Studies on process variables for natural fiber composites—effect of polyesteramide polyol as interfacial agent

A systematic study of the process variables for polyester composites based on different natural fibers like jute, sisal, ramie, and pineapple has been made with a view to determine the most suitable processing conditions for such composites. Effect of polyesteramide polyol (PEAP) as interfacial agent in such composites has also been discussed. Fracture modes of jute/polyester (JP) composite sample having different fiber volume fractions have been examined by scanning electron microscope (SEM). Fracture surfaces of untreated and PEAP-treated JP composite samples have been examined in SEM, both before and after 72 h immersion in boiling water, to study the nature of interfacial bonding on fiber treatment with PEAP. A qualitative improvement in bonding in case of PEAP-treated JP composites is evident from SEM photomicrographs. This is also supported by physicomechanical properties of the composite samples.     

Comparison of primary and secondary aminosilance coupling agents in anhuydride-curde epoxy fiberglass composites

Fourier transform infrared spectroscopy (FT-IR) has been utilized to investigate the interfacial chemical bonding at the interfaces of the aminosilanes and the nedic methyl anhydiride cured epoxy matrix in fiber-reinforced composites. It is found that the nedic methyl anhydride can react with γ-aminopropyltriethoxysilane (APS) and N-methylaminoproplytrimethoxysilane (MAPS). In comparing the relative reactivities of two coupling agents to the epoxy resin, the secondary aminosilance has a higher reactivity than the primary aminosilance. An elevated temperature is required for the copolymerization to take place between the silane and the epoxy resin. The results indicate that covalent bonds form at the coupling agents. The molecular structure of the interface in MAPS treated fiberglass reinforced composites is different from that of the APS treated fiber composites. In addition, an accelerated copolymerization initiated by the coupling agent treated surface is also found in the resin interphase which may be important in determining the mechanical properties of the composites.     

A Comparative Study on the Mechanical Properties of Jute and Sisal Fiber Reinforced Polymer Composites

The aim of the present study is to investigate and compare the mechanical properties of raw jute and sisal fiber reinforced epoxy composites with sodium hydroxide treated jute and sisal fiber reinforced epoxy composites. This is followed by comparisons of the sodium hydroxide treated jute and sisal fiber reinforced composites. The jute and sisal fibers were treated with 20% sodium hydroxide for 2 h and then incorporated into the epoxy matrix by a molding technique to form the composites. Similar techniques have been adopted for the fabrication of raw jute and sisal fiber reinforced epoxy composites. The raw jute and sisal fiber reinforced epoxy composites and the sodium hydroxide treated jute and sisal fiber reinforced epoxy composites were characterized by FTIR. The mechanical properties (tensile and flexural strength), water absorption and morphological changes were investigated for the composite samples. It was found that the sodium hydroxide treated jute and sisal fiber reinforced epoxy composites exhibited better mechanical properties than the raw jute and raw sisal fiber reinforced composites. When comparing the sodium hydroxide treated jute and sisal fiber reinforced epoxy composites, the sodium hydroxide treated jute fiber reinforced composites exhibited better mechanical properties than the latter.     

Bamboo fiber reinforced thermosetting resin composites: Effect of graft copolymerization of fiber with methacrylamide

Epoxy and polyester resins have been reinforced with methacrylamide (MAA) treated bamboo strip matting to develop bamboo fiber reinforced plastic composites. Bamboo mats were graft copolymerized with 1, 3, and 5% solution of MAA. The mechanical (tensile strength, elastic modulus, flexural strength, and flexural modulus), thermal, and water absorption properties of the composites were determined. One percent treatment of bamboo with MAA gave optimum results with epoxy resin. The mechanical properties were improved. TGA results reveal that the degradation temperature of the composite has improved after grafting. The weight loss of 1% MAA treated bamboo–epoxy composite reached a value of 95.132% at 795°C compared to 97.655% at 685°C of untreated bamboo–epoxy composite. Water absorption in the composites was studied by long term immersion and 2 h boiling in distilled water. The process of water absorption indicates Fickian mode of diffusion. MAA treatment results in reduced water uptake. There was improvement in the properties of pretreated bamboo‐polyester matrix composite as well. Three percent treatment of bamboo with MAA gave optimum results with polyester resin. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

Development of Silicon Carbide Reinforced Jute Epoxy Composites: Physical,Mechanical and Thermo-mechanical Characterizations

