Recycled carbon fiber reinforced poly(butylene terephthalate) thermoplastic composites: fabrication,crystallization behaviors and performance evaluation

The thermoplastic composites based on poly(butylene terephthalate) (PBT) and recycled carbon fiber (RCF) were prepared through simple melt compounding by a twin‐screw extruder. An effective approach was utilized to clean and treat the RCF surface with a concentrated solution of nitric acid and then a solution of diglycidyl ether of bisphenol A as macromolecular coupling agent so as to improve the interfacial adhesion between the RCF and PBT matrix. As a result, the reinforcing potential of the RCF was enhanced substantially, and the mechanical properties, heat distortion temperature, and thermal stability of PBT could be significantly improved by incorporating this surface‐treated RCF. The morphologies of fracture surfaces indicated that the RCF achieved a homogeneous dispersion in the PBT matrix due to a good interfacial interaction between fiber and PBT. The investigations on the crystallization behaviors and kinetics demonstrated that the RCF acted as a nucleation agent for the crystallization of PBT, and the crystallization rate and nucleation density of PBT were increased remarkably due to the heterogeneous nucleating effect of RCF in the matrix. These features may be advantageous for the enhancement of mechanical properties, heat resistance, and processability of PBT‐based composites. This study may provide a design guide for carbon fiber‐reinforced PBT composites with a great potential as well as a low cost for industrial and civil applications. Copyright © 2012 John Wiley & Sons, Ltd.     

The dynamic mechanical behavior of random-in-plane short fiber-reinforced epoxy resin composites

In the present paper, the dynamic mechanical properties of random-in-plane short fiber-reinforced epoxy resin composites were studied by using a rheometrics solids analyzer. The three-point bend testing of the four composites (glass fiber/913 epoxy resin, glass fiber/924 epoxy resin, carbon fiber/913 epoxy resin and carbon fiber/924 epoxy resin) was carried out over temperatures from −100°C to 200°C at a frequency of 10 Hz and strain 0.05%. The composites based on 924 epoxy resin, which has been designed specially for high temperature applications, have less energy loss than the 913 epoxy resinbased composites. For the same resin, the carbon fiber-reinforced composites have less energy loss than the glass fiber-reinforced composites. All the composites have less energy loss than their corresponding matrices; the greater the fiber content, the lower the energy loss. The beta transition of 913 epoxy resin has been shifted to a higher temperature after being reinforced. It was shifted from −50°C to −30°C after being reinforced with glass fiber and made a diffuse shoulder-like peak commencing at −30°C after being reinforced with carbon fiber. The 924 epoxy resin has undergone the same change in beta transition as the 913 resin, though to a smaller extent. The phenomenon suggested that interactions between the macromolecules of the epoxy resins and the molecules along the fiber's surface.     

Preparation of Long Glass Fiber Reinforced Poly(butylene terephthalate) Composites with Chemical Bonding Interphase

Long glass fiber reinforced poly(butylene terephthalate) composites (LGF/PBT) were prepared by a new process. PBT oligomers with low melt viscosity were impregnated into the reinforcing glass fiber and then grafted to the reinforcing glass fiber surface treated with a silane coupling agent during solid‐state polymerization. The reinforcing glass fiber, after removing ungrafted PBT from LGF/PBT, was investigated with the result showing the presence of a grafted PBT layer on the surface of treated glass fiber. The mechanical properties of the composites were significantly improved owing to the grafting of the PBT macromolecules. The fiber length distribution and fiber arrangement in the injection molded composites were also studied and the results showed that a small amount long glass fiber could be connected at junction points in the composites, which were of benefit to the mechanical properties of the composites.     

Comparison of static and fatigue interlaminar testing methods for continuous fiber reinforced polymer composites

Two different interlaminar fatigue testing methods have been compared by testing a carbon fiber reinforced epoxy (CF/EP) composite and a carbon fiber/multiwalled carbon nanotube reinforced epoxy (CF/MWCNT/EP) hybrid nanocomposite. The first, conventional fatigue testing method was the end-notched flexure (ENF) test, which was used as a reference. The second, novel technique was the fatigue interpretation of the double-notch shear (DNS) test. Both tests have been performed with static and cyclic loading to compare the evaluated properties of the different systems, the effect of transition from cyclic to fatigue loading and to demonstrate if the complex ENF test can be replaced by the simpler DNS test.The test results showed the slight beneficial effect of the nanoreinforcement in both static and cyclic load conditions, and the possibility to use the DNS test for fatigue testing of continuous fiber reinforced composites. The SEM micrographs taken of the fracture surfaces of the composites after the different interlaminar tests provide valuable data on the interlaminar failure phenomena of hybrid nanocomposites in both static and fatigue loading conditions.     

