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.     

Study on the long‐term thermal‐oxidative aging behavior of polyamide 6

The long‐term thermal‐oxidative aging behavior of polyamide 6 (PA6) was studied by comparison with the stabilized sample in this work. The variation of mechanical properties of the pure and the stabilized samples of PA6 with aging time at 110°C, 130°C, and 150°C were investigated, respectively. The aging mechanism of PA6 under heat and oxygen was studied in terms of the reduced viscosity, crystallization behavior, dynamic mechanical behavior, and chemical composition through the methods of polarized light microscopy (PLM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X‐ray photoelectron energy spectrum (XPS), and so on. The results indicated that at the initial stage of aging, the molecular crosslinking reaction of PA6 dominated resulting in the increase of the mechanical strength, reduced viscosity, and the glass transition temperature of the sample. And the molecular degradation dominated in the subsequent aging process resulting in the decrease of the melting temperature, the increase of the crystallinity, and the formation of the oxides and peroxides products. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High residual mechanical properties at elevated temperatures of bamboo/glass reinforced‐polybenzoxazine hybrid composite

We successfully added bamboo and glass fibers into bisphenol A‐aniline based benzoxazine (BA‐a) resin by hot‐pressing method. In order to improve the interfacial adhesion between bamboo fibers and the matrix, bamboo fibers were pretreated in 6 wt% NaOH solutions for 12 h. The results showed alkali‐treatment had a positive effect on mechanical properties of the composites at both room and elevated temperatures (60°C, 110°C, 160°C, and 210°C). Due to the incorporation of glass fibers, the bamboo/glass reinforced‐polybenzoxazine hybrid composites exhibited highest strength and modulus among all samples and had high residual mechanical properties at elevated temperatures (residual mechanical properties refers to the ratio of strength and modulus of the composites at elevated temperatures to that measured at room temperature). The fractured surface morphologies of the composites were observed by scanning electron microscope. The results showed with the increase of temperature, the debonding and fiber pull‐out became apparent, and the matrix softening could be clearly observed at 210°C. In addition, thermal and thermomechanical properties of neat benzoxazine and the composites were also investigated through thermogravimetric analysis and dynamic mechanical analyzer, respectively. POLYM. ENG. SCI., 59:1818–1829, 2019. © 2019 Society of Plastics Engineers     

阻燃型玻纤增强PA10T复合材料的热氧老化性能

采用溴化环氧树脂对聚对苯二甲酰葵二胺(PA10T)进行改性,并通过熔融共混法制备阻燃型玻璃纤维(GF)增强PA10T复合材料,采用人工加速热氧老化手段,研究了热氧老化对其力学性能的影响,并用扫描电子显微镜(SEM)对复合材料的冲击断面形貌进行观察。结果表明,随热氧老化时间增加,复合材料的拉伸强度、弯曲强度和缺口冲击强度均下降明显,分子链松弛过程减弱;老化10 d后,复合材料的弯曲弹性模量仅略有下降而储能模量达到最大值,表明在热氧老化初期PA10T分子链之间发生了微交联,但随老化时间继续增加,两者均下降明显。SEM结果表明GF与树脂基体之间界面粘接作用的强弱是影响材料热氧老化性能变化的主要因素。     

Synthesis of glass fiber‐multiwall carbon nanotube hybrid structures for high‐performance conductive composites

The conductive polyamide 66 (PA66)/carbon nanotube (CNT) composites reinforced with glass fiber‐multiwall CNT (GF‐MWCNT) hybrids were prepared by melt mixing. Electrostactic adsorption was utilized for the deposition of MWCNTs on the surfaces of glass fibers (GFs) to construct hybrid reinforcement with high‐electrical conductivity. The fabricated PA66/CNT composites reinforced with GF‐MWCNT hybrids showed enhanced electrical conductivity and mechanical properties as compared to those of PA66/CNT or PA66/GF/CNT composites. A significant reduction in percolation threshold was found for PA66/GF‐MWCNT/CNT composite (only 0.70 vol%). The morphological investigation demonstrated that MWCNT coating on the surfaces of the GFs improved load transfer between the GFs and the matrix. The presence of MWCNTs in the matrix‐rich interfacial regions enhanced the tensile modulus of the composite by about 10% than that of PA66/GF/CNT composite at the same CNT loading, which shows a promising route to build up high‐performance conductive composites. POLYM. COMPOS. 34:1313–1320, 2013. © 2013 Society of Plastics Engineers     

Preparation and characterization of epoxidate poly(1,2‐butadiene)–toughened diglycidyl ether bisphenol‐A epoxy composites

