Resol–vegetable fibers composites

Vegetable fibers like cotton, sisal, and sugar cane bagasse have been used as reinforcement in a polymeric matrix. Because of its low cost and affinity with lignocellulosic fibers, a phenol‐formaldehyde resin —resol— was selected as the matrix. Composites were prepared by compression molding. The influence of fiber volume fraction‐V_f‐in flexural properties and density of composites has been studied. Cotton and sugar cane bagasse composites present a V_f value at which flexural strength and modulus are maxima. However, sisal composites show a continuous rise in flexural strength and modulus as fiber volume fraction increases, up to 76%, which is the highest concentration studied. Composites made with raw cotton show the highest values of strength and stiffness. The actual density of composites is always lower than theoretical density, due to the presence of voids. Scanning Electron Microscopy reveals a good adhesion between fiber and matrix in the composites. In addition, the flexural properties were analyzed with an efficiency criterion, which relates strength and stiffness with density, and the values obtained were compared with those corresponding to typical structural materials. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1832–1840, 2000     

Polyester composites of short pineapple fiber and glass fiber: Tensile and impact properties

The tensile and impact performance of intimately mixed (IM) hybrid composites based on glass fiber (GF) and pineapple leaf fiber (PALF) was investigated. The composite was fabricated at constant volume fraction of fiber 0.3 V_f (fiber 0.3 and matrix 0.7). Keeping the volume fraction of matrix a constant (0.7 V_f), we have varied the PALF/GF ratio from 0 to 1. Incorporation of 0.1 volume fraction of GF increases the tensile strength of the hybrid composite by about 28%. The tensile strength showed a further increase when the volume fraction is changed to 0.7 and 0.9 V_f of GF. Intimately mixed hybrid composites exhibited higher impact strength than the individual fiber composites; the composite of PALF/GF ratio 70:30 showed maximum impact strength of 1203 J/m. A positive hybrid effect is observed for impact properties. Scanning electron micrographs of the fractured surfaces were examined to understand the fiber‐matrix adhesion. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Bio‐composites for structural applications: Poly‐l‐lactide reinforced with long sisal fiber bundles

Fully bio‐based and biodegradable composites were compression molded from unidirectionally aligned sisal fiber bundles and a polylactide polymer matrix (PLLA). Caustic soda treatment was employed to modify the strength of sisal fibers and to improve fiber to matrix adhesion. Mechanical properties of PLLA/sisal fiber composites improved with caustic soda treatment: the mean flexural strength and modulus increased from 279 MPa and 19.4 GPa respectively to 286 MPa and 22 GPa at a fiber volume fraction of V_f = 0.6. The glass transition temperature decreased with increasing fiber content in composites reinforced with untreated sisal fibers due to interfacial friction. The damping at the caustic soda‐treated fibers‐PLLA interface was reduced due to the presence of transcrystalline morphology at the fiber to matrix interface. It was demonstrated that high strength, high modulus sisal‐PLLA composites can be produced with effective stress transfer at well‐bonded fiber to matrix interfaces. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40999.     

Effect of layering pattern on dynamic mechanical properties of randomly oriented short banana/sisal hybrid fiber–reinforced polyester composites

Dynamic mechanical test methods have been widely employed for investigating the structures and viscoelastic behavior of polymeric materials to determine their relevant stiffness and damping characteristics for various applications. Randomly oriented short banana/sisal hybrid fiber–reinforced polyester composites were prepared by keeping the volume ratio of banana and sisal 1 : 1 and the total fiber loading 0.40 volume fraction. Bilayer (banana/sisal), trilayer (banana/sisal/banana and sisal/banana/sisal), and intimate mix composites were prepared. The effect of layering pattern on storage modulus (E′), damping behavior (tan δ), and loss modulus (E″) was studied as a function of temperature and frequency. Bilayer composite showed high damping property while intimately mixed and banana/sisal/banana composites showed increased stiffness compared to the other pattern. The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the composites. The activation energy of the intimately mixed composite was found to be the highest. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2168–2174, 2005     

Hybrid effect on mechanical properties of M40‐T300 carbon fiber reinforced Bisphenol A Dicyanate ester composites

