Thermal behavior of vinyl ester resin matrix composites reinforced with alkali‐treated jute fibers

The thermal behavior of vinyl ester resin matrix composites reinforced with jute fibers treated for 2, 4, 6, and 8 h with 5% NaOH was studied with Thermo‐gravimetric analysis and differential scanning calorimetry. The moisture desorption peak shifted to a higher temperature, from 37 to 58.3°C, for all the treated‐fiber composites because of improved wetting of the fibers by the resin and stronger bonding at the interface. The degradation temperature of the vinyl ester resin in the composites was lowered to 410.3°C from that of the neat resin, 418.8°C. The X‐ray diffraction studies showed increased crystallinity of the treated fibers, which affected the enthalpy of the α‐cellulose and hemicellulose degradation. The hemicellulose degradation temperature remained the same (299.7°C) in all the treated‐fiber composites, but the enthalpy associated with the hemicellulose degradation showed an increasing trend in the treated composites with a small increase in the weight loss. This could be attributed to the increased hydrogen bonding between the more accessible ? OH groups of the hemicellulose in the noncrystalline region of the jute fiber and the resin. The degradation temperature of α‐cellulose was lowered from 364.2 to 356.8°C in the treated composites. The enthalpy of α‐cellulose degradation showed a decreasing trend with a lowering of the weight loss. The crystalline regions of the fiber, consisting of closely packed α‐cellulose chains, were bonded with the resin mainly on the surface through hydrogen bonds and became more resistant to thermal degradation; this reduced the weight loss. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 123–129, 2004     

Study of the thermal behavior of alkali‐treated jute fibers

Jute fibers were treated with 5% NaOH solution for 2, 4, 6, and 8 h to study the performance of the fibers as a reinforcing material in the composites. Thermal analysis of the fibers was done by the DTG and DSC technique. The moisture desorption was observed at a lower temperature in the case of all the treated fibers, which might be a result of the increased fineness of the fibers, which provides more surface area for moisture evaporation. The decrease in percentage moisture loss for the fibers treated with alkali for 6 and 8 h could be the result of the increased crystallinity of the fibers. The percentage degradation of the hemicellulose decreased considerably in all the treated fibers, conforming to the fact that the hemicellulose content was lowered on alkali treatment. The decomposition temperature for α‐cellulose was lowered to 348°C from 362.2°C for all the treated fibers, and the residual char formation increased to a significant extent. The enthalpy for the thermal degradation of α‐cellulose showed a decreasing trend for the fibers treated for 2 and 4 h, which could be caused by the initial loosening of the structure, followed by an increase in the enthalpy value in the case of the 6‐ and 8‐h‐alkali‐treated fibers resulting from increased crystallinity, as evident from the X‐ray diffraction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2594–2599, 2002     

Characterization of alkali‐treated jute fibers for physical and mechanical properties

Changes occurring in jute fibers when treated with a 5% concentration of a NaOH solution for 0, 2, 4, 6, and 8 h were characterized by weight loss, linear density, tenacity, modulus, FTIR, and X‐ray measurements. A 9.63% weight loss was measured during 2 h of treatment with a drop of hemicellulose content from 22 to 12.90%. The linear density value showed no change until 2 h of treatment followed by a decrease from 33.0 to 14.5 denier by 56% after 6 h of treatment. The tenacity and modulus of the fibers improved by 45 and 79%, respectively, and the percent breaking strain was reduced by 23% after 8 h of treatment. X‐ray diffractograms showed increase in crystallinity of the fibers only after 6 h of treatment, while FTIR measurements showed much of the changes occurring by 2 h of treatment with an increased amount of OH groups. By measuring the rate of change of the modulus, tenacity, and percent breaking strain with the time of treatment, a clear transition was apparent at 4 h of treatment with the dissolution of hemicellulose, causing a weight loss and drop in the linear density before and development of crystallinity with an improvement in the properties after the transition time. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1013–1020, 2001     

Fracture characteristics of vinylester resin under impact fatigue

The impact fatigue behavior of a vinylester resin was studied with a pendulum‐type repeated‐impact tester especially designed and fabricated for the determination of single‐impact and repeated‐impact strengths. A well‐defined energy–endurance impact fatigue curve was obtained with a progressive endurance at values of the impact energy below the critical value, with the endurance limit set at an energy level of 31 N mm, 17.4% of the single‐impact energy. The nature of the crack propagation was investigated for a single impact as well as high, medium, and low impact energy levels with progressively longer endurance. The fracture characteristics varied with the impact energy imparted and the number of cycles endured. The rate of lip growth was high at the higher impact energy levels with a lower number of endurance cycles and low at the lower impact energy levels with longer endurance; the repeated impacts created large and small compressive zones through the bending of specimens with the development of long and short lips, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1995–2001, 2002     

Dynamic mechanical behavior of vinylester matrix composites reinforced by Luffa cylindrica modified fibers

Currently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A comparative study of the stress‐relaxation behavior of untreated and alkali‐treated jute fibers

In this study, we examined the effect of alkali treatment and its variables, namely, the time (2, 4, 6, or 8 h) and the concentration of alkali (1, 5, or 17.5% w/w), on the linear density, strength, and stress‐relaxation properties of jute fiber. It was demonstrated that this kind of treatment led to the creation of several voids and fiber fibrillation. Properties were measured for the alkali‐treated and dewaxed fibers. The linear density and tenacity of the fibers were reduced at higher alkali concentration and at longer dipping times. The strength increased with treatment with mild alkali and decreased with treatment with the strong alkali. A very low alkali treatment (1%) rendered low relaxation. At a 5% alkali concentration, interfibrillar matrix softening also played an important role and was prominent in the stress‐relaxation behavior. The stress‐relaxation value was much higher in the fibers treated with 17.5% NaOH compared to the dewaxed fibers; this was probably due to a loss in the fibrillar arrangement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Characterization of jute fibers treated with soap–glycerol micelles

A tossa variety of jute fiber (Corchorus olitorious) treated with soap–glycerol micelles is characterized by infrared (IR) spectroscopy, X‐ray diffraction method, and tensilometry. The IR spectra for jute fibers treated with soap–glycerol micelles show a reduced absorption band due to O H stretching at a frequency of 3420 cm⁻¹ with almost absent OH bending frequencies, prominent CH₂ stretching and bending frequencies at 2915 and 1440 cm⁻¹ and reduced skeletal vibration at 1060 cm⁻¹. The percentage crystallinity measured by the X‐ray diffraction method increases from 45 to 53% on treated jute fibers. The tensile strength and strain percent at maximum load, Young's modulus, and work done per unit volume within an elastic limit (resilience) for treated fibers increased from 1.8 ± 0.2 to 3.43 ± 0.2 GPa, from 3.98 ± 0.1 to 4.75 ± 0.1, from 75 ± 2 to 113 ± 5 GPa, and from 26 ± 2 to 74 ± 3 MJ m⁻³, respectively. Using a stabilizing agent (2%) and a swelling agent (2% KOH), the tensile strength, strain percent, Young's modulus, and resilience increase to 4.02 ± 0.2 GPa, 4.85 ± 0.3, 154 ± 5 GPa, and 95 ± 4 MJ m⁻³, respectively. Under natural weathering at 12–30°C and 30–80% relative humidity over a prolonged period of 8 weeks, all the tensile properties for micelle‐treated fibers increase during the first 2 weeks of exposure and then decrease exponentially to the starting values. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 852–856, 2000     

Effect of styrene–butadiene latex on the bond performance of macro synthetic fiber in micro jute/macro synthetic hybrid fiber‐reinforced latex‐modified cement‐based composites

This study evaluated the effect of latex content on the pullout behavior of macro synthetic fiber in hybrid fiber‐reinforced latex‐modified cement‐based composites (HFLMCCs). A bond‐strength test which utilized dog‐bone‐shaped test specimens was used to determine the pullout behavior. Micro jute fiber was incorporated at 9.00 kg/m³ and macro synthetic fiber at 0.45 kg/m³. Latex was added at 0, 5, 10, 15, 20, and 25% of the binder weight (wt %). Pullout tests showed that latex increased the area of the debonded zone of the pullout load–displacement curve. Bond strength increased with latex content up to 15% in HFLMCCs and decreased when the latex content reached 20%. The interface toughness increased until the latex content reached 20% and decreased when the latex content was 25%. These results were confirmed by microstructural analysis of the macro synthetic fiber surface, which showed that the number of scratches increased due to friction. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci, 2013     

Short jute fiber‐reinforced polypropylene composites: Dynamic mechanical study

Short jute fiber‐reinforced polypropylene (PP) composites were prepared using a high‐speed thermokinetic mixer. A compatibilizer was used to improve the molecular interaction between jute and PP. Both the percent weight fraction of the jute fiber and compatibilizer were varied to study the dynamic mechanical thermal (DMT) properties. Dynamic parameters such as storage flexural modulus (E′), loss flexural modulus (E″), storage shear modulus (G′), loss shear modulus (G″), and loss factor or damping efficiency (tan δ) were determined in a resonant frequency mode. The transition peak nature, amplitude, and temperature of E′, E″, G′, G″, and tan δ of different compositions were shown to indicate possible improvements of molecular interaction in the presence of a compatibilizer. The modulus retention term, a plot of the reduced modulus with the weight fraction of the jute fiber, also indicate its improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 531–539, 1999     

Polyethylene green composites reinforced with cellulose fibers (coir and palm fibers): effect of fiber surface treatment and fiber content

