IFSS, TG, FT-IR spectra of impregnated sugar palm (Arenga pinnata) fibres and mechanical properties of their composites

This study aimed to investigate the effect of resin impregnation on the interfacial shear strength (IFSS), thermogravimetric (TG) and fourier transform infrared (FT-IR) of sugar palm (Arenga pinnata) fibres. In addition, the effect of resin impregnation on the mechanical properties of sugar palm fibre reinforced unsaturated polyester (UP) composites was also studied. The fibres were impregnated with UP via vacuum resin impregnation process at a pressure of 600 mmHg for 5 min. Composites of 10, 20, 30, 40 and 50 % fibre loadings were fabricated and tested for tensile and flexural properties. It was observed that the impregnation process caused the fibres to be enclosed by UP resin and this gave a strong influence to the increase of its interfacial bonding by the increase of its IFSS from single fibre pull-out test. It was also observed with TG and FT-IR spectra that the impregnated fibre had lower moisture uptake than the control and there was no significant increase in thermal stability of the impregnated fibre. The sequence of fibre decomposition started from the evaporation of moisture, hemicelluloses, cellulose, lignin and finally ash content and the presence of these components were proven by FT-IR spectra. For the composite specimens, due to the high interfacial bonding of the impregnated fibre and the matrix, the impregnated composites showed consistently higher tensile strength, tensile modulus, elongation at break, flexural strength, flexural modulus and toughness than the control samples. It was also observed that 30 % fibre loading gave optimum properties.     

Polymer blends based on epoxy resin and polyphenylene ether as a matrix material for high-performance composites

The application of poly(2,6-dimethyl-1,4-phenylene ether), PPE, as a matrix material for continuous carbon fibre reinforced composites has been studied. Due to the intractable nature of PPE melt impregnation is not feasible and a novel impregnation route, using epoxy resin as a reactive solvent, was developed. The introduction of epoxy resin results in enhanced flow and a reduced processing temperature, enabling the processing of PPE and the preparation of high quality composites. Upon curing, phase separation is initiated and epoxy resin is converted into a second phase. In composites, epoxy resin preferentially accumulates at the polar fibre surface, resulting in an epoxy layer around the fibres, providing a high level of interfacial adhesion. For a high fibre volume fraction (> 50%) this results in the ultimate morphology of epoxy coated fibres in a neat PPE matrix. Due to this unique morphology the composite materials reveal outstanding mechanical properties in terms of interlaminar toughness and impact performance.     

Gravimetric determination of carbon fibre in composites on the centigram scale

Summary A gravimetric method for determining the fibre content of carbon fibre/epoxy resin composites has been adapted for samples of about 20 to 50 mg. The epoxy resin was decomposed with sulphuric acid and hydrogen peroxide; the fibres were collected and weighed on a glass-fibre filter. Means of results from the small-scale and standard methods were not significantly different. Although developed for small samples of very thin composites, the method has possible applications in investigating the homogeneity of larger composite pieces.     

亚临界水介质回收酸酐固化环氧树脂/碳纤维复合材料

研究了不同添加剂对碳纤维增强酸酐固化环氧树脂复合材料在亚临界水中降解的影响,通过IR、GC-MS等分析,确定了环氧树脂的分解机理主要为酯键的断裂。 结果表明,KOH与苯酚对酸酐固化环氧树脂的分解没有协同效应,碱性物质更有利于酯键的断裂。 甲基四氢邻苯二甲酸酐固化的环氧树脂增强碳纤维复合材料在反应温度为250 ℃、反应时间为60 min、KOH浓度为0.2 mol/L时可完全分解,回收碳纤维的拉伸强度和表面形貌未受影响。     

Soft ionisation analysis of evolved gas for oxidative decomposition of an epoxy resin/carbon fibre composite

Soft ionisation mass spectrometry was used to investigate the oxidative decomposition of an epoxy resin/carbon fibre composite using thermogravimetry (TG) coupled with mass spectrometry (MS). Through comparison between decomposition in air and in argon, it was recognized that the first step of the oxidative decomposition of the epoxy resins was similar to the decomposition in argon. During the devolatilisation process, the oxidative decomposition underwent a thermal decomposition leading to the formation of a large amount of volatile products which were subsequently oxidized into water and carbon dioxide. The gas produced in the thermal decomposition was not oxidized completely leaving some organic volatiles in the emissions. Using soft ionisation, the components of the evolved gases were identified by mass spectrometry.     

