Glass fiber-reinforced epoxy composites

Glass fiber-reinforced epoxy composites were prepared from the matrix resins tetraglycidyl diaminodiphenylmethane

1 Systematic name: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-4,4′-diaminodiphenylmethane.

(TGDDM) and tetraglycidyl bis(o-toluidino)-methane

2 Systematic name: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-4,4′-bis(o-toluidino)methane.

(TGMBT) using various amines like 4,4′-diaminodiphenylmethane (DDM), 4,4′-diaminodiphenylsulfone (DDS) and diethylene triamine (DETA) as curing agents. The fabricated laminates were evaluated for their mechanical and dielectrical properties and chemical resistance. The composites prepared using an epoxy fortifier (20 phr) showed significant improvement in the mechanical properties.     

Temperature effects on structural integrity of fiber-reinforced polymer matrix composites: A review

Fiber-reinforced polymer matrix composites (FRPMCs) are the most promising and valuable material developed in the last few decades. In response to the increased research and publications concerning the thermal stability of FRPMCs, this review has culled typical journals for publications relevant to structural stability. In this review, the effects of temperature on the structural integrity of FRPMCs are discussed from the perspective of matrix types, fiber types, nanoparticle (NP) modifications on resin matrix, and various related mechanical properties. For NP-modified FRPMCs, characterization of all anisotropic properties under various strain rates and temperatures becomes essential for analysis, design, and numerical simulations. Improving the structural stability of FRPMCs at different temperatures is an important direction. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48206.     

Interfacial adhesion study on UHMWPE fiber-reinforced composites

Ultrahigh molecular weight polyethylene (UHMWPE) fiber has many outstanding properties. However, poor interfacial adhesion of the UHMWPE fiber/polymer matrix interface limits its applications as reinforcement in high performance polymer matrix composites. Therefore, a new thermosetting resin system, named PCH, which is only composed of carbon and hydrogen elements, has been developed according to law of similar mutual solubility and the structural characteristics of UHMWPE fiber. The adhesion property was investigated by mechanical properties test, thermal performance test, and polymer solution properties test. Test results show that a strong interaction occurs between UHMWPE fiber and the PCH matrix due to the structural and polar similarity. In the case of slight difference between solubility parameters of UHMWPE fiber and cured PCH resin, it is found that the wettability of PCH resin on surface of the fiber can be improved and the difference between the coefficients of thermal expansion of the matrix and the fiber decreases with the increase of styrene added into the PCH. An optimal interfacial adhesion can be obtained as the ratio of PCH/styrene is approximately 55/45.     

Properties of UHMWPE fiber-reinforced composites

Based on our previous work, a new thermosetting resin system, named PCH, has been developed to be used as the matrix of ultrahigh-molecular-weight polyethylene (UHMWPE) fiber composites in order to get improved interface bond and mechanical properties. In this work, UHMWPE fiber/PCH composites with different ratios of PCH/styrene were prepared and the impact resistance, dynamic mechanical properties, and dielectric properties of UHMWPE fiber/PCH composites were investigated. The interlaminar shear failure characteristic of composites was analyzed by introducing a series of energy indexes indicating the energy absorbed in interlaminar shear failure process, which show good correlation with interlaminar shear strength of samples. UHMWPE fiber/PCH composites have excellent impact property, and the impact strength can reach 140.8 kJ/m² as the ratio of PCH/styrene is 60/40. Dynamic mechanical analysis showed that UHMWPE fiber/PCH composites have high storage moduli (E′) and low dissipation factor (tan δ) and these properties are influenced by the interfacial adhesion. The dielectric property test demonstrated that UHMWPE fiber/PCH composites have low dielectric constant (2.20 < ε′ < 2.55) and dielectric loss tangent (1.50 × 10^?3 < tan δ < 1.81 × 10^?2) and show good stability in a large range of frequency and temperature.     

