Effect of PPO‐g‐MA on structures and properties of PPO/PA6/short glass fiber composites

Poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polyamide 6 (PPO/PA6) blends were reactively compatibilized by maleic anhydride (MA) grafted PPO (PPO‐g‐MA) and reinforced by short glass fibers (SGF) via melt extrusion. An observation of the SGF‐polymer interface by scanning electronic microscope (SEM) together with etching techniques indicated that the PPO‐g‐MA played a decisive role in the adhesion of polymers to SGF. The rheological behavior was investigated by capillary rheometer, and the addition of PPO‐g‐MA, and SGF could increase the viscosity of the PPO/PA6 blends. The analysis of fiber orientation and distribution in the PPO/PA6/SGF composites showed PPO‐g‐MA favored to the random dispersion of SGF. The statistic analysis of SGF length showed that PPO‐g‐MA was helpful to maintain the fiber length during melt‐processing. For the composites at a given SGF content of 30 wt %, the addition of PPO‐g‐MA increased the tensile strength from 59.4 MPa to 97.1 MPa and increased SGF efficiency factor from 0.028 to 0.132. The experimental data were consistent with the theoretical predictions of the extension of Kelly‐Tyson model for tensile strength. The fracture toughness of the composites was investigated by single edge notch three‐point bending test. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2188–2197, 2009     

Sorption and diffusion of carbon dioxide in wood‐fiber/polystyrene composites

In this study, sorption and diffusion of carbon dioxide (CO₂) in wood‐fiber/polystyrene composites were investigated. The effects of gas pressure and fiber content on the solubility and diffusion coefficients were evaluated. A statistical analysis indicated that pressure is more important than fiber content in determining the solubility and diffusivity of CO₂. An increase in saturation pressure causes an increase in the solubility and diffusion coefficients, whereas inclusion of the fibers decreases both of these properties. Models were developed to predict the uptake and diffusion coefficients of CO₂ in the composite samples as functions of pressure and fiber content. A theoretical model based on Henry's law and the Langmuir equation compared favorably to the experimental data for CO₂ solubility. This dual mode model also described both the transient sorption and desorption data, but only if the concentration‐dependent value of diffusivity was treated as a history‐dependent parameter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 723–735, 2002     

Compacted UHMWPE fiber composites: Morphology and X‐ray microdiffraction experiments

The effect of compaction conditions on UHMWPE fibers is examined by microbeam X‐ray diffraction (WAXS) and scanning electron microscopy (SEM). The morphological observations indicate that melting occurs during compaction both on the surface of the fiber as well as in its internal regions. In addition, the recrystallized phase is nucleated on the fiber surface, possibly epitaxially. The recrystallized phase that originates from the internal regions of the fiber retains the initial highly oriented structure. WAXS microbeam measurements do not show any significant core‐shell structure in compacted single fibers. Considering the overall characteristics of the melting process during compaction, we can conclude that the hexagonal phase that appears upon heating of the fibers under moderate pressure is responsible for good adhesion of the fibers to each other, even more significantly than surface melting, especially because of its ability to retain the high orientation of the chains in the fibers. This information is relevant for understanding the formation and microstructure of the matrix component in the self‐reinforced composites fabricated by compaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1535–1541, 2007     

Spectroscopic analysis and kinetics of intermolecular hydrogen bond formation in poly‐pyridobisimidazole (M5) fiber

Poly‐pyridobisimiazole (M5) single filaments subjected to varying degrees of heat treatment have been analyzed using Fourier Transform Infrared (FTIR) microspectroscopy in transmission mode to detect changes in the state of intermolecular hydrogen bonding as a function of fiber annealing conditions. The FTIR absorbance bands associated with hydrogen bonding in M5 fiber have been identified, and the integrated molar absorption coefficients for the bands of interest have been determined experimentally, which allows to quantify the concentration of N? H vibration groups hydrogen‐bonded (H‐bonded) to water molecules, and the concentration of N? H vibration groups H‐bonded to adjacent polymer chains in the fiber. A dual mechanism kinetic rate expression is used to describe intermolecular H‐bond formation in M5 fiber as a function of annealing conditions, from which an activation energy for H‐bond formation of 14.8 kJ/mol is obtained. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1809–1824, 2009     

Structural and mechanical behavior of polypropylene/ maleated styrene‐(ethylene‐co‐butylene)‐styrene/sisal fiber composites prepared by injection molding

