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Crystallization and chemi-crystallization of recycled photodegraded polyethylenes

Lookup NU author(s): Dr Ian Craig, Emeritus Professor Jim White


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Test bars (3 mm thick) made from a high-density polyethylene (HOPE), a low-density polyethylene (LDPE), and a linear low-density polyethylene (LLDPE) were injection-molded from virgin polymer and from blends containing recycled photodegraded polymer of the same kind. The molded bars were then subjected to ultraviolet (UV) exposure. Crystallinity measurements were made at different depths from the exposed surface using differential scanning calorimetry. The effects caused by processing and photodegradation were separated by comparing thermograms obtained in the initial DSC run and in a reheating run, respectively. Chemi-crystallization was produced by UV exposure. The results are interpreted in terms of molecular scission and photo-initiated molecular defects. Scission accounts for the observed chemi-crystallization, whereas the molecular defects inhibit crystallization and eventually limit chemi-crystallization. After remelting, crystallization of the photodegraded materials is influenced both by the molecular mass distribution and by the defect content of the material. The changes in crystallization behavior caused by photodegradation are different for the three polyethylenes. The results obtained using blends that included photodegraded recyclate were consistent with this material acting as a pro-degradent The recyclability of the materials is discussed. © 2005 Society of Plastics Engineers.

Publication metadata

Author(s): Craig IH, White JR

Publication type: Article

Publication status: Published

Journal: Polymer Engineering and Science

Year: 2005

Volume: 45

Issue: 4

Pages: 588-595

Print publication date: 01/04/2005

ISSN (print): 0032-3888

ISSN (electronic): 1548-2634

Publisher: Wiley-Blackwell


DOI: 10.1002/pen.20314


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