E‐Glass/DGEBA/m‐PDA single fiber composites: The effect of strain rate on interfacial shear strength measurements

Precise measurements of fiber break regions have been made during the single fiber fragmentation test (SFFT) procedure on E‐glass/diglycidyl ether of bisphenol‐A (DGEBA)/meta‐phenylenediamine (m‐PDA) test specimens. From these measurements, the location and size of each fiber fragment was determined, and the resulting information was used to construct fragmentation maps of the tested fiber. By comparing these maps, the fragmentation process supports random fragmentation along the length of the fiber. Since the interfacial shear strength (IFSS) or the interfacial shear stress transfer coefficient (I‐STC) is obtained from the fragment length data at the end of the test (saturation), frequency histograms of the fragment length data were constructed to determine the repeatability of the fragmentation process. Since the SFFT is performed by sequential step‐strains of the test specimen, test protocols were developed by controlling the step size of each strain increment and the time between each step‐strain (dwell time). For the testing protocols used in this research, the E‐glass/DGEBA/m‐PDA frequency histograms of the fragment lengths were found to be generally repeatable. However, when the effective strain rate of the test was altered by changing the dwell time between strain increments, the fragment distribution at saturation of the E‐glass/DGEBA/m‐PDA SFFT specimens changed. The direction of the change was found to be inconsistent with the effect one might expect when only the nonlinear viscoelastic behavior of the matrix is considered. However, the magnitude of the change observed in the E‐glass/DGEBA/m‐PDA SFFT specimens is not universal. Fragmentation data obtained on E‐glass/polyisocyanurate SFFT specimens revealed a much smaller change in fragment length distributions with the same change in testing protocols. Consistent with the results obtained on the E‐glass/DGEBA/m‐PDA, fiber fragmentation occurs when the polyisocyanurate matrix exhibits nonlinear viscoelastic behavior. The implication of these results for interfacial shear strength measurements is discussed.     

Preparation of conductive polyaniline/nylon‐6 composite films by polymerization of aniline in nylon‐6 matrix

Polyaniline (PANI)/Nylon‐6 composite films were prepared by oxidative polymerization of aniline (ANI) inside host Nylon‐6 film. Such a composite has the desired electro‐active and mechanical properties to serve as a self‐standing functional unit. Comparative studies on sorption of ANI by Nylon‐6 matrix from various ANI containing media were conducted revealing superior ANI uptake from neutral ANI solution in water. ANI content was measured to be as high as 12%. Spectroscopic measurements showed that hydrogen bonding seemed to play important role in ANI sorption by Nylon‐6 matrix. Polymerization was monitored using atomic force microscopy and conductivity measurements. The morphology studies showed the appearance of PANI nanodomains on Nylon‐6 surface in the early stages of the polymerization. Eventually the domains coalesced during polymerization forming a continuous PANI layer. The conductivity measurements confirmed the change of the morphology from isolated islands to continuous conducting surface by drastic increase in conductivity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Interfacial effects on dielectric properties of polymethylmethacrylate‐titania microcomposites and nanocomposites

It is discussed that dielectric properties of polymethylmethacrylate (PMMA) composites are influenced by the particle size of titania as a result of changes in the structure and dynamics of polymer chains in the interphase regions around the particles. It is hypothesized that a loosely packed interphase layer, resulted from high stiffness and high cohesion energy of PMMA chains, provides enough free volume for segmental chain movements and dipole orientation along the applied electric field and causes an increase in dielectric properties of nanocomposites at low filler contents. It is shown that the attraction of PMMA toward micro‐titania and nano‐titania is similar by measuring the surface energy of fillers. Dynamics of polymer chains around fillers is investigated by dynamic‐mechanical‐thermal analysis and broadband‐dielectric spectroscopy, and presence of a loosely packed layer is confirmed by measuring thermal and mechanical glass transition temperature of composites. It is concluded that the anomalous enhancement in dielectric properties of 2 vol% nanocomposite, compared to the corresponding microcomposite, can be attributed to the higher volume fraction of loosely packed interphase layers in the nanocomposite. POLYM. COMPOS., 38:1158–1166, 2017. © 2015 Society of Plastics Engineers     

Influence of annealing treatment on the heat distortion temperature of nylon‐6/montmorillonite nanocomposites

