Abstract. Although starch foams are well known as biodegradable alternatives to foamed polystyrene, starch-lignin foams have not previously been reported. Lignin is an abundant byproduct of paper manufacture usually burned as fuel for lack of higher-value uses. We have prepared novel starch-kraft lignin foams with a known technique similar to compression molding. Replacing 20% of the starch with lignin has no deleterious effect on density or morphology as indicated by scanning electron microscopy: a thin outer layer of approximately 100 μm encloses a region of cellular structure containing 100-200 μm voids, with the major internal region of the foam consisting of large voids of up to 1 mm in size. Powder X-ray diffraction shows residual structure in both starch and starch-lignin foams. Differential scanning calorimetry displays endothermic transitions in the starch foam but not in the starch-lignin foam, indicating that lignin stabilizes the residual starch structure. Lignin decreases water absorption; diffusion constants for the starch and starch-lignin foams are 2.68·10 -6 and 0.80·10 -6 cm 2 /sec, respectively. The flexural strength of the starch-lignin foam is similar to that of foamed polystyrene, the strain at maximum stress is smaller, and the modulus of elasticity is larger.
The problem of determining conformational preferences for oligo-and polysaccharides in solution is best approached by establishing, in increasingly greater detail, the features of their potential energy surfaces as functions of the linkage dihedral angles and . Beginning with a survey of calculated in vacuo potential surfaces for cellobiose and maltose, we examine the results of optical rotation and NMR measurements and develop a picture of their potential surfaces in aqueous solution.In doing so we apply a new semiempirical theory of saccharide optical activity. The results confirm many of the previously emphasized conformational features and indicate the likely role of "folded" conformations in providing stable turn geometries for the cellulose and amylose polymers.Polysaccharides are the most plentiful biopolymer. In the biosphere there is probably more carbohydrate than all other organic matter combined, largely because of the abundance in the plant world of two polymers of D-glucose, cellulose and starch.1 The commercial exploitation of polysaccharides is growing,2 as is awareness of the breadth of their biological function.3 The progress that has been made in characterizing their structure at the molecular level has come from applying many physicochemical techniques in conjunction with one another.4™6Chiroptical properties are useful7 because of their great sensitivity to chemical structure, configuration, and conformation, and there has been a systematic improvement in the empirical and semiempirical methods of interpreting experimental data. The very early empirical rules of Hudson8 have been superseded through the work of Whiffen,9 Brewster,10 and others, from which it is now possible to rationalize, or predict, the observed molar rotation of a wide variety of molecules. Those methods are empirical in that all parameters are derived from experimental data, but the analysis that leads to the parameterization has some theoretical basis.11Rees and co-workers12,13 extended those treatments to include the conformational dependence of polysaccharide optical rotation.
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