Flexural characteristics of coir fiber reinforced cementitious composites

This study has examined the flexural properties of natural and chemically modified coir fiber reinforced cementitious composites (CFRCC). Coir fibers of two different average lengths were used, and the longer coir fibers were also treated with a 1 % NaOH solution for comparison. The fibers were combined with cementitious materials and chemical agents (dispersant, defoamer or wetting agent) to form CFRCC. The flexural properties of the composites, including elastic stress, flexural strength, toughness and toughness index, were measured. The effects of fiber treatments, addition of chemical agents and accelerated ageing of composites on the composites’ flexural properties were examined. The results showed that the CFRCC samples were 5–12 % lighter than the conventional mortar, and that the addition of coir fibers improved the flexural strength of the CFRCC materials. Toughness and toughness index, which were associated with the work of fracture, were increased more than ten times. For the alkalized long coir fiber composites, a higher immediate and long-term toughness index was achieved. SEM microstructure images revealed improved physicochemical bonding in the treated CFRCC.     

Effect of coir fiber content and compatibilizer on the properties of unidirectional coir fiber/polypropylene composites

The main objective of this research was to study the effect of fiber content variation and stearic acid (SA) treatment on the fundamental properties of unidirectional coir fiber (CF) reinforced polypropylene (PP) composites. Several percentages of filler contents were used (10–40 wt %) in order to gain insights into the effect of filler content on the properties of the composites. Coir/PP composites were fabricated by compression molding, and the properties of composites were studied by physico-mechanical and thermal properties. The results from mechanical properties such as tensile strength (TS), tensile modulus (TM) and impact strength (IS) of the CF/PP composites were found to be increased with increasing fiber content, reached an optimum and thereafter decreased with further increase in fiber content. Treatment of the coir with SA as the coupling agent enhanced the mechanical properties, crystallization temperature and crystallinity of virgin PP and water desorption of the resulting composites, resulting from the improved adhesion between the CF and PP matrix. Scanning electron micrographs (SEM) of the tensile fractured samples showed improved adhesion between fiber and matrix upon treatment with SA. Interfacial shear strength (IFSS) of the composites was measured by single fiber fragmentation test (SFFT).     

Dynamic mechanical analysis of randomly oriented short bagasse/coir hybrid fibre-reinforced epoxy novolac composites

Hybrid composites of epoxy novolac reinforced with short bagasse fibres and short coir fibres were prepared. The mechanical and dynamic mechanical properties of these bagasse-coir hybrid fibres reinforced epoxy novolac composites were investigated with reference to different layering patterns of the composites. The tensile properties of the tri-layer composites are recorded higher than those of the bi-layer composites, whereas the flexural properties of the tri-layer composites are lower than bi-layer composites. The tensile strength of the intimate mix composite is comparable with trilayer composite having bagasse as skin material. The effect of layering pattern on storage modulus (E′), damping behavior (tan δ), and loss modulus (E″) was studied as a function of temperature and frequency. The E′ values of the bi-layer composites are recorded lower than those of tri-layer (bagasse/coir/bagasse) and intimately mixed hybrid composites. The minimum E′ value is obtained for the composites made with coir as skin layer. Bi-layer composite shows maximum damping property. The theoretical modeling showed good correlation with experimental results at above glass transition temperature (T _g ), while theoretical model deviates experimental data at lower T _g . The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the composites.     

Effect of water and fiber length on the mechanical properties of polypropylene matrix composites

This paper presents the results of a current study on polypropylene matrix composites processed by injection, with two different glass fiber lengths and five different volume fractions. Physical and mechanical properties were obtained, namely flexural strength, stiffness modulus and fracture toughness. The mechanical properties of the composites increased significantly with the increase of the fibers volume fraction in agreement with the Counto model. The effect of water immersion time was also analysed. Immersion in water promotes a marked decrease in mechanical properties in the early seven-ten days, and afterwards tends to stabilize. Water causes a decrease of the relative strength which increases with fiber volume fraction and reaches about 29 % and 32 % for 20 % of 4.5 mm fiber length and for 25 % of 12 mm fiber length respectively, after 28 days immersion in water. Fracture toughness increases with fiber volume fraction and is always higher for 12 mm fiber length composites than for 4.5 mm fiber length composites.     