Hybrid composites consisting of isotactic poly(propylene) (PP), sisal fiber (SF), and maleic anhydride grafted styrene‐(ethylene‐co‐butylene)‐styrene copolymer (MA‐SEBS) were prepared by melt compounding, followed by injection molding. The melt‐compounding torque behavior, thermal properties, morphology, crystal structure, and mechanical behavior of the PP/MA‐SEBS/SF composites were systematically investigated. The torque test, thermogravimetric analysis, differential scanning calorimetric, and scanning electron microscopic results all indicated that MA‐SEBS was an effective compatibilizer for the PP/SF composites, and there was a synergism between MA‐SEBS and PP/SF in the thermal stability of the PP/MA‐SEBS/SF composites. Wide‐angle X‐ray diffraction analysis indicated that the α form and β form of the PP crystals coexisted in the PP/MA‐SEBS/SF composites. With the incorporation of MA‐SEBS, the relative amount of β‐form PP crystals decreased significantly. Mechanical tests showed that the tensile strength and impact toughness of the PP/SF composites were generally improved by the incorporation of MA‐SEBS. The instrumented drop‐weight dart‐impact test was also used to examine the impact‐fracture behavior of these composites. The results revealed that the maximum impact force (F_max), impact‐fracture energy (E_T), total impact duration (t_r), crack‐initiation time (t_init), and crack‐propagation time (t_prop) of the composites all tended to increase with an increasing MA‐SEBS content. From these results, the incorporation of MA‐SEBS into PP/SF composites can retard both the crack initiation and propagation phases of the impact‐fracture process. These prolonged the crack initiation and propagation time and increased the energy consumption during impact fracture, thereby leading to toughening of PP/MA‐SEBS/SF composites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1214–1222, 2002     

Sustainable,fire‐resistant phthalonitrile‐based glass fiber composites

The sustainable resveratrol‐based phthalonitrile was used in the preparation of E‐glass fiber‐reinforced phthalonitrile composite panels fabricated by hot pressed prepreg consolidation with bis[4‐(3‐aminophenoxy)phenyl]sulfone (m‐BAPS) as the curing additive. This amorphous monomer exhibited excellent viscosities at temperatures below 200 °C, which is applicable to standard processing conditions. Rheometric measurements were used to evaluate the cure of the composite as a function of the postcure conditions. The composite retains >95% of its room temperature storage modulus up to 450 °C based on these postcuring parameters. More importantly, flammability performance of the composite—which was determined in terms of ignitability, heat release, and mass loss rate—excels over other state‐of‐the‐art polymer/glass composites. Even under the most extreme heat fluxes (e.g., 100 kW⋅m⁻²), the composite performs exceptionally well suggesting that resveratrol‐based phthalonitrile composites can be used in fire‐resistant applications. Published 2018.^† J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1128–1132     

Studies on fracture behaviors of immiscible polypropylene/ethylene‐co‐vinyl acetate blends with multiwalled carbon nanotubes

Immiscible polypropylene/ethylene‐co‐vinyl acetate (PP/EVA) blends with two different compositions, one (PP/EVA = 80/20) exhibits the typical sea‐island morphology and the other (PP/EVA = 60/40) exhibits the cocontinuous morphology, were prepared with different contents of f‐MWCNTs. The fracture behaviors, including notched Izod impact fracture and single‐edge notched tensile (SENT) fracture, were comparatively studied to establish the role of f‐MWCNTs in influencing the fracture toughness of PP/EVA blends. Our results showed that, for PP/EVA (80/20) system, f‐MWCNTs do not induce the fracture behavior change apparently. However, for PP/EVA (60/40) system, the fracture toughness of the blend increases dramatically with the increasing of f‐MWCNTs content. More severe plastic deformation accompanied by the fibrillar structure formation was observed during the SENT test. Furthermore, SENT test shows that the significant improvement in fracture toughness of PP/EVA (60/40) with f‐MWCNTs is contributed to the simultaneous enhancement of crack initiation energy and crack propagation energy, but largely dominated by crack propagation stage. Further results based on crystalline structures and morphologies of the blends showed that a so‐called dual‐network structure of EVA and f‐MWCNTs forms in cocontinuous PP/EVA blends, which is thought to be the main reason for the largely improved fracture toughness of the sample. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1331–1344, 2009     

Electrospun fiber mats of poly(3‐hydroxybutyrate), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), and their blends

