Effect of chemical modifications of the pineapple leaf fiber surfaces on the interfacial and mechanical properties of laminated biocomposites

Natural fiber reinforced renewable resource based laminated composites were prepared from biodegradable poly(lactic acid) (PLA) and untreated or surface-treated pineapple leaf fibers (PALF) by compression molding using the film stacking method. The objective of this study was to determine the effects of surface treatment of PALF on the performance of the fiber-reinforced composites. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to aid in the analysis. The mechanical properties of the PLA laminated composites were improved significantly after chemical treatment. It was found that both silane- and alkali-treated fiber reinforced composites offered superior mechanical properties compared to untreated fiber reinforced composites. The effects of temperature on the viscoelastic properties of composites were studied by dynamic mechanical analysis (DMA). From the DMA results, incorporation of the PALF fibers resulted in a considerable increase of the storage modulus (stiffness) values. The heat defection temperature (HDT) of the PALF fiber reinforced PLA laminated composites was significantly higher than the HDT of the neat PLA resin. The differential scanning calorimeter (DSC) results suggest that surface treatment of PALF affects the crystallization properties of the PLA matrix. Additionally, scanning electron microscopy (SEM) was used to investigate the distribution of PLA within the fiber network. SEM photographs of fiber surface and fracture surfaces of composites clearly indicated the extent of fiber–matrix interface adhesion. It was found that the interfacial properties between the reinforcing PALF fibers and the surrounding matrix of the laminated composite are very important to the performance of the composite materials and PALF fibers are good candidates for the reinforcement fiber of high performance laminated biodegradable biocomposites.     

A numeric model for the kinetics of water vapor sorption on cellulosic reinforcement fibers

Some natural fibers like flax, hemp and others show excellent mechanical properties that make them a promising choice for the reinforcement of polymers. The increasing research on natural fiber reinforced composites has still left important questions open, mainly concerning the fiber–matrix interface. Compared to the well optimized glass fibers, cellulose fibers show very different interaction with matrix polymers and adhesion promoters. The hydrophilic cellulose structure allows for the penetration of a considerable amount of water into the amorphous regions of the fibers, eventually exceeding 20% by mass, depending on fiber type, preparation and environmental humidity. Even embedded in totally apolar polymers the cellulose partly retains its ability for water sorption, which results in unfavorable effects, such as dimensional changes, decrease in strength, roughening of the surface, etc. The interaction of differently prepared fibers with water vapor and the effect of surface treatment is investigated by measuring the dynamics of water vapor sorption. An exponential model is used for the numerical evaluation of the sorption and desorption kinetics. The model not only allows for an excellent fit of the experimental isotherms, but without any further assumptions it immediately gives evidence of the existence of two distinct mechanisms for the exchange of water vapor, related to different sorption sites. These specific mechanisms are represented by individual sorption–desorption isotherms as components of the total isotherms. The model provides a clearer differentiation of the effects of fiber preparation and modification with respect to interfacial interactions.     

Cellulose-based biocomposites: comparison of different multiphasic systems

Biocomposites (biodegradable composites) are obtained by blending biodegradable polymers and fillers. Since the main components are biodegradable, the composite as a whole is also expected to be biodegradable. This paper presents various biocomposites that have been elaborated with cellulose or lignocellulose fibers from diverse sources, with different lignin contents. This paper is targeted on the analysis of 'fiber–matrix' interactions of two types of biocomposites based on agropolymer (plasticized wheat starch) and biopolyester (polybutylene adipate-co-terephthalate), named APB and BPB, respectively. Processing and main properties of both biocomposites are shown and compared. Polyolefin-based composite (PPC), which is known to present very poor 'fiber–matrix' interactions, is used as a reference. Through the Young's modulus, mechanical properties have shown that the reinforcement, by increasing fiber content, is much more significant for APB compared to BPB. The evolution of chains mobility, evidenced through shift of T _g values, according to the increase in fiber content and thence in interfacial area, have shown that the fiber–matrix interactions are higher for APB. BPB presents intermediate values, higher than PPC ones. These results are in agreement with the analysis of the composite morphologies performed by SEM on cryogenic fractures. Finally, by determining the theoretical works of adhesion and the interfacial tensions from contact angle measurements, it is shown that these parameters are partially able to predict the level of interaction between the fibers and the matrix. We could show that the perspectives of such work seem to be of importance to tailor new materials with a controlled end-use.     

