Study of jute fiber reinforced polyester composites by dynamic mechanical analysis

Cyanoethylation of jute fibers in the form of nonwoven fabric was studied, and these chemically modified fibers were used to make jute–polyester composites. The dynamic mechanical thermal properties of unsaturated polyester resin (cured) and composites of unmodified and chemically modified jute–polyester were studied by using a dynamic mechanical analyzer over a wide temperature range. The data suggest that the storage modulus and thermal transition temperature of the composites increased enormously due to cyanoethylation of fiber. An increase of the storage modulus of composites, prepared from chemically modified fiber, indicates its higher stiffness as compared to a composite prepared from unmodified fiber. It is also observed that incorporation of jute fiber (both unmodified and modified) with the unsaturated resin reduced the tan δ peak height remarkably. Composites prepared from cyanoethylated jute show better creep resistance at comparatively lower temperatures. On the contrary, a reversed phenomenon is observed at higher temperatures (120°C and above). Scanning electron micrographs of tensile fracture surfaces of unmodified and modified jute–polyester composites clearly demonstrate better fiber–matrix bonding in the case of the latter. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1505–1513, 1999     

Dielectric properties of cyanoethylated bagasse composites

Bagasse was converted into a thermo-moldable material by cyanoethylation. The effect of reaction conditions employed during the preparation of cyanoethylated bagasse (CE-B) fibers on dielectric properties of hot-pressed composites was studied. Increase in the nitrogen content of the cyanoethylated fiber, i.e., the nitrile groups resulted in an increase in the dielectric constant and a decrease in the dissipation factor (tan δ) peak of the composites. Increase in the reaction temperature and the alkali concentration resulted in a decrease in the dielectric constant and tan δof the composites. Thickness swelling (TS) and equilibrium moisture content of composites conditioned at different relative humidities (RHs) were studied and the extent of the effect of the absorbed moisture on the dielectric properties was also studied. Increase in the nitrogen content, the alkali concentration, and the reaction temperature during the preparation of cyanoethylated fibers resulted in a decrease in TS and moisture absorption of the composites formed. The dielectric properties of the composites conditioned at 60 or 90% RH deteriorated severely. The effect of temperature on the dielectric constant and tan δof a selected CE-B composite was studied. The dielectric constant and tan δincreased as the temperature increased.     

Studies on jute-reinforced composites,its limitations,and some solutions through chemical modifications of fibers

Jute, unlike other natural fibers, absorbs moisture and its moisture regain property is quite high. Water migration and subsequent degradation of jute-based composites can be a problem. Because jute is hydrophilic and the matrix resins are mostly hydrophobic, wetting of the fibers with resins is poor, for which high resin consumption may occur that would increase the cost of composites. To reduce the moisture regain property of jute fiber, it is essential to pretreat the jute fiber so that the moisture absorption is reduced and the wettability of the resin is improved. Jute fiber in the form of nonwoven jute has been pretreated with precondensate like phenol formaldehyde, melamine formaldehyde, cashew nut shell liquid-formaldehyde, and polymerized cashew nut shell liquid. The moisture content of the pretreated nonwoven jute has been determined by conventional methods and by a differential scanning calorimetric technique. Treatment of jute with precondensate causes the reduction of water regain property in jute. Pretreated nonwoven jute has been impregnated with phenol formaldehyde resin, and the composite board has been prepared therefrom. The jute composite board has been tested for bending strength, tensile strength, thickness swelling, and water absorption. Thermal analyses, such as differential scanning calorimetry and thermogravimetry, have also been conducted on jute and pretreated jute fibers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1093–1100, 1998     

Enzyme‐mediated surface modification of jute and its influence on the properties of jute/epoxy composites

Surface modification of jute fibers is necessary to improve the adhesion and interfacial compatibility between fibers and resin matrix before using fibers in polymer composites. In this study, dodecyl gallate (DG) was enzymatically grafted onto the jute fiber by laccase to endow the fiber with hydrophobicity. A hand lay‐up technique was then adopted to prepare jute/epoxy composites. Contact angle and wetting time measurements showed that the surface hydrophobicity of the jute fabric was increased after the enzymatic graft modification. The water absorption and thickness swelling of the DG‐grafted jute fabric/epoxy composite were lower than those of the other composites. The tensile and dynamic mechanical properties of the jute/epoxy composites were enhanced by the surface modification. Scanning electron microscopy images revealed stronger fiber–matrix adhesion in composites with modified fibers. Therefore, the enzymatic graft modification increased the fiber–matrix interface area. The fiber–matrix adhesion was enhanced, and the mechanical properties of the composites were improved. POLYM. COMPOS., 38:1327–1334, 2017. © 2015 Society of Plastics Engineers     