Electrospinning of poly(3‐hydroxybutyrate) (PHB), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and their blends was first carried out in chloroform at 50 °C on a stationary collector. The average diameter of the as‐spun fiber from PHB and PHBV solutions decreased with increasing collection distance and increased with increasing solution concentration and applied electrical potential. In all of the spinning conditions investigated, the average diameter of the as‐spun pure fibers ranged between 1.6 and 8.8 μm. Electrospinning of PHB, PHBV, and their blends was carried out further at a fixed solution concentration of 14% w/v on a homemade rotating cylindrical collector. Well‐aligned, cross‐sectionally round fibers without beads were obtained. The average diameter of the as‐spun pure and blend fibers ranged between 2.3 and 4.0 μm. The as‐spun fiber mats appeared to be more hydrophobic than the corresponding films and much improvement in the tensile strength and the elongation at break was observed for the blend fiber mats over those of the pure fiber ones. Lastly, indirect cytotoxicity evaluation of the as‐spun pure and blend fiber mats with mouse fibroblasts (L929) indicated that these mats posed no threat to the cells. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2923–2933, 2006     

Rheological behavior of biocomposites of silk fibroin fiber and poly(ε‐caprolactone): Effect of fiber network

Rheological behavior was examined for biocomposites of rod‐like silk fibroin (SF) fiber and poly(ε‐caprolactone) (PCL) to investigate an effect(s) of the SF fiber network therein on the mechanical properties. At 160 °C where PCL was a homogeneous melt, linear viscoelastic tests revealed that the SF/PCL composites hardly relax to behave essentially as elastic solids (more precisely, plastic solids before yielding) at low frequencies. The corresponding equilibrium modulus G₀ increased strongly with the SF volume fraction ?_SF (G₀ ～ ?) and was attributable to the elastic bending of the SF fibers incorporated in the network. The Doi‐Kuzuu model for non‐Brownian rods was modified for the SF/PCL composites by incorporating the rod–rod contact at equilibrium. The G₀ calculated from this model was satisfactorily close to the data, in both ?_SF dependence and magnitude, lending support to the assignment of the composite elasticity to the fiber bending. The storage modulus G′ measured under large‐amplitude oscillatory shear (LAOS) was smaller than the linear viscoelastic G′, and this difference between the linear and nonlinear moduli was enhanced for the composites with a larger SF content and at lower frequencies. This nonlinear effect was attributable to a decrease of the effective fiber–fiber contacts sustaining the elasticity under LAOS. Under steady shear, the SF/PCL composites exhibited nonlinear (plastic) flow behavior associated with the stress overshoot, and their apparent viscosity was comparable to/lower than the viscosity of neat PCL matrix. The overshoot became much less significant on application of a second shear immediately after the first shear, while the overshoot was partly recovered after a quiescent rest between the first and second shears. These nonlinear features were attributable to slippage between shear‐oriented fibers and PCL matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1957–1970, 2009     

Fracture toughness of nylon‐6 blends with maleated rubbers

The fracture toughness of blends of nylon‐6 with maleated ethylene–propylene rubber and maleated styrene/hydrogenated butadiene/styrene triblock copolymer was investigated with a single‐edge‐notched three‐point‐bending instrumented Dynatup test. The blends for which the rubber particle size was less than 0.7 μm fractured in a ductile manner over the whole range of ligament lengths, whereas the blends with particles larger than 0.7 μm showed a ductile‐to‐brittle transition with the ligament length. In this regime, ductile fracture was observed for specimens with short ligaments, whereas brittle fracture was seen for those with long ligaments. The ductile fracture behavior was analyzed with the essential‐work‐of‐fracture model, whereas linear elastic fracture mechanics techniques were used to analyze the brittle fracture behavior. The fact that the ductile fracture energy was larger for the blends with the styrene/hydrogenated butadiene/styrene triblock copolymer than for those with ethylene–propylene rubber was due to the larger dissipative energy density of the blends based on the styrene/hydrogenated butadiene/styrene triblock copolymer. Both the critical strain energy release rate (G_IC) and the plane‐strain critical stress intensity factor (K_IC) increased as the rubber particle size decreased for both blend systems. The G_IC and K_IC parameters had similar values, regardless of the rubber type, when the rubber particle size was fixed. The transition ligament length was near the size criterion for plane‐strain conditions for both blend systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1739–1758, 2004     

Active fiber length distribution and its application to determine the critical fiber length

A new test and evaluation method has been developed to determine the critical fiber length characteristic of short fiber reinforced composites. From the so-called active ‘barbe’ (beard) length distribution calculated from the length distribution of the fibers in the composite and from the length distribution of the fibers protruding from the fracture surface, measurable characteristics have been derived, from which the critical fiber length can be determined. In order to demonstrate the applicability of the method, some measurements and calculations have been performed for injection molded glass fiber reinforced poly(ethylene-terephthalate) samples and the critical length determined has been compared with that obtained from droplet pull-out tests. It has been concluded that the new method provides an easily evaluated result, which is closer to reality than those obtained by other methods.     

