1,720,986 research outputs found
ADVANCED ‘GREEN’ COMPOSITES BASED ON AGRICUTURAL BY-PRODUCTS
No full text97 pagesConcerns regarding environmental deterioration as well as issues regarding the sustainability of fast depleting petroleum resources used to make conventional plastics have forced the scientific community to focus on developing and manufacturing new and novel ‘green’ materials that are fully biodegradable and derived from renewable, plant-based resources. In the present study a non-edible starch, extracted from avocado (Persea americana) seed starch (AVS), a waste product of avocado processing, was developed for fabricating ‘green’ composites. AVS was crosslinked using a green crosslinker, 1,2,3,4-butane tetracarboxylic acid (BTCA), and a catalyst, sodium hypophosphite (SHP), to prepare a rigid thermoset resin with improved water resistance. Two cellulose based reinforcements, micro-fibrillated cellulose (MFC) with average diameter of 50 nm and velvet leaf (a common weed) stem derived microfibers (VLF) with average diameters of 12 μm were used to fabricate green composites. Properties of these green composites were fully characterized and compared with different compositions. In addition, advanced ‘green’ composites with excellent mechanical properties were fabricated by combining liquid crystalline cellulose (LCC) fibers with MFC blended AVS (MFC/AVS) resin. LCC fibers were modified using a combination of alkali and heat treatments to further improve their tensile strength from 1.5 GPa to over 1.9 GPa. The advanced green composites prepared by simple hand layup showed average tensile strength of 380 MPa and Young’s modulus of 25 GPa with only 40% of LCC fibers by volume. This study clearly demonstrates the potential of AVS based green composites for industrial applications such as automotive, packaging, construction and others
Green hydrophobic treatment for cotton fabrics
Full text linkGreener approaches for hydrophobic treatment of cotton fabric were studied. In the first method, fatty acid was grafted onto cotton (cellulose) fiber surface to decrease the surface energy. Acetic anhydride was used to facilitate the reactivity. Microwave heating, an energy efficient method, was used to reach the reaction temperature. The ‘green’ method developed here resulted in hydrophobic cotton fabric with a water contact angle of 137.48o (±2.79). In addition, it was shown that the hydrophobicity lasted for 37 cycles of laboratory laundry washes. A second method involved using of amine-silica nanoparticles to increase the surface roughness of cotton fabric. The effects of attaching single or dual size nanoparticles as well as chemical and physical attachment of particles onto cotton fiber surface were studied. Cotton fabric with deposited particles was further crosslinked to obtain possible ‘permanent’ surface topography. Different crosslinkers were used to test wash durability of final products. Resulting cotton fabrics were treated by fatty acid hydrophobic treatment, water contact angle as high as 153.41o (±2.33) was achieved. These fabrics with water contact angles of greater than 150 o can be considered as superhydrophobic. Resulting crosslinked and hydrophobic cotton fabric allowed 24 cycles of laboratory laundering without the loss of hydrophobicity
SELF-HEALING THERMOSET GREEN RESINS
No full text105 pagesThe goals of this research were to prepare different types of microcapsules containing green healant and evaluate the self-healing efficiencies and mechanical behaviors of green resins containing different loadings of these microcapsules. Soy protein isolate (SPI) exhibits high water solubility and great potential for crosslinking to improve the properties. Further, it is a fully sustainable plant-based protein that is commercially available in all parts of the world. Therefore, SPI was chosen as the resin as well as the healing agent in the present research. Glutaraldehyde (GA) was chosen as the SPI crosslinker in this research due to its easy availability and fast reactivity with SPI. Microcapsules were prepared using the evaporation technique. Poly(DL-lactide-co-glycolide) (PLGA) was used as the shell material to encapsulate the SPI healant. Two microcapsule-preparation techniques were developed and are discussed in this thesis. To produce uniform-sized microcapsules, a membrane emulsification technique2 was used. Instead of using Shirasu Porous Glass (SPG) membrane, which is frequently used in the preparation of monodispersed particles and microcapsules, syringe filters were used to reduce the production costs. Results showed that the diameters of the spherical microcapsules produced with the aid of the syringe filter ranged between 0.5 μm and 2 μm with an average diameter of 1.30 μm. In addition to spherical microcapsules with a narrow size distribution, elongated