Preparation and properties of poly (p-phenylene sulfide)/multiwall carbon nanotube composites obtained by melt compounding

In this paper, electrical and mechanical properties of Poly (p-phenylene sulfide) (PPS)/multi-wall carbon nanotubes (MWNTs) nanocomposites were reported. The composites were obtained just by simply melt mixing PPS with raw MWNTs without any pre-treatment. The dispersion of MWNTs and interfacial interaction were investigated through SEM &TEM and Raman spectra. The rheological test and crystallization behavior were also investigated to study the effects of MWNTs concentration on the structure and chain mobility of the prepared composites. Though raw MWNTs without any pre-treatment were used, a good dispersion and interaction between PPS and MWNTs have been evidenced, resulting in a great improvement of electrical properties and mechanical properties of the composites. Raman spectra showed a remarkable decrease of G band intensity and a shift of D bond, demonstrating a strong filler–matrix interaction, which was considered as due to π–π stacking between PPS and MWNTs. The storage modulus (G′) versus frequency curve presented a plateau above the percolation threshold of about 2–3 wt% with the formation of an interconnected nanotube structure, indicative of ‘pseudo-solid-like’ behavior. Meanwhile, a conductive percolation threshold of 5 wt% was achieved and the conductivity of nanocomposites increased sharply by several orders of magnitude. The difference between electrical and rheological percolation threshold, and the effect of critical percolation on the chain mobility, especially on crystallization behavior of PPS, were discussed. In summary, our work provides a simple and fast way to prepare PPS/MWNTs nanocomposites with good dispersion and improved properties.     

Structure evolution of conductive polymer composites revealed by solvent vapor induced time-dependent percolation

The authors of this paper synthesized a series of amphiphilic triblock copolymers of polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) having different PEG/PS ratios with nearly identical molecular weights of the entire copolymers. The interfacial interactions in the composites consisting of carbon black and the copolymers can thus be tailored. When these conducting composites are exposed to certain solvent vapors, their electrical resistances greatly increase, showing the gas sensitivity. The present work indicated that this switching behavior is controlled by the structural relaxation of the composites because matrix swelling acts as the main mechanism. The response time has been correlated with absolute temperature by Arrhenius equation, and the estimated activation energy reflects mobility of the fillers involved in the solvent induced expansion of the surrounding polymer. Therefore, by using the gas sensibility of the conductive composites, the structure evolution of the composite materials in solid state and the effect of filler/matrix interfacial interaction on the relaxation property of the matrix polymer has been inspected. It was found that lower activation energy represents stronger interfacial interaction in case good solvent of the matrix was used for the test.     

Mechanical and electrical properties of carbon nanotube/poly(phenylene sulphide) composites incorporating polyetherimide and inorganic fullerene-like nanoparticles

The mechanical and electrical properties of single-walled carbon nanotube (SWCNT) reinforced poly(phenylene sulphide) (PPS) composites prepared by melt-extrusion have been evaluated. The wrapping of SWCNTs in polyetherimide (PEI) and the addition of inorganic fullerene-like tungsten disulfide (IF-WS₂) nanoparticles provided an effective method for dispersing the SWCNTs, leading to enhanced properties of the resulting hybrid composites. Mechanical tests demonstrated significant enhancements in stiffness, strength and toughness by the addition of both nanofillers, and the Young’s modulus of the hybrid composites was fairly well predicted by two-phase modelling. The electrical conductivity of PPS improved dramatically at low SWCNT content (0.1-0.5 wt%). At higher concentrations, the replacement of part of the SWCNTs with IF-WS₂ maintained the level of conductivity of the composites. Overall, the hybrids possess superior performance than composites reinforced solely with wrapped or non-wrapped SWCNTs, and their properties can be tailored by modifying the SWCNT/IF-WS₂ ratio.     

