1,721,109 research outputs found
Thermal Behavior of Composites Based on Poly(vinyl alcohol) and Sugar Cane Bagasse
No full textPoly(vinyl alcohol) (PVA) and sugar cane bagasse (SCB) mixtures have been formulated as aimed at the production of hydro-mulching composites and melt processed biobased composite items. Glycerol and urea have been proposed as suitable plasticizers and eventually, in the case of urea, for the realization also of slow release fertilizing hydro-mulching. The investigation of thermal stability of raw components and relevant mixture is an important parameter to be assessed in view of processing and ultimate applications. PVA/SCB composites appeared suitable for melt processing up to 200 °C. The urea containing PVA/SCB composites while resulted particularly suited for hydro-mulching applications did not appear processable from the melt, due to urea thermal instability
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
Composite Films Based on Waste Gelatin. Thermal-Mechanical Properties and Biodegradation
No full textCharacterization 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
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
Environmentally degradable polymeric materials (EDPM) in agricultural applications - an overview
No full textCharacteristics 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
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