Short fiber-reinforced oxide fiber composites

This paper presents a novel fiber spraying process for the manufacturing of short fiber bundle-reinforced Nextel™ 610/Al₂O₃-ZrO₂ oxide fiber composites (SF-OFC) and its characterization. First, the influence of varying fiber lengths (7, 14, and 28 mm, continuous fibers) and fiber orientations (unidirectional 0°, quasi-isotropic, ±45°) was investigated using hand-laid SF-OFC. Due to the weak matrix, the hand-laid material exhibited a strongly fiber-dominated material behavior, that is, variations in fiber length and orientation had a strong influence on the material properties. Second, the automated sprayed SF-OFC, however, exhibited a random orientation of the fiber bundles, which resulted in in-plane isotropic material properties. Average bending strengths of up to 177 MPa, strains of .39%, and a quasi-ductile fracture behavior were achieved. The strain was, therefore, in the range of fabric-reinforced OFC. While the bending strength of the SF-OFC was somewhat lower than that of fabric-reinforced OFC with the fiber orientation parallel to the loading direction, it was more than two times higher than the strength in 45° direction relative to the fabric reinforcement. Combined with good drapability and lower material costs compared to fabric-reinforced OFC, SF-OFC is, therefore, a promising material for industrial applications.     

Weathering of fiber-reinforced epoxy composites

Unless suitably stabilized and coated, fiber-reinforced composites are subject to photoinitiated oxidation which results in a degradation of the resin surface and an eventual reduction in the composite's mechanical properties. The photo-oxidation, which is initiated by UV-absorbing oxidation products created during cure, is relatively amenable to detection by techniques of analytical chemistry. Mechanical test results, which reflect a wide range of material properties, are more subject to variability and misinterpretation.     

Acid-base interfaces in fiber-reinforced polymer composites

The role of Lewis acid-base interactions at the fiber-matrix interface in composites is studied with both glass and Teflon fibers. In the glass fiber case, surface chemistry is modified with amino-, methacryloxy- and glycidoxy-silane coupling agents (A-1100, A-174 and A-187, respectively). Silane adsorption mechanisms as well as the properties of filament-wound, unidirectional epoxy and polyester composites are explained by a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and flow microcalorimetry. The heats of adsorption of pyridine and phenol prove that the coupling agents add acidic sites to the glass fiber surface as well as stronger basic sites. The subsequent adhesion of the matrix polymers and the short beam shear strengths of composites are explained on this basis. The Teflon fibers are first etched with sodium naphthalene solutions, and then sequentially hydroborated and acetylated, producing approximately monofunctional hydroxyl (acidic) and ester (basic) groups on the surfaces, as determined by XPS, FTIR, and electrophoretic mobility analyses. Composites prepared with the acetylated fibers and a chlorinated polyvinyl chloride (acidic) matrix are superior in tensile properties, and SEM fractography shows PTFE fibrillation, indicative of good fiber-matrix adhesion and stress transfer, in this case only.     

Short silk fiber-reinforced polychloroprene rubber composites

The reinforcement of polychloroprene rubber by short silk fiber has been studied in the presence of three different dry bonding systems, viz.: (a) “cohedur RK–cohedur A–silica”; (b) “cohedur RK–cohedur A–carbon black”; (c) “resorcinol–hexamethylenetetramine–silica.” The degree of fiber–rubber adhesion of the different bonding systems follows the order (a) > (b) > (c). Scanning electron microscopy studies of tensile, tear, abrasion, and flex failed surfaces of both unfilled and fiber–filled composites containing “cohedur–silica” bonding system have also been made in order to gain an insight to the mechanism of failure.     

Thermal and dynamic mechanical investigations on fiber-reinforced polypropylene composites

