Studies on the characterization of piassava fibers and their epoxy composites

This paper presents morphology, physical and strength properties of piassava fiber, a very rigid fiber having a potential to be used as composite reinforcement. Composites of continuous and aligned piassava fibers with and without alkali treatment dispersed in epoxy matrix were subjected to three point bend, tensile, and Izod impact tests. Composites with fibers above 20 vol.% showed an effective reinforcement behavior both in flexural and tensile tests, while the impact energy linearly increased for the amount of piassava fibers used in this study. Fractographic study revealed a relatively weaker fiber/matrix adhesion acting as preferential site for crack nucleation. Evidence was also found for crack arrest by the fiber above 20 vol.%. This, together with spiny surface protrusion in the piassava fibers, was found to be responsible for the reinforcement of the epoxy composites.     

Investigation of structure,mechanical and tribological properties of short carbon fiber reinforced UHMWPE-matrix composites

Structural, mechanical and tribological properties of composite materials based on ultra-high molecular weight polyethylene reinforced with carbon fibers were investigated. The effect of surface modification of carbon fibers on the interaction at the fiber–matrix interface in UHMWPE based composites was studied. It was found that the thermal oxidation of carbon fibers by air oxygen at 500 °C can significantly enhance the interfacial interaction between the polymer matrix and carbon fibers. This allowed us to form composite materials with improved mechanical and tribological properties.     

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.     

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.     

Excellent dielectric properties of PVDF-based composites filled with carbonized PAN/PEG copolymer fibers

Weak interfacial bonding between carbon materials and polymer matrix impedes the formation of homogeneous composites, challenging to the enhancement of dielectric properties of such systems. In this work, we designed novel carbonized polyacrylonitrile/polyethylene glycol copolymer fibers (CPCFs) and then used them as fillers to enhance the dielectric properties of poly(vinylidene fluoride) (PVDF)-based composites. These CPCFs are rich in nitrogen (8.55%) and oxygen (3.94%) atoms on the surface of them. The results of molecular dynamic (MD) simulations indicate that the existence of these atoms significantly increase the interaction energy between CPCFs and PVDF matrix from −45.13 kcal/mol to −62.22 kcal/mol, which promotes the intercalation of conductive CPCFs into insulated PVDF matrix to form ultrathin microcapacitors. As a result, the largest dielectric constant of CPCFs/PVDF composites can reach 1583 (1 kHz), which is about 150 times higher than that of pure PVDF.     

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.     

Improved cryogenic interlaminar shear strength of glass fabric/epoxy composites by graphene oxide

The cryogenic interlaminar shear strength (ILSS) at cryogenic temperature (77 K) of glass fabric (GF)/epoxy composites is investigated as a function of the graphene oxide (GO) weight fraction from 0.05 to 0.50 wt% relative to epoxy. For the purpose of comparison, the ILSS of the GF/epoxy composites is also examined at room temperature (RT, 298 K). The results show that the cryogenic ILSS is greatly improved by about 32.1% and the RT ILSS is enhanced by about 32.7% by the GO addition at an appropriate content of 0.3 wt% relative to epoxy. In addition, the ILSS of the composite at 77 K is much higher than that at RT due to the relatively strong interfacial GF/epoxy adhesion at 77 K compared to the RT case.     

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.     

Controlled retting of hemp fibres: Effect of hydrothermal pre-treatment and enzymatic retting on the mechanical properties of unidirectional hemp/epoxy composites

The objective of this work was to investigate the use of hydrothermal pre-treatment and enzymatic retting to remove non-cellulosic compounds and thus improve the mechanical properties of hemp fibre/epoxy composites. Hydrothermal pre-treatment at 100 kPa and 121 °C combined with enzymatic retting produced fibres with the highest ultimate tensile strength (UTS) of 780 MPa. Compared to untreated fibres, this combined treatment exhibited a positive effect on the mechanical properties of hemp fibre/epoxy composites, resulting in high quality composites with low porosity factor (α_pf) of 0.08. Traditional field retting produced composites with the poorest mechanical properties and the highest α_pf of 0.16. Hydrothermal pretreatment at 100 kPa and subsequent enzymatic retting resulted in hemp fibre composites with the highest UTS of 325 MPa, and stiffness of 38 GPa with 50% fibre volume content, which was 31% and 41% higher, respectively, compared to field retted fibres.     

