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Banana fibers are an agricultural waste material with a great exploitation potential due to their cellulose-rich content. Raw banana fibers (RBF) were treated with 3-aminopropyltriethoxy silane and glycidoxypropyltrimethoxy silane to improve the inherent limitations of banana fibers, namely its poor cell adhesion. The fibers’ modification was evaluated by inverse gas chromatography (IGC). Similar γ values were observed between the RBF and silane-treated fibers (39–41 mJ/m2), which indicates similar reactivity towards apolar probes. However, the decrease in the entropic parameter indicates the silane covalent bonding with the cellulose chains making a stiffer structure. Organosilane grafting was confirmed by an increased basic character in the silane-treated fibers (Kb/Ka from 1.03 to 2.81). The surface morphology also changed towards higher contact area (SBET increases 6.7 times) and porosity (Dp increases up to 67%). Both morphological and functional group reactivity changes suggest that the organosilane treatment offers new opportunities for these fibers to be used as adsorbents for proteins as well as to cell adhesion. Therefore, IGC proved a simple and viable technique in the characterization of silane-treated fibers.

To develop bio-nanocomposites using natural biopolymers, nanocomposite films were prepared based on sodium alginate and kapok nanofibrils (CNFs). CNFs when subjected to TEMPO-mediated oxidation gave rise to cellulose nanocrystals (TOCNCs), with carboxyl groups at the surface (Ka/Kb = 3.64). The differences between the two types of nanocelluloses (nanofibrils and nanocrystals) and their impact in the preparation of bio-nanocomposites, were studied. When incorporated in the matrix, the CNFs particles have the tendency to form surface aggregation (Ka/Kb = 2.37), distorting the alginate network, creating heterogeneous films, with high surface roughness (Sa = 29.37 nm), porosity (Dp = 0.087 cm2/min) and vulnerability to heat. The TOCNCs present good dispersion creating a 3D network, which forms uniform (Dp = 0.122 cm2/min) and homogeneous films, with smooth surface (Sa = 16.83 nm). The ultrasonication treatment facilitated the dispersion improving the interfacial interaction between the reinforcing phase and the matrix. The results show the reinforcement potential of kapok nanocellulose in an industrially and medically important biopolymer, sodium alginate, especially when TOCNCs and ultrasonication were used., Materials science; Nanotechnology; Nanomaterials; Materials characterization; Materials property; Agricultural technology; Nanofibrils; Nanocrystals; TEMPO-Mediated oxidation; Sodium alginate; Kapok fiber; Nanocomposite

Polypropylene (PP)/banana fiber (BF) composites were fabricated from PP fiber and short BF by novel commingling method. The dynamic mechanical analysis (DMA) of the composites was performed with reference to BF loading and fiber surface treatments. By the incorporation of BF into the PP matrix, the storage modulus and loss modulus have been found to increase, whereas damping factor has been found to decrease. Glass transition temperature was found to increase with increase in BF loading. The viscoelastic properties of the composites were also found to depend on fiber surface treatments. The activation energy of the composites for the glass transition has been found to be increased by the increase in BF loading. Surface treatment of the BF further increased the activation energy of the composites, indicating a stronger interface for treated fiber composites. Scanning electron microscopy (SEM) photographs of the BF showed the physical changes induced by the surface treatments. Fourier transform infrared spectroscopy (FTIR) was used to ascertain the existence of the type of interfacial bonds. The use of theoretical equations to predict the storage modulus has also been discussed. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Hybrid composites of glass and banana fiber (obtained from the pseudo stem of Musa sapientum) in polyester matrix, are subjected to dynamic mechanical analysis over a range of temperature and three different frequencies. The effect of temperature on the storage modulus (E′), loss modulus (E′′), and loss factor or damping efficiency (tan δ) is determined. All the properties are compared with those of the neat polyester samples and the un-hybridized composites. The effects of the layering pattern of the two fibers on the ultimate viscoelastic behavior of the composites are also investigated. Composites are prepared with banana as the surface layer and glass as the surface layer and also as an intimate mixture of glass and banana. At temperatures above T g,, the storage modulus values are found to decrease even with the addition of glass fiber for the geometry where glass is the core material. The value of the storage modulus of the composites with the above mentioned geometry is found to be different, above and below Tg, the value above Tg being lower than that below Tg unlike in unhybridized composite. The loss modulus curves and the damping peaks are found to be flattened by the addition of glass. Layering pattern or the geometry of the composites is found to have a profound effect on the dynamic properties of the composite. An intimately mixed composite is found to have the highest storage modulus values in all compositions. The values are consistent with the results of tensile strength. The tan δ curve is found to be affected by the layering pattern followed and gives insight into the interaction in the material. The dielectric behavior of the composites are also found to be dependent on the glass fiber volume fraction as well as the layering pattern employed.