Mechanical properties of graphene films enhanced by homo-telechelic functionalized polymer fillers via π–π stacking interactions

Most researches on graphene/polymer composites are focusing on improving the mechanical and electrical properties of polymers at low graphene content instead of paying attention to constructing graphene’s macroscopic structures. In current study the homo-telechelic functionalized polyethylene glycols (FPEGs) were tailored with π-orbital-rich groups (namely phenyl, pyrene and di-pyrene) via esterification reactions, which enhanced the interaction between polyethylene glycol (PEG) molecules and chemical reduced graphene oxide (RGO) sheets. The π–π stacking interactions between graphene sheets and π-orbital-rich groups endowed the composite films with enhanced tensile strength and tunable electrical conductivity. The formation of graphene network structure mediated by the FPEGs fillers via π–π stacking non-covalent interactions should account for the experimental results. The experimental investigations were also complemented with theoretical calculation using a density functional theory. Atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), UV–vis and fluorescence spectroscopy were used to monitor the step-wise preparation of graphene composite films.     

Enhanced thermal resistance of phenolic resin composites at low loading of graphene oxide

By incorporating graphene oxide (GO) into phenolic resin (PR), GO/PR composites were prepared, and the effects of the content and reduction degree of GO on thermal resistance of GO/PR composites were studied. The peak degradation temperature of the PR was increased by about 14 °C with GO which was heat treated. The char yield of GO/PR composite at a GO weight fraction of 0.5% was about 11% greater than that of PR. The interactions such as covalent bonds and π–π stacking between GO and PR were regarded as the main reason for the enhancement. Located at the GO–PR interface, GO effectively anchored and structured PR molecular near the surfaces of GO sheets, and thus facilitated the formation of char. The superiority of GO/PR composites over PR in terms of thermal properties enhancement should also be related to the promoting graphitization by the addition of GO.     

Excellent dielectric properties of PVDF-based composites filled with carbonized PAN/PEG copolymer fibers

Weak interfacial bonding between carbon materials and polymer matrix impedes the formation of homogeneous composites, challenging to the enhancement of dielectric properties of such systems. In this work, we designed novel carbonized polyacrylonitrile/polyethylene glycol copolymer fibers (CPCFs) and then used them as fillers to enhance the dielectric properties of poly(vinylidene fluoride) (PVDF)-based composites. These CPCFs are rich in nitrogen (8.55%) and oxygen (3.94%) atoms on the surface of them. The results of molecular dynamic (MD) simulations indicate that the existence of these atoms significantly increase the interaction energy between CPCFs and PVDF matrix from −45.13 kcal/mol to −62.22 kcal/mol, which promotes the intercalation of conductive CPCFs into insulated PVDF matrix to form ultrathin microcapacitors. As a result, the largest dielectric constant of CPCFs/PVDF composites can reach 1583 (1 kHz), which is about 150 times higher than that of pure PVDF.     

Poly(phenylene sulphide) and poly(ether ether ketone) composites reinforced with single-walled carbon nanotube buckypaper: II – Mechanical properties,electrical and thermal conductivity

The mechanical properties, electrical and thermal conductivity of single-walled carbon nanotube (SWCNT) buckypaper (BP) embedded in poly(ether ether ketone) (PEEK) or poly(phenylene sulphide) (PPS) matrices were investigated. Dynamic mechanical analysis demonstrated a significant increase in the storage modulus and glass transition temperature of the polymers, indicating strong SWCNT–matrix interfacial adhesion. The composites showed improved stiffness and strength, as revealed by tensile and flexural tests, while their ductility and toughness moderately decreased. Exceptional enhancements in the electrical and thermal conductivity of PPS and PEEK were found. Their Young’s moduli and thermal conductivities were compared with the predictions of theoretical models. This investigation indicates that SWCNT-BPs possess great potential to improve the performance of thermoplastics and satisfy a wide variety of demands in multi-disciplinary technological applications.     