The thermal behavior and dynamic mechanical properties of isotactic polypropylene (PP) and reactor blend PP/ethylene-propylene copolymer (EPM), reinforced with different amounts of short glass fibers (GF) and/or polyester fibers (PETF), were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermoanalysis (DMTA) of imposed tensile load on rectangular film specimens. DSC measurements exhibited an increase of the crystallization temperature of PP in the presence of fibers, but indicated no change in its percentage of crystallinity. DMTA spectra revealed an increase in the stiffness and a decrease of the damping with increasing GF content. The positions of the primary relaxations of PP and EPM did not change, but a significant broadening of the α-relaxation in the crystalline phase was observed, due to the induced reinforcement and interfacial interactions. The addition of PETF to PP enhanced its damping values at low temperatures and promoted the α-transition. The DMTA behavior was studied in dependence on the preconditioning and the frequency excitation. Heat treatment changed the characteristics of the β-relaxation of PP, due to enhanced molecular motion of the polymer segments. The variation of frequency affected the secondary relaxations considerably and, in the presence of GF, the glass transitions. For the different relaxations, activation energies from peak shift and loss peak areas were determined. Experimental data of loss peaks were fitted to phenomenological equations. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1143–1154, 1997     

A dynamic mechanical study on unidirectional carbon fiber-reinforced polypropylene composites

Fiber-reinforced polymer composites show high specific strength and stiffness. The alignment of reinforcing fibers results in anisotropy of the material. This anisotropic behavior has been studied through dynamic mechanical analysis of unidirectional carbon fiber-reinforced polypropylene (CFRPP) composites measured in both parallel and transverse directions to fiber arrangement. Several parameters such as storage modulus (E′), loss modulus (E″), loss factor or damping factor (tan δ), and complex viscosity (MU^*) have been determined over a wide range of frequencies and at a fixed temperature. Relaxation and retardation spectra have been constructed for these composites. Modulus enhancement occurs due to stiffness imparted by the fiber and efficient stress transfer at the interface. Relaxation of the polymer matrix ceases with increase in the volume fraction of the fibers. α′-relaxation is observed for the composite having a 13% volume fraction of fibers and is ascribed to relaxation in the crystalline phase where the additional crystallinity arises out of the transcrystalline growth at the fiber–matrix interface. There exists a good correlation between theroretical curves with the experimental ones. Relaxation and retardation spectra and the dynamic parameters determined for these composites show a good correlation with the volume fraction of fibers as well as the direction of the applied load. © 1994 John Wiley & Sons, Inc.     

Computer simulation of crystallization kinetics in fiber-reinforced composites

A computer simulation model was developed to investigate spherulitic growth in polymers of infinite and plate-limited volume as well as in fibre-reinforced polymer composite systems. Parameters like thermal nucleation rate and athermal nucleation density, plate distance, and fibre content were varied. The simulation crystallization process was evaluated following Avrami's method in the case of infinite volume and by stepwise approximation by Avrami functions in the case of limited volume. In addition, the simulation method allows the visualization of the growing entities at any phase of crystallization. Therefore the geometry of growing entities can be easily compared with the corresponding crystallization exponent. A good agreement between the crystallization exponent and the growth geometry was found. Depending on nucleation mode, “infinite” systems yield Avrami exponents of 3 and 4. In plate-limited volume, a transcrystallization effect was observed in case of high athermal nucleation density on plate surface and large plate distances. This particular skin effect decreases the three-dimensional growth to a one-dimensional needle-shaped one. Small plate distance changes the spherical to a disk-like growth, resulting in crystallization exponents of 2 or 3, depending on nucleation mode. The crystallization behaviour of fibrereinforced composite systems is more complex. Low fibre content or large fibre distance and high athermal nucleation density on the fibre surface induce the formation of transcrystalline zones. The three-dimensional growth of the spheres at the beginning is restricted by their neighbours, so that their geometry changes to a pyramidical one. They grow with a front normal to the fibre surface and the crystallization exponent is shifted in between 2.0 and 2.6 depending on nucleation density. High fibre content leads to a growth along the triangular channels between three adjacent fibres; the corresponding exponent amounts to 1.6. © 1994 John Wiley & Sons, Inc.     

