Natural fibers are gaining popularity as reinforcement materials for thermoset resins over the last two decades. Natural fibers are inexpensive, abundant, renewable and environmentally friendly. Kenaf fibers are one of the natural fibers that can potentially be used for reinforcing unsaturated polyester (UPE). As a polymer matrix, UPE enjoys a 40% market share of all the thermoset composites. This widespread application is due to many favorable characteristics including low cost, ease of cure at room temperature, ease of molding, a good balance of mechanical, electrical and chemical properties. One of the barriers for the full utilization of the kenaf fiber reinforced UPE composites, however, is the poor interfacial adhesion between the natural fibers and the UPE resins. The good interfacial adhesion between kenaf fibers and UPE matrix is essential for generating the desired properties of kenaf-UPE composites for most of the end applications. Use of a coupling agent is one of the most effective ways of improving the interfacial adhesion. In this study, six novel effective coupling agents were developed and investigated for kenaf-UPE composites: DIH-HEA, MFA, NMA, AESO-DIH, AESO-MDI, and AESO-PMDI. All the coupling agents were able to improve the interfacial adhesion between kanaf and UPE resins. The coupling agents were found to significantly enhance the flexural properties and water resistance of the kenaf-UPE composites. Fourier transform infrared spectroscopy (FTIR) confirmed all the coupling agents were covalently bonded onto kenaf fibers. Scanning electron microscopy (SEM) images of the composites revealed the improved interfacial adhesion between kanaf fibers and UPE resins. / Graduation date: 2013

Kenaf (Hibiscus cannabinus L.) was introduced in 2005 as a fibre crop on a commercial scale in the KwaZulu-Natal Province of South Africa. No herbicides have yet been registered for use in this crop. The purpose of this study was to determine the tolerance of kenaf to a total of five pre-emergence and four post-emergence herbicides under semi- and fully controlled conditions. The herbicides were chosen based on their potential safety for use in Hibiscus spp. as well as on the weed spectra they are registered for in other crops. Several additional factors were also taken into consideration, such as: temperature, soil depth and timing of herbicide application. Four pot trials were conducted to determine the separate and combined effects of herbicide, temperature, planting depth and application timing. During the first trial the effects of five pre-emergence herbicides and four post-emergence herbicides were researched. The pre-emergence herbicides were: S-dimethenamid, imazethapyr, fluometuron/prometryn, pendimethalin, S- metolachlor and the post-emergence herbicides were: bentazone, 2,4-DB, monosodium methanearsonate and pyrithiobac sodium. The trials were conducted under either semi-controlled conditions in a glasshouse or in growth cabinets under fully controlled conditions at the Hatfield Experimental Farm of the University of Pretoria. All experiments were conducted with a Hutton soil with 22% clay. Each trial lasted about 40 days to allow for maximum phytotoxicity damage manifestation on the kenaf seedlings. Measurements that were taken included plant height, herbicide damage, weed control efficiency, fresh plant weight, dried plant weight, and dried root weight. The data were subjected to analysis of variance (ANOVA) to determine the statistical likelihood of damage to plants from the herbicides. In Trial 2, 3 and 4 the interaction effects of herbicide and plant depth, herbicide and temperature, and herbicide and application timing were researched respectively. Neither planting depth nor application timing affected the kenaf seedlings negatively, but low temperature in combination with the application of herbicides during germination of seed and seedling emergence had serious deleterious effects on the young kenaf seedlings. Based on the findings the majority of the herbicides can be included in further field trials on Hibiscus cannabinus L. with the exception of S-dimethenamid and fluometuron/prometryn which caused substantial injury to the kenaf seedlings. Copyright / Dissertation (MInstAgrar)--University of Pretoria, 2011. / Plant Production and Soil Science / unrestricted

Kenaf fiber is increasingly getting the attention of the industries due to its excellent mechanical properties, feasibility, growth rate, and ease of cultivation. On the other hand, cellulose nanofibril is one of the important building blocks of all the bast fibers which significantly contributes to their mechanical properties. However, most of the studies in the literature have estimated the value of axial elastic modulus for fiber-bundles which has some unavoidable issues resulting in incorrect modulus. Moreover, the transverse elastic modulus is another important parameter that also needs to be studied. Hence, to compensate for the gap in the literature, a single unit of both kenaf microfiber and cellulose nanofibril have been subjected to nanomechanical characterization to analyze their surface morphology and determine their elastic modulus in the axial and transverse direction. The experiments also pave to a protocol to characterize micro and nanofibrils nanomechanically and determine their elastic moduli.

