Thermoset composites functionalized with carbon nanofiber sheets for EMI shielding

Carbon nanofiber sheets were developed through filtering well‐dispersed carbon nanofiber (CNF) through filtering well‐dispersed aqueous solution of CNF particles with 0.4 μm hydrophilic polycarbonate membrane by the aid of high‐pressure air. They were used to functionalize composites by the resin transfer molding method. Their functionalized composites were characterized with scanning electron microscopy (SEM), four‐point probes and a vector network analyzer to measure their morphologies, electrical conductivity, and electromagnetic interference (EMI) shielding performance over the frequency range of 8–12 GHz (X band), respectively. Their morphologies show that CNF particles are overlapped and tightly connected with each other in their interconnected networks. The CNF sheets are exposed on the surface, although their networks are partially penetrated by polyester resins. Their electrical conductivity can be 3.0 ± 0.2 Scm^?1 or so, much higher by ten orders of magnitude than the reported electrical conductivity of CNF‐filled composites. Their EMI shielding effectiveness slightly varies in a range of ?30 dB to ?35 dB as a function of frequency, much higher than that of most CNF or carbon nanotube–filled composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41873.     

Effect of high‐temperature annealing on the elastoplastic response of isotactic polypropylene in loading–unloading tests

A series of uniaxial tensile loading–unloading tests is performed on isotactic polypropylene at room temperature. Prior to mechanical testing, injection‐molded specimens are annealed for 24 h at temperatures T = 145, 150, 155, 158, 160, 163, and 165°C, which cover the entire region of high‐temperature annealing temperatures. A constitutive model is developed for the elastoplastic behavior of a semicrystalline polymer at small strains. The stress–strain relations are determined by six adjustable parameters that are found by matching observations in cyclic tests. Fair agreement is demonstrated between the experimental data and the results of numerical simulation. It is shown that all material constants are affected by the annealing temperature, which is explained by changes in the crystalline morphology driven by thermal treatment. Some of the adjustable parameters experience finite jumps in the vicinity of the critical temperature T_c = 159°C. These jumps are attributed to the α₂ → α₂′ phase transformation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 186–196, 2003     

Microstructure and shape memory effect of acidic carbon nanotubes reinforced polyvinyl alcohol nanocomposites

Specimens of acidic multi‐walled carbon nanotubes (AMWNTs) reinforced polyvinyl alcohol (PVA) nanocomposites (AMWNTs‐PVA) were prepared using different amounts of AMWNTs by the traditional solution casting, involving ultrasonic wave agitation. The microstructures and tensile properties of AMWNTs‐PVA were investigated by scanning electron microscopy, dynamic mechanical analysis, and quasi‐static tensile testing. AMWNTs had good compatibility with PVA and dispersed evenly in the PVA matrix. The incorporation of AMWNTs improved the tensile modulus and strength of the PVA. The shape recovery testing revealed the shape recovery capacity of AMWNTs‐PVA. It was observed that the recovery ratio increased, and the shape recovery rate slightly decrease with the increase of AMWNTs content. The results showed that the AMWNTs had strong interaction with the segments of the PVA and hence affected the shape recovery behavior of PVA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Libraries of modified polyacrylamides using post‐synthetic modification

Polyacrylamide‐based (PAM) polymers are the most widely used synthetic water‐soluble polymer so they are applied in a range of industries. However, they suffer from a number of limitations which requires the development of synthetic routes that can accurately control polymer structure and hence function. This study describes a carbodiimide mediated coupling reaction (CMC) that is used to generate modified polyacrylamide (PAM) including hydrophobically modified water‐soluble polymers (HMWSP). The reaction proceeds efficiently in water and does not require organic solvents or high temperatures. The approach is flexible due to the efficiency of the CMC reaction allowing for accurate control over polymer structure and function. This is confirmed using acid‐base titration, spectroscopy, viscometry, and rheology. The viscosity of the polymers varies over a broad range with those containing larger hydrophobic group (dodecyl) showing the highest viscosity. The hydrophobicity of the pendent group determines how it influences viscosity and using this new synthetic approach polymer with the same molecular weight can be compared. Linear hydrocarbon pendent groups are more hydrophobic than the cyclic versions resulting in higher viscosity. However, the spatial arrangement of the pendent group (linear or cyclic) also affects the viscosity at higher pendent group contents. The number of modified PAMs that can be generated is expansive because the approach works with a number of different functional groups and base polymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42797.     

