Michael A. Fuqua

Natural Fiber Reinforced Composites

In this review, insight into the use of bio-based fibers as composite reinforcement has been addressed. Specifics on the varieties of natural fibers, and the resultant properties from their constituents and hierarchal structures are described. The methods used to enhance the interface of these fibers with a variety of polymer matrices are reviewed. In addition, the influence of textile operations on creating various fiber architectures with resulting reinforcing capabilities, along with the methods in which natural fiber reinforced composites can be processed, are addressed. Finally, discussion of the correlation between structure, processing, and final composite properties are provided.

A plant fiber reinforced polymer composite prepared by a twin-screw extruder.

Polypropylene (PP) composites reinforced using a novel plant fiber, sunflower hull sanding dust (SHSD), were prepared using a twin-screw extruder. Thermal and mechanical properties of the SHSD/PP composites were characterized and compared to an organically modified clay (organo-clay)/PP composite. Differential scanning calorimetry (DSC) analysis showed that the crystallization temperature and the degree of crystallinity of PP exhibited changes with addition of SHSD and organo-clay. Mechanical properties of the PP were enhanced with the addition of SHSDs. Both the flexural strength and flexural modulus of the PP composites containing 5% (w/w) SHSD were comparable to that of the 5% (w/w) organo-clay reinforced PP. Scanning electron microscope (SEM) observation showed that no obvious agglomeration of SHSD existed in the PP matrix. Compared to the neat PP and organo-clay/PP, the SHSD/PP composites exhibited a relatively decreasing rate of thermal degradation with increase in temperature. Experimental results suggest that SHSD, as a sunflower processing byproduct, may find promising applications in composite materials.

Processing and characterization of a polypropylene biocomposite compounded with maleated and acrylated compatibilizers

Polypropylene (PP) biocomposites containing 20 wt.% sunflower hull as a particulate reinforcement were compounded and tested under tensile, flexural, and impact loadings. The incorporation of the sunflower hull without compatibilizer resulted in diminished tensile strength and impact energy absorption but increased flexural strength and both tensile modulus and flexural modulus when compared to neat PP. Formulations containing three different chemical compatibilizers were tested to determine their effectiveness in improving the interfacial adhesion between the fiber surface and PP chains. Maleic anhydride grafted with PP (MA-g-PP) achieved greater improvements in tensile strength but reduced impact strength in comparison to an acrylic-acid-grafted PP compatibilizer (AA-g-PP). The molecular weight, graft level, and the ability to affect strength, modulus, and absorbed impact energy were also investigated for the compatibilizers. A MA-g-PP having high molecular weight and low graft level was most effective in improving the investigated properties of a sunflower hull-reinforced polypropylene biocomposite.

Flax fibre quality and influence on interfacial properties of composites

Flax fibre holds the potential to serve as an alternative to glass fibre as reinforcement in composite applications. To fully achieve this, the interaction between fibre and matrix must be improved and more consistently controlled. Only then will industry accept natural fibres as a sustainable engineering material choice. Traditionally, interfacial strength improvement has been accomplished through expensive and time consuming chemical surface modification(s). To achieve improved market potential and viability, new methods of developing composite ready flax fibre must be researched and developed through an assessment of the impact of fibre traits for unmodified fibre. Metal, fungal, bacterial, wax and glucose content were examined in this study to determine their correlative effects upon interfacial adhesion, as were fibre characteristics such as colour, density, fineness, fibreshape thickness, conductivity and pH levels. Composite performance was evaluated using fibre pullout and interfacial shear strength tests. These first attempts at correlating as-received flax fibre traits and resulting flax fibre composite properties contain the initial steps towards identifying key flax fibre characteristics that influence composite performance so that proper growth and fibre processing approaches can be developed.

