Polyurethanes (PUs) are an important class of polymers due to their low density and thermal conductivity combined with their interesting mechanical properties—they are extensively used as thermal and sound insulators, as well as structural and comfort materials. Despite the broad range of applications, the production of PUs is still highly petroleum-dependent. The use of carbohydrates in PU synthesis has not yet been studied extensively, even though, as multihydroxyl compounds, they can easily serve as crosslinkers in PU synthesis. Partially or potentially biobased di-, tri- or poly-isocyanates can further be used to increase the renewable content of PUs. In our research, PU films could be easily produced using two bio-based isocyanates—ethyl ester L-lysine diisocyanate (LLDI] and ethyl ester l-lysine triisocyanate (LLTI)—, one commercial isocyanate—isophorone diisocyanate (IPDI), and a bio-based white dextrin (AVEDEX W80) as a crosslinker. The thermal and mechanical properties are evaluated and compared as well as the stability against solvents.
Four hydrophobic amino acids (Leu, Tyr, Phe, Trp) were oligomerized by the protease papain in homo-oligomerization, binary co-oligomerization and ternary co-oligomerization. After 24 h, solid polydisperse reaction products of the homo-oligomerization were obtained in yields ranging from 30-80% by weight. A DP avg was calculated based on MALDI-ToF MS results using the ion counts for the chains in the product. Based on the DP avg and the yield of the homo-oligomerization it was determined that the amino acids can be ranked according to reactivity in the order: Tyr > Leu > Phe > Trp. Thermal degradation of the homo-oligomers shows two degradation steps: at 178-239 °C and at 300-330 °C. All the products left a significant amount of char ranging from 18-57% by weight at 800 °C. Binary co-oligomers were obtained as a polydisperse precipitate with a compositional distribution of the chains. Both the compositional and chain length distribution are calculated from MALDI-ToF mass spectra. By comparing the amount of each amino acid present in the chains it was determined that the amino acids are incorporated with a preference: Leu > Tyr > Phe > Trp. Ternary co-oligomers were also obtained as a precipitate and analyzed by MALDI-ToF MS. The compositional distribution and the chain length distribution were calculated from the MALDI-ToF data. The quantity of every amino acid in the chains was determined. Also determined was the influence on the DP avg when the oligomers were compared with corresponding binary co-oligomers. From the combined results it was concluded that in the co-oligomerization of three amino acids the reactivity preference is Leu > Tyr > Phe > Trp. OPEN ACCESSPolymers 2012, 4 711Thermal degradation of all the co-oligomers showed a weight loss of 2 wt% before the main oligomer degradation step at 300-325 °C.
thermoplasticity and water resistance to the modified starch over the unmodified one. Modified starch-based materials are used in industry as glues, adhesives, and auxiliaries of a wide range of rheological and functional properties.It was found that the properties of polysaccharide-based plastics are strongly dependent on the degree of modification as well as on the regioselectivity of the substitution. So far, sophisticated experimental techniques, solvents, or systems of solvents, were used to achieve homogeneous modification of the chosen polysaccharide. However, these techniques are expensive, typically use toxic solvents in highly alkaline conditions at high temperatures, are not viable for the large-scale industrial production of modified starches, and/or bear health risks when utilized.Biswas et al. were able to show an elegant yet simple approach toward cellulose, starch, and other polysaccharides using acetic anhydride in the presence of a catalytic amount of iodine. [10] Iodine seems to be an excellent acylating reagent for both starch and cellulose as it activates the carbonyl group of acetic anhydride, making the latter more reactive toward the carbohydrates. This method was already used by several groups for very interesting cellulose modifications [11][12][13] and esterification of whole grain starches. [14][15][16] In our current work, we studied the feasibility of this procedure in more detail for the esterification (acetylation, propionation, and esterification with longer fatty acids) of white potato dextrins (AVEDEX W80) and "waxy potato" starch containing more than 95% amylopectin (ELIANE) [17][18][19] -both are commercial carbohydrates used in various applications from food to paints. [20,21] Dextrins are frequently used in paper coatings as they readily form an adhesive paste when mixed with water. White dextrins, such as AVEDEX W80, are derived from starch by partial thermal degradation under acidic conditions. [22] The difference between white dextrins and other dextrins is that they can form a viscous paste in cold water, making them attractive for water-borne coatings. [23] ELIANE is a commercially available 100% amylopectin potato starch obtained via innovative classical breeding techniques. [24] Amylose has very low water solubility and amylose solutions are very unstable-amylopectin is highly soluble in water and forms stable solutions. ELIANE is therefore a very attractive high-molecular-weight [25] polysaccharide for stable high-content polysaccharide solutions and is at the moment mainly used in food applications. [26] Both used carbohydrates are (highly) branched and hold a high amount of functional groups per molecule, which is especially attractive for industrial purposes [27] offering a high functionality, broad variety of functional groups, high solubility, and a unique rheological behavior. [28,29] The reported modification of these carbohydrates can be used to adjust their properties for specific Polysaccharide ModificationThe iodine-catalyzed esterification (acetylation...
Several new eco-friendly materials have the potential to replace conventional petroleum-derived materials and monomers. Among them are natural polysaccharides. The use of polysaccharides in polyurethane (PU) synthesis has not yet been studied extensively, even though as multihydroxyl compounds, they can easily serve as crosslinkers in PU synthesis. One naturally occurring (hyper-) branched polymer is amylopectin, a component of starch. In this work, we report the PU synthesis and film-forming capacity using the asymmetric cyclic aliphatic diisocyanate-isophorone diisocyanate (IPDI) with acetylated and pristine partially hydrolyzed amylopectin/ white dextrin (AVEDEX W80) as a crosslinker.
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