Function Of Fiber Content Research Articles

Degradation kinetics of PLA/hemp biocomposites: Tradeoff between nucleating action and pro-hydrolytic effect of natural fibers

Natural fibers are not only a sustainable alternative to synthetic reinforcement materials, but can also be used to produce truly sustainable biocomposites with fast degradation kinetics. Indeed, due to their hygroscopicity, lignocellulosic fibers allow water and/or degrading organisms from the external environment to penetrate inside the host matrix and trigger its hydrolysis. The latter is the rate-limiting step for the degradation of bio-polyesters, which exhibit unacceptably slow degradation kinetics at ambient temperature and humidity. However, fibers also promote crystallization of the host matrix and thus slow down its degradation kinetics. To better understand and potentially control the degradation kinetics of biocomposites, here we investigate the ability of hemp shives, a hygroscopic by-product of hemp fiber production, to accelerate the hydrolysis of poly (lactic acid) (PLA). The degradation kinetics and degree of crystallinity of PLA are monitored in water and mature compost as a function of fiber content, which was varied across the percolation threshold (Φc) to study the effect of fiber interconnectivity. Above Φc, the fibers accelerate PLA hydrolysis in water despite their nucleating effect. Conversely, in compost the shielding effect of fiber-induced crystallinity prevails, and the fibers eventually slow down the degradation kinetics of PLA.

Mechanical and morphological properties of unsaturated polyester resin composites reinforced with recycled PET fibers of varying lengths

Purpose This study aims to deal with both the development and mechanical investigations of unsaturated polyester matrix (UPR) composites containing recycled polyethylene terephthalate (PET) fibers as new fillers. Design/methodology/approach UPR/PET fibers composites have been developed as mats by incorporating 5, 8, 13 and 18 parts per hundred of rubber (phr) of 6-, 10- and 15-mm length PET fibers from the recycling of postconsumer bottles. The mechanical and physical properties of the composites were investigated as a function of fiber content and length. A significant increase in stress at break and in ultimate stress (sr) were observed for composites reinforced with 5 and 8 phr of 15-mm length PET fibers. The Izod impact strength of UPR/mat PET fiber composites as a function of fiber rate and length showed that the 5 and 8 phr composites for the 15-mm length PET fiber have the optimal mechanical properties 13.55 and 10.50 Kj/m2, respectively. The morphological study showed that the strong adhesion resulting from the affinity of the PET fiber for the UPR matrix. The ductile fracture of materials reinforced with 5 and 8 phr is confirmed by the fiber deformation and fracture surface roughness. Findings This study concluded that the PET fiber enhances the properties of composites, a good correlation was observed between the results of the mechanical tests and the structural analysis revealing that for the lower concentrations, the PET fibers are well dispersed into the resin, but entanglements are evidenced when the fiber content increases. Originality/value It can be shown from scanning electron microscopy micrographs that the fabrication technique produced composites with good interfacial adhesion between PET fibers and UPR matrix.

Simulation of Compression Molding with Matrix-Fibre Separation and Fibre Orientation for Long Fibre-Reinforced Thermoplastics**

Abstract A model is presented which can be used to predict the flow under consideration of fibre-matrix separation and fibre orientation during sheet-like parts compression molding of long fibre-reinforced thermoplastics for isothermal state. During a molding, fibre content and fibre orientation distributions are calculated from the separation and orientation equations, and the viscosity of composites is expressed as a function of fibre content and fibre orientation. Based on the viscosity, the model was developed using the finite element method, and random and unidirectional reinforced composites are simulated. By comparing the theory with experimental results, the model accurately predicts mold filling patterns for the composite materials.

Influence of different dispersing systems on rheological and microstructural properties of citrus fiber suspensions

The propensity of edible fiber to structure aqueous suspensions can be tuned also by modifying the process adopted to disperse it in water. In this paper a rotor-stator homogenizer and a high pressure microfluidizer are used to produce fiber aqueous suspensions with increasing fiber content, investigating the effects of process conditions on rheological properties and particles-size distribution of these materials. An isoenergy criterion was chosen to vary the power supplied by the rotor-stator device to suspensions, and, on the other hand, two operating pressures were used to produce a second set of suspensions via microfluidization. The obtained results highlighted the greater propensity of microfluidizer to disrupt particles, stabilizing the final system by varying mainly the network extension. Finally, a fractal model was adopted to predict the rheological behavior of suspensions as a function of fiber content.

Meta-Analysis of Steel Fiber-Reinforced Concrete Mixtures Leads to Practical Mix Design Methodology.