The aim of the present study was to investigate the physical and thermo-mechanical characterization of silicon carbide filled needle punch nonwoven jute fiber reinforced epoxy composites. The composite materials were prepared by mixing different weight percentages (0–15 wt.%) of silicon carbide in needle punch nonwoven jute fiber reinforced epoxy composites by hand-lay-up techniques. The physical and mechanical tests have been performed to find the void content, water absorption, hardness, tensile strength, impact strength, fracture toughness and thermo-mechanical properties of the silicon carbide filled jute epoxy composites. The results indicated that increase in silicon carbide filler from 0 to 15 wt.% in the jute epoxy composites increased the void content by 1.49 %, water absorption by 1.83 %, hardness by 39.47 %, tensile strength by 52.5 %, flexural strength by 48.5 %, and impact strength by 14.5 % but on the other hand, decreased the thermal conductivity by 11.62 %. The result also indicated that jute epoxy composites reinforced with 15 wt.% silicon carbide particulate filler presented the highest storage modulus and loss modulus as compared with the unfilled jute epoxy composite.     

Preparation and characterization of an epoxy resin modified by a combination of MDI‐based polyurethane and montmorillonite

The present work investigates the modification of epoxy resin by using a combination of nanoclay (montmorillonite—Cloisite 30B) and a liquid polymeric modifier (polyurethane). Polyurethane was obtained from 4,4′‐diphenylmethane diisocyanate and polydiols with different molecular weight: polyethylene glycol (PEG 400) and polyoxypropylene diols with molecular weight 1000 g/mol and 2000 g/mol. The impact strength, the critical stress intensity factor as well as the flexural strength were evaluated as functions of modifiers content. The obtained results showed that hybrid composites exhibit enhanced mechanical properties without significant changes of the glass transition temperature. FTIR analysis showed that chemical reactions took place between the hydroxyl groups of epoxy resin and the isocyanate groups of polyurethane, explaining an improvement of the mechanical properties of epoxy resin. However, XRD results demonstrated the formation of an exfoliated structure for the hybrid compositions with both polyurethane and montmorillonite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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 bamboo polymer composites with polyester amide polyol as interfacial agent

The effect of surface treatment on the properties of bamboo/epoxy, bamboo/polyester composites was investigated. An improvement in the properties was observed when the surfaces of the bamboo fibers were modified with polyesteramide polyol (PEAP). The performance of surface treated bamboo composites in terms of water resistance is significantly better than that of untreated bamboo composites. Polyester amide polyol treated bamboo composites exhibited better mechanical strength properties. Fractographic evidence such as fiber breakage/splitting and matrix adherence on the pulled‐out fiber surface explains such behavior.     

Mechanical properties of E‐glass fiber reinforced siliconized epoxy polymer composites

Siliconized epoxy‐matrix systems have been developed by an interpenetrating mechanism using epoxy resins GY 250 and LY 556 (Ciba‐Geigy) and hydroxyl terminated polydimethylsiloxane with γ‐aminopropyltriethoxysilane as crosslinker in the presence of dibutyltindilaurate catalyst. Aliphatic amine (HY 951, Ciba‐Geigy), aromatic amine (HT 972, Ciba‐Geigy) and polyamidoamine (HY 840, Ciba‐Geigy) are used as curing agents for epoxy resins. The tentative level of 10% siloxane introduction into epoxy resin has been ascertained from experimental studies to obtain reasonable improvements in the impact behavior without compromising other mechanical properties. The impact behavior of E‐glass reinforced composites made from the siliconized epoxy resin is enhanced to 2–4 times over that measured on the composites made from a pure epoxy resin. Composites cured with aromatic amine impart better mechanical properties than those cured with aliphatic amine and polyamidoamine.     

Improvement of functional properties of jute‐based composite by acrylonitrile pretreatment

