Interfacial micromechanics and effect of moisture on fluorinated epoxy carbon fiber composites

Carbon fiber composites have witnessed an increased application in aerospace and other civil structures due to their excellent structural properties such as specific strength and stiffness. However, unlike other structural materials, carbon fiber composites have not been as widely studied. Hence, their increased application is also accompanied with a serious concern about their long‐term durability. Many of these applications are exposed to multiple environments such as moisture, temperature, and UV radiation. Composites based on conventional epoxies readily absorb moisture. However, recently synthesized fluorinated epoxies show reduced moisture absorption and hence potentially better long‐term durability. The aim of this project is to study the effect of moisture absorption on fluorinated‐epoxy‐based carbon fiber composites and their comparison with conventional epoxy carbon fiber‐based composites. Microbond tests are performed on fluorinated and nonfluorinated epoxy‐based single fiber samples before and after boiling water degradation. It is found that fluorinated epoxy‐based single fiber coupons showed relatively reduced degradation of interface when compared with the nonfluorinated epoxy single fiber coupons. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Influence of epoxy sizing of carbon‐fiber on the properties of carbon fiber/cyanate ester composites

The high modulus carbon fiber (M40J) sized by epoxy resin E51 and E20 reinforced bisphenol A dicyanate (2,2′‐bis(4‐cyanatophenyl) isopropylidene resin composite was prepared in order to investigate the influence of epoxy sizing of the fiber on the properties of the composite. Differential scanning calorimetry (DSC) and fourier transforms infrared (FTIR) analysis showed that epoxy resin have catalytic effect on cure reaction of cyanate ester. Mechanical properties of the composite revealed that M40J fiber sized by epoxy resin could improve the flexural strength and interlaminar shear strength of M40J/bisphenol A dicyanate composites. The micro‐morphology of the composite fractures was studied by means of scanning electron microscopy (SEM). Reduced flaws were observed in the M40J‐bisphenol A dicyanate interface when the sized fiber was used. Water absorption of the composites was also investigated. It was found that the water absorption descended at the initial boiling stage (12 h). POLYM. COMPOS, 27: 591–598, 2006. © 2006 Society of Plastics Engineers     

Wood‐fiber‐reinforced poly(lactic acid) composites: Evaluation of the physicomechanical and morphological properties

This article presents the results of a study of the processing and physicomechanical properties of environmentally friendly wood‐fiber‐reinforced poly(lactic acid) composites that were produced with a microcompounding molding system. Wood‐fiber‐reinforced polypropylene composites were also processed under similar conditions and were compared to wood‐fiber‐reinforced poly(lactic acid) composites. The mechanical, thermomechanical, and morphological properties of these composites were studied. In terms of the mechanical properties, the wood‐fiber‐reinforced poly(lactic acid) composites were comparable to conventional polypropylene‐based thermoplastic composites. The mechanical properties of the wood‐fiber‐reinforced poly(lactic acid) composites were significantly higher than those of the virgin resin. The flexural modulus (8.9 GPa) of the wood‐fiber‐reinforced poly(lactic acid) composite (30 wt % fiber) was comparable to that of traditional (i.e., wood‐fiber‐reinforced polypropylene) composites (3.4 GPa). The incorporation of the wood fibers into poly(lactic acid) resulted in a considerable increase in the storage modulus (stiffness) of the resin. The addition of the maleated polypropylene coupling agent improved the mechanical properties of the composites. Microstructure studies using scanning electron microscopy indicated significant interfacial bonding between the matrix and the wood fibers. The specific performance evidenced by the wood‐fiber‐reinforced poly(lactic acid) composites may hint at potential applications in, for example, the automotive and packaging industries. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4856–4869, 2006     

Non‐fickian three‐dimensional hindered moisture absorption in polymeric composites: Model development and validation

A new, three‐dimensional, anisotropic non‐Fickian diffusion model is developed to characterize moisture absorption in polymeric composites. The new hindered diffusion model extends the classical Fickian theory to include the effects of the interaction of diffusing molecules with the chemical and physical structure of polymeric composites. The numerical solution of the hindered diffusion model is obtained for a three‐dimensional, anisotropic domain by using a forward‐time, centered‐space finite difference technique. The moisture weight gain over time predicted by the model is shown to mimic a wide variety of anomalous absorption behavior, often exhibited by anisotropic composite laminates. The accuracy of the numerical solutions is verified by comparing the results to known analytical solutions of a one‐dimensional, “Langmuir‐type” diffusion model and for the limiting case of the three‐dimensional Fickian model. The utility of the proposed hindered diffusion model is demonstrated by accurately recovering the absorption behavior of three different material systems reported in literature. First, it is shown that the hindered diffusion model can accurately predict the moisture absorption data for unidirectional glass‐reinforced epoxy plates of varying dimensions exposed to a relative humidity of 80%. Second, the one‐dimensional version of the model is applied to experimental moisture absorption data for isotropic epoxy resin samples of different thicknesses. Anomalous effects due to sample thickness reported in the original article are accurately captured. Third, the proposed model is shown to be more accurate than a two‐stage diffusion model applied to moisture absorption data obtained from a woven 3‐ply carbon fiber reinforced bismaleimide composite. POLYM. COMPOS., 34:1144–1157, 2013. © 2013 Society of Plastics Engineers     

