Effects of plasma treatment of carbon fibers on interfacial properties of BMI resin composites

High performance continuous fiber surface modification by inductively coupled RF plasma (ICP) and dielectric barrier discharge (DBD) low temperature plasma were conducted. X-ray photoelectron spectroscopy (XPS) and other analytical testing methods systematically studied plasma treatment time, discharge power, discharge pressure, etc, on fiber surface state, surface composition, and surface shape changes in the appearance and wetting properties. The results show that after plasma treatment the surface of the fiber is grafted with a large number of polar functional groups such as carboxyl groups and hydroxyl groups. The surface roughness increases, the surface free energy increases, and the fiber wetting property is significantly improved, resulting in improvement in interlaminar shear strength (ILSS) between the fiber and the resin matrix. Finally, the surfaces of the fibers and its relationship with interfacial properties of fiber reinforced bismaleimide composites are also discussed.     

Study of nanocarbon black as synergist on improving flame retardancy of ethylene-vinyl acetate/brucite composites

Nanocarbon black (CB) was introduced into ethylene-vinyl acetate/brucite (EM) composites to investigate the synergistic effect of CB and metal hydroxide on improving the flame retardancy of EVA. Flammability properties of the as-prepared EVA composites were investigated by thermogravimetric analysis, limiting oxygen index (LOI), UL-94 test and cone calorimetry test. The results indicated that the optimum mass ratio of CB/brucite was 1/54, at which the EVA composites displayed dramatic improvement on thermal stability and flame retardancy. The LOI value was as high as 35.3%, the UL-94 passed the V-0 rating, and the peak heat release rate reduced 79% in comparison with pure EVA. Based on the morphology and structure analysis for residue chars, the flame-retardant mechanism was attributed mainly to the positive synergistic effect of CB and brucite on promoting the formation of better carbon protective layer during combustion.

     

Thermal and mechanical characteristics of polyurethane/curaua fiber composites

Polyurethane composites reinforced with curaua fiber at 5, 10 and 20% mass/mass proportions were prepared by using the conventional melt-mixing method. The influence of curaua fibers on the thermal behavior and polymer cohesiveness in polyurethane matrix was evaluated by dynamic mechanical thermal analysis (DMTA) and by differential scanning calorimetry (DSC). This specific interaction between the fibers and the hard segment domain was influenced by the behavior of the storage modulus E′ and the loss modulus E″ curves. The polyurethane PU80 is much stiffer and resistant than the other composites at low temperatures up to 70°C. All samples were thermoplastic and presented a rubbery plateau over a wide temperature range above the glass transition temperature and a thermoplastic flow around 170°C.     

Effect of fluid-phase equilibria on ethylene-vinyl acetate copolymer composition

Literature reports indicate that in the copolymerization of ethylene with vinyl acetate, the reactivity ratios change with pressure. There is general agreement that r_eth ? r_vac ? 1 at high pressure, but deviations reportedly occur at low pressure. It is shown here that this “pressure dependence” in fact arises from a failure to recognize adequately the importance of fluid-phase equilibria in the ethylene–solvent system. In order to delineate the two-phase region, the ethylene–benzene critical locus was measured from the ethylene critical point to 125°C. It was found that the maximum pressure was at about 1700 psia. Above the critical locus the two components are miscible in all proportions, forming a single homogeneous phase. As predicted by phase rule considerations, ethylene-vinyl acetate copolymers prepared at constant temperature and pressure below the critical locus had fixed compositions. Copolymerizations conducted above the critical locus were not similarly constrained, and polymer compositions varied with operating procedure. This phenomenon is best understood in light of degrees of freedom afforded by the fluid phase equilibria. In either fluid regime the reactivity ratios are shown to be unity and independent of pressure. This was demonstrated at pressures as low as 50 atm.     

Microfibrillated cellulose/cellulose acetate composites: Effect of surface treatment

Microfibrillated cellulose (MFC), which consists of a web‐like array of cellulose fibrils having a diameter in the range of 10–100 nm, was incorporated into a cellulose acetate (CA) matrix to form a totally biobased structural composite. Untreated and a 3‐aminopropyltriethoxysilane (APS) surface treated MFC was combined with a CA matrix by film casting from an acetone suspension. The effectiveness of the surface treatment was determined by infrared spectroscopy and X‐ray photoelectron spectroscopy. The Young's moduli of APS treated MFC composite films increase with increasing MFC content from 1.9 GPa for the CA to 4.1 GPa at 7.5 wt % of MFC, which is more than doubled. The tensile strength of the composite film increases to a maximum of 63.5 MPa at 2.5 wt % compared to the CA which has a value of 38 MPa. The thermal stability of composites with treated MFC is also better than the untreated MFC. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 153–161, 2010     

