Synthesis and characterization of fire-retardant layers onto Polyolefin substrates

First goal of this work was to produce thick fire-resistant coatings, which are able to withdraw the direct contact to flames. Preliminary tests had shown that thicknesses more than 10 µm are needed to measure effects on flammability. Here, 40 µm thick layers are prepared. The adhesion of such thick layers mainly depends on the use of surface treatment of polyolefin substrates. Plasma exposure and deposition of plasma polymer layers are easiest and most efficient methods to promote the adhesion of thick layers used for the fire protection of materials. Indeed, plasma processing doesn’t modify the intrinsic properties of materials such as the mechanical properties, easily processed, and can be applied over a wide range of materials even though for metals. To achieve very high adhesion of such thick coatings to the polymer substrates it has to be considered that the chemical nature of coating and polymers is different, strong different thermal expansion coefficients exist and therefore adhesion was most oftenabsent. Different techniques were used to prepare such thick layers and to promote strong adhesion. Coatings have to withdraw high temperatures at exposure to flame without self-peeling; elsewise flames and oxygen have access to the subjacent easy flammable polymer substrates. Combinations of two deposition techniques allow fulfilling these preconditions. Generally, plasma pre-treatment was used to improve the adhesion property of polyolefin substrates and deposition of plasma polymers onto the plasmapretreated polyolefin served as adhesion-promoting basecoat responsible for maximal adhesion between polyolefin and thick coating. This basecoat was 0.1 to 1.0 µm thick. To deposit layers with thickness of 20 or 40 µm this plasma technique was too much timeconsuming. Therefore, the thick layers were deposited onto such basecoat by simple dipping into coating solution or by spraying. Such combination of adhesion-promoting basecoats and thick coatings were tested using peel strength measurements and flammability tests. The most important problem was to find a suitable basecoat, which adheres very well onto the nonpolar polymer substrates (or plasma-pretreated substrates) but show also good adhesion to the dip or spray coating material as well as balancing of thermally induced stress at the interface ofsubstrate and coating.