Effect of an epoxy‐based bonding agent on the cure characteristics and mechanical properties of short‐nylon‐fiber‐reinforced acrylonitrile–butadiene rubber composites

The cure characteristics and mechanical properties of short‐nylon‐fiber‐reinforced acrylonitrile–butadiene rubber composites with and without an epoxy resin as a bonding agent were studied. The epoxy resin was a good interfacial‐bonding agent for this composite system. The minimum torque showed a marginal increase with the resin concentration. The maximum–minimum torque showed only a marginal change with the resin. The scorch time decreased with the fiber concentration and resin content. The tensile strength and abrasion resistance were improved and the tear resistance and resilience were reduced with the resin concentration. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 532–539, 2006     

Moisture absorption properties of wood‐fiber‐reinforced recycled polypropylene matrix composites

To reduce the moisture absorption of wood‐fiber‐reinforced recycled plastic composites (WRPCs), a coupling agent (KH550), methyl methacrylate (MMA), and maleic anhydride (MA) were used to modify the wood fibers. The surface‐treated wood fibers were mixed with recycled polypropylene and processing agents to fabricate the WRPCs. The mechanical properties and moisture absorption behavior of the WRPCs were determined. The results showed that the three surface treatment methods could effectively reduce the moisture absorption and thickness swelling of WRPCs. In Comparison to the properties of untreated wood‐fiber‐reinforced WRPCs, the moisture absorption ratio of WRPCs with wood fibers treated by MMA, KH550, and MA was reduced by 31.4%, 49.8%, and 38.2%, respectively, and the tensile strength was increased by 22.1%, 26.3%, and 4.2%, respectively. The impact toughness of the WRPCs was increased by 36.2% KH550 treatment and 19.2% for MMA treatment but was decreased by 4.2% for MA treatment. Coupling treatment of the wood fibers was the best way to reduce the moisture absorption of WRPCs, and this kind of WRPC possessed the best comprehensive properties. J. VINYL ADDIT. TECHNOL., 2010. © 2009 Society of Plastics Engineers     

A review on oil palm empty fruit bunch fiber‐reinforced polymer composite materials

Natural fiber‐reinforced polymer composite materials have emerged in a wide spectrum of area of the polymer science. The composite produced from these types of materials are low density, low cost, comparable specific properties, and most importantly they are environmental friendly. The composite materials produced from oil palm fibers and commercially available polymers have offered some specific properties that can be comparable to conventional synthetic fiber composite materials. However, these properties are greatly dependent on the compatibility of oil palm fibers and matrix phase with moisture absorption as one of the critical issues that becomes the drawbacks of the oil palm fiber polymer composite materials. Apparently, it greatly affects the physical as well as mechanical properties of the composite materials. The present review reports the work on oil palm empty fruit bunch (OPEFB) fiber‐reinforced polymer composites with some interest on the OPEFB physical structure, and chemical compositions. Finally, the incorporation of OPEFB into polymeric materials leads to several interesting consequences on the water absorption characteristics and the mechanical properties, which have been reviewed. POLYM. COMPOS., 31:2079–2101, 2010. © 2010 Society of Plastics Engineers     

Comparison of foam core sandwich panel and through‐thickness polymer pin–reinforced foam core sandwich panel subject to indentation and flatwise compression loadings