Natural fibers have the potential to replace glass fibers in fiber-reinforced composite applications. However, the natural fibers’ intrinsic properties cause these issues: 1) the mechanical property variation; 2) moisture uptake by natural fibers and their composites; 3) lack of sound, cost-effective, environmentriendly fiber-matrix compounding processes; 4) incompatibility between natural fibers and polymer matrices; and 5) low heat-resistance of natural fibers and their composites. This dissertation systematically studied the use of kenaf bast fiber bundles, obtained via a mechanical retting method, as a light-weight reinforcement material for fiber-reinforced thermoset polymer composites for automotive applications. Kenaf bast fiber bundle tensile properties were tested, and the effects of locations in the kenaf plant, loading rates, retting methods, and high temperature treatments and their durations on kenaf bast fiber bundle tensile properties were evaluated. A process has been developed for fabricating high fiber loading kenaf bast fiber bundle-reinforced unsaturated polyester composites. The generated composites possessed high elastic moduli and their tensile strengths were close to specification requirements for glass fiber-reinforced sheet molding compounds. Effects of fiber loadings and lengths on resultant composite’s tensile properties were evaluated. Fiber loadings were very important for composite tensile modulus. Both fiber loadings and fiber lengths were important for composite tensile strengths. The distributions of composite tensile, flexural and impact strengths were analyzed. The 2-parameter Weibull model was found to be the most appropriate for describing the composite strength distributions and provided the most conservative design values. Kenaf-reinforced unsaturated polyester composites were also proved to be more cost-effective than glass fiber-reinforced SMCs at high fiber loadings. Kenaf bast fiber bundle-reinforced composite’s water absorption properties were tested. Surface-coating and edge-sealing significantly reduced composite water resistance properties. Encapsulation was a practical method to improve composite water resistance properties. The molding pressure and styrene concentrations on composite and matrix properties were evaluated. Laser and plasma treatment improved fiber-to-matrix adhesion.

The objective of this research was to investigate the hydrophilic and mechanical properties of kenaf fiber treated with vinyl tris(2-ethoxymethoxy) silane (VTEMS) and the resulting fiber/resin composite. The hypothesis was that silane-modified kenaf fibers, when used to make Sheet Molding Compounds (SMCs), would improve the water resistance and mechanical properties compared to unmodified kenaf fibers, and these potentially improved SMCs may be a useful material for the automotive and other industries. Fourier transform infrared (FTIR) spectroscopy was used to analyze the modified fibers and the resulting SMCs, and some silica-lignocellulosic bonding was observed. The water absorption of composites decreased as the loading of the silane reagent increased. The MOR and MOE mechanical properties of the SMCs also initially improved as the silane reagent levels increased from 0 (untreated) to 10% silane, but at levels above 10% VTEMS no further enhancement in the mechanical properties was obtained.

In this study, composite system was developed to enhance mechanical properties of plastic pallets. The potential of graphite nanoplatelets (GnP)/PP composites for the application in packaging was scrutinized by examining mechanical properties, thermal properties, flow properties, and morphology as a function of GnP loading and by comparison of two mixing methods: physical melt compounding (PMC) and chemical pretreatment compounding (CPC) processes. Incorporation of the GnP into PP resulted in a significant enhancement in the mechanical strength (tensile, impact, and flexural strength) and thermal decomposition temperature compared to the neat PP specimen. The CPC process clearly shows good exfoliation and better distribution on the PP matrix compared to the PMC method based on morphological evaluation measured by SEM. The impact test at low temperature revealed that the composites made by the CPC process showed 64% higher impact strength than neat PP due to higher even-distribution of GnP molecules into the PP matrix. We attempted to discover the degree of dispersion of natural fiber (kenaf) and graphite nanoplatelets (GnP) into the polypropylene (PP) polymer matrix and the effect of filler-adding sequence on physical and mechanical properties. Tensile strength of the composites was increased up to 25%. In the case of Young's modulus, composites showed a 56% enhancement compared to the control. However, the impact strength decreased as a result of the increased brittleness when kenaf fiber was added. Another study investigated the effects of hybrid filler systems (graphite nanoplatelets (GnP)/commercially available modified calcium carbonate (mCaCO3) nanoparticles) on mechanical and physical properties of polypropylene nanocomposites with three variables, filler loading amount, the number of compounding processes, and the compounding order of two different fillers. The impact strength of composite samples, containing 1wt% of GnP and mCaCO3 nanoparticles, increased up to 64% compared to neat PP. Among all tested samples, the highest tensile strength was found at 1wt% of mCaCO3 nanoparticles regardless of the presence or absence of GnP addition. There was no significant difference in flexural strength regardless of any nano-filler addition. However, both the flexural modulus and Young's modulus increased significantly when 10wt% of mCaCO3 nanoparticles were added. The number of compounding processes did not affect any strength, and the single compounding process was found to be more effective than the double compounding process. It may be contributed by thermal degradation of polymeric structure by double heat processing. This study can be able to provide a solution for value-added high-end products in various industries such as application in logistics, aerospace or electric automobile, where carbon-based nanomaterials are more affordable. / Doctor of Philosophy / Pallets are the basic structure of a unit load which allows handling and storage efficiency. The advantages of plastic pallets are durability, cleanliness, and performance reliability, However, those are expensive and have lower mechanical properties than that of wood, such as low strength, creeps and deformation. Therefore, hybrid composites were fabricated using various fillers, such as graphite nanoplatelets, kenaf fiber or calcium carbonate on polypropylene matrix to enhance mechanical properties for plastic pallets. In order to fabricate the composites, two methods were utilized and compared: physical melt compounding (PMC) and chemical pretreatment compounding (CPC) processes. Graphite nanoplatelets (GnP) reinforced polypropylene (PP) composites made by both PMC and CPC process showed significance in the mechanical process compared to the neat PP. Moreover, the CPC process showed better dispersion on the PP matrix resulting in higher impact strength in low temperature. Based on the first chapter, we attempted to focus on reducing weight and sustainability using natural fiber. At the same time, when two or more fillers are reinforced in a polymer matrix, I wondered if the order in which the fillers were added could affect properties. Kenaf fiber and GnP were reinforced in the PP matrix through the CPC process to discover the degree of dispersion of fillers and the effect of filler-adding sequence on physical and mechanical properties. Tensile strength of the composites was increased up to 25%. In the case of Young's modulus, composites showed a 56% enhancement compared to the control. However, the impact strength decreased as a result of the increased brittleness when kenaf fiber was added. Another study investigated the effects of hybrid filler systems (GnP/commercially available modified calcium carbonate (mCaCO3) nanoparticles) on mechanical and physical properties of polypropylene nanocomposites with three variables, filler loading amount, the number of compounding processes, and the compounding order of two different fillers. This study was concentrating on the impact strength based on the result that the material adding sequence affects the mechanical strength when manufacturing the hybrid composites. The hybrid composite system on GnP/mCaCO3/PP resulted in enhancement of impact strength, tensile strength, flexural modulus and Young's modulus. The number of compounding processes did not affect any strength, and the single compounding process was found to be more effective than the double compounding process. Enhancement of impact strength in low temperature, and effect of filler-adding sequence on mechanical properties in hybrid composite system can be able to provide a solution for value-added high-end products in various industries such as application in logistics, aerospace or electric automobiles, where carbon-based nanomaterials are more affordable.