Fabrication and Flexural Properties of Bagasse Fiber Reinforced Biodegradable Composites

Biodegradable composites made from bagasse fiber and biodegradable resin were fabricated and the flexural properties of the composites investigated in terms of the effects of fiber length, fiber volume fraction, and different alkali treatments of the bagasse fibers. The flexural properties of the composites increased with the increase in fiber length but decreased below the critical fiber length. The flexural properties increased with the increase in fiber volume fraction. The scanning electron microscope (SEM) micrographs showed that compression of the cellulose structure of bagasse fiber after preparation could have caused enhancement in the flexural properties. Furthermore, when comparing the effects of different alkali treatments of the bagasse fibers, maximum improvement in the flexural properties was observed for the 1% NaOH solution treated fiber composites. After alkali treatment, fibrillation occurred and the surface of the treated fibers became finer; this could contribute to improvement in the fiber‐matrix adhesion and result in enhancing the flexural properties.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

Predictions of Young's Modulus of Polymer Composites Reinforced with Short Natural Fibers

Polymers reinforced with natural fibers are beneficial to prepare biodegradable composite materials. A new expression for the Young's modulus of short, natural fiber (SNF) reinforced polymer composites was derived based on a micro-mechanical model. The Young's moduli of poly(lactic acid) reinforced with reed fibers and low-density polyethylene (LDPE) reinforced with sisal fibers, from literature data, were estimated in the fiber weight fraction range from 0 to 50% using the equation and both the compounding rule and the Halpin–Tsai equation, and the estimations were compared with the reported measured data. The results showed that the predictions of the Young's moduli by means of the new Young's modulus equation were close to the measured data from the low density polyethylene/sisal fiber composites, as well as the poly(lactic acid)/reed composites at high fiber concentration. Comparing with other Young's modulus equations, the new Young's modulus equation would be more convenient to use owing to the parameters in the equation being easily determined.     

Fabrication of optically transparent chitin nanocomposites

This paper demonstrates the preparation of chitin nanofibers from crab shells using a simple mechanical treatment. The nanofibers are small enough to retain the transparency of neat acrylic resin. Possessing hydroxyl and amine/N-acetyl functionalities, water suspension of chitin nanofibers was vacuum-filtered 9 times faster than cellulose nanofibers to prepare a nanofiber sheet of 90 mm in diameter. This is a prominent advantage of chitin nanofibers over cellulose nanofibers in terms of commercial application. Interestingly, chitin acrylic resin films exhibited much higher transparency than cellulose acrylic resin films owing to the close affinity between less hydrophilic chitin and hydrophobic resin. Furthermore, the incorporation of chitin nanofibers contributes to the significant improvement of the thermal expansion and mechanical properties of the neat acrylic resin. The properties of high light transmittance and low thermal expansion make chitin nanocomposites promising candidates for the substrate in a continuous roll-to-roll process in the manufacturing of various optoelectronic devices such as flat panel displays, bendable displays, and solar cells.     

Optically transparent composites reinforced with plant fiber-based nanofibers

The fibrillation of pulp fiber was attempted by two methods, a high-pressure homogenizer treatment and a grinder treatment. The grinder treatment resulted in the successful fibrillation of wood pulp fibers into nanofibers. The nanofibers demonstrate promising characteristics as reinforcement material for optically transparent composites. Due to the size effect, the nanofiber-reinforced composite retains the transparency of the matrix resin even at high fiber content such as 70 wt %. Since the nanofiber is an aggregate of semi-crystalline extended cellulose chains, its addition also contributes to a significant improvement in the thermal expansion properties of plastics while maintaining its ease of bending. Cellulose nanofibers have tremendous potential as a future resource since they are produced in a sustainable manner by plants, one of the most abundant organic resources on earth. PACS 81.05.Lg; 81.05.Qk     