Cyanoethylation of jute fiber in the form of nonwoven fabric was successfully achieved using an acrylonitrile monomer which is said to react with the hydroxyl groups of fiber constituents. The degrees of cyanoethylation to different extents were undertaken by varying the reaction time. An IR study showed that extent of cyanoethylation increases with increase of the reaction time. Cyanoethylated fibers thus obtained were further treated with unsaturated polyester resin to obtain modified fiber composites. These composites have been found to be tolerant against cold and boiling water where water absorption and thickness swelling are much reduced compared to those of unmodified fiber composite. It is also observed that the moisture content of the modified fiber composites is remarkably reduced. Cyclic tests reveal that use of cyanoethylated fiber leads to improvement of the dimensional stability of the fiber composites. The mechanical properties of the modified fiber composites improved remarkably due to better bonding at the fiber–matrix interface and this effect is more pronounced with a higher degree of cyanoethylation. A scanning electron micrograph of the fractured surfaces of cyanoethylated jute composite showed excellent retention of resin on broken fiber ends, whereas the unmodified composite showed uncoated fibers and holes in the matrix. DSC data demonstrated that the moisture content of the composites reduces with increase of the cyanoethylation. Both TG and DSC thermograms showed an additional peak due to decomposition of cyanoethyl group which is shifted to a higher value with the extent of cyanoethylation. However, the cellulose degradation temperature remained almost the same. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 495–506, 2000     

Zum Verhalten von Jute- und Flachsfaser-Epoxidharz-Verbunden mit alkalibehandelten Fasern bei Feuchteexposition

Investigations on the influence of exposure to water on the physical properties of untreated and alkali-treated jute and flax fibers and their composites with an epoxy resin were carried out. The moisture uptake led to a strong anisotropic swelling which was more significant for the alkali treated fibers. In general, jute fibers lost roughly 30% of their tenacity after this water exposure, while the tenacity of flax fibers remained unaffected. Due to this, the tensile strength of jute-epoxy composites decreases with increasing water content, while the strength of comparable flax-epoxy composites increases slightly. The dynamic strength of the composites was improved by the use of alkali-treated fibers, the loss of this characteristic value after a 49-days water storage was influenced by the type of fiber and their treatment.     

纳米SiO2/竹纤维/环氧树脂复合材料性能研究

将竹纤维加入到环氧树脂中以形成增强环氧复合材料,研究了竹纤维竹粉和纳米二氧化硅（SiO2）对环氧树脂的力学性能和耐溶剂浸蚀性能的影响。竹纤维含量为15%时,竹纤维/环氧树脂的冲击强度比纯环氧树脂提高50%。纳米SiO2能同时增强和增韧竹纤维/环氧树脂,并提高其耐溶剂浸蚀性能,纳米SiO2含量为4%时,纳米SiO2/竹纤维/环氧树脂三元复合材料的冲击和拉伸强度分别比未添加纳米SiO2的竹纤维/环氧树脂提高40%和30%。当纳米SiO2/竹纤维/环氧树脂的质量比为4/15/85时,三元复合材料的综合性能较好。     

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     

Toughening of epoxy resin using hydroxyl‐terminated polyesters

Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by relatively low toughness. Several approaches to improve epoxy resin toughness include the addition of fillers, rubber particles, thermoplastics, or their hybrids, as well as interpenetrating networks and flexibilizers, such as polyols. It seems that this last approach did not receive much attention. So in an attempt to fill this gap, the present work deals with the use of hydroxyl‐terminated polyester resins as toughening agents for epoxy resin. For this purpose, the modifier, that is, a hydroxyl‐terminated polyester resin (commercially referred to as Desmophen), which is a polyol, has been used at different concentrations. The prepared modified structure has been characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. Two types of Desmophen (800 and 1200) have been used as modifiers. The obtained results showed that hydroxyl‐terminated polyester improves the epoxy toughness. In fact, the impact strength increases with Desmophen content and reaches a maximum value of 7.65 J/m at 10 phr for Desmophen 800 and 9.36 J/m at 7.5 phr for Desmophen 1200, respectively. At a critical concentration (7.5 phr), Desmophen 1200 (with higher molecular weight, longer chains, and lower branching) leads to better results. Concerning K_c, the effect of Desmophen 800 is almost negligible; whereas a drastic effect is observed with Desmophen 1200 as K_c reaches a maximum of 2.41 MPa m^1/2, compared to 0.9 MPa m^1/2 of the unmodified epoxy prior to decreasing. This is attributed to the intensive hydrogen bonding between epoxy and Desmophen 1200, as revealed by FTIR spectroscopy. Finally, the SEM analysis results suggested that the possible toughening mechanism for the epoxy resin being considered, which might prevail, is through localized plastic shear yielding induced by the presence of the Desmophen particles. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 29–38, 1999     

Fabrication and evaluation of some mechanical and electrical properties of jute‐biomass based hybrid composites