Interply and intraply hybrid composites based on Bisphenol A Dicyanate ester (BADCy), high strength carbon fibers T300, and high modulus carbon fibers M40 were prepared by monofilament dip‐winding and press molding technique. The tensile, flexural, interlaminar shear properties and SEM analysis of the hybrid composites with different fiber content and fiber arrangement were investigated. The results indicated that the mechanical properties of intraply hybrid composites were mainly determined by fiber volume contents. When the ratio of fiber volume content was close to 1:1, the intraply hybrid composites possessed lowest tensile and flexural strength. The mechanical properties of interply hybrid composite mainly depended on the fiber arrangement, instead of the fiber volume contents. The hybrid composites using T300 fiber layout as outside layer possessed high flexural strength and low flexural modulus, which was close to that of T300/BADCy composites. The hybrid composites ([(M40)_x/(T300)_y]_S) using M40 fiber layout as outside layer and T300 fibers in the mid‐plane had high flexural modulus and interlaminar shear strength. POLYM. COMPOS., 2010. © 2010 Society of Plastics Engineers     

Natural fiber hybrid composites—A comparison between compression molding and resin transfer molding

Short randomly oriented intimately mixed banana and sisal hybrid fiber‐reinforced polyester composites having varying volume fraction of fiber were fabricated by compression molding (CM) and resin transfer molding (RTM) techniques by keeping the volume ratio of banana and sisal, 1:1. The static mechanical properties such as tensile, flexural, and impact behavior were studied. The dynamic mechanical properties were also evaluated. Resin transfer molded composites showed enhanced static and dynamic mechanical properties, compared with the compression molded samples. To analyze the fracture surface morphology of the composites, scanning electron microscopy (SEM) was also performed. Water sorption studies revealed that the water uptake of RTM fabricated composites was lower than that of the compression molded composites. The void content of the RTM composites was also found to be lower than that of the other one. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Three‐dimensionally braided carbon fiber–epoxy composites,a new type of materials for osteosynthesis devices. II. Influence of fiber surface treatment

Interfacial adhesion between carbon fiber and epoxy resin plays an important role in determining performance of carbon–epoxy composites. The objective of this research is to determine the effect of fiber surface treatment (oxidization in air) on the mechanical properties (flexural strength and modulus, shear and impact strengths) of three‐dimensionally (3D) braided carbon‐fiber‐reinforced epoxy (C_3D/EP) composites. Carbon fibers were air‐treated under various conditions to improve fiber–matrix adhesion. It is found that excessive oxidation will cause formation of micropits. These micropits are preferably formed in crevices of fiber surfaces. The micropits formed on fiber surfaces produce strengthened fiber–matrix bond, but cause great loss of fiber strength and is probably harmful to the overall performance of the corresponding composites. A trade‐off between the fiber–matrix bond and fiber strength loss should be considered. The effectiveness of fiber surface treatment on performance improvement of the C_3D/EP composites was compared with that of the unidirectional carbon fiber–epoxy composites. In addition, the effects of fiber volume fraction (V_f) and braiding angle on relative performance improvements were determined. Results reveal obvious effects of V_f and braiding angle. A mechanism was proposed to explain the experimental phenomena. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1040–1046, 2002     

Toughening of wood particle composites—Effects of sisal fibers

Sisal fibers were added to wood particle composites to enhance their toughness. The selected matrix was a commercial styrene diluted unsaturated polyester thermoset resin. Fracture tests were carried out using single‐edge notched beam geometries. Stiffness, strength, critical stress intensity factor K_IQ, and work of fracture W_f of notched specimens were determined. The incorporation of sisal fibers into wood particle composites significantly changed the fracture mode of the resulting hybrid composite. For the neat matrix and the wood particle composites, once the maximum load was reached, the crack propagated in a catastrophic way. For hybrid composites, fiber bridging and pull‐out were the mechanisms causing increased crack growth resistance. Addition of a 7% wt of sisal fibers almost doubled the K_IQ value of a composite containing 12% wt of woodflour. Moreover, the W_f increased almost 10‐fold, for the same sample. In general, the two composite toughness parameters K_IQ and W_f increased when the fraction of sisal fibers was increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1982–1987, 2006     

Dynamic mechanical analysis of pineapple leaf/glass hybrid fiber reinforced polyester composites

