Surface and Interface Characterization of Untreated and SMA Imide-Treated Hemp Fiber/Acrylic Composites

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The hydrophilic nature of natural fibers adversely affects adhesion to a hydrophobic matrix, and consequently it may unfavorably influence the strength of the composite. Therefore, modifying the fiber or the matrix is essential to obtain optimum composite properties. In this work, hemp fibers were modified applying a paper sizing technique using SMA Imide resin (copolymer of styrene and dimethylaminopropylamine maleimide) as a surface modifying agent. The performance of the hemp/acrylic composite was improved significantly using the treated fibers. Inverse gas chromatography (IGC) and pull-out test were employed to study the hemp fiber/matrix interface and the surface characteristics of untreated and treated hemp fibers. The IGC results demonstrated that treated fibers had slightly higher dispersive force compared with untreated fibers. Moreover, modification of fibers with SMA Imide resin slightly decreased the basic character and significantly increased the acid character of hemp fibers. From the pull-out test, the average stress to pull the SMA-treated fibers out was 71% higher than that calculated for untreated fibers. The higher interfacial strength for the treated fibers shows that the SMA treatment had a beneficial influence on the adhesion of the acrylic resin to the hemp fibers. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers

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... There are many interfacial strength test methods to estimate interfacial adhesion performance, such as micro-indentation, fiber push-in and pull-out test. Compared with others, single fiber pull-out method is very convenient to measure the shear strength of fiber/matrix interface [6]. When used, a single fiber is embedded in a matrix block, and an increasing force is applied on the free fiber end to pull it out of the matrix. ...
... When used, a single fiber was embedded into the bulk polymer host and the load is applied on fiber end with host martial fixed. Fiber pull-out and fiber breakage may occur in pull-out test [6]. Generally, the two damage modes depend on the applied loads and yield or fracture strength of single fiber and matrix. ...
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Shape memory alloy (SMA) composites are the desirable candidate for smart materials that used in intelligent structures. However, the overall mechanical performance of SMA composites depends immensely on the quality of the interaction between SMA and polymer matrix. Therefore, it is necessary to find out an approach to enhance the interfacial property of this composite. In this paper, we modified nickel–titanium SMA wire with nano-silica particles before and after acid treatment. The modification effect on the interfacial strength between SMA and epoxy resin was evaluated. Contact angle analysis, scanning electron microscopy (SEM) observation, and single fiber pull-out test were carried out. The bonding characteristics between modified wire and liquid/cured resin were investigated. We then embedded SMA wire into woven glass fabric/epoxy composite laminates, and manufactured this hybrid composites via vacuum assisted resin transfer molding processing. Three-point-bending test of the hybrid composites was performed to validate the modification effect. Fiber pull-out experiment demonstrates that the interfacial shear strength increases by 6.48% by nano-silica particles coating, while it increases by 52.21% after 8 h acid treatment and nano-silica particles coating simultaneously. For hybrid composites, flexural strength of the two specimens increases by 19.8 and 48.2%, respectively. In SEM observation, we observed large debonding region in unmodified composites, while interfacial adhesion between modified wire and epoxy keeps strong after flexural damage.
The main methods for mechanical characterization of the single fibre-polymer matrix interfacial adhesion are described: fibre pull-out, single fibre fragmentation and microdebonding tests. The basis of each method, assumptions and main advantages and drawbacks are discussed. A review of lignocellulosic polymer fibre-matrix interface adhesion data is presented. The effect of different surface treatments and also the effect of different processing parameters are also shown.
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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
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Natural fibers are emerging as low cost, lightweight and apparently environmentally superior alternatives to glass fibers in composites. We review select comparative life cycle assessment studies of natural fiber and glass fiber composites, and identify key drivers of their relative environmental performance. Natural fiber composites are likely to be environmentally superior to glass fiber composites in most cases for the following reasons: (1) natural fiber production has lower environmental impacts compared to glass fiber production; (2) natural fiber composites have higher fiber content for equivalent performance, reducing more polluting base polymer content; (3) the light-weight natural fiber composites improve fuel efficiency and reduce emissions in the use phase of the component, especially in auto applications; and (4) end of life incineration of natural fibers results in recovered energy and carbon credits.
