INFLUENCE OF EXTRUSION COATING CONDITIONS ON STRUCTURE AND TENSILE PROPERTIES OF POLYETHYLENES
Titel:
INFLUENCE OF EXTRUSION COATING CONDITIONS ON STRUCTURE AND TENSILE PROPERTIES OF POLYETHYLENES
Auteur:
Toft, Nils Rigdahl, Mikael
Verschenen in:
International journal of polymeric materials
Paginering:
Jaargang 53 (2004) nr. 9 pagina's 809-828
Jaar:
2004-09
Inhoud:
It is well known that the properties of a final polymer product are determined not only by the polymer characteristics but also, via process-related structural changes, by the processing technique and by processing conditions such as cooling rate and machine speed. In this study, the influence of the extrusion coating process on the structure and properties of LDPE-, LLDPE-, and m-LLDPE-grades was evaluated. Process variables such as the melt temperature, the draw ratio, the length of the air gap between the die exit, and the laminating nip and the machine speed were studied. The primary interest was in the influence of the process parameters on the degree of orientation and its corresponding impact on the tensile and barrier properties (water vapor transmission rate) of the polymer films. The degree of orientation of the films, assessed by shrinkage measurements, was found to be directly related to the elongational strain rate imposed on the films during the drawing stage of the coating process. Furthermore, the strain at break of the films in the machine direction correlated well with the shrinkage of the films, that is, the strain at break was strongly related to the imposed elongational strain rate. The relation is naturally also dependent on the polymer grade used and on how its rheological properties are affected by the process temperature. The melt temperature had a distinct influence on the water vapor transmission rate through the polymer films. This is discussed in terms of the orientation of the specimens.
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