Fiber-matrix Interfacial Adhesion Research Articles

Sugar Palm Fibre-Reinforced Unsaturated Polyester Composite Interface Characterisation by Pull-Out Test

Polymer composites using natural fibres as the reinforcing agents have found their use in many applications. However, they do suffer from a few limitations, due to the hydrophilicity of the natural fibres which results in low compatibility with the hydrophobic polymer matrices. This paper aims to determine the best sugar palm (Arenga pinnata) fibre surface treatment to improve the fibre-matrix interfacial adhesion. Fibre surface modifications were carried out by water retting process where the fibres were immersed in sea water, pond water and sewage water for the period of 30 days. The test samples were fabricated by placing a single fibre in an unsaturated polyester resin. Single-fibre pull-out tests showed that freshwater-treated fibres possessed the highest interfacial shear strength, followed by untreated fibres, sewage water-treated fibres, and sea water-treated fibres. Further surface analyses of the samples were performed using a Scanning Electron Microscope (SEM) and an Energy Dispersive X-ray Spectroscopy (EDS) system.

Effect of Fiber Loading on the Mechanical Strength of NFR Hybrid Composites

Ortho-type UP resin is reinforced with long abaca and short bagasse fibers to produce a novel type of natural fiber-reinforced (NFR) hybrid composite material that is environment-friendly, has a long service life, possesses the properties of both long and short FRP’s, and has also acquired the advantages of utilizing two different types of natural fiber reinforcements. The abaca and bagasse fibers are treated in 5wt% NaOH(aq) solution at 80°C for 9 hours and pressed into continuous, unidirectional fiber sheets and random fiber mats, respectively. The fibers are then incorporated into the resin matrix by hand lay-up method, producing FRP laminates with the same uniform thickness but subjected to varying fiber loading conditions: (1) the stacking of long fiber sheets are done in cross-ply and parallel orientation; (2) the abaca and bagasse fibers are stacked in different alternating sequence patterns, and (3) the fibers are added into the ortho-UP matrix at increasing fiber fraction. The alkali-treated FRP laminates show an increase in fiber-matrix interfacial adhesion as compared to the untreated FRP’s, based on the overall improvement in the composite mechanical strength, as well as from the lesser visible fiber pull-out observed from SEM images on their fracture surfaces. Also, as expected, the tensile and flexural strengths of the abaca/bagasse hybrid FRP measures intermediate to those of abaca and bagasse FRP’s. The strength has also improved with increasing fiber content, although this increase has also caused an increased occurrence of void spaces that may consequently become detrimental to the NFR composite’s performance.

Hybridization Effect of Glass Fibre on Mechanical, Morphological and Thermal Properties of Polypropylene-Bamboo/Glass Fibre Hybrid Composites

Polypropylene/bamboo fibre-reinforced composites (BFRP) and polypropylene-bamboo/glass fibre based hybrid composites (BGRP) using an intermeshing counter-rotating twin-screw extruder followed by injection moulding in which maleic anhydride grafted polypropylene (MAPP) was used as a compatibilizer. The effect of hybridization on the mechanical performance of hybrid composites has been assessed. It was observed that replacement of 15 wt.% of bamboo fibre by 15 wt.% of glass fibre with 2 wt.% of MAPP on a total amount of 30 wt.% of fibre content showed optimum mechanical performance. The water uptake of the hybrid composites was also found to be less than that of their unhybridized counterpart. The crystallization, melting behaviour and thermal stability of the hybrid composites were investigated employing differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA ). TGA thermograms showed an increase in thermal stability of the matrix polymer after incorporation of bamboo and glass fibres, confirming the effect of hybridization and efficient fibre matrix interfacial adhesion. The fibre-matrix interfacial morphology of the tensile fractured specimens was studied using scanning electron microscopy (SEM) which showed less fibre pullout and fewer gaps between the fibre and the base matrix in case of MAPP-treated hybrid composites.

Sorção de agua em compósitos de poliéster insaturado reforçados com tecido de juta e juta/vidro modelagem, simulação e experimentação

Estudos de compósitos reforçados com fibras naturais mostram que as dificuldades associadas ao uso de fibras vegetais como reforço em compósito de polímeros são freqüentemente relacionadas à absorção de umidade. A presença de umidade leva à impregnação e adesão interfacial fibra-matriz imperfeitas, que geram tensões internas, porosidade e falha prematura do sistema. Este problema pode ser reduzido usando fibra híbrida tramada ou tecidos tricotados. Neste sentido, este trabalho tem como objetivo estudar numérica e experimentalmente a sorção de água em compósitos de juta e juta/vidro. Os compósitos de poliéster insaturados moldados por compressão e reforçados com tecido de juta e tecido híbrido de juta-vidro têm composições em peso de: a) 26% de juta/74% poliéster insaturado; e b) 26% juta/32% vidro/42% poliéster insaturado, e dimensões de 20,00 × 20,00 × 2,30 mm³ e 20,00 × 20,00 × 2,82 mm³, respectivamente. Um modelo matemático tridimensional de difusão transiente foi desenvolvido para predizer a transferência de massa durante a absorção de água. A formulação matemática foi resolvida numericamente usando o método de volumes finitos e um esquema de interpolação totalmente implícito. Os resultados da distribuição do teor de umidade dentro destes compósitos e cinética de absorção de água são mostrados e analisados. O conhecimento da distribuição de umidade permite verificar áreas mais favoráveis a problemas de delaminação devido à fraqueza da interface fibra-matriz e, por conseguinte redução nas propriedades mecânicas.

Solvent Uptake and Accelerated Solar Aging Studies of Cotton – Polypropylene Commingled Composite Systems

Natural fibre-reinforced thermoplastic composites have a significant role in non-structural applications. Natural fibres are biodegradable, renewable and of low cost, high toughness and possess good thermal properties. This work involved the study of solvent absorption of cotton/polypropylene (PP) side-by-side commingled composites in different solvents, its variation by chemical treatments, temperature, fibre content etc., the extent of tensile property deterioration by solar radiation in a solar light concentrator and by water diffusion. It was observed that though cotton is highly hydrophilic, the diffusion was a matrix-dominated phenomenon. The extent of moisture absorption increased with the fibre content but decreased on treatment with maleic anhydride-modified PP. The former added a greater number of hydrophilic hydroxyl groups while the latter consumed them and enhanced the fibre–matrix interfacial adhesion. Increase in temperature accelerated the rate of moisture absorption and reduced the time required for equilibrium swelling. Exposure to sunlight in solar concentrator deteriorated mechanical properties such as tensile strength and tensile modulus by weakening the fibre–matrix interfacial adhesion and by chain scission.

Pre-Treatment by Water Retting to Improve the Interfacial Bonding Strength of Sugar Palm Fibre Reinforced Epoxy Composite

Polymer composites using natural fibres as the reinforcing agents have found their use in many applications. However, they do suffer from a few limitations, due to the hydrophilicity of the natural fibres which results in low compatibility with the hydrophobic polymer matrices. This paper presents the alternative low-cost methods of sugar palm (Arenga pinnata) fibre surface treatments to improve the fibre-matrix interfacial adhesion. Fibre surface modifications were carried out by water retting process where the fibres were immersed in sea water, pond water and sewage water for the period of 30 days. The results showed that the tensile and flexural strengths of the treated fibre reinforced composites increased as the fibre treatment duration increased. This indicates that the treatments had significantly improved the fibre-matrix bonding strength.

Physico-mechanical properties of chemically treated coir reinforced polypropylene composites

The physico-mechanical properties of coir reinforced polypropylene (PP) composites been investigated. In order to attain improved mechanical properties of the composites coir was chemically treated with o-hydroxybenzene diazonium salt. Both raw and treated coir samples were utilized for the fabrication of the composites. The mechanical properties of the composites prepared from chemically treated coir are found to be much better compared to those of untreated ones. Tensile strengths of the composites of both raw and chemically treated coir-PP composites showed a decreasing trend with increasing filler content. However, the values for the chemically treated coir-PP composites at all mixing ratios are found to be higher than that of neat PP. The surface morphologies of the fractured surfaces of the composites were recorded using scanning electron microscopy (SEM) to gain information about the fiber–matrix interfacial adhesion in the composites.

Mechanical and Morphological Properties of Chemically Treated Coir-Filled Polypropylene Composites

In the present work, coir was chemically treated first with sodium perchlorate and then with 2,4-dinitrophenyl hydrazine (DNPH) to improve the mechanical properties of the coir−PP composites. Untreated, oxidized, and DNPH-treated coir samples at different mixing ratios were utilized to prepare the composites. Mechanical properties of the composites prepared from both perchlorate and DNPH-treated coir were found to be better than those of untreated ones. The tensile strengths of both untreated and treated coir−PP composites decreased with an increase in fiber content. However, the values were found to be higher than those of corresponding values of untreated ones. Treated coir−PP composites were found to absorb a lower amount of water than the untreated ones. To understand why the mechanical properties of composites prepared under different conditions of coir were different, surface morphologies of the tensile fractured surfaces of the specimens were recorded using scanning electron microscopy (SEM). The SEM images clearly revealed that there were fewer fiber agglomerations, microvoids, and fiber pull out traces in both perchorate and DNPH-treated coir−PP composite than in the untreated one, indicating that better distribution of the fiber into the matrix as well as stronger fiber matrix interfacial adhesion occurred upon treatment of coir.

Influence of Network Structure on Dynamic Mechanical Properties of Cross-Linked Polystyrene / Glass Fiber Composites

The cross-linked polystyrene prepolymer was synthesized with divinylbenzene (DVB) as crosslinker via free-radical crosslinking copolymerization (FCC) and used as the matrix materials for E-glass fiber reinforced composites. The surface modification was performed by treatment of E-glass fiber with γ-methacryloylpropyl trimethoxysilane (MPS) solution. Fourier transform infrared spectroscopy (FTIR) was used to identify the functional groups on the surface modified glass fibers. Dynamic mechanical thermal analysis (DMTA) of these composites revealed that the dynamic storage modulus (E′) was gradually enhanced with the increasing content of DVB (0~3.0 wt %) whereas the damping parameter (tanδ) peaks are lower and broader, indicating better load bearing capacity. Moreover, the Tg was shifted to higher temperature corresponding to the increasing of crosslinking density. Morphology of fracture surfaces for these composites showed different fiber-matrix interfacial adhesion which was mainly attributed to the variation of crosslinking network structure in the interface.

Influence of short bamboo/glass fiber on the thermal, dynamic mechanical and rheological properties of polypropylene hybrid composites

The present article summarizes the development of polypropylene-bamboo/glass fiber reinforced hybrid composites (BGRP) using an intermeshing counter rotating twin screw extruder followed by injection molding. Maleic anhydride grafted polypropylene (MAPP) has been used as a coupling agent to improve the interfacial interaction between the fibers and matrix. The crystallization and melting behavior were investigated employing differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) indicates an increase in thermal stability of the matrix polymer with incorporation of bamboo and glass fibers, confirming the effect of hybridization and efficient fiber matrix interfacial adhesion. The dynamic mechanical analysis (DMA) showed an increase in storage modulus ( E′) indicating higher stiffness in case of hybrid composites as compared with untreated composites and virgin matrix. The rheological behavior of the hybrid composites has also been studied using time–temperature superposition (TTS) principle and corresponding viscoelastic master curves have been constructed.

Influence of fibre-surface treatment on structural, thermal and mechanical properties of jute fibre and its composite

Jute fibres (Corchorus olitorious), an environmentally and ecologically friendly product, were chemically modified and treated with 5% NaOH solution at room temperature for 2 h, 4 h and 8 h. The above samples were characterized and morphologically analysed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and Instron 1185. Alkali treatment affects the supramolecular structure of the fibre as shown by XRD by improving the degree of crystallinity of the fibre. Surface chemistry of the fibre also altered as depicted by FT-IR studies. This chemical treatment was also found to alter the characteristic of the fibre surface topography as seen by the SEM. From the mechanical single fibre test it was found that the tenacity and modulus of the fibre improved after alkali treatment. This might be due to the improvement in the crystallinity. DSC data demonstrated that the thermal degradation temperature for the cellulose get lowered from 365·26°C to 360·62°C after alkali treatment led to the reduction in fibre thermal stability. Jute fibre reinforced composite were prepared with treated and untreated jute fibre (15 wt%) reinforced unsaturated polyester (UPE). Effectiveness of these composites was experimentally investigated through the study of the composites by DSC, Instron 1195 for mechanical property of composites, volume fraction of the porosity and hydrophobic finishing of the composite. From the DSC analysis it was found that thermal stability enhanced for treated fibre reinforced composite. This could be due to the resistance offered by the closely packed cellulose chain in combination with the resin. Flexural strength of the composite prepared with 2 h and 4 h alkali treated fibre were found to increase by 3·16% and 9·5%, respectively. Although 8 h treated fibre exhibited maximum strength properties, but the composite prepared with them showed lower strength value. Alkali treatment helped in the development of hydrophobicity and reduction in volume fraction of the porosity. This may be due to the better fibre matrix interface adhesion caused due to the fibre surface treatment by alkali.

Polypropylene—Bamboo/Glass Fiber Hybrid Composites: Fabrication and Analysis of Mechanical, Morphological, Thermal, and Dynamic Mechanical Behavior

Hybrid composites of polypropylene reinforced with bamboo and glass fibers (BGRP) were fabricated using an intermeshing counter rotating twin screw extruder followed by injection molding. Maleic anhydride grafted polypropylene (MAPP) has been used as a coupling agent to improve the interfacial interaction between the fibers and matrix. The mechanical properties of the hybrid composites were studied from tensile, flexural, and impact tests. Mechanical tests indicated an increase in tensile, flexural, and impact strength of the BGRP hybrid composites at a bamboo:glass fiber ratio of 15:15 ratio in the presence of 2 wt% of MAPP. Nearly, 69, 86, and 83% increase in tensile flexural and impact strength respectively has been observed as compared with virgin PP. The fiber matrix interfacial morphology of the tensile fractured specimens was studied using scanning electron microscopy (SEM) which showed less fiber pullout and comparatively less gaps between the fiber and the base matrix in the case of MAPP treated hybrid composites. The crystallization, melting behavior and thermal stability of the hybrid composites were investigated employing differential scanning electron microscopy (DSC) and thermogravimetric analysis (TGA). Thermogravimetric analysis (TGA) showed an increase in thermal stability of the matrix polymer with incorporation of bamboo and glass fibers, confirming the effect of hybridization and efficient fiber matrix interfacial adhesion. The dynamic mechanical analysis (DMA) showed an increase in storage modulus (E′) indicating higher stiffness in case of hybrid composites as compared with untreated composites and virgin matrix. The tan δ spectra presented a strong influence of fiber content and coupling agent on the α and γ relaxation process of PP.

Effect of chemical modifications of the pineapple leaf fiber surfaces on the interfacial and mechanical properties of laminated biocomposites

Natural fiber reinforced renewable resource based laminated composites were prepared from biodegradable poly(lactic acid) (PLA) and untreated or surface-treated pineapple leaf fibers (PALF) by compression molding using the film stacking method. The objective of this study was to determine the effects of surface treatment of PALF on the performance of the fiber-reinforced composites. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to aid in the analysis. The mechanical properties of the PLA laminated composites were improved significantly after chemical treatment. It was found that both silane- and alkali-treated fiber reinforced composites offered superior mechanical properties compared to untreated fiber reinforced composites. The effects of temperature on the viscoelastic properties of composites were studied by dynamic mechanical analysis (DMA). From the DMA results, incorporation of the PALF fibers resulted in a considerable increase of the storage modulus (stiffness) values. The heat defection temperature (HDT) of the PALF fiber reinforced PLA laminated composites was significantly higher than the HDT of the neat PLA resin. The differential scanning calorimeter (DSC) results suggest that surface treatment of PALF affects the crystallization properties of the PLA matrix. Additionally, scanning electron microscopy (SEM) was used to investigate the distribution of PLA within the fiber network. SEM photographs of fiber surface and fracture surfaces of composites clearly indicated the extent of fiber–matrix interface adhesion. It was found that the interfacial properties between the reinforcing PALF fibers and the surrounding matrix of the laminated composite are very important to the performance of the composite materials and PALF fibers are good candidates for the reinforcement fiber of high performance laminated biodegradable biocomposites.

Effect of fiber surface modification on the mechanical properties of sisal fiber‐reinforced benzoxazine/epoxy composites based on aliphatic diamine benzoxazine

AbstractSisal fibers were incorporated into a mixture of benzoxazine and bisphenol A type epoxy resins to form a unidirectionally reinforced composite. Surface modifications of the sisal fibers were carried out with sodium hydroxide, γ‐aminopropyltrimethoxysilane, and γ‐glycidoxypropyltrimethoxysilane. The surface treatments led to changes in the morphology, chemical groups, and hydrophilicity of the fibers. The effect of the fiber surface treatments on the fiber–matrix interfacial adhesion and mechanical properties of the composites were also studied. The results showed that surface treatments with sodium hydroxide and a silane coupling agent led to improved fiber–matrix adhesion; this could be seen in the scanning electron micrographs of the fractured surfaces from mechanical testing and the reduction in the impact strength of the composites made from treated fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Dynamic and steady state viscoelastic behavior and morphology of MAPP treated PP/sisal composites

The present paper summarizes an experimental study on the molten viscoelastic behavior of PP/sisal composites under steady and dynamic state. Variations in melt viscosity and die swell of the composites with an increase in shear rate, fibre loading and coupling agent concentration have been investigated using capillary rheometer. It was observed that with the addition of sisal fibers and MAPP, the melt viscosity of the composites increased due to improved fiber–matrix interfacial adhesion. Further the dynamic viscoelastic behavior measured, employing parallel plate rheometer revealed an increase in the storage modulus ( G′) indicating higher stiffness in case of fibre filled composites as compared with the virgin matrix. Time temperature superposition was applied to generate various viscoelastic master curves. The fiber–matrix morphology of the extrudates was also examined using scanning electron microscopy, which corroborated the findings of the rheological properties. The extrudate cross sections of the composites displayed uniform distribution of fibers within the PP matrix with lesser surface irregularities at high shear rates.

Single‐polymer composites based on slowly crystallizing polymers

AbstractAn approach of using slowly crystallizing polymers to form single‐polymer composites (SPCs) was investigated. The method was demonstrated using poly(ethylene terephthalate) (PET) as a model system, with which two distinct physical forms, namely, amorphous PET films and highly crystalline PET fibers can be readily obtained. Because of the large difference between the rubbery softening temperature of the amorphous phase and the melting temperature of the crystalline phase, the new process is characterized by its wide process window and enhanced manufacturability. The heating temperature and holding time were found to play a profound role in influencing the properties of the SPC. Excellent fiber–matrix interfacial adhesion was obtained at heating temperature 180°C and holding time 10 s. The results also indicated that the heating rate plays a significant role in affecting the fusion and adhesion of the composite. With reduced heating rates, the fusion and adhesion properties are rapidly deteriorated. POLYM. ENG. SCI., 46: 1223–1230, 2006. © 2006 Society of Plastics Engineers

Use of an epoxidized oil‐based resin as matrix in vegetable fibers‐reinforced composites

AbstractHemp fibers were used as natural reinforcement in composites of thermosetting vegetal oil based resin. Boards with fibers content from 0 to 65 vol % were produced by hot pressing. The mechanical properties were investigated with flexural testing. The effect of effect has been observed on both modulus and strength, indicating a good fiber–matrix interfacial adhesion, which was confirmed by means of scanning electron microscopy observations. Dynamic mechanical analysis also showed an important reinforcement effect in the polymer rubbery region, where at 180°C the storage modulus increased from 17 MPa for the neat resin to 850 MPa for 65 vol % fiber content composites. It also revealed an glass transition temperature decrease when fiber amount in the composite increased. Additional experiments based on differential scanning calorimetry show a weakly accelerated cure when fibers content increases, which usually lead to a lower Tg. But, this phenomenon alone cannot explain the observed Tg change. Contact angle on hemp evolution with time for the resin components show that anhydride is totally absorbed after a few seconds, whereas contact angle of epoxydized oil decreases slowly. This indicates probably a preferential anhydride absorption that leads to a lower amount of anhydride in the matrix and as a consequence to a reduced Tg. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4037–4043, 2006