It has been recognized that the incorporation of nanoscale montmorillonite (MMT) layers into polymer matrix enhances significantly the heat resistance of the resultant nanocomposites, especially for nylon‐6 (N6)/clay nanocomposites (NCNs). In the present work, the heat distortion temperature (HDT) of NCNs, including the intercalated N6/Na‐montmorillonite (Na‐MMT) and the exfoliated N6/organo‐montmorillonite (OMMT) ones, have been investigated for both non‐annealed and annealed testing specimens in comparison with the neat N6. As expected, the incorporation of MMT obviously improved HDT of NCNs, with the highest HDT value obtained in the N6/OMMT system due to its exfoliated nano‐structure. After an annealing treatment at 80°C for 6 hr, the HDT revealed noticeable increase for all the samples, particularly for the intercalated N6/Na‐MMT nanocomposite that showed the highest increment of 34°C. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR) techniques were employed to clarify the origin of the variation in HDT after annealing, and the results suggest that the increases in the crystallinity, the glass transition temperature, and the order degree of hydrogen bonding may account for the noticeable increases in the HDT of the nanocomposites after annealing. POLYM. ENG. SCI., 45:1247–1253, 2005. © 2005 Society of Plastics Engineers     

Effect of reactive compatibilization on the interfacial slip in nylon‐6/EPR blends

The viscosity of uncompatibilized polymer blends often shows a negative deviation from a log‐additivity rule at shear rates relevant to processing. This deviation has been attributed to interfacial slip, which is related to the loss of entanglements at the interface. In this work interfacial slip and the effect of reactive compatibilization on this phenomenon are studied in blends consisting of ethylene‐propylene rubber and nylon‐6. The viscosity and morphology of blends with various compositions and compatibilizer content are investigated systematically. The results indicate that interfacial slip can indeed be important in uncompatibilized systems whereas it is suppressed in compatibilized blends. This is further supported by a study of the viscosity of multilayer structures. Both the effect of reactive compatibilization and of the number of layers on the rheology are studied. Again it is demonstrated that reactive compatibilization suppresses interfacial slip.     

Studies on nylon‐6/EVOH/clay ternary composites

Nylon‐6 (Ny‐6)/EVOH blends are interesting host multiphase systems for incorporation of low clay contents. The Ny‐6/EVOH blend is a unique system, which tends to chemically react during melt‐mixing, affecting thermal, morphological and mechanical properties of the ternary systems containing clay. The addition of clay seems to interrupt the chemical reaction between the host polymers at certain compositions, leading to lower blending torque levels when clay is added. A competition between Ny‐6 and EVOH regarding the intercalation process takes place. Ny‐6 seems to lead to exfoliated structure, whereas EVOH forms intercalated structure, as revealed from XRD and TEM analyses, owing to thermodynamic considerations and preferential localization of the clay in Ny‐6. Hence, the ternary systems have combined intercalated and delaminated morphology or complete exfoliated morphology depending on blend composition and clay content. Selective extraction experiments (gel content) indicate the formation of chemical reaction between the Ny‐6 and EVOH, and give an indirect indication of the polymer content residing in the galleries. The thermal properties of the polymers were found to be affected by the occurrence of chemical reaction, the level of intercalation and exfoliation and plasticizing effect of the low molecular weight onium ions treating the clay. Of special interest is the increased storage modulus attained upon the addition of only 1.5 wt% clay. POLYM. COMPOS. 27:15–23, 2006. © 2005 Society of Plastics Engineers     

Structure and property study of nylon‐6/clay nanocomposite fiber

The crystal structures of nylon‐6 and nylon‐6/clay fibers were investigated on annealing and drawing. Annealing increased the γ‐crystalline form of both fibers, as indicated by the DSC curves, and its effect was dominant in nylon‐6/clay fiber. On drawing, the γ‐crystalline form was easily converted into the α form in nylon‐6, whereas it was still observed at a relatively high spin‐draw ratio in nylon‐6/clay fiber. However, although the α‐crystal form was dominant in nylon‐6, the γ‐crystal form was dominant in nylon‐6/clay with annealing and drawing, on the basis of the XRD data. The fast crystallization rate of nylon‐6/clay compared with pure nylon‐6 was confirmed, on the basis of the Avrami exponent. The initial modulus of nylon‐6/clay fiber was 30 % higher than the neat nylon‐6 fiber. The reinforcing effect of clay on the dynamic storage modulus was observed. Copyright © 2004 Society of Chemical Industry     

