Flexural properties loss of unidirectional epoxy/fique composites immersed in water and alkaline medium for construction application

Epoxy fique composites were evaluated for construction applications and compared with conventional wood used in construction. The composites studied were made with fique fibers treated using Na(OH) solution at 18 w/v%, untreated fique fibers were also used. The matrices were epoxy and epoxy with 5 wt.% of chemically modified C30B montmorillonite. Unidirectional composites of 90 mm × 20 mm × 4 mm were elaborated by pultrusion processing technique. The flexural properties loss occurred over 20 days of composites submitted to three types of environments: (i) water, (ii) saturated calcium hydroxide solution and (iii) mortar with w/c ratio of 0.45 and 540 kg/m³ of cement, cured in a saturated solution of lime stone at 50 °C. Results showed that fiber treatment and montmorillonite addition improved the flexural modulus and strength of composites in 40% and 34% respectively. Moreover the flexural properties of composites before and after ageing resulted comparable or even better than conventional wood used in construction.     

Flexural properties loss of unidirectional epoxy/fique composites immersed in water and alkaline medium for construction application

Epoxy fique composites were evaluated for construction applications and compared with conventional wood used in construction. The composites studied were made with fique fibers treated using Na(OH) solution at 18 w/v%, untreated fique fibers were also used. The matrices were epoxy and epoxy with 5 wt.% of chemically modified C30B montmorillonite. Unidirectional composites of 90 mm × 20 mm × 4 mm were elaborated by pultrusion processing technique. The flexural properties loss occurred over 20 days of composites submitted to three types of environments: (i) water, (ii) saturated calcium hydroxide solution and (iii) mortar with w/c ratio of 0.45 and 540 kg/m³ of cement, cured in a saturated solution of lime stone at 50 °C. Results showed that fiber treatment and montmorillonite addition improved the flexural modulus and strength of composites in 40% and 34% respectively. Moreover the flexural properties of composites before and after ageing resulted comparable or even better than conventional wood used in construction.     

Toughening effect of short carbon fibers in the ZrB2–ZrSi2 ceramic composites

The toughening effect of the short carbon fibers in the ZrB₂–ZrSi₂ ceramic composites were investigated, where the ZrB₂–ZrSi₂ ceramics without carbon fibers were used as the reference. The mechanical properties were evaluated by means of flexural and SENB tests, respectively. The microstructure was characterized by SEM equipped with EDS. The results found that the short carbon fibers were uniformly incorporated in the ZrB₂–ZrSi₂ matrix and the relative density was about 97.92%. The flexural strength of short carbon fiber-reinforced ZrB₂–ZrSi₂ composites is 437 MPa; the fracture toughness and the work of fracture are 6.89 MPa m^1/2 and 259 J/m², respectively, which increased significantly in comparing with composites without fibers. The microstructure analysis revealed that the improved fracture toughness could be attributed to the fiber bridging, the fiber–matrix interface debonding and the fiber pullout, which consumed more fracture energy during the fracture process.     

Supercritical carbonation treatment on extruded fibre–cement reinforced with vegetable fibres

The objective of this research was to evaluate the effects of supercritical carbonation treatment for 2 h on the main hydrated phases of the cement matrix (calcium hydroxide and calcium silicate hydrate) and durability of extruded fibre–cement reinforced with bleached eucalyptus pulp and residual sisal chopped fibres. The thermal analysis, bulk density, porosity, physical characteristics and mechanical performance were evaluated before and after 200 soaking and drying cycles for following the degradation of the material under accelerated ageing conditions. The higher carbonation rate during the early stage of curing period decreased the porosity by sealing the opened pores around vegetable fibres and, consequently, led to lower water absorption and higher bulk density in the composites. The average MOR-values showed a significant increase in the case of the supercritical carbonated extruded fibre–cement in the initial age and after accelerated ageing. Besides, after 200 soaking and drying ageing cycles, the average values of energy of fracture (γ_WoF) of the carbonated composites decrease only 28%, showing evidences of the preservation of microstructural stability and toughness of the fibre–cement composites after supercritical CO₂ treatment.     

