Effects of postcure temperature variation on hygrothermal‐mechanical properties of an out‐of‐autoclave polymer composite

The effects of cure temperature variation on the properties of an out‐of‐autoclave polymer composite manufactured using Cycom 5320 8HS prepreg were investigated using different postcure temperatures of a two‐stage cure cycle. In addition, the effects of adverse environmental conditions on the cure temperature variation were studied by conditioning the samples in an environmental chamber until they reached moisture equilibrium. The state of cure was obtained using a differential scanning calorimeter and dynamic mechanical analyzer. The mechanical properties were obtained using short‐beam shear (SBS) and combined loading compression (CLC) test methods. The state of cure obtained showed increases in total heat of reaction, degree of cure, and glass transition temperature as the postcure temperature increased. The SBS and CLC strengths showed an increasing trend as postcure temperature increased. Good correlations were obtained between the material's cure temperatures, state of cure, and mechanical properties for room temperature dry and hot wet conditions. The study showed that the state of cure can be used to define, monitor, and verify the cure quality. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3090–3097, 2013     

Evolution of mechanical properties during cure for out‐of‐autoclave carbon‐epoxy prepregs

Extent of cure and rheological properties were obtained for out‐of‐autoclave materials, Cycom 5320‐8HS and Cycom 5320‐PW, for the manufacturer recommended cure cycle using differential scanning calorimeter and encapsulated sample rheometer (ESR), respectively. Rheological properties from ESR were further used in designing the cure cycles to study the evolution of mechanical properties. Five panels were cured at different cure stages using the designed cure cycles and coupons were tested for short beam shear and combined loading compression properties at different cure stages. To correlate the mechanical properties with its respective glass transition temperature, dynamic mechanical analyzer was used to obtain the glass transition temperature for the coupons obtained from the respective panels. Statistical results showed significant difference in short beam shear and combined loading compression properties up to vitrification, however, no significant difference was observed on these mechanical properties after vitrification. The observed linear trend between degree of cure (DOC) and glass transition temperature (T_g) was validated using DiBenedetto relation. Linearly increasing trend between DOC and glass transition temperature (T_g) for different cure states suggests that both DOC and T_g can be used interchangeably to define the state of material. A good correlation was observed between material cure state and the mechanical properties. A mathematical model was also proposed to determine the short beam shear and combined loading compression properties based on material cure state. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41548.     

Nitrile functionalized benzoxazine/bismaleimide blends and their glass cloth reinforced laminates

A novel high‐performance resin blend composed of nitrile functionalized benzoxazine (CNBZ) and bismaleimide (4,4′‐bismaleimidodiphenyl methane) (BMI) was prepared via solvent method. Its curing behaviors, thermal properties, and mechanical properties were studied by differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and universal testing machine, respectively. The results showed that the addition reaction between phenolic hydroxyl group and the double bond occurred except for the homopolymerization of CNBZ and BMI. When BMI content was more than 40%, the cured CNBZ/BMI blends exhibited higher glass transition temperatures (T_gs) than CNBZ and BMI homopolymers, which reached up to 334°C. Meanwhile, when BMI content was 40%, the tensile strength, flexural strength, and shearing strength reached up to 69, 235, and 12.9 MPa, respectively, which exhibited the comparable mechanical properties with BT resin. Furthermore, the glass cloth (GF) reinforced laminates based on these blends were prepared. The results showed that when BMI content was 40%, their tensile strength, flexural strength, and impact strength reached up to 334 MPa, 593 MPa, and 145 KJ m^?2, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41072.     

High glass transition temperature bismaleimide‐triazine resins based on soluble amorphous bismaleimide monomer

A novel bismaleimide (DOPO‐BMI) with unsymmetrical chemical structure and DOPO pendant group has been prepared. The particular molecular structure makes DOPO‐BMI show an intrinsic amorphous state with a T_g about 135°C and excellent solubility in most organic solvents, which is beneficial to the processability of bismaleimide composite materials. A series of bismaleimide‐triazine (BT) resins have been prepared based on DOPO‐BMI and 2,2‐bis(4‐cyanatophenyl)propane at various weight ratios. The prepared BT resins show outstanding solubility in organic solvent and low viscosity about 10–671 mPa s at 180°C. The cured BT resins exhibit high glass transition temperature (T_g) over 316°C. As the weight ratio of DOPO‐BMI increases to 80% (BT80), the T_g can rise to 369°C (tan δ). The cured BT resins also show good thermal stability with the 5% weight loss temperature over 400°C under both nitrogen and air atmosphere. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42882.     