Preparation and characterization of nylon‐6/PPy/MMT composite of nanocomposite

Series of composites consisting of polypyrrole/montmorillonite nanocomposites in the matrix of Nylon6 has been synthesized and characterized in this work. The composites were processable, so that test samples were prepared by compression‐molding of the materials for electrical property measurements. Intercalated structures were confirmed by wide‐angle X‐ray diffraction and TEM studies for PPy/MMT nanocomposites. A two‐phase structure was determined for the fused samples consisting of two separated N6 and PPy phases by using scanning electron microscopy analyses. A conductivity threshold was measured at 15%(w/w) loading level of PPy in the composites. Electrical resistivity–temperature behavior of the samples was investigated and a resistivity peak was observed at 100°C for the samples. It was proved that the glass transition temperature of PPy around 100°C should be the responsible factor for the observed resistivity peak, as studied by thermogravimetic analysis and differential scanning calorimetry thermal methods. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Electrospun gelatin/nylon‐6 composite nanofibers for biomedical applications

We describe the preparation and characterization of gelatin‐containing nylon‐6 electrospun fibers and their potential use as a bioactive scaffold for tissue engineering. The physicochemical properties of gelatin/nylon‐6 composite nanofibers were analyzed using field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, TGA and contact angle and tensile measurements. FE‐SEM and TEM images revealed that the nanofibers were well oriented and showed a good incorporation of gelatin. FTIR spectroscopy and TGA also revealed that there was good interaction between the two polymers at the molecular level. The adhesion, viability and proliferation properties of osteoblast cells on the gelatin/nylon‐6 composite nanofibers were analyzed by an in vitro cell compatibility test. Our results suggest that the incorporation of gelatin can increase the cell compatibility of nylon‐6 and therefore the composite mat obtained has great potential in hard tissue engineering. © 2012 Society of Chemical Industry     

Hybrid organic inorganic nylon‐6/SiO2 nanocomposites: Transport properties

Organic‐inorganic hybrid membranes of nanosized SiO₂‐filled polyamide composites were prepared via film casting and their transport properties were studied. Gas permeation measurements were performed at room temperature, and the membrane exhibited an increase in membrane permeability performance. In contrast to the performance of traditional dense filled polymer systems, the permeability increased with an increased number of nanosilica particles. The nanocomposites were studied using positron annihilation lifetime spectroscopy (PALS). From the ortho‐positronium (o–Ps) lifetime (τ₃), the size of the local free volume (holes) was estimated. The increase in permeability is ascribed to the additional free volume obtained. This is created by the presence of nanoparticles that alter the PA chain packing. Furthermore, wide angle X‐ray diffraction (WAXD) patterns revealed that the incorporation of silica induced the structural modification of polymer chains by modifying the degree of crystallinity in comparison with the neat polymer. Polym. Eng. Sci. 44:1240–1246, 2004. © 2004 Society of Plastics Engineers.     

Friction and wear studies on nylon‐6/SiO2 nanocomposites

Composites of nanometer‐sized silica (SiO₂) filler incorporated in nylon‐6 polymer were prepared by compression molding. Their friction and wear properties were investigated on a pin on disk tribometer by running a flat pin of steel against a composite disc. The morphologies of the composites as well as of the wear track were observed by scanning electron microscopy (SEM). The addition of 2 wt % SiO₂ resulted in a friction reduction (μ) from 0.5 to 0.18 when compared with neat nylon‐6. This low silica loading led to a reduction in wear rate by a factor of 140, whereas the influence of higher silica loadings was less pronounced. The smooth morphology obtained after the wear test indicated the negligible contribution to friction of the pin to the nanocomposite. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1855–1862, 2004     

Flame retardancy and char microstructure of nylon‐6/layered silicate nanocomposites