Through‐thickness polymer pin–reinforced foam core sandwich (FCS) panels are new type of composite sandwich structure as the foam core of this structure was reinforced with cylindrical polymer pins, which also rigidly connect the face sheets. These sandwich panels are made of glass fiber–reinforced polyester face sheets and closed‐cell polyurethane foam core with cylindrical polymer pins produced during fabrication process. The indentation and compression behavior of these sandwich panels were compared with common traditional sandwich panel, and it has been found that by reinforcing the foam core with cylindrical polymer pins, the indentation strength, energy absorption, and compression strength of the sandwich panels were improved significantly. The effect of diameter of polymer pins on indentation and compression behavior of both sandwich panels was studied and results showed that the diameter of polymer pins had a large influence on the compression and indentation behavior of through‐thickness polymer pin–reinforced FCS panel, and the effect of adding polymer pins to FCS panel on indentation behavior is similar to the effect of increasing the thickness of face sheet. The effect of strain rate on indentation behavior of FCS panel and through‐thickness polymer pin–reinforced FCS panel were studied, and results showed that both types of composite sandwich panels are strain rate dependent structure as by increasing strain rate, the indentation properties and energy absorption properties of these structures are increased. POLYM. COMPOS., 37:612–619, 2016. © 2014 Society of Plastics Engineers     

Investigating the acoustical properties of carbon fiber‐, glass fiber‐, and hemp fiber‐reinforced polyester composites

Wood is one of the main materials used for making musical instruments due to its outstanding acoustical properties. Despite such unique properties, its inferior mechanical properties, moisture sensitivity, and time‐ and cost‐consuming procedure for making instruments in comparison with other materials (e.g., composites) are always considered as its disadvantages in making musical instruments. In this study, the acoustic parameters of three different polyester composites separately reinforced by carbon fiber, glass fiber, and hemp fiber are investigated and are also compared with those obtained for three different types of wood specimens called poplar, walnut, and beech wood, which have been extensively used in making Iranian traditional musical instruments. The acoustical properties such as acoustic coefficient, sound quality factor, and acoustic conversion factor were examined using some non‐destructive tests based on longitudinal and flexural free vibration and also forced vibration methods. Furthermore, the water absorption of these polymeric composites was compared with that of the wood samples. The results reveal that the glass fiber‐reinforced composites could be used as a suitable alternative for some types of wood in musical applications while the carbon fiber‐reinforced composites are high performance materials to be substituted with wood in making musical instruments showing exceptional acoustical properties. POLYM. COMPOS., 35:2103–2111, 2014. © 2014 Society of Plastics Engineers     

Aspects of foaming a glass‐reinforced polypropylene with chemical blowing agents

This work explores the influence of a chemical blowing agent on different aspects of producing a short glass‐fiber‐reinforced polypropylene foam, examining the rheology of the system, the developed morphology of the part, and the resulting mechanical properties. Two different forms of an endothermic blowing agent, namely powder versus masterbatch, were compared to determine their effects on the process history and properties of an injection molded part. Samples were produced on an injection molding machine between 230 and 270°C using the low‐pressure foaming technique. Rheology of the resulting plasticized melt by the two different blowing agents was measured on an in‐line rheometer, showing a greater reduction in shear viscosity for the masterbatch additive, which correspondingly reduced the extent of fiber breakage observed. The final molded samples were analyzed for their foam structure (i.e., cell size, cell density, and skin thickness) as well as the properties of the glass fibers incorporated (namely, fiber length distribution). Tensile properties were found to diminish with increasing blowing agent content, though differences were observed based on the type of CBA used despite the similarities in foam structure produced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4696–4706, 2006     

Effects of nanoclay on the properties of cardanol‐modified‐resol‐epoxy‐novolac composite material

A nanocomposite based on nanoclay and resol that was modified with cardanol, a natural alkyl phenol, shows improvement for the glass‐fiber‐reinforced epoxy‐composite system. Dispersion of the nanocomposite was investigated by X‐ray, showing good results obtained by the in situ polymerization method. The mechanical properties of the final composites were improved by doping a 6 wt% of nanoclay in cardanol‐modified‐resol (CMR) into the epoxy matrix. The results show that a 15 wt% of CMR in epoxy is a most suitable ratio. Using polyamide as a curing agent instead of other traditional systems, such as anhydrides or amines for epoxy resin, overcame important limitations, further allowing for improved processability. The overall composite performance was enhanced. Additionally, the thermal stability of the system was investigated by thermal gravimetric analysis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3238–3242, 2007     

Moisture uptake and resulting mechanical response of bio‐based composites. II. composites

