Evaluation of Sustainable Microspheres for
Enhanced Processing and Surface Quality of EPDM Extrudate

Introduction

Spherix® manufactures post-industrial aluminosilicate ceramic microspheres with a mean particle size of 3-4 μm. The solid, incompressible spheres mechanically facilitate ingredient dispersion, processing speed, and improved surface quality within many polymer systems during mastication and downstream processing. The untreated product is size classified to a 98% distribution of particles measuring below 20 microns and designated as Spherix® 20M.

With the growing need to impart specific benefits to polymeric systems, such as enhanced lubricity and compatibility of dissimilar polymers, Spherix® employs various surface chemistries to modify ceramic microspheres to provide these benefits. Fortimix® SC is designed to increase compatibilization within sulfur-cured elastomeric systems while providing the same mechanical benefit to the processing as Spherix® 20M.

Mixing

Three 350 phr EPDM formulas were mixed in a 1.6 L Lab Banbury® mixer using an EPDM upside-down mix method in which all ingredients were added at the beginning. The batch was discharged at 200°F and transferred to a two-roll mill for sheeting before testing.

For this study, 7 phr of Spherix® 20M and Fortimix® SC were independently added to two separate mixes of an EPDM formulation and then compared against a Control. The trial then utilizes a lab extruder to process the mixed material with Garvey-type ASTM Die to quantify the improvements to processing, dispersion, surface quality, and color consistency.

Extrusion and Color Properties

In Table 1, extruded samples demonstrate how Spherix® 20M and Fortimix® SC contribute to improvements over the Control by reducing nerve and increasing edge precision. The edge quality and the surface sheen were found to be of higher quality in the experimental extrusions, with Fortimix® SC (4/4) edging out Spherix® 20M (3/4) by one point in the Garvey Die test standard for edge sharpness. The Control managed to rupture the blowout disc in the 10 RPM run. The use of microspheres creates the ability to run faster with highly filled compounds by improving the flow of ingredients within a molten polymer matrix and maintaining head pressure within workable parameters.

The color modification data outlined in Table 2 shows Spherix® 20M and Fortimix® SC providing maximized levels of dispersion and agglomeration minimization to prevent color shifts from the beginning of the extrudate to the end. The Control experienced an enhanced shift darker (Δ L* of -9.84) from the beginning of the extrudate to the end compared to the Spherix® 20M and Fortimix® SC specimens. In general, color consistency is a good indicator of the level of dispersion within a compound as the pigmenting ingredients have been optimally and evenly dispersed. Color consistency is indicative of other ingredients’ levels of incorporation and dispersion.

Figure 1 shows the clear ridges in the Control extrudate sample while Figure 2 shows the clear surface quality superiority when just 7 phr of Spherix® 20M is added in the mix.