Mechanical behaviour of bamboo and bamboo composite

The tensile, flexural and impact strengths of bamboo and bamboo fibre-reinforced plastic (BFRP) composite have been evaluated. The high strengths of bamboo, in the fibre direction, have been explained by its anatomical properties and ultra structure. Bamboo fibres and bamboo orthogonal strip mats (bamboo mat) have been used to reinforce epoxy resin. BFRP composites with unidirectional, bidirectional and multidirectional strengths have been made. In bamboo mat composites, the fibre volume fraction,V _f, achieved was as high as 65%. The tensile, flexural and impact strengths of bamboo along the fibres are 200.5 MN m^–2, 230.09 MN m^–2 and 63.54 kJ m^–2, respectively, whereas those of bamboo fibre composites and bamboo mat composites are 175.27 M N m^–2, 151.83 MN m^–2 and 45.6 kJ m^–2, and 110.5 MN m^–2, 93.6 M N m^–2 and 34.03 kJ m^–2, respectively. These composites possess a close to linear elastic behaviour. Scanning electron microscopy studies of the fractured BFRP composite specimens reveal a perfect bonding between bamboo fibres and the epoxy. Furthermore, high strength, low density, low production cost and ease of manufacturing make BFRP composite a commercially viable material for structural applications.     

Microstructure and mechanical properties of carbon fiber reinforced multilayered (PyC–SiC)n matrix composites

Carbon fiber reinforced multilayered (PyC–SiC)_n matrix (C/(PyC–SiC)_n) composites were prepared by isothermal chemical vapor infiltration. The phase compositions, microstructures and mechanical properties of the composites were investigated. The results show that the multilayered matrix consists of alternate layers of PyC and β-SiC deposited on carbon fibers. The flexural strength and toughness of C/(PyC–SiC)_n composites with a density of 1.43 g/cm³ are 204.4 MPa and 3028 kJ/m³ respectively, which are 63.4% and 133.3% higher than those of carbon/carbon composites with a density of 1.75 g/cm³. The enhanced mechanical properties of C/(PyC–SiC)_n composites are attributed to the presence of multilayered (PyC–SiC)_n matrix. Cracks deflect and propagate at both fiber/matrix and PyC–SiC interfaces resulting in a step-like fracture mode, which is conducive to fracture energy dissipation. These results demonstrate that the C/(PyC–SiC)_n composite is a promising structural material with low density and high flexural strength and toughness.     

Flexural performance of fiber-reinforced ultra lightweight cement composites with low fiber content

This paper presents an experimental study on flexural performance of ultra lightweight cement composites (ULCC) with 0.5 vol% fibers. Low density of the ULCC is achieved by using cenospheres from coal-fired power plants as micro aggregates. Effects of shrinkage reducing admixture (SRA) and fiber types on compressive strength and flexural performance of the ULCC are investigated. ULCC with density of 1474 kg/m³, compressive strengths of 68.2 MPa, flexural strength of 8 MPa, and deflection hardening behavior can be produced. Such good performance could be attributed primarily to the SRA which reduced entrapped air in paste matrix and densified fiber–matrix interface. The improvement on the flexural performance of the ULCC depends on fibers used and bond between fibers and matrix. Improvement of the flexural performance of the steel fiber (coated with brass) reinforced ULCC due to the densification effect by SRA was more significant than that of the PE fiber reinforced ULCC.     

A Study on flexural properties of wildcane grass fiber-reinforced polyester composites

The main objective of this study is to introduce a new natural fiber as reinforcement in polymers for making composites. Wildcane grass stalk fibers were extracted from its stem using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were intentionally reinforced in a polyester matrix unidirectionally, and the flexural properties of the composite were determined. The fibers extracted by retting process have a tensile strength of 159 MPa, modulus of 11.84 GPa, and an effective density of 0.844 g/cm³. The composites were formulated up to a maximum fiber volume fraction of 0.39, resulting in a flexural strength of 99.17 MPa and flexural modulus of 3.96 GPa for wildcane grass fibers extracted by retting. The flexural strength and the modulus of chemically extracted wildcane grass fiber composites have increased by approximately, 7 and 17%, respectively compared to those of composites made from fibers extracted by retting process. The flexural strength and the modulus of KMnO₄-treated fiber composites have increased by 12 and 76% over those of composites made from fibers extracted by retting process and decreased by 3 and 48% over those of composites made from fibers extracted by chemical process, respectively. The results of this study indicate that wildcane grass fibers have potential as reinforcing fillers in plastics in order to produce inexpensive materials with high toughness.     