The electromagnetic shielding effectiveness of kenaf bast fiber based composites with different iron oxide impregnation levels was investigated. The kenaf fibers were retted to remove the lignin and extractives from the pores in fibers, and then magnetized. Using the unsaturated polyester and the magnetized fibers, kenaf fiber based composites were manufactured by compression molding process. The transmission energies of the composites were characterized when the composite samples were exposed under the irradiation of electromagnetic (EM) wave with a changing frequency from 9 GHz to 11 GHz. Using the scanning electron microscope (SEM), the iron oxide nanoparticles were observed on the surfaces and inside the micropore structures of single fibers. The SEM images revealed that the composite’s EM shielding effectiveness was increased due to the adhesion of the iron oxide crystals to the kenaf fiber surfaces. As the Fe content increased from 0% to 6.8%, 15.9% and 18.0%, the total surface free energy of kenaf fibers with magnetizing treat increased from 44.77 mJ/m2 to 46.07 mJ/m2, 48.78 mJ/m2 and 53.02 mJ/m2, respectively, while the modulus of elasticity (MOE) reduced from 2,875 MPa to 2,729 MPa, 2,487 MPa and 2,007 MPa, respectively. Meanwhile, the shielding effectiveness was increased from 30-50% to 60-70%, 65-75% and 70-80%, respectively.

This study evaluated physical and biological treatments of bio-oil process water to decrease organic contaminants. A three-sequential-column filtration system compared four treatments: three columns filled with kenaf only; three columns filled with wood shavings only; first column filled with wood shavings and two with kenaf; and first column filled with kenaf and two with wood shavings. The kenaf and wood shavings were composted after filtration. The filtrate water underwent further bio-treatment by adding aeration and selected bacteria. After filtration and bio-treatment, oil and grease concentrations were reduced over 80 percent and toxicity reduced over 90 percent. There were no significant differences among filtration treatments. Most of the oil and grease was removed by the first column. Aeration significantly decreased the concentration of oil and grease and toxicity in the filtrate water. Composting of the bioiltration matrices significantly reduced the oil and grease concentrations at day 45 by 80 percent.

In this research, the adsorptive capacities of kenaf in the forms of chopped whole stalk, chopped core, and bast materials were evaluated for the removal of lead, zinc, and toluene from contaminated synthetic waste streams using traditional adsorption isotherm techniques. The effect of surface oxidation using ozone was observed with respect to the adsorption of metals. Hydraulic conductivity experiments were conducted to evaluate the head loss associated with packing a column with kenaf fibers and to determine the suitability of its use in dynamic packed column systems. B.E.T. surface areas were determined as well. Under increasingly stringent regulatory requirements, even low level organic and inorganic contamination (under 100 ppm) in surface and ground waters must be treated. This study is part of an ongoing multi-year research effort aiming to develop a kenaf-based biosorptive process to improve treatment of contaminated aqueous streams at reduced costs and technical complexity.

A dissertation submitted to the Faculty of Engineering and the built environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering Johannesburg, October 2017 / An investigation was carried out to determine the effect of the addition of clay on the mechanical properties of a Natural Fibre Composite consisting of a polypropylene matrix with kenaf fibre reinforcement. The kenaf fibres were treated using various chemical treatments to improve the strength of the composites manufactured. Four treatments using different 3-mercaptopropyltrimethoxy silane (MPS) concentrations were investigated to determine which treatment resulted in the best mechanical properties. [Abbreviated Abstract. Open document to view full version] / MT 2018