Hybrid Nanoparticle/Microfiber‐Filled Injection‐Molded Composites

The structure and some properties of hybrid injection‐molded polypropylene (PP) composites, containing carbon fibers (CF) and nanoparticles, were studied. The effects of nanoparticle type, size, and content were investigated. All studied hybrid composites exhibited unexpected fiber disorientation (oriented even transverse to the melt‐flow direction), disappearance of the typical skin/core structure in fiber‐containing moldings and, surprisingly, very low fiber length. Different types of nanoparticles resulted in different levels of fiber breakage: the shortest fibers were observed in composites containing nano‐TiO₂ and longer ones in composites containing nano‐Al₂O₃ and carbon black (CB). Moreover, smaller nanoparticles resulted in higher levels of fiber length attrition. Electrical conductivity of the composites was found to drop drastically upon incorporation of several volume percents of insulating nanoparticles, although the content of CF when by itself was above the percolation threshold. Tensile modulus values, in the melt‐flow direction, of hybrid composites were also inferior to those of the only–CF‐reinforced composites, while rheological properties were dominated by CF, being practically not affected by the presence of nanoparticles. Based on the present and previous studies, the effect of nanoparticles on fiber orientation and their length attrition in hybrid injection moldings could be generalized to systems containing combinations of brittle fibers and hard nanoparticles.     

利用近红外光谱鉴别纺织用竹纤维和麻纤维

利用近红外光谱技术对竹原纤维、竹粘胶纤维和苎麻纤维进行了快速定性鉴别研究.首先扫描3种纤维的近红外光谱,利用化学计量学分析软件,对谱图进行一阶导数预处理,建立不同纤维的光谱数据库,并分别建立竹原纤维、竹粘胶纤维和苎麻纤维的判别模型.利用判别模型,对未知样品进行判别.结果表明,近红外光谱可以在不破坏样品的情况下,可以快速鉴别竹原纤维、竹粘胶纤维和苎麻纤维.     

Mechanical and Tribological Properties of Self-Reinforced Polyphenylene Sulfide Composites

25%, 50%, and 75% polyphenylene sulfide (PPS) long fiber reinforced PPS resin were prepared by a hot pressing method. Neat resin PPS and PPS fiber samples were also prepared to compare with the self-reinforced PPS composites. The reinforcing fibers were preheat treated at 240°C for 24 h. The tribological properties of the self-reinforced PPS composites against an AISI 1045 steel ring were determined by a block on ring type friction tester. Differential scanning calorimetry (DSC) results indicated that a higher degree of crystallinity was retained in the self-reinforced PPS composites than in neat PPS resin after hot pressing. Therefore, the addition of PPS fiber improved both the mechanical and tribological properties of PPS resin significantly. Dynamic mechanical analysis (DMA) demonstrated that the PPS fibers increased the glass transition temperature (Tg) of the PPS resin. SEM images of the fracture surfaces indicated that the toughness of the samples increased with increasing PPS fiber content. Additionally, PPS fibers improved the tribological properties of PPS resin by significantly reducing the friction coefficient and wear rate.     

Effect of fiber surface treatments on the fiber–matrix interaction in banana fiber reinforced polyester composites

Cellulosic fibers have been used as cost-cutting fillers in plastic industry. Among the various factors, the final performance of the composite materials depends to a large extent on the adhesion between the polymer matrix and the reinforcement and therefore on the quality of the interface. To achieve optimum performance of the end product, sufficient interaction between the matrix resin and the cellulosic material is desired. This is often achieved by surface modification of the resin or the filler. Banana fiber, the cellulosic fibers obtained from the pseudo-stem of banana plant (Musa sepientum) is a bast fiber with relatively good mechanical properties. The fiber surface was modified chemically to bring about improved interfacial interaction between the fiber and the polyester matrix. Various silanes and alkali were used to modify the fiber surface. Modified surfaces were characterized by SEM and FTIR. The polarity parameters of the chemically modified fibers were investigated using the solvatochromic technique. The results were further confirmed by electrokinetic measurements. Chemical modification was found to have a profound effect on the fiber–matrix interactions. The improved fiber–matrix interaction is evident from the enhanced tensile and flexural properties. The lower impact properties of the treated composites compared to the untreated composites further point to the improved fiber–matrix adhesion. In order to know more about the fiber–matrix adhesion, fractured surfaces of the failed composites where further investigated by SEM. Of the various chemical treatments, simple alkali treatment with NaOH of 1% concentration was found to be the most effective. The fiber–matrix interactions were found to be dependent on the polarity of the modified fiber surface.     