By the oxidation of liquid poly(1,2‐butadiene) (LPB) with H₂O₂/HCOOH, epoxidate poly(1,2‐butadiene) (ELPB) was obtained as a toughening agent to prepare diglycidyl ether bisphenol‐A (DGEBA) epoxy composites by using V115 polyamide(PA) as a cross‐linking agent. DGEBA, ELPB, and the composites were effectively cured by PA at 100°C for 2 h followed by postcuring at 170°C for 1 h. Thermal gravimetric analysis results in air and nitrogen atmosphere showed that the thermal stability of composites could be improved by the addition of ELPB. Compared with DGEBA/PA, the composites exhibited a decrease in strength at yield but an increase in strain at break with the increase in ELPB amount. The composite with 10% ELPB exhibited both thermal stability and tenacity superior to those of DGEBA/PA and composites with 5 and 20% ELPB, respectively. The improvements in thermal and mechanical properties of composites depended on the formation of Inter Penetrating Networks (IPN) among DGEBA/PA/ELPB and their distributions in the matrix. At an appropriate ELPB amount, the IPN, mostly made of DGEBA/PA/ELPB, may be distributed more evenly in the matrix; less ELPB resulted in the formation of IPN mainly made of DGEBA/PA; excessive addition of ELPB resulted in the local aggregation of ELPB/PA and phase separations. The toughening mechanism was changed from chemically forming IPN made of DGEBA/PA/ELPB to physically reinforcing DGEBA/PA by ELPB/PA with the increase in ELPB addition. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Semiaromatic polyamide poly(hexamethylene terephthalamide)‐co‐polycaprolactam: Thermal and flame‐retardant properties

The poly(hexamethylene terephthalamide)‐co‐polycaprolactam (PA6T/6; 50:50) copolymer was synthesized with a reactive extrusion method and subsequently mixed with a certain content of glass fibers (GFs) and different ratios of flame‐retardant aluminum diethyl phosphinate (AlPi) to fabricate a series of composites. These resulting composites were found to have excellent mechanical (tensile strength = 119–154 MPa) and thermal properties (heat‐deflection temperature = 263–293 °C). It is particularly worth mentioning that the value of the limiting oxygen index reached 29.5% and a UL‐94 V‐0 rating (1.6 mm) was achieved with the addition of 20 portions of AlPi. Also, the values of the peak heat‐release rate and total heat release in cone calorimetry were found to decrease with the addition of the flame‐retardant AlPi, which acted mainly as a flame inhibitor in the gas phase. Through visual observation, scanning electron microscopy after cone calorimetry testing, and thermogravimetric analysis, the condensed‐phase flame‐retardant mechanism of the PA6T/6–GF–AlPi system was confirmed to have a synergetic role. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46451.     

Effect of ortho‐diallyl bisphenol A on the processability of phthalonitrile‐based resin and their fiber‐reinforced laminates

Sluggish and narrow process window of phthalonitrile resin has tremendously limited their wide applications. In this work, a novel phthalonitrile containing benzoxazine (4,4′‐(((propane‐2,2‐diylbis (2H‐benzo [e] [1,3]oxazine‐6,3 (4H)‐diyl) bis(3,1‐phenylene))bis(oxy)) diphthalonitrile, BA‐ph) with ortho‐diallyl bisphenol A (DABPA) was investigated. The processing window of the BA‐ph/DABPA blends were found from 50°C to 185°C, which was significantly broader than that of the pure BA‐ph (120–200°C). The composites were prepared through a curing process involving sequential polymerization of allyl moieties, ring‐opening polymerization of oxazine rings and ring‐forming polymerization of nitrile groups. BA‐ph/DABPA/GF(glass fiber) composite laminates were prepared in this study, and the composite laminate with BA‐ph/DABPA molar ratio of 2/2 showed an outstanding flexural strength and modulus of 560 MPa and 37 GPa, respectively, as well as a superior thermal and thermo‐oxidative stability up to 408 and 410°C. These outstanding properties suggest that the BA‐ph/DABPA/GF composites are suitable candidates as matrices for high performance composites. POLYM. ENG. SCI., 56:150–157, 2016. © 2015 Society of Plastics Engineers     

Effect of thermal shock on interlaminar strength of thermally aged glass fiber‐reinforced epoxy composites

