Fibre reinforced nanocomposites: Mechanical properties of PA6/clay and glass fibre/PA6/clay nanocomposites

In this paper, the effect of two different reinforcements: clay at the nanoscale and glass fibres at the micro-scale, on the mechanical properties of PA/clay and GF/PA/clay are studied. The Halpin-Tsai model is used to predict the modulus of PA/Clay and GF/PA/Clay, both of which are influenced by two factors: reinforcement shape and volume fraction. The relationships between the modulus and reinforcement shape and volume fraction are discussed. Tensile modulus, measured in tensile tests is used to fit the Halpin-Tsai models. The results demonstrate a synergy between the reinforcements at the two different scales.     

Polyurethane/clay nanocomposites foams: processing, structure and properties

Polyurethane (PU)/montmorillonite (MMT) nanocomposites were synthesized with organically modified layered silicates (organoclays) by in situ polymerization and foams were prepared by a batch process. Clay dispersion of polyurethane nanocomposites was investigated by X-ray diffraction and transmission electron microscopy. The morphology and properties of PU nanocomposites and foams greatly depend on the functional groups of the organic modifiers, synthesis procedure, and molecular weight of polyols because of the chemical reactions and physical interactions involved. Silicate layers of organoclay can be exfoliated in the PU matrix by adding hydroxyl and organotin functional groups on the clay surface. The presence of clay results in an increase in cell density and a reduction of cell size compared to pure PU foam. In the polyurethane with high molecular weight polyol, a 6 °C increase in T_g, 650% increase in reduced compressive strength, and 780% increase in reduced modulus were observed with the addition of 5% organically treated clays. Opposite effects were observed in PU nanocomposite foams with highly crosslinked structure. The interference of the H-bond in the presence of clay is probably the reason.     

Effect of electron beam irradiation on mechanical and dielectric properties of polypropylene films

In the present investigation the effect of electron beam irradiation on the mechanical properties of thin films of Polypropylene (PP) were measured. The dielectric properties of PP films were carried out in the frequency range from 20 Hz to 1 MHz at various DC bias potential. All measurements were carried out at room temperature. It is found that the electron beam irradiation caused an increase in Young's Modulus of PP film dose of up to 70 kGy were applied, but tensile strength and % elongation at break were found to be decrease with the increasing dose rate. The significant changes were observed in the case of dielectric constant and dielectric loss for electron irradiated PP films. The DSC results indicate that irradiation on PP films changes the thermal behavior. Minor differences in FTIR spectra were observed after irradiation treatment. It is observed that, the effect of radiation damage results in improvement in mechanical strength of the films. The increased dielectric constant and dependence of the bias voltage in case of irradiated and unirradiated PP films has been reported. It is suggested that, the PP films modified with the electron beam irradiation can be used as a good dielectric material for different electronic devices. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and mechanical properties of isotactic polypropylene and iPP/talc blends functionalized by electron beam irradiation

The structure and mechanical properties of isotactic polypropylene (iPP) functionalized by electron beam irradiation are investigated by differential scanning calorimetry, wide‐angle X‐ray diffraction, thermogravimetry, thermomechanical analysis, melt index and mechanical measurements. The experimental results show that the degree of crystallinity, the thermal degradation temperature and the dimensional stability increase with dose in the range 0–5 kGy. At 5 kGy, the initial and final degradation temperatures of the irradiated iPP are raised by 66 °C and 124 °C, respectively. The melt index increases with increasing dose. The mechanical measurements show that the stiffness of iPP is greatly enhanced by electron beam irradiation. A small dose of irradiation (0.75 kGy) can increase the Young's modulus to 1284 MPa compared with 1112 MPa for unirradiated iPP. Adding 10 % by weight of irradiated iPP powder into iPP/talc (70/20 % by weight) blends, changes the processing parameters significantly and makes the Young's modulus rise substantially. At a dose of 40 kGy the Young's modulus of iPP/talc blend jumps to 3611 MPa against the original 2201 MPa. © 2000 Society of Chemical Industry     

Thermal,mechanical, and corrosion resistance properties of vinyl ester/clay nanocomposites for the matrix of carbon fiber‐reinforced composites exposed to electron beam