The analysis of hundreds of SFRC mixtures compiled from papers published over the last 20 years is reported. This paper is focused on the relationships between the size and dosage of steel fibers and the relative amounts of the constituents of SFRC mixtures. Multiple linear regression is applied to the statistical modeling of such relationships, leading to four equations that show considerable accuracy and robustness in estimating SFRC mixture proportions as a function of fiber content and dimensions, maximum aggregate size, and water-to-cement ratio. The main trends described by these equations are discussed in detail. The importance of the interactions between aggregates, supplementary cementitious materials, and fibers in proportioning SFRC mixtures, as well as implications for workability and stability, are emphasized. The simplicity of these data-driven equations makes them a valuable tool to guide the proportioning of SFRC mixtures. Their predictive performance when used together as a data-driven mix design methodology is confirmed using a validation dataset.

The Effect of Physical Aging on the Mechanical Properties of Raw, Treated and Compatibilized Coir Fibers-Based Polyisoprene Bio-Composites

Abstract The production of bio-composites based on vulcanized rubber reinforced by natural fibers has been widely studied. However, the aging phenomenon occurring during the long-term storage generating irreversible damage is limiting the performance of this kind of composites which has not been studied in details. So the objective of this work was to characterize and understand the structure-mechanical property relationships in these bio-composites and to correlate the effective crosslinking density with physical aging as a function of fiber content (0, 20, 30 and 40 wt.%) and fiber surface modification (alkali treatment) for the system polyisoprene (PI) and coir fibers. Furthermore, interfacial adhesion was improved by using maleic anhydride grafted polyisoprene as a coupling agent. From the samples produced, a complete set of morphological (scanning electron microscopy) and mechanical (shear and tension) characterization was performed before and after natural aging. The results showed that the tensile modulus increased with fiber content for the range of conditions studied and the presence of a coupling agent always gave higher tensile strength due to better interfacial stress transfer. However, important elasticity loss (strain at break) was observed due to the low fiber elasticity. Finally, different physical aging mechanisms led to changes in the molecular configuration and a reduction of free volume caused by a post-curing phenomenon of the polyisoprene matrix and low environmental stability of the fibers. These phenomena were shown to increase the Young’s modulus of the neat matrix by eight times compared to the unaged neat polyisoprene, but a smaller variation (five times) was observed for the bio-composites which was related to different crosslinking density and coir fibers state of dispersion in the vulcanized matrix

Fabrication and bend testing of DHAK fiber composites

In the current work, composite specimens were fabricated using DHAK fiber up to a maximum volume fraction of about 0.188. The retting and manual processes have been used to extract the fibers. Density of DHAK is found to be 1098.5 Kg/m3. The bend properties of the composites were examined as a function of fiber content. It is found that the bend strength of the composite increases with an increase in fiber content up to 0.15 vol fraction and thereafter decreases. It has been observed that the maximum mean bend strength of the composite is 223.54 MPa for the volume fraction 0.15 which is about 3.15 times greater than that of resin. The maximum mean flexural modulus of the composite is calculated as 3.88 GPa for volume fraction 0.15, which is about 2.62 times higher than that of a base resin. These results show that there could exist a strong solid bond between the fiber and resin at the volume fraction of 0.15. It has been concluded that incorporating DHAK fiber in a base resin leads to higher bend strength as well as modulus of a new formulated composite material.

Effects of the infill pattern on mechanical properties of fused layer modeling (FLM) 3D printed wood/polylactic acid (PLA) composites

In this paper, possible influences of various infill orientations (deposition angles) on specific material characteristics—such as tensile strength, compressive strength, charpy impact strength and heat deflection temperature (HDT)—of fused layer modeling (FLM) processed test specimens were evaluated. Two specially made wood filaments, made of the same polylactic acid (PLA) polymer but two different wood fiber contents, were used for sample manufacturing and evaluated as a function of fiber content as well as infill orientation. In the context of the wood fiber content, formulations containing 15 wt. % as well as 25 wt. % of fibers were examined. In connection with infill orientation, the influence factor of seven FLM 3D printing infill orientations (deposition angles)—in particular 0°, 15° crossed, 30° crossed, 45° crossed, 60° crossed, 75° crossed and 90°—on several material properties was investigated. It could be proven that there is a direct interaction between the infill orientation (deposition angle) and the resulting mechanical performance of the test specimens. This is not exclusively a direct correlation, but there is a mutual dependency. Apart from that, the analysis showed that the higher the fiber content in the filament, the higher the resulting mechanical properties.