Characteristics of kenaf fibre/epoxy composites subjected to thermal degradation

Kenaf fibres are receiving much attention in the natural fibre composite industry due to its potential as polymer reinforcements. However, like all natural fibres, kenaf fibres have lower thermal resistance as compared to synthetic fibres. In this current work, the characteristics of kenaf fibre/epoxy composites, both treated and untreated using alkalization process, exposed to high temperature were studied. Thermogravimetric analysis (TGA) was used to study the thermal decomposition behaviour of treated and untreated kenaf/epoxy composites as well as their components, kenaf fibre and neat epoxy from room temperature up to 600 °C. The weight loss and physical changes of these samples were observed through furnace pyrolysis. Surface morphology of the composites after degradation was observed using scanning electron microscopy (SEM). The results from the TGA showed that the addition of kenaf fibres into the epoxy slightly improves both the charring and thermal stability of the samples. However, it was observed that alkalization causes reduction in these behaviours for the kenaf/epoxy composite. Generally, increased exposure time causes higher weight loss of the composites only up to 150 °C. At higher temperature, duration of exposure has little influence on the weight loss. Fibre-matrix debondings were observed on degraded samples implying mechanical degradation of the composites had occurred.     

Flame retardancy of fibre-reinforced epoxy resin composites for aerospace applications

The applicability of phosphorus-containing reactive amine, which can be used in epoxy resins both as crosslinking agent and as flame retardant, was compared in an aliphatic and an aromatic epoxy resin system. In order to fulfil the strong requirements on mechanical properties of the aircraft and aerospace applications, where they are mostly supposed to be applied, carbon fibre-reinforced composites were prepared. The flame retardant performance was characterized by relevant tests and mass loss type cone calorimeter. Besides the flame retardancy, the tensile and bending characteristics and interlaminar shear strength were evaluated. The intumescence-hindering effect of the fibre reinforcement was overcome by forming a multilayer composite, consisting of reference composite core and intumescent epoxy resin coating layer, which proved to provide simultaneous amelioration of flame retardancy and mechanical properties of epoxy resins.     

Characterization of sugar palm (Arenga pinnata) fibres

The aim of this study was to characterize tensile and thermal properties of sugar palm (Arenga pinnata) fibres obtained from different heights (1, 3, 5, 7, 9, 11, 13, and 15?m) of sugar palm tree. This study has confirmed that in a mature sugar palm tree, degradation was occurred and altered the properties of its fibre. Fibres obtained at the area of live (green) palm frond were found to have a better tensile properties as a result of its optimum chemical composition especially cellulose, hemicelluloses and lignin. For the fibre obtained from the upper part of sugar palm tree, it shows slightly decreasing trend in tensile properties compared to mature fibres. It is due to the fibres are juvenile where their cell walls are progressively built up thus give slightly lower properties than matured fibres. For the fibre obtained from the area of dead palm frond, the fibres are considered to be degraded biologically. It is believed that polymeric chains in microfibrils were broken and their cellulose content was decreased which demonstrated inferior properties (tensile strength, modulus, elongation at break and toughness). The use of such fibre for application as reinforcing fibre in composite is not recommended since the strength of the fibre and composite will be reduced. There were four phases of decomposition of the fibres where the sequence of decomposition started with decomposition of moisture, followed by hemicelluloses, then cellulose and next is lignin while the ash was the last component left. The thermal degradation of these components were found in ranges of 45?C123, 210?C300, 300?C400, 160?C900 and 1723?°C, respectively. Thermogravimetric analysis and derivative thermogravimetric analysis curves showed that the fibre of 1?m showed higher thermal stability than the fibres of 3?C15?m. The different thermal stability for each fibre was due to different chemical compositions especially when the fibre containing high ash content which result in higher thermal stability.     

