Reticulate
When reticulation is an aftertreatment of foams , to achieve a liquid, air or gas permeability.
Development of the procedure
The process in plastics technology was patented in 1965 by Scott Paper & Co in the USA. The polyurethane that is permeable to liquids and gases is called reticulated . Such permeable plastics can be used as mechanical filters . By coating the surface with activated carbon , further filter types can be implemented.
Methods
During reticulation, the thin “skins” between the individual foam cells that make the product impermeable to air are destroyed during production.
Water reticulation
A mixture of gaseous, flammable substances (e.g. oxyhydrogen ) is mixed with steam (under pressure) at a temperature of approx. + 185 ° C at the same time as the ignition pulse. An exothermic reaction is initiated and this is caused by the explosively released heat of reaction according to the equation
the perforation of the foam cell walls and their targeted sintering to a web thickness of the structural substance of the foam. Here, the flame propagation of a so-called hard reticulation is thwarted. The gas mixture still contains parts of other gases and the like. a. Propane and butane .
The heat released further heats the water vapor to be precisely dosed, and this is then transferred to the foam in a targeted manner. This can be used if you want to reticulate white or very light foams without any discoloration from the "burn marks". In addition, through this targeted input of the water vapor, the thickness of the web, which is created during the thermal reaction due to the melting of the cell web, can be determined as desired. The desired strength and design of the cell web varies from customer to customer. Depending on the filling pressure and gas mixture (must be calculated for each foam type), a more even distribution of the combustible gas mixture in the raw block to be reticulated is achieved.
Vaporous pollutants that are harmful to health do not arise in this reticulation process when water is added, since the foams are neither exposed to high temperatures nor to the action of open flames.
If the pre-pressure at which the hydrogen-air-water-oxygen mixture is ignited is raised above 2.5 bar, "discontinuities" occur somewhat above the stoichiometric composition. However, the explosions do not proceed more violently and there is also no noticeable congestion / compression of the combustion fumes, which in turn would result in an increase in pressure. The formation of flames due to the water present is or can be reliably prevented. If these flammable mixtures are ignited multiple times, the described reaction is always triggered despite the water content. If no ignition occurs due to any unforeseeable effects, the existing non-ignited reticulating atmosphere can be removed via a gas valve and the vacuum system and replaced with normal atmosphere .
The INT.TT Muetzelfeldt process only works if the foam is somewhat "deposited". Incidentally, there is hardly any odor. It only works optimally if the ester or ether foam is absolutely dry and well matured (older than a week) before it is introduced into the reaction vessel. A certain type of silicone should also be used in the foam process, especially with coarse-pored polyester (<15ppi).
Embrittlement fracture reticulation
In this process, the closed, cross-linked cells are mechanically at least partially opened by cooling the foam to a temperature below its embrittlement temperature T V and then subjecting it to mechanical stress.
literature
- Konrad Uhlig: Polyurethane paperback . ISBN 978-3446403079
Individual evidence
- ↑ limited preview in the Google book search
- ↑ Fire bulkhead made of a highly porous structure with an intumescent coating and process for its manufacture
- ↑ Technical article plastic foam catalytic converter ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 841 kB)
- ↑ Process for manufacturing an open celled and cross-linked polyolefine foam