N-Silylated Benzothiazolium Dye as a Coupling Agent for Polylactic Acid/Date Palm Fiber Bio-composites

This work proposes a benzothiazole derivative bearing a silane moiety as a new coupling agent for polylactic acid (PLA) reinforced by date palm fibers (DPFs). The bio-composites are prepared by solution blending followed by melt compounding. From the samples produced, a complete characterization is performed including morphological, mechanical and thermal properties as a function of fiber content. The results show that the proposed fiber treatment is an easy and effective method to improve the interfacial properties and fiber dispersion leading to better material performance. For example, the addition of only 1 wt% of the dye–IPTMS to the bleached DPF not only improved the thermal stability of the biocomposites, but also led to a significant increase of the Young’s modulus at 7 wt% and higher torsion modulus up to 5 wt% (optimum value).

Effect of randomly distributed polypropylene fiber reinforcement on the shear behavior of sandy soil

Abstract The inclusions of geosynthetic materials (fibers, geomembranes and geotextiles) is a new improvement technique that ensures uniformity in the soil during construction. The use of tension resisting discreet inclusions like polypropylene fibers has attracted a significant amount of attention these past years in the improvement of soil performance in a cost-efficient manner. A series of direct shear box tests were conducted on unreinforced and reinforced Chlef sand with different contents of fibers (0, 0.25, 0.5 and0.75%) in order to study the mechanical behavior of sand reinforced with polypropylene fibers. Samples were prepared at three different relative densities 30%, 50% and 80% representing loose, medium dense and dense states,respectively, and performed at normal stresses of 50, 100 and 200 kPa. The experimental results show that the mechanical characteristics are improved with the addition of polypropylene fibers. The inclusion of randomly distributed fibers has a significant effect on the shear strength and dilation of sandy soil. The increase in strength is a function of fiber content, where it has been shown that the mechanical characteristics improve with the increase in fiber content up to 0.75%, this improvement is more significant at a higher normal stress and relative density.

Experimental Study on the Influence of Polypropylene Fiber on the Swelling Pressure Expansion Attributes of Silica Fume Stabilized Clayey Soil

Expansive soil shows dual swell–shrink which is not suitable for construction. Several mitigating techniques exist to counteract the problem promulgated by expansive clayey soils. This paper explored the potential mecho-chemical reinforcement of expansive clayey soil to mitigate the effect of upward swelling pressure and heave. The polypropylene fiber is randomly distributed in the soil for mechanical stabilization, and the industrial residual silica fume is used as a chemical stabilizer. The experimental analysis was made in three phases which involved tests on mechanically-reinforced expansive soil, using randomly distributed polypropylene fibers with different percentages (0.25%, 0.50%, and 1.00%), and which were 12 mm length. The second phase of experiments was carried out on chemical stabilized expansive soil with different percentages (2%, 4%, and 8%) of silica, and the next phase of the experiment focused on the combination of mecho-chemical stabilization of the expansive soil with different combinations of silica (i.e., 2%, 4%, and 8%) and polypropylene fibers (i.e., 0.25%, 0.50%, and 1.00%). Maximum dry density (MDD), optimum moisture content (OMC), liquid limit (LL), plastic limit (PL), plastic index (PI), grain size, and constant volume swelling pressure tests were performed on unreinforced and reinforced expansive soil, to investigate the effects of polypropylene fiber and silica fume on the engineering properties of expansive clayey soil. The experimental results illustrate that the inclusion of polypropylene fiber has a significant effect on the upward swelling pressure and expansion property of expansive soil. The reduction in the upward swelling pressure and expansion is a function of fiber content. These results also indicated that the use of silica fume caused a reduction in upward swelling potential, and its effect was considerably more than the influence of fiber.

Alfa fiber-polyurethane composite as a thermal and acoustic insulation material for building applications

The aim of the present work pointed out the introduction of natural alkalised alpha fibres as reinforcement in the preparation of partially biodegradable green insulation material composite. Thermal conductivity, mechanical properties and acoustical performances of composites were investigated as a function of fibre content. We found that 10% of alkali solution improve the hydrophobic character, mechanical and interfacial properties of the fibers. Composites made of alfa fibers-polyurethane resin has exhibited good mechanical and acoustical properties. At 20% of reinforcement the Young modulus and tensile stress increased by 48.14% and 74.12%, respectively.