Vinyl ester/clay nanocomposites with 1, 3, and 5% nanoclay contents were prepared. X‐ray diffractography patterns and Scanning Electron micrographs showed that nanocomposites with the exfoliated structure were formed. Thermogravimetric analysis, water absorption test, and Tafel polarization method, respectively, revealed the improvements in thermal resistance, water barrier properties, and corrosion resistance properties of the samples with an increase in the amount of the incorporated nanoclay. Tensile tests showed that nanoclay also enhanced the mechanical properties of the polymer, so that the tensile strength of the samples with 5% nanoclay was more than 3 times higher than tensile strength of pure vinyl ester samples. Overall, the best properties were observed for the samples containing 5% nanoclay. Pure vinyl ester and nanocomposite with 5% nanoclay content were exposed to the electron beam radiation and their mechanical properties improved up to 500 kGy irradiation dose. Finally, pure vinyl ester and vinyl ester/nanoclay (5%) matrixes were reinforced with carbon fiber and the effect of electron beam irradiation on their mechanical properties was examined. The tensile strength and the modulus of the samples initially increased after exposure to the radiation doses up to 500 kGy and then a decrease was observed as the irradiation dose rose to 1000 kGy. Moreover, nanoclay moderated the effect of the irradiation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42393.     

电子束辐射接枝对PAN基碳纤维的表面改性

采用电子束加速器辐射接枝方法对聚丙烯腈(PAN)基碳纤维进行表面改性,研究了接枝单体种类对接枝率及其环氧树脂基复合材料力学性能的影响,分析了辐射接枝前后PAN基碳纤维的表面形貌与化学结构以及其复合材料界面断口的形貌变化。结果表明:电子束辐射接枝改性的PAN基碳纤维表面粗糙度增加,表面活性官能团增多,与树脂的机械锲合作用增强,其树脂基复合材料断口表而较为平整;乙二胺/水溶液体系是辐射接枝改性的理想溶液,在200 kGy的电子束辐射下,PAN基碳纤维表面的接枝率为6.66%,复合材料的层间剪切强度提高了45.1%。     

Effect of controlled electron beam irradiation on the rheological properties of nanosilica‐filled LDPE‐EVA based thermoplastic elastomer

The effect of controlled electron beam irradiation on the rheological properties of a model LDPE‐EVA thermoplastic elastomer (TPE) system filled with silica nanoparticles is explored in this article. The pristine silica particles were mixed with LDPE‐EVA system in molten condition by varying the sequence of addition and amount of nanosilica. In one composition, Si69 was used to improve the state of dispersion of nanosilica. The rheological behavior of irradiated TPE systems is influenced remarkably by irradiation dose, loadings of silica, variation of sequence, and addition of Si69. All filled TPE systems register an increase in elastic response with increasing frequency and with increase in irradiation dose. Upon irradiation, melt viscosity increases when compared with the unirradiated samples because of the crosslinking effect and improvements in interfacial bonding. The viscoelastic response varies markedly with the temperature. The radiation sensitizing effect of silica is reflected from the rheological data. The dynamic and steady shear rheological properties do not follow a simple correlation. Finally, the rheological behavior is correlated with the morphology of the irradiated systems processed at various shear rates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dynamic mechanical properties of electron beam modified fluorocarbon rubber

The dynamic mechanical properties of electron beam modified fluorocarbon rubbers (terpolymer: F content, 68% and H, 1.4%; copolymer: F content, 65% and H, 1.9%) were studied. With an increase in the radiation dose, the loss tangent maximum decreases and the glass transition temperature increases. The influence of the polyfunctional vinyl monomer, trimethylolpropane triacrylate (TMPTA), is to decrease the loss tangent value, especially at higher doses. At a particular level of the multifunctional monomers tripropylene glycol diacrylate (TPGDA), TMPTA, and tetramethylolmethane tetracrylate, the dynamic mechanical thermal analysis indicated the lowest degree of crosslinking for the system based on TPGDA. MgO-based systems register a decrease of the loss tangent peak height and an increase in the storage moduli compared to the control rubber. The results are explained on the basis of gel fraction, scission reactions, and structural changes as measured with the help of IR-attenuated total reflectance spectroscopy. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2079–2087, 1998     