Matrix modification with silane coupling agent for carbon fiber reinforced epoxy composites

To improve interfacial adhesion between carbon fiber and epoxy resin, the epoxy matrix is modified with N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (YDH602) and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (YDH792), respectively. And the effect of matrix modification on the mechanical performance of carbon/epoxy composites is investigated in terms of tensile, flexural and interlaminar properties. The flexural properties indicate that the optimum concentration of silane coupling agents YDH602 and YDH792 for the matrix modification is approximately 0.5 wt% of the epoxy resin system, and the mechanical properties of the YDH792-modified epoxy composites is better than that of the YDH602-modified epoxy composites at the same concentration. Compared to unmodified epoxy composite, the incorporation of 0.5 wt% YDH792 results in an increase of 4, 44 and 42 % in tensile, flexural and interlaminar shear strength (ILSS) values of the carbon/epoxy composite, respectively, while the corresponding enhancement of tensile and flexural modulus is 3 and 15 %. These improvements in mechanical properties can be considered to be an indication of better fiber/matrix interfacial adhesion as confirmed by SEM micrographs of the fracture surface after interlaminar shear testing. The viscosity of the modified epoxy resin system can be reduced by incorporation of silane coupling agent YDH792, which is beneficial for fiber impregnation or wetting during liquid composite molding process.     

Investigations on mechanical characteristics of glass fiber reinforced epoxy composite modified with amino-terminated hyperbranched polymer

Glass fiber, GF, which was first hydroxylated and silanized, was incorporated into epoxy resin modified with amino-terminated hyperbranched polymer (ATHBP) to obtain high performance composite. The effects of GFs content on the mechanical properties of composites were investigated, discussing the results from flexural, tensile, and impact tests. The composites revealed noticeable improvement in flexural strength, tensile strength as well as impact strength but slow decrease in elongation at break, compared to the epoxy/ATHBP thermoset. FESEM morphology results indicated the good compatibility between epoxy matrix and GF in the appearance of ATHBP and showed that the toughening mechanism was mainly attributed to the stress transfer mechanism.     

The influence of graphene reinforced electrospun nano-interlayers on quasi-static indentation behavior of fiber-reinforced epoxy composites

The aim of this research is to investigate the development and evaluation of hybrid multi-scale aramid/epoxy composites interleaved with electrospun graphene nanoplatelets/nylon 66 (GNPs/PA66) mats. The reinforced nanofiber mats were explored for their best mechanical properties and PA66 nanofibers with 1 wt% GNPs were selected for composite production. Quasi-static indentation tests were performed on both pristine and nanofiber-modified composites. The experimental results revealed that the introduction of reinforced interleaves within the interlaminar interfaces of composites promotes fracture toughness compared to pristine interleaves. It is shown that there is a particular interleaf thickness for optimum toughening effect of nanofibers. The optimum thicknesses for pristine and reinforced interleaves are 35 and 17.5 μm, respectively.     

Experimental investigation of mechanical behavior of Jute-Flax based glass fiber reinforced composite

Present technological development and innovation needs a better class of material that meets all the practical applications along with its environmental friendly nature and economical value. Hybrid natural fiber composites, a sector of natural composites meets these requirements. This paper deals with fabrication, mechanical characterization of a hybrid (Jute+Flax+GFRP) composite and also the comparison of it with the (Jute+GFRP) based composite. These composites are fabricated using hand lay-up technique. The arrangement of hybrid composite is such that a layer of vertically laid flax fiber is flanked between layers of horizontally laid jute fiber. Epoxy resin alongside with HY951 hardener is used as the binding agent throughout the layer. Glass fiber laminates are used on both sides for improving the surface finish and surface hardness. The volumetric fraction is such that one third of total volume is occupied by Jute and Flax fibers. Test results shows that the hybrid natural composite has excellent properties under tensile, flexural loading. At last failure morphology analysis is done using Scanning Electron Microscope (SEM) and the internal structure of the broken specimen is discussed.     

