Unlocking renewable alternatives to PTFE waxes for wood coatings

Wei Zhang, Technical Business Development Manager, Coatings & Inks APAC, Clariant BU Adsorbents & Additives, presents test findings on renewable polymer-based waxes as alternatives for a new challenge for the coatings industry – restrictions on PFAS and PTFE

Modifying coatings formulations in order to address evolving end user demands and increasingly stringent regulatory requirements is a familiar reality for coatings manufacturers. Now, as regulators around the world are considering the banning of PFAS, the entire class of per- and polyfluoroalkyl substances, formulators face the new challenge of replacing Polytetrafluoroethylene (PTFE) or PTFE-containing micronised waxes in their products.

These waxes have traditionally had unique importance in the industry due to their excellent slip, scratch resistance and extraordinary thermal stability. However, because PFAS is added or generated during PTFE production and use, finding a future alternative to deliver that performance is essential.

The good news is that substitute options are already available to wood coatings’ formulators.

Exploration into PTFE alternative solutions

Clariant has been focusing on the development of sustainable formulation ingredients for many years, exploring suitable PTFE-alternative solutions for different coating applications.

Optimal outcomes have been achieved with its products based on renewable polymers or modified natural waxes, with capabilities to functionally replace PTFE or PTFE-containing products.

Main products with attributes of particular relevance to wood coatings include Ceridust® 8330 and 8360, which have excellent abrasion resistance; Ceridust 1041 Vita and Ceridust 1060 Vita with excellent slip performance; and Ceridust 8090 Vita and Ceridust 8091 Vita, which are scratch-resistant with easy dispersibility in aqueous systems. The Vita-designated products are bio-based and have been developed on a variety of renewable polymer platforms, with at least 98% Renewable Carbon Index (RCI) content.

In addition to regulatory-related support, they show wider suitability for various coating systems than PTFE products. Since PTFE is difficult to disperse in aqueous systems, it is rarely used in waterborne coatings. Consequently, there has always been a certain gap in the slip performance and scratch resistance of aqueous coatings compared with solvent-based systems.

The alternative bio-based micronised waxes are suitable for a wide range of coatings, including waterborne coating systems, meaning that waterborne coating users can also benefit from bio-based micronised wax products that significantly improve coating performance.

The following tests demonstrate their characteristics and performance in both wood coating systems.

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Renewable polymer-based waxes that can replace PTFE waxes

Ceridust 8330 and Ceridust 8360 have particle sizes D50 of 5.5 microns and 12um respectively. They are compounds of bio-based polymer and metallocene polyethylene waxes. The renewable polymer in the products has excellent mechanical resistance and excellent thermal stability and does not melt or decompose below 240⁰C. The metallocene polyethylene part provides low coefficient of friction (CoF) and hardness. The unique combination of the additive delivers excellent abrasion resistance, good slip and excellent thermal stability. These products can not only be applied to solvent systems but also aqueous systems.

A comparison test of 1% Ceridust 8330 and 1% PTFE/PE wax in 2K polyurethane solventborne wood paint (WFT 100um), shows that Ceridust 8330 provides comparable slip (CoF, Coefficient of friction) and scratch resistance with PTFE/PE, and better clarity (transparency and haze) (Figure 1).

Figure 1. Comparison in a 2K PU solventborne wood paint

Ceridust 1041 Vita and Ceridust 1060 Vita are modified natural waxes with particle sizes of D50 8um and 12um respectively. They feature very low coefficient of friction and good matting properties. In wood paints, they offer a pleasant smooth soft touch and excellent scratch resistance, making them ideal for high-end wood coating applications.

A comparison test of 1% Ceridust 1060 Vita and 1% PTFE/PE wax in solventborne 2K polyurethane wood coating indicates that Ceridust 1060 Vita can improve the CoF hand scratch resistance compared to PTFE/PE formulations (Figure 2).

Figure 2. Comparison in a solventborne 2K PU wood coating

The performance of 1% Ceridust 1060 Vita, 1% oxidized polyethylene wax, and 1% amide-modified polyethylene wax was tested in waterborne acrylic wood coatings and indicates that Ceridust 1060 provides excellent slip and scratch resistance in this application (Figure 3).

Figure 3. Comparison in a waterborne acrylic wood coating

Ceridust 8090 Vita and Ceridust 8091 Vita are representatives of another renewable polymer-based micronised wax product. Incorporation and wetting behavior are outstanding and can be dispersed homogenously without surfactants, with minimum impact on the viscosity of aqueous systems.  Easy-to-use is a key feature of these products. In addition to good scratch resistance, these two products can provide wood coatings with the pleasant feel of natural wood and adjust the coefficient of friction to meet differentiated end market demand.

Figure 4. Dispersibility comparison in aqueous acrylic coatings formula at low speed stirring

Application tests of dispersibility between Ceridust 8091 Vita and oxidised polyethylene wax (product A) in an aqueous acrylic coating formula show that Ceridust 8091 Vita can be easily wetted at low speed stirring, while oxidised polyethylene wax is difficult to wet (Figure 4).  After 1000 RPM stirring for 1 min, Ceridust 8091 Vita has been dispersed homogeneously, and the oxidised polyethylene wax has pronounced undispersed coarse particles (Figure 5).

Figure 5: Dispersibility after stirring at higher speed

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Product clarity improvements

A recognised disadvantage of PTFE micronised wax is that it affects transparency, which has a significant impact on applications like wood paint. Clariant’s bio-based micronised waxes have good clarity in general, which outperforms the coating performance with PTFE additives.

Wider application

Tests in metal packaging coatings indicate the possibilities for replacing PTFE-containing additives with renewable polymer-based options in applications beyond wood coatings, such as can coatings, coil coatings, printing inks and powder coatings.

Assessment of 1% Ceridust 8330 with 1% PTFE/PE wax in a solventborne polyester can coating (DFT 10-12um) shows that Ceridust 8330 is close to PTFE/PE in slip (CoF) and scratch resistance (Sheen Scratch). Ceridust 8330 also shows significantly better abrasion resistance than PTFE/PE formulations (Taber abrasion) (Figure 6).

Figure 6.  Assessment of Ceridust 8330 in a solventborne polyester can coating

Testing of 1% Ceridust 1060 Vita and 1% PTFE/PE wax shows that Ceridust 1060 Vita can effectively increase slip (CoF measured with leather sleigh and metal ball sleigh respectively).

Figure 7. Assessment of Ceridust 1060 Vita in a solventborne polyester can coating (DFT 10-12um)

Summary

It has been demonstrated that bio-based micronised waxes can not only replace PTFE-containing waxes, but also outperform PTFE-containing waxes in some important aspects.

Many renewable polymers have special properties that are different to synthetic waxes due to their special chemical structure. Such properties can be excellent abrasion resistance, as for Ceridust 8330 and Ceridust 8360, or very low coefficient of friction (slip), as in the case of Ceridust 1041 Vita and Ceridust 1060 Vita.  They also include excellent wettability, as the results shown above for Ceridust 8090 Vita and Ceridust 8091 Vita indicate.

These renewable polymer based materials can be developed into high-performing alternatives to PTFE-containing products that enhance coating end product performance aspects. The environmental profiles of these market-defining products also support sustainability efforts in the coatings industry regarding the reduction of hazardous materials and fossil carbon content, by helping users develop finished products with a lower environmental impact. Clariant offers product carbon footprints of the referenced Ceridust products, created by its CliMate Tool according to ISO 14067, to further assist customers.

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