Effect of chemical modifications on the thermal stability and degradation of banana fiber and banana fiber‐reinforced phenol formaldehyde composites

Banana fiber has been modified by treatments with sodium hydroxide, silanes, cyanoethylation, heat treatment, and latex treatment and the thermal degradation behavior of the fiber was analyzed by thermogravimetry and derivative thermogravimetry analysis. Both treated and untreated fibers showed two‐stage decomposition. All the treatments were found to increase the thermal stability of the fiber due to the physical and chemical changes induced by the treatments. The thermal degradation of treated and untreated banana fiber‐reinforced phenol formaldehyde composites has also been analyzed. It was found that the thermal stability of the composites was much higher than that of fibers but they are less stable compared to neat PF resin matrix. Composite samples were found to have four‐stage degradation. The NaOH treated fiber‐reinforced composites have very good fiber/matrix adhesion and hence improvement in thermal stability is observed. Though both silane treatments increased the thermal stability of the composite the vinyl silane is found to be more effective. Heat treatment improves the crystallinity of the fiber and decreases the moisture content, hence an improved thermal stability. The latex treatment and cyanoethylation make the fiber surface hydrophobic, here also the composite is thermally more stable than untreated one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Sorption behavior and crystallinity of jute fiber at higher alkali treatments

Moisture regain of jute fiber was studied at different alkali concentrations and temperatures. It was found that the moisture regain increased up to 4.5N alkali treatment and then leveled off. Variation in swelling temperature had no significant effect on moisture regain. Amorphous fraction calculated from Valentine's equation using sorption ratio was compared with infrared crystallinity. The accessibility was increased with decreasing crystallinity in alkali-treated jute fiber, where as in cyanoethylated jute fiber it increased with increasing the degree of cyanoethylation.     

Jute felt composite from lignin modified phenolic resin

Raw and dewaxed jute felt composites were prepared with resol and lignin modified phenol formaldehyde resin. Four different types of lignin modified resins were used by replacing phenol with lignin. The lignin modified resins were prepared from purified lignin obtained from paper industry waste black liquor. To investigate bonding between jute and resin, IR spectroscopy of jute felts and composites was carried out. The thermal stability of the composites was assessed by DSC and TGA. It was found that the lignin resin jute composite is thermally more stable than resol composite. XRD of jute felt and composite shows that the crystallinity of the jute fiber increases after composite preparation. The lignin resin composites were tested for water absorption and thickness swelling, and it was found that the results are comparable with those of resol jute composite. Composites prepared from lignin phenol formaldehyde resin with 50% phenol replacement has shown 75% tensile strength retention to that of pure resol jute composite.     

Studies on cyanoethylation of jute fiber

Changes of reaction variables upon the reaction of jute fiber with acrylonitrile, like concentration of sodium hydroxide, reaction time, and reaction temperature, were studied in the present work. Benzene and dioxane were used as diluents for acrylonitrile and reactions were conducted in their presence in different amounts. Jute fibers were delignified progressively and their effect on the cyanoethylation reaction was studied. It was found that fiber swelled with ethylene diamine, prior to cyanoethylation, gave a higher yield of cyanoethylated jute. Some preliminary work was done to investigate the distribution of reacted chemicals among its major constituents. An FTIR study was performed to show the partial substitution of hydroxyl groups by the cyanoethyl group. The FTIR study also revealed that not only did hydroxyl groups of the cellulosic component of jute react with acrylonitrile but hydroxyl groups of lignin also took part in the reaction. © 1996 John Wiley & Sons, Inc.     