Glass fiber/epoxy composites were thermally conditioned at 50, 100, 150, 200, and 250°C for different periods of time and then immediately quenched directly in ice‐cold water from each stage of conditioning temperature. The polymerization or depolymerization by thermal conditioning and the debonding effect by concurrently following thermal shock in polymer composites are assessed in the present study. The short‐beam shear tests were performed at room temperature on the quenched samples to evaluate the value of interlaminar shear strength of the composites. The short conditioning time followed by thermal shock resulted in reduction of shear strength of the composites. The strength started regaining its original value with longer conditioning time. Conditioning at 250°C and thereafter quenching yielded a sharp and continuous fall in the shear strength. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2062–2066, 2006     

Design of the phthalonitrile‐based composite laminates by improving the interfacial compatibility and their enhanced properties

Phthalonitrile containing benzoxazine (BA‐ph) and cyanate ester (CE) were chosen as the thermosetting matrix and the glass fiber (GF) reinforced laminates formed at low temperature were designed. The polyarylene ether nitriles containing pendent carboxyl groups (CPEN) was selected to modify the interfacial interaction between the resin matrix and GFs. Two methods of introducing CPEN were compared and the effects of CPEN on curing behaviors and properties of the composites were investigated. Results showed that with the CPEN, exothermic peaks shifted to lower temperature and curing temperatures of BA‐ph/CE decreased slightly. The mechanical and thermal properties of GF‐reinforced composites were discussed and the results indicated that the composites of modified GFs with CPEN exhibited outstanding mechanical properties, higher glass transition temperature (T_g > 290 °C) than that of composites composed of CPEN mixed with BA‐ph/CE. Moreover, GF‐reinforced composites showed stable dielectric constants (3.8–4.5) and low dielectric loss (0.005–0.01), which were independent of the frequency. In sum, the various methods of the introduction of CPEN in the GF‐reinforced composites may provide a new route to prepare improved composites, meanwhile, composites with outstanding processability and excellent mechanical and thermal properties are expected to be widely applied in the fields of high‐performance structural materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45881.     

Thermal aging performance of glass fiber/polyphenylene sulfide composites in high temperature

In order to use the glass fiber reinforced polyphenylene sulfide composites (GF/PPS) in high temperature environments, thermal aging performance of two kinds of commercial grade PPS composites, reinforced by 40% glass fiber, PPS-G40 HM and 1140L4, in thermal aging temperature of 250°C was compared by tensile strength, oxidized layer, color, crystallization and melting behavior. The results showed that tensile strength of GF/PPS composites is significantly decreased with increasing of aging time below 200 h and the tensile strength of aged PPS-G40 HM is higher than that of aged 1140L4. The thickness of dark color area is increased with increasing of aging time. The thickness of oxidized layer of 1140L4 is thinner than that of PPS-G40 HM. However, the color of oxidized layer of PPS-G40 HM is lighter than that of 1140L4. The recrystallization in thermal aging results in the formation of crystal with higher melting point and increased melting temperature of GF/PPS composites. It is found that addition of epoxy resin can increase the initial mechanical property and improve the thermal aging performance of GF/PPS composites. A novel modified GF/PPS composite with higher thermal aging properties was obtained.     

Mechanical and physical characteristics of cellulose‐fiber‐filled polyacetal composites

We investigated the mechanical and physical characteristics of composites composed of polyacetal [alternatively called polyoxymethylene (POM)] and cellulose fiber (CelF) derived from wood pulp [10–52 wt % (9.3–50.1 vol %)] without any fiber surface treatment. The modulus, deflection temperature under load, and thermal conduction coefficient of the POM/CelF composites were effectively enhanced with increasing CelF content, and the composites had an advantage of specific modulus compared to glass fiber (GF)‐filled POM. The flexural modulus of POM/CelF 40 wt % (38.2 vol %) was measured to be about 6 GPa, which was comparable to that of POM/GF 20 wt % (12.1 vol %). In the composites, the CelFs were distributed randomly as monofilaments, and the debonding of the interface between the fibers and POM matrices in the fracture faces was confirmed as less by scanning electron microscopy observation. The POM/CelF composites possessed lower specific wear rates than the POM/GF composites, and they had damping behaviors near that of neat POM. No clear dependence of the melt flow index of the base POM on these characteristics was observed, except on Charpy impact strength. The composites studied here were unique in their performance and ability to be designed in accordance with specific demands, and they could be potential replacements for mineral‐filled and GF‐filled POM composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of thermo‐oxidative aging on vibration damping characteristics of conventional and graphene‐based carbon fiber fabric composites