Oxidation of a carbon/glass reinforced cyanate ester composite

The decomposition/oxidation behaviour of a carbon/glass fibre reinforced thermosetting pre-impregnated material based on polymerized aromatic cyanate ester compounds (commercial name GURIT-PN900-C582-43) has been investigated. Experiments were carried out for thermally thick samples exposed in a preheated reaction chamber (temperatures between 650–950 K) and a continuous gas flow (inlet velocity between 0.6 and 4.2 cm/s). Temperature measurements indicate that, in air, the process takes place under a mixed kinetic-diffusive control with three main dynamic stages corresponding to oxidative decomposition, heterogeneous ignition delay and oxidation. The oxidative decomposition stage is always much faster than the total duration of the ignition delay and oxidation stages (factors of 60–85). SEM pictures show dramatic changes in the material structure with amounts of solid residue, at the conclusion of the conversion process, varying from about 62% (resin char, glass and carbon fibres) to 29% (essentially the glass fibres) (against 85–75% for thermal degradation). Also, with the aid of thermogravimetric curves measured in air for the composite material and a charred residue, a three-step oxidation mechanism is proposed consisting of the oxidative decomposition of the resin, the oxidation of the resin char and the oxidation of the carbon fibres with estimated activation energies of 95, 136 and 185 kJ/mol, respectively.     

The mechanical properties of plasma‐treated carbon fiber reinforced PA6 composites with CNT

The aim of this work is the evaluation of the effects of plasma treatment and the addition of CNT on the mechanical properties of carbon fibre/PA6 composite. A powder impregnation process with integrated inline continuous plasma of carbon fibers was used to produce CF/PA6 composite. CF/PA6 composite was processed into test laminates by compression moulding, and interface dominated composite properties were studied. The tensile and impact strength of composites containing CNT and plasma‐treated carbon fibres improved obviously. The tensile strength of nanocomposite largely increases with the increasing of the CNT content and then decreases when the CNT content is over 2%. The hydroxyl groups of the fibers surface are in favor of the wettability of carbon fibers by the polar matrix resin, which is resulting in a further interaction of the fiber surface with the curing system of the matrix resin.     

Recyclable carbon fiber‐reinforced plastics (CFRP) containing degradable acetal linkages: Synthesis,properties, and chemical recycling

Two epoxy resins containing degradable acetal linkages were synthesized by the reaction of cresol novolak‐type phenolic resin (CN) with vinyl ethers containing a glycidyl group [cyclohexane dimethanol vinyl glycidyl ether (CHDMVG) and 4‐vinyloxybutyl glycidyl ether (VBGE). Carbon fiber‐reinforced plastics (CFRPs) were prepared by heating laminated prepreg sheets with CN‐CHDMVG resin (derived from CN and CHDMVG) and CN‐VBGE resin (derived from CN and VBGE), in which carbon fibers are impregnated with epoxy resins containing curing agents [dicyandiamide (DICY)] and curing accelerator [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU)]. CN‐CHDMVG‐based CFRPs and CN‐VBGE‐based CFRPs exhibited almost the same tensile strength as the conventional bisphenol‐A‐based CFRPs. CN‐CHDMVG‐based CFRPs and CN‐VBGE‐based CFRPs underwent smooth breakdown with the treatment of hydrochloric acid in tetrahydrofuran at room temperature for 24 h to regenerate strands of carbon fibers. The surface conditions of the recovered carbon fibers had little changes during degradation and recovery processes on the basis of scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The recovered carbon fibers exhibited almost the same tensile strength as virgin carbon fibers and hence would be reused for the production of CFRPs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1052–1059     

Improving the interfacial property of carbon fibre/epoxy resin composites by grafting amine-capped cross-linked poly-itaconic acid

