As for nanofillers in general, the properties of carbon nanotube (CNT) -polymer composites depend strongly on the filler arrangement and the structure of the filler network. This article reviews our actual understanding of the relation between processing conditions, state of CNT dispersion and structure of the filler network on the one hand, and the resulting electrical, melt rheological and mechanical properties, on the other hand. The as-produced rather compact agglomerates of CNTs (initial agglomerates, >1 µm), whose structure can vary for different tube manufacturers, synthesis and/or purification conditions, have first to be well dispersed in the polymer matrix during the mixing step, before they can be arranged to a filler network with defined physical properties by forming secondary agglomerates. Influencing factors on the melt dispersion of initial agglomerates of multi-walled CNTs into individualized tubes are discussed in context of dispersion mechanisms, namely the melt infiltration into initial agglomerates, agglomerate rupture and nanotube erosion from agglomerate surfaces. The hierarchical morphology of filler arrangement resulting from secondary agglomeration processes has been found to be due to a competition of build-up and destruction for the actual melt temperature and the given external flow field forces. Related experimental results from in-line and laboratory experiments and a model approach for description of shear-induced properties are presented

Multiwalled carbon nanotubes (MWNTs) have been introduced into blends of polycarbonate (PC) and poly(styrene-acrylonitrile) (SAN) by melt mixing in a microcompounder. Co-continuous blends are prepared by either pre-compounding low amounts of nanotubes into PC or SAN or by mixing all three components together. Interestingly, in all blends, regardless of the way of introducing the nanotubes, the MWNTs were exclusively located within the PC phase, which resulted in much lower electrical resistivities as compared to PC or SAN composites with the same MWNT content. The migration of MWNTs from the SAN phase into the PC phase during common mixing is explained by interfacial effects.

In melt mixed multiphase polymer blends, the mechanisms determining the spatial distribution and localization of solid particles smaller than the blend domain sizes are still not completely understood. From theoretical considerations of a previous paper of one of the authors, it was derived that the transfer dynamics as well as the stability of different solid fillers at the blend interface reveal a strong dependence on the particle’s aspect ratio. Low interfacial stabilities and high transfer speeds between the blend phases can be deduced for fillers with very high aspect ratios, entitled as the “Slim-Fast Mechanism” (SFM). The SFM appears suitable to explain in retrospect important features of several previous studies that address the localization of differently shaped nanoscaled particles in polymer blends. The SFM was evaluated by investigating the simultaneous transfer of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) from a poly(styrene acrylonitrile) (SAN) precompound into the thermodynamically preferred initially unfilled polycarbonate (PC) phase during melt mixing.

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Polycarbonate (PC) composites containing 1 wt % multiwalled carbon nanotubes (MWNT) were produced in a small-scale DACA microcompounder under variation of mixing temperature and mixing speed at fixed mixing time according to a two-factor and threelevel factorial design. The extruded strands were compression molded under comparable conditions, and their volume resistivity values indicated differences of about 14 orders of magnitude as well as big differences in the state of MWNT agglomerate dispersion (evaluated as macrodispersion index) are observed. The results indicate that mixing at high melt temperature and high speed can lead to the composites having low resistivity and high dispersion index at low mixing energy input. The influence of compression molding parameters was investigated on precompounded PC composites containing 1 and 2 wt % MWNT. Compression molding parameters such as temperature, time, and speed were varied according to a three-level and three-factor factorial design. By adjusting compression molding parameters, the volume resistivity of PC with 1 wt % MWNT composites can be varied over eight orders of magnitude, whereas for 2 wt % MWNT, the variation was within one decade. The electrical volume resistivity results indicate the highest influence of the compression molding temperature followed by time.