Preparation and characterization of chemically modified Jute–Coir hybrid fiber reinforced epoxy novolac composites

In this study, the effects of fiber surface modification and hybrid fiber composition on the properties of the composites is presented. Jute fibers are cellulose rich (>65%) modified by alkali treatment, while the lignin rich (>40%) coconut coir fibers consist in creating quinones by oxidation with sodium chlorite in the lignin portions of fiber and react them with furfuryl alcohol (FA) to create a coating around the fiber more compatible with the epoxy resins used to prepare polymer composites. The maximum improvement on the properties was achieved for the hybrid composite containing the jute–coir content of 50 : 50. The tensile and flexural strength are recorded as 25 and 63 MPa at modified coir fiber content of 50 vol %, respectively, which are 78% and 61% higher than those obtained for unmodified fiber reinforced composites, i.e., tensile and flexural strength are 14 and 39 MPa, respectively. The reinforcement of the modified fiber was significantly enhanced the thermal stability of the composites. SEM features correlated satisfactorily with the mechanical properties of modified fiber reinforced hybrid composites. SEM analysis and water absorption measurements have confirmed the FA-grafting and shown a better compatibility at the interface between chemically modified fiber bundles and epoxy novolac resin. Hailwood–Horrobin model was used to predict the moisture sorption behavior of the hybrid composite systems. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and properties of successive alkali treated completely biodegradable short jute fiber reinforced PLA composites

The natural fiber reinforced biodegradable polymer composites were prepared with short jute fiber as reinforcement in PLA (Poly lactic acid) matrix. The short jute fiber is successively treated with NaOH at various concentrations (5%, 10%, and 15%) and H₂O₂. The composites were prepared with untreated and treated short jute fibers at different weight proportions (up to 25%) in PLA and investigated for mechanical properties. The results showed that the composite with successive alkali treated jute fiber at 10% NaOH and H₂O₂ with 20% fiber loading has shown 18% higher flexural strength than neat PLA and untreated jute/PLA composite. The flexural modulus of the composite at 25% fiber loading was 125% and 110% higher than that of composites with untreated fibers and neat PLA, respectively. The impact strength of composite with untreated fibers at higher fiber weight fraction was 23% high as compared to neat PLA and 26% high compared to composite with treated fibers. The water absorption was more for untreated jute/PLA composite at 25% fiber loading than all other composites. The composite with untreated fibers has high thermal degradation compared with treated fibers but lower than that of pure PLA matrix. The enzymatic environment has increased the rate of degradation of composites as compared to soil burial. Surface morphology of biodegraded surfaces of the composites were studied using SEM method. POLYM. COMPOS., 37:2160–2170, 2016. © 2015 Society of Plastics Engineers     

Moisture absorption phenomenon in permeable fiber polymer composites

Studies were conducted on the moisture absorption characteristics of jute fiber composites based on polyester and epoxy resin systems, under constant humidity (ø) and ambient temperature (T) conditions. The initial slope of the moisture absorption curve (a direct measure of the composite diffusivity) increased with increased superficial fiber volume fraction (V_f), where as the time (t_m'), needed to reach the equilibrium moisture absorption value showed a reversed trend. This behavior is just a reverse to that observed¹ in case of composites with practically impermeable fibers (e.g., glass and graphite) in the same resin matrices. The theoretical expressions governing moisture diffusion phenomenon in impermeable fiber composites were modified and analyzed for the case of composites containing a permeable fiber. The experimental data obtained on the latter were then discussed in relation to the modified theory. The meaning of a correct fiber volume fraction (V_f,) as applicable to permeable fiber composites was defined.     

Effect of lactic acid chain length on thermomechanical properties of star‐LA‐xylitol resins and jute reinforced biocomposites

Star‐shaped bio‐based resins were synthesized by direct condensation of lactic acid (LA) with xylitol followed by end‐functionalizing of branches by methacrylic anhydride with three different LA chain lengths (3, 5 and 7). The thermomechanical and structural properties of the resins were characterized by ¹³C NMR, Fourier transform IR spectroscopy, rheometry, DSC, dynamic mechanical analysis (DMA), TGA and flexural and tensile tests. An evaluation of the effect of chain length on the synthesized resins showed that the resin with five LAs exhibited the most favorable thermomechanical properties. Also, the resin's glass transition temperature (103 °C) was substantially higher than that of the thermoplast PLA (ca 55 °C). The resin had low viscosity at its processing temperature (80 °C). The compatibility of the resin with natural fibers was investigated for biocomposite manufacturing. Finally, composites were produced from the n5‐resin (80 wt% fiber content) using jute fiber. The thermomechanical and morphological properties of the biocomposites were compared with jute‐PLA composites and a hybrid composite made of the impregnated jute fibers with n5 resin and PLA. SEM and DMA showed that the n5‐jute composites had better mechanical properties than the other composites produced. Inexpensive monomers, good thermomechanical properties and good processability of the n5 resin make the resin comparable with commercial unsaturated polyester resins. © 2017 Society of Chemical Industry     