The effect of thermo‐oxidative aging on the vibration damping characteristics of the conventional fabric composites reinforced by three‐dimensional (3D) and four‐directional (4Dir) braided preform and laminated plain woven fabric and the 3D‐4Dir braided graphene‐based carbon fiber composites was investigated. Specimens were isothermally aged at 140 °C for various periods of time up to 1,200 h. The results indicated that the thermo‐oxidative aging resulted in deterioration of the matrix and interface performance, in the form of chain scissions, weight loss, microcracks and interfacial debonding, which should be responsible for the decrease of nature frequency and the increase of damping coefficient of the composites. After aging for 1,200 h, the first nature frequency and first damping coefficient retention rates of 3D‐4Dir braided graphene‐coated carbon fiber/epoxy composite were 5.5% and 6.4% higher than those of laminated composite, respectively. One of the reasons was the integrated structure of 3D‐4Dir braided composite exposed lower fiber end area to air than that of laminated composite, leading to less interface oxidation. Another reason was that the graphene reinforced gradient interphase provided an effective shield against interface oxidation and restricted the movement of the different phase of the materials at the composites interface. This synergetic reinforcing effect of 3D‐4Dir braided structure and graphene reinforced hierarchical interface provides an easy and effective way to design and improve the thermo‐oxidative stability of carbon fiber reinforced polymer composites. POLYM. COMPOS., 37:2871–2883, 2016. © 2015 Society of Plastics Engineers     

Synergistic enhancement of glass fiber and tetrapod‐shaped ZnO whisker on the mechanical and thermal behavior of isotactic polypropylene

Improvement of mechanical and thermal properties is always the goal of high‐performance general plastic for engineering applications. Herein, isotactic polypropylene/glass fiber/tetrapod‐shaped zinc oxide (iPP/GF/T‐ZnOw) composites are developed via melt‐extrusion on twin‐screw extruder. To improve the distribution of T‐ZnOw in iPP matrix, T‐ZnOw is first modified by various silane coupling agents and its structure is characterized by scanning electron microscopy, Fourier transform infrared spectra, and X‐ray diffraction (XRD). The optimized treatment condition is determined via comparison of activation index. The introduction of GF and T‐ZnOw could improve the mechanical properties including tensile strength, elastic modulus, flexural strength, flexural modulus, and impact strength, indicating that the surface modification and compatibilizer could enhance the interfacial interaction of iPP/GF/T‐ZnOw composites. Moreover, XRD and differential scanning calorimentryresults show that T‐ZnOw as a novel β‐nucleating agent could induce the formation of β‐crystal and the existence of GF counteracts the formation of β‐crystal induced by T‐ZnOw. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44217.     

Fabrication and mechanical properties of glass fiber‐reinforced wood plastic hybrid composites

To fully utilize the resource in the municipal solid waste (MSW) and improve the strength and toughness of wood plastic composites, glass fiber (GF)‐reinforced wood plastic hybrid composites (GWPCs) were prepared through compounding of recycled high‐density polyethylene (HDPE) from MSW, waste wood fibers, and chopped GF. Mechanical tests of GWPCs specimens with varying amounts of GF content were carried out and the impact fractured surface of GWPCs was observed through scanning electron microscope (SEM). The tensile strength of GWPCs and the efficiency coefficient values were predicted by Kelly‐Tyson method. The results indicated that the tensile strength and impact strength of GWPCs could be improved simultaneously by adding type L chopped GF (L‐GF), and would be dropped down when type S chopped GF (S‐GF) was included. The tensile strength of GWPCs was well accordant with the experimental result. The efficiency coefficient values of S‐GF and L‐GF are ?0.19 and 0.63, respectively. Inspection of SEM micrographs indicated that L‐GF had achieved full adhesion with the plastic matrix through addition of maleic anhydride‐g‐polyethylene. The main fracture modes of GWPCs included pullout of GF, broken of matrix, and interfacial debonding. Because of the synergistic effects between hybrid components in GF/wood fiber/HDPE hybrid system, a special 3D network microstructure was formed, which was the main contribution to the significant improvement in the tensile strength and impact strength of L‐GF‐reinforced hybrid composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and properties of an oxide fiber‐reinforced silica matrix composite

Oxide (Nextel? 440) fiber‐reinforced silica composites, with the density and porosity of 1.97 g/cm³ and 21.8%, were prepared through sol‐gel. Their average flexure strength, elastic modulus, shear strength, and fracture toughness at room temperature were 119.7 MPa, 25.6 GPa, 10.8 MPa, and 4.0 MPa·m^1/2, respectively. The composites showed typical toughened fracture behavior, and distinct pullout fibers were observed at the fracture surface. Their mechanical properties were performant up to 1000°C, with the maximum flexural strength of 132.2 MPa at 900°C. Moreover, the composites showed good thermal stability, even after thermal aging and thermal shock at elevated temperatures.     