Design of a super‐ductile polypropylene/polycarbonate blend with high heat resistance by using reactive plasticizer

High‐performance blend of polypropylene (PP) and polycarbonate (PC) has not been explored. The difficulty is caused by the big differences in melt viscosity (PP: low viscosity vs. PC: high viscosity) and polarity (PP: nonpolar vs. PC: polar). We put forth a new approach using a reactive plasticizer which is preferentially soluble with PC and polymerizable by organic peroxide. As the plasticizer, diallyl phthalate and triallyl cyanurate (TAC) were used. By reactive extrusion of PP/PC/plasticizer/dicumyl peroxide (e.g., 80/14/6/0.12 wt. ratio), reaction‐induced phase decomposition took place in the dispersed PC particles to develop a regularly phase‐separated nanostructure and the graft copolymer of PP and polymerized plasticizer was in situ generated at the interface. The extruded blend showed an excellent ductile behavior with about 500%‐elongation at break. TAC was very effective to elevate the heat resistance. Then, a super‐ductile PP/PC blend with high heat resistance was successfully developed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Interfacial crystallization of low‐crystallinity elastomer incorporated by multi‐walled carbon nanotubes: Mechanical reinforcement,structural evolution and enhanced thermal stability

In this paper, we report interfacial crystallization in olefin block copolymer (OBC) with low crystallinity incorporated by multi‐walled carbon nanotubes (MWCNTs). A hybrid shish‐kebab (HSK) superstructure in nanocomposites is observed that MWCNTs act as central shish and OBC crystals grow perpendicular to the nanotubes axis. The mechanical properties of nanocomposites are significantly improved with incorporation of MWCNTs. The most ideal reinforcing and toughening effect is both observed in nanocomposites with MWCNTs content of 1 wt % that can increase tensile strength by 122% as well as elongation at break by 36%. Efficient load transfer are confirmed with in‐situ Raman spectra that G’ band of MWCNTs in OBC matrix exhibit a downshifting trend and symmetric broadening of line shape which reveals additional macroscale strain from axial extension of MWCNTs in nanocomposites, thus suggesting a certain load is carried by HSK superstructure. The structural evolution of OBC and nanocomposites are investigated by in‐situ wide‐angle X‐Ray Diffraction (WAXD). The Herman's orientation factor of nanocomposites with 2 wt % MWCNTs incorporation is lower than that of neat matrix at mall and intermediate strains, indicating a heterogeneous stress distribution and low compliance of HSK superstructure, which is consistent with in‐situ Raman results. Moreover, the nanocomposites presents significantly enhanced thermal stability. The onset decomposition temperature of nanocomposites with 3 wt % MWCNTs can be 60.2°C higher than that of neat OBC. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42368.     

Surface grafting of carbon fibers with artificial silver‐nanoparticle‐decorated graphene oxide for high‐speed electrical actuation of shape‐memory polymers

Poor heat conduction in the interface between the carbon fiber and polymer matrix is a problem in the actuation of shape‐memory polymer (SMP) composites by Joule heating. In this study, we investigated the effectiveness of grafting silver‐nanoparticle‐decorated graphene oxide (GO) onto carbon fibers to improve the electrothermal properties and Joule‐heating‐activated shape recovery of SMP composites. Self‐assembled GO was grafted onto carbon fibers to enhance the bonding of the carbon fibers with the polymeric matrix via van der Waal's forces and covalent crosslinking, respectively. Silver nanoparticles were further self‐assembled and deposited to decorate the GO assembly, which was used to decrease the thermal dissimilarity and facilitate heat transfer from the carbon fiber to the polymer matrix. The carbon fiber was incorporated with SMP to achieve the shape recovery induced by Joule heating. We found that the silver‐nanoparticle‐decorated GO helped us achieve a more uniform temperature distribution in the SMP composites compared to those without decoration. Furthermore, the shape‐recovery behavior and temperature profile during the Joule heating of the SMP composites were characterized and compared. A unique synergistic effect of the carbon fibers and silver‐nanoparticle‐decorated GO was achieved to enhance the heat transfer and a higher speed of actuation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41673.     

