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This work aims to investigate the fire performance of novel polyethylene-based single polymer composites. Fumed silica nanoparticles and magnesium hydroxide microfiller were added at an optimized concentration to a linear low-density polyethylene matrix, which was then reinforced with ultra-high molecular weight polyethylene fibers. Through the optimization of the production process, it was possible to limit the porosity inside the single polymer composites, thus retaining the pristine mechanical properties of the fibers. The addition of SiO2 and magnesium hydroxide determined an increase in the elastic modulus in both the longitudinal and transversal direction, but it concurrently led to a reduction in ductility, especially in the transversal direction. The fillers were proved to bring interesting improvements of the thermal degradation resistance and of the flame behaviour. Thermogravimetric analysis tests highlighted an increase in the onset degradation temperature and in the temperature associated to the maximum degradation rate. Moreover, both the oxidation onset temperature and limiting oxygen index were considerably improved. Cone calorimetry tests evidenced that filled single polymer composites were characterized by lower peak heat release rate and total heat released with respect to neat single polymer composites. [ABSTRACT FROM AUTHOR]

For the first time, nanocomposite filaments consisting of polyvinyl alcohol and carbon nanotubes were successfully used for additive manufacturing by fused deposition modeling. Polyvinyl alcohol and carbon nanotubes were mixed in a water solution using hexadecyl trimethyl ammonium bromide as a surfactant. Filaments with various concentrations of carbon nanotubes (up to a maximum content of 3 wt.%) were obtained with a single screw extruder and used to feed a commercial desktop 3D printer. Carbon nanotubes increase the glass transition temperature of the printed samples; however, the presence of CTAB reduces this effect. The viscosity of the material increases with the addition of carbon nanotubes and the 3D-printed samples become tougher as the carbon nanotubes amount increases. Elastic modulus and creep compliance are remarkably improved by the presence of carbon nanotubes, while ultimate mechanical properties are not affected. The high reduction of electrical resistivity found on the filaments was not found on the 3D-printed samples. This was attributed to the prevalent location of carbon nanotubes in the core region of the 3D-printed samples as documented by scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Kenaf fibres of different aspect ratios (L/D = 30 and 160) were melt compounded in an internal mixer with two types of starch-grafted-polypropylene matrices (G906PF and G906PJ) at various loadings, i.e. 10, 20 and 30 wt%. The compound was then compression-moulded into plaques of 1-mm thickness. Thermal, rheological and dynamic mechanical properties of the composite samples were investigated by several techniques involving differential scanning calorimetry, thermogravimetric analysis, melt flow index, Vicat softening point and dynamic mechanical thermal analysis. The results indicated that both thermal and mechanical properties of the composites were remarkably improved by kenaf fibres. Loss modulus and loss factor showed a shift of peak transitions to higher temperatures. Finally, the properties of the investigated composite materials were not affected by the fibre aspect ratio. [ABSTRACT FROM AUTHOR]

The effects of various types and amounts of fumed silica and graphite nanoplatelets on the microstructure and thermomechanical properties of polypropylene composites containing 5, 10, and 20 wt% of short glass fibers have been analyzed. Hybrid composites were produced by melt compounding and compression molding. The aspect ratio of the short glass fiber decreased with the fiber loading and the nanofiller amount. The tensile strength and elastic modulus increased, while the elongation at break decreased as the content of both short glass fiber and nanofiller increased. A two-population model, based on the Halpin–Tsai and Tsai–Pagano composite theories, was used to predict the elastic modulus of the nano-micro hybrid composites. Experimental values appear to be reasonably consistent with model predictions. Tensile energy to break under impact conditions increased with the short glass fiber content but decreased with nanofiller amount. Moreover, storage modulus and creep stability were remarkably enhanced in short glass fiber composites by the presence of both nanofillers. [ABSTRACT FROM AUTHOR]

Basalt and E-glass fibers fabrics were combined with carbon fiber fabrics in order to prepare epoxy-based interlaminar hybrid composites and to investigate the hybridization effect on the flexural and impact properties of the resulting laminates. The flexural modulus of the composites depended on their composition according to a rule of mixture, while an important synergistic effect was detected for the ultimate flexural properties. Charpy impact tests evidenced a strength increase as basalt and glass fibers content increased. Interestingly, hybridization with basalt fibers promoted an increase of the adsorbed impact energy due to an enhancement of the fracture propagation component. [ABSTRACT FROM AUTHOR]