Combustion behavior and thermal stability of ethylene-vinyl acetate composites based on CaCO3-containing oil sludge and carbon black

CaCO₃-containing oil sludge (OS) is a by-product from petroleum industry, with great amount of production. Therefore, an effective processing methods for CaCO₃-containing OS is urgently needed. Herein, ethylene-vinyl acetate (EVA) composites based on CaCO₃-containing OS and carbon black (CB) were prepared by melt blending method. The combustion behavior and thermal stability of flame-retardant EVA/OS/CB composites were investigated by cone calorimeter test, limiting oxygen index (LOI), scanning electron microscopy (SEM), smoke density test (SDT), and thermogravimetry-Fourier infrared spectrometry. The heat release rate and smoke production rate of the ternary composites containing 3% CB significantly decreased compared with the EVA/OS composites and pure EVA. Moreover, addition of a certain amount of CB could evidently increase LOI values. The morphologies and structures of the residues, revealed by SEM, ascertained that a better carbonaceous protective layer was formed on the ternary composites than the EVA/OS composite. It was obtained from SDT that CB in the material could retard the smoke production with the application of the pilot flame. The EVA/OS/CB composites assumed a higher thermal stability than the EVA/OS composites and pure EVA.

     

The interfacial enhancement of LLDPE/whisker composites via interfacial crystallization

Interfacial interaction plays a key role in the preparation of high performance polymer composites. In this work, in order to explore the possibility to enhance the interfacial interaction via interfacial crystallization of polymer matrix onto the filler surface, interfacial crystallization structure and mechanical properties of linear low density polyethylene (LLDPE)/whisker composites were investigated. The composites were firstly prepared by melt compounding, followed by processing in both traditional and dynamic injection molding. DSC, WAXD, SEM were used to characterize the interfacial crystallization structure. And the mechanical properties were measured by tensile testing. An imperfect shish‐calabash structure, with whisker served as shish, and irregular LLDPE spherulite as imperfect calabash, was formed during common injection molding processing. Such a structure was considered as the main reason for the strong interfacial adhesion and the obviously improved tensile strength and modulus. Furthermore, introducing shear could cause the formation of relatively perfect shish‐calabash structure, leading to the stronger interfacial adhesion. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of different compatibilizing agents on the interfacial adhesion properties of polypropylene/magnesium oxysulfate whisker composites

The effects of maleic anhydride-grafted polypropylene(PP-g-MAH) and maleic anhydride-grafted polyolefin elastomer(POE-g-MAH) on interfacial adhesion properties of the polypropylene/magnesium oxysulfate whiskers(PP/MOSw) composites were investigated via mechanical, thermal, ATR-FTIR and rheological tests. Although significant increases in yield strength and Young's modulus were observed in PP-g-MAH treated composites, a sharp decline in these properties was observed in POE-g-MAH treated composites. ATR-FTIR results indicated that esterification occurred between the hydroxyl groups of MOSw and the carbonyls of anhydrides of both compatibilizers but POE-g-MAH was still incompatible with the PP matrix, as verified by the presence of shoulder peaks in DTG curves and numerous voids in SEM micrographs. On the other hand, PP-g-MAH was highly compatible with the PP matrix, as evidenced by the peaks in DTG curves and vague interfaces with wrapped melts on the surface of MOSw. Rheological behaviors also confirmed that introducing PP-g-MAH resulted in a transition from liquid-like to solid-like, which was attributed to the stronger interfacial adhesion between MOSw and the PP matrix. POE-g-MAH treated composites, in contrast to PP-g-MAH, maintained liquidlike rheological behaviors as typical molten polymers. There is likely a MOSw network formed in the PP/15PP-gMAH/15 MOSw composite as suggested by the significant deviation of G′ versus G″ plots and the two crossover frequencies observed in plots of tan? versus frequency.     

Effects of accelerated aging on mechanical,thermal and morphological behavior of polyurethane/epoxy/fiberglass composites

Wind blades, an important application of polymeric composite materials, are subject to natural weathering. This study aims to evaluate mechanical, thermal and morphological behavior during accelerated aging in three thicknesses of epoxy and fiberglass polyurethane-coated composite plates used in wind turbines, in addition to testing with two acoustic emission techniques. An accelerated aging chamber simulated natural weathering mechanisms for 45, 90, 135 and 180 days. This degradation primarily reduced the mechanical properties of the thinner composites, with some damaged specimens exhibiting fiber-matrix debonding. Thermal properties deteriorated. There were no morphological changes on the polyurethane–epoxy interface; however, degradation occurred in the fiber-matrix interface on the surface exposed to radiation. The degree of chalking indicated coating deterioration on the external surface of the polyurethane. The acoustic wave propagation speed and attenuation coefficient measured prior to mechanical testing indicated the presence of damage areas.     