To improve the interfacial properties of carbon fibre-reinforced polymer composites, a surface treatment was used to cap cross-linked poly-itaconic acid onto carbon fibres via in-situ polymerization after itaconic acid grafting. The chemical composition of the modified carbon fiber (CF) surface was characterized by X-ray photoelectron spectral and Fourier-transform infrared spectroscopy. Scanning electron microscopy and atomic force microscopy images showed that the poly-itaconic acid protective sheath was uniformly capped onto the CF surface and that the surface roughness was obviously enhanced. Chemical bonds also played a key role in the interfacial enhancement. The results showed that the interfacial shear strength of the composites with poly-itaconic acid on the carbon fibres (72.2 MPa) was significantly increased by 89.5% compared with that of the composites with pristine CF (38.1 MPa). Moreover, the poly-itaconic acid sheath promoted a slight increase in mono-fibre tensile strength. In addition, the interfacial mechanisms were also discussed. Meanwhile, the mechanical property of the functionalized CF/epoxy resin composites was also significantly improved.     

Effect of electrospun polyamide 6 nanofibres on the mechanical properties of a glass fibre/epoxy composite

Recently, several types of nanoparticles are frequently incorporated in reinforced epoxy resin composites. A homogeneous dispersion of these nanoparticles is still a problem. Thermoplastic nanofibrous structures can tackle this dispersion issue. Therefore, this paper investigated the effect of electrospun polyamide 6 nanofibrous structures on the mechanical properties of a glass fibre/epoxy composite. The nanofibres were incorporated in the glass fibre/epoxy composite as stand-alone interlayered structures and directly spun on the glass fibre reinforcement. Both ways of nanofibre incorporation have no negative effect on the impregnation of the epoxy. Moreover, the nanofibres remain well dispersed within the matrix. Incorporation of nanofibres increases the stress at failure in the 0°-direction, the best results are obtained when the nanofibres are directly electrospun onto the glass fibres. Optical microscopic images also demonstrate that nanofibres prevent delamination when a 90° crack reaches a neighbouring 0° ply. Furthermore, mode I tests showed a small improvement when a thin nanofibrous structure is deposited directly onto the glass fibres. When the composites are loaded under 45°, it is proven that, for an identical stress, the glass fibre composite with deposited nanofibres has less cracks than when interlayered nanofibrous structures are incorporated. Generally, it can be concluded that the addition of polyamide 6 nanofibres improves some mechanical characteristics of a glass fibre/epoxy composite.     

Synthesis and Characterization of Fluorinated Acrylic Polymer and the Properties of Epoxy Thermosets Modified With It

A novel fluorinated acrylic polymer poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)-r-poly(glycidyl methacrylate) (PHFMA-r-PGMA) was synthesized and used to modify the general performances of epoxy resin. Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H-NMR) successfully verified the synthesis of PHFMA-r-PGMA. In order to study the effect of epoxy groups in PHFMA-r-PGMA on the properties of modified epoxy resin, corresponding fluoropolymer without epoxy group (PHFMA) was also prepared, and the properties of epoxy thermosets modified by two kinds of fluoropolymers were comparatively studied. The contact angle measurements indicated that the PHFMA-r-PGMA and PHFMA modified thermosets both showed considerable hydrophobicity and lipophobicity. For further comparison, it was also found that the thermosets modified by PHFMA-r-PGMA had a little worse hydrophobicity and lipophobicity but better surface stability than which modified by PHFMA because the epoxy groups in PHFMA-r-PGMA “locked” more fluoropolymers in the bulk matrix of the thermosets, but PHFMA was more freely able to migrate to the surface of the thermosets. SEM images of the fracture surface of PHFMA-r-PGMA and PHFMA modified epoxy thermosets displayed “irregular ripples” or “protuberant island” structures, which suggesting both of these two copolymers could significantly toughen epoxy resin. The results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the thermosets modified by PHFMA-r-PGMA had better thermal stability than which modified by PHFMA due to the higher crosslinking density between PHFMA-r-PGMA and epoxy resin because of the epoxy groups in PHFMA-r-PGMA. The mechanical properties were investigated by tensile testing and impact testing. Although the tensile strength of the PHFMA-r-PGMA and PHFMA modified epoxy thermosets both declined slightly with growing the content of fluoropolymers, the elongation at break and impact strength both increased first and then decreased in the meantime, which indicated that the two kinds of modified thermosets had better toughness than pure epoxy resin. It may be because the macro-phase separation between the long fluorine carbon chain segments and epoxy resin during curing could absorb the impact energy effectively.     