Failure Processes in Fiber-Reinforced Liquid-Crystalline Polyester Composites

A hierarchical structural model for liquid-crystalline polyester reinforced with short glass fibers has been determined by using injection-molded bars. The gradient structure showed similar orientations between the glass fibers and the molecular orientation of the matrix. In the fiber-reinforced composites, the core failed prior to the skin by matrix cracking and transverse fiber pull-out as evidenced by the initial growth of parabolic cracks in the core. In the 30 wt% composite this was followed by complex cooperative phenomena involving fiber breakage, debonding, pull-out, and matrix deformation in the skin. The 50 wt% composite failed prematurely due to inadequate fiber/matrix interactions in the skin structure. Acoustic emission coupled with microscopy provided mechanistic insight throughout this work into the amount and intensity of specific failure mechanisms.     

New additives in glass reinforced polyolefins

Poly(butyl acrylate)-g-poly(4-vinylpyridine) graft copolymer and polypropylene modified with maleic anhydride or poly(maleic anhydride) have been prepared and characterised. These products have been tested as coupling agents in glass reinforced polyolefins. The adhesion of glass fiber or glass filler to polyolefin has been evaluated by “Single fiber composite” method or studying the volume variation under tensile strength. The results indicate that all the prepared additives improve the adhesion between olefin matrix and glass filler or fiber.     

Influence of the fibre/matrix interface on ageing mechanisms of glass fibre reinforced thermoplastic composites (PA-6,6, PET, PBT) in a hygrothermal environment

A study of the properties of short glass fibre reinforced thermoplastic composites based on poly(ethylene terephthalate), poly(butylene terephthalate) and polyamide-6,6 in an aggressive environment is reported. The influence of the fibre/matrix interface on the composite behaviour in a moist environment is especially studied. Competitive phenomena may explain differences observed according to the nature of the fibre surface treatment. Among them these characteristics may be an intrinsic fragility of some chemical interfacial bonds, the hydrophilicity of some chemical groups, the presence of long macromolecular chains neighbouring the interface or of a transcrystalline interfacial area.     

Novel preparation of glass fiber reinforced polytetrafluoroethylene composites for application as structural materials

A novel method was developed to fabricate continuous glass fiber reinforced polytetrafluoroethylene (PTFE/GF) composites which includes the use of conventional sintering and vacuum assisted resin transfer molding (VARTM), successively. The RTM resin (coded as M4506‐1) “fills” the porosity and defects of original PTFE/GF composites prepared by traditional sintering processing, improves the overall interface bonding between the matrix and fibers, and thus significantly improves the mechanical properties such as the flexural and interlaminar shear strength of fiber reinforced PTFE composites. The present work suggests a new way to produce fiber (especially continuous fiber) reinforced PTFE composites with high mechanical properties, and thus make it potentially possible to use PTFE‐based composites as structural materials. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of loading frequency on the fatigue behaviour of coir fibre reinforced PP composite

The influence of loading frequency on the fatigue behaviour of a coir fibre reinforced polypropylene (PP) composite was studied. The mechanical behaviour was assessed through monotonic tensile and flexural tests, followed by cyclic bending fatigue tests employing a new specimen geometry, with loading frequencies ranging from 5 to 35 Hz. Results revealed that higher strain rates during monotonic loading lead to higher flexural strength, and higher loading frequencies in cyclic tests promote reduction in fatigue life. Fractographic examination showed that one of the reasons for reduced fatigue life under higher loading frequencies might be related to increased heat generation by hysteresis, leading to a fatigue damage mechanism governed by temperature effects. The results, thus, encourage the development of good practices regarding test frequencies in order to be able to uncouple thermal and mechanical effects and provide relevant data for structural integrity assessments.     

Study on tribological behaviors of short glass fiber and polytetrafluoroethylene reinforced polycarbonate composites via a d‐optimal mixture design

This study analyzed variations of tribological behaviors that depend on the injection molding techniques during the blending of short glass fiber (SGF) and polytetrafluoroethylene (PTFE) reinforced polycarbonate (PC) composites. The proposed planning of blending experiments is to use a D‐optimal mixture design (DMD). The tribological behaviors of friction coefficient and wear mass loss were selected for discussion. Nine experimental runs, based on a DMD method, utilized to train the back‐propagation neural network (BPNN) and then the simulated annealing algorithm (SAA) approach is applied to search for an optimal mixture ratio setting. In addition, the result of BPNN integrating SAA was also compared with response surface methodology (RSM) approach. The results of confirmation experiment show that DMD, RSM, and BPNN integrating SAA method are effective tools for the optimization of reinforced process. Furthermore, the scanning electron microscope (SEM) images show that the abundant debris are peeled off from the matrix materials and predominant delamination mechanisms and plastic deformation are shown on the worn surface after tribological behavior tests. Copyright © 2010 John Wiley & Sons, Ltd.     

