1,720,990 research outputs found
Properties of Injection Molded Composites Containing Corn Fiber and Poly(Vinyl Alcohol)
No full textComposites based on natural polymers alone are extremely sensitive to moisture and their mechanical properties deteriorate upon the absorption of water, limiting their usefulness in practical applications. Ongoing research cooperation between USDA and the University of Pisa, Italy, has yielded several composites based on poly(vinyl alcohol) (PVA) and corn fibers (CF). In this study, variable amounts of CF and PVA were processed in the presence of both dry and liquid plasticizers, glycerol and pentaerythritol. Cornstarch was introduced in the formulation to reduce the cost and to further increase the composition of natural components in the composites. Composites made with as low as 30% PVA were injection molded into tensile bars and evaluated. The addition of starch moderately reduced the tensile properties of the composites, lowering the elongation (∼600% to 400%) and increasing Young's modulus (∼36 MPa to ∼100 MPa) while the ultimate tensile strength remained constant at about 8 MPa. Composites prepared from CF and PVA showed little change in their mechanical properties even after conditioning them at various relative humidities, or after soaking in water. Composites tested after storage for one year, at 50% relative humidity and 23°C, exhibited mechanical properties similar to those of freshly prepared composites
Characteristics and Degradation of Hybrid Composite Films Prepared from PVA, Starch and Lignocellulosics
No full textA research cooperation between USDA and the University of Pisa led to the development of several composite blends of poly(vinyl alcohol) (PVA) and lignocellulosic fibers. The cast films were prepared by blending orange fibers (OR-fibers) and PVA with and without cornstarch to yield flexible and cohesive films. To improve properties, films were also prepared by crosslinking PVA, starch and OR-fibers with hexamethoxymethylmelamine (HMMM). Films were evaluated for their thermal stability, water permeability and biodegradation. Thermal gravimetric analyses indicated the potential usefulness of such blends in several thermoplastic applications. Films were permeable to water, and retained the moisture content in the soil while retaining their integrity. Films generally biodegraded within 30 days in compost, achieving between 50-80% mineralization. Both neat PVA and blends that had been crosslinked showed comparatively slow degradation. A possible stimulating effect of lingocellulosic fillers on the biodegradation of PVA in blends has been observed
Characterization of biodegradable composite films prepared from blends of poly(vinyl alcohol) cornstarch, and lignocellulosic fiber
No full textSeveral composite blends of poly(vinyl alcohol) (PVA) and lignocellulosic fibers were prepared and characterized. Cohesive and flexible cast films were obtained by blending lignocellulosic fibers derived from orange waste and PVA with or without cornstarch. Films were evaluated for their thermal stability, water permeability and biodegradation properties. Thermogravimetric analysis (TGA) indicated the suitability of formulations for melt processing, and for application as mulch films in fields at much higher temperatures. Composite films were permeable to water, but at the same time able to maintain consistency and composition upon drying. Chemical crosslinking of starch, fiber and PVA, all hydroxyl functionalized polymers, by hexamethoxymethylmelamine (HMMM) improved water resistance in films. Films generally biodegraded within 30 days in soil, achieving between 50-80% mineralization. Both starch and lignocellulosic fiber degraded much more rapidly than PVA. Interestingly, addition of fiber to formulations enhanced the PVA degradation
Foamed Articles Based on Potato Starch, Corn Fibers and Poly(vinyl alcohol)
No full textSingle-use packaging materials made of expanded polystyrene (EPS) have been identified as suitable items to be replaced by biodegradable materials. Plates made with EPS represent a source of non-degradable waste that is difficult to collect and to recycle. Potato starch based foamed plates have been prepared by a baking process. Presently, foam plates have been prepared by baking aqueous mixtures of potato starch, corn fibers, and poly(vinyl alcohol) (PVA) inside a hot mold. The effects of the addition of corn fibers, a co-product of bio-ethanol production, on mechanical properties and moisture resistance of potato starch based foamed plates were investigated. The addition of corn fiber to potato starch batter increased baking time and an increased batter volume is needed to form a complete tray. The mechanical properties of the trays decreased with added corn fiber. In previous studies PVA has been added as aqueous solution to improve strength, flexibility, and water resistance of baked starch trays. In this study, 88% hydrolyzed PVA was added as a powder in the mixture, avoiding the time consuming and costly step of pre-dissolving the PVA. The addition of PVA to potato starch batters containing corn fiber mitigated the reduction in tensile properties seen in trays with added corn fiber. Starch-based trays produced with a high fiber ratio and PVA, showed improved water resistance