In this study, the influence of synthetic boehmite alumina nanoparticles with various surface treatments on the morphology, crystallization behavior and mechanical properties of polypropylene copolymer nanocomposites was studied. In particular, a series of polypropylene/boehmite alumina nanocomposites, containing up to 10 wt% of untreated and of octylsilane-functionalized boehmite alumina nanoparticles, were prepared by melt compounding and film blowing. A third type of composite was produced by incorporation of boehmite alumina nanoparticles treated with benzene sulfonic acid. Scanning electron microscopy indicated that boehmite alumina nanoparticles were finely and uniformly dispersed, though agglomerated, in the polypropylene nanocomposites. Surface-treated boehmite alumina nanoparticles were better dispersed in the matrix than the untreated boehmite alumina nanocomposites. The melt viscosity of nanocomposites remained unaltered or decreased by nanofiller incorporation at low concentration (2.5 and 5 wt%), while it slightly increased at higher concentrations (10 wt%). Uniaxial tensile tests indicated that the nanoparticles can induce a remarkable stiffening effect even at a rather low filler content, especially in the case of surface-treated particles. The plane stress fracture toughness of the material, evaluated by the essential work of fracture approach, showed a noticeable improvement due to boehmite alumina incorporation, with an optimal effect for a filler concentration of about 2.5 wt%. [ABSTRACT FROM AUTHOR]

Fabrics of basalt (BFs), E-glass (GFs), and carbon (CFs) fibers with the same areal density were used to prepare epoxy-based laminates. The BF laminates presented elastic moduli and strength values higher than those of the corresponding GF laminates, with tensile strength values near to that of CF laminates. Investigation of the behavior under fatigue conditions indicated superior performances of BF laminates with respect to the corresponding GF composites, with an improved capability of sustaining progressive damaging and slightly higher damping properties. As far as the fatigue behavior is concerned, BFs may therefore represent a valid substitute of GFs in structural composites. [ABSTRACT FROM AUTHOR]

Various kinds of organo-modified clays were dispersed at different amounts in an epoxy matrix. After clay addition, the viscosity of the epoxy resin resulted still acceptable for a possible usage as matrices for fiber-reinforced composites. The formation of intercalated microstructures led to substantial improvements of the thermal (glass transition temperature) and mechanical (fracture toughness) properties of the epoxy matrix. E-glass fiber/matrix interfacial shear strength was evaluated by the single-fiber microdebonding method. The introduction of organo-modified clays led to the formation of a stronger fiber-matrix interface, with an increase of the interfacial shear strength of about 30%. Concurrently, the evaluation of the fiber/matrix contact angle revealed an improved wettability when organo-modified clays were added. [ABSTRACT FROM PUBLISHER]

Thin transparent films of polyurethane—clay nanocomposites were prepared by dispersing different amounts of commercial organo-modified clay in a mixture of cycloaliphatic amines used as chain extender of a blocking prepolymer, in order to investigate the role of the filler content on the thermo-mechanical behavior of the resulting composites. X-ray diffraction measurements evidenced the formation of an intercalated structure, regardless to the clay loading. Furthermore, the optical clarity of the samples was not substantially compromised by the nanofiller addition even at elevated clay amounts. Interestingly, the relatively strong polymer—filler interaction led to a substantial reduction of the matrix crosslinking degree for high clay loadings. Consequently, the relative thermal lifetime was positively affected by the presence of clay up to a filler content of 7 wt%, while uniaxial tensile tests under quasi-static and impact conditions evidenced an increase of the elastic modulus proportional to the clay concentration, without impairing the original tensile properties at break. [ABSTRACT FROM PUBLISHER]

The influence of glass fibers content and testing conditions (frequency and mean load) on the fatigue crack propagation rate in injection molded neat and fiber reinforced polypropylene has been investigated. The resistance to fatigue crack propagation increases as the fiber volume fraction increases. The fatigue resistance of either neat and fiber reinforced polypropylene is tremendously dependent on the crack propagation direction, with higher values for crack propagating transversely to the melt flow direction in the molded plaques. A dramatic increase of the crack growth rate per cycle by decreasing frequency, at any given crack length was found for all the materials investigated. Analysis of data obtained at various frequencies and applied mean loads suggests that crack propagation is determined mostly by viscoelastic creep processes at the crack tip, the role of pure fatigue appearing quite secondary. [ABSTRACT FROM PUBLISHER]