PP is toughened with reclaimed EPDM. (Keeping up with Compounding).

Patented reactive compounding technology developed by the University of Massachusetts at Lowell is being used commercially to create high-impact graft alloys of recycled vulcanized EPDM rubber in polypropylene. Re-engineered Composite Systems (RECS) LLC, a start-up venture in Houston, licensed the technology last year and entered a marketing and sublicense joint venture with compounder Spectrum Polymers in Mansfield, Texas. Spectrum has been producing developmental RePoly resins since last fall. Spectrum is a unit of Doscocil Manufacturing in Arlington, Texas, which is testing the high-strength compounds for use in its own line of gun and pet carrying cases.

Both Spectrum and RECS will sell the pelletized compounds, of which five have been developed so far. These grades are said to be unusual in that the reclaimed rubber is reactively grafted to the PP. Also unusual are the high levels of rubber achieved--up to 80%. RePoly is intended to compete with PP/EPDM thermoplastic vulcanizates (TPVs) by trading lower cost for somewhat lower properties. The first two commercial grades are RePoly 750125 with 60% rubber, which costs 95Cents to $1.20/lb, depending on quantity; and RePoly 750126 with 25% rubber at 65Cents to 75Cents/lb.

A paper published by Associate Prof. Joey Mead and Prof. Ross Stacer of Lowell's Dept. of Plastics Engineering says that post-industrial crosslinked EPDM scrap is ground to 80 and 170 mesh before being mixed into PP. Large rubber particles typically improve impact strength, while smaller particles improve ultimate elongation, the authors say. Ground rubber is blended into the melted PP using reactive extrusion with peroxide to compatibilize the two polymers and promote additional crosslinking between rubber particles. Without compatibilization, strength would drop as EPDM content increased.

Mead and Stacer found that elongation depends on the PP's MFR, with higher MFR producing lower ultimate elongation. Besides carrying cases, the compounds target flooring, roofing, and car trunk and window seals. Spectrum Polymers [phone], www.petmate.com; RECS [phone], www.re-engineeredcomposites.com; U. Mass. Lowell [phone]

PROPERTIES OF FOUR REPOLY GRADES

                         RePoly  RePoly    RePoly    Developmental
                         750126  750125    750130    880003

EPDM content, %          25      60        60        25
Density, g/cc            0.95    1.03      0.97      0.93
Ult. Tens. Str., psi     2872    NA        1250      2800
Flex. Mod., psi          96,300  NA        NA        50,000
Hardness, Shore A        >90     80        73        >90
Elong. @ break, %        140     230       420       430
Notched Izod, ft-lb/in.  2.8     No Break  No Break  3.6
Gardner Impact, in-lb
   @ 70 F                278     320       NA        388
   @ 0-10 F              123     320       NA        341