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.     

Effect of hydrothermal pretreatment on the properties of moso bamboo particles reinforced polyvinyl chloride composites

Bamboo plastic composites were fabricated from polyvinyl chloride (PVC) and moso bamboo particles (BP). In order to improve the interfacial interaction between BP and PVC, as well as to obtain composites with outstanding mechanical properties, the roles of hydrothermal treating temperatures (120, 140, 160, 180, 200, 220, 240, 260 and 280 °C) on characteristics of BP and properties of the PVC/BP composites were investigated. Results showed that hydrothermal modification improved the surface property of BP and wiped off hemicelluloses and pectin. A uniform dispersion of BP in PVC matrix was observed by SEM with hydrothermal treatment. Tensile strength, tensile modulus and flexural strength of the composites achieved their maximal values of 15.79 MPa, 6702.26 MPa and 39.57 MPa, respectively, with 180 °C hydrothermal treatment. The highest values of elongation at break and flexural deformation were 3.75 ± 0.20% with 200 °C hydrothermal modification and 36.22 ± 2.70% with 140 °C hydrothermal modification, respectively. Due to more decomposition of hemicellulose, the composites expressed lower water absorption and higher thermal stability when the hydrothermal treating temperature exceed 160 °C.     

Structural and mechanical properties of cellulose composites made of isolated cellulose nanofibers and poly(vinyl alcohol)

A composite of cellulose-nanofibers (Cel-F)/polyvinyl alcohol (PVA) was made through a developed water-jet nano-isolation process called the Star Burst processing (SB). The structural and the mechanical properties of the pure Cel-F and the Cel-F/PVA composites were analyzed for comparison. The microstructural analyses revealed the step-by-step nano-isolation procedures of the SB processing, eventually constructing nanofibers with the minimum diameter of ∼23 nm. It was also found that the crystallinity of Cel-F was rapidly increased by 14% at the early stage of the SB process, subsequently becoming almost constant, irrespective of the number of the SB treatments. Additionally, Cel-F were homogenously dispersed in PVA matrix after 40 SB treatments. Young’s modulus of the resulting composite was increased by 48%. The results were in good agreement with the outcome of the short-fiber composite theory, indicating a highly potential use of the SB-processed cellulose nanofibers as new reinforcement materials.     

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.     

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.     

Greatly enhanced cryogenic mechanical properties of short carbon fiber/polyethersulfone composites by graphene oxide coating

In order to employ polyethersulfone (PES) in cryogenic engineering field, its cryogenic mechanical performance should be examined and should also be improved to meet the high requirement for cryogenic engineering application. In this work, pure PES, graphene oxide (GO)/PES, short carbon fiber (SCF)/PES, GO/SCF/PES and GO-coated SCF/PES composites are prepared using the extrusion compounding and injection molding techniques. The tensile and flexural properties of these composites are systematically investigated at a typical cryogenic temperature (77 K). It is shown that the cryogenic mechanical properties are enhanced by the addition of GO, SCFs and coated-SCFs. In particular, the GO-coated SCF/PES composites display the greatly enhanced cryogenic mechanical properties with the highest values compared to other PES composites. In addition, it is exhibited that the cryogenic mechanical properties at 77 K of PES and its composites are far higher than those at room temperature (RT).     

Light-weight poly(vinyl chloride)-based soundproofing composites with foam/film alternating multilayered structure

Poly(vinyl chloride)-based (PVC) multilayered composites with alternating foam and film layer structure were designed through a multilayered co-extrusion system. Light-weight composites with good soundproofing properties were obtained. The effects of foaming process, acoustic impedance mismatch, and layer number on the soundproofing properties were investigated. Sound transmission loss (STL) was used to characterize the soundproofing properties. The experimental results revealed that the foam/film multilayered composites showed higher STL and lower density than the film/film multilayered composite without foaming process. In addition, the multilayered composite presented better soundproofing properties when there was a bigger acoustic impedance mismatch between adjacent layers. Moreover, as the layer number increased from 2 to 16, the STL of the PVC composite increased gradually and reached a maximum at 8 layers (an average value of 26.3 dB). However, the STL of 16-layer composite decreased because of the reduction of scattering and reflection of sound waves among the bubbles.     

Procedural influences on compression and injection moulded cellulose fibre-reinforced polylactide (PLA) composites: Influence of fibre loading,fibre length,fibre orientation and voids

The influence of fibre loading (20, 30, 40 mass%), fibre fineness, and the processing procedure (compression moulding – CM and injection moulding – IM) on the tensile and impact strength of lyocell/PLA composites was examined. The results revealed a significantly higher tensile and impact strength for CM composites compared to IM composites. An increase in strength up to a fibre loading of 40% was determined for CM composites, while for IM composites the highest values were measured at a fibre loading of 30%. Composites were investigated for their void content, fibre orientation, fibre length and process-induced fibre damage. A better fibre/matrix adhesion and compaction of IM composites was found while fibre orientation as well as mechanical properties of extracted fibres show no significant differences between CM and IM composites. The different mechanical characteristics of CM and IM samples are attributed predominantly to the fibre aspect ratio and the distribution of voids.     