Effect of processing conditions on physical properties of 3‐aminophenoxyphthalonitrile/epoxy laminates

To develop high performances of polymer composite laminates, differential scanning calorimetry and dynamic rheological analysis studies were conducted to show curing behaviors of 3‐aminophenoxyphthalonitrile/epoxy resin (3‐APN/EP) matrix and define cure parameters of manufacturing processes. Glass fiber reinforced 3‐APN/EP (GF/3‐APN/EP) composite laminates were successfully prepared through different processing conditions with three parameters such as pressures, temperatures, and time. Based on flexure tests, dynamic mechanical analysis, thermal gravimetric analysis, and scanning electron microscope, the complementary catalytic effect of the three processing parameters is investigated by studying mechanical behavior, thermomechanical behavior, thermal behavior, and fracture morphology of GF/3‐APN/EP laminates. The 50/50 GF/3‐APN/EP laminates showed a significant improvement in flexural strength, glass transition temperature (T_g), and thermal stability with favorable processing parameters. It was also found that the T_g and thermal stability were significantly improved by the postheated treatment method. The effect of manufacturing process provides a new and simple route for the polymer–matrix composites application, which indicates that the composites can be manufactured at low temperatures. But, they can be used in a high temperature environment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39746.     

Characterization of shear stress at the tool‐part interface during autoclave processing of prepreg composites

In this article, shear stress between an aluminum tool and a carbon fiber‐epoxy prepreg is characterized during cure using polymeric release agent and release film at the tool‐part interface. The effects of surface roughness, release materials, pull‐out speed, temperature, and normal force (autoclave pressure) on the shear stress are investigated using a customized friction rig. Results show that the interfacial shear stress decreases as the temperature increases and it increases as the normal force increases when using either the release film or the release agent. Additionally, changes in surface roughness from 1.35 to 0.18 μm decrease the shear stress 10–27% while the use of release agent shows a decrease between 23% and 51% in the shear stress. Furthermore, strong adhesion between the tool and the part is observed when using release agent and pull‐out speeds of 0.05 mm/min (static/dynamic friction ratio of 5.29 ± 0.19). Using the experimental data, a mathematical approach based on the Coulomb's friction model is proposed to predict the friction force at the tool‐part interface. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Response surface predictions of the viscoelastic properties of vapor‐grown carbon nanofiber/vinyl ester nanocomposites

A full factorial design of experiments and response surface methodology were used to investigate the effects of formulation, processing, and operating temperature on the viscoelastic properties of vapor‐grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. Factors included VGCNF type (pristine, oxidized), use of a dispersing agent (DA) (no, yes), mixing method (ultrasonication, high‐shear mixing, and a combination of both), VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)), and temperature (30, 60, 90, and 120°C). Response surface models (RSMs) for predicting storage and loss moduli were developed, which explicitly account for the effect of complex interactions between nanocomposite design factors and operating temperature on resultant composite properties; such influences would be impossible to assess using traditional single‐factor experiments. Nanocomposite storage moduli were maximized over the entire temperature range (～20% increase over neat VE) by using high‐shear mixing and oxidized VGCNFs with DA or equivalently by employing pristine VGCNFs without DA at ～0.40 phr of VGCNFs. Ultrasonication yielded the highest loss modulus at ～0.25 phr of VGCNFs. The RSMs developed in this investigation may be used to design VGCNF‐enhanced VE matrices with optimal storage and loss moduli for automotive structural applications. Moreover, a similar approach may be used to tailor the mechanical, thermal, and electrical properties of nanomaterials over a range of anticipated operating environments. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Particleboards from peanut‐shell flour

Peanuts have been cultivated worldwide for hundreds, if not thousands, of years. However, most peanuts are sold without the shell, and so large quantities of peanut shells remain as byproducts in the field, not being used properly. In this work, the feasibility of making particleboard from milled peanut shells was studied. To obtain medium‐density panels, a low compaction pressure and a high fiber content were used. The physical and mechanical properties of the panels were similar to those reported for wood‐based particleboard when 80 wt % filler was used. The void content of the panels was experimentally determined and used in an attempt to predict the mechanical response of the panels. The stiffness of the particleboard could be greatly improved by a reduction of the porosity, but even a low void content had a critical effect on the strength of the composites. The stiffness of the composites could only be reasonably represented with simple theoretical models when the effect of the porosity was incorporated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 916–923, 2005     

Preparation and characterization of quartz‐fiber‐cloth‐reinforced,polymerization‐of‐monomer‐reactant‐type polyimide substrates with a high impact strength