Fabrication and characterization of three dimensional woven carbon fiber/silica ceramic matrix composites

Carbon fiber reinforced fused silica composites exhibit the advantages of excellent mechanical properties, high heat resistance, low thermal expansion and low density, but low impact resistance or toughness. A novel modified slurry impregnation and hot pressing (SIHP) method was adopted to fabricate a new type of three dimensional orthogonal woven structure carbon fiber reinforced silica ceramic matrix composites (3D Cf/SiO₂ CMCs) with higher density and lower porosity. Physical characterization, flexural behavior, impact performance and toughening mechanism of the composites were investigated by three-point bending tests, impact tests, and scanning electron microscopy analysis. The 3D Cf/SiO₂ CMC showed a higher flexural strength in both warp (201.6%) and weft (263.6%) directions than those of pure SiO₂ and failed at a non-brittle mode due to the fiber debonding and pullout, and a delaminated failure of the 3D preform. The maximum impact energy absorption of the 3D Cf/SiO₂ CMC was 96.9 kJ/m², almost 4 times as much as those for typical other carbon fiber reinforced CMCs.     

Mechanically pulped sisal as reinforcement in cementitious matrices

The performance as reinforcement of fibres obtained from commercial and by-product sisal (Agave sisalana) by thermomechanical pulping and chemi-thermomechanical pulping (CTMP) processes was investigated. Ordinary Portland cement (OPC) and chemically activated blast furnace slag (BFS) were examined as binders. The flexural strengths of OPC- and BFS-based composites incorporating 8% fibre reinforcement by mass were similar at 28 days and ranged from 18 to 22 MPa. Corresponding modulus of elasticity values were in the region of 11 GPa for the OPC-based composites and 7 GPa for the BFS-based composites. Water absorption values at 8% fibre content lay in the range of 21–31% by mass and density values in the region of 1.5 g/cm³. Fracture toughness increased with fibre content, reaching a value of 1.6 kJ/m² at a content of 12% in the case of by-product sisal CTMP in the BFS matrix. Scanning electron microscopy provided interfacial bonding information that can be related to the mechanical performance of these fibre-reinforced pastes.     

Using a synthetic body fluid (SBF) solution of 27 mM HCO3− to make bone substitutes more osteointegrative

A Tris–HCl-buffered synthetic body fluid (SBF) solution, mimicking the human blood plasma, with the following ion concentrations of 27 mM HCO₃⁻, 2.5 mM Ca²⁺, 1.0 mM HPO₄²⁻, 142 mM Na⁺, 125 mM Cl⁻, 5 mM K⁺, 1.5 mM Mg²⁺, and 0.5 mM SO₄²⁻ was used as an aqueous medium to process a number of bone substitute materials under the so-called biomimetic conditions of 37 °C and pH 7.4. This solution was named as Tris–SBF-27 mM. Firstly, collagen sponges were soaked in Tris–SBF-27 mM solution at 37 °C and were found to be fully covered with nanoporous apatitic calcium phosphate (Ap-CaP). The composites of collagen–Ap-CaP biomaterials are expected to be used in orthopedic and dental surgery. Secondly, Ap-CaP short whiskers or microrods with a novel nanotexture and surface areas higher than 45 m²/g were synthesized in Tris–SBF-27 mM solution. Thirdly, calcium sulfate cements doped with CaHPO₄ (monetite), were shown to have apatite-inducing ability upon ageing in Tris–SBF-27 mM. CaHPO₄ addition in calcium sulfate was found to improve its mechanical strength, measured after cement setting reaction. Pure calcium sulfate cement pellets were not stable in Tris–SBF-27 mM solutions and crumbled into a powder. All the samples were characterized by SEM, XRD, FTIR, surface area and mechanical strength measurements.     

Development of vegetable fibre–mortar composites of improved durability

The primary concern for vegetable fibre reinforced mortar composites (VFRMC) is the durability of the fibres in the alkaline environment of cement. The composites may undergo a reduction in strength and toughness as a result of weakening of the fibres by a combination of alkali attack and mineralisation through the migration of hydration products to lumens and spaces. This paper presents several approaches used to improve the durability performance of VFRMCs incorporating sisal and coconut fibres. These include carbonation of the matrix in a CO₂-rich environment; the immersion of fibres in slurried silica fume prior to incorporation in the ordinary Portland cement (OPC) matrix; partial replacement of OPC matrix by undensified silica fume or blast-furnace slag and a combination of fibre immersion in slurried silica fume and cement replacement. The durability of the modified VFRMC was studied by determining the effects of ageing in water, exposure to cycles of wetting and drying and open air weathering on the microstructures and flexural behaviour of the composites. Immersion of natural fibres in a silica fume slurry before their addition to cement-based composites was found to be an effective means of reducing embrittlement of the composite in the environments studied. Early cure of composites in a CO2-rich environment and the partial replacement of OPC by undensified silica fume were also efficient approaches in obtaining a composite of improved durability. The use of slag as a partial cement replacement had no effect on reducing the embrittlement of the composite.     

