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Dimensional stability of single‐site ethylene copolymers in rotational molding
Author(s) -
Bellehumeur C.T.,
Medina A.,
Xu H.
Publication year - 2009
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.21017
Subject(s) - materials science , crystallinity , comonomer , copolymer , molding (decorative) , composite material , crystallization , ethylene , mold , polymer , polymer chemistry , catalysis , chemical engineering , organic chemistry , chemistry , engineering
The dimensional stability of ethylene copolymers in rotational molding was studied by comparing the warpage observed for a series of conventional and single‐site catalyzed ethylene copolymers. Bench‐scale molding trials were carried out under controlled molding conditions. The rapid cooling of the mold using a water spray resulted in greater warpage. Under such conditions, molded parts made using the single‐site resins showed less warpage compared to the Ziegler‐catalyzed copolymers with otherwise comparable densities. The Ziegler‐catalyzed copolymers were characterized by a faster crystallization rate, and were shown to generate larger crystallinity gradients through the part thickness during the cooling process. Second to temperature gradients, crystallinity gradients are a leading cause for the development of residual stresses and causing warpage. Differences in the crystallization rates between single‐site and Ziegler‐catalyzed copolymers are discussed based on their intermolecular comonomer distributions. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers