Investigation of Physico-Chemical Properties of Alkali-Treated Prosopis juliflora Fibers

There is ever-increasing interest in using natural fibers in polymer composite systems and textile industry. Prosopis juliflora fibers (PJFs) possess ideal characteristics that make them suitable for various applications. Alkali treatment of PJFs was primarily aimed to change their physico-chemical properties; 5% (w/v) NaOH concentration and 60 min of soaking time were found to be optimal. It is intriguing to note that optimally treated PJFs had higher cellulose (72.27 wt.%), lower hemicellulose (4.02 wt.%) and lignin (12.09 wt.%) contents, higher crystallinity index (73%), tensile strength, and thermal stability.     

Effect of fiber surface treatments on the essential work of fracture of HDPE-continuous henequen fiber-reinforced composites

Lignocellulosic fibers, such as henequen, sisal, coconut fiber (coir), jute, palm and bamboo, have been used as reinforcement materials for different thermosetting and thermoplastic resins because of their attractive physical and mechanical properties. Unlike the traditional engineering fibers, e.g. glass and carbon fibers, and mineral fillers, these lignocellulosic fibers are able to impart certain benefits such as low density, less machine wear, no health hazards, and a high degree of flexibility to the composite. The last attribute is especially true because these lignocellulosic fibers will bend rather than fracture, like glass fibers do, during processing of the composite. The mechanical properties and fracture behavior of a natural fiber reinforced polymer composite depend, not only on the properties of constituents, but also on the properties of the region surrounding the fiber, known as the interphase, where the stress transfer takes place. Moreover, the tailoring of the interphase by means of surface treatments, and carefully characterizing it, gives a better understanding of the performance of natural-fiber reinforced composites. The fracture toughness resulting from the use of natural fibers as reinforcing materials is quite different between ductile and brittle polymers, as well as between quasi-static and impact loading rates. The aim of this paper is to study the effect of the interphase properties, resulting from well controlled surface treatment of the natural fibers, on the behavior of a ductile polymer matrix composite under quasi-static loading using the essential work of fracture criteria. Specifically, the contribution of each of the different fiber-matrix interfacial adhesion levels towards the dissipation energy were analyzed and discussed. In the case of the plastic work βw_p, there seems to be a synergy between the frictional and chemical interactions observed for both, low and high strain rates. The nonlinear mechanical behavior of the natural fiber under combined tensile-shear loads has also an effect on the fracture behavior of the composite. Additionally, different fiber surface treatments change the microstructural nature of the natural fiber, further affecting its behavior, particularly under high loading rates.     

Effect of Chemical Treatment and Fiber Loading on Mechanical Properties of Borassus (Toddy Palm) Fiber/Epoxy Composites

The aim of the present study was to investigate and compare the mechanical properties of untreated and chemically modified Borassus fiber–reinforced epoxy composites. Composites were prepared by the hand lay-up process by reinforcing Borassus fibers with epoxy matrix. To improve the fiber-matrix adhesion properties, alkali (NaOH) and alkali combined with silane (3-aminopropyltriethoxysilane) treatment of the fiber surface was carried out. Examinations through Fourier transform-infrared spectroscopy and scanning electron microscopy (SEM) were conducted to investigate the structural and physical properties of the Borassus fibers. Tensile properties such as modulus and strength of the composites made with chemically modified and untreated Borassus fibers were studied using a universal testing machine. Based on the experimental results, it was found that the tensile properties of the Borassus-reinforced epoxy composites were significantly improved as compared with the neat epoxy. It was also found that the fiber treated with a combination of alkali and silane exhibited superior mechanical properties to alkali-treated and untreated fiber composites. The nature of the fiber/matrix interface was examined through SEM of cryo-fractured samples. Chemical resistance of composites was also found to be improved with chemically modified fiber composites.     

Interfacial studies on the ozone and air‐oxidation‐modified carbon fiber reinforced PEEK composites

In this work, ozone modification method and air‐oxidationwere used for the surface treatment of polyacrylonitrile(PAN)‐based carbon fiber. The surface characteristics of carbon fibers were characterized by XPS. The interfacial properties of carbon fiber‐reinforced (polyetheretherketone) PEEK (CF/PEEK) composites were investigated by means of the single fiber pull‐out tests. As a result, it was found that IFSS (interfacial shear strength) values of the composites with ozone‐treated carbon fiber are increased by 60% compared to that without treatment. XPS results show that ozone treatment increases the amount of carboxyl groups on carbon fiber surface, thus the interfacial adhesion between carbon fiber and PEEK matrix is effectively promoted. The effect of surface treatment of carbon fibers on the tribological properties of CF/PEEKcomposites was comparativelyinvestigated. Experimental results revealed that surface treatment can effectively improve the interfacial adhesion between carbon fiber and PEEK matrix. Thus the wear resistance was significantly improved. Copyright © 2009 John Wiley & Sons, Ltd.     

The interfacial feature of thermoplastic polystyrene composite filled with nitric acid oxidized carbon fiber

The quality of interfacial interaction is dictated by the surface chemistry of the carbon fibers and the composition of the matrix. The composition of polystyrene was modified by the addition of maleic anhydride (MAH) grafted polystyrene. The surface properties of the various matrix formulations were characterized by contact angle. Carbon fibers were modified by oxidation in nitric acid. The surface composition of the carbon fibers was characterized. The interaction between modified polystyrene and the carbon fibers was studied by single fiber pull‐out tests. The best adhesion behavior was achieved between polystyrene containing grafted MAH and nitric acid oxidation carbon fibers. The addition of MAH‐grafted polystyrene to the unmodified polystyrene caused the interfacial shear strength (IFSS) to increase. The IFSS of this fiber‐matrix combination allowed for the full utilization of the tensile strength of polystyrene. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of surface treatment with potassium permanganate on ultra-high molecular weight polyethylene fiber reinforced natural rubber composites

The effects of surface treatment using potassium permanganate on ultra-high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were investigated. The results showed the surface roughness and the oxygen-containing groups on the surface of the modified fibers were effectively increased. The NR matrix composites were prepared with as-received and modified UHMWPE fibers added 0–6 wt%. The treated fibers increased the modulus and tensile stress at a given elongation. The tear strength increased with increasing fiber mass fraction, attained maximum values at 4 wt%. The hardness of composites exhibited continuous increase with increasing the fiber content. The dynamic mechanical tests showed that the storage modulus and the tangent of the loss angle were decreased in the modified UHMWPE fibers/NR composites. Several micro-fibrillations between the treated fiber and NR matrix were observed, which meant the interfacial adhesion strength was improved.     

Thermal,Mechanical and Morphological Properties of Composites Developed from Glycerol and Dicarboxylic Acids Reinforced with Piassava Fiber

Summary: Vegetable fibers are being widely used as reinforcement in polymer composites. These composites can be applied in several fields, such as automotive, packaging and even construction. The polymer matrix used was synthesized from glycerol with phthalic and terephthalic acids in order to open future perspectives in the use of glycerin generated from the production of purified biodiesel. Composites with 2, 5, 10 wt% untreated and treated piassava fiber were obtained. Thermal, morphological and mechanical properties were evaluated. The tensile stress-strain curve of the polyester synthesized and composites was typical of a ductile material. SEM of the surface of fracture showed that the adhesion between fiber and matrix was enhanced after chemical treatment. However, the fiber content was more efficient than the superficial treatment when incorporated into the matrix. Therefore, the material under study is promising for the industrial marketplace, due to its good compatibility with natural fibers.     

Short Twaron aramid fiber reinforced thermoplastic polyurethane

Mechanical, dynamic mechanical, and rheological behaviors of a short p‐aramid fiber reinforced thermoplastic polyurethane (TPU) have been studied in the range of 0–30 wt% of fibers. The tensile strength of the composite is improved slightly at higher fiber content with a minimum at around 10 wt% of fibers. The addition of fibers markedly reduces elongation at break and entails a steady increase in the elastic modulus, but decreases the wear resistance of the matrix. Storage modulus (E′) is increased and the shapes of loss tangent (tan δ) peaks point to a possible fiber–matrix interaction. Rheological studies show a power law behavior for all composites and increased viscosity with fiber loading. Study of the tensile and cryogenic fracture surfaces by scanning electron microscopy (SEM) indicates good correlation between the modes of failure and strength of the composites. The micrographs reveal good interfacial adhesion and extensive peeling and fibrillation of the fibers in the compounded and fractured composites. Theoretical models have been used to fit the experimental modulus data. Copyright © 2008 John Wiley & Sons, Ltd.     

Flexural properties of fiber‐reinforced polypropylene composites with and without a transcrystalline layer

The flexural properties of isotactic polypropylene (PP) matrix composites reinforced with 5–30 vol% of unidirectional pitch‐based carbon, polyacrylonitrile (PAN)‐based carbon, e‐glass or aramid fibers were measured using both static and dynamic test methods. Previous research has shown that these pitch‐based carbon and aramid fibers are capable of densely nucleating PP crystals at the fiber surface, leading to the growth of an oriented interphase termed a “transcrystalline layer” (TCL), while the e‐glass and PAN‐based carbon fibers show no nucleating ability. The PP matrices examined included unmodified homopolymers, nucleated homopolymers and PP grafted with maleic anhydride (MA). The composites based on the unmodified PP homopolymers all exhibited poor fiber/matrix adhesion, regardless of fiber type and presence or absence of a TCL. The addition of nucleating agent to the PP matrix had no measurable effect on either the amount of TCL material in pitch‐based carbon‐fiber‐reinforced composites, as measured by wide‐angle X‐ray scattering, WAXS, or the static flexural properties of the composites reinforced with either type of carbon fiber. However, MA grafting reduced the transcrystalline fraction of the matrix in pitch‐based carbon‐fiber‐reinforced composites; at the highest level of MA grafting, the TCL was completely suppressed. In addition, high levels of MA grafting improved the transverse flexural modulus of the composites containing both types of carbon fibers, and reduced the extent of fiber pull‐out, indicating an improvement in fiber/matrix adhesion. Copyright © 1999 John Wiley & Sons, Ltd.     

In situ polymerization and characterization of graphene oxide‐co‐poly(phenylene benzobisoxazole) copolymer fibers derived from composite inner salts

A facile and efficient strategy for preparing well dispersed graphene oxide (GO)‐co‐Poly(phenylene benzobisoxazole) (PBO) copolymer fibers was carried out by direct in situ polycondensation of composite inner salts. The composite inner salts were achieved to improve the dispersivity, solubility, reactivity, and interfacial adhesion of GO in PBO polymer matrix. The structure and morphology of GO‐co‐PBO copolymer fibers have been characterized. It was demonstrated that GO were covalently incorporated with PBO molecular chains and dispersed considerably well in PBO fiber even the GO reach to 3 wt %. Meanwhile, the tensile modulus, tensile strength and thermal stability of GO‐co‐PBO copolymer fibers increased considerably with GO. The mechanism and theoretical calculation of GO enhanced PBO fiber were also discussed. The main reasons for the improvement on performance of PBO fiber should be attributed to good dispersion GO in PBO matrix and covalent bonding networks at the interface between GO and PBO molecular chains. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Cornstarch/Poly(vinyl alcohol) Biocomposite Blend Films: Mechanical Properties,Thermal Behavior,Fire Retardancy,and Antibacterial Activity

In the present study, biocomposite films of starch/poly(vinyl alcohol) (St/PVA) reinforced with delignified Grewia optiva fiber and methyl methacrylate (MMA) grafted fibers were prepared using citric acid as a plasticizer and glutaraldehyde as the cross-linker. The biocomposite films were subjected to evaluation of mechanical properties, biodegradability, and antibacterial properties. The biocomposite films were characterized by using Fourier transform-infrared (FT-IR) spectrophotometry, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA/DTA/DTG). SEM showed good adhesion between St/PVA blend matrix and fibers. The antimicrobial activity of biocomposite films against pathogenic bacteria such as Staphylococcus aureus and Escherichia coli was also explored. The results confirmed that the biocomposite films may be used for food packaging.     