Functionalization, compatibilization and properties of polypropylene composites with Hemp fibres

Composites of isotactic polypropylene (PP) with Hemp fibres ( Cannabis sativa), functionalized by means of melt grafting reactions with glycidyl methacrylate (GMA) and prepared by batch mixing, were examined. Either the modification of fibres (Hemp-GMA) and polyolefin matrix (PP- g-GMA), as well as the addition of various compatibilizers (PP- g-GMA, SEBS, SEBS- g-GMA) were carried out to improve the fibre–matrix interactions. The modified components and their composites were characterised by FT-IR analysis, POM and SEM microscopy, RX, DSC, TGA and mechanical tests. The properties of binary (PP/Hemp, PP/Hemp-GMA, PP- g-GMA/Hemp) and ternary (PP/Hemp/compatibilizer) composites were analysed as a function of the fibre amount and compatibilizer content. All modified composites showed improved fibre dispersion in the polyolefin matrix and higher interfacial adhesion when compared to the unmodified system (PP/Hemp) as a consequence of chemical bonding between fibre and polymer. The thermal stability and phase behaviour of the composites resulted to be largely affected by the fibre and matrix modification. Changes in the spherulitic morphology and crystallisation behaviour of PP were observed in the composites due to the nucleating effect of Hemp fibres. Moreover, a marked increase of PP isothermal crystallisation rate (in the range 120–138 °C) was recorded with increasing the Hemp-GMA content. All composites displayed higher tensile modulus (about 2.9 GPa) and lower elongation at break as compared to plain PP; compatibilization with PP- g-GMA (10 phr) resulted in an increased stiffness of the composites as consequence of an improved fibre–matrix interfacial adhesion.

Effect of filler‐to‐matrix blending ratio on the mechanical strength of palm‐based biocomposite boards

AbstractThe effect of the blending ratio of a polyurethane matrix and oil‐palm empty fruit bunch (EFB) fibers on the mechanical properties of biocomposite boards has been studied. The PU matrix and EFB fibers were used at blending ratios of 25:75, 30:70 and 35:65 (by weight). The mechanical property of hardness was studied. The intention of this study was to produce fiberboard from a vegetable oil‐based polyester as the matrix and biomass from the palm oil industry, namely EFB. It was found that the blending ratio with a lower filler loading (35:65) gave higher impact and flexural strengths due to better fiber encapsulation which enhanced the fiber–matrix interfacial adhesion. Copyright © 2005 Society of Chemical Industry

Evaluation of Initiation of the Interfacial Debonding in Single Fiber Composite (Energy Balance Method Considering an Energy Dissipation of the Plastic Deformation)

Fiber-matrix interfacial adhesion in composites is traditionally evaluated by means of a stress-based parameter. Recently, an interfacial energy parameter is suggested to be a valid alternative. However, the energy-based approaches overestimated the energy release rate to initiate the interfacial debonding (interfacial energy), since the plastic deformation in the vicinity of the debonding was neglected for simplicity. An effect of the plastic deformation on the interfacial energy of a fiber-reinforced polymer matrix composite is studied to evaluate the initiation of the interfacial debonding. The fragmentation tests with a model of glass fiber-reinforced vinylester matrix composite were performed, and the interfacial energy with the energy balance method taking into account an energy dissipation of the plastic deformation was calculated. The following results are confirmed; the plastic deformation has a significant influence on the interfacial energy, and the energy balance scheme taking into account the plastic energy dissipation leads to the constant interfacial energy without reference to the amount of the released potential energy. The differences between our model and the previous one are discussed.