腰果酚接枝黄麻纤维不饱和聚酯复合材料的力学性能及界面调控

用甲苯二异氰酸酯与腰果酚(CNSL)合成大分子偶联剂接枝黄麻纤维。以接枝的黄麻纤维为增强体,通用的不饱和聚酯树脂为基体,采用热压方式制备复合材料。比较了纯饱和聚酯树脂、5 %CNSL增韧的不饱和聚酯树脂、25 %碱处理的黄麻纤维不饱和聚酯树脂复合材料和25 %的CNSL接枝黄麻纤维不饱和聚酯树脂复合材料的拉伸强度和冲击强度。结果表明,CNSL接枝于黄麻纤维上;CNSL的加入能提高材料的韧性,黄麻纤维能提高材料的拉伸强度而不能提高材料韧性;25 %CNSL接枝的黄麻纤维不饱和聚酯树脂能提高材料的拉伸强度和韧性,25 %CNSL接枝的黄麻纤维增强含5 %CNSL的不饱和聚酯复合材料,其冲击强度为12.10 kJ/m^2。     

Jute fabric reinforced engineering thermoplastic sandwich composites. I. The effect of molding time

Jute fabric‐reinforced sandwich composites were fabricated using engineering thermoplastics. The jute fabrics were precoated with thermosetting resin to improve their thermal resistance before molding of the composites. Thermal gravimetric analysis (TGA) studies revealed that the resin coated fabrics decomposed at higher temperature than the uncoated jute. The onset of degradation of the coated fibers also falls between that of jute fibers and the thermoset resins. This indicates the presence of good interfacial bonding between jute fibers and both resins. Isothermal TGA studies revealed that jute could withstand brief exposure to higher temperature at 270 and 290°C. The sandwich composites were fabricated at 270°C by compression molding for 1.5 and 3 min in each case, and then characterized by flexural, tensile and morphological studies, i.e., SEM and optical microscopy. The uncoated jute fabric yielded composites of superior mechanical properties even with 3 mins molding at 270°C which is close to the degradation temperature of uncoated jute fibers. This is an indication that it is feasible to prepare jute fiber filled engineering polymer composites provided the exposure time at high temperature during processing does not exceed 3 mins as determined by TGA isothermal studies. SEM studies revealed strong fiber/matrix interfacial bonding between jute and the thermoset resins while the inferior mechanical properties of the resin coated sandwich composites could be attributed to the poor interfacial bonding between the already cured thermoset coating and the matrix based on optical microscopy of the polished cross‐sections. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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     

Novel eco‐friendly biodegradable coir‐polyester amide biocomposites: Fabrication and properties evaluation

Biocomposites are prepared from a cheap, renewable natural fiber, coir (coconut fiber) as reinforcement with a biodegradable polyester amide (BAK 1095) matrix. In order to have better fiber‐matrix interaction the fibers are surface modified through alkali treatment, cyanoethylation, bleaching and vinyl grafting. The effects of different fiber surface treatments and fiber amounts on the performance of resulting bio‐composites are investigated. Among all modifications, cyanoethylated coir‐BAK composites show better tensile strength (35.50 MPa) whereas 7% methyl methacrylate grafted coir‐BAK composites show significant improvement in flexural strength (87.36 MPa). The remarkable achievement of the present investigation is that a low strength coir fiber, through optimal surface modifications, on reinforcement with BAK show an encouraging level of mechanical properties. Moreover, the elongation at break of BAK polymer is considerably reduced by the incorporation of coir fibers from nearly 400% (percent elongation of pure BAK) to 16‐24% (coir‐BAK biocomposites). SEM investigations show that surface modifications improve the fiber‐matrix adhesion. From biodegradation studies we find that after 52 days of soil burial, alkali treated and bleached coir‐BAK composites show significant weight loss. More than 70% decrease in flexural strength is observed for alkali treated coir‐BAK composites after 35 days of soil burial. The loss of weight and the decrease of flexural strength of degraded composites are more or less directly related.     