The durability of entirely bio‐based composites with respect to the exposure to elevated humidity was evaluated. Different combinations of bio‐based resins (Tribest, EpoBioX, Envirez) and cellulosic fibers (flax and regenerated cellulose fiber rovings and fabrics) were used to manufacture unidirectional and cross‐ply composite laminates. Water absorption experiments were performed at various humidity levels (41%, 70%, and 98%) to measure apparent diffusion coefficient and moisture content at saturation. Effect of chemical treatment (alkali and silane) of fibers as protection against moisture was also studied. However, fiber treatment did not show any significant improvement and in some cases the performance of the composites with treated fibers was lower than those with untreated reinforcement. The comparison of results for neat resins and composites showed that moisture uptake in the studied composites is primarily due to cellulosic reinforcement. Tensile properties of composites as received (RH = 24%) and conditioned (RH = 41%, 70%, and 98%) were measured in order to estimate the influence of humidity on behavior of these materials. Results were compared with data for glass fiber reinforced composite, as a reference material. Previous results from study of unreinforced polymers showed that resins were resistant to moisture uptake. Knowing that moisture sorption is primarily dominated by natural fibers, the results showed that some of the composites with bio‐based resins performed very well and have comparable properties with composites of synthetic epoxy, even at elevated humidity. POLYM. COMPOS., 36:1510–1519, 2015. © 2014 Society of Plastics Engineers     

Unsaturated polyester‐toughened epoxy composites: Effect of sisal fiber on thermal and dynamic mechanical properties

In the present study, the mechanical and thermal properties of sisal fiber‐reinforced unsaturated polyester (UP)‐toughened epoxy composites were investigated. The sisal fibers were chemically treated with alkali (NaOH) and silane solutions in order to improve the interfacial interaction between fibers and matrix. The chemical composition of resins and fibers was identified by using Fourier‐transform infrared spectroscopy. The UP‐toughened epoxy blends were obtained by mixing UP (5, 10, and 15 wt%) into the epoxy resin. The fiber‐reinforced composites were prepared by incorporating sisal fibers (10, 20, and 30 wt%) within the optimized UP‐toughened epoxy blend. Scanning electron microscopy was used to analyze the morphological changes of the fibers and the adhesion between the fibers and the UP‐toughened epoxy system. The results showed that the tensile and flexural strength of (alkali‐silane)‐treated fiber (30 wt%) ‐reinforced composites increased by 83% and 55%, respectively, as compared with that of UP‐toughened epoxy blend. Moreover, thermogravimetric analysis revealed that the (alkali‐silane)‐treated fiber and its composite exhibited higher thermal stability than the untreated and alkali‐treated fiber systems. An increase in storage modulus and glass transition temperature was observed for the UP‐toughened epoxy matrix on reinforcement with treated fibers. The water uptake behavior of both alkali and alkali‐silane‐treated fiber‐reinforced composites is found to be less as compared with the untreated fiber‐reinforced composite. J. VINYL ADDIT. TECHNOL., 23:188–199, 2017. © 2015 Society of Plastics Engineers     

Effect of layering pattern on the physical,mechanical, and thermal properties of jute/bagasse hybrid fiber‐reinforced epoxy novolac composites

In this study, randomly oriented short jute/bagasse hybrid fiber‐reinforced epoxy novolac composites were prepared by keeping the relative volume ratio of jute and bagasse of 1:3 and the total fiber loading 0.40 volume fractions. The effect of jute fiber hybridization and different layering pattern on the physical, mechanical, and thermal properties of jute/bagasse hybrid fiber‐reinforced epoxy novolac composites was investigated. The hybrid fiber‐reinforced composites exhibited fair water absorption and thickness swelling properties. To investigate the effect of layering pattern on thermomechanical behavior of hybrid composites, the storage modulus and loss factor were determined using dynamic mechanical analyzer from 30 to 200°C at a frequency of 1 Hz. The fracture surface morphology of the tensile samples of the hybrid composites was performed by using scanning electron microscopy. The morphological features of the composites were well corroborated with the mechanical properties. Thermogravimetric analysis indicated an increase in thermal stability of pure bagasse composites with the incorporation of jute fibers. The incorporation of hybrid fibers results better improvement in both thermal and dimensional stable compared with the pure bagasse fiber composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Shear properties and load–deflection response of cross–ply glass–epoxy composite short–beams subjected to three‐point‐bending tests,and the effect of moisture absorption

The extensive use of composites in aerospace, chemical, marine, and structural applications leads to exposure to humidity and water immersion. Hence, there is a need to study the effect of moisture absorption on the mechanical properties of composite materials, especially the matrix dominated properties, such as the interlaminar shear strength (ILSS). The horizontal shear test with a short‐beam specimen in three‐point‐bending is used as a general method of evaluation for the shear properties in fiber‐reinforced composites because of its simplicity. In this work, the ILSS of cross‐ply glass‐epoxy resin composites is determined in seven different fiber directions with short‐beam three‐point‐bending tests, before and after moisture conditioning. It is found that moisture absorption reduces ILSS and stiffness of the examined composites whereas it leads to larger failure deflections. It is also found that the direction of fibers strongly affects the load–deflection response and the ILSS of the dry and conditioned specimens. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical and anticorrosion properties of furan/epoxy‐based basalt fiber‐reinforced composites