Conference Paper
Natural fiber reinforced polymer composites are beginning to find their way into the commercial automotive market. But, inadequate adhesion between hydrophilic natural fibers and hydrophobic matrix materials affects the performance of the resulting composites. In this study the effect of an environmental friendly fungal treatment on the adhesion characteristics of natural fibers is investigated. Firstly, changes in acid-base characteristics of the modified hemp fibers were studied using Inverse Gas Chromatography (IGC). Afterwards, composites were prepared using Resin Transfer Molding (RTM) process and the effect of modification on performance and durability of the composites was investigated.
The final performance of a composite material depends strongly on the quality of the fibre-matrix interface. The interactions developed at the interface were studied using the acid-base or acceptor-donor concept.The surface characteristics of the carbon fibres and the epoxy matrix were studied using a tensiometric method and the inverse gas chromatography technique. Acid-base surface characters could be determined allowing the interactions at the interface to be described by a specific interaction parameter.It was shown that the shear strength of the interface, as measured by a fragmentation test, is strongly correlated to this specific interaction parameter, demonstrating the importance of acid-base interactions in the fibre-matrix adhesion.
Gas adsorption of n-alkanes and polar probes on the surface of several carbon fibers has been investigated by inverse gas chromatography. Dispersive as well as electron donor-acceptor interactions were shown to contribute independently to measured retention volumes. Separation of these effects allowed us to determine the influence of fiber treatment and sizing on the acid—base character of carbon fiber surfaces.
Inverse gas chromatography (IGC) has become an accurate, reliable and fast method for the physicochemical characterization of polymers and their blends, fibers, modified silica and other surfaces, surfactants, as well as, commercial stationary phases and their mixtures and petroleum pitches, heavy residues of oil distillation.Possibilities of application of inverse gas chromatography in the characterization of solid surfaces are presented. The most important parameters used for the description of dispersive and acid–base properties of examined materials are discussed.
Conference Paper
This book reports on inverse gas chromatography (IGC), a useful technique for characterizing synthetic and biological polymers, copolymers, polymer blends, glass and carbon fibers, coal, and solid foods. The technique involves creating within a column a stationary phase of the solid material of interest. The stationary phase may be a thin polymeric coating on an inert substrate, a finely divided solid, or a thin polymeric coating on the column wall. A volatile probe of known characteristics is passed through the column via an inert mobile phase and the output is monitored. The residence time of the probe and the shape of the chromatogram indicate the characteristics of the stationary phase and its interaction with the probe. Thus, IGC is a variation of conventional gas chromatography.
Inverse gas chromatography (IGC) was applied to characterize the surface of birch wood meal. The isosteric heat of adsorption, q(st), the dispersive component of the surface energy, gamma(s)D, and the acid/base character of birch wood meal surface were estimated by using the retention time of different nonpolar and polar probes at infinite dilution. The specific interaction parameter I(sp), the specific enthalpy of adsorption DELTAH(A)sp, and the enthalpy of acid-base interaction DELTAH(A)ab of polar probes on wood metal surface were determined. DELTAH(A)sp and DELTAH(A)ab were correlated with the donor (DN) and modified acceptor (AN) numbers of the probes to quantify the acidic K(A) and the basic K(B) parameters of the substrate surface. The values of K(A) and K(B) suggest that the extractives free wood meal surface is amphoteric, with predominantly acceptor electron sites.
PMMA, a basic polymer, is found to adsorb strongly from neutral organic solvents onto the acidic silanol sites of a silica filler, providing 50 times more adsorption per unit area than is observed on the basic surface of a calcium carbonate filler. Acidic solvents tend to solvate and neutralize the basic groups of the polymer and will prevent adsorption if the solvent is more acidic than the surface sites of the acidic filler; the acidity of competing solvents is a measure of the acidity of surface sites. Similarly, basic solvents tend to neutralize the acidic silanol sites of the silica filler and will prevent adsorption if the solvent is more basic than the ester groups of the polymer; the basicity of competing solvents is a measure of the basicity of the polymer. These rules are found to govern both adsorption and desorption. Similar findings resulted with post-chlorinated PVC, an acidic polymer, in adsorption studies with calcium carbonate, a basic filler. Dipole-dipole interactions between these polar polymers and polar adsorbents appear to be negligibly small compared to the acid-base interactions.