New strategy to reinforce and toughen composites via introducing thorns-like micro/nanofibers

In this work, we report a new strategy of introducing thorns-like fiber into composites, so that the resultant composites substantially benefit from strong fiber–matrix interface adhesion. Specifically, the “thorns” could increase in interlocking molecules chains and entangle with the surrounding matrix resin, which could impede the mobility of polymer chains, as like the roots with uplift capacity. Strong interfacial adhesion between fibers and matrices is suggested by the SEM images and the DMA studies. After the thorns-like fibers are embedded into epoxy resin, the glass transition temperature (T_g) and the storage modulus (E′) are higher than these of neat epoxy and untreated fibers-reinforced epoxy, respectively, and the flexural properties of the composites reinforced with thorns-like fibers are significantly increased. Therefore these novel three dimensional thorns-like fibers will be applicable for composite materials based upon its unique architecture, making it an attractive alternative to increase the performance of any matrix resin.     

Continuous cellulose fiber-reinforced cellulose ester composites. I. Manufacturing options

Thermoplastic fiber composites were prepared using high modulus lyocell (regenerated cellulose) fibers for reinforcement and cellulose acetate butyrate (CAB) as matrix. Choices were made with regard to fiber options (fabric versus continuous tow) and method of matrix deposition (prepregging by powder coating, film stacking, or solution impregnating). The results suggest that solution-prepregged fiber tow consolidated at circa 200°C produced unidirectional consolidated panels with tensile strength, modulus, and strain at failure values of approximately 250MPa,>20GPa and 3–4%, respectively, at fiber volume contents of approximately 60%. Modulus and ultimate tensile strength increased with fiber content, and modulus followed rule-of-mixture behavior. Adequate surface wetting and matrix-fiber adhesion were found with solution-prepregged composites. The unexpectedly low strain at failure (2 to <4%) was attributed to brittle matrix failure, and failure surfaces revealed that the fibers, for the most part, remained intact after the matrix had failed.     

Kinetics of water sorption in flax and PET fibers

Composite materials are usually reinforced by synthetic fibers as carbon, glass etc…. Because of their good mechanical properties and low density, natural fibers are being considered more preferentially as reinforcement. The application of natural fibers as reinforcements in composite materials requires a strong adhesion between the fiber and the matrix. The poor resistance towards water absorption is one of the drawbacks of natural fibers which makes it more important to understand the dynamic properties of penetration of water molecules through these heterogeneous materials. Water vapour sorption kinetics in natural flax fibers have been performed at 25 °C by using an electronic microbalance (IGA, Hiden). By using the Fickian model for a complete cylinder water diffusion coefficients have been determined and calculated at short times (first half-sorption) and long times (second half-sorption) of kinetic curve and for different water activities. The values obtained for D₁ and D₂ are rather similar on the all range of water activity. Generally, water diffusivity increases and then decreases with water activity. The increase of diffusivity at low water activities may be explained on the basis of the dual mode sorption (Langmuir and Henry sorption’s combination) whereas the decrease for the higher activities can be attributed to the immobilization of sorbed water molecules due to the water clustering.     