Statistical analysis for freeze–thaw resistance of cement mortars containing marble dust and glass fiber

This paper investigated the usability of marble dust and glass fiber against the harmful effects of freeze–thaw (FT) cycles on cement mortars as experimentally and statistically. To this end, the cement mortar specimens containing marble dust (0%, 20%, 40% and 50% by volume) and glass fiber (0 kg/m³, 0.25 kg/m³, 0.50 kg/m³, 0.75 kg/m³) were prepared. The compressive and flexural strengths of the specimens were determined after being exposed to FT cycles. In order to reduce the numbers of experiments, an L₁₆ (4² × 2¹) Taguchi orthogonal array was adopted to the study. Amounts of glass fiber, percentages of marble dust and cycles of freeze–thaw, were changed to explore their effects on the compressive and flexural strengths of the mortar specimens. Statistically effects of the factors were also determined by using analysis of variance (ANOVA) method. Finally, experimental findings were compared with statistical results and a good agreement between them was achieved.     

Improvement of Mechanical Properties of Oligomer-modified Acrylic Bone Cement with Glass-fibers

Some mechanical properties of oligomer-modified acrylic bone cement with glass-fibers were studied. Under wet environments, oligomer-filler forms a porous structure in the acrylic bone cement. Test specimens were manufactured using commercial bone cement (Palacos^® R) with different quantities of an experimental oligomer-filler (0–20 wt%), and included continuous unidirectional E-glass fibers (l=65 mm) or chopped E-glass fibers (l=2 mm). The specimens were either tested dry, or after being immersed under wet environments for one week. The three-point bending test was used to measure the flexural strength and modulus of the acrylic bone cement composites (analysis with ANOVA). A scanning electron microscope (SEM) was used to examine the surface structure of the acrylic bone cement composites. Using continuous glass-fiber reinforcement, the dry flexural strength was 145 MPa and modulus was 4.6 GPa for the plain bone cement. For the test specimens with 20 wt% of oligomer-filler and continuous unidirectional glass-fibers, the dry flexural strength was 118 MPa and modulus was 4.2 GPa, whereas the wet flexural strength was 66 MPa and modulus was 3.0 GPa. The results suggest that the reduced flexural properties caused by the porosity of oligomer-modified bone cement can be compensated with glass-fiber reinforcement.     

Hot-pressed ZrB2–SiC–YSZ composites with various yttria content: Microstructure and mechanical properties

ZrB₂–10 vol%SiC–20 vol%YSZ composites were prepared by hot-pressed sintering with yttria content ranging from 2 mol% to 8 mol% in YSZ. The phase constitution, microstructure and mechanical properties of the composites were found to be strongly dependent on the yttria content. The average grain size became bigger for the composites with higher yttria content. When the yttria content was below 3 mol%, there is no cubic zirconia in the polished surface of composites, and the flexural strength of the composites was above 740 MPa. With the increase in yttria content, the fracture toughness fell down from 6.4 MPa m^1/2 to 5.6 MPa m^1/2. Vickers’ hardness of the hot-pressed composites varied above 18 GPa without obvious effect of the yttria content.     

Influence of the diameter of CaCO<Subscript>3</Subscript> particles on the mechanical and rheological properties of PVC composites

PVC composites filled with CaCO₃ particles with different diameter (about 40, 80, 500, 25000 nm) were prepared by using a single-screw extruder. The mechanical and rheological properties of the composites were investigated. The results showed that while the diameter of CaCO₃ nanoparticles was smaller, the mechanical properties of composites were higher. By adding 40-nm CaCO₃ nanoparticles into the PVC matrix, the single-notched impact strength of the nanocomposite at room temperature reached 82.4 kJ/m², which was 3.5 times that of the PVC matrix without CaCO₃ (23.3 kJ/m²) and 4.6 times that of the PVC blend filled with micro-CaCO₃ (17.9 kJ/m²). The tensile and flexural properties of nanocomposites were also prior to those of the composites with 500-nm and 25-μm CaCO₃ particles. The CaCO₃ particles could make the rheological property of PVC composites worse. Moreover, the effect of mass ratio of nano-CaCO₃ and micro-CaCO₃ on the properties of PVC door and window profile in industry was studied. When the mass ratio was 2.5/9, the profile could obtain good mechanical properties.     