Enhancement of ablative and interfacial bonding properties of EPDM composites by incorporating epoxy phenolic resin

Effects of epoxy phenolic resin (EPR) on ablative and interfacial bonding properties of EPDM composites were evaluated. Ablative properties of EPDM composites were enhanced by two folds with incorporating 10 phr EPR. This significant enhancement was attributed to positive effect of EPR on thermal stability and thermal insulating properties of EPDM composites as well as formation of compact char layer onto composites. Furthermore, interfacial shear strength of EPDM composites with carbon fiber/epoxy (CF/EP) composites was increased by 55.6% with incorporating 10 phr EPR, due to interfacial chemical reaction of epoxide groups of EPR molecule from EPDM composites with amine group of hardener from CF/EP composites.     

Enhancement of mechanical performance of epoxy/carbon fiber laminate composites using single-walled carbon nanotubes

Carbon nanotubes (CNT) in their various forms have great potential for use in the development of multifunctional multiscale laminated composites due to their unique geometry and properties. Recent advancements in the development of CNT hierarchical composites have mostly focused on multi-walled carbon nanotubes (MWCNT). In this work, single-walled carbon nanotubes (SWCNT) were used to develop nano-modified carbon fiber/epoxy laminates. A functionalization technique based on reduced SWCNT was employed to improve dispersion and epoxy resin-nanotube interaction. A commercial prepregging unit was then used to impregnate unidirectional carbon fiber tape with a modified epoxy system containing 0.1 wt% functionalized SWCNT. Impact and compression-after-impact (CAI) tests, Mode I interlaminar fracture toughness and Mode II interlaminar fracture toughness tests were performed on laminates with and without SWCNT. It was found that incorporation of 0.1 wt% of SWCNT resulted in a 5% reduction of the area of impact damage, a 3.5% increase in CAI strength, a 13% increase in Mode I fracture toughness, and 28% increase in Mode II interlaminar fracture toughness. A comparison between the results of this work and literature results on MWCNT-modified laminated composites suggests that SWCNT, at similar loadings, are more effective in enhancing the mechanical performance of traditional laminated composites.     

Toughness,flexural, damping and interfacial properties of hybridized GFRE composites with MWCNTs

As the improved damping in fiber-reinforced composites can affect the other mechanical properties, therefore, the aim of this work is to investigate the effect of multiwall carbon nanotube (MWCNT) on the interfacial bond strength, flexural strength and stiffness, toughness and damping properties of hybridized glass-fiber reinforced epoxy (GFRE) composites. Nanophased epoxy resin was used to hybridize unidirectional and quasi-isotropic GFRE composites with [0/±45/90]_s and [90/±45/0]_s stacking sequences. Results from the interfacial characterizations of the hybridized composites showed improvement up to 30% compared to the control laminates. Hybridization of GFRE laminates with MWCNTs leads to decreasing the flexural and storage moduli, increasing flexural strength, toughness, natural frequencies and damping ratio. A high correlation coefficient of 0.9985 was obtained between static flexural and dynamic storage moduli. The highest flexural strength, flexural and storage moduli and natural frequency of quasi-isotropic laminate were observed for [0/±45/90]_s stacking sequence and vice versa for damping ratio.     

Post fire behavior of carbon fibers Polyphenylene Sulfide- and epoxy-based laminates for aeronautical applications: A comparative study

Through the comparison of two carbon fiber-reinforced polymers (Epoxy and Polyphenylene Sulfide – PPS), this work was aimed at investigating the influence of different fire conditions on the high temperature tensile mechanical behavior. In order to better understand the influence of matrix nature on post-fire properties, the fiber – or matrix-dominated mechanical responses of laminates have been investigated by means of quasi-isotropic or angle-ply stacking sequences. Compared to carbon/PPS laminates, the mechanical properties of carbon/Epoxy laminates are higher in the virgin state (no prior fire exposure). The analysis of the post fire tensile properties shows that prior severe fire exposures are more detrimental to carbon/Epoxy than to carbon/PPS laminates. Although the PPS matrix behavior is highly ductile at a test temperature higher than glass transition temperature, it clearly appears that the decrease in the tensile properties laminates of PPS-based composites is much slower than the one observed in carbon/Epoxy laminates subjected to severe prior fire conditions. Provided the heat flux is high enough to lead to the outset of pyrolysis, PPS-based composites yield higher amounts of char, whose formation retains the structural integrity of fire-damaged composites.     