The Effect of ZrO2 Interphase on Interfacial Frictional Stresses in SiC/ZrO2/SiCf Composites

Two types of SiC fiber tows (Hi-Nicalon? and Hi-Nicalon S?) were coated with stabilized ZrO₂ and composited using preceramic polymer impregnation pyrolysis to form SiC/SiC_f minicomposites. Properties of the fiber/matrix interface in composites were investigated using the indentation method in which a pyramidal indenter was used to push on an individual fiber and cause sliding at the interface. The interfacial frictional stresses were determined from the force–displacement relation. The composites reinforced by the ZrO₂-coated fibers have smaller interfacial frictional stresses than composites reinforced by the initial fibers and show fibers sliding relatively more easily with respect to the SiC matrix.     

The effect of morphological changes from pulp fiber towards nano-scale fibrillated cellulose on the mechanical properties of high-strength plant fiber based composites

Fibrillated kraft pulp impregnated with phenolic resin was compressed under an extremely high pressure of 100 MPa to produce high strength cellulose nanocomposites. To evaluate how the degree of fibrillation of pulp fiber affects the mechanical properties of the final composites, kraft pulp subjected to various levels of refining and high pressure homogenization treatments was used as raw material with different phenolic resin contents. It was found that fibrillation solely of the surface of the fibers is not effective in improving composite strength, though there is a distinct point in the fibrillation stage at which an abrupt increase in the mechanical properties of composites occurs. In the range between 16 and 30 passes through refiner treatments, pulp fibers underwent a degree of fibrillation that resulted in a stepwise increment of mechanical properties, most strikingly in bending strength. This increase was attributed to the complete fibrillation of the bulk of the fibers. For additional high pressure homogenization-treated pulps, composite strength increased linearly against water retention values, which characterize the celluloses exposed surface area, and reached maximum value at 14 passes through the homogenizer. PACS 81.05.Lg; 81.05.Qk     

Interface and its effect on the interlaminate shear strength of novel glass fiber/hyperbranched polysiloxane modified maleimide-triazine resin composites

Interface is the key topic of developing advanced fiber reinforced polymeric composites. Novel advanced glass woven fabric (GF) reinforced composites, coded as GF/mBT, were prepared, of which the matrix resin was hyperbranched polysiloxane (HBPSi) modified maleimide-triazine (mBT) resin. The influence of the composition of the matrix on the interfacial nature of the GF/mBT composites were studied and compared with that of the composite based on GF and BT resin using contact angle, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and dielectric properties over wide frequency and temperature ranges. Results show that the interfacial nature of the composites is dependent on the chemistries of the matrices, mBT matrices have better interfacial adhesion with GF than BT resin owing to the formation of chemical and hydrogen bonds between mBT resin and GF; while in the case of mBT resins, the content of HBPSi also plays an important role on the interfacial feature and thus the macro-performance. Specifically, with increasing the content of HBPSi in the matrix, the interlaminate shear strength of corresponding composites significantly improves, demonstrating that better interfacial adhesion guarantees outstanding integrated properties of the resultant composites.     