Magnetically processed carbon nanotube/epoxy nanocomposites: Morphology, thermal, and mechanical properties

The processing-structure-property relationships of multiwalled carbon nanotubes (MWNTs)/epoxy nanocomposites processed with a magnetic field have been studied. Samples were prepared by dispersing the nanotube in the epoxy and curing under an applied magnetic field. The nanocomposite morphology was characterized with Raman spectroscopy and wide angle X-ray scattering, and correlated with thermo-mechanical properties. The modulus parallel to the alignment direction, as measured by dynamic mechanical analysis, showed significant anisotropy, with a 72% increase over the neat resin, and a 24% increase over the sample tested perpendicular to the alignment direction. A modest enhancement in the coefficient of thermal expansion (CTE) parallel to the alignment direction was also observed. These enhancements were achieved even though the nanotubes were not fully aligned, as determined by Raman spectroscopy. The partial nanotube alignment is attributed to resin a gel time that is faster than the nanotube orientation dynamics. Thermal conductivity results are also presented.     

Effect of interfacial interaction on the mechanical properties of electron beam irradiated HDPE/STC blend

Some oxygen‐containing groups (mainly C?O group) are introduced on the molecular chain of HDPE during electron beam irradiation in air. The affinity between HDPE and sericite–tridymite–cristobabite (STC), the dispersion of STC in HDPE matrix are improved owing to the polar groups introduced. By treating STC with amino‐containing silane coupling agent, the interfacial adhesion between irradiated HDPE (e‐HDPE) and treated STC (t‐STC) is further improved, the mechanical properties of e‐HDPE/t‐STC blend are improved quite a lot. The experimental results show that due to the improvement of interfacial interaction, the interfacial phase can transmit the stress subjected to the HDPE matrix and make the matrix absorb energy by plastic yield or deformation; the impact strength of e‐HDPE/t‐STC blend is thus improved. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 814–820, 2002; DOI 10.1002/app.10345     

碳纤维增强水泥/混凝土材料力学性能的若干研究

本文通过对水泥基体掺入碳纤维进行研究，得出了复合体抗压强度、劈拉强度与碳纤维掺量的关系。同时文中还利用聚丙烯腈纤维作对比研究，得出目前碳纤维作为增强体的优缺点，为碳纤维增强水泥基复合材料的推广应用提供更多的实验依据。     

Synthesis of chain-extended organifier and properties of polyurethane/clay nanocomposites

Clay organifier with hydroxyl end-group and relatively high molecular weight was synthesized. The clay treated with the organifier was suspended in DMF and the dispersibility of organoclay in polyurethane matrix was enhanced by applying the sonication to the suspension of organoclay in DMF. The d-spacing of organoclay was found to be 2.29 nm compared to 1.18 nm of pristine montmorillonite. The polyurethane/clay nanocomposites formed an intercalated structure with some disorder and their d-spacings were about 2.6-2.7 nm. The barrier property, thermal stability and tensile properties significantly increased with increasing the dispersibility of organoclay. A 2.9-fold increase in tensile strength with 1 wt% of well-dispersed organoclay, a 41% decrease in oxygen permeability and a 1.7-fold increase in Young's modulus at 5 wt% of well-dispersed organoclay were achieved.     

A new model for estimation of the thermal conductivity of polymer/clay nanocomposites

High density polyethylene– and polypropylene–clay nanocomposites are synthesized by melt blending, in which polyethylene glycol and polypropylene glycol are used as compatibilizers to increase the space of galleries. The morphology properties of nanocomposites are explored by X‐ray diffraction and transition electron microscopy. The thermal conductivity coefficient (K) of nanocomposites is also measured along with the thermal stability. A conventional model based on developed Maxwell‐Garnett formula is also established to predict the thermal conductivity of polymer/clay nanocomposites with clay loading. Morphology results indicate that two intercalated and exfoliated structures are formed. The established model satisfactorily predicts the K values of nanocomposites for low range of clay content. Thermogravimetric analysis shows remarkable thermal stability of nanocomposites with 10 wt % of clay content. The deviation of our model from experimental result for 10 wt % of clay can be attributed to the intercalated structure of layered silicates into the matrices. Although the K values do not considerably increase in 5 wt % with respect to the increase occurs for 10 wt % of clay, but it increases about 28 and 37% at 50°C for high density polyethylene– and polypropylene–clay nanocomposites, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of crosslinked chitosan by electron beam irradiation in the presence of CCl4

