Injection Molding a Polyolefin-Based Nanocomposite versus a Talc-Filled TPO
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Injection Molding a Polyolefin-Based Nanocomposite versus a Talc-Filled TPO David A. Okonski Materials and Processes Laboratory General Motors Research & Development Center, MC: 480-106-710 Warren, MI 48090, U.S.A. ABSTRACT General Motors Research and Development and Basell Polyolefins have jointly developed a family of polyolefin-based nanocomposites for use in the injection molding of body-side claddings. Basell Polyolefins commercialized one of these materials as Hifax DX277 in September of 2000, and General Motors has exclusive use of this material. Confidence in the ability of DX277 to perform as intended is being reinforced by molding trials at various Tier 1 locations. In addition to mass savings, the nanocomposite material is showing a much wider processing window than conventional talc-filled TPO’s – allowing Tier 1 molders the opportunity to process away problems rather than initiating a tooling change. This paper will describe the processing advantages associated with the injection molding of a polyolefin-based nanocomposite over a conventional talc-filled TPO. INTRODUCTION To the best of our knowledge, Hifax DX277 is the first and only polyolefin-based nanocomposite material to be commercialized for use in the injection molding of body-side claddings and rocker panels. This particular nanocomposite was developed to compete against the conventional talc-filled polyolefins approved to General Motors GMP.E/P.063 & .068 material specifications for painted and molded-in-color parts. Hifax DX277 is uniquely distinguished from these conventional polyolefins by its very low content of inert filler – just 3% (by mass) of a specially treated montmorillonite clay is used during compounding as opposed to as much as 28% talc. The physical properties exhibited by a nanocomposite depend on the effective aspect ratio of the clay filler. At 100% exfoliation of all platelets, the theoretical aspect ratio for the clay filler is 2000:1, which is 500 times greater than the highest aspect ratios measured for talc-filled systems. Physical properties also depend on how well the nano-sized platelets are dispersed within the polyolefin matrix; this is strictly a function of compounding. As an indication of what has been achieved with Hifax DX277, the polyolefin matrix without filler has a flex modulus of 690 MPa and a flex modulus of 1000 MPa when compounded with 3% clay. Since being commercialized in September of 2000, General Motors Research and Development has worked with Basell Polyolefins to get Hifax DX277 approved within the Corporation for use on body-side claddings and rocker panels. The path to approval requires the participation of Tier 1 molders who must understand and be willing to accept the risks associated with launching any new technology material. To develop confidence in DX277’s ability to perform as intended, General Motors Research and Development has been conducting molding trials at various Tier 1 locations using both prototype and production tooling. It has been observed routinely during these molding tria
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