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.     

The method of cells and the mechanical properties of textile composites

The method of cells has been gaining ground as a method for predicting the elastic properties of textile reinforced composite materials. This method deals away with the constant stress/strain assumption present in most analytical models allowing for a more accurate prediction of the elastic properties, with computational cost only a fraction in comparison with finite element analysis. A new implementation is presented here, which links this method to a mechanistic predictive geometry preprocessor allowing the presented model to deal with 2D and 3D textile reinforced composites. Numerical results for prediction of stiffness and strength of textile composites are generated and compared to other methods.     

Hybrid effect of nanoparticles with carbon fibers on the mechanical and wear properties of polymer composites

Polyetheretherketone (PEEK) composites reinforced with carbon fibers (CFs) and nano-ZrO₂ particles were prepared by incorporating nanoparticles into PEEK/CF composites via twin-screw extrusion. The effects of nanoparticles on the mechanical and wear properties of the PEEK/CF composites were studied. The results showed that the incorporation of nano-ZrO₂ particles with carbon fiber could effectively enhance the tensile properties of the composites. The tensile strength and Young’s modulus of the composites increased with the increasing nano-ZrO₂ content. The enhancement effect of the particle was more significant in the hybrid reinforced composites. The compounding of the two fillers also remarkably improved the wear resistance of the composites under water condition especially under high pressures. It was revealed that the excellent wear resistance of the PEEK/CF/ZrO₂ composites was due to a synergy effect between the nano-ZrO₂ particles and CF. CF carried the majority of load during sliding process and prevented severe wear to the matrix. The incorporation of nano-ZrO₂ effectively inhibited the CF failures through reducing the stress concentration on the carbon fibers interface and the shear stress between two sliding surfaces. It was also indicated that the wear rates of the hybrid composites decreased with the increasing applied load and sliding distance under water lubrication. And low friction coefficient and low wear rate could be achieved at high sliding velocity.     

Improvement of properties for biobased composites from modified soybean oil and hemp fibers: Dual role of diisocyanate

An environmentally friendly composite was developed from hemp fibers (HFs) and a biobased thermosetting resin that was formulated from the copolymerization of acrylated epoxidized soybean oil (AESO) and N-vinyl-2-pyrrolidone. The properties of the composites were enhanced through the incorporation of isophorone diisocyanate (IPDI). The FTIR and ¹³C NMR spectra reveal that the incorporated IPDI could react with the hydroxyl groups of both HFs and AESO by forming urethane connections; hence, IPDI plays two roles in composites, i.e., as a crosslinker and a coupling agent. The results show that both effects greatly contribute to increasing the tensile and flexural properties, storage modulus, and glass transition temperature of the resulting composites. However, the modification does not significantly influence the impact strength and slightly decreases the thermal stability of the composites. Further, the addition of IPDI into AESO resins results in resins with improved processability due to the lower viscosity and curing temperature.     

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.     

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.     

Effect of oxygen plasma treatment of PPTA and PBO fibers on the interfacial properties of single fiber/epoxy composites studied by Raman spectroscopy

The interfacial micromechanics of single poly(p-phenylene terephthalamide (PPTA) and poly(p-phenylene benzobisoxazole (PBO) fibers embedded in an epoxy resin has been investigated by determining the interfacial shear stress distributions along the fiber length. The effects of an oxygen plasma treatment on the interfacial shear stress of the fiber-epoxy systems are analyzed. Raman spectroscopy was used to map the stress distributions along the fiber when the composite is subjected to a small axial tensile strain (3.5% for PPTA and 2.5% for PBO). The quality of the interface or adhesion was improved after the surface treatment, supporting the ability of plasma oxidation to enhance the adhesion of high-performance fibers to epoxy resins. The tensile behavior of fiber-reinforced systems was different in each case. PPTA reinforcements underwent fragmentation, likely by fiber microfailure, whereas debonding or bridging is the most probable fragmentation mechanism in the case of PBO.     