microcapsules with aspect-ratios greater than one were observed using the syringe filter emulsification technique. Microcapsules with various geometrical shapes including spherical, rod-like, dog-bone and elliptical, were prepared. It was found that the aspect-ratio of elongated microcapsules observed reached as high as 20. Even though polyvinyl alcohol (PVA) was introduced onto the surfaces of microcapsules to enhance their bonding with the resins, the results showed that the interfacial adhesion was still not strong enough as many unbroken microcapsules were observed at the fracture surfaces. This raised the possibility that cracks would go around the microcapsules instead of fracturing the microcapsules, adversely affecting the self-healing efficiency. To further improve the microcapsule/resin adhesion, a second microcapsule-production technique was developed by incorporating ground bacterial cellulose (GBC) into microcapsules. Due to its exceptional mechanical properties and morphology, GBC was used as a reinforcing agent as well as a surface modifier in this research. A spraying technique was used in the course of preparing microcapsules with GBC. A porous structure was constructed as a result of applying this technique. Another geometry made from the spraying technique was the elongated microcapsules with aspect-ratio as high as 50. The benefit of incorporating GBC in the microcapsules is to increase the surface roughness and to improve the self-healing efficiency by bridging the fracture surfaces. As the results have shown, microcapsules coated with GBC adhered to the resin tightly so that both tensile strength and fracture toughness were enhanced due to the presence of GBC. The structural resins embedded with the four kinds of microcapsules mentioned above demonstrate healing behaviors and displayed the highest self-healing efficiency (strength recovery) of about 47% compared to 14% for the control group (virgin resin) and 63% toughness recovery compared to 24% of the control group. With the help of self-healing properties, the application of green resins and composites can be expanded. This can help reduce petrochemical products and wastes generated at the end of their life and promote sustainability in modern society
Lcc Fiber Reinforced ‘Green’ Composites Derived From Raw Plantain Starch
No full textSignificant research is being conducted to derive environment-friendly, sustainable and fully biodegradable polymers and composites. These help avoid the environmental pollution created by the conventional non-degradable plastics that end up in landfills. Starch is a yearly renewable plant-based resource that is most abundantly available around the world. Increasing number of scientists have modified starches from potato, corn, rice, etc., to create resins that can replace the more common petroleum based ones. Understanding the gravity of the situation, the major objectives of this research are as follows: 1. To develop a fully 'green' resin using raw plantain starch and banana microfibrils with the help of minimal and green/ food grade chemicals. 2. To study the effects of chemical and mechanical treatments on morphology, orientation, crystallinity and ultimately tensile strength of the inherently strong liquid crystalline cellulose fibers. 3. To devise an easy to scale up method for fabricating advanced 'green' fiber reinforced composites as a contribution to the greener world. On these lines, starch was isolated from raw plantain pulp using alkaline and non-alkaline methods. A comparative study of the processes used and resulting starch contents was carried out. Starch content of above 80% was successfully isolated from the plantain fruit by alkaline steeping method using Sodium bisulfite (NaHSO3), a food grade chemical. The physical and mechanical properties of the obtained starch were characterized and compared with the conventional starches. An environment-friendly cross linker 1,2,3,4-butane tetracarboxylic acid (BTCA) along with a catalyst, Sodium hypophosphite-monohydrate (SHP), was used to crosslink the plantain starch into a thermoset resin. Further, banana stem fibers were harnessed to extract cellulosic microfibrils and used as the reinforcing element to enhance the modulus (stiffness) of the resin and make it truly 'green'. Liquid Crystalline Cellulose fibers were used as fillers to make a fiber reinforced composite using RP starch based resin. These fibers were characterized for their tensile properties, diameter and crystallinity in order obtain control data and device methods to improve them further. The fibers were subjected to physical (tension) and chemical treatments to enhance their mechanical properties and make them high strength. Various parameters like treatment chemical, load value, duration were varied to carry out a deep study of their effect