of nanoparticles from slurries in the polymer matrix.

By working synergistically, the newly-developed technologies ensure high and consistent product quality through adaptive control. This new control system has been tested on industrial scale by two small enterprises within the consortium, representative of large base of potential small enterprise customers. It was consistently able to generate the most appropriate response, using signals emanating from the compounding process.

Precise control over PNC extrusion process parameters and, subsequently, the final product characteristics, was not possible in the past. The NANOONSPECT project has now opened the door to high-quality, tailor-made PNC products. The reduced environmental impact will also have benefits for manufacturers in terms of lower energy and raw material consumption.