Mechanical properties of pineapple leaf fiber-reinforced polyester composites

Pineapple leaf fiber (PALF) which is rich in cellulose, relatively inexpensive, and abundantly available has the potential for polymer reinforcement. The present study investigated the tensile, flexural, and impact behavior of PALF-reinforced polyester composites as a function of fiber loading, fiber length, and fiber surface modification. The tensile strength and Young's modulus of the composites were found to increase with fiber content in accordance with the rule of mixtures. The elongation at break of the composites exhibits an increase by the introduction of fiber. The mechanical properties are optimum at a fiber length of 30 mm. The flexural stiffness and flexural strength of the composites with a 30% fiber weight fraction are 2.76 GPa and 80.2 MPa, respectively. The specific flexural stiffness of the composite is about 2.3 times greater than that of neat polyester resin. The work of fracture (impact strength) of the composite with 30% fiber content was found to be 24 kJ m⁻². Significant improvement in the tensile strength was observed for composites with silane A172-treated fibers. Scanning electron microscopic studies were carried out to understand the fiber-matrix adhesion, fiber breakage, and failure topography. The PALF polyester composites possess superior mechanical properties compared to other cellulose-based natural fiber composites. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1739–1748, 1997     

Tensile properties of short sisal fiber-reinforced polyethylene composites

Sisal fibers (Agave-Veracruz) have been used as reinforcements in low-density polyethylene (LDPE). The influence of the processing method and the effect of fiber content, fiber length, and orientation on tensile properties of the composites have been evaluated. The fiber damage that normally occurs during blending of fiber and polyethylene by the meltmixing method is avoided by adopting a solution-mixing procedure. The tensile properties of the composites thus prepared show a gradual increase with fiber content. The properties also increased with fiber length, to a maximum at a fiber length of about 6 mm. Unidirectional alignment of the short fibers achieved by an extrusion process enhanced the tensile strength and modulus of the composites along the axis of fiber alignment by more than twofold compared to randomly oriented fiber composites. © 1993 John Wiley & Sons, Inc.     

Biologically degradable fiber-reinforced urethane composites from wheat straw

Urethane type adhesive mixtures containing poly(MDI) were used to prepare biodegradable urethane type composites containing wheat stalks. According to the mechanical properties, i.e., tensile strength, bending strength, and hardness of the composites, the ratio of wheat stalks to sticking mixtures, the technological pressure used, and the size of the wheat stalks were optimized. The mechanism of the possible chemical reaction is also discussed.     

Mechanical properties of ultrahigh-molecular-weight polyethylene fiber-reinforced PE composites

Three types of high-strength polyethylene (PE) fiber-reinforced composite sheets were made by compression molding at the vicinity of melting point of the fiber. Sheet I was molded from only PE fibers. Sheets II and III were prepared by the compression molding of PE fiber with conventional high- and low-density polyethylene films, respectively. The mechanical properties, thermal behavior, and morphologies of the sheets have been investigated and compared with each other. The tensile strength and elastic modulus of sheet III are 660 MPa and 14 GPa, respectively, which were 60 and 30 times higher than those of typical low-density PE film. Although the elastic modulus of sheet III is 6 GPa less than that of sheet II, the tensile strength of 660 MPa is highest in the three types of sheets prepared in this study. The mechanical properties of sheets II and III were about half of predicted theoretical ones. It was concluded that the interfacial adhesion between PE fiber and PE matrix was an important factor to improve the mechanical properties of this PE sheet. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1431–1439, 1998     

Friction and wear behavior of graphite fiber-reinforced composites

Friction and wear behavior of continuous graphite fiber composites was studied for different fiber orientations against the sliding direction. The effect of fiber orientation on friction and wear of the composite and on deformation of the counterface was investigated experimentally. A pin on disk type testing machine was built and employed to generate friction and wear data. A graphite fiber composite plate was produced by the bleeder ply molding in an autoclave and machined into rectangular pin specimens with specific fiber orientations, i.e., normal, transverse, and longitudinal directions. Three different wear conditions were employed for two different periods of time, 24 and 48 hours. The wear track of the worn specimens and the metal counterface was examined and a scanning electron microscope (SEM) to observe the damaged fibers on the sliding surface of the specimen and wear film generation on the counterface. A wear mechanism of the continuous graphite fiber composite during sliding wear is proposed based on the experimental results.     