Effect of linear density and yarn structure on the mechanical properties of ramie fiber yarn reinforced composites

Effects of linear density and yarn structure on both static and dynamic mechanical properties of ramie fiber yarn reinforced composites (RYRCs) were investigated. The failure mechanisms of RYRCs were analyzed with the aid of ultrasonic C-scan and Scanning electronic microscopy (SEM). The results showed that the tensile strength of RYRCs increased gradually with increase of the linear density of the single yarns. The maximum tensile strength was obtained when the linear density reached 67.3 tex. However, a downtrend of the tensile strength was observed with further increase of the linear density of ramie single and plied yarns. The interlaminar fracture toughness was relatively high for RYRCs made from yarns with lower linear density due to the extensive fiber bridging observed during the double cantilever beam test. Meanwhile, the linear density and structure of ramie yarn had remarkable influence on the failure mode of RYRCs during the drop weight impact test.     

The effect of graphene presence in flame retarded epoxy resin matrix on the mechanical and flammability properties of glass fiber-reinforced composites

The effect of adding graphene in epoxy containing either an additive (MP) or reactive-type (DOPO) flame retardant on the thermal, mechanical and flammability properties of glass fiber-reinforced epoxy composites was investigated using thermal analysis; flexural, impact, tensile tests; cone calorimetry and UL-94 techniques. The addition of MP or DOPO to epoxy had a thermal destabilization effect below 400 °C, but led to higher char yield at higher temperatures. The inclusion of 10 wt% flame retardants slightly decreased the mechanical behavior, which was attributed to the poor interfacial interactions in case of MP or the decreased cross-linking density in case of DOPO flame retarded resin. The additional graphene presence increased flexural and impact properties, but slightly decreased tensile performance. Adding graphene further decreased the PHRR, THR and burning rate due to its good barrier effect. The improved fire retardancy was mainly attributed to the reduced release of the combustible gas products.     

Development of woven fabric reinforced all-polypropylene composites with beta nucleated homo- and copolymer matrices

In the present work self-reinforced polypropylene composites (SRPPC) were developed and investigated. As reinforcement a fabric, woven from highly stretched split PP yarns, whereas as matrix materials α and β crystal forms of isotactic PP homopolymer and random copolymer (with ethylene) were selected and used. The composite sheets were produced by film-stacking method and compression moulded at different processing temperatures keeping the holding time and pressure constant. The quality of the composite sheets was assessed by optical microscopy, density and peel-strength measurements. The SRPPC specimens were subjected to static tensile and flexural, and dynamic falling weight impact tests and the related results were analyzed as a function of processing temperature and polymorphic composition. Based on the results the optimum processing temperature was determined and found by 20–25 °C above the related matrix melting temperature. It was established that the β-modified PP homopolymer based one-component SRPPCs possessed similar attractive mechanical properties as the intensively studied α-random PP copolymer based two-component ones.     

Effects of CNT diameter on mechanical properties of aligned CNT sheets and composites

Drawing, winding, and pressing techniques were used to produce horizontally aligned carbon nanotube (CNT) sheets from free-standing vertically aligned CNT arrays. The aligned CNT sheets were used to develop aligned CNT/epoxy composites through hot-melt prepreg processing with a vacuum-assisted system. Effects of CNT diameter change on the mechanical properties of aligned CNT sheets and their composites were examined. The reduction of the CNT diameter considerably increased the mechanical properties of the aligned CNT sheets and their composites. The decrease of the CNT diameter along with pressing CNT sheets drastically enhanced the mechanical properties of the CNT sheets and CNT/epoxy composites. Raman spectra measurements showed improvement of the CNT alignment in the pressed CNT/epoxy composites. Research results suggest that aligned CNT/epoxy composites with high strength and stiffness are producible using aligned CNT sheets with smaller-diameter CNTs.