Effect of surface‐grafted ionic groups on the performance of cellulose‐fiber‐reinforced thermoplastic composites

The influence of the surface chemistry of the cellulose fiber and polymer matrix on the mechanical and thermal dynamic mechanical properties of cellulose‐fiber‐reinforced polymer composites was investigated. The cellulose fiber was treated either with a coupling agent or with a coupling‐agent treatment followed by the introduction of quaternary ammonium groups onto the fiber surface, whereas the polymer matrix, with opposite polar groups such as polystyrene incorporated with sulfonated polystyrene and poly(ethylene‐co‐methacrylic acid), was compounded with the fiber. The grafting of the fiber surface was investigated with Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. Experimental results showed that an obvious improvement in the mechanical strength could be achieved for composites with an ionic interface between the fiber and the polymer matrix because of the adhesion enhancement of the fiber and the matrix. The improved adhesion could be ascribed to the grafted ionic groups at the cellulose‐fiber surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2022–2032, 2003     

Thermal‐crosslinked polyacrylonitrile fiber compacts

Polyacrylonitrile (PAN) textile fibers, in the form of fabrics or threads, were compacted in a heat‐pressure cycle and crosslinked by nitrile polymerization to form a thermoset composite article, whose mechanical properties were found to surpass those of commercially available polypropylene (PP) fiber counterparts. Additional advantages of the PAN compacts included their significant thermal stability (>300°C, i.e., twice that of PP) in addition to their flame retardancy, thereby rendering them as the structural material of choice for applications where heat protection and fire resistance are essential. Copyright © 2009 John Wiley & Sons, Ltd.     

An investigation into the relationship between internal stress distribution and a change of poly‐p‐phenylenebenzobisoxazole (PBO) fiber structure

This study concerns stress distribution induced by external force in individual poly‐p‐phenylenebenzobisoxazole (PBO) molecules in fiber. In reality, there are no fibers having an ideal structure (i.e., composed of infinitely long complete crystal elongated parallel to the fiber axis without defects that disconnect stress transfer in the crystal structure). Normally, real fiber structure has some structural incompletion, such as molecular ends, molecular misorientation, and density fluctuation (inhomogeneity) along the fiber axis. They play the role of heterogeneous stress distribution and reduction of fiber modulus in the fiber under tensile deformation. To carry out such analysis, meridional X‐ray diffraction peaks of the PBO fiber under stress were measured and discussed. Distribution of the diffraction peak profile (half‐height width of the diffraction profile) was especially considered. Change of the molecular orientation induced by external stress to the fiber was also estimated by measuring distribution of equatorial spots along the Debye ring. It was found that the distribution of the meridional diffraction spots became wider in the meridian, while the peak profile along the azimuthal direction became narrower as external stress was added for all three fibers. The degrees of response against stress came in this order: AS (180 GPa) > HM (280 GPa) > HM+ (360 GPa). Hosemann's analysis was adopted to analyze real crystallite size and disorder parameter (g) of crystallites. It indicated that the crystalline size does not vary but the ordering of periodicity in the crystal lattice starts to loosen as applied stress to the fiber is increased. The stress seems to affect only local micro regions in the crystal structure. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2901–2911, 2000     

Evaluation of short term–high intensity thermal degradation of graphite fiber reinforced laminates via ultrasonic spectroscopy

In certain fire situations, a structural or load‐bearing polymer matrix composite (PMC) may be exposed to excessive thermal loads that degrade the matrix. In this paper, we report the results of a study to assess the utility of ultrasonic spectroscopy as a means of assessing the residual physical and mechanical characteristics of PMCs exposed to excessive thermal loads. We show that the measured power spectra of ultrasonic energy correlates with performance of graphite fiber epoxy matrix composites exposed to thermal degradation. Unidirectional composites were exposed to short term–high intensity thermal loads at one end of the specimen. Thus, inducing a thermal gradient along the length of the specimen. Simultaneous thermogravimetric analysis–differential scanning calorimetry (TGA/DSC) and Fourier transform infrared spectroscopy (FTIR) analysis of the aged specimens revealed a gradient in thermal degradation. The thermal loads induced substantial degradation of the composite. However, the amplitude of the power spectra is observed to increase gradually then sharply prior to its complete attenuation due to delaminations. Mode I fracture toughness tests correlate with the observed changes in the ultrasonic spectra. FTIR, TGA/DSC, fracture toughness, and ultrasonic spectral analysis all indicate the same critical temperature at which thermally induced damage sharply increased. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2601–2610, 1999     

