1,721,010 research outputs found
"Structure-Property" relationships of genetically modified starch
No full textStarch is an attractive raw material for biodegradable plastic applications. However, the use of starch in biodegradable plastic applications is yet limited by its structural and functional properties, which are dictated by its genetic makeup. This chapter discusses the characterizations of a range of biotechnologically derived novel starches from different cereal sources to elucidate the relationship between starch structure and functionality. In summary, the following starch structure-functionality relationships are deduced. The variation in starch macromolecular properties can be attributed to their corresponding mutation of starch biosynthetic gene expression. Differences in starch amylose content affect the extent of structural order inside the granules, while the double-helix packing arrangement is influenced by the amylopectin chain length distribution. Starch gelatinization (MTDSC) thermal properties are mainly influenced by the amylopectin chain length distribution, while the swelling power and rheological properties are mainly affected by the amylose content
Reactive extrusion for thermoplastic starch-polymer blends
No full textThis chapter briefly reviews reactive extrusion developments for thermoplastic starch polymers. Then, a case study for thermoplastic starch polymer/biopolyester nanocomposite blend will be examined. In this example, maleic anhydride and dicumyl peroxide were used as cross-linking agent and initiator, respectively, for blending starch and a biodegradable synthetic aliphatic polyester using reactive extrusion. Blends were characterized using dynamic mechanical and thermal analysis. Optical micrographs of the blends revealed that in the optimized blend, starch was evenly dispersed in the polymer matrix. Optimized blends exhibited better tensile properties than the uncompatibilized blends. X-ray photoelectron spectroscopy supported the proposed structure for the starch-polyester complex. Variation in the compositions of cross-linking agent and initiator had an impact on the properties and color of the blends
Mechanical properties of starch-based plastics
No full textMechanical properties of starch depend on similar factors to those of synthetic polymers but with added considerations of water sensitivity and the influences of starch source, formulation, processing, and aging/retrogradation. Amylose/amylopectin ratios vary with starch source with high-amylose starches generally giving materials of higher strength and ductility. The amylose/amylopectin ratio also affects gelatinization processes, which generate the uniform amorphous thermoplastic by the action of heat and mechanical work in the extruder. Gelatinization is aided by suitable plasticizers, usually low-molecular-weight polyols and water. These also lower melt viscosity and T. Correct selection of plasticizers increases the toughness of the starch but decreases strength and modulus. Water content can vary with ambient conditions and directly affects mechanical properties. Increased water content has a similar effect to decreased strain rate or increased temperature. Quantifying these variables is important for use of starch materials in different applications
Starch applications: state of market and new trends
No full textBioplastics are currently experiencing strong growth worldwide due to concern about the environment, limited fossil fuel resources, and climate change and government initiatives promoting sustainability worldwide. Starch is a cheap and very widely available natural resource that makes an excellent biodegradable plastic product that can be readily manufactured on existing processing equipment with little or no modification. For these reasons, it is one of the most established alternatives to petrochemical plastics. This review covers the market drivers behind the growth in bioplastics, the state of the global bioplastics market, the main processing methodologies for starch plastic and its current applications, and key issues, barriers, and opportunities. A summary of the key producers is also given
Starch polymers: from the field to industrial products
No full textThis chapter will set the scene for the book and summarize some of the important technologies involved in producing starch polymers: from the field to industrial applications. Different topics are presented such as the main sources of starch and the corresponding levels of world and European productions.In a global approach "from the field to industrial products," this introductory chapter gives the principal outputs based on nonfood starch in terms of applications and industrial products. Biodegradable multiphase materials for short-term applications, which are described at the end of this chapter, are the subject of a growing number of publications during the two last decades. This strong evolution is on agreement with the market progression, with an increasing number of real concretizations and product outputs
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
Starch modification to develop novel starch-biopolymer blends: state of art and perspectives
No full textNative starches have limited use in industrial applications due to their poor water resistance, pasting, and mechanical properties. These behaviors can be amended by altering the starch structure by introducing ionic or hydrophobic groups in the starch structure. Structural modifications tend to stabilize the starch granules, impart hydrophilicity or hydrophobicity, heat resistance, desirable rheological properties, and increased processability. Physical modifications of starch can be achieved by various drying techniques, treatment with acids and alcohols, extrusion, etc. On the other hand, chemical modification can be achieved by chemical reactions, e.g., conversion, oxidation, dextrinization, cross-linking, and stabilization of starches. This review investigated the synthesis of modified starches and their physicochemical properties and use in various industries such as paper making, gelling agent, food additives, and pharmaceutics. In addition, the current understanding of modified starches as enzyme-resistant starch, biodegradable thermoplastic starch, and encapsulating and control release agent is also discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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