PLA/algae composites: Morphology and mechanical properties

Bio-composites with poly(lactic) acid as matrix and various algae (red, brown and green) as filler were prepared via melt mixing. Algae initial size (below 50 μm and between 200 and 400 μm) and concentration (from 2 to 40 wt%) were varied. First, algae morphology, composition and surface properties are analysed for each algae type. Second, an example of algae particle size decrease during processing is given. Finally, tensile properties of composites are analysed. The surface of algae flakes was covered with inorganic salts affecting filler–matrix interactions. The Young’s modulus of composites increased at 40 wt% load of algae as compared with neat PLA although the strain at break and tensile strength decreased. In most cases the influence of algae type was minor. Larger flakes led to better mechanical properties compared to the smaller ones.     

Effects of organic peroxide and polymer chain structure on morphology and thermal properties of sisal fibre reinforced polyethylene composites

The effect of polymer chain structure, addition of dicumyl peroxide (DCP) to initiate grafting onto the fibre, and different fibre loadings on the morphology and thermal properties of polyethylene/sisal fibre composites was investigated. The gel content results suggest both crosslinking between the polyethylene chains and grafting onto the sisal fibres. There were significant differences in gel contents between the composites because of the differences in the polyethylene molecular structures. The SEM micrographs of the samples show clear evidence of grafting, particularly in the case of the LDPE and LLDPE composites. The presence of the sisal fibres gave rise to thermally less stable composites compared to the neat matrices, whereas marginal differences in stability were observed between the untreated and peroxide treated composites. The DSC results show interesting trends in terms of the influence of fibre content and dicumyl peroxide treatment on the crystallisation behaviour of the composites.     

Enhancement of fracture toughness,mechanical and thermal properties of rubber/epoxy composites by incorporation of graphene nanoplatelets

Carboxyl terminated butadiene acrylonitrile (CTBN) was added to epoxy resins to improve the fracture toughness, and then two different lateral dimensions of graphene nanoplatelets (GnPs), nominally <1 μm (GnP-C750) and 5 μm (GnP-5) in diameter, were individually incorporated into the CTBN/epoxy to fabricate multi-phase composites. The study showed that GnP-5 is more favorable for enhancing the properties of CTBN/epoxy. GnPs/CTBN/epoxy ternary composites with significant toughness and thermal conductivity enhancements combined with comparable stiffness to that of the neat resin were successfully achieved by incorporating 3 wt.% GnP-5 into 10 wt.% CTBN modified epoxy resins. According to the SEM investigations, GnP-5 debonding from the matrix is suppressed due to the presence of CTBN. Nevertheless, apart from rubber cavitation and matrix shear banding, additional active toughening mechanisms induced by GnP-5, such as crack deflection, layer breakage and separation/delamination of GnP-5 layers contributed to the enhanced fracture toughness of the hybrid composites.     

Preparation,characterization and properties of polycaprolactone diol-functionalized multi-walled carbon nanotube/thermoplastic polyurethane composite

Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized to prepare thermoplastic polyurethane (PU) composites with enhanced properties. In order to achieve a high compatibility of functionalized MWCNTs with the PU matrix, polycaprolactone diol (PCL), as one of PU’s monomers, was selectively grafted on the surface of MWCNTs (MWCNT–PCL), while carboxylic acid groups functionalized MWCNTs (MWCNT–COOH) and raw MWCNTs served as control. Both MWCNT–COOH and MWCNT–PCL improved the dispersion of MWCNTs in the PU matrix and interfacial bonding between them at 1 wt% loading fraction. The MWCNT–PCL/PU composite showed the greatest extent of improvement, where the tensile strength and modulus were 51.2% and 33.5% higher than those of pure PU respectively, without sacrificing the elongation at break. The considerable improvement in both mechanical properties and thermal stability of MWCNT–PCL/PU composite should result from the homogeneous dispersion of MWCNT–PCL in the PU matrix and strong interfacial bonding between them.     

