Icap-Sira Chemicals/Polymers SpA : Textile co...
Icap-Sira Chemicals/Polymers SpA

Textile coating with inherently flame-retarded acrylic polymers

Cotton horizontal flame-resistance test (Source: Icap-Sira)
Cotton horizontal flame-resistance test (Source: Icap-Sira)

The production of textiles in Europe is focusing on materials that combine aesthetics with enhanced technological performances. For a wide range of articles, one of these required properties is fire safety. Textile coatings are widely used to provide chemical, physical and structural properties to the end article; these coatings as well can be used as a protection from combustion.

These specific coatings can be produced by compounding flame-retardant molecules into a polymer dispersion or solution or can be prepared by an inherently flame-retarded polymer where the flame-retardant chemical is incorporated into the polymer chain.
Compounding flame-retardant chemicals has the advantage of tailoring the product properties and stiffness but has the drawbacks of possible exudation of liquid additives and of the matt aesthetics of powder ones. These drawbacks can be avoided by using inherently flame-retarded polymers.

Up till now the most common fire-retarded polymers for coating applications are chlorinated polymers in water-based dispersion. These polymers are generally quite stiff and suffer from extended yellowing so they can find applications in textile finishing only in a limited number of applications.

Halogenated organic molecules are well known effective flame retardants; they are often used in synergy with metals as magnesium or antimony. However, studies have shown that halogenated flame retardants pose serious health risks. Thus, the environmental and health concerns regarding halogenated and other potentially toxic flame retardants are expected to act as major restraint during the next years. Consequently, there is a growing focus on the development of harmless alternatives across the world on halogen-free flame retardants.
Extensive research is being conducted in the field, with various efforts being implemented for synergistic reactions, compounding optimizations, and combination of flame retardants. Trying to fulfill to all the requirements, Icap-Sira developed a new range of halogen-free acrylic polymers with flame-retardant properties.

Although the technical requirements (beyond flame-retardant specifications) are often as varied as the applications of textiles and it is difficult or impossible to produce a universal solution, the flame-retardant chemistry of these polymers was selected to obtain the best balance in their combustion curbing mechanism and make it suitable for natural and synthetic fibers.

Once selected the correct combination of the flame-retarded segments, the selection of the acrylic monomers allows the production of polymers with different elongation modulus from very soft to very hard ones. Differing cross-linking can be used in order to reach high washing and chemical resistance when needed.
As an example, 3 very soft polymers with differing acrylic-based composition were tested in comparison with a very soft non-flame-retarded polymer and with a chlorinated flame-retarded polymer.

These polymers were used in padding onto 2 non-flame-retarded fabrics (cotton and polyester) and tested according to UNI ISO 3795:1992 – ASTM D5132-04 – FMVSS 302. The specimens were placed in horizontal position and a butane-propane flame was applied at the edge of the specimen for 15 s then removed. Time of flame propagation over the specimen was recorded. The results are listed in the table.

All the flame-retarded samples show a curbing of the combustion of the impregnated fabric when compared with the non-flame-retarded polymer. On cotton the behavior of the 3 samples prepared with Icap-Sira’s new monomer composition is definitely better than the one with the chlorinated reference. In particular with these polymers there is always flame extinction, with samples 2 and 3 combustion stopped when it was just out of the butane-propane flame area.

All the flame-retarded polymers give rise to char formation but this is more consistent and stable with the 3 non-halogenated ones (Fig. see top).

On polyester the behavior of the 3 specimens prepared with Icap-Sira’s polymers show almost the same flame propagation speed of the chlorinated reference. The flame-retardant behavior is nevertheless better because the chlorinated samples show an extensive dripping which helps the extinguishing of the flame but is not admissible in textiles for furniture or clothing.

In conclusion, the new range of inherently flame-retarded acrylic polymers shows:
-    higher safety levels and reduced yellowing if compared to chlorinated polymers
-    the same stiffness flexibility of flame-retarded compounds without the drawbacks of exudation and matting.
-    suitability for application on both natural and synthetic fibers.
This article was published in Technical Textiles 3/2021

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