Effect of gamma‐irradiation on the mechanical behavior of EPDM rubber‐recycled newsprint microfibers composites

Waste newsprint paper was collected from the local market and subjected to chemical pulping using 2 M NaOH. The fiber, after getting rid of water, was treated again using 2 M HCl solution for the same time period. The obtained newsprint microfibers (NPFs) were characterized by using scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Fourier transform infrared spectra. Then the dried and grounded NPF batch was mixed with ethylene propylene diene monomer (EPDM) rubber using different concentrations ranged from 5 to 50 phr. The prepared composites were irradiated by using gamma rays at different doses from 20 to 100 kGy. The mechanical properties of prepared EPDM/NPFs composites such as tensile strength (Ts), elongation at break (Eb%), tensile modulus (M100), toughness (Tt), and crosslink density (Cd) were measured as a function of fiber contents and irradiation dose. The results indicated that the tensile strength (Ts) increases with increasing microfibers contents up to 10 phr and irradiation dose up to 40 kGy, while Eb% decreases as the fibers content and irradiation dose increase. M100 and Cd values increase with increasing fibers content up 50 phr fibers and irradiation dose up to 60 kGy. The results also concluded that the toughness values of EPDM/NPFs composites reach its maximum degree when using 10 phr NPFs concentration and 60 kGy irradiation dose. J. VINYL ADDIT. TECHNOL., 25:198–212, 2019. © 2018 Society of Plastics Engineers

Effect of Gamma irradiation on mechanical behavior of EPDM rubber-recycled news print microfibers composites

The waste newsprint paperswere collected from local market and submitted to chemical pulping in a kneader with 2M NaOH. The fiber after getting rid of water, treated again using 2M HCL solution for the same time period. Then the news print pulped microfibers (NPMF) batch obtained was mixed with Ethylene propylene diene monomer rubber (EPDM) on roll mill with differnet contents ranged from 5 to 50phr (part per hundred part of rubber). The prepared composites subjected to gamma irradiation at different doses from 20 up to 100kGy. The characterization of the microfibers carried out by different tools like scanning electron microscopy (SEM), X-ray diffraction (XRD),Forrier Transform Infrared spectra (FTIR) and Thermogravimetric analysis (TGA). The mechanical properties of prepared composites like tensile strength (Ts), Elongation at break (Eb%), tensile modulus(M100) , tensile toughness and crosslink density (Cd) were measured as a function of fiber contents and irrdaition dose. The results indicated the Ts was increased with increasing fiber content up to 10phr and incresed with increasing irradiation dose up to 40kGy, while Eb% decreased by fiber content and irradiation dose. M100 and Cd were incresed with invreasing fiber content up 50phr fiber and increased by irradiation dose up to 60kGy. The results concluded that toughness values of EPDM/ news print fiber composite reach maximum using 10phr fiber concentration and 60kGy irradiation dose.

Undrained behaviour of polypropylene fibre reinforced sandy soil under monotonic loading

ABSTRACTSoil improvement using fibres is widely used in soil stabilisation to prevent sand liquefaction. In order to study the undrained behaviour and liquefaction resistance of sand reinforced with polypropylene fibres, a series of triaxial compressive tests were conducted on unreinforced and reinforced Chlef sand with different contents of polypropylene fibres (0, 0.3, 0.5 and 0.8%). Samples were prepared at 30% and 80% relative densities representing loose and dense states respectively, and triaxial tests were performed at confining pressures of 50, 100 and 200 kPa. Tests results show that fibre inclusion has a significant effect on the shear strength and dilation of sandy soil. The increase in strength is function of fibre content, relative density and confining pressure. The maximum strength improvement for both loose and dense fibre-reinforced sand is more pronounced at higher confining pressure and at higher fibre content.

Mechanical and thermal conductivity properties of hemp fiber reinforced polyurethane composites

The aim of the present work is to introduce natural hemp fiber as reinforcement in the preparation of partially biodegradable green composites. Composite of rigid polyurethane (PU) and hemp fiber (H.F) ​​were prepared at different loading rates in (H.F) ​​(5%, 10%, 15%, 20%, 25% and 30%). Water absorption, thermal conductivity, and mechanical properties of composite were investigated as a function of fiber content. The results show that, the thermal conductivity of composites increases linearly with density. The mechanical properties of composites with 15% wt fibers loading provided a 40% increase in strength. Measured properties showed that polyurethane- hemp fibers composite present good insulating properties compared to the traditional insulation materials (glass wool, mineral wool etc.). Therefore, (PU-HF) insulation may provide a promising solution for building insulation.