Kinetics and mechanism of formation of adhesive joints based on ethylene-vinyl acetate copolymers

The structure of transient zones in PVC-poly(ethylene-co-vinyl acetate), PET-poly(ethylene-co-vinyl acetate), and steel-poly(ethylene-co-vinyl acetate) adhesion systems is studied. It is shown that PET-poly(ethylene-co-vinyl acetate) and PVC-poly(ethylene-co-vinyl acetate) are related in incompatible and partially compatible systems, respectively. In the temperature range 100?C180°C, diffusion coefficients and the activation energy of diffusion are determined. The depth of penetration of copolymer macromolecules into the PVC phase is calculated. The kinetics of adhesive-joint formation is studied. For all systems, the increase in joint strength has a common character; for each temperature, the steady state is attained. The results are analyzed in terms of wetting and diffusion theories. Both models satisfactorily describe the kinetics of joint formation in compatible and incompatible systems (including steel-poly(ethylene-co-vinyl acetate). The effective activation energy of the kinetics of adhesive-joint formation is determined and compared with the activation energies of diffusion, the viscous flow of copolymers, the ?? transition, and the rate of conformation rearrangements in the surface layers of ethylene-vinyl acetate copolymers. It is suggested that the data obtained can be generalized in terms of the Bikerman theory of a ??weak boundary layer.??     

Effect of chemical treatment of Kevlar fibers on mechanical interfacial properties of composites

In this work, the effects of chemical treatment on Kevlar 29 fibers have been studied in a composite system. The surface characteristics of Kevlar 29 fibers were characterized by pH, acid-base value, X-ray photoelectron spectroscopy (XPS), and FT-IR. The mechanical interfacial properties of the final composites were studied by interlaminar shear strength (ILSS), critical stress intensity factor (K(IC)), and specific fracture energy (G(IC)). Also, impact properties of the composites were investigated in the context of differentiating between initiation and propagation energies and ductile index (DI) along with maximum force and total energy. As a result, it was found that chemical treatment with phosphoric acid solution significantly affected the degree of adhesion at interfaces between fibers and resin matrix, resulting in improved mechanical interfacial strength in the composites. This was probably due to the presence of chemical polar groups on Kevlar surfaces, leading to an increment of interfacial binding force between fibers and matrix in a composite system.     

Effects of the molecular structure of styrene-isoprene block copolymers on the interfacial characteristics of polystyrene/polyisoprene blends

The effects of the molecular structure of the styrene-isoprene block copolymer on the interfacial tension, the morphology and the interfacial adhesion of polystyrene/polyisoprene were investigated. A reduction in interfacial tension is observed with the addition of a small amount of copolymer, followed by a leveling off as the copolymer concentration exceeds the critical micelle concentration. The reduction in interfacial tension between polystyrene and polyisoprene is more significant when the isoprene-rich diblock copolymer is added than the cases when the symmetric or styrene-rich diblock copolymer is added. The interfacial tension data seem to be consistent with the phase morphology and the interfacial adhesion: the lower the interfacial tension, the smaller the domain size of dispersed phase and the better the interfacial adhesion. © 1996 John Wiley & Sons, Inc.     

Effects of surface properties of colloidal silica particles on redispersibility and properties of acrylic-based polyurethane/silica composites

Nanosilica particles with different surface properties were designed and prepared using colloidal silica particles and four different qualitative silane coupling agents (SCA), namely methyltriethoxysilane (MTES), octyltriethoxysilane (OTES), vinyltriethoxysilane (VTES) and methacryloxypropyltrimethoxysilane (MATMS), and further applied in acrylic resins and corresponding polyurethane coats by in situ polymerization. It was found that different qualitative SCA molecules had very different impacts on the redispersibility of nanosilica particles, the adsorbed acrylic polyol molecules, the viscosities of acrylic polyol/silica hybrid resins, and the properties of acrylic-based polyurethane/silica composites.     

Synergistic effects on polyurethane/lead zirconate titanate/carbon black three-phase composites

Synergistic processes in hybrid composites have frequently been described in the literature over the past few years, opening doors to new studies and applications for this type of material. In this study, three-phase composites were obtained using polyurethane (PU) as the matrix, lead zirconate titanate (PZT) as the ferroelectric ceramic and carbon black (CB) as the conductive phase. The discussion is primarily focused on a comparison of the electrical, thermal and dielectric properties of three-phase composites with those of PU_CB and PU_PZT biphasic composites. The study describes a synergistic effect between the PU/PZT/CB phases involved in the generation of charges between the particles, implying better homogeneity of the composites as well as influence over the PU crystallization. The PU_CB conductivity profile showed a phenomenon of multi-step percolation thresholds attributed to the molecular structure and repulsive surface charge of CB particles. The surface charge phenomenon restricted the percolation curve analysis of the three-phase composites by means of classic percolation theory, shown by distortion of the critical exponents. The dielectric constant three-phase composites increased gradually as a function of CB in accordance with the percolation profile.     