Polyamide-6/cellulose nanocomposites: Influence of fiber treatment and screw rotation on nanofibrillation of jute during extrusion process

The present work studied the preparation of nanocomposites of polyamide-6 (PA6) containing nanofibrillated cellulose by melt blending in a twin screw extruder at different screw rotations to verify the fibrillation of cellulose fibers. Initially, the jute fibers were purified, hydrolyzed, and modified with titanium isopropoxide and aminopropyl silane, as well as with the two chemical modifications. They were incorporated into the polymeric matrix aiming that the shear in processing further aids in fiber fibrillation. The scanning electron microscopy analysis images of the composites showed the presence of fibers with nanodiameters dispersed in the PA6 matrix. The doubly modified fibers resulted in more fibrillation during extrusion. Increasing the screw speed of the extruder improved the degree of crystallinity for the composites with the modified fibers. The thermogravimetric measurements showed that the composite containing the doubly modified fibers increased the maximum degradation temperature. The storage modulus increased for the composites with the insertion of the treated fibers, and the glass transition temperature decreased in some composites. The composites showed higher pseudoplastic behavior, especially at high shear rates.     

Physical and mechanical characterization of jute fabric composites

As‐received and washed jute fabrics were used as reinforcement for a thermoset resin. The mild treatments performed on the jute fabrics did not significantly affect their physical and thermal behaviors. The washed fibers absorbed less water than the unmodified (as received) ones, indicating that the coating used to form the fabrics was hygroscopic. Measurements of the fiber mechanical properties showed a high dispersion due to fiber irregularities, although the values obtained were in agreement with data reported in the literature. These results were also analyzed with the Weibull method. To investigate the effect of the jute treatments on the interface properties, impact, compression, and tensile tests were carried out. The composites made from as‐received jute had the highest impact energy, which was probably associated with weak interfacial adhesion. Composite samples behaved more ductilely in compression than in tensile situations due to the brittle characteristics of the resin used as matrix. The effect of the orientation of the fibers with respect to the direction of the applied force in the different mechanical tests was also studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 639–650, 2005     

Chemical modification of hemp,sisal, jute,and kapok fibers by alkalization

Plant fibers are rich in cellulose and they are a cheap, easily renewable source of fibers with the potential for polymer reinforcement. The presence of surface impurities and the large amount of hydroxyl groups make plant fibers less attractive for reinforcement of polymeric materials. Hemp, sisal, jute, and kapok fibers were subjected to alkalization by using sodium hydroxide. The thermal characteristics, crystallinity index, reactivity, and surface morphology of untreated and chemically modified fibers have been studied using differential scanning calorimetry (DSC), X‐ray diffraction (WAXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), respectively. Following alkalization the DSC showed a rapid degradation of the cellulose between 0.8 and 8% NaOH, beyond which degradation was found to be marginal. There was a marginal drop in the crystallinity index of hemp fiber while sisal, jute, and kapok fibers showed a slight increase in crystallinity at caustic soda concentration of 0.8–30%. FTIR showed that kapok fiber was found to be the most reactive followed by jute, sisal, and then hemp fiber. SEM showed a relatively smooth surface for all the untreated fibers; however, after alkalization, all the fibers showed uneven surfaces. These results show that alkalization modifies plant fibers promoting the development of fiber–resin adhesion, which then will result in increased interfacial energy and, hence, improvement in the mechanical and thermal stability of the composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2222–2234, 2002     

Chemical modification of starch. II. Cyanoethylation

Rice starch was cyanoethylated by reacting it with acrylonitrile in presence of sodium hydroxide at different concentrations of acrylonitrile and various reaction temperatures. The effect of cyanoethylation on the rheological and solubility properties of starch was examined. It was found that the extent of the cyanoethylation reaction [expressed as %N and degree of substitution (DS)] increased by increasing acrylonitrile concentration provided that the latter was not less than 8 ml acrylonitrile per 10 g starch. A temperature of 50°C constituted the optimal temperature for the cyanoethylation of starch under the conditions studied. Examination of the rheological properties of the modified starch revealed that regardless of the DS, cyanoethylated starches are characterized by pseudoplastic behavior of particular interest were the results of the viscosity. Cyanoethylated starch having smaller amounts of cyanoethyl groups had higher viscosity than those of relatively larger amounts. On the other hand, the cyanoethylated starches were soluble in water regardless of the extent of cyanoethylation.