Polystyrene cellulose fiber composites: effect of the processing conditions on mechanical and dynamic mechanical properties

The usage of natural fibers on the composites development has grown rapidly in the recent years due to the fibers plentiful availability, renewable source, low density and biodegradability. However, there are some drawbacks, for instance, the fiber dispersion on a polyolefin matrix. In this work, the influence of processing speed on the mechanical and dynamic mechanical properties of polystyrene (PS) filled with cellulose fiber composites was investigated. The composites were processed on a twin-screw co-rotating extruder, using screw speeds of 200 rpm, 400 rpm and 600 rpm. The dynamic mechanical properties and the mechanical properties were investigated as a function of fiber content. The composites processed on a screw speed of 400 rpm had presented an increase on flexural and impact strength, compared to the composites processed at 200 rpm. The flexural and storage modulus had increased when increasing the fiber content, as well as increasing the processing speed. The greater fiber dispersion obtained at a screw speed of 400 rpm hinders the agglomeration arrangement and distributes the fibers more equally on the matrix. The increase on processing speed probably generates a fiber size reduction, increasing the fiber superficial area and generating a greater contact with the matrix as well. Therefore, the efforts transference of matrix to fibers is improved, originating an increase on the evaluated properties.

Polyaniline coated cellulose fiber / polyvinyl alcohol composites with high dielectric permittivity and low percolation threshold

Cost effective, high performance dielectric composites based on polyvinyl alcohol, cellulose fibers and polyaniline were prepared and the dielectric properties were studied as a function of fiber content, fiber dimensions and polyaniline content over a frequency range of 40 Hz to 30 MHz. The short cellulose fibers were size-reduced to micro and nano levels prior to coating with polyaniline. Fiber surface was coated with Polyaniline (PANI) by an in situ polymerization technique in aqueous medium. The composites were then prepared by solution casting method. Short cellulose fiber composites showed a dielectric constant (DEC) of 2.3 x 105 at 40 Hz. For the micro- and nano- cellulose fiber composites the DEC was increased to 4.5 x 105 and 1.3 x 108, respectively. To gain insight into the inflection point of the dielectric data polynomial regression analysis was carried out. The loss tangent of all the composites remained at less than 1.5. Further, AC conductivity, real and imaginary electric moduli of all the composites were evaluated. PVA nanocomposite attained an AC conductivity of 3 S/m. These showed that by controlling the size of the fiber used, it was possible to tune the permittivity and dielectric loss to desired values over a wide range. These novel nanocomposites, combining high dielectric constant and low dielectric loss, can be effectively used in applications such as high-charge storage capacitors.

Mechanical and wear behaviors of untreated and alkali treated Roselle fiber-reinforced vinyl ester composite

In the present communication, the effect of mercerization or alkali (NaOH) treatment on mechanical and wear behavior of chopped roselle fiber-reinforced vinyl ester (CRFRV) composite have been studied as the function of fiber content. The results show that the tensile, flexural and impact strength values of untreated and treated fiber composites increased with increasing fiber content up to 40 wt.% and then dropped. But, the tensile and flexural modulus values were increased continuously from 10 to 50 wt.%. After the careful study, it was observed that the optimum fiber content for better or optimum mechanical properties is 40 wt.% at both the untreated and treated fiber composites. Fractographic study of the fractured surface of treated and untreated fiber composites was carried out using scanning electron microscopy (SEM). The wear resistance of the composites fabricated with treated roselle fibers were found to be good compared to composite fabricated with untreated fibers.

Mechanical performance of woven kenaf-Kevlar hybrid composites

Hybrid composites offer a combination of advantages of constituent components to produce a material with determined properties. In the present work, woven hybrid composite was prepared by hand lay-up method in laminate configuration. Kevlar/kenaf hybrid composites were fabricated with total fibre content of 30% and the ratio of Kevlar/kenaf varies in weight fraction of 78/22, 60/40, 50/50, 26/74, and 32/68, respectively. The Kevlar/epoxy and kenaf/epoxy were also prepared for comparison. The mechanical properties of hybrid, kenaf/epoxy, and Kevlar/epoxy composites were tested. Morphological properties of tensile fracture surface of hybrid composites were studied by scanning electron microscopy. Results have established that the mechanical properties of kenaf-Kevlar hybrid composites are a function of fibre content. The hybrid composites with Kevlar/kenaf (78/22) ratio exhibited better mechanical properties compared to other hybrid composites. This result indicates the potential of Kevlar-kenaf hybrid composite for impact applications.