Hybrid composites based on bisphenol‐C‐formaldehyde resin and jute mat with rice, wheat, sugar cane, and jamun husks have been fabricated at 150°C under 30.4 MPa pressure for 2 h. The resin content in composites was 50% of fibers. Tensile strength, flexural strength, electric strength, and volume resistivity of hybrid composites have been evaluated and compared with those of jute‐bisphenol‐C‐formaldehyde composites. It is observed that the tensile strength of composites is found to decrease by 53–72%, which is mainly due to random orientation of sandwiched fibers. Flexural strength has increased by 53–153% except jute–rice husk composite for which it is decreased by 26%. A little change in dielectric breakdown strength (1.89–2.11 kV/mm) is found but volume resistivity of Jute–wheat husk and Jute–jamun husk composites has improved by 437–197% and it is slightly decreased(2.3–25.2%) for the remaining two composites. Thus, hybrid composites possess good mechanical and electrical properties signifying their importance in low strength and light weight engineering applications as well as low cost housing units such as partition and hard boards. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1754–1758, 2006     

Effects of surface modification on rheological and mechanical properties of CNT/epoxy composites

Despite superior properties of carbon nanotubes (CNTs), physical properties of the CNT/epoxy composites are not improved significantly because interfacial bonding between the CNTs and the polymer matrix is weak. CNTs were treated by an acidic solution to remove impurities and modified subsequently by amine treatment or plasma oxidation to improve interfacial bonding and dispersion of nanotubes in the epoxy matrix. The functional groups on the surface of treated CNTs were investigated by X-ray photoelectron spectroscopy. The surface modified CNTs were embedded in the epoxy resin by ultra-sonication and the cured nanotube containing composites were characterized by field emission scanning electron microscopy. Rheological properties of nanotube containing epoxy resin and mechanical properties of the modified CNT/epoxy composites were improved because the modification of CNTs improved dispersion and interaction between the CNT and the epoxy resin.     

环氧改性水性聚氨酯涂料的合成与性能研究

采用环氧树脂与聚醚、二羟甲基丙酸（DMPA）和甲苯二异氰酸酯（TDI）反应制备水性聚氨酯涂料。研究发现随着所用的环氧树脂的环氧值的降低，改性水性聚氨酯涂膜的硬度和拉伸强度逐渐提高，断裂伸长率则随着降低。选用环氧值为0．44的环氧树脂所合成的改性水性聚氨酯的涂膜硬度达到玻璃硬度0．70；随着环氧树脂添加量增大，涂膜机械性能增加。采用后添加环氧树脂的合成工艺，可制备贮存稳定的水性聚氨酯乳液；凝胶渗透色谱（GPC）分析表明环氧树脂改性水性聚氨酯提高了聚氨酯的分子量。性能测试表明环氧改性水性聚氨酯涂料具有涂膜硬度高、耐水性好和耐溶剂性好等优点。     

Effect of particulate fillers on short jute fiber-reinforced natural rubber composites

The effect of carbon black on the processing characteristics and physical properties of jute fiber-reinforced composites and the role of silica and carbon black in promoting the adhesion between jute fiber and natural rubber have been studied. It was found that presence of silica is not essential to develop adhesion between fiber and rubber in the presence of carbon black. However, silica and carbon black can improve adhesion by minimizing the resin formation and controlling it to a low molecular weight species. Processing properties like green strength and mill shrinkage are improved by the addition of fiber. Carbon black does not affect mill shrinkage, but improves the green strength. Breakage of jute fiber during mixing is severe, but the extent of breakage is not affected by the presence of carbon black. The minimum loading of fiber to achieve reinforcement is reduced in the presence of carbon black. It was also found that the presence of clay in jute fiber rubber composites impairs the properties. Scanning electron microscopy (SEM) has been used to assess the failure criteria.     

Computer simulation of structure and properties of crosslinked polymers: application to epoxy resins

In this work, a methodology has been developed for construction of atomistic models of crosslinked polymer networks. The methodology has been applied to low molecular weight water soluble epoxy resins crosslinked with different curing agents that are being considered for use as a primer coating on steel. The simulations allowed the crosslink density and the amount of free crosslinking sites in the coatings to be predicted. Shrinkage of the resin upon curing was reproduced by the simulation. In addition, the barrier properties of the model coatings were estimated. The interface between an inorganic substrate and cured epoxy resin has been constructed and the strength and molecular mechanisms of adhesion have been revealed. The developed methodology has a potential to significantly impact on the design and development of new coatings with improved barrier and adhesion properties.