Mechanical and thermal properties of (Ag/C nanocable)/epoxy resin composites

A novel Ag/C nanocable and epoxy resin composite was obtained by compounding Ag/C nanocables and epoxy resin. The nanocable is composed of a nanowire (core) wrapped with one or more outer layers (shell). Scanning electron microscopy images proved that the nanocables consisted of a silver nanowire core and a carbon outer shell. The Ag/C nanocables were modified by hyperbranched poly (amine ester) to improve their mechanical properties for further application. We separately compounded raw and modified Ag/C nanocables with epoxy resin, and then tested the thermal performance, tensile properties, and fracture morphology of each composite. We found that the tensile strengths of the two composite systems were enhanced by the epoxy resin, with the modified (Ag/C)/epoxy resin composite system improving more significantly. Differential scanning calorimeter (DSC) results showed that the glass transition temperature of the unmodified (Ag/C)/epoxy resin composite is increased when the Ag/C nanocable is filled, while that of the modified system slightly decreased. Fracture morphology results showed that both (Ag/C)/epoxy composite systems featured increased toughness. The modified Ag/C nanocables had better compatibility with the epoxy resin. The relationship between the properties and microstructure of the composites were discussed in detail to explain the mechanism behind the observed changes in material properties.     

Matrix properties and composite failure

The influence of matrix extensibility on the properties of a composite was studied using two glassy polymers of almost identical chemical structure but differing crosslink densities. The lower crosslink density gave a 73 % increase in tensile elongation at break and a 56% increase in specific fracture energy. Unidirectional laminates of glass, carbon, and Kevlar^® fibres were prepared with these two polymers and tested for shear strength, transverse tension, and dynamic fatigue.The shear strengths of the polymers were found to be almost independent of crosslink densities (about 100 MPa). The interlaminar shear strengths of the carbon fibre laminates corresponded to those of the matrix polymers (Kevlar^® fibre laminates failed at 60 %). In accordance with Griffith's equation the more extensible polymer and its laminates performed better in tensile tests transverse to the fibres due to improved fracture energy. Failure criteria based on strain magnification were useful in the case of glass fibre laminates, but proved inadequate for laminates based on anisotropic fibres such as carbon and Kevlar^®.The dynamic fatigue strengths of the two matrix polymers were unaffected by the difference in crosslink densities. Almost the same fatigue strengths were obtained for the matrix polymers as for the laminates (carbon, glass) transverse to the fibres. A lack of processability of the polymer with high functionality was identified as a source of deteriorating effects.     

Preparation and characterization of functionalized graphene oxide/carbon fiber/epoxy nanocomposites

Graphene oxide (GO) was functionalized using three different diamines, namely ethylenediamine (EDA), 4,4′-diaminodiphenyl sulfone (DDS) and p-phenylenediamine (PPD) to reinforce an epoxy adhesive, with the aim of improving the bonding strength of carbon fiber/epoxy composite. The chemical structure of the functionalized GO (FGO) nanosheets was characterized by elemental analysis, FT-IR and XRD. Hand lay-up, as a simple method, was applied for 3-ply composite fabrication. In the sample preparation, the fiber-to-resin ratio of 40:60 (w:w) and fiber orientations of 0°, 90°, and 0° were used. The GO and FGO nanoparticles were first dispersed in the epoxy resin, and then the GO and FGO reinforced epoxy (GO- or FGO-epoxy) were directly introduced into the carbon fiber layers to improve the mechanical properties. The GO and FGO contents varied in the range of 0.1–0.5 wt%. Results showed that the mechanical properties, in terms of tensile and flexural properties, were mainly dependent on the type of GO functionalization followed by the percentage of modified GO. As a result, both the tensile and flexural strengths are effectively enhanced by the FGOs addition. The tensile and flexural moduli are also increased by the FGO filling in the epoxy resin due to the excellent elastic modulus of FGO. The optimal FGO content for effectively improving the overall composite mechanical performance was found to be 0.3 wt%. Scanning electron microscopy (SEM) revealed that the failure mechanism of carbon fibers pulled out from the epoxy matrix contributed to the enhancement of the mechanical performance of the epoxy. These results show that diamine FGOs can strengthen the interfacial bonding between the carbon fibers and the epoxy adhesive.     