Much research related to the use of natural fibers in polymeric matrix composites has been developed. The presence of OH groups in the chemical components of the natural fibers generates an important hydrophylic tendency that produces adhesion lacks with hydrophobic polymeric matrices. In this work natural fiber bundles mechanically extracted from both stem and bunch of cultivation banana wastes have been modified by both alkalization and silanization treatments. To evaluate the changes introduced by treatments on the chemical structure of fibers, Fourier-transform infrared spectrophotometry has been employed. The evaluation of advancing dynamic contact angles along with the determination of total surface free energy by using the Owens–Wendt method indicate that the treatments allow reduction of their hydrophilic tendency by alterations on the physicochemical characteristics of the fibers. This behavior is confirmed by the reduction of moisture uptake, analyzed by thermogravimetric analysis. Small differences on noncellulosic components of stem and bunch fiber bundles have been found. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1489–1495, 2004
Natural cellulosic fibers, including hemp, are increasingly being used for composite reinforcement. However, their poor adhesion with synthetic resins limits their use as reinforcing agent. It is generally accepted that interfacial adhesion can be best described in terms of dispersion forces and acid–base interactions. Therefore, there is a need for quantitative determination of acid–base character of natural cellulosic fibers. In this study, acid–base characteristics and dispersion component of surface energy of hemp fibers have been determined using inverse gas chromatography. Effect of alkalization and acetylation on acid–base characteristics has also been examined. The results indicate that alkalization and acetylation make the hemp fiber amphoteric, thereby improving their potential to interact with both acidic and basic resins. Finally, a parallel is drawn between the changes in fiber-matrix acid–base interactions and the actual improvement in the mechanical properties of the composites manufactured using resin transfer molding process. POLYM. ENG. SCI. 46:269–273, 2006. © 2006 Society of Plastics Engineers
Biocomposites were made with nonwoven hemp mats and unsaturated polyester resin (UPE). The hemp fiber volume fraction was optimized by mechanical testing. The effect of four surface treatments of industrial hemp fibers on mechanical and thermal properties of biocomposites was studied. The treatments done were alkali treatment, silane treatment, UPE (matrix) treatment, and acrylonitrile treatment. Bending strength, modulus of elasticity, tensile strength, tensile modulus, impact strength, storage modulus, loss modulus, and tan δ were evaluated and compared for all composites. The mechanical as well as thermal properties of the biocomposites improved after surface treatments. The properties of the above biocomposites were also compared with E-glass–mat composite. To achieve balance in properties, a hybrid composite of industrial hemp and glass fibers was made. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1055–1068, 2006
The interfacial adhesion between wood fiber and thermoplastic matrix polymer plays an important role in determining the performance of wood-polymer composites. The objectives of this research were to elucidate the interaction between the anhydride groups of maleated polypropylene (MAPP) and hydroxyl groups of wood fiber, and to clarify the mechanisms responsible for the interfacial adhesion between wood fiber and polypropylene matrix. The modification techniques used were bulk treatment in a thermokinetic reactive processor and solution coating in xylene. FT-IR was used to identify the nature of bonds between wood fiber and MAPP. IGC and wood veneer pull-out test was used to estimate the interfacial adhesion. Mechanical properties of injection molded woodfiber-polypropylene composites were also determined and compared with the results of esterification reaction and interfacial adhesion tests. Confocal Microscopy was employed to observe the morphology at the wood fiber-polypropylene interface, and the dispersion and orientation of wood fiber in the polypropylene matrix, respectively. The effectiveness of MAPP to improve the mechanical properties (particularly the tensile strength) of the composites was attributed to the compatibilization effect which is accomplished by reducing the total wood fiber surface free energy, improving the polymer matrix impregnation, improving fiber dispersion, improving fiber orientation, and enhancing the interfacial adhesion through mechanical interlocking. There was no conclusive evidence of the effects of ester links on the mechanical properties of the composites.