The dynamic mechanical properties of randomly oriented intimately mixed hybrid composites based on pineapple leaf fibers (PALF) and glass fibers (GF) in unsaturated polyester (PER) matrix were investigated. The PALFs have high‐specific strength and improve the mechanical properties of the PER matrix. In this study, the volume ratio of the two fibers was varied by incorporating small amounts of GF such as PALF/GF, 90/10, 80/20, 70/30, and 50/50, keeping the total fiber loading constant at 40 wt%. The dynamic modulus of the compositeswas found to increase on GF addition. The intimately mixed (IM) hybrid composites with PALF/GF, 80/20 (0.2 V_f GF) showed highest E′ values and least damping. Interestingly, the impact strength of the composites was minimum at this volume ratio. The composites with 0.46 V_f GF or PALF/GF (50/50) showed maximum damping behavior and highest impact strength. The results were compared with hybrid composites of different layering patterns such as GPG (GF skin and PALF core) and PGP (PALF skin and GF core). IM and GPG hybrid composites are found more effective than PGP. The activation energy values for the relaxation processes in different composites were calculated. The overall results showed that hybridization with GF enhanced the performance properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

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 Properties of PPS/PC/GF/Nano-CaCO3 Hybrid Composites

A kind of nanometer calcium carbonate (nano-CaCO₃) filled glass fibre-reinforced polyphenylene sulfide/polycarbonate (PPS/PC/GF) hybrid composites were fabricated with a twin-screw extruder in this paper, and the surface of the nanometer particles was pretreated with stearic acid in a high speed mixer before melt blending. The Young's modulus, tensile strength, tensile elongation at break, flexural modulus and strength of these hybrid composites were measured at room temperature by using a universal materials testing machine, to identify the influence of the nano-CaCO₃ content on the mechanical properties of these hybrid composites. It was found that there were relatively evident reinforcing and toughening effects of the nano-CaCO₃ on the PPS/PC/GF hybrid composites. The Young's modulus, tensile strength, flexural strengt and elongation at break of these composites increased nonlinearly with an addition of the nano-CaCO₃ weigh fraction (φ _f ) when φ _f was less than 6%, and they reached the maximum at φ _f of 6%, and then decreased; while the flexural modulus increased as φ _f was less than 4%, and then decreased.     

Mechanical behavior and correlation between dynamic fragility and dynamic mechanical properties of curaua fiber composites

In this study, the mechanical properties and physical–chemical characteristics of curaua composites were evaluated using tensile and short beam testing and dynamic mechanical analysis. Curaua/polyester composites with different pretreatment (washing and drying), fiber length (10–50 mm) and fiber volume fraction (%V_f) (11, 22, and 38 vol%) were studied. The results show that the composites produced using 50 mm long washed/dried fibers and %V_f of 38 vol% achieved better mechanical properties, such as tensile strength and modulus and short beam strength. Fragility index “m” of the composites increased upon curaua incorporation, which may be attributed to a reduction in polyester chemical interactions (due to fiber dwelling of the polyester network). The energy required in initiating the cooperative motion at the “ideal” glass transition temperature and the cooperative rearrangement regions (CRR) also increased upon curaua incorporation, since CRR is considered the subsystem of the sample and for higher fiber content the greater the molecular heterogeneity. Finally, the Angell fragility concept was successfully applied to polymer composite systems. POLYM. COMPOS., 35:1078–1086, 2014. © 2013 Society of Plastics Engineers     

Impact Toughness and Flexural Properties of PPS/GF/Nano-CaCO3 Ternary Composites

To identify the influence of the content and surface treatment of nano-CaCO₃ on the mechanical properties of nanometer calcium carbonate (nano-CaCO₃)-filled glass fiber (GF)-reinforced polyphenylene sulfide ternary composites, the impact strength, flexural modulus, and strength were measured at room temperature. It was found that the notched impact strength and flexural strength of these composites increased with an increase of the nano-CaCO₃ weight fraction (φ _f ) when φ _f was less than 2% and then they decreased, and the unnotched impact strength of these composites roughly nonlinearly increased with an addition of φ _f , whereas the effect of φ _f on the flexural modulus was insignificant. The impact strength and flexural strength for these filled systems with the particle surface pretreated with titanate coupler were greater than those of the filled systems with the particle surface pretreated with sttaric aicd.     