We investigated the effect of organically modified clay alone and in combination with zinc borate on the thermal/flammability behavior of nylon‐6 nanocomposites. Differential thermogravimetric analysis indicated that the peak decomposition temperature was not affected by the addition of clay, but the rate of weight loss decreased with increase in clay concentration. Nanocomposite films of approximately 0.5 mm thickness with 2.5 and 5 wt % clay burned for almost the same duration as neat nylon‐6 but with reduced dripping in horizontal flame test. The 10 wt % clay nanocomposite sample burned without any dripping and the flame spread rate was reduced by 25–30%. Zinc borate/clay containing nanocomposite developed into a very good intumescent system in cone calorimeter test, swelling about 10–13 mm height prior to ignition forming a cellular char structure. This was found to be an effective composition in reducing the heat release and mass loss rate of nylon‐6 by about 65% and at par with 10 wt % clay nanocomposite. Flame retardant behavior could be attributed to distinct char morphologies observed through scanning electron microscopy. Fourier transform infrared spectroscopy of the 10 wt % clay nanocomposite char showed the presence of amides, indicating possible residual polymer within the shielded char. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1540–1550, 2007     

Effect of packing on void morphology in resin transfer molded E‐glass/epoxy composites

Effects of applying a packing pressure on void content, void morphology, and void spatial distribution were investigated for resin transfer molding (RTM) E‐glass/epoxy composites. Packing pressures of zero and 570 kPa were respectively applied to center‐gated composites containing 17.5% randomly oriented, E‐glass fiber preform. Radial samples of these disk‐shaped composites were utilized to evaluate voidage via microscopic image analysis. Two adjacent surfaces were cut from each molded disk in order to evaluate void presence from both through‐the‐thickness and planar views. The packed composite was found to contain almost 92% less void content than the unpacked composite. While void fractions of 2.2 and 2.6% were measured, respectively, from the through‐the‐thickness and planar surfaces of the unpacked composite, only 0.2% void content was observed in the packed composite from both surfaces. Digital images obtained from through‐the‐thickness surface showed that average void size dropped from 59.3 μm in the unpacked composite to 31.7 μm in the packed composite. A similar reduction in average void size from 66.7 to 41.1 μm was observed from the planar surfaces. Circular voids were found to experience higher removal rates at 99%, followed by cylindrical and elliptical voids at 83 and 81%, respectively; while irregular voids show slightly lower void removal rates at 67%. Void proximity to fiber bundles was also observed to affect void reduction as voids located inside fiber tows experience lower void reduction rates. Along the radial direction of the molded disks, removal of voids with different proximities to fibers seems to depend on their arrangement at the end of the filling stage. These findings are believed to ascertain packing as an effective void removal method for RTM and similar liquid composite molding processes. POLYM. COMPOS., 26:614–627, 2005. © 2005 Society of Plastics Engineers     

Effects of maleated styrene–(ethylene‐co‐butene)–styrene on compatibilization and properties of nylon‐12,12/nylon‐6 blends

Effects of a maleated triblock copolymer of styrene–(ethylene‐co‐butene)–styrene (SEBS‐g‐MA) on compatibilization and mechanical properties of nylon‐12,12/nylon‐6 blends were investigated. The results showed that addition of SEBS‐g‐MA could improve the compatibility between nylon‐12,12 and nylon‐6. Nylon‐12,12 could disperse very well in nylon‐6 matrix, although the dispersion of nylon‐6 was poor when nylon‐6 was the dispersed phase. At a fixed nylon‐12,12/nylon‐6 ratio of 30/70, supertoughness was achieved with addition of 15% SEBS‐g‐MA in weight. Scanning electron microscopy of the impact‐fractured surface indicated that cavitation and matrix shear yielding were the predominant mechanisms of impact energy dissipation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1446–1453, 2004     

Mechanical properties and morphology of nylon‐6 hybrid composites

In this investigation, the influence of filler type and filler content on the mechanical properties of nylon‐6 is investigated. The mineral fillers were selected on the basis of their shape and size: flake‐like kaolin and talc, spherical glass beads or fibrous wollastonite. These fillers were added to nylon‐6 individually or in mixed combinations. They were added at different percentages varying between 10 and 30% w/w. Samples of the composites were prepared by the injection moulding process. Uniaxial tensile, Izod impact and flexural tests were carried out. Tensile strength, elongation at break, modulus of elasticity and impact energy were obtained and compared. In case of single fillers the results showed that the tensile strength, modulus of elasticity and their flexural values for nylon‐6 composite improve with the increase in filler content while mixed compounds showed no significant changes above 15% + 15% w/w filler. However, for single and mixed filler up to 10% w/w, the impact strength and maximum elongation at break showed significant decrease. In general, the maximum improvement in mechanical the addition of 10–15% w/w filler. Copyright © 2003 Society of Chemical Industry     