Influence of surface properties on the interfacial adhesion in carbon fiber/epoxy composites

A polyacrylonitrile‐based carbon fiber was electrochemically oxidized in an aqueous ammonium bicarbonate solution with current density of up to 2.76 A/m² at room temperature. X‐ray photoelectron spectroscopy revealed that the oxygen content increased with increasing current density before approaching saturation. The increase can be divided into two regions, the rapid increase region (0–1.78 A/m²) and a plateau region (1.78–2.76 A/m²). The surface chemistry analysis showed that the interlaminar shear strength (ILSS) value of the carbon fiber/epoxy composite could be improved by 24.7%. The carbon structure was examined using Raman spectroscopy in terms of order/disorder in the graphite structure and the results indicated that the relative percentage of graphite carbon in the form of sp² hybridization increased above a current density of 1.39 A/m². The increasing non‐polar graphite carbon on the carbon fiber surface decreased the surface energy. As a result, both the surface free energy () and its polar component () decreased when current density increased above 1.78 A/m². The ILSS value had no direct relationship with the nature and surface density of the oxygen‐containing functional groups nor with the carbon structure. It is the surface free energy (), especially the polar component (), which played a critical role in affecting the interfacial adhesion of carbon fiber/epoxy composites. The ILSS value changed with increasing current density and could be divided into three distinct regions, as chemical interaction region (I), anchor force region (II) and matrix damage region (III). Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of heat treatment on electrical conductivity of HDPE/CB composites

The influence of heat treatment on the electrical conductive behavior of carbon black (CB) filled high density polyethylene (HDPE) composites was investigated. The results showed that the effects of annealing temperature on the resistivity and the PTC intensity of the HDPE/CB composites were significant; the resistivity and the PTC intensity of the composites varied with increasing number of thermal cycles; while the variation became small after the third thermal cycle. Furthermore, the variation of the resistivity was 1.7 times higher than that of the composites without annealing, and the variation of the PTC intensity of the composites was 0.22, which were smaller than those of the specimens without heat treatment. A suitable annealing heat treatment could reduce the resistivity and enhance the PTC intensity of the composites; it was also helpful to improve the stability of the properties of the composites and the repeatability of the PTC effect.     

Shrinkability of ethylene vinyl acetate/polyurethane blends and their characterization

Heat shrinkability of the polymer, which depends on the elastic memory, is being utilized in various applications, mainly in the field of encapsulation. The elastic memory is introduced into the system in the form of an elastomeric phase. Here the blends of ethylene vinyl acetate and polyurethane were studied with reference to their shrinkability, introducing crosslinking in both the phases. It is found that with increase in elastomer content the shrinkage increased to a certain level and then decreased. With increase in cure time shrinkage is decreased. It is seen that high‐temperature (HT) stretched samples showed higher shrinkage than room temperature (RT) stretched one. Generally, the crystallinity of the HT stretched sample is higher than that of low‐temperature stretched sample, which is again higher than that of original sample. From high temperature differential scanning calorimetry it is found that with increase in PU content stability towards oxygen is increased and further high temperature processing decreases the initial degradation temperature but enhances the rate of degradation. From scanning electron microscopy it is seen that an HT stretched sample is more elongated than an RT stretched one. Copyright © 2000 John Wiley & Sons, Ltd.     

Electrochemical reduction of functional groups in the cathodic exfoliation of an ethylene-vinyl acetate copolymer

A study was carried out on the electrochemical processes involving the functional groups of an ethylene-vinyl acetate copolymer upon its cathodic exfoliation from metal. Electron transfer to the polymer is facilitated by the activation effect of an adhesion interaction with the metal.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 6, pp. 346–349, November–December, 1994.     

Preparation and characterization of cellulose acetate/polysiloxane composites

Composites of cellulose acetate and polysiloxane were prepared using 3-isocyanatepropyltriethoxysilane, as a coupling agent. The structure, the thermal and dynamic-mechanical behaviors, and the morphology of the obtained composites were investigated. The composites showed phase separation which was confirmed by the presence of siloxane micro- and nano-domains dispersed in the cellulose acetate matrix, with good interfacial adhesion between the phases. The results demonstrated that the incorporation of a polysiloxane phase on a cellulose acetate matrix caused a decrease in the glass transition temperature, storage modulus and hardness. The proposed methodology was seen to be convenient for the preparation of cellulose acetate/polysiloxane composites with useful properties.