A series of novel quartz‐fiber‐cloth‐reinforced polyimide substrates with low dielectric constants were successfully prepared. For this purpose, the A‐stage polyimide solution was first synthesized via a polymerization‐of‐monomer‐reactant procedure with 2,2′‐bis(trifluoromethyl)benzidine and 3,3′,4,4′‐oxydiphthalic anhydride as the monomers, and cis?5‐norbornene‐endo‐2,3‐dicarboxylic anhydride as the endcap. Then, an A‐stage polyimide solution (TOPI) was impregnated with quartz‐fiber cloth (QF) to afford the prepregs, which were thermally molded into the final substrate composites. The influence of the curing temperature and the resin content on the mechanical properties of the composite were examined. The composites exhibited a high glass‐transition temperature over 360°C, a low and steady dielectric constant below 3.2 at a test frequency of 1–12 GHz, and a volume resistance over 1.8 × 10¹⁷ Ω cm. Meanwhile, they also showed a high mechanical strength with flexural and impact strengths in ranges 845–881 MPa and 141–155 KJ/m², respectively. The excellent mechanical and thermal properties and good dielectric properties indicated that they are good candidates for integrated circuit packaging substrates. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42358.     

PET interleaving veils for improved fracture toughness of glass fibre/low‐styrene‐emission unsaturated polyester resin composites

The use of interleaved polyethylene terephthalate (PET) veils to increase the interlaminar fracture toughness of glass fiber‐reinforced, low‐styrene emission, unsaturated polyester resin composites, was investigated. PET, being chemically similar to the unsaturated polyester resin, was expected to exhibit good wetting and strong interaction with the matrix. Composite laminates were manufactured by hand lay‐up, with the veil content varying up to 7%. The effects of PET veils on the interlaminar shear strength, flexural strength, flexural modulus, glass transition temperature, damping parameters, and Mode‐I interlaminar fracture toughness of the composite were studied. The veils were found to enhance most of these properties, with only minor negative effects on flexural stiffness and T_g. The PET/resin bonding did indeed prove to be strong, but the enhancement of fracture toughness was not as much as expected, because of the weaker glass/resin interface providing an alternative crack propagation path. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42877.     

Influence of fiber volume fraction and aspect ratio in resol–sisal composites

Vegetable fibers are being used as reinforcements in polymeric matrices with a wide variety of applications. Among these fibers, sisal is of particular interest due to the high impact strength and moderate tensile and flexural properties of its derivated composites. Because of its low cost and affinity, a phenol–formaldehyde resin, resol, has been selected as the matrix to obtain resol–sisal composites. The influence of fiber length and volume fraction on flexural properties has been studied. An optimum for the fiber length as well as for the fiber volume fraction was found. The improvement of the properties occurred up to a length of about 23 mm. The use of longer fibers lead to reduced properties because they tended to curl and bend during processing. Besides, actual composite densities were lower than theoretical ones mainly due to the presence of voids. This undesirable porosity produced a reduction in flexural properties at high fiber contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2714–2722, 2003     

Mechanical enhancement of amine‐functionalized TiO2 reinforced polyimine composites

Polyimine vitrimers are known for their malleability, which endows these materials with properties such as self‐healing, recycling, and reshaping. To enhance the mechanical properties of the polyimine vitrimers, composites were fabricated by incorporating amine‐functionalized TiO₂ microspheres (amTiO₂MS) into polyimine matrix. The pure polyimine matrix and polyimine composites hybridized with TiO₂ microspheres (TiO₂MS) without surface modification were also obtained and examined as the controls in characterization. X‐ray powder diffraction, scanning electron microscopy, and energy dispersive X‐ray spectroscopy were employed to demonstrate the presence and distribution of amTiO₂MS and TiO₂MS in the polyimine matrices. The investigation of mechanical properties of the amTiO₂MS enhanced polyimine composites and control samples indicated that incorporation of amTiO₂MS and TiO₂MS exhibited different characteristic distribution, which strongly affected the performance of the composites. The optimal filling concentration of amTiO₂MS was found to be 3%, with which the microspheres were uniformly distributed in the polyimine matrix. The self‐healing behavior of the polyimine‐amTiO₂‐X was also studied. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46446.     

