A phosphorus‐containing inorganic compound as an effective flame retardant for glass‐fiber‐reinforced polyamide 6

A novel inorganic compound, aluminum hypophosphite (AP), was synthesized successfully and applied as a flame retardant to glass‐fiber‐reinforced polyamide 6 (GF–PA6). The thermal stability and burning behaviors of the GF–PA6 samples containing AP (flame‐retardant GF–PA6) were investigated by thermogravimetric analysis, vertical burning testing (with a UL‐94 instrument), limiting oxygen index (LOI) testing, and cone calorimeter testing (CCT). The thermogravimetric data indicated that the addition of AP decreased the onset decomposition temperatures, the maximum mass loss rate (MLR), and the maximum‐rate decomposition temperature of GF–PA6 and increased the residue chars of the samples. Compared with the neat GF–PA6, the AP‐containing GF–PA6 samples had obviously improved flame retardancy: the LOI value increased from 22.5 to 30.1, and the UL‐94 rating went from no rating to V‐0 (1.6 mm) when the AP content increased from 0 to 25 wt % in GF–PA6. The results of CCT reveal that the heat release rate, total heat release, and MLR of the AP‐containing GF–PA6 samples were lower than those of GF–PA6. Furthermore, the higher additive amount of AP affected the mechanical properties of GF–PA6, but they remained acceptable. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of thermooxidative aging on the static and dynamic mechanical properties of long‐glass‐fiber‐reinforced polyamide 6 composites

The static and dynamic mechanical properties, thermal behaviors, and morphology of pure long‐glass‐fiber‐reinforced samples [polyamide 6 (PA6)/long glass fiber (LGF)] with different thermal exposure times at 160°C were studied by comparison with stabilized samples in this study. The aging mechanism of the PA6/LGF samples under heat and oxygen was studied with the methods of thermal Fourier transform infrared (FTIR), differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy (SEM), and so on. The results indicate that the static mechanical strength, melting temperature, and crystallization temperature decreased because of the decomposition of the macromolecular chain of PA6 resin and the debonding of the interface between the glass fibers and matrix. The glass‐transition temperature and crystallinity also increased and decreased, respectively, after aging. The macromolecular chain decomposition dominated in the subsequent aging process; this resulted in many sharp and brittle microcracks appearing on the surfaces of the aged samples, as shown by SEM and the FTIR spectra. The existence of stabilizers endowed the PA6/LGF composites with better retention of static and dynamic mechanical properties. The reason was that the metal ions of the copper salt antioxidant acted as an anti‐aging catalyst in the reinforced PA6 system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39594.     

Fatigue characteristics of a glass‐fiber‐reinforced polyamide

This paper deals with prediction of the temperature rise in the stress‐controlled fatigue process of a glass‐fiber‐reinforced polyamide and the application of a temperature and frequency superposition procedure to the S‐N curve. An experimental equation was derived to predict the temperature rise from calculations based on the fatigue test conditions and viscoelastic properties of the material. The temperature rise (ΔT) can be expressed as a product of a coefficient term Φ(L, κ) concerning heat radiation and the test‐specimen shape and a function term P_fat concerning the viscoelastic properties and fatigue test conditions. Φ(L, κ) was found experimentally to derive the equation for predicting the temperature rise blow or above the glass transition temperature (T_g) of the material. The equation σ_R = −S_Tf A log N_fR + S_Tf B was obtained as a procedure for applying temperature and frequency superposition to S‐N curves in consideration of ΔT. This procedure was obtained by combining both temperature‐ and frequency‐superposition techniques. Here, σ_R and log N_fR represents the stress and the fatigue lifetime calculated at a given temperature and frequency, A and B denote the slope and intercept of any arbitrarily chosen S‐N curve, and S_Tf is a shift factor for temperature and frequency superposition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1783–1793, 1999     