PMMA composites of single‐walled carbon nanotubes‐graft‐PMMA

To facilitate the dispersion of single‐walled carbon nanotubes (SWCNT) into poly(methyl methacrylate) (PMMA), SWCNT were functionalized with a RAFT chain transfer agent, and PMMA was grafted from the SWCNT by reversible addition–fragmentation transfer (RAFT) polymerization to give SWCNT‐g‐PMMA containing 6 wt % PMMA. SWCNT‐g‐PMMA in the form of small bundles was dispersed into PMMA matrices. The SWCNT‐g‐PMMA filler increased the glass transition temperature (T_g) of the composite when the matrix molecular weight M_n was less than the graft molecular weight, but not when the matrix M_n was equal to or greater than the graft M_n. The threshold of electrical conductivity of the composites as a function of weight percent SWCNT increased from 0.2% when matrix M_n was less than graft M_n to about 1% when matrix M_n was greater than graft M_n. Dynamic mechanical analyses of the composites having graft M_n less than or equal to matrix M_n showed broader rubbery plateaus with increased SWCNT content but no significant differences between samples with different grafted PMMAs. The results indicate that lower M_n matrix wets the SWCNT‐g‐PMMA whereas higher M_n matrix does not wet the SWCNT‐g‐PMMA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39884.     

Enhancing particle erosion resistance of glass‐reinforced polymeric composites using carbon nanofiber‐based nanopaper coatings

Sand erosion may cause severe damage of blades in wind turbine and helicopter blades as well as many surface components of airplanes. In this study, thin nanopapers made of carbon nanofibers (CNFs) are used to enhance the resistance of solid particle erosion of glass fiber (GF)/wind epoxy composites. Finite element computer simulations are used to elucidate the underlying mechanisms. The much higher particle erosion resistance of nanopapers compared to GF‐reinforced epoxy composites is attributed to the high strength of CNFs and their nanoscale structure. The excellent performance in particle erosion resistance makes the CNF‐based nanopaper a prospective protective coating material for the turbine blades in the wind energy industry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhanced dielectric properties of polyamide 11/multi‐walled carbon nanotubes composites

Composites with multi‐walled carbon nanotubes (MWNTs) involved in polyamide 11 (PA11) were prepared via a conventional melt blending method. The structure, morphology, crystallization behavior, electrical, and dielectric properties of composites were investigated. The results demonstrated that the dispersed uniformly MWNTs favored the formation of α crystal of PA11 when the composites were quenched from melt. The dielectric constant of composites was dependent on the electric field frequency and MWNTs content, and the highest value of dielectric constant was as high as 350 for the composite with 1.21 vol % MWNTs at 10³ Hz, accompanied by a low dielectric loss. The enhanced dielectric properties could be interpreted by the formation of abundant nanocapacitors within the composites and the interfacial polarization effect resulting from accumulation of charge carriers at the internal interfaces between MWNTs and PA11. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42642.     

Synergistic effects of β‐modification and impact polypropylene copolymer on brittle‐ductile transition of polypropylene random copolymer

In this work, the synergistic effects of β‐modification and impact polypropylene copolymer (IPC) on brittle–ductile (B–D) transition behavior of polypropylene random copolymer (PPR) have been investigated. It is interesting to find that adding both IPC and β‐nucleating agent into PPR has three effects: (i) leading to a significant enhancement in β‐crystallization capability of PPR, (ii) contributing to the shift of B–D transition to lower temperatures, (iii) increasing the B–D transition rate. The reason for these changes can be interpreted from the following two aspects. On one hand, the transition of crystalline structure from α‐form to β‐form reduces the plastic resistance of PPR matrix, thus causing the initiation of matrix shear yielding much easier during the impact process. On the other hand, the well dispersed rubbery phase in IPC with high molecular mobility at relatively low temperatures is beneficial to the shear yielding of PPR matrix and, subsequently, the great improvement in impact toughness of the ternary blends. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal,mechanical, and rheological properties of poly(ε‐caprolactone)/halloysite nanotube nanocomposites