Nano-fibrillation of pulp fibers for the processing of transparent nanocomposites

Pulp fibers were fibrillated uniformly into nano-sized fibers using a grinder with a specially designed set of grinding disks. To investigate the effect of the fibrillation through the grinder on the physical properties of the composites, dissolved pulp fibers were subjected to various passes through the grinder, and the resulting fibrillated pulp fibers were used to make fibrillated pulp fibers/acrylic resin composites. Scanning electron microscopy observations showed that at above five passes, the structure of the fibrillated pulp fibers did not change significantly. The light transmittances of the composites were increased to 80% up to five passes through the grinder, and did not change after further passes. However, the tensile test and thermal expansion analysis indicated that a degradation of the fibrillated pulp occurred during the grinding treatment. To evaluate the fiber degradation, the degree of crystallinity and degree of polymerization of cellulose were measured. Both decreased as the number of passes through the grinder increased. In addition, to reduce the thermal expansion of composites, the fibrillated pulp fibers were additionally treated by sulfuric acid. The thermal expansion of composites was decreased, because the amorphous region of cellulose was removed. PACS 81.05.Lg; 81.05.Qk; 81.07.-b     

Thermal behavior of chemically treated and untreated sisal fiber reinforced composites fabricated by resin transfer molding

Using thermogravimetric analysis (TGA), the thermal behavior of sisal fibers and sisal/polyester composites, fabricated by resin transfer molding (RTM), has been followed. Chemical treatments have been found to increase the thermal stability, which has been attributed to the resultant physical and chemical changes. Scanning electron microscopy (SEM) and infrared (FT-IR) studies were also performed to study the structural changes and morphology in the sisal fiber during the treatment. The kinetic studies of thermal degradation of untreated and treated sisal fibers have been performed using Broido method. In the composites, as the fiber content increases, the thermal stability of the matrix decreases. The treated fiber reinforced composites have been found to be thermally more stable than the untreated derivatives. The increased thermal stability and reduced moisture behavior of treated composites have been correlated with fiber/matrix adhesion.     

A review on abaca fiber reinforced composites

This paper reviews literatures and information on Abaca fibers (Musa textilis Nee) as reinforcing material for aerospace composite materials. Characterization of Abaca as well properties of Abaca reinforced composites and its applications were discussed. Therefore, challenges and future works for Abaca Reinforced composites were explored. Studies reveal that Abaca fiber pre-treatment helps in improving the mechanical properties of the composite. In addition, there have been efforts in combining Abaca fibers to existing mixture of synthetic composites to improve its mechanical properties and environmental performance. The future of Abaca is seen as one of the potent sources of reinforcing fiber for various material construction including aerospace materials.     

Effect of transcrystallization in carbon fiber reinforced poly(p-phenylene sulfide) composites on the interfacial shear strength investigated with the single fiber pull-out test

The effect of transcrystallinity in carbon fiber reinforced poly(p-phenylene sulfide (PPS) composites on the apparent shear strength was investigated with the single fiber pull-out test. Transcrystalline zones around the reinforcing fibers do not seem to improve the adhesion level significantly. Neighbor fibers hinder the formation of the transcrystalline zone and a ductile fracture behavior can be observed. However, the apparent strength level is slightly higher for composites containing such reinforcing neighbor fibers compared with single fiber composite samples. During annealing a brittle interface can be formed in the multifiber composite yielding a higher level of the apparent shear strength.     

Correlations among micro- and macromechanical properties of composite materials based on the interphase concept

In this paper an attempt was made to define microstructural properties of carbon fiber/PP composites, with respect to fiber surface chemistry and morphology. In order to define the effects of the fiber surface sizings and morphology on the polymer microstructure, the interphase and mechanical properties of the composites, carbon fibers with similar, but not identical surface chemistry (CH and CT) were used. Characterization was performed by several techniques: SEM, POM, reflection microscopy, DSC, FTIR, XPS, contact angle measurements. For microstructural analysis, the geometrical method, method of intercept and DIF method were used. It was found that both carbon fibers have a strong influence on the nucleation mechanism and crystallization as well as on the microstructural parameters in the model and macro composites. Nucleation efficiency of the fibers has been confirmed by the nucleation parameter Q, measured by Muchova–Lednicky method and by the interfacial energy parameters. Microstructural analysis based on the photographs obtained by POM, SEM and reflection microscopy has shown that in the CH/PP model and macrocomposites the sieve-grain network was formed, which indicates better mechanical properties. The results obtained for the macromechanical properties of PP composites reinforced with CH and CT have confirmed the prediction based on micostructural analysis.