Creep behavior of glass‐fiber‐reinforced nylon 6 products

The creep properties, that is, the velocity constant, activation energy, stress index, and time index, of a test piece (TP) cut from a glass‐fiber‐reinforced nylon 6 product were successfully determined by a compression creep test. In the determination of the creep properties, the experimental creep curves for the TP were fitted by finite element analysis (FEA). Fiber‐reinforced nylon 6 beams with different fiber orientations were also prepared, and their creep properties were successfully determined by a combination of the bending creep test and the corresponding analysis. The creep behavior of the press‐fit component composed of a metal collar and a fiber‐reinforced nylon 6 product was predicted by FEA with the determined creep properties of the TP. The predicted retention forces were in good agreement with the experimental ones. The effects of the fiber orientation on the long‐term reliability of the press‐fit component are also discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Measurement and numerical simulation of three‐dimensional fiber orientation states in injection‐molded short‐fiber‐reinforced plastics

To determine three‐dimensional fiber orientation states in injection‐molded short‐fiber composites, a confocal laser scanning microscope (CLSM) is used. Since the CLSM optically sections the specimen, more than two images of the cross sections on and below the surface of the composite can be obtained. Three‐dimensional fiber orientation states can be determined by using geometric parameters of fiber images obtained from two parallel cross sections. For experiments, carbon‐fiber‐reinforced polystyrene is examined by the CLSM and geometric parameters of fibers on each cross‐sectional plane are measured by an image analysis. In order to describe fiber orientation states compactly, orientation tensors are determined at different positions of the prepared specimen. Three‐dimensional orientation states are obtained without any difficulty by determining the out‐of‐plane angles utilizing fiber images on two parallel planes acquired by the CLSM. Orientation states are different at different positions and show the shell–core structure along the thickness of the specimen. Fiber orientation tensors are predicted by a numerical analysis and the numerically predicted orientation states show good agreement with measured ones. However, some differences are found at the end of cavity. They may result from the fountain flow effects, which are not considered in the numerical analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 500–509, 2003     

Enhancement of interlaminar fracture toughness of carbon fiber–epoxy composites using polyamide‐6,6 electrospun nanofibers

In this study, carbon fiber–epoxy composites are interleaved with electrospun polyamide‐6,6 (PA 66) nanofibers to improve their Mode‐I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three‐point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode‐I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass‐transition temperature of the composites is not affected by the addition of PA 66 nanofibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45244.     

Tensile stress relaxation of short‐coir‐fiber‐reinforced natural rubber composites

The stress relaxation behavior of natural rubber (NR) and its composites reinforced with short coir fibers under tension was analyzed. The rate of stress relaxation was a measure of the increase in the entropy of the compounds: the higher the rate was, the greater the entropy was. At lower strain levels, the relaxation mechanism of NR was independent of strain level. However, the rate of relaxation increased with the strain level. Also, the strain level influenced the rate of stress relaxation considerably in the coir‐reinforced NR composites. However, the relaxation mechanisms of both the unfilled compound and the composite were influenced by the strain rate. The rate of relaxation was influenced by fiber loading and fiber orientation. From the rate of stress relaxation, we found that fiber–rubber adhesion was best in the composite containing fibers subjected to a chemical treatment with alkali, toluene diisocyanate, and NR solutions along with a hexaresorcinol system as a bonding agent. In this study, the stress relaxation curves could not be viewed as segments with varying slopes; however, a multitude of inflection points were observed on the curves. Hence, we propose neither a two‐step nor three‐step mechanism for the coir‐fiber‐reinforced NR composites as reported for some other systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 96–104, 2004     

Reducing water sorption of injection‐molded polyamide 6 bars by polymerization‐induced diffusion of styrene and grafting with polystyrene

