Surveying the Scene

Excerpt: A new sensor system developed in Germany can not only carefully control drying processes in industrial ovens, but can deliver reliable air humidity measurements even at high temperatures

Novel sensor system improves reliability of high-temperature humidity measurements

A new sensor system developed in Saarbrücken, Germany can not only carefully control drying processes in industrial ovens, but can deliver reliable air humidity measurements even at high temperatures and in the presence of other background vapours. Professor Andreas Schütze, project manager Tilman Sauerwald and their research team at Saarland University have developed with partner companies a sensor system that precisely monitors industrial drying, baking and cooking processes. The new system improves product quality, optimizes the production process and lowers process energy demands. The project has received funding from the Federal Ministry of Education and Research's priority funding programme 'KMU-Innovativ' that promotes innovative technology in small and medium-sized enterprises.

The engineers showcased their heat-resistant sensor system from the 1st to the 5th of April at this year's Hannover Messe (Hall 2, Stand B46).

When food is being baked or steamed as part of an industrial production process, it is important to keep a close eye on humidity levels. If bread or baked goods lose too much moisture or lose it too quickly, the final products will not have the required properties. If, on the other hand, you can control the humidity in the oven precisely, the croissants will come out perfectly fluffy and the bread will have a deliciously crisp crust. 'Precision monitoring of humidity can have a crucial effect on the quality of the products. Knowing the humidity levels allows us to carefully control the temperature and air volumes during the production process, and thus also save on energy,' says Professor Andreas Schütze of Saarland University – an expert in the field of sensor and measuring technology. Precise measurements of moisture content is also critical when drying wood, textiles and coatings in industrial dryers – particularly to prevent heat damage to the materials.

When making humidity measurements it is essential that temperature fluctuations are recorded precisely, as incorrect temperature readings can falsify the humidity data.

Another problem that has to be addressed is the fact that other gases are also released at the high drying temperatures used in industrial ovens and dryers. For example, alcohol is emitted during the baking process and numerous volatile compounds are released when paints or coatings are dried or cured. Up until now, conventional humidity sensors have struggled to monitor relative water vapour levels due to the presence of these other substances in the hot air. And these airborne compounds can significantly shorten the lifetime of the sensors or even damage them. 'In such cases, we talk about the sensor becoming poisoned,' explains Tilman Sauerwald, senior scientist in Schütze's team. When all these factors are taken together, it explains why the humidity measuring systems available up to now have had short service lives and have been either not particularly precise or very expensive.

Measurement technology experts at Saarland University have developed a sensor system that can determine the humidity in industrial ovens and dryers with very high accuracy even at extreme temperatures and in the presence of background interference from other gases. The measurement technology used is complex, but it does far more than simply recording data on individual quantities. 'We use a special ceramic sensor in combination with a Fourier transform impedance spectrometer. This allows us to make measurements across a large dynamic range and gives us excellent resolution over a wide range of temperatures,' explains Henrik Lensch, a PhD student in Professor Schütze's team.

The researchers measure the electrical impedance (i.e. the frequency-dependent resistance to current flow) at different frequencies and compute from this the equivalent resistance and equivalent capacitance values as well as a broad spectrum of other quantities. 'The resulting spectral data then undergoes model-based analysis,' explains Tilman Sauerwald. The analyser unit uses mathematical models to extract those parameters that are relevant to the humidity measurements. The analyser is capable of identifying and filtering out those interference signals that have nothing to do with the humidity. Using this approach, the sensor system can also identify when an error condition or fault occurs.

The research project is a collaboration between Professor Schütze's team and the companies Canway Technology and UST Umweltsensortechnik. The research scientists are looking for partners with whom they can develop their technology for new applications.

Polyurethanes restriction may come in the EU by 2020 at the earliest

Mr Peter Kruppa, Senior Vice President, Head of Application & Technology Development for Coatings and Adhesives, Covestro, in a recent interview with ECJ has said that the regulation for the restriction of substances with more than 0.1 % free polyisocyanates is likely to comes into force by 2020 at the earliest and will most probably be accompanied by a four years transition time. “That basically means for the industry that if a formulation exceeds a threshold 0.1 wt% of diisocyanates, then all the people that are in contact with the formulation need to pass a training. This training is mandatory and needs to be repeated every four years. Covestro has already started to launch a new product line last year which is having a diisocyanate content lower than 0.1 wt % which basically protects people from the need to go into any additional training. And we expect the industry to follow the trend and that we will see many more products like this in the years to come”, he said.

Mr Kruppas said “We see a general trend towards efficiency and performance, especially when it comes to high solids and water-borne systems. They are experiencing a high growth rate in the last years, especially in the APAC region. Also, anything that helps curing at lower temperatures, faster curing speed or reduction of coating layers is what we expect as major trends for the years to come. And we are pretty much in it to supply materials to our customers”.

Mr Karsten Danielmeier, senior VP R&D, Covestro said the “Sustainability is at the very core of Covestro, it is part of our DNA. Innovation inspired by sustainability is a key driver for our activities. Technically that means that we try to reduce the specific CO2 emissions of our processes. We also develop low VOC-products, we use bio-based materials and we have materials with very good catalytic activities which reduce curing temperatures. All this feeds into sustainability for our customers. And last but least we have certainly activities in recycling and recyclable materials”.

Ulrich Meier-Westhues, Karsten Danielmeier and Peter Kruppa later talked about their new book on Polyurethanes.

Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are characterized by their flawlessness and lose their value due to micro-scratches. A new paint from Saarbrücken researchers now could provide a solution: Due to the special arrangement of its molecules, maize starch based coating is able to repair small scratches by itself through moderate heat treatment. The cross-linking via ring-shaped molecules makes the material flexible, so that it compensates for the scratches and they disappear again. The new coating was developed by INM experts together with scientists from Saarland University.

The developers presented the coating with a live demonstration at this year's Hannover Messe from 1 to 5 April at Stand C54 in Hall 5.

The scientists used ring-shaped derivatives of corn starch, so-called cyclodextrins, for the network structure of the lacquers. These cyclodextrins were threaded like pearls onto long-chain polymer molecules. In the polyrotaxanes produced in this way, the cyclodextrins on the polymer thread can move almost freely on certain sections on the linear polymer and are prevented from unthreading by bulky stopper molecules. The pearl chains are cross-linked by a chemical reaction. “The resulting network is flexible and elastic like a stocking,” explains Carsten Becker-Willinger, head of the Nanomers program division at the INM. When exposed to heat, the cyclodextrin rings migrate back along the plastic threads into the area of the surface scratch, thus compensating for the gap formed by the scratch.

For a functional coating with higher mechanical stability and weather resistance, the INM scientists changed the composition of the polyrotaxanes by adding further ingredients such as heteropolysiloxanes and inorganic nanoparticles. At the same time, they were able to reduce the original repair time from several hours to just a few minutes. “As part of numerous application tests for different mixing ratios in combination with artificial weathering tests, we investigated pre-painted surfaces on which we applied the new coating as a topcoat,” says chemist Becker-Willinger. It is now possible to remove micro-scratches in just one minute at 100 degrees Celsius. In their series of tests, the scientists took into account the standard ISO guidelines of the paint industry. “An industrial application is only conceivable if we fulfil these standard guidelines,” Becker-Willinger summarizes the current state of research.

The scientists are currently working on transferring the production of the coating from the laboratory scale to the pilot plant scale. Only then the basis be will provided for large-scale production. The INM is open to cooperation with interested companies for the next step in converting development into applications.

The coating has been funded by the Federal Ministry of Education and Research (BMBF) with a total of 1.1 million euros as part of the research project ” Selbstheilende Fahrzeuglacke auf Basis von Cyclodextrin-Polyrotaxanen ” (FKz. 03VP01052) as part of the VIP+ funding measure since 2016. This funding measure aims to close the gap between initial results from basic research and a possible application.

RMIT scientists turn carbon dioxide back into Coal

Researchers have used liquid metals to turn carbon dioxide back into solid coal, in a world-first breakthrough that could transform our approach to carbon capture and storage.

The research team led by RMIT University in Melbourne, Australia, have developed a new technique that can efficiently convert CO2 from a gas into solid particles of carbon.

Published in the journal Nature Communications, the research offers an alternative pathway for safely and permanently removing the greenhouse gas from our atmosphere.

Current technologies for carbon capture and storage focus on compressing CO2 into a liquid form, transporting it to a suitable site and injecting it underground.

But implementation has been hampered by engineering challenges, issues around economic viability and environmental concerns about possible leaks from the storage sites.

RMIT researcher Dr Torben Daeneke said converting CO2 into a solid could be a more sustainable approach. “While we can't literally turn back time, turning carbon dioxide back into coal and burying it back in the ground is a bit like rewinding the emissions clock,” Daeneke, an Australian Research Council DECRA Fellow, said.

“To date, CO2 has only been converted into a solid at extremely high temperatures, making it industrially unviable. By using liquid metals as a catalyst, we've shown it's possible to turn the gas back into carbon at room temperature, in a process that's efficient and scalable. While more research needs to be done, it's a crucial first step to delivering solid storage of carbon.”

How the carbon conversion works

Lead author, Dr Dorna Esrafilzadeh, a Vice-Chancellor's Research Fellow in RMIT's School of Engineering, developed the electrochemical technique to capture and convert atmospheric CO2 to storable solid carbon. To convert CO2, the researchers designed a liquid metal catalyst with specific surface properties that made it extremely efficient at conducting electricity while chemically activating the surface.

The carbon dioxide is dissolved in a beaker filled with an electrolyte liquid and a small amount of the liquid metal, which is then charged with an electrical current.

The CO2 slowly converts into solid flakes of carbon, which are naturally detached from the liquid metal surface, allowing the continuous production of carbonaceous solid. Esrafilzadeh said the carbon produced could also be used as an electrode.

“A side benefit of the process is that the carbon can hold electrical charge, becoming a supercapacitor, so it could potentially be used as a component in future vehicles. The process also produces synthetic fuel as a by-product, which could also have industrial applications.”

The research was conducted at RMIT's MicroNano Research Facility and the RMIT Microscopy and Microanalysis Facility, with lead investigator, Honorary RMIT and ARC Laureate Fellow, Professor Kourosh Kalantar-Zadeh (now UNSW). The research is supported by the Australian Research Council Centre for Future Low-Energy Electronics Technologies (FLEET) and the ARC Centre of Excellence for Electromaterials Science (ACES).

The collaboration involved researchers from Germany (University of Munster), China (Nanjing University of Aeronautics and Astronautics), the US (North Carolina State University) and Australia (UNSW, University of Wollongong, Monash University, QUT).

The paper is published in Nature Communications (“Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces”.