Acid treatment for functionalizing polyethylene fiber surfaces for enhanced adhesion to epoxy resins

The utility of high-strength, high-modulus polyethylene fibers in fiber-reinforced composites is limited due to its poor interfacial adhesion to various polymeric matrices. One way to overcome this limitation is to introduce reactive functionalities on the fiber surface capable of covalently bonding to matrix resins. Ultra high-strength polyethylene (UHSPE) fibers were treated with chlorosulfonic acid. The surface acid groups were found to considerably improve the interfacial adhesion between polyethylene fibers and epoxy resins as shown by the microbond test. These surface functionalities were found to improve the fiber wettability, as shown by contact angle measurements using the Wilhelmy balance method. Colorimetric measurements of methylene blue absorption were used to quantify the surface concentrations of the acid groups. It was possible to functionalize the UHSPE fiber surfaces using this method to obtain fibers that formed a stronger adhesive bond with epoxy resins; this was achievable without sacrificing other fiber mechanical properties.     

Preparation of starch-based biocomposites reinforced with mercerized lignocellulosic fibers: Evaluation of their thermal,morphological, mechanical,and biodegradable properties

In the present paper, starch-based biocomposites have been prepared by reinforcing corn starch matrix with mercerized Abelmoschus esculentus lignocellulosic fibers. The effect of fiber content on mechanical properties of composite was investigated and found that tensile strength, compressive strength, and flexural strength at optimum fiber content were 69.1%, 93.7% and 105.1% increased to that of cross-linked corn starch matrix, respectively. The corn starch matrix and its composites were characterized by Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric (TGA) analysis. The fiber reinforced composites were found to be highly thermal stable as compared to natural corn starch and cross-linked corn starch matrix. Further, water uptake and biodegradation studies of matrix and composites have also been studied.     

Adhesion efficiency between phases in fibre-reinforced polymers by means of the concept of boundary interphase

Summary The role of the boundary interphase on the adhesion efficiency between fiber and matrix in the case of polymers reinforced with unidirectional fibers was investigated. A theoretical model was introduced considering that the composite material consists of three phases; that is, the fiber, the matrix and the interphase, material which is the part of the polymer matrix lying at the close vicinity of the fiber surface. The interphase material, having different physical properties from those of the bulk matrix, affects the overall behavior of the composite. Moreover, the quality of adhesion between the two main phases depends greatly on the nature of the interphase material. In this study we have considered that the interphase material is inhomogeneous in nature, with properties varying continuously from the fiber surface to the bulk matrix. The theory developed resulted in a criterion of the adhesion quality and in a prediction of the longitudinal modulus of elasticity of the fiber-composite.With 4 figures and 1 table     

The oxidation‐treated interface on tribological properties of carbon fibers‐reinforced PTFE composite under oil‐lubricated condition

The effect of air oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil‐lubricated condition was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF–PTFE) composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air‐oxidated composites. X‐ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen‐containing groups on CF surfaces was largely increased. The increase in the amount of oxygen‐containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with PTFE matrix and large scale rubbing‐off of PTFE was prevented, therefore, the tribological properties of the composite were improved. Copyright © 2009 John Wiley & Sons, Ltd.     

提高PBO纤维/环氧树脂复合材料界面结合的研究

本文采用表面化学蚀刻与溶胀法结合、化学偶联法与氩气低温等离子体表面处理技术结合的方法对聚苯撑苯并二。唑（PBO）纤维进行表面改性。探讨了不同改性方法对纤维表面性能的影响。同时，采用FTIR和SEM等方法对处理前后纤维表面化学结构及形态进行了表征。     

Radiation-induced grafted UHMW–PE chopped fibers as reinforcing filler in polychloroprene

Ultrahigh molecular weight polyethylene (UHMW-PE) has been grafted with acrylonitrile using gamma radiation. The graft yield of the monomer was controlled by the proper choice of radiation dose and monomer concentration. The grafted chopped fibers were introduced in polychloroprene (CR) rubber mixes in order to improve the interfacial adhesion between fibers and matrix. It has been found that the improvement in the mechanical properties of rubber composites obtained depended markedly on the fiber concentration in the rubber mixture. Scanning electron micrographs showed the presence of a continuous phase of rubber adhered to the surface of grafted fiber. © 1997 John Wiley & Sons, Ltd.