Effect of soaking corrosion on flexural properties of carbon fiber reinforced epoxy syntactic foams

The fiber-reinforced syntactic foam is a type of lightweight materials. In this paper, hollow glass microspheres/epoxy syntactic foams reinforced by carbon fibers are prepared. Carbon fibers of five mass fractions are used to obtain five types of reinforced syntactic foams. The effect of the fiber content and soaking corrosion on the flexural properties of syntactic foams are investigated. The results of soaking test show that the moisture rate in distilled water is greater than that in seawater. The flexural test results show that the flexural strength of syntactic foams increases obviously by adding fibers. The maximum value increases 25.5 % than that of composites without adding fibers when fiber-mass fraction is 5 %. Soaking corrosion reduces the flexural properties of the syntactic foams. The flexural strengths of syntactic foams immersed in water and seawater with 5 % fiber-mass fraction decrease 34.4 % and 37.5 % respectively. The main reasons of the flexural strength reduction of syntactic foams with soaking corrosion are discussed.     

Physical and mechanical properties of jute, bamboo and coir natural fiber

A systematic study has been carried out to investigate the mechanical and physical properties of jute, bamboo and coir (brown and white) single fibers. The tensile properties (tensile strength, Young’s modulus and strain to failure) were determined by varying span length. Scanning electron microscopic analysis was also carried out to determine the physical properties of fibers in order to correlate with its strength, Young’s modulus and strain to failure. The Young’s modulus and strain to failure were corrected using newly developed equations. The study revealed that with increasing test span length the Young’s modulus increased and tensile strength as well as strain to failure decreased. This is because no extensometer could be used in this test set-up and machine displacement (denoted by α) was used for the modulus determination. It is also attributed that larger span length helps to minimize the machine displacement compared to smaller ones due to the reduced relative effect of slippage in the clamps. Among all fibers, the Young’s modulus of bamboo fiber was the highest. Jute fiber had smoother surface compared to other three examined fibers.     

Effect of reinforcement and chemical treatment of fiber on The Properties of jute-coir fiber reinforced hybrid polypropylene composites

Present research investigates the mechanical properties of jute-coir fiber reinforced hybrid polypropylene (PP) composite with fiber loading variation and observes the effect of chemical treatment of fiber on property enhancement of the composites. Composites were manufactured using hot press machine at four levels of fiber loading (5, 10, 15 and 20 wt%). Fiber ratio’s were varied (jute:coir=1:1, 3:1 and 1:3) for 20 % fiber loaded composites. Both jute and coir fiber was treated using 5 % and 10 % NaOH solutions. Composites were also prepared using treated fiber with jute-coir fiber ratio of 3:1. Tensile, flexural, impact and hardness tests and Fourier transform infrared spectroscopic analysis were conducted for characterization of the composites. Tensile test of composite showed a decreasing trend of tensile strength and increasing trend of the Young’s modulus with increase in fiber loading. During flexural, impact and hardness tests, the flexural strength, flexural modulus, impact strength and hardness values were found to be increased with increase in fiber loading. All these properties enhanced with the enhancement of jute content except impact strength. 5 % NaOH treatment provided an improving trend of properties whereas, 10 % NaOH treatment showed the reverse one. The FTIR analysis of the composites indicated decrease of hemicelluloses and lignin content with alkali treatment.     

Effect of Ni-coated short carbon fibers on the mechanical and electrical properties of epoxy composites

Ni-coated short carbon fibers (Ni-SCFs) were prepared using an electrodeposition method. Short carbon fiber (SCF) reinforced epoxy composites were prepared by changing the fiber content (0.1–0.7 wt%). To investigate the effect of Ni-coated short carbon fibers on the mechanical and electrical properties of the composites, we prepared two kinds of reinforcements: the short carbon fibers treated by 400 °C (400 °C treated SCFs) and Ni-SCFs. Fracture characteristics of the composites revealed the Ni coatings and the epoxy matrix had a better interface, so that the results of tensile and bending strength were better in epoxy/Ni-SCFs composites than those in epoxy/400 °C treated SCFs composites. The 400 °C treated SCFs decreased the electrical resistivity of the epoxy composites, compared to the pure epoxy. However the epoxy/Ni-SCFs composites had lower electrical resistivity than epoxy/400 °C treated SCFs with the same fiber content.     