Naturally available halloysite nanotubes (HNTs) with hollow nanotubular structures were used as reinforcement in poly(ε‐caprolactone) (PCL). The PCL/HNT nanocomposites were prepared by melt mixing the polymer with as‐received HNTs up to 10 wt % in an internal batch mixer. Transmission electron microscopy analysis indicated that the HNTs were dispersed uniformly on the nanoscale throughout the PCL matrix. Differential scanning calorimeter studies revealed that the PCL crystallinity was decreased in the nanocomposites, and the HNTs dispersed in the PCL matrix led to an increase in the non‐isothermal crystallization temperature of the PCL. Tensile and dynamic mechanical tests showed great enhancement in strength and stiffness at low HNT content, while still maintaining the ductility of the PCL. The glass transition temperature (T_g) of the pristine PCL was substantially increased with increase in filler loading, which indicates good reinforcing effect imparted by the addition of HNT. Melt rheological studies revealed that the nanocomposites exhibited strong shear thinning behavior, and a percolated network of HNT particles was formed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Surface modification of polyimide fibers by novel alkaline–solvent hydrolysis to form high‐performance fiber‐reinforced composites

We modified polyimide (PI) fibers by a novel hydrolysis approach and fabricated PI‐fiber‐reinforced novolac resin (NR) composites with enhanced mechanical properties. We first used an alkaline–solvent mixture containing potassium hydroxide liquor and dimethylacetamide (DMAc) for the surface modification of the PI fibers. The results indicate that the surface roughness and structure of the PI fibers were controlled by the hydrolysis time and the content of DMAc. With the optimized hydrolysis conditions, the tensile modulus of modified PI fibers improved 15% without compromises in the fracture stress, fracture strain, or thermal stability. The interfacial shear strength between the modified PI fibers and NR increased 57%; this indicated a highly enhanced interfacial adhesion. Finally, the tensile and flexural strengths of the composites increased 72 and 53%, respectively. This research provides an effective method for the surface modification of PI fibers and expands their applications for high‐performance composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46595.     

Segmental dynamics of functional graphene‐filled poly(ether sulfone ether ketone ketone) nanocomposites

The segmental dynamics of functional graphene (fGR)/poly(ether sulfone ether ketone ketone) (PESEKK) nanocomposites were investigated via differential scanning calorimetry and dynamic mechanical analysis (DMA) measurements. First, fGR was prepared using graphene oxide and sodium dodecylbenzene sulfonate. Subsequently, a series of fGR/PESEKK nanocomposites were prepared through solution blend. When the sulfone groups were introduced into the segments of PESEKK polymers, the glass transition temperature (T_g) of PESEKK was higher than that of free sulfone functionalized poly(ether ketone ketone). The fGR/PESEKK nanocomposites displayed a uniform nanostructure because of the strong interfacial interaction between fGR and PESEKK. With the increase in the fGR contents, the T_g values of fGR/PESEKK nanocomposites decreased. Two loss factor peaks were noted in the fGR/PESEKK nanocomposites, which were characterized via DMA. The α′‐relaxation of the nanocomposites at low temperature was assigned to polymer chains close to the polymer/filler interface with mobility higher than that in the bulk unfilled PESEKK (α‐relaxation). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44391.     

Silica supported single‐walled carbon nanotubes as a modifier in polyethylene composites

Composites have been made from single‐wall carbon nanotubes in a polyethylene (PE) matrix, in which different methods of preparation were used to disperse the nanotubes. The study includes using either the refined pure nanotubes (P‐NT) as the source, or the original silica supported nanotubes (SS‐NT). SS‐NT contained nanotubes still incorporated in and around the silica as originally grown. Composites were then made by (1) coprecipitation from a suspension of P‐NT or SS‐NT in a PE solution, or (2) by forming a polymerization catalyst from the SS‐NT, and using it to polymerize ethylene, which ruptures and expands the silica as polymer builds up in the pores. Extrusion was also studied as a method of additional dispersion. Nanotubes were found to have a powerful effect on the melt rheology, increasing the low shear viscosity dramatically. Increasing the nanotube concentration also increased the flexural and tensile moduli, decreased the elongation, and increased the electrical conductivity. Consistent trends were observed from all of these diverse properties: SS‐NT had a stronger effect than P‐NT, and within the SS‐NT group the choice of silica type also had a major effect. Polymerization was generally preferred as the method of dispersing the nanotubes. The conductivity, which in some cases was quite high, was found to be pressure sensitive. Conductive NT/PE composites could be molded into films or extruded into other shapes, or comolded with other PE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Flexural behavior of methyl methacrylate modified unsaturated polyester polymer concrete beams reinforced with glass‐fiber‐reinforced polymer sheets