Mechanical and thermal properties of bio‐based CaCO3/soybean‐based hybrid unsaturated polyester nanocomposites

Bio‐based calcium carbonate nanoparticles (CaCO₃) were synthesized via size reduction of eggshell powder using mechanical attrition followed by high intensity ultrasonic irradiation. The transmission electron microscopic (TEM) and BET surface area measurements show that these particles are less than 10 nm in size and a surface area of ～44 m²/g. Bio‐based nanocomposites were fabricated by infusion of different weight fractions of as‐prepared CaCO₃ nanoparticles into Polylite® 31325‐00 resin system using a non‐contact Thinky® mixing method. As‐prepared bio‐nanocomposites were characterized for their thermal and mechanical properties. TEM studies showed that the particles were well dispersed over the entire volume of the matrix. Thermal analyses indicated that the bio‐nanocomposites are thermally more stable than the corresponding neat systems. Nanocomposite with 2% by weight loading of bio‐CaCO₃ nanoparticles exhibited an 18°C increase in the glass transition temperature over the neat Polylite 31325 system. Mechanical tests have been carried out for both bio‐nanocomposites and neat resin systems. The compression test results of the 2% Bio‐CaCO₃/Polylite 31325 nanocomposite showed an improvement of 14% and 27% in compressive strength and modulus respectively compared with the neat system. Details of the fabrication procedure and thermal and mechanical characterizations are presented in this article. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1442–1452, 2013     

Layer‐by‐layer fabrication of nacre inspired epoxy/MMT multilayered composites

The organic–inorganic hybrid multilayered composites are prepared using a unique combination of poly[(o‐cresyl glycidyl ether)‐co‐formaldehyde] (CNER), amino modified montmorillonite (NH₂‐MMT), and polyethyleneimine (PEI). This tricomponent composite multilayer PEI(CNER/NH₂‐MMT/PEI)_n deposited via layer ‐ by ‐ layer technique is based upon synergistic combination of covalent and hydrogen bonding. The growth of multilayer was monitored using UV–vis spectroscopy and ellipsometry. When subjected to optical analyses, the prepared multilayered composite films revealed profound optical transmittance ～83%–87%. The surface morphological analysis by atomic force microscopy and scanning electron microscopy revealed uniform arrangement of organic–inorganic components with relative increase in intensity of elements (C, N, O, Si) as confirmed by X‐ray photoelectron spectroscopy studies. The multilayered composites possess 1.99 GPa hardness making them potential candidate for a number of applications where mechanical strength is desired. Moreover, significant resistance against alkaline and organic solvents at minimal deterioration of circa 0.12% has also been observed for the prepared films. The epoxy clay based thin films being robust, scratch resistant, hydrophilic, chemically inert, and mechanically strong are potential candidates for advanced environmental applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46079.     

Improved shape memory effects in multiwalled‐carbon‐nano‐tube reinforced thermosetting polyurethane composites

Shape memory thermosetting polyurethane (SMPU) composites containing different amount of multiwalled carbon nanotube (MWCNT) ranging from 0 to 0.250 phr were prepared. The shape memory behavior, tensile stress, and recovery stress were determined by using conventional thermomechanical cycle; however, the modified thermomechanical cycle designated as progressive stretch–relax–stretch (PSRS) cycle was also employed to create shape memory effects in studied composites. The test was carried out in water bath which was equipped with an electric heater, temperature controller, and tensile stress and strain measuring setup. The recovery and tensile stresses both were showing higher values for PSRS samples as compared with conventional samples. Loading of MWCNT improved the recovery stress of SMPU, thereby confirming reinforcing effect. The maximum recovery stress of 2.17 MPa for 0.188 phr MWCNT loading was observed as compared with 1.09 MPa of unreinforced SMPU specimen. The recovery time was also improved on reinforcement as demonstrated in this article. The morphology of fractured surface and degree of dispersion of MWCNT was studied using Field Emission Scanning Electron Microscope. The impact on glass transition temperature was also observed for MWCNT reinforcement on SMPU, which depends on the degree of dispersion and loading of MWCNT in the specimen. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44389.     

Thermal degradation kinetics,mechanical, and flame retardant properties of epoxy‐HDPE fabric‐clay composite laminates

Addition of particulates into laminates has been found to influence thermal and mechanical properties. Composite laminates of epoxy‐high density polyethylene (HDPE) fabric‐clay were prepared by reinforcing clay in the range of 0.1–0.7 phr into epoxy‐HDPE fabric laminates. These laminates are characterized for their mechanical, thermal, and flame retardant performances. With the addition of clay, an increase was found in impact resistance, tensile strength, flexural strength, and Young's modulus to an extent of 0.2 phr clay, after which there is a decrease in these properties. The thermal stability is found to decrease with the addition of clay. The improved mechanical properties are obtained at the slight expense of thermal stability. UL‐94 tests indicate a reduction in the burning rate. Morphology of the broken samples indicate better dispersion at lower clay load and tactoid formation at higher clay loading. These materials have potential applications in agriculture, construction, and decorative purposes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40751.     