Electromagnetic shielding properties of iron oxide impregnated kenaf bast fiberboard

The electromagnetic shielding effectiveness of kenaf fiber based composites with different iron oxide impregnation levels was investigated. The kenaf fibers were retted for removing the lignin and extractives from the fibers and magnetized. Using the unsaturated polyester and the magnetized fibers, kenaf fiber based composites were manufactured by the compression molding process. The transmission energies of the composites were characterized when the composite samples were exposed under the irradiation of electromagnetic (EM) wave with a variable frequency from 9 GHz to 11 GHz. Using the Scanning Electron Microscope (SEM), the iron oxide nanoparticles were observed on the surfaces and inside the micropore structures of single fibers. As the Fe content increased from 0% to 6.8%, 15.9% and 18.0%, the total surface free energy of kenaf fibers with the magnetizing treatments increased from 44.8 mJ/m² to 46.1 mJ/m², 48.8 mJ/m² and 53.0 mJ/m², respectively, while the modulus of elasticity reduced from 2875 MPa to 2729 MPa, 2487 MPa and 2007 MPa, respectively. Meanwhile, the shielding effectiveness was increased from 30–50% to 60–70%, 65–75% and 70–80%, respectively.     

Ground iron blast furnace slag as a matrix for cellulose-cement materials

The use of ground iron blast furnace slag (BFS) as a low-cost alternative to ordinary Portland cement (OPC) binders in fibre-cement products was examined. Both high quality softwood fibres and residual sisal from agricultural waste were chemically pulped and used as reinforcement. Composites based on several different binder formulations consisting of slag chemically activated by mixtures of gypsum and hydrated lime displayed their optimum strength and fracture toughness properties at fibre contents between 8% and 12%, with values in the ranges of 14.7–24.5 MPa and 1.13–2.36 kJ/m², respectively. Corresponding flexural moduli lay in the range 4.3–7.8 GPa and, at 12% fibre content, the composites possessed water absorption values up to 34% by mass and densities in the region of 1.3 g/cm³. A formulation of BFS activated by 10% gypsum and 2% lime presented a good compromise between strength and energy absorption combined with a reasonable price.     

Influence of filler/reinforcing agent and post-curing on the flexural properties of woven and unidirectional glass fiber-reinforced composites

The aim of this study is to investigate the reinforcing effect of woven and unidirectional glass fibers and the effect of post-curing on the flexural strength and flexural modulus of glass fiber-reinforced composites. A series of composites containing 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane and triethyleneglycol dimethacrylate matrices and different reinforcements of unidirectional or woven glass fibers were prepared. The samples, 25 × 2 × 2 mm, were cured with a halogen curing lamp, followed by additional curing by thermal treatment at 135 ± 5 °C temperature and 60 psi pressure. Samples were tested before and after post-curing in order to determine the flexural strength and flexural modulus. The degree of reinforcement with glass fibers was varied between 14 and 57 wt% or 7.64 and 38.44 vol% by changing the number of unidirectional bundles or woven glass fiber bands in the composites, respectively. The obtained flexural strength values were in the range of 95.20–552.31 Mpa; the flexural modulus ranged between 2.17 and 14.7 GPa. The highest flexural strength and flexural modulus values were recorded for samples with unidirectional glass fibers. The mechanical qualities of the glass fibers-reinforced composites increased after post-curing treatment. Increasing of the glass fiber amount in the experimental composites improves both flexural strength and modulus. SEM micrographs of fractured composites indicate a strong interfacial interaction between the glass fibers and the polymer matrix.     

Influence of alkali treatment on the interfacial and physico-mechanical properties of industrial hemp fibre reinforced polylactic acid composites

The focus of this work was to produce short (random and aligned) and long (aligned) industrial hemp fibre reinforced polylactic acid (PLA) composites by compression moulding. Fibres were treated with alkali to improve bonding with PLA. The percentage crystallinity of PLA in composites was found to be higher than that for neat PLA and increased with alkali treatment of fibres which is believed to be due to the nucleating ability of the fibres. Interfacial shear strength (IFSS) results demonstrated that interfacial bonding was also increased by alkali treatment of fibres which also lead to improved composite mechanical properties. The best overall properties were achieved with 30 wt.% long aligned alkali treated fibre/PLA composites produced by film stacking technique leading to a tensile strength of 82.9 MPa, Young’s modulus of 10.9 GPa, flexural strength of 142.5 MPa, flexural modulus of 6.5 GPa, impact strength of 9 kJ/m², and a fracture toughness of 3 MPa m^1/2.