An innovative method for reducing water sorption of injection‐molded polyamide 6 (PA6) bars by polymerization‐induced diffusion of styrene and grafting with polystyrene (PS) is reported. The process involves diffusion of styrene into PA6 bar in aqueous medium, addition of benzoyl peroxide to initiate polymerization of styrene, and further diffusion of styrene into the bar during polymerization. A hydrophobic PS‐rich shell consisting mainly of PS‐g‐PA6 can be formed in the surface layer of the PA6 bar, and as a result, the water sorption and dimensional change of PS‐modified PA6 bars reduce significantly. An incorporation of only 1.2% PS is sufficient, showing the advantage of this method over conventional melt mixing. The tensile modulus and strength of 1.2% PS‐modified PA6 bar increase slightly compared to those of neat PA6 bar due to reinforcement effect of rigid PS and reduced level of water‐caused plasticization, while maintaining the good ductility. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46243.     

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

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

Effects of sizing materials on the properties of carbon fiber‐reinforced polyamide 6,6 composites

This article aims to study the effect of the sizing materials type on the mechanical, thermal, and morphological properties of carbon fiber (CF)‐reinforced polyamide 6,6 (PA 6,6) composites. For this purpose, unsized CF and sized CFs were used. Thermogravimetric analysis was performed, and it has been found that certain amounts of polyurethane (PU) and PA sizing agents decompose during processing. The effects of sizing agent type on the mechanical and thermomechanical properties of all the composites were investigated using tensile, Izod impact strength test, and dynamic mechanical analysis. Tensile strength values of sized CF‐reinforced composites were higher than that of unsized CF‐reinforced composites. PA and polyurethane sized CF‐reinforced composites exhibited the highest impact strength values among the other sized CF‐reinforced composites. PU and PA sized CF‐reinforced composites denoted higher storage modulus and better interfacial adhesion values among the other sizing materials. Scanning electron microscope studies indicated that CFs which were sized with PU and PA have better interfacial bonding with PA 6,6 matrix among the sized CFs. All the results confirmed that PA and PU were suitable for CF's sizing materials to be used for PA 6,6 matrix. POLYM. COMPOS., 34:1583–1590, 2013. © 2013 Society of Plastics Engineers     

Short‐term flexural creep behavior and model analysis of a glass‐fiber‐reinforced thermoplastic composite leaf spring

Present work investigated the short‐term flexural creep performance of fiber reinforced thermoplastic injection molded leaf springs. Unreinforced polypropylene, 20 wt % short and 20 wt % long glass fiber reinforced polypropylene materials were injection‐molded into constant thickness varying width mono leaf spring. Short‐term flexural creep tests were performed on molded leaf springs at various stress levels with the aid of in‐house developed fixture integrated with the servo‐hydraulic fatigue machine. Spring rate reduction is reported as an index for the accumulated damage. Experimental creep performance of molded leaf springs for 2 h was utilized to predict the creep performance with the aid of four parameter HRZ model and compared with 24‐h experimental creep data. Test results revealed that HRZ model is sufficient enough to predict short‐time flexural creep performance of engineering products over wide range of stress. Test results also confirmed the suitability of long fiber reinforced thermoplastic material for creep application over other considered materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tribological behavior of short‐fiber‐reinforced polyimide composites under dry‐sliding and water‐lubricated conditions

Polyimide composites reinforced with short‐cut fibers such as carbon, glass, and quartz fibers were fabricated by the polymerization of monomer reactants process. The mechanical properties of the composites with different fiber contents were evaluated. The friction and wear properties of the polyimide and its composites were investigated under dry‐sliding and water‐lubricated conditions. The results indicated that the short‐carbon‐fiber‐reinforced polyimide composites had better tensile and flexural strengths and improved tribological properties in comparison with glass‐fiber‐ and quartz‐fiber‐reinforced polyimide composites. The incorporation of short carbon fibers into the polyimide contributed to decreases in the friction coefficient and wear rate under both dry and water‐lubricated conditions and especially under water lubrication because of the boundary lubrication effect of water. The polyimide and its composites were characterized by plastic deformation, microcracking, and spalling under both dry and water‐lubricated conditions, which were significantly abated under the water‐lubricated condition. The glass and quartz fibers were easily abraded and broken; the broken fibers transferred to the mating metal surface and increased the surface roughness of mating stainless steel, which led to the wear rate increasing for the glass‐fiber‐ and quartz‐fiber‐reinforced polyimide composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Dissolution window in in situ polymerization preparation of polyamide single-polymer composites

