Researchers for Hoechst Celanese Corp. claim that blending acetal and polypropylene scrap results in a material stronger than virgin PP. The discovery means that separations of the two resins, especially in applications such as automobile parts, may not be crucial to use the recycled resins in autos.
Michel Bitritto, director of recovery and recycling for Hoechst's advanced materials group, said at the Intersociety Polymer Conference in Baltimore in mid-October that the firm had experimented with mixing its Celcon brand acetal copolymer with unfilled PP from scrap auto parts. He said it was found to have somewhat higher tensile strength than virgin resin, as well as increased flex modulus.
``The findings have important implications for automotive designers wishing to use engineering resins but still trying to facilitate recycling of bulk materials such as polypropylene,'' Bitritto said. ``Cost-effective recovery is a particular challenge for engineering plastics like acetal copolymers. They are often molded into small parts used in larger systems of different plastics.''
Hoechst's figures showed that about 16 percent of an auto-mobile's weight is PP, while 1 percent is acetal. Typically, the acetal is used in seat belt buckles, and interior clips that are difficult to separate from larger PP parts in the recycling process. Hoechst's findings indicated the acetal parts need not be separated from the bulk of the PP in the scrap stream, and that the parts could be blended with virgin materials using conventional equipment into a viable recycled resin.
In an actual case, Hoechst researchers considered an auto-maker's need for a small plastic rod used for support. If molded of virgin PP, it lacked the necessary mechanical support properties. If molded of acetal, the part was too expensive, but a mixture of unfilled PP scrap with 25 percent glass-filled reclaimed acetal yielded a blend with greater flex strength, increased flex modulus and higher notched Izod impact rating.
The obvious thrust of the findings is that car and other recyclers, who receive mixed waste plastic containing acetal, need no longer separate the acetal, said Frank Colucci of Ardrey Inc., a public relations firm for Hoechst.
The company plans to unveil the test results for the first time for automakers and dismantlers at the Auto Recycle Conference in Dearborn Mich., Nov. 15-16, Colucci said.