Biodegradable nanocomposite films were prepared by incorporation of cellulose nanofibrils (CNF) into alginate biopolymer using the solution casting method. The effects of CNF content (2.5, 5, 7.5, 10 and 15 wt %) on mechanical, biodegradability and swelling behavior of the nanocomposite films were determined. The results showed that the tensile modulus value of the nanocomposite films increased from 308 to 1403 MPa with increasing CNF content from 0% to 10%; however, it decreased with further increase of the filler content. Incorporation of CNF also significantly reduced the swelling percentage and water solubility of alginate-based films, with the lower values found for 10 wt % in CNF. Biodegradation studies of the films in soil confirmed that the biodegradation time of alginate/CNF films greatly depends on the CNF content. The results evidence that the stronger intermolecular interaction and molecular compatibility between alginate and CNF components was at 10 wt % in CNF alginate films.

The role of fibre/matrix interactions in chemically modified banana fibre composites were investigated using dynamic mechanical analysis and compared with those of untreated fibre composites. The dynamic modulus value and damping parameter, used to quantify interfacial interaction in composites were investigated with special reference to the effect of temperature and frequency. Increased dynamic modulus values and low damping value show the improved interactions between the fibre and the matrix. The damping peaks were found to be dependent on the nature of chemical treatment. Both storage modulus and damping values measured experimentally are consistent and point to the effectiveness of silane A174 coupling agent (γ-methacryloxypropyl trimethoxy silane) for improving fibre–matrix adhesion. Activation energy values for the transitions of the composites were determined from Arrhenius plots. Cole–cole plots were made to evaluate the heterogeneity of the system.

Natural fibers are replacing synthetic fibers as reinforcement in various matrices. The composites so prepared can effectively be used as a substitute for wood and also in various other technical fields like automobile parts. However, to improve the adhesion between the fiber and matrix, chemical modification is suggested. The effect of chemical modification on the dynamic mechanical properties of banana fiber reinforced polyester composites has been analyzed to investigate the interfacial properties. The interfacial phenomenon in turn was found to be related to the acid base interactions involved, which occur due to the specific interactions between less reactive functional groups of each partner at the interface. The acid base interactions were investigated, by solvatochromy and the zeta potential measurements. Solvatochromy revealed that the overall polarity parameter was highest for the silane A151 (vinyl tri ethoxy silane) treated fiber, compared to other treatments. ζ-Potential measurements of the untreated and variously treated fibers also showed that the chemical modification alters the polarity of the already acidic cellulose fibers. The observations of the solvatochromic measurements and ζ-potential measurements are consistent. The results of the polarity parameters were correlated with the results of dynamic mechanical analysis. The storage modulus value was found to be the highest for the silane A151 treated fiber composite.

The dynamic mechanical analysis of banana fiber reinforced polyester composites was carried out with special reference to the effect of fiber loading, frequency and temperature. The intrinsic properties of the components, morphology of the system and the nature of interface between the phases determine the dynamic mechanical properties of the composite. At lower temperatures (in the glassy region), the E ′ values are maximum for the neat polyester whereas at temperatures above T g , the E ′ values are found to be maximum for composites with 40% fiber loading, indicating that the incorporation of banana fiber in polyester matrix induces reinforcing effects appreciably at higher temperatures. The loss modulus and damping peaks were found to be lowered by the incorporation of fiber. The height of the damping peaks depended on the fiber content. When higher fiber content of 40% was used, an additional peak in the tan δ curve, pointing to micro mechanical transitions due to the immobilized polymer layer was evident. The glass transition temperature associated with the damping peak was lowered up to a fiber content of 30%. The T g values were increased with higher fiber content. Cole–Cole analysis was made to understand the phase behavior of the composite samples. A master curve was constructed based on time–temperature super position principle, which allows the prediction of long-term effects. Apparent activation energy of the relaxation process of the composites was also analyzed. The value was found to be maximum for composites with 40% fiber content.