Structure and properties of hybrid PLA nanocomposites with inorganic nanofillers and cellulose fibers

Polylactide reinforced with 3 wt% of organo-modified montmorillonite, 5 wt% of stearic acid-modified calcium carbonate nanoparticles, 15 wt% of cellulose fibers (PLA/MMT, PLA/NCC, PLA/CF) and hybrid composites containing 15 wt% of fibers in addition to montmorillonite (PLA/MMT/CF) or calcium carbonate (PLA/NCC/CF) were prepared and examined. The nanoparticles were dispersed in polylactide almost homogeneously; montmorillonite was exfoliated during processing. T_g of polylactide remained unaffected but its cold crystallization was enhanced; the cold-crystallization behavior of the hybrid composites was dominated by nanofillers nucleating ability. The fibers and calcium carbonate decreased whereas exfoliated montmorillonite improved the thermal stability of the materials. Polylactide, PLA/NCC and PLA/MMT exhibited ability to plastic deformation, although the latter the weakest. Tensile behavior of the hybrid composites was strongly influenced by the fibers and similar to that of PLA/CF. All the fillers increased the storage modulus below T_g; that of PLA/MMT/CF and PLA/NCC/CF was improved with respect to polylactide by 50% and 45%, respectively.     

Fluorinated graphene reinforced polyimide films with the improved thermal and mechanical properties

In order to explore the addition effect of fluorinated graphene (FG) on the mechanical and thermal performances of polyimide (PI) matrix, FG sheets are first prepared and employed as the nanofillers to construct PI/FG nanocomposite films. The prepared film is optically transparent at low content of FG and experimental results demonstrate that the addition of FG can effectively enhance the properties of PI matrix. Especially, compared with pure PI matrix, the addition of 0.5 wt% FG in PI can endow 30.4% increase in tensile stress and 115.2% increase in elongation at break. Experimental analyses considering the morphology and microstructure are also conducted, and the results indicate that the improved mechanical properties of the PI/FG nanocomposite films are mainly attributed to the good dispersibility of FG sheets in PI host, and the effective stress transfer between the polymer and the FG.     

Thermal and mechanical properties of phenolic-based composites reinforced by carbon fibres and multiwall carbon nanotubes

The thermal, mechanical and ablation properties of carbon fibre/phenolic composites filled with multiwall carbon nanotubes (MWCNTs) were investigated. Carbon fibre/phenolic/MWCNTs were prepared using different weight percentage of MWCNTs by compression moulding. The samples were characterized by scanning electron microscopy (SEM), flexural tests, thermal gravimetric analysis and oxyacetylene torch tests. The thermal stability and flexural properties of the nanocomposites increased by increasing MWCNTs content (wt% ⩽1), but they decreased when the content of MWCNTs was 2 wt%. The linear and mass ablation rates of the nanocomposites after modified with 1 wt% MWCNTs decreased by about 80% and 52%, respectively. To investigate the material post-test microstructure, a morphological characterization was carried out using SEM. It was shown that the presence of MWCNTs in the composite led to the formation of a strong network char layer without any cracks or opening.     

Highly thermally conductive POSS-g-SiCp/UHMWPE composites with excellent dielectric properties and thermal stabilities

Polyhedral oligomeric silsesquioxane grafting thermally conductive silicon carbide particle (POSS-g-SiCp) fillers, are performed to fabricate highly thermally conductive ultra high molecular weight polyethylene (UHMWPE) composites combining with optimal dielectric properties and excellent thermal stabilities, via mechanical ball milling followed by hot-pressing method. The POSS-g-SiCp/UHMWPE composite with 40 wt% POSS-g-SiCp exhibits relative higher thermal conductivity, lower dielectric constant and more excellent thermal stability, the corresponding thermally conductive coefficient of 1.135 W/mK, the dielectric constant of 3.22, and the 5 wt% thermal weight loss temperature of 423 °C, which holds potential for packaging and thermal management in microelectronic devices. Agari’s semi-empirical model fitting reveals POSS-g-SiCp fillers have strong ability to form continuous thermally conductive networks.     

Fabrication and mechanical properties of well-dispersed multiwalled carbon nanotubes/epoxy composites

Multiwalled carbon nanotubes (MWCNTs)/epoxy nanocomposites were fabricated by using ultrasonication and the cast molding method. In this process, MWCNTs modified by mixed acids were well dispersed and highly loaded in an epoxy matrix. The effects of MWCNTs addition and surface modification on the mechanical performances and fracture morphologies of composites were investigated. It was found that the tensile strength improved with the increase of MWCNTs addition, and when the content of MWCNTs loading reached 8 wt.%, the tensile strength reached the highest value of 69.7 MPa. In addition, the fracture strain also enhanced distinctly, implying that MWCNTs loading not only elevated the tensile strength of the epoxy matrix, but also increased the fracture toughness. Nevertheless, the elastic modulus reduced with the increase of MWCNTs loading. The reasons for the mechanical property changes are discussed.     

