He explained that his firm’s recently commercialised Slentite aerogel is a high-performance material designed for use in thermal insulation. Aerogels are very insulating, he said, but added that traditional aerogels are brittle and difficult to handle successfully.
The Slentite materials are produced by a controlled liquid phase chemical reaction that gives a three-dimensional polyurethane network. After the reaction is complete, the gel must be carefully dried, while maintaining the highly porous structure and without loss of volume.
The BASF material has lambda the value of 17 mW/mK which is "an unprecedented insulation performance” Fricke claimed. “With this material, a 20 to 25% thinner insulation is possible requiring less space, particularly for subsequent insulation," he added.
He explained that the "unprecedented thermal insulating properties of aerogel results from the interaction between small pore sizes and large internal surfaces in the network structure".
Conventional insulation materials based on other types of foam have cells that are more than 1000 times larger than the gases that the cells contain. In these foam cells, gas molecules have enough space to transfer their kinetic energy to each other, and to the foam. The collisions are converted to heat, and this is transmitted through the foam, he explained.
"The pore structure in aerogels is at about the same size as the mobility range of an individual gas molecule, so that heat transfer by collision is significantly reduced,” he said. This effect can be experimentally proven, and is why aerogels have lower thermal conductivity than air, even though the pores are filled only with air, Fricke explained.
Stick around
Marcus Korner explained that the change in foam properties has been a constant source of challenges for his employer, Henkel, which makes adhesives for a range of materials.
A number of requirements are placed on modern foam adhesives. The most important of these are easy processibility, and non-toxicity during processing and use. Additionally, when they are applied, they must produce adhesive layers that have good flexibility, good temperature and chemical resistance, as well as long-term ageing stability.
Korner said solvent-free adhesive systems have become increasingly important in mattress and furniture manufacturing. Hot melt and water-based dispersion adhesives are increasingly being used, he added. Korner suggested that polychloroprene latex adhesives represent a valid alternative to solvent based adhesives. This is because latex polymers coagulate under the mechanical stress caused by joining foam pieces, giving good initial tack.
In most cases, this initial tack is enough to permit further handling of the parts, and the final strength is achieved when the film is completely dried. Therefore, he said, with comparatively simple and cost-effective application methods it is possible to generate glued joints with properties comparable to those of solvent-based adhesives. But, he warned, the bonded parts must dry for several hours before packaging to prevent mould formation in the finished product.
Korner suggested that hot melt technology, where polymers are melted to temperatures between around 130°C and 170°C to reduce the material’s viscosity sufficiently for it to be used, is a valid alternative to non-solvent adhesives. Hot melt adhesive can be sprayed or extruded onto the polyurethane substrate, he said.
Hot melts, he continued, reach their final strength quickly on cooling. However, hot melt adhesives often become brittle when they cool, and he claimed this has led to problems with delamination, and bonded seams coming apart in the mattresses.
Another disadvantage of this adhesive technology is the relatively high capital investment needed to buy the application equipment, he said.
Alfons Wurm and Felix Zimmerman from cutting machinery firm Albrecht Baumer told delegates about some of the developments in producing mattresses and upholstered furniture. They said that this is "strongly characterised by the bringing together all bonding of very different materials". They went on to give an overview of current trends in the sector.
Standards and safety
The machinery theme continued with Rudiger Simon of Sitola, who took a German perspective on industrial health and safety regulations. These were updated in June 2015, and have resulted in a significant change in the way that older machinery is treated.