Coir and palm fibers from agricultural waste were investigated as reinforcement for low density polyethylene (LDPE). The effect of fiber preparation with alkaline treatment and with/without bleaching on fiber physical properties was also an objective of this study. The chemical composition and FTIR (Fourier transform infrared spectroscopy) results confirmed that palm fibers had less impurity than coir fibers. This could be the reason for a greater fiber-matrix interfacial interaction of the palm fibers as compared to that of coir fibers, which was in good agreement with the estimation of surface free energy of the dispersion component. Moreover, fiber bleaching improved the single fiber pullout stress. Composites with both alkaline treated and bleached fibers, at different fiber contents (5, 10, 15, and 20 wt.%), were manufactured using a compression molding machine. Addition of both fibers in the LDPE matrix resulted in composites with a higher Young’s modulus compared to that of homopolymer. The Young’s modulus of the composites increased with the effect of either fiber content or fiber bleaching. Differential scanning calorimetry (DSC) showed that composites reinforced with both types of fibers had a single melting temperature peak, indicating the existence of only one type of crystalline species. Moreover, there were no significant differences in the melting temperatures for the fiber reinforced composites and the homo-LDPE. The heat of fusion decreased in the case of fiber reinforced composites.     

Mechanical properties of jute fibers and interface strength with an epoxy resin

Four different forms of jute fibers, namely untreated jute filament (UJF), sliver jute filament (SJF), bleached jute filament (BJF), and mercerized jute filament (MJF), have been subjected to tensile strength analysis following Weibull's theory. The MJF and BJF were obtained by the chemical modification of the UJF. A minimum of 50 fibers of each type, at three different gauge lengths, i.e., 15, 30, and 50 mm, were used to study the strength distribution and the effect of gauge length. The mean fiber strength was found to be the maximum for UJF followed, in the order, by BJF, MJF, and SJF (∼ 700, ∼ 660, ∼ 580, and ∼ 540 MPa, respectively, at 50‐mm gauge length). The strength was also found to decrease with an increase in gauge length. In all cases, good agreement was found with Weibull's statistical model. Single fiber composite tests, with an epoxy resin as the matrix, were carried out determine the critical fragment lengths and interfacial strength, following the Kelly–Tyson approach. The BJF was found to have the maximum interfacial adhesion (τ ≈ 140 MPa) followed by UJF, SJF, and MJF having τ values of ∼ 83, ∼ 57, and ∼ 47 MPa, respectively. Scanning electron microscope pictures showed the fiber surface was physically modified by the various treatments. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1585–1596, 2000     

Melt rheological behavior of starch‐based matrix composites reinforced with short sisal fibers

A systematic analysis of the melt rheological behavior of a commercial starch‐based (MaterBi®) matrix composite reinforced with short sisal fibers is presented. The effects of shear rate, temperature, fiber content and treatment were analyzed by parallel‐plate rheometry, and classical non‐Newtonian models were applied to analyze the pseudoplasticity behavior of the molten composite systems. It is reported that shear rate is the most influential processing condition, while, from the point of view of the material structure, the intercalation effectiveness of the matrix in the fibers is directly linked to the rheological behavior. In fact, processing techniques with high stresses and more efficient mechanical mixing promote the opening of fiber bundles, increasing the aspect ratio of the fibers and the average viscosity of the molten composite. A similar effect on the increase of the aspect ratio and composite viscosity is observed when treated fibers are used. Polym. Eng. Sci. 44:1907–1914, 2004. © 2004 Society of Plastics Engineers.     

Carbon fiber‐reinforced gelatin composites. II. Swelling behavior

Carbon fiber‐reinforced gelatin composites have been prepared in our laboratory to obtain a novel biomaterial of improved mechanical properties. The swelling behavior (swelling rate, swelling kinetics, maximum solvent uptake, etc.) for both continuous carbon fiber‐reinforced gelatin composite (C_L/Gel) and short carbon fiber‐reinforced gelatin composite (C_S/Gel) are investigated. Experimental data show that the swelling process of the original gelatin and gelatin matrixes in both composites follows a second‐order kinetics. The swelling of the gelatin matrixes in both composites proceeds slower than that of the pristine gelatin, and depends on fiber form and fiber volume fraction (Vf). Results indicate that the presence of carbon fibers suppresses the swelling of the gelatin matrixes in both composites. It is found that the gelatin matrix in C_S/Gel possesses a smaller swelling rate and maximum solvent uptake than that in C_L/Gel. A mechanism governing these phenomena is discussed in this article. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 994–998, 2000     

Thermal and electrical behavior of vinylester resin matrix composites filled with fly ash particles

