ONLINE EXCLUSIVE: Reducing Fischer-Tropsch Wax Content in Hot-Melt Adhesives

In light of the current global shortage of Fischer-Tropsch waxes (F-T waxes), this article provides a guide to formulating hot-melt adhesives with reduced F-T wax content.

Table 1. Typical Physical Properties of Epolene Waxes

The adhesive industry continues to experience raw-material shortages. In particular, adhesive manufacturers are concerned about the current global shortage of Fischer-Tropsch waxes (F-T waxes). This shortage has been especially challenging for adhesive manufacturers of EVA-based hot-melt packaging adhesives. As F-T waxes have been placed on allocation, hot-melt adhesive (HMA) manufacturers and end users have found it necessary to seek alternative adhesive formulations with reduced F-T wax content.

Table 2. Molecular Weight Distribution of Epolene Waxes

To provide adhesives formulators with options, Eastman Chemical Co. has evaluated HMA formulations with reduced levels of F-T waxes. These adhesive formulations are based on either full or partial substitution of F-T waxes.

The adhesive formulations presented are intended to be starting-point formulations and may be optimized by adjusting the proportion of components or by adding various performance-enhancing additives used by most adhesives formulators

Table 3A. Examples of HMA Formulations with Full Substitution of F-T Wax

The following information presents test data generated to illustrate the use of these products in an HMA formulation. The products highlighted in this piece include the following.

Epolene N-14 Polyethylene Wax* - A nonemulsifiable medium-density, relatively low molecular weight polyethylene homopolymer. Due to its relatively low viscosity, Epolene N-14 can be used to modify flow properties and set speed in HMAs.
Epolene N-21 Polyethylene Wax* - A nonemulsifiable, higher density polyethylene wax. Because of its relatively high softening point and relatively low viscosity, Epolene N-21 is used as an additive to adjust set speed in HMAs.
Permalyn 3100 Synthetic Resin* - A hard, low-color, thermoplastic pentaerythritol (PE) ester of rosin. The use of Permalyn 3100 offers useful properties in HMAs by providing specific adhesion, improved wetting characteristics to various substrates, as well as viscosity control.

Table 3B. Examples of HMA Formulations with Partial Substitution of F-T Wax

Based on the data shown in Table 4, results suggest that full or partial replacement of F-T wax with Epolene N-14 or Epolene N-21 in the proposed EVA adhesive formulation results in similar adhesion and cohesion as evidenced by peel adhesion failure temperature (PAFT), shear adhesion failure temperature (SAFT) and low-temperature fiber tear results.

Table 4. Adhesive Properties of HMA Formulations with Reduced F-T Wax Content

As illustrated in Figures 1 and 2, the set times as determined by dynamic mechanical analysis (DMA) correlate very well with set times determined by the use of an Olinger Bond Tester (see Table 4). The F-T wax has the shortest set time, followed by Epolene N-14 and then Epolene N-21. It should be noted that the use of Epolene waxes results in higher formulated viscosity and longer open time. It may be possible to fine tune these parameters by increasing the paraffin wax or tackifier level by adjusting the adhesive application temperature.

Figure 1. Full Substitution

Conclusion

These concepts are intended solely as initial work to evaluate HMAs with properties similar to those of a control formula using 15 wt. % F-T wax. Based on these concepts, it may be possible to reduce F-T wax content.

As shown by PAFT, SAFT and low-temperature fiber tear results, full or partial substitution of F-T wax in an adhesive formulation with Epolene waxes provides formulators with similar adhesion, cohesion and set time. In general, the use of Epolene waxes provide higher formulated viscosity and longer open time than F-T waxes.