In this article, we report the synthesis of crosslinked chitosan using 8 MeV electron beam (EB) irradiation in the presence of carbon tetrachloride. The crosslinked chitosan is characterized by dissolution, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning colorimetry (DSC), and nanoindentation studies. The insolubility of irradiated films in acetic acid indicates that chitosan has undergone crosslinking reaction. FTIR analysis also confirms the crosslinked structure of chitosan. Mechanical properties such as elastic modulus and hardness are calculated from the nanoindentation data. Modulus and hardness of chitosan increase with increase in the irradiation dose due to the increase in the crosslinking. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization,mechanical, and thermal properties of gamma irradiated starch films reinforced with mineral clay

Composite fabricated from starch and different concentrations of clay was prepared by solution casting method. The casted film was irradiated to different gamma irradiation doses 10, 20, 30, and 40 kGy. The dispersion of clay into starch was investigated by using X‐ray diffraction (XRD). The structural morphology of the composite was measured by scanning electron microscope and infrared spectroscopy. Film properties, such as water vapor transmission, mechanical, and thermal properties were also measured. The gel content and swelling behavior of the starch/clay composite were investigated. It was found that the gel content increases with increasing clay content and irradiation dose. The results obtained indicate that the starch/clay composite showed an increase in the tensile strength, thermal stability. Moreover, there is a decrease in water vapor transmission (WVRT) which improves its barrier properties. Both XRD and infrared spectroscopy showed that starch can be intercalated into the clay galleries. Also antibiotic drug Chlortetracycline HCl was loaded into the starch/clay composite by direct adsorption method. Chlortetracycline HCl adsorption capacity of composite was found to increase from 1.13 to 4.20 mg Chlortetracycline HCl per gram dry film with increasing amount of drug concentration. In vitro drug release studies in different buffer solutions showed that the basic parameters affecting the drug release behavior of the film are pH of the solution, drug concentration, and time. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of electron beam irradiation on mechanical properties of high density polyethylene and its blends with sericite‐tridymite‐cristobalite

Some oxygen containing groups (mainly the CO group) are formed on the molecular chain of high density polyethylene (HDPE) during electron beam irradiation in air. The affinity between HDPE and sericite‐tridymite‐cristobalite (STC), the dispersion of STC in the HDPE matrix, and the mechanical properties of the HDPE/STC blend are improved quite a lot by the introduction of polar groups. Compared with HDPE, the tensile and impact strength of electron beam irradiated HDPE (30 kGy)/STC (60/40) are increased to 29.0 MPa and 518 J/m, respectively, from 24.5 MPa and 215 J/m; the tensile and impact strength of irradiated HDPE (30 kGy)/STC (50/50) are 31.1 MPa and 424 J/m, respectively. The Ceast impact test showed that the increase of impact strength was mainly due to the strong interfacial adhesion between irradiated HDPE and STC, thus preventing the spreading of cracks over wide areas. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 243–249, 2000     

Curing green fibres infusible by electron beam irradiation for the preparation of SiBNC ceramic fibres

Curing green fibres infusible is an essential procedure for the preparation of SiBNC ceramic fibres. Previously, green fibres had been fabricated by one-pot synthesis of polyborosilazane (PBSZ) and melt-spinning. In this paper, we attempted to use the method of electron beam irradiation to crosslink green fibres. The variation of molecular structures from green fibres to cured fibres and the properties of sintered SiBNC fibres were investigated. Via electron beam irradiation, the free radicals are formed at the C atoms and Si atoms on the -N-SiH(CH₃)- main chain units and terminal -Si(CH₃)₃ groups. The radicals react with each other to produce cross-linking, coupling and grafting among PBSZ chains, which all contribute to improvement of the cross-linking density of green fibres. The cured fibres performed a high ceramic yield of 80.4 wt%. After pyrolysis at 1500 °C, SiBNC ceramic fibres were acquired, which exhibited a good flexibility with 12 µm in diameter and 1.22 GPa in tensile strength. The obtained fibres could remain amorphous up to 1700 °C and showed no mass loss at this temperature.     