Development of multiwalled‐carbon‐nanotube‐welded carbon fibers and evaluation of the interfacial strength in epoxy composites

Multiwalled carbon nanotube (MWCNT)‐welded carbon fibers (CFs) were prepared by a three‐step process, which included polyacrylonitrile (PAN) coating, MWCNT absorption, and heat treatment. The structure of these materials was characterized by scanning electron microscopy, Fourier‐transform infrared spectroscopy, and Raman spectroscopy. The MWCNTs were uniformly assembled on the surface of the PAN‐coated CFs and welded by a PAN‐based carbon layer after heat treatment. The contact angle of the MWCNT‐welded CFs in the epoxy resins was 41.70°; this was 22.35% smaller than that of the unsized CFs. The interfacial shear strength (IFSS) of the MWCNT‐welded CF–epoxy composite was 83.15 MPa; this was 28.89% higher than that of the unsized CF–epoxy composite. The increase in the IFSS was attributed to the enhancement of adhesions between the CFs and polymer matrix through the welding of the MWCNTs on the CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45027.     

Preparation and properties of high performance phthalide‐containing bismaleimide reinforced polydicyclopentadiene

A series of phenolphthalein‐containing bismaleimide (PPBMI) reinforced polydicyclopentadiene blends (PPBMI/polyDCPD) were prepared via the ring‐opening metathesis polymerization of DCPD in the presence of PPBMI. The crosslinked networks between PPBMI and polyDCPD backbones resulted in the reinforced structures. The curing behavior, thermal, and mechanical properties were investigated. Differential scanning calorimetry investigations showed the samples exhibit similar singular exothermic peak, and the exothermic peak of the PPBMI/polyDCPD blends slightly shifted to a lower temperature direction compared with the unfilled polyDCPD, meanwhile, the exothermic peak of the PPBMI/polyDCPD blends slightly shifts back to a higher temperature direction with the PPBMI content increased. Both dynamic mechanical analysis and thermo gravimetric analysis measurements revealed the optimal thermal performance of PPBMI/polyDCPD was obtained with 20 wt % loading of PPBMI. In addition, while PPBMI content increased, the weight loss peak at 100–200°C disappeared and the temperature of maximum rate of decomposition (T_d,max) increased. Moreover, bending tests showed the best mechanical performance was achieved at 5 wt % loading of PPBMI in blends. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40474.     

In situ synthesis and characterization of ZnS/epoxy nanocomposites via gas‐liquid state reaction method

In this article, the ZnS/epoxy nanocomposites were successfully prepared by the reaction of zinc acetate and H₂S gas via a simple step. Epoxy resin acted as the matrix for the formation of ZnS nanoparticles (10–20 nm) in the reaction system and kept them from agglomerating. The structure, composition, and mechanical properties of the resultant products were successfully investigated by powder X‐ray diffraction, transmission electron microscope, field emission scanning electron microscope, energy dispersive X‐ray fluorescence, and universal testing machine. Meanwhile, by employing differential scanning calorimetry (DSC) we had studied, under nonisothermal condition, the kinetic analysis of the cure reaction which was performed using two classic models: Kissinger and Flynn‐Wall‐Ozawa. The activation energy of curing reaction was 74.63 kJ/mol and 77.57 kJ/mol, respectively, by Kissinger's and Flynn‐Wall‐Ozawa's methods. The possible mechanism of preparation of ZnS/epoxy composites was discussed in this article. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A comparison of efficiency of two photoinitiators for polymerization of light‐cure dental composite resins

The purpose of the study was to compare the effect of two photoinitiators, (?)camphorquinone (CQ) and 1‐phenyl‐1,2‐propanedione (PPD) on curing performance of light‐cure dental composite resins. Bisphenol A‐glycidyl methacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) monomer mixture was used as the resin matrix. The resin matrix was mixed with CQ and/or PPD along with 0.25% of 4‐(dimethyl amino) phenethyl alcohol (DMAPEA) catalyst. The effect of photoinitiator on curing performance was evaluated and compared in terms of properties such as depth of cure, diametral tensile strength (DTS), flexural strength (FS), flexural modulus (FM), vickers hardness number (VHN), water sorption (WS), and solubility of cured composite. Statistical evaluation using Analysis of Variance (single factor) showed that the photosensitization efficiency of CQ and PPD are comparable. However, their combination showed synergistic effect for properties such as DTS and solubility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008