on the mechanical properties of LCC fibers. A gradual increase in the percentage crystallinity and mechanical properties was seen on optimizing each parameter. A dramatic increase compared to the control fibers was obtained in the tensile modulus and strength on testing the Sodium bisulfite treated fibers under tension at optimum parameters. In summary, a convenient and easy to scale up process was developed to obtain a fiber reinforced composite from plantain-based resin using its pulp, banana stem fibers and LCC yarns. The mechanical and physical properties of this starch suggest that it can be used in place of conventional starch based resins. In addition, the developed process allows using large quantities of raw cull plantains and potentially eliminating the waste problem created by excess production as well as damage caused during their harvest and transportation
Surface Modification Of Microporous Polypropylene Membrane By Uv-Initiated Grafting With Poly(Ethylene Glycol) Diacrylate
Full text linkIn this study, poly(ethylene glycol) diacrylate (PEGDA) was surface grafted, through UV-initiated grafting, on to a microporous polypropylene (PP) membrane in order to develop and control a moisture-sensitive porous structure. Based on the concentration of the PEGDA grafting solution, as well as other variables, the pores of the membrane were filled to varying degrees with cross-linked PEGDA hydrogel, decreasing the pore sizes. This decrease in pore size was highly dependent on the grafting degree, or weight add-on of the grafted polymer. The grafting degree can be controlled by altering various grafting conditions. The surface grafted PEGDA is expected to swell significantly when exposed to moisture, through change in relative humidity or a liquid-borne pathogen, causing the pore sizes to decrease even further. This provides a microporous polypropylene membrane with improved hydrophilicity and moisture-responsive pores. The membranes will have varying levels of breathability based on the amount of moisture exposure. This will allow for a functional membrane that limits the transport of liquid-borne pathogens while providing transport of moisture vapor away from the body
FULLY GREEN STARCH-BASED THERMOCHROMIC COMPOSITES
No full text106 pagesGreen thermochromic (TC) materials are an emerging field of research. Recently, researchers have sought to develop “greener” alternatives by replacing one or more petroleum-based plastic and toxic chemical components of intrinsic or doped thermochromic materials. In this study, a fully green thermochromic system was developed using coaxial electrospinning to form a nontoxic, binary thermochromic dye-based core and poly (lactic acid) (PLA) sheath composite fibers. These fibers were integrated into a crosslinked waxy maize starch resin to form composite films. Chlorophenol red (CPR), a sulfonephthalein dye, was used to form an aqueous binary dye which was integrated, as core, into PLA fibers for the purpose of shielding the dye from other competing chromic interactions and pre-mature environmental degradation. These thermochromic fibers exhibited a reversible color shift in which the fibers transitioned from a deep red color to a bright yellow color between -5°C and 0°C, respectively. The colorimetric properties of the CPR dye and the fiber were characterized using a colorimetry. The color differences, ∆E, of the TC transition of the CPR dye and the electrospun TC fiber membrane were determined to be 9.68 and 2.17, respectively, with the shielding of PLA attributed to the smaller color difference exhibited in the fiber. The presence of the CPR dye inside the fiber was confirmed using confocal microscopy. The nonporous, wrinkled morphology of the TC fibers was analyzed using SEM and Cryo-FIB SEM. The wide distribution of fiber diameters, a characteristic of electrospinning, in the TC fiber membrane led to a variance in the chemical composition of the fiber which was analyzed using UV-Vis and ATR-FTIR analyses. The thermal properties of the TC fiber membrane and composite were investigated using DSC and TGA. The tensile properties of the composite were investigated. The Young’s Modulus was found to be higher in the composite at 8.01 MPa, while the ultimate tensile stress, elongation, and toughness were higher in the starch resin at 7.11 MPa, 501%, and 2188 kJ/m3, respectively. Future applications for this technology exist in SMART frozen food packaging due to its transition temperature of around 0°C. There are opportunities to adjust the transition temperature and expand this technology to other applications such as biocompatible systems, temperature monitoring systems for infants, and other potentially-ingestible plastics in novelty items
HYBRID GREEN COMPOSITES UTILIZING RENEWABLE LIGNOCELLULOSIC FIBERS TO REINFORCE SOY-BASED RESINS