This study represents the behavior of flexural test of methyl methacrylate modified unsaturated polyester polymer concrete beam reinforced with glass‐fiber‐reinforced polymer (GFRP) sheets. The failure mode, load–deflection, ductility index, and separation load predictions according to the GFRP reinforcement thickness were tested and analyzed. The failure mode was found to occur at the bonded surface of the specimen with 10 layers of GFRP reinforcement. For the load–deflection curve, as the reinforcement thickness of the GFRP sheet increased, the crack load and ultimate load greatly increased, and the ductility index was found to be the highest for the beam with the thickness of the GFRP sheet at 10 layers (6 mm) or 13 layers (7.3 mm). The calculated results of separation load were found to match only the experimental results of the specimens where debonding occurred. The reinforcement effect was found to be most excellent in the polymer concrete with 10 layers of GFRP sheet reinforcement. The appropriate reinforcement ratio for the GFRP concrete beam suggested by this study was a fiber‐reinforced‐plastic cross‐sectional ratio of 0.007–0.008 for a polymer concrete cross‐sectional ratio of 1 (width) : 1.5 (depth). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Elaboration of performance of tea dust–polypropylene composites

In this research work, dynamic, mechanical, and thermophysical properties of untreated and 5, 7, and 10 wt % styrene treated tea dust (TD):polypropylene (PP) composites prepared by injection‐molding machine were elaborated. There were distinctive and significant improvement observed in mechanical properties (tensile strength, tensile modulus, and elongation at break), physical analysis (water swelling), dynamic mechanical properties (storage modulus, loss modulus, and tan δ), and thermal behavior and surface morphological properties of styrene treated TD:PP (40:60) composites as compared to that of untreated one. The tensile strength (from 7.00 to 9.95 MPa), tensile modulus (from 350 to 715 MPa), storage modulus (from 8500 to ～10,500 MPa), and loss modulus (from ～150 to ～200 MPa) increased on 10 wt % styrene treatment of TD over the untreated TD:PP (40:60) composites. The styrene treated TD:PP (40:60) composites behaved as more elastic than their pure counterpart. Styrene treated TD:PP (40:60) composites were more thermally more stable (85 °C difference) as compared to virgin PP. Overall, this research also indicates the use of TD waste. An improvement in dispersion of styrene treated TD particles in PP was also observed in the preparation of the PP composites due to good compatibility of styrene with PP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44750.     

Electromagnetic interference shielding effectiveness of graphite‐filled polypropylene and poly(ether imide) based composites

The electromagnetic interference shielding characteristics of polypropylene (PP) and poly(ether imide) (PEI) filled with synthetic graphite composites were studied. The thermal properties were characterized by differential scanning calorimetry and thermogravimetric analysis, whereas the morphologies of the composites were studied by scanning electron microscopy. The viscosity measurements were studied by advance rheometry. The measurements of shielding effectiveness (SE) were carried out in the frequency range 8–12 GHz (X‐band range). The return loss and loss due to absorption were also measured as a function of frequency in the X‐band range. It was observed that the SE of the composites was frequency dependent, and it increased with increasing frequency. The SE also increased with increasing filler loading. The PEI‐based composites showed a higher SE compared to that of the PP‐based composites. The correlation between SE and the conductivity of the various composites is also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nitroxide polymer brushes as efficient and recoverable catalysts for the selective oxidation of primary alcohols to aldehydes

2,2,6,6‐Tetramethylpiperidinyloxyl (TEMPO)‐containing polymer brushes were grafted onto crosslinked polystyrene microspheres via surface‐initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) of 2,2,6,6‐tetramethyl‐4‐piperidyl methacrylate, followed by an oxidation process with 3‐chloroperoxybenzoic acid as oxidant. The synthesized nitroxide polymer brushes included homopolymer brushes, block copolymer brushes, and random copolymer brushes with various TEMPO contents and molecular weights. They were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. These nitroxide brushes bearing high TEMPO contents were used as recoverable catalysts for the hypochlorite and aerobic oxidation of primary alcohols to aldehydes. The effects of polymer brush structure on the catalytic properties were studied and discussed. The results showed that these nitroxide polymer brushes had excellent catalytic properties and good recycling performances. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44365.