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.     

Effect of shearing on the orientation, crystallization and mechanical properties of HDPE/attapulgite nanocomposites

High density polyethylene (HDPE)/attapulgite (AT) nanocomposites, prepared by conventional injection molding (CIM) and dynamic packing injection molding (DPIM), were investigated with focus on AT-induced crystallization and orientation under shear. Infrared spectroscopy (FTIR) analysis showed there is no special chemical interaction between HDPE and AT, but shear induced significant changes on the material structure and properties. Differential scanning calorimetry (DSC) analysis showed strong nucleation effect by AT especially under shear. And more, shear will induce much better dispersion of AT in the DPIM sample vs. CIM. AT nanorods and lamellae of HDPE are more organized in the DPIM sample while there is only random distribution in the CIM sample. Most AT nanorods embed in the HDPE lamellae and form a brush-like hybrid structure due to shear. The shear-induced orientation will be enhanced with higher AT loading. The mechanical performance of the composites was significantly improved via DPIM.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

Effect of electron donor/acceptor substituents on the Seebeck coefficient and thermoelectric properties of poly(3-methylthiophene methine)s/graphite composites

Recently, the use of polymers as thermoelectric materials has attracted considerable attention. However, relatively few studies have investigated the effects of polymer structures on the corresponding thermoelectric properties of the polymers. In this work, a series of poly(3-methylthiophene methine)s (PMMs) were synthesized for use as thermoelectric materials, and the effects on the Seebeck coefficient of donor or acceptor side groups at the methine carbon were studied. The PMMs with strongly electron-withdrawing and electron-donating groups exhibited the highest Seebeck coefficients. Motivated by the high Seebeck coefficients of the selected PMMs, PMM/graphite composites were prepared via solution mixing followed by mechanical ball milling and cold pressing. The thermoelectric properties of the composites were investigated as a function of the graphite (G) concentration. The highest ZT (6.23 × 10⁻³) was measured for the poly[(3-methylthiophene-2,5-diyl) (p-(methoxy)benzylidene)]/G composite that contained 90 wt% G. The results of this work suggest that the thermoelectric properties of polymer-inorganic composites can be improved by designing polymers with high Seebeck coefficients.     

Effect of ZnO nanoparticles doped graphene on static and dynamic mechanical properties of natural rubber composites

In this work, effect of ZnO nanoparticles doped graphene (Nano-ZnO–GE) on static and dynamic mechanical properties of natural rubber composites were studied. Nano-ZnO–GE was synthesized by sol–gel method and thermal treatment. With the incorporation of nano-ZnO–GE into the matrix, the mechanical properties of NR nanocomposite significantly improved over that of NR composite containing with 5 phr of conventional-ZnO. The results demonstrated that the presence of nano-ZnO on the surface of graphene sheets not only conduces to suppressing aggregation of graphene sheets but also acts as a more efficient cure-activator in vulcanization process, with the formation of excellent crosslinked network at low nano-ZnO–GE content. This work also showed that NR/Nano-ZnO–GE nanocomposites exhibited higher wet grip property and lower rolling resistance compared with NR/Conventional-ZnO composite, which makes nano-ZnO–GE very competitive for the green tire application as a substitute of conventional-ZnO, enlarging versatile practical application to prepare high-performance rubber nanocomposites.     

Mechanical and thermal properties of chicken feather fiber/PLA green composites

Chicken feather fiber (CFF)/reinforced poly(lactic acid) (PLA) composites were processed using a twin-screw extruder and an injection molder. The tensile moduli of CFF/PLA composites with different CFF content (2, 5, 8 and 10 wt%) were found to be higher than that of pure PLA, and a maximum value of 4.2 GPa (16%↑) was attained with 5 wt% of CFF without causing any substantial weight increment. The morphology, evaluated by scanning electron microscopy (SEM), indicated that an uniform dispersion of CFF in the PLA matrix existed. The mechanical and thermal properties of pure PLA and CFF/PLA composites were compared using dynamic mechanical analysis (DMA), thermomechanical analysis (TMA) and thermogravimetric analysis (TGA). DMA results revealed that the storage modulus of the composites increased with respect to the pure polymer, whereas the mechanical loss factor (tan δ) decreased. The results of TGA experiments indicated that the addition of CFF enhanced the thermal stability of the composites as compared to pure PLA. The outcome obtained from this study is believed to assist the development of environmentally-friendly composites from biodegradable polymers, especially for converting agricultural waste – chicken feather into useful products.     