Structure and morphology of isotactic polypropylene functionalized by electron beam irradiation

The structure and morphology of isotactic polypropylene (iPP), functionalized by electron beam irradiation at room temperature in air, are investigated by elementary analysis, FT‐infrared (FTIR) spectroscopy, electron spectroscopy for chemical analysis (ESCA), polariscope, and static contact angle. Elementary analysis reveals that the element oxygen has been introduced onto iPP chains after electron beam irradiation. In addition, as shown from FTIR spectra, oxygen‐containing groups, such as carbonyl, carboxyl, and ether groups, are introduced onto iPP molecular chains. The dependence of oxygenation extent (as measured by O_1S/C_1S value of ESCA spectra) on electron beam dose is obtained. Under polariscope, it can be observed that the dominant alpha phase appears to become more enhanced, and there is no crystalline phase transition. The static contact angle of iPP decreases with increasing dose. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 75–82, 2000     

Effect of electron beam irradiation on polyacrylonitrile precursor fibers and stabilization process

The electron beam was imposed on the polyacrylonitrile precursor fibers before the fibers were stabilized. The effect of electron beam irradiation on the chemical structure, transverse section, and surface morphology and thermal properties of the fibers in the process of stabilization was characterized by the use of Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and differential scanning calorimeter, respectively. A parameter η = I(C?N)/[I(C?N) + I(C?N)] was defined to evaluate the extent of cyclization in the stabilization process. The kinetic parameters, viz. activation energy (E) and pre‐exponential factor (A) of the stabilization reactions, were calculated by Kissinger method. FTIR analysis indicated that the cyclization of nitrile groups was initiated at room temperature by electron beam irradiation. The transformation of C?N groups to C?N ones was accelerated in the process of stabilization. The extent of cyclization of the stabilized fibers was increased. SEM analysis indicated that irradiation could also decrease the internal and surface defects of the stabilized fibers treated at 300°C. The activation energy of cyclization reaction was reduced from 302 to 280 kJ/mol and 260 kJ/mol through 100 and 200 kGy electron beam irradiation, respectively. The reaction temperature range was expanded, and the exothermic rate was slowed down in the process of stabilization, which was the reason why the stabilized fibers have improved cyclization degree and less internal defects. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Physico-chemical,thermal, and mechanical properties of PLA-nHA nanocomposites: Effect of glass fiber reinforcement

In this study, tri-layered composites were prepared by reinforcing poly-lactic acid (PLA) nano-hydroxyapatite (n-HA) (1 and 5 wt%) and 20 mol% continuous phosphate glass fibers (PGF). Initially, the effect of addition of 1 and 5% n-HA on the structural, thermal, mechanical, and thermo-mechanical properties of 100% PLA was investigated. With 5 wt% n-HA addition the tensile modulus (TM), flexural modulus (FM), tensile strength (TS), and flexural strength (FS) of 100% PLA was improve by 14.9, 47.4, 6, and 32.9%, respectively. Whereas, the un-notched impact strength of the nanocomposites suffer 2% deterioration. However, T _g decreased by 0.3°C and T _c increased by 10°C as 5 wt% n-HA was added to 100% PLA. Afterwards, the 5% n-HA/PLA composite were reinforced with 20 mol% continuous PGF and the TM, FM, TS, and FS of the tri-layered composites were 162.6, 412.5, 28.4, and 157.4% higher as compared to 100%PLA. Furthermore, the storage modulus of the 1% n-HA-filled composites was 500 MPa lower than 100%PLA, while 5 wt% n-HA-filled composites showed similar storage modulus as 100% PLA. 5 wt% n-HA-filled composite showed the highest peak of loss modulus which may be attribute to the chain segment of PLA matrix after the incorporation of HA. Thus, n-HA and PGF reinforcement resulted in improved mechanical properties of the composites and have great potential as biodegradable bone fixation device with enhanced load-bearing ability.