Mechanical,thermal, and water absorption properties of melamine–formaldehyde‐treated sisal fiber containing poly(lactic acid) composites

The present study focuses on the melamine–formaldehyde (MF) coating ratio and silanization of PLA/sisal composites. Poly(lactic acid) (PLA) was melt blended with short sisal fiber with and without MF resin coating. MF was applied at different weight ratios (sisal:MF = 1:1; 1:3, and 1:5) to coat the untreated or silanized sisal fibers which were incorporated up to 20 parts per hundred resin (phr) amount in PLA. PLA/sisal composites were produced by compression molding. It was found that the sisal:MF coating ratio at 1:1 by weight improved the tensile strength and tensile modulus of the composite with 10 phr sisal by 4% and 57%, respectively, compared to the virgin PLA. The initial and final decomposition (T_i) and (T_f) of PLA with untreated sisal were changed from 330.8 and 367.1 to 336.2 and 370.4 °C, respectively, after MF‐coating (sisal:MF weight ratio = 1:1). This enhancement in thermal stability was attributed to the strong interaction between the MF and sisal fiber. The water absorption of PLA/MF–sisal composites slightly decreased with increasing sisal:MF ratio. This is due to the fact that the MF‐coating substantially reduced the hydrophilic properties of sisal. Moreover, FTIR spectra and SEM images proved that sisal fibers were coated by MF resin successfully. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45681.     

香蕉纤维的表面改性及其增强环氧树脂复合材料的性能研究

采用硅烷偶联剂(A-174)偶联、高锰酸钾接枝和乙酰化包覆等3种方法对香蕉纤维进行表面改性,制备了改性香蕉纤维增强环氧树脂复合材料,测试其拉伸、弯曲、压缩、冲击等力学性能。结果表明,偶联、接枝、包覆等表面改性均能明显改善香蕉纤维与基体树脂的相容性,提高复合材料的力学性能,其中偶联改性的效果最好。当改性香蕉纤维含量为10wt%时,与未改性的香蕉纤维比较,复合材料的拉伸强度、弯曲强度、压缩强度分别提高了1.8、1.0、2.6倍;随着纤维含量的增加,复合材料的力学性能明显提高。     

Influence of interfacial adhesion on the structural and mechanical behavior of PP‐banana/glass hybrid composites

Hybrid composites of polypropylene (PP), reinforced with short banana and glass fibers were fabricated using Haake torque rheocord followed by compression molding with and without the presence maleic anhydride grafted polypropylene (MAPP) as a coupling agent. Incorporation of both fibers into PP matrix resulted in increase of tensile strength, flexural strength, and impact strength upto 30 wt% with an optimum strength observed at 2 wt% MAPP treated 15 wt% banana and 15 wt% glass fiber. The rate of water absorption for the hybrid composites was decreased due to the presence of glass fiber and coupling agent. The effect of fiber loading in presence of coupling agent on the dynamic mechanical properties has been analyzed to investigate the interfacial properties. An increase in storage modulus (E′) of the treated‐composite indicates higher stiffness. The loss tangent (tan δ) spectra confirms a strong influence of fiber loading and coupling agent concentration on the α and β relaxation process of PP. The nature of fiber matrix adhesion was examined through scanning electron microscopy (SEM) of the tensile fractured specimen. Thermal measurements were carried out through differential scanning calorimetry (DSC) and the thermogravimetric analysis (TGA), indicated an increase in the crystallization temperature and thermal stability of PP with the incorporation of MAPP‐treated banana and glass fiber. POLYM. COMPOS., 31:1247–1257, 2010. © 2009 Society of Plastics Engineers     

Comparison of mechanical performance and fracture behavior of gelatin composites reinforced with carbon fibers of different fiber architectures

Gelatin‐based composites reinforced, respectively, with continuous carbon fibers, short carbon fibers, plain woven carbon fibers, and carbon fiber felt were investigated. Tensile and shear strengths, and their changes with fiber volume fraction (V_f) of these four composites were compared. It was demonstrated that at all fiber levels, the composite containing continuous carbon fibers showed the largest strength, while the composite reinforced with carbon fiber felt exhibited the lowest strength of the four composites. The above results were analyzed by comparing the fracture surfaces of the four composites. SEM confirmed the great differences in fracture surfaces for composites of different fiber architectures. The presence of a large number of pores in the C_F/Gel composite was responsible for its lowest strength, and cracks within fiber tows caused the lower strength of the C_W/Gel composite when compared to its C_L/Gel counterpart. It was suggested that fiber architecture exerted a great effect on composite performance and the effect was dependent on the nature of the matrix material.     