Carbon fiber-reinforced composites: Effect of fiber surface on polymer properties

Dynamic mechanical measurements in a torsional (shear) mode have been used to characterize an unfilled epoxy (Epon 828/m-phenylene diamine) and A series of uniaxial graphite fiber (Hercules types A and HM) composites. In unfilled resins containing an excess of the epoxy component, M_c—the average molecular weight between crosslinks—decreases with increasing temperature and duration of cure, suggesting a temperature-dependent side reaction. In fiber-reinforced composites, the dynamic mechanical response is sensitive to fiber type and curing schedule; elevation of T_g by as much as 45°C has been observed. Comparison of the dynamic data with properties predicted by micromechanical models shows only a fair agreement at room temperature, which rapidly worsens at higher temperatures. Surface treatment of type A fibers gives enhanced interlaminar shear strength (ILSS), both at ambient conditions and after hydrothermal aging. Dynamic data for surface-treated systems during hydrothermal aging show a sharper drop in G′ and increase in tan δ. The dynamic data and ILSS results are interpreted in terms of a balance of polymer-fiber interactions, a weak but widespread preferential adsorption of epoxy oligomers on the graphite basal planes at the fiber surface, and a low concentration of covalent bonds between polymer and fiber-surface-functional groups.     

Effect of particulate fillers on short jute fiber-reinforced natural rubber composites

The effect of carbon black on the processing characteristics and physical properties of jute fiber-reinforced composites and the role of silica and carbon black in promoting the adhesion between jute fiber and natural rubber have been studied. It was found that presence of silica is not essential to develop adhesion between fiber and rubber in the presence of carbon black. However, silica and carbon black can improve adhesion by minimizing the resin formation and controlling it to a low molecular weight species. Processing properties like green strength and mill shrinkage are improved by the addition of fiber. Carbon black does not affect mill shrinkage, but improves the green strength. Breakage of jute fiber during mixing is severe, but the extent of breakage is not affected by the presence of carbon black. The minimum loading of fiber to achieve reinforcement is reduced in the presence of carbon black. It was also found that the presence of clay in jute fiber rubber composites impairs the properties. Scanning electron microscopy (SEM) has been used to assess the failure criteria.     

Bamboo fiber-reinforced polypropylene composites: Crystallization and interfacial morphology

Bamboo fiber-reinforced polypropylene (PP) composites were prepared. PP and two maleated polypropylenes (s-MAPP and m-MAPP) were used as matrices. Crystallization and interfacial morphology were studied by using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and optical microscopy. It has been shown that the addition of bamboo fiber to any of the three polymers causes an increase in the overall crystallization rate. A considerable amount of β-form crystallinity was produced in the PP, s-MAPP, and m-MAPP by mixing with bamboo fiber; and all the bamboo fiber-filled samples contain both the α- and the β-forms. The relative amount of the β-form in the samples was calculated from WAXD data by the K value. There is no β-form observed in the pure PP, s-MAPP, and m-MAPP. Bamboo fiber acted as both a reinforcement and a β-nucleator. The nucleation density of both s-MAPP and m-MAPP at the fiber surface is remarkably higher than that of PP because an improved interfacial adhesion is reached in the case of s-MAPP and m-MAPP as matrices. The transcrystalline growth of s-MAPP and m-MAPP on the bamboo fiber surface was observed under optical microscope with crossed polars. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1267–1273, 1997     

Off-axis damage tolerance of fiber-reinforced composites for aerospace systems

Off-axis strength retention of continuous carbon fiber-reinforced dense ZrB₂-based ceramics (C_f/ZrB₂) after thermal or indentation damage was evaluated. Thermal damage was in-situ induced and characterized by cyclic dilatometric analysis. Indentation damage was induced through Vickers indentation and then characterized by digital microscopy. The investigation of Vickers imprints suggested that residual stresses promoted the material pileup onto the fibers’ plane and the appearance of out-of-plane freed fibers (OFF). On the other hand, thermal damage reduced the residual stresses and left inner freed fibers (IFF) that enhanced the elastic response. Finally, the flexural tests on damaged specimens unexpectedly revealed that C_f/ZrB₂ kept its load bearing capability either after thermal or indentation damage (in both cases) and showed damage insensitivity although tested in fully matrix-dominated loading configuration (off-axis configuration).