Single-polymer composites (SPCs) are promising composite materials in which the reinforcement and matrix have the same chemical composition. In situ polymerization shows a broad application potential for producing SPCs due to its wide temperature window. However, the dissolution of fiber reinforcements in the liquid monomer destroys the oriented chain structure of the fibers and affects the properties of SPCs. In this study, the polymerization time was adjusted by varying the activator dosage. The influence of the dissolution of fibers on the properties and the structure of SPCs was investigated. The maximum tensile strength was achieved at the highest activator dosage. A longer duration was required for the polymerization due to the low-activator dosage, which led to the destruction of the oriented chain structure and the formation of a large amount of oligomers on account of the dissolution. Eventually, SPCs showed a low strength and a high deformation at break. In order to realize a good reinforcing effect, a sufficiently large dissolution window must be created by reducing the polymerization time. This study enhanced our understanding of the structure–property relationships of SPCs and provided a way to improve their mechanical characteristics.     

Distribution and diffusion coefficients of NaCl in polyamide (nylon‐6,6 and polyxylyleneadipamide) membranes

Thin membranes of an aliphatic polyamide (nylon‐6,6) and an aromatic polyamide (polyxylyleneadipamide) (PXAP) were prepared, and their distribution (K) and overall diffusion (D) coefficients of sodium chloride were measured with the unsteady‐state and steady‐state dialysis method. The overall diffusion coefficients at a zero concentration [D⁽⁰⁾] of sodium chloride for nylon‐6,6 and PXAP were 1.3–0.8 μm²/s (from 2 min of interfacial polymerization to 4 min) and 0.078, respectively. D⁽⁰⁾ for PXAP was about 3 times greater than that of a cellulose acetate (CA) membrane (0.024 μm²/s). The K values for nylon‐6,6 and PXAP were 0.7–0.5 from 2 to 4 min and 0.05, respectively. K for PXAP was almost the same as K for CA (0.06). A two‐part (dense and porous) model of the membrane structure was applied to obtain D_d (the diffusion coefficient in the dense part of the membrane) and D_p (the diffusion coefficient in the porous part of the membrane) for CA, PXAP, and nylon‐6,6 thin membranes. The values of D_d were almost the same for both nylon‐6,6 and PXAP (0.05–0.061 μm²/s) and about 10 times greater than the value for the CA membrane (5.6 × 10^?3 μm²/s). D_p for PXAP was almost the same as D_p for CA. However, D_p for the nylon‐6,6 membrane was 10–16 times greater than D_p for the PXAP membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2605–2612, 2002     

Mechanical properties and processibilty of glass‐fiber‐, wollastonite‐, and fluoro‐rubber‐reinforced silicone rubber composites

The reinforcement of silicone rubber (SR) imparted by different types of fillers was investigated. Glass fiber (GF), wollastonite and fluoro rubber (FR) as nontraditional filler for rubber were compounded SR and mechanical properties of the prepared composites were evaluated. The addition of silane pretreated GF and wollastonite into SR, tensile strength, abrasion resistance and tear strength of the composites improved considerably. The improvement in the properties was assigned to an increased interaction between the filler and the polymer matrix. For the SR/FR composites system, the elongation at break was increase with increasing concentrations of FR due to sponge like structure resulting from poor compatibility between the two components. To investigate the production potential of extrusion processing method, prepared composites were extruded in a rod type sample. During the curing stage, GF, wollastonite and FR lead to the formation of void in the matrix resin. When GF and wollastonite were treated with silane, the void formations were reduced significantly. The silane treatment process improves not only mechanical strength but also processibility of SR composites in dry conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Barrier properties for short‐fiber‐reinforced epoxy foams