Mechanical,thermal, and morphological properties of maleic anhydride‐g‐polypropylene compatibilized and chemically modified banana‐fiber‐reinforced polypropylene composites

Composites were prepared with chemically modified banana fibers in polypropylene (PP). The effects of 40‐mm fiber loading and resin modification on the physical, mechanical, thermal, and morphological properties of the composites were evaluated with scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Infrared (IR) spectroscopy, and so on. Maleic anhydride grafted polypropylene (MA‐g‐PP) compatibilizer was used to improve the fiber‐matrix adhesion. SEM studies carried out on fractured specimens indicated poor dispersion in the unmodified fiber composites and improved adhesion and uniform dispersion in the treated composites. A fiber loading of 15 vol % in the treated composites was optimum, with maximum mechanical properties and thermal stability evident. The composite with 5% MA‐g‐PP concentration at a 15% fiber volume showed an 80% increase in impact strength, a 48% increase in flexural strength, a 125% increase in flexural modulus, a 33% increase in tensile strength, and an 82% increase in tensile modulus, whereas the heat deflection temperature increased by 18°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The influence of chemical surface modification on the performance of sisal‐polyester biocomposites

This article concerns the effectiveness of various types and degrees of surface modification of sisal fibers involving dewaxing, alkali treatment, bleaching cyanoethylation and viny1 grafting in enhancing the mechanical properties, such as tensile, flexural and impact strength, of sisal‐polyester biocomposites. The mechanical properties are optimum at a fiber loading of 30 wt%. Among all modifications, cyanoethylation and alkali treatment result in improved properties of the biocomposites. Cyanoethylated sisal‐polyester composite exhibited maximum tensile strength (84.29 MPa). The alkali treated sisal‐polyester composite exhibited best flexural (153.94 MPa) and impac strength (197.88 J/m), which are, respectively, 21.8% and 20.9% higher than the corresponding mechanical properties of the untreated sisal‐polyester composites. In the case of vinyl grafting, acrylonitrile (AN)‐grafted sisal‐polyester composites show better mechanical properties than methyl‐methacrylate (MMA)‐grafted sisal composites. Scanning electron microscopic studies were carried out to analyze the fiber‐matrix interaction in various surface‐modified sisal‐polyester composites.     

Micromechanics for fiber volume percent with a photocure vinyl ester composite

Micromechanics for fiber volume percent (V_f) from 0.0V_f to 54.0 V_f were conducted using (3 mm long × 9 μm diameter) high‐purity quartz fibers in a visible‐light vinyl ester particulate‐filled photocure resin. MTS fully articulated four‐point bend fixtures were used with a 40 mm test span and 50 × 2 × 2 mm³ sample dimensions. Specimens were tested following the combined modified ASTM standards for advanced ceramics ASTM‐C‐1161–94 and polymers ASTM‐D‐6272–00 for modulus, flexural strength, and yield strength. Experimental data provided reliable statistical support for the dominant fiber contribution expressed through the rule‐of‐mixtures theory as a valid representation of micromechanical physics. The rule‐of‐mixtures micromechanics described by V_f could explain 92, 85, and 78% of the variability related to modulus, flexural strength, and yield strength respectively. Statistically significant improvements with fiber addition began at 10.3V_f for modulus, 5.4V_f for flexural strength, and 10.3V_f for yield strength, p < 0.05. In addition, correlation matrix analysis was performed for all mechanical test data. An increase in V_f correlated significantly with increases in modulus, flexural strength, and yield strength as measured by the four‐point bending test, p < 10⁻¹⁰. All mechanical properties in turn correlated highly significantly with one another, p < 10⁻⁹. POLYM. COMPOS., 28:294–310, 2007. © 2007 Society of Plastics Engineers