Sustainability, industrial ecology, eco-efficiency, and green chemistry are guiding the development of the next generation of materials, products, and processes. Biodegradable plastics and bio-based polymer products based on annually renewable agricultural and biomass feedstock can form the basis for a portfolio of sustainable, eco-efficient products that can compete and capture markets currently dominated by products based exclusively on petroleum feedstock. Natural/Biofiber composites (Bio-Composites) are emerging as a viable alternative to glass fiber reinforced composites especially in automotive and building product applications. The combination of biofibers such as kenaf, hemp, flax, jute, henequen, pineapple leaf fiber, and sisal with polymer matrices from both nonrenewable and renewable resources to produce composite materials that are competitive with synthetic composites requires special attention, i.e., biofiber–matrix interface and novel processing. Natural fiber–reinforced polypropylene composites have attained commercial attraction in automotive industries. Natural fiber—polypropylene or natural fiber—polyester composites are not sufficiently eco-friendly because of the petroleum-based source and the nonbiodegradable nature of the polymer matrix. Using natural fibers with polymers based on renewable resources will allow many environmental issues to be solved. By embedding biofibers with renewable resource–based biopolymers such as cellulosic plastics; polylactides; starch plastics; polyhydroxyalkanoates (bacterial polyesters); and soy-based plastics, the so-called green bio-composites are continuously being developed.
Chemical treatment of natural reinforcements can enhance their adhesion to polymer matrices. This work reports the effects of different treatments on the fibre–matrix compatibility in terms of surface energy and mechanical properties of composites. The composites were compounded with two kinds of flax fibres (natural flax and flax pulp) and polypropylene. The applied treatments were maleic anhydride (MA), maleic anhydride-polypropylene copolymer (MAPP) and vinyl trimethoxy silane (VTMO). The treatment effects on the fibres have been characterised by Infrared Spectroscopy. Two techniques have been used to determine the surface energy values: the Dynamic Contact Angle method for the long flax fibres and the Capillary Rise method for the irregular pulps. The use of different methods involves a small discordance in the wettability values. Nevertheless, the three treatments reduce the polar component of the surface energy of the fibre. Composites containing MAPP-treated did the highest mechanical properties, whilst the MA and VTMO-treated fibre gave similar values to that for the untreated ones.
Although sisal fibers have been used by several authors, the Brazilian variety has not yet been thoroughly characterized. In this work the surface of sisal fibers was modified by treatment with NaOH or N-isopropyl-acrylamide solutions. Lignin content and density of fibers are reduced with the chemical treatment and the N-isopropyl-acrylamide treatment causes a significant reduction in moisture absorption. Tensile tests of NaOH (0.25, 0.5, 1, 2, 5, and 10% w/w) and N-isopropyl-acrylamide (1, 2, and 3% w/w) treated fibers were carried out and a reinforcement effect of the sisal treated with 2% solutions was observed. TGA measurements showed that with the NaOH treatment the fiber becomes more thermally resistant. SEM micrographs and crystallinity index of sisal indicated how different treatments alter the fiber surface. Pull-out tests in polyester resin were performed, evidencing that all treatments were effective in improving interfacial adhesion. The best results were obtained with the 2% N-isopropyl-acrylamide treatment. The main advantages of pull-out tests is that without considering composite processing variables, good performance sisal/polyester composites may be selected before their laborious and material-consuming preparation step.
Thesis (M.A.Sc.)--University of Toronto, 2005. Includes bibliographical references.
The adsorption of n -heptane, n -octane, n -nonane, and n -decane on untreated wood fiber and wood fiber treated with maleated polypropylene was studied by inverse gas chromatography (IGC) at infinite dilution or zero surface coverage. The specific retention volume increased with increasing probe chain length, decreased with increasing column temperature, and increased with increasing maleated polypropylene concentration. The enthalpy of adsorption increased with increasing chain length of the probe vapors. The enthalpy of adsorption remained constant after the treatment of wood fiber. The London dispersive component of the surface free energy decreased with the column temperature and showed no dependency with either the type of wood fiber or the maleated polypropylene concentration.
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