Nanocellulose was successfully extracted from five different lignocellulosic biomass sources viz. banana rachis, sisal, kapok, pineapple leaf and coir using a combination of chemical treatments such as alkaline treatment, bleaching and acid hydrolysis. The shape, size and surface properties of the nanocellulose generally depend on the source and hydrolysis conditions. A comparative study of the fundamental properties of raw material, bleached and nanocellulose was carried out by means of Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, birefringence, X-ray diffraction, inverse gas chromatography and thermogravimetric analysis. Through the characterization of the nanocellulose obtained from different sources, the isolated nanocellulose showed an average diameter in the range of 10–25 nm, high crystallinity, high thermal stability and a great potential to be used with acid coupling agents due to a predominantly basic surface. This work provides an insight into the effective utilization of a variety of plant biomass as a potential source for nanocellulose extraction.

The effect of saponin on the surface properties of banana fibres was studied by Inverse Gas Chromatography (IGC). Parameters including the dispersive component of the surface energy, surface heterogeneity, surface area, as well as acid–base surface properties were determined for saponin modified banana micro and nanofibres. These parameters show a more extensive saponin coating on the nanofibres with a network formation which is explained by the higher reactivity of nanofibres due to the higher surface energy, specific interaction and higher surface area presented by the nanofibres. The energetic profile indicates that both micro and nanofibres coated with saponin interact with the same, or similar, energy active sites. Saponin treatment reduces considerably the surface area of the fibres, with the consequent decrease in the monolayer capacity. The interaction with the polar probes clearly indicates that saponin treatment creates new polar active sites for specific interactions in both samples. However, the treatment increases predominately the basicity of the fibre surface with more relevance to the nanofibres. This behaviour will lead to better polymer/fibre interaction during composite preparation.

The effect of steam explosion coupled with chemical treatment, on the surface properties of banana fibres obtained from the pseudo-stem of banana plant Musa sapientum was studied in detail by inverse gas chromatography (IGC). IGC experiments were performed in banana fibres from macro to nano stages at 293, 298 and 303 K. The analyzed fibres showed dispersive component of the surface energy between 39.59 and 48.03 mJ/m2, at 298 K. The interaction between the fibres and the high and low DN/AN* probes indicate the presence of both acidic and basic active sites on the fibres surface. The values of Ka and Kb suggest that predominantly basic active sites are involved in the specific adsorption process in the nanofibres. During the thermochemical treatment, changes occur in the arrangement of macromolecular chains with the reduction of dispersive groups and the increase in some polar groups. This susceptibility of the surface to change its acid–base characteristics combined with a change in dispersive properties enhance the possibility of specific intermolecular interactions with different solvents, plasticizers, polymers or fillers, which is important to the practical applications of the nanofibres.

Stress relaxation behavior of banana fiber-reinforced polyester composites were investigated with special reference to the effect of fiber loading, fiber treatment, hybridization with glass fiber and also as woven fabric composites. It was observed that incorporation of fiber in the polyester matrix reduces the rate of relaxation. The nature of the relaxation curve was found to depend on the quantity of fiber as well as the surface characteristics of fiber used as reinforcement. The decrease in stress relaxation modulus was greatest for the neat polyester sample whereas it was at a minimum for composites with 40% fiber loading. Chemical modification of the fiber surface was found to affect the degree of adhesion and thereby the nature of relaxation at the initial stages. Of the various chemical modifications chosen in the present study, the decrease in stress was found to be the lowest for composites made out of banana fiber treated with NaOH. Hybridisation of banana fiber with glass was found to decrease the rate of relaxation further. However, stress relaxation values of woven glass and banana gave even lower values.

This paper describes the tensile, impact, flexural properties and aging behavior of short banana fiber reinforced polyester composites with special reference to the effect of fiber length and fiber content. Maximum tensile strength was observed at 30 mm fiber length while impact strength gave the maximum value for 40 mm fiber length. Incorporation of 40% untreated fibers gave a 20% increase in the tensile strength and a 341% increase in impact strength. On treatment with silane coupling agent, composites showed a 28% increase in tensile strength and a 13% increase in flexural strength. Aging studies showed a decrease in tensile strength of the composites. The experimental tensile strength values were compared with theoretical predictions according to Piggot equation. Scanning electron microscopy studies were carried out to understand the morphology of the fiber surface, fiber pullout and interface bonding. Water absorption studies showed an increase in water uptake with increase in fiber content. Finally, the properties of banana fiber reinforced polyester composites have been compared with other natural fiber reinforced composites.