Stress distribution in poly‐p‐phenylenebenzobisoxazole (PBO) fiber estimated from vibrational spectroscopic measurement under tension. II. Analysis of inhomogeneous stress distribution in PBO fiber

Fourier transform Raman spectra were measured for poly‐p‐phenylenebenzobisoxazole (PBO) fiber subjected to a tensile stress, and the Raman shift factor (the frequency shift caused by 1 GPa tensile stress) depended strongly on the sample‐preparation condition. To clarify the reasons of this dependency, a mechanical series parallel model was adopted that could successfully and quantitatively explain the observed Raman shift factors and gave a concreate heterogeneous stress distribution in the PBO fibers. As a result, a mechanical series model was reasonable for PBO fiber. Broadening of Raman bands, which was observed when the PBO fiber was tensioned, could also be interpreted on the basis of an idea of heterogeneous stress distribution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1281–1287, 2002     

Transcrystallization of PTFE fiber/PP composites. II. Effect of transcrystallinity on the interfacial strength

It has been found that transcrystallinity of polypropylene (PP) develops easily on the polytetrafluoroethylene (PTFE) fiber surface in spite of the low surface energy of the fiber. Effect of the transcrystallinity on the interfacial strength has been extensively investigated using a single-fiber pull-out test. By controlling the crystallization temperature, range 25–130°C, the thickness of the transcrystalline layer varied from 0 to 175 μm for thick specimens, ca. 1 mm thick. Measurements of the adhesive fracture energy, the interfacial shear strength and the frictional stress were carried out for specimens with different embedded fiber lengths. Results show that interfacial strength and fracture energy are independent of the transcrystalline thickness. The calculated value of interfacial shear strength is 3.6 MPa, and the fracture energy for debonding is 2.1 J/m². The presence of transcrystallinity does not promote the level of adhesion in PTFE/PP composites. However, the frictional stresses at the debonded fiber/matrix interface increase with transcrystalline thickness. It is attributed to the residual stresses which arise from shrinkage when specimens are cooled from crystallization temperature to room temperature. © 1996 John Wiley & Sons, Inc.     

An analysis of deformation process on poly‐p‐phenylenebenzobisoxazole fiber and a structural study of the new high‐modulus type PBO HM+ fiber

This study is concerned with fiber structure of new high‐modulus type PBO fiber. Crystal modulus and molecular orientation change with stress was surveyed. Standard‐modulus type PBO (AS) fiber has hysteresis effect to applied stress while high‐modulus type PBO (HM) fiber shows reversible change. In order to raise actual PBO fiber modulus higher, nonaqueous coagulation process was adopted with conventional heat treatment. The fiber (HM+) so made gives 360 GPa in the Young's modulus and an absence of small‐angle X‐ray scattering pattern that is characteristic for aqueous‐coagulated PBO fiber with heat treatment (Zylon™ HM). The crystal structure form and crystal size for the HM+ fiber are the same as those of the HM fiber. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1605–1611, 2000     

The effect of length of single‐walled carbon nanotubes (SWNTs) on electrical properties of conducting polymer–SWNT composites

DC conductivity of conjugated polymer‐single‐walled carbon nanotube (SWNT) composite films has been measured for different SWNT concentrations. The composite was prepared by dispersing SWNTs in the poly (3‐octylthiophene), P3OT matrix already dissolved in xylene. The conductivity of the composite films showed a rapid increase as the SWNT concentration increases beyond a certain value. This behavior is explained in terms of percolating paths provided by the SWNTs in the volume of polymer matrix. To investigate the effect of length of nanotubes on the percolation conductivity, different SWNT samples were employed with similar diameter but varying tube lengths. It was found that the conductivity of the composite films is strongly dominated by the length of the nanotubes. Lower percolation limit and high conductivity value of composite films is observed for longer nanotubes. Furthermore, the conductivity is observed to be dependent on the size of the host polymer molecule also. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 89–95, 2010