A furan/epoxy blend applicable to composite manufacture was studied and corresponding basalt fiber‐reinforced composites were prepared. The processability, mechanical properties, and reasons for the improved mechanical properties of this blend were investigated by rheology machine, mechanical testing machine, and scanning electron microscopy. With excellent processability, furan/epoxy was suitable for manufacturing composites. Furan/epoxy with the ratio of 5/5 showed the best properties, and the impact strength, flexural strength and flexural modulus were 15.43 kJ/m², 102.81 MPa, and 3209.40 MPa, respectively. The river‐like fracture surface of the furan/epoxy system was well consistent with the mechanical properties. The mechanical and anti‐corrosive properties of basalt fiber‐reinforced furan/epoxy composites were also studied. The mechanical properties of composites changed the same as those of furan/epoxy matrix did. Furan resin effectively improved the anti‐acid but not anti‐alkali property of composites, probably because furan could be cured in acidic condition and basalt fiber was resistant to acid and alkali. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44799.     

Short‐beam and three‐point‐bending tests for the study of shear and flexural properties in unidirectional‐fiber‐reinforced epoxy composites

The bending properties of composite materials are often characterized with simply supported beams under concentrated loads. The results from such tests are commonly based on homogeneous beam equations. For laminated materials, however, these formulas must be modified to account for the stacking sequence of the individual plies. The horizontal shear test with a short‐beam specimen in three‐point bending appears suitable as a general method of evaluation for the shear properties in fiber‐reinforced composites because of its simplicity. In the experimental part of this work, the shear strength of unidirectional‐glass‐fiber‐reinforced epoxy resin composites was determined in different fiber directions with the short‐beam three‐point‐bending test. Also, the elastic constants and flexural properties of the same materials were determined from bending experiments carried out on specimens in the 0, 15, 30, 45, 60, 75, and 90° fiber directions with high span–thickness ratios. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 63–74, 2004     

Recycled milk pouch and virgin low‐density polyethylene/linear low‐density polyethylene based coir fiber composites

The viability of the thermomechanical recycling of postconsumer milk pouches [a 50 : 50 low‐density polyethylene/linear low‐density polyethylene (LDPE–LLDPE) blend] and their use as polymeric matrices for coir‐fiber‐reinforced composites were investigated. The mechanical, thermal, morphological, and water absorption properties of recycled milk pouch polymer/coir fiber composites with different treated and untreated fiber contents were evaluated and compared with those of virgin LDPE–LLDPE/coir fiber composites. The water absorption of the composites measured at three different temperatures (25, 45, and 75°C) was found to follow Fickian diffusion. The mechanical properties of the composites significantly deteriorated after water absorption. The recycled polymer/coir fiber composites showed inferior mechanical performances and thermooxidative stability (oxidation induction time and oxidation temperature) in comparison with those observed for virgin polymer/fiber composites. However, a small quantity of a coupling agent (2 wt %) significantly improved all the mechanical, thermal, and moisture‐resistance properties of both types of composites. The overall mechanical performances of the composites containing recycled and virgin polymer matrices were correlated by the phase morphology, as observed with scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Micro‐Driving behavior of carbon‐fiber‐reinforced epoxy resin for standing‐wave ultrasonic motor

The application of the friction drive of carbon‐fiber‐reinforced composites to a standing‐wave ultrasonic motor was investigated. Friction drive tests were conducted on carbon‐fiber‐reinforced epoxy resins (CF/epoxy) by home‐made test rig, which was based on plate‐rod vibrator. The effects of fiber orientation and ply thickness on dynamic drive and dynamic normal forces were investigated. Fiber orientation angle and ply thickness affected friction drive. Different dynamic drive forces, which varied both in amplitude and period, were observed for CF/epoxy composites with different winding angles. A CF/epoxy composite with a winding angle of 30° showed the largest dynamic drive force (∼0.45 N) and the shortest contact period (∼26 μs). The period of dynamic normal force was uniform (∼65 μs) for various CF/epoxy composites. Wear traces of different composites exhibited different wear modes, such as scuffing, peeling, and shearing. The anisotropic property of CF/epoxy material affected the drive process of standing‐wave ultrasonic motor. The current study taking the carbon‐fiber‐reinforced epoxy resin as an example of anisotropic materials arise more enough attention on inexpensive, biodegradable, and renewable alternatives for the efficient and durative drive of a standing‐wave ultrasonic motor. POLYM. COMPOS., 37:2152–2159, 2016. © 2015 Society of Plastics Engineers