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Water-assisted, or more generally liquid-mediated, melt compounding of nanocomposites is basically a combination of solution-assisted and traditional melt mixing methods. It is an emerging technique to overcome several disadvantages of the above two. Water or aqueous liquids with additives, do not work merely as temporary carrier materials of suitable nanofillers. During batchwise and continuous compounding, these liquids are fully or partly evaporated. In the latter case, the residual liquid is working as a plasticizer. This processing technique contributes to a better dispersion of the nanofillers and affects markedly the morphology and properties of the resulting nanocomposites. A survey is given below on the present praxis and possible future developments of water-assisted melt mixing techniques for the production of thermoplastic nanocomposites.

In this study thermoplastic starch (TPS) matrix-based microfibrillated cellulose (MFC) reinforced microcomposites were prepared via extrusion compounding in one-step. Starch was plasticized with a combination of glycerol and water. The native starch/glycerol and the plasticized starch/water ratios were set for 4/1 and 6/1, respectively. Two different MFC types (of varying mean length and diameter) were incorporated up to 20 wt.% in the plasticizer-containing premix prior to its compounding in a twinscrew extruder. The mechanical properties of the TPS biocomposites were markedly enhanced by the introduction of MFC. The yield strength was improved by ~50%, whereas the stiffness by ~250% upon adding 20 wt.% MFC compared to the parent TPS. Dynamic mechanical analysis (DMA) revealed that the reinforcing effect of the MFC was more prominent in the starch-than in the glycerol (plasticizer)-rich phase of the TPS. The mean length and diameter of the MFCs, yielding similar aspect ratio values lying below the estimated critical one, influenced the mechanical, thermal and thermo-mechanical properties marginally.

In this work, all-polypropylene composites (all-PP composites) were manufactured by injection moulding. Prior to injection moulding, pre-impregnated pellets were prepared by a three-step process (filament winding, compression moulding and pelletizing). A highly oriented polypropylene multifilament was used as the reinforcement material, and a random polypropylene copolymer (with ethylene) was used as the matrix material. Plaque specimens were injection moulded from the pellets with either a film gate or a fan gate. The compression moulded sheets and injection moulding plaques were characterised by shrinkage tests, static tensile tests, dynamic mechanical analysis and falling weight impact tests; the fibre distribution and fibre/matrix adhesion were analysed with light microscopy and scanning electron microscopy. The results showed that with increasing fibre content, both the yield stress and the perforation energy significantly increased. Of the two types of gates used, the fan gate caused the mechanical properties of the plaque specimens to become more homogeneous (i.e., the differences in behaviour parallel and perpendicular to the flow direction became negligible)

Impact resistant all-poly(lactic acid) composites were prepared by filmstacking of highly crystalline poly(lactic acid) (PLA) fibres with fully amorphous PLA films. The flammability of the self-reinforced PLA composites (PLA-SRCs) was effectively reduced by incorporating ammonium polyphosphate based flame retardant (FR) additive and montmorillonite clays in a weight ratio of 10 to 1 into the matrix layers. As low as 16 wt% FR content proved to be sufficient for achieving self-* Corresponding author: tel: +36 1/463-1348, e-mail: kbocz@mail.bme.hu, address: Műegyetem rkp. 3., Budapest, 1111, Hungary 2 extinguishing behaviour, i.e. UL94 V-0 rating, and to achieve 50% and 40% reduction of peak of heat release rate and total heat emission, respectively. The introduction of FR additives improved also important mechanical properties compared to the FR-free all-PLA composite. The stiffness of the PLA-SRCs increased steadily with the FR contents of their matrix layers, furthermore, owing to the improved fibre-matrix bonding, prominent energy absorption capacity (impact perforation energy as high as 16 J/mm) was determined for the effectively flame retarded PLA-SRC.

This study presents the applicability of different types (exothermic and endothermic) of chemical blowing agents (CBAs) in the case of poly(lactic acid) (PLA). The amount of foaming agent is a fixed 2 wt%. We used a twin-screw extruder and added the individual components in the form of dry mixture through the hopper of the extruder. We characterized the PLA matrix and the chemical blowing agents with different testing methods. In case of the produced foams we carried out morphological and mechanical tests and used scanning electron microscopy to examine cell structure. We showed that PLA can be successfully foamed with the use of chemical blowing agents. The best results were achieved with an exothermic CBA and with PLA type 8052D. The cell population density of PLA foams produced this way was 4.82 × 105 cells/cm3, their expansion was 2.36, their density 0.53 g/cm3 and their void fraction was 57.61%.

This study presents the investigation of different content of thermally expandable microsphere (EMS) type of a physical blowing agent added to polylactic acid (PLA). The effects of the different doses of EMS, processing temperatures, and d-lactide content of the polylactic acid were analyzed for foam properties and structures. We characterized the different PLAs and the physical blowing agent with different testing methods (gel permeation chromatography, rotational rheometry, isothermal thermogravimetric analysis, and thermomechanical analysis). The amounts of the foaming agent were 0.5, 1, 2, 4, 8 wt%, and processing temperatures were 190 °C, 210 °C, and 230 °C. The foam structures were produced by twin-screw extrusion. We used scanning electron microscopy to examine the cell structure of the foams produced, and carried out morphological and mechanical tests as well. The result of extrusion foaming of PLA using different amounts of EMS shows that an exponentially decreasing tendency of density reduction can be achieved, described by the following equation, ρ(x ) = 1.062 · e − x 7.038 + 0.03 (R2 = 0.947) at 190 °C. With increasing processing temperature, density decreases at a lower rate, due to the effect that the microspheres are unable to hold the pentane gas within the polymer shell structure. The d-lactide content of the PLAs does not have a significant effect on the density of the produced foam structures.

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