Hybrid Composite Based on Poly(vinyl alcohol) and Fillers from Renewable Resources
No full textHybrid composite laminates consisting of polyvinyl alcohol (PVA) as continuous phase (33% by weight) and lignocellulosic fillers, derived from sugarcane bagasse, apple and orange waste (22% by weight) were molded in a carver press in the presence of water and glycerol such as platicizers agents. Corn starch was introduced as a biodegradation promoter and gluing component of the natural filler and synthetic polymeric matrix in the composite (22% by weight). The prepared laminates were characterized for their mechanical properties and degradative behavior in simulated soil burial experiments. The fibers type and content in composite impacted mechanical properties. Materials based on PVA and starch with apple wastes and sugarcane bagasse fillers were much harder (Young's Modulus respectively, 57, 171 MPa) than materials prepared with orange wastes (17 Mpa). Respirometric test revealed that soil microbes preferentially used natural polymers and low molecular weight additive as a carbon source compared to biodegradable synthetic polymer. The presence of PVA in formulations had no negative effect on the degradation of lignocellulosic fibers
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Environmentally Compatible Foamed Articles Containing Potato Starch, Corn Fiber and Poly(Vinyl Alcohol)
No full textPotato starch foam trays based on blends of poly(vinyl alcohol) and corn fibers (CFs), co-product of the corn-wheat wet-milling process, are prepared by baking the blended mixtures in a preheated mold. Materials are evaluated for processing parameters, foam strength, flexibility, and water resistance as a function of fibers content. Addition of CF in formulations improved not only moisture resistance of foam, but has a potential to lower the overall cost of the foamed materials substantially. Interestingly, addition of up to 45% fiber in formulations was possible without compromising the foaming process. Degradability is evaluated both in compost than simulating a disposal in the environment (soil burying and soil surface). Trays are biodegraded within 30-60 days in compost and soil. Particularly, trays containing starch and fiber degraded at much faster rates than trays prepared using starch without natural fillers
Injection Molded hybrid Composites Based on Corn Fibers and Poly(vinyl alcohol)
No full textOngoing research cooperation between USDA and the University of Pisa, Italy has yielded several composite blends of poly(vinyl alcohol) (PVA) and corn fibers (CF). The USA is the largest producer of ethanol from cereal grains. Composites based on natural fibers alone are extremely sensitive to water. Their mechanical properties deteriorated upon the absorption of water, thus suggesting a limited usefulness of such formulations in practical applications. In this study, corn-fibers produced during the wet milling process of corn for fuel ethanol were used to prepare composites. CIF and PVA were processed in variable amounts in the presence of both dry/fluid plasticizers, such as glycerol and pentaerythritol. Composites prepared from CF in combination with PVA showed little change in their mechanical properties even after conditioning at variable relative humidities, as well as complete soaking in water. Composites tested after storage for one year under 50% relative humidity and 23degreesC exhibited mechanical properties similar to those of freshly prepared composites. Cornstarch was introduced in the formulation for the purpose of reducing the cost of the final product and to further increase the composition of natural components in the composites. Addition of starch moderately reduced the mechanical properties of the composites
Oxidation and biodegradation of PE films containing pro-oxidant additives: Synergistic effects of sunlight exposure, thermal aging and fungal biodegradation
No full text- …