Review of the mechanical properties of carbon nanofiber/polymer composites

In this paper, the mechanical properties of vapor grown carbon nanofiber (VGCNF)/polymer composites are reviewed. The paper starts with the structural and intrinsic mechanical properties of VGCNFs. Then the major factors (filler dispersion and distribution, filler aspect ratio, adhesion and interface between filler and polymer matrix) affecting the mechanical properties of VGCNF/polymer composites are presented. After that, VGCNF/polymer composite mechanical properties are discussed in terms of nanofibers dispersion and alignment, adhesion between the nanofiber and polymer matrix, and other factors. The influence of processing methods and processing conditions on the properties of VGCNF/polymer composite is also considered. At the end, the possible future challenges for VGCNF and VGCNF/polymer composites are highlighted.     

The effect of alkaline and silane treatments on mechanical properties and breakage of sisal fibers and poly(lactic acid)/sisal fiber composites

The main goals of this work were to study the effect of different chemical treatments on sisal fiber bundles tensile properties as well as on tensile properties of composites based on poly(lactic acid) (PLA) matrix and sisal fibers. For this purpose, sisal fibers were treated with different chemical treatments. After treating sisal fibers the tensile strength values decreased respect to untreated fiber ones, especially when the combination of NaOH + silane treatment was used. Taking into account fiber tensile properties and fiber/PLA adhesion values, composites based on silane treated fibers would show the highest tensile strength value. However, composites based on alkali treated and NaOH + silane treated fibers showed the highest tensile strength values. Finally, experimental tensile strength values of composites were compared with those values obtained using micromechanical models.     

Nanocomposites based on polystyrene-b-poly(ethylene-r-butylene)-b-polystyrene and exfoliated graphite nanoplates: Effect of nanoplatelet loading on morphology and mechanical properties

Exfoliated graphite nanoplates (xGnPs)/polystyrene-b-poly(ethylene-r-butylene)-b-polystyrene (SEBS) nanocomposites have been prepared by the simple melt-compounding approach. The structural, mechanical and viscoelastic properties of these composites were studied and compared. Wide-angle X-ray diffraction (WAXD) studies indicated that the processing of nanocomposites did not change the original d-spacing of xGnPs. Scanning electron microscopy observation on the fracture surfaces of the composites shows a uniform dispersion of xGnPs throughout SEBS matrix and strong interfacial adhesion between oxidized xGnPs and the matrix, which are responsible for the considerable enhancement of mechanical properties of the composites. It is found that the addition of xGnPs particles improved both the elastic modulus and storage modulus of pure SEBS significantly and the higher the xGnPs content, the higher the modulus of the nanocomposite. Moreover, the effects of dispersed xGnPs on the microphase separation of SEBS have also been investigated using small angle X-ray scattering (SAXS).     

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.     

Effect of carbon nanotubes on the mechanical properties and crystallization behavior of poly(ether ether ketone)

Pristine carbon nanotubes (CNTs) and noncovalently functionalized carbon nanotubes (f-CNTs) were used to prepare poly(ether ether ketone) (PEEK) composites (CNTs/PEEK and f-CNTs/PEEK) via melt blending. Noncovalently functionalized multiwalled nanotubes were synthesized using hydrogen-bonding interactions between sulfonic groups of sulfonated poly(ether ether ketone) (SPEEK) and carboxylic groups of nanotubes treated by acid (CNTs–COOH). The effects of these two kinds of nanotubes on the mechanical properties and crystallization behavior of PEEK were investigated. CNTs improved mechanical properties and promoted the crystallization rate of PEEK as a result of heterogeneous nucleation. Better enhancement of mechanical properties appeared in the f-CNTs/PEEK composites, which is ascribed to the good interaction between f-CNTs and PEEK. However, the strong interaction of f-CNTs and PEEK chains decreased the crystallization rate of PEEK for high content of f-CNTs.     

Effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of unidirectional hemp/epoxy composites

The objective of this study was to investigate the effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of hemp fibre/epoxy composites. Pectin removal by EDTA and endo-polygalacturonase (EPG) removed epidermal and parenchyma cells from hemp fibres and improved fibre separation. Hemicellulose removal by NaOH further improved fibre surface cleanliness. Removal of epidermal and parenchyma cells combined with improved fibre separation decreased composite porosity factor. As a result, pectin removal increased composite stiffness and ultimate tensile strength (UTS). Hemicellulose removal increased composite stiffness, but decreased composite UTS due to removal of xyloglucans. In comparison of all fibre treatments, composites with 0.5% EDTA + 0.2% EPG treated fibres had the highest tensile strength of 327 MPa at fibre volume content of 50%. Composites with 0.5% EDTA + 0.2% EPG → 10% NaOH treated fibres had the highest stiffness of 43 GPa and the lowest porosity factor of 0.04.