The barrier properties of short‐fiber‐reinforced epoxy foam are characterized and compared with unreinforced epoxy foam in terms of moisture absorption, flammability properties, and impact properties. Compression and shear properties are also included to place in perspective the mechanical behavior of these materials. Compared with conventional epoxy foam, foam reinforced with aramid fibers exhibits higher moisture absorption and lower diffusion, while glass‐fiber‐reinforced foam is significantly stiffer and stronger. In addition, the polymeric foam composites studied present superior fire‐resistance compared with conventional epoxy foam systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3266–3272, 2006     

Kudzu fiber‐reinforced polypropylene composite

Kudzu fiber‐reinforced polypropylene composites were prepared, and their mechanical and thermal properties were determined. To enhance the adhesion between the kudzu fiber and the polypropylene matrix, maleic anhydride‐grafted polypropylene (MAPP) was used as a compatibilizer. A continuous improvement in both tensile modulus and tensile strength was observed up to a MAPP concentration of 35 wt %. Increases of 24 and 54% were obtained for tensile modulus and tensile strength, respectively. Scanning electron microscopy (SEM) showed improved dispersion and adhesion with MAPP. Fourier transform infrared (FTIR) spectroscopy showed an increase in hydrogen bonding with an increase in MAPP content. Differential scanning calorimetry (DSC) analysis indicated little change in the melting temperature of the composites with changes in MAPP content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1961–1969, 2002     

Durability of glass‐fiber‐reinforced polymer composites in an alkaline environment

This study investigated the aging of urethane and urethane‐modified vinyl ester (UMVE) GFRPs (glass fiber reinforced polymers) when they were exposed to alkaline solution for six months under a sustained load of 34.5 MPa or 16–20% of their tensile strength. The second experiment exposed both types of GFRP to alkaline solution without load for 6 months. The final experiment determined the alkaline solution diffusion coefficients into GFRP and neat polymer resin samples by measuring the change in mass of each sample as a function of time. After the GFRP samples were aged for 6 months, their tensile strengths were measured and compared with that of non‐aged samples to determine the aging effect. It was found that alkaline solution alone without sustained load did not significantly reduce or change the tensile strength of any GFRP sample. However, the presence of sustained load greatly increased the aging effect, particularly more for urethane GFRP than on UMVE GFRP. Urethane GFRP experienced a tensile strength reduction of 57.5%, while UMVE GFRP lost 27.3% of its original tensile strength. J. VINYL ADDIT. TECHNOL., 13:221–228, 2007. © 2007 Society of Plastics Engineers     

Dielectric studies of hyperbranched aromatic polyamide and polyamide‐6,6 blends

The objective of this work was to study the interactions between polyamide‐6,6 (PA‐6,6) and hyperbranched (HB) polyamide with different functional end groups. The investigation focused on the thermal, dielectric, and viscoelastic properties of two kinds of HB polyamides, with amine and alkyl end groups, prepared by a one‐pot process, in a polyamide‐6,6 matrix. Thermal analysis (by TGA and DSC) allowed us to observe decomposition and glass‐transition temperatures of these polymers. The melting point, crystallization temperature, and crystallinity ratio remained practically independent of HB content. Dielectric relaxation spectroscopy (DRS) showed two secondary relaxation (γ and β) and one primary (α) relaxation in the HB polymers and in the blends similar to those observed in polyamide‐6,6 with comparable activation energies and distribution parameters. An increase of the glass‐transition temperature was observed, showing a reinforcement of the polymer matrix and a decrease of the molecular mobility of the polyamide chains when the percentage of amine‐terminated HB polyamide increased in the matrix. DRS results found on the alkyl‐terminated HB polymer blend were indistinct from those of the polyamide‐6,6 matrix. Viscoelastic experiments confirmed the results observed in DRS. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1522–1537, 2005