Structure and properties of composite polyolefin materials
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Abstract
This thesis is based on three main studies, all dealing with structure-property
investigation of semicrystalline polyolefin-based composites. Low density poly(ethylene)
(LDPE) and isotactic poly(propylene) (iPP) were chosen as parts of the composites materials
and they were investigated either
separately (as homoploymers), either in blend systems with
the composition LDPE/iPP 80/20 or as filled matrix with layered silicate (montmorillonite).
The beneficial influence of adding ethylene-co-propylene polymer of amorphous
nature, to low density poly(ethylene)/isotactic poly(propylene) (80/20) blend is demonstrated.
This effect is expressed by the major improvement of mechanical properties of ternary blends
as examined at a macroscopic size scale by means of tensile measurements. The structure
investigation also reveals a clear dependence of the morphology on adding ethylene-copropylene
polymer. Both the nature and the content of ethylene-co-propylene polymer affect
structure and properties. It is further demonstrated that the extent of improvement in
mechanical properties is to be related to the molecular details of the compatibilizer.
Combination of high molecular weight and high ethylene content is appropriate for the
studied system where the poly(ethylene) plays the
role of matrix.
A new way to characterize semicrystalline systems by means of Brillouin
spectroscopy is presented in this study. By this method based on inelastic light scattering, we
were able to measure the high frequency elastic constant (c11) of the two microphases in the
case where the spherulites size is exhibit size larger than the size of the probing phonon
wavelength. In this considered case, the sample film is inhomogeneous over the relevant
length scales and there is an access to the transverse phonon in the crystalline phase yielding
the elastic constant c44 as well. Isotactic poly(propylene) is well suited for this type of
investigation since its morphology can be tailored through different thermal treatment from
the melt. Two distinctly different types of films were used; quenched (low crystallinity) and
annealed (high crystallinity). The Brillouin scattering data are discussed with respect to the
spherulites size, lamellae thickness, long period, crystallinity
degree and well documented by
AFM images.
The structure and the properties of isotactic poly(propylene) matrix modified by
inorganic layered silicate, montmorillonite, are discussed with respect to the clay content.
Isotactic poly(propylene)-graft-maleic anhydride was used as compatibilizer. It is clearly
demonstrated that the property enhancement is largely due to the ability of layered silicate to
exfoliate. The intimate dispersion of the nanometer-thick silicate result from a delicate
balance of the content ratio between the isotactic poly(propylene)-graft-maleic anhydride
compatibilizer and the inorganic clay.