Experimental investigation of carbon fiber reinforced poly(phenylene sulfide) composites prepared using a double-belt press

The high-performance carbon fiber reinforced poly(phenylene sulfide) composites were continuously fabricated using thermoplastic prepregs in a double-belt press. The effects of process velocity on the composite consolidation quality and mechanical properties were investigated. It is found that the tensile and interlaminar shear properties of composites prepared using the double-belt press are comparable to that of compression-molded composites when the process velocity is no more than 0.20 m·min⁻¹. The composite fracture morphologies also show different failure mechanisms between different samples and indicate that the interfacial adhesion strength may play a vital role in the mechanical properties of CF/PPS composites. Furthermore, experimental results show that the heating time above 330 °C should be over 440 s and the void content should be lower than 2.38% in order to obtain high performance CF/PPS composites.     

Investigation of structure,mechanical and tribological properties of short carbon fiber reinforced UHMWPE-matrix composites

Structural, mechanical and tribological properties of composite materials based on ultra-high molecular weight polyethylene reinforced with carbon fibers were investigated. The effect of surface modification of carbon fibers on the interaction at the fiber–matrix interface in UHMWPE based composites was studied. It was found that the thermal oxidation of carbon fibers by air oxygen at 500 °C can significantly enhance the interfacial interaction between the polymer matrix and carbon fibers. This allowed us to form composite materials with improved mechanical and tribological properties.     

Diketopyrrolopyrrole (DPP)‐Based Donor–Acceptor Polymers for Selective Dispersion of Large‐Diameter Semiconducting Carbon Nanotubes

Low‐bandgap diketopyrrolopyrrole (DPP)‐based polymers are used for the selective dispersion of semiconducting single‐walled carbon nanotubes (s‐SWCNTs). Through rational molecular design to tune the polymer–SWCNT interactions, highly selective dispersions of s‐SWCNTs with diameters mainly around 1.5 nm are achieved. The influences of the polymer alkyl side‐chain substitution (i.e., branched vs linear side chains) on the dispersing yield and selectivity of s‐SWCNTs are investigated. Introducing linear alkyl side chains allows increased polymer–SWCNT interactions through close π–π stacking and improved C–H–π interactions. This work demonstrates that polymer side‐chain engineering is an effective method to modulate the polymer–SWCNT interactions and thereby affecting both critical parameters in dispersing yield and selectivity. Using these sorted s‐SWCNTs, high‐performance SWCNT network thin‐film transistors are fabricated. The solution‐deposited s‐SWCNT transistors yield simultaneously high mobilities of 41.2 cm² V^?1 s^?1 and high on/off ratios of greater than 10⁴. In summary, low‐bandgap DPP donor–acceptor polymers are a promising class of polymers for selective dispersion of large‐diameter s‐SWCNTs.     

Processing dependent morphology, interfacial interaction and shear behavior of short carbon fiber reinforced PEEK

Shear properties of compression-molded discontinuous AS4 carbon fiber reinforced poly(ether ether ketone) composites are evaluated with Iosipescu tests. It is found that both shear modulus and shear strength strongly depend on the molding conditions. A comparison between shear behavior of the composites and composites morphology reveals that fusion of the composite pellets and fiber/matrix interfacial interaction on molecular scale are the two dominant factors which determine the processing dependent shear properties of the materials studied.     