Kinetics of the solid‐state polymerization of nylon‐6

The kinetics of the thermally induced solid‐state polymerization (SSP) of nylon‐6 were examined in both a fixed‐bed reactor and a rotary reactor. Factors such as the regulator content, the reaction temperature and time, the particle size, the type and geometry of the nylon‐6 prepolymer, the nitrogen gas flow rate, the water content of the nitrogen gas flow, and the polymerization process were studied. The results showed that the regulator content, the reaction temperature and time, and the particle size were the primary factors, and that the others were negligible. Moreover, the SSP rate and number‐average molecular weight (M_n) increased with increasing reaction temperature and time and decreasing particle size. The SSP rate and M_n had maximum values with increasing regulator content in an experimental range of 0.03–0.07 wt %. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 616–621, 2002; DOI 10.1002/app.10341     

Effect of temperature and strain rate on the tensile deformation of polyamide 6

The effects of the draw temperature and the strain rate on the tensile deformation of polyamide 6 (PA6) were investigated using three PA6 samples with different initial shapes and physical dimensions. It is observed that the special double yielding phenomenon is indeed present in PA6, provided that certain temperature and strain rate are given, as well as the appropriate initial structure. The results also show that the dependence of the first yield stress on temperature is nearly linear while on strain-rate is logarithmic. The temperature and strain-rate sensitivity change at the draw temperature in the vicinity of the glass transition temperature of PA6. The double yielding of PA6 is not only the combination of two thermally activated rate processes depending on temperature and strain rate, but also associated with the initial structure of samples. The yielding manner for PA6 seems to be determined by the synergetic effect of both the deformation of amorphous and crystalline phases. Thus some special structure involving the crystalline and amorphous phases should come into being in PA6 exhibiting double yielding. Especially the important role of inter- and intra-link should be taken into account. The theory of partial melting-recrystallization cannot account fully for the double yielding of PA6.     

Morphology of polypropylene/silica nano‐ and microcomposites

The aim of this study was to compare the effects of different silica grades on the structure and morphology of isotactic polypropylene (iPP)/silica composites to better understand their structure–property relationships. Isotactic polypropylene composites with 2, 4, 6, 8 vol % of added silica fillers differing in particle size (micro‐ vs. nanosilica) and surface modification (untreated vs. treated surface) were prepared by nonisothermal compression molding and characterized by different methods. The addition of all silica fillers grades to the iPP matrix significantly influenced the spherulitic morphology, while phase characteristics of the iPP matrix seemed to be unaffected. Surface modification of silica fillers exhibited stronger effects on spherulite size than size of silica particles. Nonpolar silica particles, more miscible or compatible with iPP chains than polar silica particles, enabled better spherulitic growth. The spherulite sizes tended to reach equal values at 8 vol % of added silicas showing that spherulite size became independent of filler concentration and surface modification above optimum filler concentration. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Low‐temperature hygrothermal degradation of ambient cured E‐glass/vinylester composites

Freeze and freeze‐thaw durability characteristics of fiber reinforced polymer (FRP) composites, especially in the presence of moisture, need to be investigated prior to the widespread implementation of these materials in civil, polar, and offshore structural components and systems. The hygrothermal degradation characteristics of an ambient cure E‐glass/vinylester system due to exposure to ?10°C conditions and conditions of freeze‐thaw, including in the presence of water and seawater, was investigated. Changes in mechanical characteristics such as strength and modulus, and thermo‐mechanical dynamic characteristics such as storage and loss moduli, and glass‐transition temperature were measured, and short‐term effects of environmental exposure were assessed. It is seen that the presence of moisture/solution has a significant effect; both in terms of physical and chemical aging, and in terms of microcracking and fiber–matrix debond initiation. Results indicate the critical importance of cure characteristics and diffusion related phenomena. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2255–2260, 2002