Effect of chemical modifications on the performance of biodegradable photocured coir fiber

Coir fibers (Cocos nucifera) were treated with 1-ethyl-2-pyrrolidone (1-E-2-P) mixed with methanol (MeOH) under UV radiation. A series of solutions of different concentrations of 1-E-2-P in methanol along with a photoinitiator, Darocur-1173, were prepared. Monomer concentration, soaking time, and radiation dose were optimized in terms of grafting and mechanical properties. Ten percent 1-E-2-P, 6 min soaking time, and a 15th pass of radiation produced higher tensile strength (53 %) and elongation at break (230 %) than those of virgin fiber, as well as the highest grafting value (4.9 %). The effect of additives (1 %), such as urea and silane (3-trimethoxysilyl propyl methacrylate) on the properties of coir fiber was studied. Among the additives used, silane showed the best performance. For further improvement of the properties, the fibers were treated with alkali (potassium hydroxide) solution of different temperatures (0–60 °C). A 10 % alkali-treated fiber showed the best properties such as grafting (6.2 %), tensile strength (72 %) and elongation at break (330 %) over virgin fiber. The silane-treated fiber produced the minimum loss of the properties, as well as a lower water uptake than those of the untreated one. The effect of simulating weathering on the degradation properties of samples was also performed.     

Thermal characteristics of basalt fiber reinforced epoxy-benzoxazine composites

This study investigates the possibility of utilizing basalt chopped fiber in order to prepare a thermally stable fiber reinforced composite. Bi-component resin system using epoxy and benzoxazine monomer is proposed and its cure characteristic is evaluated by FT-IR and DSC. Copolymerization of epoxy resin upon curing with benzoxazine is carried out in the absence of a strong catalyst. Through the evaluation of T _g of the epoxy-benzoxazine copolymer resin and its composite, it is clear that the incorporation of basalt fiber in composite has a great role and advantage. Also, this study systematically evaluates the apparent char yield and net char yield gain of the composites using TGA thermograms. Based on the results of DSC and TGA, it is advised that the favorable composite composition can be prepared from the range of 20 % to 50 % of epoxy content with 10 % of basalt fiber.     

Development of mathematical models and estimation for the mechanical properties of organic fiber reinforced polyester composites

Organic fiber from animal waste was used for the development of environmentally friendly animal fiber based polyester composites using cow hair. The cow hair fibers were cut into 10 mm lengths to produce the needed short fiber for random dispersion in the matrix. Before use, some of the fibers were treated with sodium hydroxide for fiber surface modification while some were left as untreated. Composites were developed using predetermined proportions of the fibers in an open mould production process. Samples were formed into tensile and flexural shape in their respective moulds and were stripped off the moulds after curing while further curing was ensured for 27 days before testing. Tensile and flexural properties of the cow hair fiber reinforced polyester composites were evaluated from which it was discovered that the untreated fiber reinforced composites possess better enhancement of mechanical properties compared to the treated fiber reinforced composites and the unreinforced polyester material. Mathematical models for the tensile and flexural properties were developed using statistical packages and estimation using developed software. The developed models revealed high degree of correlation between the experimental values and the predicted values. This denotes that the models can be used to predict the mechanical properties of cow hair reinforced polyester composites for various reinforcement contents.     

Batch foaming of short carbon fiber reinforced polypropylene composites

In this paper, the short carbon fiber (SCF)/PP composite foams with fine open cell were prepared with batch foaming technique using supercritical CO₂. The effects of SCF contents, saturation pressure and depressurization rate on the cell morphology were studied. The experimental results indicate that the cell morphology of foamed composites was significantly influenced by the SCF contents and saturation pressure. It is found that the cell size increased and cell density decreased with the increment of SCF contents while the saturation pressure had the opposite effect. However, depressurization rate showed little impacts on the cell morphology due to the presence of SCF.     