Mechanical properties and toughening mechanisms of polypropylene/barium sulfate composites

The effect of interfacial interaction on the mechanical performance of a group of polypropylene (PP)/barium sulfate (BaSO₄) composites were studied. It was found that PP can be toughened with specially treated BaSO₄ particles. The interfacial modification contributes to the toughening in two aspects. The first is to provide a proper interfacial adhesion and control the interfacial debonding occurs at well-timed stages. This ensures the inorganic particles transfer the stress and stabilizes the cracks at the initial stage of the deformation, and satisfy the stress conditions for plastic deformation of matrix ligaments subsequently via debonding. The second is that the modified interface between PP matrix and filler particles increases the nucleating ability of the fillers and retards the motion of the PP chains. This leads to the formation of PP crystals with less perfection and smaller size in the matrix and promotes plastic deformation of the matrix after the debonding occurs.     

Mechanical and electrical properties of carbon nanotube/poly(phenylene sulphide) composites incorporating polyetherimide and inorganic fullerene-like nanoparticles

The mechanical and electrical properties of single-walled carbon nanotube (SWCNT) reinforced poly(phenylene sulphide) (PPS) composites prepared by melt-extrusion have been evaluated. The wrapping of SWCNTs in polyetherimide (PEI) and the addition of inorganic fullerene-like tungsten disulfide (IF-WS₂) nanoparticles provided an effective method for dispersing the SWCNTs, leading to enhanced properties of the resulting hybrid composites. Mechanical tests demonstrated significant enhancements in stiffness, strength and toughness by the addition of both nanofillers, and the Young’s modulus of the hybrid composites was fairly well predicted by two-phase modelling. The electrical conductivity of PPS improved dramatically at low SWCNT content (0.1-0.5 wt%). At higher concentrations, the replacement of part of the SWCNTs with IF-WS₂ maintained the level of conductivity of the composites. Overall, the hybrids possess superior performance than composites reinforced solely with wrapped or non-wrapped SWCNTs, and their properties can be tailored by modifying the SWCNT/IF-WS₂ ratio.     

Structure and properties of highly oriented polyoxymethylene/multi-walled carbon nanotube composites produced by hot stretching

Highly-oriented polyoxymethylene (POM)/multi-walled carbon nanotube (MWCNT) composites were fabricated through solid hot stretching technology. With the draw ratio as high as 900%, the oriented composites exhibited much improved thermal conductivity and mechanical properties along the stretching direction compared with that of the isotropic samples before drawing. The thermal conductivity of the composite with 11.6 vol.% MWCNTs can reach as high as 1.2 W/m K after drawing. Microstructure observation demonstrated that the POM matrix had an ordered fibrillar bundle structure and MWCNTs in the composite tended to align parallel to the stretching direction. Wide-angle X-ray diffraction results showed that the crystal axis of the POM matrix was preferentially oriented perpendicular to the draw direction, while MWCNTs were preferentially oriented parallel to the draw direction. The strong interaction between the POM matrix and the MWCNTs hindered the orientation movement of molecules of POM, but induced the orientation movement of MWCNTs.     

Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites

Mechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy nanocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T_g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix.     

Fluorographene/polyimide composite films: Mechanical,electrical, hydrophobic,thermal and low dielectric properties

Nowadays, dielectric materials with excellent mechanical and hydrophobic properties are desired for use in the integrated circuits (ICs). For this reason, low dielectric constant fluorographene/polyimide (FG/PI) composite films were prepared by a facile solution blending method, suggesting that the mechanical, electrical, hydrophobic and thermal properties were significantly enhanced in the presence of FG. With addition of 1 wt% FG, the tensile strength, Young’s modulus and elongation at break were dramatically increased by 139%, 33% and 18% respectively when compared with pure PI film. Furthermore, composite films exhibit superior hydrophobic and thermal stability performance. Especially, the FG/PI film with 0.5 wt% of FG possessing a low dielectric constant of 2.48 and a good electrical insulativity that is lower than 10⁻¹⁴ S m⁻¹. Therefore, by their excellent performance, FG/PI hybrid films represent suitable candidate solutions with applications in the microelectronics and aerospace industries.     