超临界正丁醇对回收碳纤维复合材料的降解及表征

采用响应面分析方法设计超临界正丁醇降解废弃的碳纤维/环氧树脂(CF/EP)复合材料降解实验,用以回收碳纤维.通过Design-Expert V8.0建立环氧树脂降解率和工艺参数之间的数学模型,获得了最优工艺参数;通过图形优化研究了工艺参数对环氧树脂基体降解率的影响规律;通过场发射电子扫描显微镜、原子力显微镜、X射线光电子能谱仪、显微共焦激光拉曼光谱仪及单丝拉伸等分析最优工艺参数下回收的碳纤维的表面形貌、表面化学、石墨化程度及力学性能.结果表明,建立的数学模型拟合误差范围为±5.5%,实现了回收工艺参数的预估;单因素对环氧树脂基体降解率的影响程度为:反应温度保温时间添加剂浓度正丁醇含量;最优工艺参数为:反应温度330℃,保温时间60 min,添加剂浓度0.0538 mol/L,投料比0.024g/mL.回收的碳纤维表面无残留树脂,没有发生明显的石墨化,且表面平均粗糙度与原碳纤维相近;与原始碳纤维相比,回收的碳纤维的拉伸强度约为原碳纤维的93.58%,杨氏模量约为原碳纤维的94.87%.     

Combined effect of zeolite and boric acid on thermal behavior of epoxy composites

The particles of natural zeolite in combination with boric acid were incorporated into the epoxy resin ED-20 in order to improve the thermal stability of epoxy polymer. Epoxy resin was cured using polyethylenepolyamine. Characterization of the epoxy composites was carried out by using Fourier transform infrared spectrometry, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) under flow of air and argon. The thermal behavior of the zeolite/boric acid-based epoxy composites (total percentage 15 mass%) were compared with that of 15 mass% boric acid-based epoxy system and the neat epoxy resin. TG and DSC results revealed that the combination of 5 mass% zeolite and 10 mass% boric acid significantly increased the mid-point temperature and residue, and decreased the maximum decomposition rate of the epoxy composites at the heating.     

Effects of electrochemical and plasma treatments on carbon fibre surfaces

This paper summarizes the chemical changes induced on carbon fibre surfaces (examined by X-ray photoelectron spectroscopy, XPS) by a variety of electrochemical treatment in aqueous electrolytes together with the improvements in fibre/resin bonding in the corresponding composite materials. It was found that there was no correlation between the amount of chemical functionality introduced onto the fibre surface and the fibre/resin bond strength, i.e. chemical bonding does not play a major role in fibre resin adhesion. This does not rule out the possibility of chemical bonding between the fibre and resin—it simply implies that it is not the governing factor. It is suggested that the immediate surface concentration of chemical groups is too low to make a significant contribution. To tailor interfacial properties it would be desirable to promote chemical bonding between fibre and matrix. The use of a specially designed plasma treatment cell has led to an increase in the surface concentration of chemical groups ( C OH, hydroxyl) that have the potential to react chemically with the resin. By exploiting grazing angle data taken from XPS analysis, it is shown that changes in the chemical nature of the fibres only occurs in the outermost layers, whereas the electrochemical reaction proceeds well into the fibre sublayers. Selective introduction of nitrogen-containing functionality (such as amines,  NH₂) has been achieved. The reactivity towards a particular plasma is shown to be largely dependent on the structure of the fibre surface. The number of C/N groups produced on higher modulus fibres was undesirably low. Their concentration was increased by biasing the fibres to a negative potential (10–30 V) during plasma exposure.