Mechanical properties of fragrant screwpine fiber reinforced unsaturated polyester composite: Effect of fiber length,fiber treatment and water absorption

Fragrant screwpine fiber reinforced unsaturated polyester composites (FSFRUPC) were subjected to water immersion tests in order to examine the effect of water absorption on the mechanical properties. FSFRUP composite specimen containing 30 % fiber volume fraction with fiber length of 3 mm and 9 mm was considered in this study. Water absorption test was performed by immersing specimen in sea, distilled and well water at room temperature under different time durations (24, 48, 72, 96, 120, 144, 168, 192, 216, 240 hours). The tensile, flexural and impact properties of the water absorption specimen were appraised and compared with those of the dry composite specimen as per the ASTM standard. The tensile, flexural and impact properties of FSFRUPC specimen were found to decrease with the increase in the percentage of moisture uptake. The percentage of moisture uptake of composite was reduced after alkali treatment with 3 % NaoH for 3 hours. In moisture absorption test, the lowest diffusion coefficient, D (6.62513×10^-13 m²/s) and swelling rate parameter, K _sr (6.341×10^-3 h^-1) were obtained through the specimen immersed in sea water. The chemical composition, elemental composition of fiber and surface morphology of the FSFRUPC were analysed by using Fourier transform infrared spectroscopy (FTIR), Energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) respectively.     

Mechanical behavior of composites reinforced with fibers caroa

Composites were prepared with 13, 23 30 and 40 % fiber and evaluated the mechanical performance in tensile, flexural and impact. The mechanical properties of these composites were also evaluated function of time at 110 °C thermal exposure. Caroa fibers were characterized by techniques such as thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the best mechanical properties were achieved for composites containing 23 to 30 % fiber. The incorporation of 23 % fiber caroa increased both the modulus of elasticity in the tensile test as the flexural strength and impact, the composite with 30 % fiber caroa showed higher tensile strength. The results show that the tensile and flexural strength of the composite decreased with time of thermal exposure. The thermal aging at 110 °C caused a decrease in tensile properties of the composites.     

Effect of concentration and surface modification of single walled carbon nanotubes on mechanical properties of epoxy composites

Single walled carbon nanotubes (SWNTs) are considered as a highly potential reinforcement material for the epoxy composites. Dispersion of SWNTs in epoxy and poor interfacial strain transfer are two major challenges. Surface functionalization is one efficient way to change the dispersion and interfacial properties of SWNTs. In this study, five different modification methods of SWNTs were used, and the functional groups on the SWNTs were tested by X-ray photoelectron spectroscopy and Raman spectroscopy. The SWNTs/epoxy composite were prepared using dimethylformamide (DMF) as the solvent. SWNTs at two concentration levels of 0.05 wt% and 0.5 wt% and with five different surface modifications were filled in to epoxy resins. The dispersion of the nanotubes in epoxy resin was evaluated by light optical microscope (LOM), with high content of SWNTs more aggregates appear. The interfacial strain transfer was tested by Raman shift of the 2D band when applying a strain on the epoxy composite sample. With equal strain levels in the composite more strain was transferred from epoxy matrix to SWNTs with 0.05 wt% of SWNTs than the 0.5 wt% of SWNTs filled epoxy resin. Mechanical properties were influenced by the strain transfer efficiency and the curing degree of the samples.     

Effect of temperature and time on mechanical and electrical properties of HDPE/glass fiber composites

In recent years, composites based on glass fiber reinforced polymer have been widely used in order to meet increasing durability and safety regulations, particularly in the power cable, automotive and plane industry. In this paper, mechanical and electrical properties of high density polyethylene (HDPE) and HDPE containing glass fiber polymer composites were investigated and compared at different temperatures. Composite materials were prepared with the hot pressing method. Tensile strength, % elongation and the modulus of elasticity (or Young’s modulus) were determined for each sample at different temperatures. In addition to this, at different temperatures τ _σ and τ _E have mechanical and electrical lifetime respectively, corresponding to mechanical tension (σ) and electrical strength (E), and this was investigated for each sample. As compared to the mechanical and electrical properties of neat HDPE, HDPE/0.5 % glass fiber composites have been found to have better mechanical and electrical durability.