Fabrication and characterization of Al-matrix composites reinforced with amino-functionalized carbon nanotubes

We report the fabrication of Al-matrix composites reinforced with amino-functionalized carbon nanotubes (fCNTs) using powder metallurgy process. Functionalization of the nanotubes was carried out by ball milling multiwalled carbon nanotubes (MWCNTs) in the presence of ammonium bicarbonate. It has been found that the mechanical properties of Al-fCNT composites were much superior to the composites fabricated using non-functionalized or acid functionalized carbon nanotubes. The enhancement in mechanical properties in these composites are attributed mainly to the better and homogeneous dispersion of fCNT in Al matrix as compared to non-functionalized or acid functionalized carbon nanotubes and the formation of a strong interfacial bonding between fCNT and Al matrix leading to an efficient load transfer from Al matrix to fCNT following high-resolution transmission electron microscopy.     

The incorporation of single-walled carbon nanotubes into polymerized high internal phase emulsions to create conductive foams with a low percolation threshold

New methods for the incorporation of single-walled carbon nanotubes (SWCNTs) into styrene-divinylbenzene-based high internal phase emulsions (HIPEs) are addressed with specific attention to minimizing the SWCNT loading while maintaining a high level of conductivity of the final polyHIPE–SWCNT composites. Stable HIPEs were achieved using sodium dodecyl sulfate-stabilized SWCNTs, thus eliminating the necessity of SWCNT functionalization. PolyHIPE–SWCNT composites were made with water: oil ratios (vol/vol) of 75:25 and of 84:16. The percolation threshold was determined to be 0.2 and 0.1 wt%, respectively. These threshold values are lower than that obtained for non-porous, polystyrene–SWCNT composites made by means of a latex-based route followed by melt-processing.     

CF/Epoxy复合材料的界面自组装

提出了一种新的炭纤维表面改性方法——分子自组装, 即在表面金属化的炭纤维上进行有机分子的自组装。表面增强拉曼散射光谱 (SERS)分析证实了含氮或含硫的芳杂环化合物化学吸附在银的表面, 并形成了平躺取向的自组装膜结构。X射线光电子能谱 (XPS)测试进一步证实了自组装膜通过S或N原子和Ag形成配位共价键吸附在炭纤维表面。表面经组装改性后的炭纤维和环氧复合后界面粘结强度得到了不同程度的提高, 揭示了界面区域微观结构与性能的关系。      

The effect of molecular weight on the interfacial properties of GF/PP injection molded composites

It is well established that the molecular weight of recycled PP decreases significantly as compared to the virgin material. Hence this study involved 2 PP grades of different molecular weights in order to simulate the recycling process. The effect of weight–average molecular weight on interfacial adhesion between GF and PP was investigated. Tensile test was done and the fiber length distribution around the fracture zone in both composites was compared with the distributions from similar locations of unstressed composites. The effect of PP-grafted maleic anhydride coupling agent was also studied. It was found that a decrease in weight–average molecular weight of PP improved interfacial adhesive strength between GF/PP. The lower molecular weight matrix has a lower viscosity that enables its molecules to penetrate easily into the silane interphase. In that case, the interfacial area that is available for coupling is higher, leading to a more effective coupling. The higher interfacial shear strength between the glass fiber and the lower molecular weight matrix induced more breakage of the glass fiber during tensile test.     

Poly(phenylene sulphide) and poly(ether ether ketone) composites reinforced with single-walled carbon nanotube buckypaper: I – Structure,thermal stability and crystallization behaviour

Single-walled carbon nanotube (SWCNT) buckypaper (BP) reinforced-poly(phenylene sulphide) (PPS) and poly(ether ether ketone) (PEEK) composite laminates were manufactured through hot-press processing. Scanning and transmission electron microscopies were used for morphological characterization and qualitative evaluation of the impregnation degree of the BP. The thermal stability, resin and void content of the composites were evaluated through thermogravimetric analysis; a strong increase in the degradation temperatures of the polymers was found. Raman spectra revealed the existence of strong filler–matrix interactions. The glass transition temperature, crystallization and melting behaviour of the composites were investigated through differential scanning calorimetry and their crystalline structure was analyzed by wide angle X-ray diffraction. This investigation confirms that SWCNT-BPs can be used to fabricate high-loading CNT/thermoplastic composites with improved thermal properties.