Semicrystalline Polyamide Engineering Thermoplastics Based on the Renewable Monomer, 1,9-Nonane Diamine: Thermal Properties and Water Absorption

A series of poly(1,9-nonamethylene adipamide-co-1,9-nonamethylene terephthalamide) copolymers were produced using melt polymerization and the thermal properties, crystal structure, and moisture uptake characterized. The results confirmed that the copolymers exhibit isomorphism. As expected, glass transition temperature and the apparent melting temperature increased with increasing terephthalmide content. Using the difference in the apparent melting temperature to the crystallization temperature as a measure of relative crystallization rate, it was observed that crystallization rate decreased as the terephthalamide content of the copolymer was increased from 0 to 50 mole % but then sharply increased when increased beyond 50 mole %. This behavior may be the result of extensive inter- and intramolecular interactions in the melt associated with terephthalmide units in the polymer chain that nucleate crystallization upon cooling below the equilibrium melting temperature. Comparing the thermal properties of copolymers possessing an excess of terephthalmide units to the commodity polyamide Nylon 6,6, it is believed that these copolymers may have utility as partially renewable engineering thermoplastics.

Utilization of Agricultural By-products as Fillers and Reinforcements in ABS

Lignocellulosic agricultural by-products can be utilized for an array of biocomposite material applications. Biocomposite properties can approach those of synthetic conventional composites. They are highly suitable for automotive applications, where the thrust is toward fuel economy, weight-reduction, and higher renewability. A common automotive polymer for biocomposite application is alloyed acrylonitrile butadiene styrene (ABS), whose extensive usage can be attributed to its exceptional balance of properties. However, the low sustainability of ABS in environmental degradation entails the addition of fillers. In this study, the UV blocking properties of lignin component of natural fibers will be analyzed for their use as additives in a natural ABS grade and will be compared to an ABS grade compounded with a traditional UV inhibitor.

Development of flax fiber/soy-based polyurethane composites for mass transit flooring application

In this study, soy-based polyurethane foam was reinforced with random oriented flax fiber to create green composite paneling. This paneling can be used as replacement for plywood in mass transit flooring. To establish optimal material properties, the flax/foam composites density was modified through manipulation of both fiber volume fraction and foam void content in order to determine processing modification upon mechanical performance. Both static flexural testing and dynamic low velocity impact was performed. Mechanical characterization was performed by both flexural testing and screw fastener pullout studies. Resultant properties demonstrate the feasibility of lower maintenance renewable composite materials as replacement for current transit flooring.

Influence of Plasticizers on Properties of Polymers Made from Canola Protein Polyester Blends

Canola meal protein isolate blended with polyesters were used to prepare injection-molded plastic specimens. The plasticization effect of four types of plasticizers (glycerol, sorbitol, polyethylene glycol, and polyvinyl alcohol) was investigated. Properties of canola based plastics such as tensile strength, flexural strength, modulus, and water absorption, were studied. Morphology of the fractured surfaces of tensile specimens was examined using scanning electron microscopy. Plasticized specimens showed a ductile type of fracture where as the specimens produced without plasticizers showed a brittle failure. The use of glycerol as a plasticizer resulted in the highest values for tensile strength, elongation, and toughness. Water absorption of plasticized specimens were generally lower than that of unplasticized specimens. The highest flexural strength and modulus were obtained using PVA as a plasticizer.

Preparation and Characterization of Polypropylene Composites Reinforced with Modified Lignocellulosic Corn Fiber

As technology develops towards the utilization of agricultural byproducts, lignocellulosic fibers have shown strong potential as reinforcement in polymer matrix composites. In this study, polypropylene was reinforced with corn chaff and distillers dried grains (DDGS), byproducts of the ethanol process, for evaluation of composite properties. The corn fibers investigated underwent various treatments to advance reinforcement properties and surface interaction with the polymer chains. Fibers were modified using both chemical treatments and mechanical fractionation to break down the micro-sized lignocellulosic fibers into smaller, predominantly cellulose based crystallite fibers. Organo-silane and maleic anhydride grafted polypropylene were utilized to improve the surface adhesion between the fibers and matrix polymer. Fibers were melt blended together using a twin-screw extruder, and then molded into test specimens. Mechanical testing was performed to qualify both the reinforcement properties of the modified corn fibers and their bonding characteristics with the polypropylene matrix. Analysis of the data reveals discrepancies in properties between the lignocellulosic fibers, as well as the importance of modifiers for proper matrix compatibility.