Improvement of interfacial adhesion for plasma‐treated aramid fiber‐reinforced poly(phthalazinone ether sulfone ketone) composite and fiber surface aging effects

Interfacial adhesion between the fiber and the matrix in a composite is a primary factor for stress transfer from the matrix to the fiber. In this study, oxygen plasma treatment method was applied to modify the fiber surface for improving interfacial adhesion of aramid fiber‐reinforced poly(phthalazinone ether sulfone ketone) (PPESK) composite. Composite interfacial adhesion properties were determined by interlaminar shear strength (ILSS) using a short‐beam bending test. The composite interfacial adhesion mechanism was discussed by SEM. The changes of chemical composition and wettability for plasma‐treated fiber surfaces stored in air as long as 10 days were investigated by XPS and dynamic contact angle analysis (DCAA), respectively. Results indicated that oxygen plasma treatment was an effective method for improving interfacial adhesion; plasma‐treated fiber surface suffered aging effects during storage in air. Copyright © 2008 John Wiley & Sons, Ltd.     

聚合物二元体系动态力学性能的估算

动态热机械分析是多相聚合物体系的一个重要研究手段.分析动态力学性能可以研究共混高聚物的相容性、复合材料的界面特性以及高分子运动机理等.本文综述了聚合物二元体系,即填充、纤维增强、共混体系动态力学性能的估算方法.在填充体系中,分别概述有无界面作用两种情况,当存在界面作用时,界面作用越强,模量越大,阻尼越小.对纤维增强体系,讨论了玻璃纤维有无取向的情况下模量和阻尼的估算.特别对于聚合物二元共混体系,分"海-岛"结构和双连续相两种情况,分别讨论了模量与阻尼的估算.     

Effect of silane coupling agent on mechanical interfacial properties of glass fiber‐reinforced unsaturated polyester composites

A silane coupling agent, γ‐methacryloxypropyltrimethoxysilane, for the surface modification of glass fibers was varied between 0.1 and 0.8 wt %. To understand the role of interfacial adhesion of glass fiber/unsaturated polyester composites, contact angles of the silane‐treated glass fibers were measured by the wicking method on the basis of the modified Washburn equation with deionized water, diiodomethane, and ethylene glycol as testing liquids. As a result, silane‐treated glass fibers led to increased surface free energy, mainly because of their increased specific or polar component. The mechanical interfacial behaviors based on the interlaminar shear strength (ILSS) of the composites determined by short‐beam tests and the critical stress‐intensity factor (K_IC) were also improved in the case of silane‐treated composites. The surface free energy and the mechanical interfacial properties especially showed the maximum value in the presence of 0.4 wt % silane coupling agent. It revealed that the increase of a specific component of the surface free energy or hydrogen bonding between the glass fibers and the coupling agents plays an important role in improving the degree of adhesion at interfaces in a composite system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 55–62, 2003     

Processing,microstructure and properties of bulk metallic glass composites

A Zr-Nb-Cu-Ni-Al bulk metallic glass was reinforced with up to 80 volume-percent (% V_f) continuous fibers, short fibers or particles. Characterization based on X-ray diffraction, differential scanning calorimetry, electron microprobe and scanning electron microscopy is presented. The metallic glass matrix remains amorphous after adding reinforcements. Reactions at the matrix/reinforcement interfaces were examined using transmission electron microscopy. A narrow band of crystalline particles typically forms adjacent to the reinforcement. The composites were tested in compression. Compressive strain-to-failure increased by up to factor of 12 compared to the unreinforced bulk metallic glass. The increase in compressive strain-to-failure is due to the particles restricting shear band propagation, promoting the generation of multiple shear bands and additional fracture surface area.     