Thermal–oxidative degradation and accelerated aging behavior of polyamide 6/epoxy resin‐modified montmorillonite nanocomposites

Polyamide 6 (PA6) nanocomposites based on epoxy resin‐modified montmorillonite (EP‐MMT) were prepared by melt processing using a typical twin‐screw extruder. X‐ray diffraction combined with transmission electron microscopy was applied to elucidate the structure and morphology of PA6/EP‐MMT nanocomposites, suggesting a nearly exfoliated structure in the nanocomposite with 2 wt % EP‐MMT (PA6/2EP‐MMT) and a partial exfoliated‐partial intercalated structure in PA6/4 wt %EP‐MMT nanocomposite (PA6/4EP‐MMT). The thermogravimetric analysis under air atmosphere was conducted to characterize the thermal–oxidative degradation behavior of the material, and the result indicated that the presence of EP‐MMT could inhibit the thermal‐oxidative degradation of PA6 effectively. Accelerated heat aging in an air circulating oven at 150°C was applied to assess the thermal–oxidative stability of PA6 nanocomposites through investigation of reduced viscosity, tensile properties, and chemical structure at various time intervals. The results indicated that the incorporation of EP‐MMT effectively enhanced the thermal–oxidative stability of PA6, resulting in the high retention of reduced viscosity and tensile strength, and the low ratio of terminal carboxyl group to amino group. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40825.     

Performance and structure changes of the aromatic co‐polysulfonamide fibers during thermal‐oxidative aging process

The changes in performance during thermal‐oxidative aging process of the aromatic co‐polysulfonamide (co‐PSA) fibers over a broad temperature range from 250 °C to 320 °C have been investigated. In addition, the mechanism of thermal‐oxidative aging process has been studied by using structural information obtained from the fibers at varying length scales. The results showed that a significant reduction in tensile strength was observed compared with that of initial modulus during aging process. Macroscopically, thermal‐oxidative aging mainly causes color changes of fibers and thermally induced macro defects begin to appear only at 320 °C for 100 h. On a micro level, the crystal structure of fibers remained stable and did not show significant changes expect that aging at 320 °C. In addition, thermo‐degradation as well as crosslinking has been observed primarily in amorphous region. With the increase of temperature and time duration, the crosslinking became more dominant and crosslinking density increases. Correspondingly, the fibril length decreases due to degradation and then increases due to the formation of crosslinked structures within the fibers. The results suggest that molecular degradation is the main cause of strength loss and the formation of crosslinking structure within the fibers contributes to the retention of modulus and improvement of creep resistance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44078.     

Bismaleimide‐modified methyl‐di(phenylethynyl)silane blends and composites: Cure characteristics,thermal stability,and mechanical property

Reactive blends of organic‐inorganic hybrid monomer, methyl‐di(phenylethynyl)silane (MDPES) and a modified bismaleimide resin (BMI/DBA) have been prepared. The thermal and oxidative stabilities of MDPES‐BMI/DBA blends were characterized by thermogravimetric analysis, derivative thermogravimetry, differential thermal analysis, dynamic mechanical analysis, and flexural strength retention at 240°C. Scanning electron microscopy was employed to study the surface morphology of MDPES‐BMI/DBA composite after thermal oxidative treatment. With the increase of concentration of BMI/DBA, flexural strength of composites increased from 78 to 331 MPa. The results showed that MDPES‐BMI/DBA blends exhibited excellent thermal and thermal oxidative properties, and the interface between MDPES and glass fiber was improved by the incorporation of BMI/DBA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermoplastic composites of polyamide‐12 reinforced by cellulose nanofibers with cationic surface modification

Cellulose nanofibers (CNFs) have many useful properties, including high strength and low thermal expansion, and are also environmentally friendly, readily renewable, safe, and biodegradable. The focus of this study was the development of lightweight thermoplastic polymer composites with good mechanical properties based on the incorporation of CNFs that have undergone surface pretreatment with a cationic reagent. The polyamide (PA12) was mixed with surface‐treated CNFs using a twin screw extruder and the resulting pellets were injection molded. The Izod impact strength without notch of CNF‐based composites exceeded that of composites incorporating organophilic montmorillonite (OMMT), a representative nanocomposite material. When the Izod impact test without notch, the impact hammer was stopped by the specimen with incorporation of surface treated CNF. Furthermore, the bending modulus and strength were equal to or greater than that of OMMT composites. The heat distortion temperature was improved as 33°C from neat PA12, and moreover improved as 29°C from OMMT composites. Cationic pretreatment of the CNF surfaces was found to increase the dispersion of the fibers and also to greatly improve the mechanical and thermal properties of the composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40920.