Effects of nanoparticles on the density reduction and cell morphology of extruded metallocene polyethylene/wood fiber nanocomposites

Fabrication of Porous Recycled HDPE Biocomposites Foam: Effect of Rice Husk Filler Contents and Surface Treatments on the Mechanical Properties

In this study, a biodegradable, cheap and durable recycled high-density polyethylene (rHDPE) polymer reinforced with rice husk (RH) fibre was fabricated into a foam structure through several processes, including extrusion, internal mixing and hot pressing. The effect of filler loading on the properties of the foam and the influence of RH surface treatments on the filler–matrix adhesion and mechanical properties of the composite foam were investigated. The morphological examination shows that 50 wt.% filler content resulted in an effective dispersion of cells with the smallest cell size (58.3 µm) and the highest density (7.62 × 1011 sel/cm³). This small cell size benefits the mechanical properties. Results indicate that the tensile strength and the Young’s modulus of the alkali-treated RH/rHDPE composite foam are the highest amongst the treatments (10.83 MPa and 858 MPa, respectively), followed by UV/O₃, which has shown considerable increments compared with the untreated composite. The flexural and impact tests also show the increment in strength for the composite foam after chemical treatment. Although the UV/O₃ surface treatment has minor influence on the mechanical enhancement of the composite foam, this method may be a reliable surface treatment of the fibre-reinforced composite.

Influence of graphene on the cell morphology and mechanical properties of extruded polystyrene foam

The incorporation of nanoparticles to polymer foams not only reinforces the cell walls and struts but can also lead to a decrease of cell size and enhanced cell morphology which in turn, yield foams with superior mechanical properties. For this purpose, several studies have focused on identifying close-to-ideal nucleating agents as well as understanding the influence of processing parameters on foam cell morphology.

This research provides a systemic approach to low-density polystyrene foams produced with graphene (thermally reduced graphite oxide), talc and carbon nanotubes (MWCNTs) via foam extrusion. Remarkably, the cell morphologies of polystyrene/thermally reduced graphite oxide foams show enhanced cell homogeneity with a tremendous increase of the cell densities by more than one order of magnitude compared to neat polystyrene and its counterparts.

A Design-of-Experiment Study on the Microcellular Extrusion of Sub-critical CO2 Saturated PLA Pellets

In this study we explore the use of solid-state nucleation in pellets as a means to decouple cell nucleation from cell growth in extrusion. This is achieved by feeding the extruder with gas-saturated PLA pellets. Cell nucleation occurs, similar to that of the well-studied solid-state batch foaming process, when gas-saturated pellets are crushed and heated in the feed section of the extruder. The polymer melt consequently contains the nucleated cells. Further, the gas content in the pellets provides a means to deliver a controlled amount of blowing agent for cell growth at the die exit. It was found that gas concentrations in partially desorbed pellets offers greater control of part density and foam morphology compared to that of fully saturated pellets at 2 MPa. Using Design-of-Experiment statistical methods it was found that gas concentration in the polymer was the most significant variable influencing foam density, whereas the extrudate cooling method was found to control cell size.

Cellular biocomposites from polylactide and microfibrillated cellulose

This paper describes the production of “green” microfibrillated cellulose-reinforced polylactide cellular biocomposites using a wet mixing technique combined with supercritical carbon dioxide foaming. The effect of composition on the morphology, density and compression modulus of foams was investigated for different processing parameters, along with the use of a chain extender to modify the melt elasticity. Foams with mean densities ranging from 0.18 to 0.32 g/cm3 were obtained for the neat polylactide and polylactide/5 wt% microfibrillated cellulose, respectively, and there was a corresponding increase in compressive modulus from 25 to 47 MPa. The addition of the chain extender is argued to compensate the molar mass loss induced by the different processing steps, promoting more uniform foam structures and allowing a density reduction of up to 75%.

Preparation and foaming extrusion behavior of polylactide acid/polybutylene succinate/montmorillonoid nanocomposite

Polylactic acid (PLA)/polybutylene succinate (PBS) and the PLA/PBS/montmorillonite (MMT) composites were prepared by melt extrusion. The morphology structure, mechanical, thermal, and dynamic rheological properties of the composites were characterized, as well as foaming extrusion behavior of the composites was also studied. The results showed that MMT particles were intercalated into the PLA/PBS matrix forming an ‘intercalation’ structure. The toughness of PLA could be improved by blending with PBS. The comprehensive evaluation of mechanical properties of PLA/PBS was further improved by adding MMT. MMT could play the role of heterogeneous nucleation to improve the crystallization effect of PLA/PBS composite. The melt strength of PLA could be significantly increased by the synergies of MMT and PBS. Meanwhile, MMT could act as a compatibilizer to enhance the interfacial interaction between PLA and PBS. The synergies of PBS and MMT effectively reduced the density of PLA blend foam products, and increased their cell density, uniformity of cell size, and shape distribution.