Data di Pubblicazione:
2007
Citazione:
Clay-induced preferred orientation in polyethylene/compatibilized clay nanocomposites / A. FAMULARI, P. AROSIO, S. FILIPPI, C. MARAZZATO, P. MAGAGNINI, L. MINKOVA, S.V. MEILLE. - In: JOURNAL OF MACROMOLECULAR SCIENCE. PHYSICS. - ISSN 0022-2348. - 46:2(2007), pp. 355-371.
Abstract:
Nanocomposites of the organically modified clay Cloisitew 15A (CL15A) dispersed in
HDPE-g-MA were prepared by melt-compounding. Microcomposites of the same clay
with HDPE were also obtained with similar procedures. The spherulitic morphology of
the polymer matrix was evidenced by optical microscopy in thin films, whereas the
structure of the up to 2-mm–thick, compression-molded samples was investigated by
WAXD and SAXS. Preferred orientation of both the clay and the HDPE crystallites
were evidenced in the microcomposites and, to a greater extent, in nanocomposites,
whereas in HDPE and HDPE-g-MA control specimens hardly any anisotropy was
detected. The degree of orientation of PE crystals increases with CL15A concentration,
but also with clay exfoliation, with lower cooling rates and decreasing sample thickness.
The orientation of the clay platelets parallel to the compression-molded surface appears
to be determined by the platelets anisotropy and by shear in the mixing and the compression-
molding procedures. In turn, it determines the preferred uniaxial orientation
of HDPE crystals, which have their crystallographic a axis orthogonal, while b and c
are coplanar, to the sample surface, as already reported in the literature for melt-crystallized
HDPE films with thickness below 0.3 mm. It is proposed that the HDPE orientation
results fromconfined crystallization between parallel clay platelets which are on average
less than 0.1 mm apart. Simple models, qualitatively accounting for the observed orientation
of HDPE, are discussed. Organized architectures resulting from confined crystallization
of the polymer matrix in nanocomposites with appropriate anisotropic fillers may
be a general feature, important in determining key properties of these systems
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Confined crystallization; Nanocomposites; Polyethylene; Preferred orientation; X-ray diffraction
Elenco autori:
A. FAMULARI, P. AROSIO, S. FILIPPI, C. MARAZZATO, P. MAGAGNINI, L. MINKOVA, S.V. MEILLE
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