Vinylester resin matrix composites were fabricated with 30, 40, 50, and 60% fly ash loading by room temperature casting method. The composites were subjected to thermogravimetric analysis. The 30 and the 60% composites showed a faster degradation at a lower temperature, whereas, the 40 and the 50% composites showed a higher onset temperature. The activation energy was calculated following Broido's equation and was found to be lowered in all the composites compared to the unfilled resin. The residue increased in all the composites proportionately with the increase in the fly ash content. The temperature variation resistance of the unfilled resin, 30 and 60% filled composites were measured and all the samples showed semi conducting nature in 40–60°C temperature range. POLYM. COMPOS., 29:58–62, 2008. © 2007 Society of Plastics Engineers     

Stab resisting behavior of polymeric resin reinforced p‐aramid fabrics

The stab resistant performance of p‐aramid fabrics reinforced with thermoplastic LDPE resin and thermoset epoxy resin was investigated by quasi‐static or drop tower stab resistance testing, and the stab resistance behavior against different shapes of impactors was also evaluated. The destruction behavior of LDPE reinforced p‐aramid fabrics against a knife impactor shows three distinctive steps; the initial penetration step with maximum strength, the cutting step by knife edge, and the destruction step of accumulated fiber bundles. On the other hand, epoxy resin reinforced p‐aramid fabrics against a knife impactor exhibit just two steps without the accumulation of fiber bundles. In the case of a spike impactor, the maximum stab resistant strength is observed from the initial penetration step; however, the stab resistant strength after initial penetration drastically decreased regardless of the reinforcing resins. It is also found that, even if the LDPE reinforced fabrics are multilayered, the performance improvement by resin reinforcement is observed only from the initial penetration step and the stab resistant strengths of the cutting step and the fiber accumulation step are not improved. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Water absorption behavior of acrylonitrile‐butadiene (NBR) latex impregnated jute nonwoven fabric composites

Composites were fabricated by impregnating the jute nonwoven fabric in acrylonitrile–butadiene (NBR) latex. The effect of different pickup ratio (dry, wt/wt) of NBR latex to jute nonwoven fabric, viz., 0.5 : 1, 1 : 1.5, 1.5 : 1, 2 : 1, and 2.5 : 1 on the water absorption behavior of the composites were evaluated. Water absorption studies were carried out at different temperatures, viz. 30, 50, and 70°C, based on immersion weight gain method. From the sorption result, the diffusion (D) and permeation (P) coefficients of water penetrant have been calculated. Significant increase in the diffusion and permeation coefficients was observed with increase in the temperature of sorption experiments. Drastic reductions in diffusion and permeation coefficients were noticed with increase in the pickup ratio of NBR on to jute nonwoven fabric. Attempts were made to estimate the empirical parameters like n, which suggests the mode of transport, and K is a constant that depends on the structural characteristics of the composite in addition to its interaction with water. The temperature dependence of the transport coefficients has been used to estimate the activation energy parameter for diffusion (E_D) and permeation processes (E_p) from Arrhenius plots. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2045–2050, 2006     

碳纤维增强树脂基复合材料的应用研究

碳纤维增强树脂基复合材料以其优异的综合性能成为当今世界材料学科研究的重点。本文介绍了的碳纤维增强复合材料的性能，简述了增强机理、成型工艺及其应用领域和发展趋势。     

FTIR spectra and physico-chemical behavior of vinyl ester participated transesterification and curing of jute

In this article we report the transesterification of jute with n-Butylacrylate (BA) under appropriate condition using NaOH, Pyridine (Py), and a Pyridine–acetone mixture as a catalyst. The modified vinylog jute was subsequently cured with benzoylperoxide (BPO) in acetone at 50–60°C. The parent and chemically modified jute were characterized by FTIR spectra. The percent moisture regain, mechanical strength, and behavior to common chemical reagents of the parent and modified fibers have also been tested. Transesterification and curing of jute lowered the percentage of moisture regain, imparted mechanical strength, and resistance to common chemical reagents. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 575–581, 2001     

Characterization of the fracture behavior of glass fiber reinforced thermoplastics based on PP,PE‐HD,and PB‐1

This article deals with the influence of the polymeric matrix, such as isotactic polypropylene (iPP), polyethylene (PE‐HD), and isotactic polybutene‐1 (iPB‐1), and the glass fiber content on the material behavior of short glass fiber reinforced thermoplastics. The glass fiber content of all materials ranged between 0 and 50 wt %, which corresponds to a volume content between 0 and approx. 0.264. To describe the mechanical properties of all materials, the stiffness, strength, hardness, and toughness behavior were determined. The crack toughness behavior regarding unstable crack propagation was also assessed by applying fracture mechanics concepts. It was found that the energy‐determined J‐values for the PP material system reach their maximum at a glass fiber content of 0.135. In contrast, the crack toughness of the PE‐HD materials increases continuously with increasing glass fiber content due to the unchanged deformation ability at simultaneously increasing strength. The toughness level of the PB‐1 materials is nearly the same independent of the glass fiber content due to the opposite trend of the load and the deformation ability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010