Non-isothermal crystallization kinetics of continuous glass fiber-reinforced poly(ether ether ketone) composites

Current studies on crystallization kinetics for glass fiber-reinforced poly(ether ether ketone) mainly focused on short glass fiber-reinforced composites and their isothermal crystallization. It is worth noting that continuous glass fiber-reinforced poly(ether ether ketone) composite (CGF/PEEK) possesses relatively higher mechanical performance than short fiber-reinforced PEEK under high temperature. Here, for the first time, we investigate the non-isothermal crystallization kinetics and melting behavior of CGF/PEEK by differential scanning calorimetry at four different cooling rates. By evaluating the crystallite size of CGF/PEEK using X-ray diffraction, it is found that with the decreasing cooling rate, the crystallite size distribution evolves more uniform, and the size of crystallites enlarges. Besides, by systematical analysis, we find the modified Avrami equation can well describe crystallization behavior of the CGF/PEEK. The higher Avrami value of CGF/PEEK than pure PEEK indicates that CGF could introduce a more complex geometry effect on the crystallization. The addition of CGF greatly reduces the absolute value of crystallization activation energy of PEEK, suggesting that CGF can reduce the nucleation energy barrier. The obtained results illustrate that CGF can accelerate the nucleation rate due to heterogeneous nucleation while reduce the growth rate due to retarded polymer chain mobility. And the cooling conditions can influence crystal growth and morphology.

     

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.     

Experimental investigation on the mechanical properties of Co-polypropylene/GF/CaCO<Subscript>3</Subscript> hybrid nanocomposites

This study aimed to acquire a balance of mechanical properties comprising impact, tensile and flexural performances in PP based blend. In this respect, co-PP was employed as matrix because of its intrinsic high impact behavior. Hybrid nanocomposites based on co-PP and containing 10 wt % micron-sized short glass fibers (GF) and 2 to 8 wt % nano precipitated CaCO₃ (NPCC) particles were produced by applying a two-step melt compounding method. Maleic anhydride grafted polypropylene (MAPP) was used as compatibilizer. Strong glass fiber-matrix adhesion and relatively uniform distribution of nano-CaCO₃ particles were observed in SEM images. The maximum tensile strength was observed in co-PP hybrid nanocomposite containing 10 wt % glass fiber and 5 wt % nano-CaCO₃ which was 58% more than that of neat co-PP. Flexural strength raised as much as 11% by adding glass fiber. The maximum flexural strength was obtained by incorporating 10 wt % glass fiber and 8 wt % nano-CaCO₃ into co-PP matrix which was 24% higher than that of neat co-PP. The impact strength decreased upon addition of 10 wt % glass fiber and 5 and 8 wt % nano-CaCO₃, this was attributed to the inherent high impact behavior of co-PP as well as strong interfacial interaction between dispersed phases and polymeric matrix.     

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.     

The synergetic effect of zinc phthalate and carboxymethyl cellulose–carbon nanotube of glass fibers surfaces on improving strength and toughness of polypropylene composite

The interfacial interaction between glass fibers (GFs) and polypropylene (PP) resin is the key factor which affects the properties of GFs reinforced PP composites. The β-transcrystallization (β-TC) structure induced by β-nucleating agent (β-NA) at the interface is beneficial to improving the interfacial performance and comprehensive mechanical properties. However, due to the poor adhesive ability, it is difficult to introduce β-NAs onto GFs surface directly. In this work, for solving above problem, the sodium carboxymethyl cellulose (CMC) and  NH₂ functionalized multiwalled carbon nanotubes (CNTs) were used to construct the network structure on GFs (CMC-CNT-GF) through plenty of active groups. Furthermore, the zinc phthalate (ZnPht, β-NA) was synthesized and coated on GFs surface by hydrogen bonds interaction with CMC-CNT and physical anchoring effect (ZnPht@CMC-CNT-GF). Finally, the hybrid GFs reinforced PP composite (iPP/ZnPht@CMC-CNT-GF) was prepared, which exhibited enhanced tensile, flexural, and impact strength by 20.1, 9.3, and 33.3%, respectively when compared with the iPP/raw GF due to the formation of β-TC and improvement of interfacial adhesion. This study provides an effective strategy to introduce β-NAs on GFs with network structure for improving interfacial properties by inducing β-TC to enhance the strength and toughness of composite, which could be applied in other fiber/semicrystalline polymer systems.     

Quantitative determination of interfacial adhesion in composites with strong bonding

An approach was proposed for the quantitative determination of adhesion strength in composites, in which adhesion is created by other mechanisms than secondary interactions. The approach is based upon a model, which gives debonding stress as a function of interfacial adhesion. Debonding stress was determined by acoustic emission experiments. The mechanism of deformation was checked by SEM experiments and the approach was verified on composites with known interfacial adhesion. The results showed that the use of functionalized polymer in PP/CaCO₃ composites resulted in adhesion strength one order of magnitude larger than without the coupling agent. The application of various surface modification techniques in PP/glass bead composites yielded different adhesion values covering a range of about one order of magnitude. The quantitative determination of interfacial adhesion makes possible the design and optimization of most surface modification techniques in particulate filled and short fiber reinforced composites.