Pristine and amino functionalized carbon nanotubes reinforced glass fiber epoxy composites

Multi-phase composites have been studied by incorporating carbon nanotubes (CNTs) as a secondary reinforcement in an epoxy matrix which was then reinforced with glass fiber mat. Different types of CNTs e.g. amino functionalized carbon nanotubes (ACNT) and pristine carbon nanotubes (PCNT) were homogeneously dispersed in the epoxy matrix and two-ply laminates were fabricated using vacuum-assisted resin infusion molding technique. The issues related to CNT dispersion and interfacial bonding and its affect on the mechanical properties have been studied. An important finding of this study is that PCNT scores over ACNT in composites prepared under certain conditions. This is a very significant finding since PCNT is available at a much lower cost than ACNT.     

Processing, compatibilization and properties of ternary composites of Mater-Bi with polyolefins and hemp fibres

Ternary composites of a biodegradable thermoplastic matrix, Mater-Bi® (MB), with various polyolefins (PP, HDPE and PS) and hemp fibres (H) were obtained by melt mixing and characterized by SEM, OM, DSC, TGA and tensile tests. The properties of composites were compared with those of MB/polyolefin and MB/H blends. Maleic anhydride functionalized polyolefins were employed as compatibilizers. Crystallization behaviour and morphology of the composites were found to be affected by the composition, phase dispersion and compatibilizer. Thermogravimetric analysis indicated that the thermal stability of the polyolefin phase and fibres was influenced by the composition and phase structure. A significant improvement of tensile modulus and strength was recorded for composites of MB with PE and PS as compared to MB/H composites. The results indicate that incorporation of polyolefins in the biodegradable matrix, compared to binary matrix/fibre system, may have significant advantages in terms of properties, processability and cost.     

Flammability,thermal and physical-mechanical properties of cationic polymer/montmorillonite composite on cotton fabric

The flammability, thermal and mechanical properties on cotton fabric were improved by being finished with the composite containing montmorillonite. To this aim, polymer dimethyl diallyl ammonium chloride-allyl glycidyl ether (P_DMDAAC-AGE) was prepared and its structure characterized by Fourier transform infrared (FT-IR) and Nuclear magnetic resonance (¹H NMR). The quaternary ammonium salt copolymer/montmorillonite composite (P_DMDAAC-AGE/MMT) was obtained by polymer intercalation method. The X-ray diffraction (XRD) indicated that the MMT interlayer spacing increased after the polymer intercalation. Composite materials were loaded onto the cotton fabrics by a dip-pad-dry method. The thermo gravimetric analysis (TGA), vertical flame test and limiting oxygen index (LOI) results showed that the thermal and flammability properties of the cotton fabric were improved after it was finished with the composite. Tensile testing revealed an increase on mechanical properties of the finished fabric, but the physical properties hardly changed from the bending length and whiteness results. Scanning electron microscope (SEM) and energy disperse X-ray spectroscope (EDX) results verified the improvement of those properties due to the presence of montmorillonite in the composite.     

Effect of mechanical activation pretreatment on the properties of sugarcane bagasse/poly(vinyl chloride) composites

This current work is concerned with the pretreatment of sugarcane bagasse (SCB) by mechanical activation (MA) using a self-designed stirring ball mill and surface modification of SCB using aluminate coupling agent (ACA). The untreated and differently treated SCBs were used to produce composites with poly(vinyl chloride) (PVC) as polymer matrix. The activation grade (A_g) measurement and Fourier transform infrared (FTIR) analysis of SCB showed that MA enhanced the condensation reaction between ACA and hydroxyl groups of the SCB fibres, which obviously increased the hydrophobicity of SCB. It was found that the mechanical properties of both the PVC composites reinforced by SCB with and without ACA modification increased with increasing milling time (t_M). Scanning electron microscopy (SEM) analysis showed that MA pretreatment significantly improved the dispersion of SCB in the composites and interfacial adhesion between SCB and PVC matrix, resulting in better mechanical properties of the composites.     

Mechanical properties of epoxy composites with high contents of nanodiamond

Mechanical properties and thermal conductivity of composites made of nanodiamond with epoxy polymer binder have been studied in a wide range of nanodiamond concentrations (0-25 vol.%). In contrast to composites with a low content of nanodiamond, where only small to moderate improvements in mechanical properties were reported before, the composites with 25 vol.% nanodiamond showed an unprecedented increase in Young’s modulus (up to 470%) and hardness (up to 300%) as compared to neat epoxy. A significant increase in scratch resistance and thermal conductivity of the composites were observed as well. The improved thermal conductivity of the composites with high contents of nanodiamond is explained by direct contacts between single diamond nanoparticles forming an interconnected network held together by a polymer binder.