No full text135 pagesPlant-based green composites have recently emerged as sustainable alternatives to petroleum-based polymer matrix composites (PMC) in applications such as transportation and packaging.PMC techniques were employed to produce commercial-scale green composites made using one of the most wasted plant fibers, i.e., rice straw (RS). Thermoset resin sheets were prepared by denaturing soy protein isolate (SPI) and crosslinking it with glutaraldehyde. SPI resin was reinforced by hybrid RS/jute fabric (JFa) mats, to fabricate layered composites with high fiber content (up to 60%). Needle felting was used to interlace RS and JFa together and fabricate hybrid green PMC composites. The hybrid composites were characterized for their moisture absorption, tensile properties, flexural properties, interfacial shear strength (IFSS), dynamic mechanical properties, fracture surface analyses, and thermal stability. The obtained results reflect the geometric complexity of these systems, their hygroscopic nature, and enable further utilization of fiber waste in low-mechanical resistant composites. Mechanical properties of all composites were affected by moisture absorption, except their ductility. Triple-layered composites with the lowest fiber content (40%) resulted in enhanced Young’s modulus (Ey) and ultimate tensile strength (UTS), from 0.3 to 0.9 GPa and from 7.2 to 10.6 MPa, respectively, compared to pure resin. However, contrary to the logic, an inverse relationship was found between fiber content and each of the following: Ey and UTS; flexural modulus and ultimate flexural stress; and storage modulus. IFSS results as well as fracture analyses attributed this inverse relationship to the relatively weak fiber/resin interface, and to the deduction that fiber content has exceeded the resin’s capacity of fully wetting the fibers. Moisture absorption in addition to the weak interfacial strengths were the primary reasons to lowering the mechanical resistance of the hybrid green composites. These hybrid composites can be used in many applications, from furniture to housing and from transportation to packaging
Reactivity And Continued Activity Of Immobilized Zinc Oxide Nanoparticles On Methyl Parathion Decontamination
Full text linkSilk Synthesis: Fibroin-Based Digital Fabrication of Screen Wall Systems
No full text45 pagesSilk is a natural fiber produced by the silkworm and other insect species. Humans have cultivated and used silk for thousands of years, primarily in the textile industry. However, over the last decade several novel applications of silk have been discovered, with the potential to revolutionize different technologies such as electronics, printing, optics, sensors, and biomedicine. Currently these applications operate only at the micro-scale with only a few examples exploring the possibilities of expanding the material in a larger context. This thesis aims to build upon the latest innovative works that have been produced with silk as a biomaterial. The focus of this research is concentrated on the potential architectural applications that silk can offer as a biomaterial. Through a digital bio-fabrication process, a silk-chitosan solution is deposited over custom 3D printed frames to create hybridized bio-composite panels. The panels developed are used to inform the design and development of a parametric screen wall system
FABRICATION AND CHARACTERIZATION OF ‘GREEN’ RESINS AND ‘GREEN’ HYBRID COMPOSITES USING CHICKEN FEATHER FIBERS, SOY PROTEIN ISOLATE, AND JUTE FABRIC
No full text185 pagesDwindling petroleum sources and rising levels of non-biodegradable plastic pollution have led researchers to develop sustainable and environmentally friendly alternatives to replace the petroleum-based plastics and composites that are so ubiquitously used today. In this work, chicken feather fibers (CFF), soy protein isolate (SPI), and jute fabric (JF) were used to produce fully green CFF/SPI resins and fully green JF/(CFF/SPI) hybrid composites. The necessity of an external crosslinking reagent was explored through the comparison of glutaraldehyde (GA) crosslinked CFF/SPI resins and JF/(CFF/SPI) composites with their GA-free counterparts. The results suggested that for most properties, GA-free CFF/SPI resins and JF/(CFF/SPI) composites were superior. In the few instances that GA improved properties, the difference was not significant and was further minimized with the addition of CFF. In addition, this work resulted in neat (GA- and CFF-free) SPI resins that differed visually (in color), mechanically, thermally, and spectrally than previous iterations of neat SPI resins. The results suggested that this difference could potentially be due to semi-crystallinity and/or internal crosslinks, possibly derived from the alternative resin preparation
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