The rheological properties of a dispersion of cellulose nanocry stals (CNC) in an aqueous sol ution of poly ox y ethy lene (PEO) hav e been inv estigated. A peculiar behav ior is reported. Upon adding CNC, the v iscosity of the suspension first decreases and then increases. Adsorption of PEO chains on the surface of the nanoparticles has been suspected. Freeze-dry ing of this PEO-adsorbed CNC dispersion was performed and the ensuing ly ophilisate was ex truded with low density poly ethy lene. Compared to neat CNC-based nanocomposites, both improv ed dispersibility and thermal stability were observ ed. This simple and phy s ical method constitutes an approach of choice for the melt processing of CNC-based nanocomposites with a hy drophobic poly meric matrix applicable at industrial scale.

A methodology for estimating the entanglement density in the amorphous phase of semicrystalline polyolefins was developed. The method is based on the analysis of the density of physical network junctions in the amorphous phase by 1 H NMR T 2 relaxation experiments. The density of the entanglement network was estimated for melt-and high-pressure-crystallized highdensity polyethylenes (HDPEs) at temperatures close to and gradually approaching melting. Its value is lower for high-pressure-crystallized HDPE than for the same melt-crystallized polymer. The network of entanglements is characterized by the fraction of entangled network chains, the weight-average molecular weight of the network chains between apparent chain entanglements, M e , and the volume average density of apparent chain entanglements. The entanglement network was studied in a series of low-and high-molecular-weight HDPEs and bimodal HDPE samples with different molecular weight characteristics and densities controlled by different contents of the 1-butene comonomer. It turns out that the molecular weight characteristics of the HDPEs influence the entanglement network. The fraction of network chains and the average density of apparent chain entanglements decrease with decreasing molecular weight M n due to the "dilution" effect caused by disentangled chain-end segments increasing the M e . The current methodology is of interest for studying the effect of crystallization conditions, molecular structures, and short-chain branches on phase composition, melting behavior, and chain entanglements in the amorphous phase of polyolefins. The method allows estimation of the fraction of network chains, which potentially can form tie-chain segments during deformation. The effect of short-chain branches and molecular weight characteristics on the creep response of polyolefins is discussed.

Self-reinforced polypropylene is a very tough material. It is even thought that its impact resistance increases with decreasing temperature. This was investigated by examining the constituent tapes and matrix. Tensile tests on both drawn polypropylene tapes and self-reinforced polypropylene were similar: the stiffness increased and the failure strain slightly decreased at low temperatures. The matrix, however, embrittled below room temperature due to the glass transition. In contrast with literature data on Izod impact resistance, the penetration impact resistance did not increase at low temperatures. At lower temperatures, the damaged area after non-penetration impact was significantly reduced. This was caused by a change in the damage mode from tape-matrix debonding to matrix cracking, as the matrix went through its glass transition. These conclusions provide the first understanding of the failure behaviour of self-reinforced polypropylene below room temperature, and can be exploited to further optimise the excellent impact resistance of self-reinforced polymers.

The roles of the rubber particle size, the rubber particle size distribution and the constitutive behaviour of the isotactic polypropylene matrix have been studied by combining the Lazerri–Bucknall energy criterion for cavitation with the Van der Sanden–Meier–Tervoort ligament model adapted for impact conditions. It is concluded that an optimised morphology offers great potential to achieve enhanced mechanical properties with far less rubber and hence achieve a superior stiffness/toughness/processing balance.