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Tailoring cementitious materials with modified microbial exopolysaccharides: a biologically inspired approach towards high-performance construction materials

 

Professor Dr. Johann Plank, Technische Universität München, Fakultät für Chemie, Lehrstuhl für Bauchemie, Lichtenbergstraße 4, 85747 Garching,

Professor Dr. Volker Sieber, Technische Universität München, Wissenschaftszentrum Straubing, Lehrstuhl für Chemie Biogener Rohstoffe, Petersgasse 18, 94315 Straubing,

  
Four microbial polysaccharides, namely welan gum, scleroglucan, diutan gum and EPS I, a modification of xanthan gum, were chosen for the fabrication of bio-nanocomposites based on layered double hydroxides.
 
The intercalation abilities of welan gum and scleroglucan has been ascertained. The reaction products were synthesized via direct coprecipitation of Zn(NO3)2 and Al(NO3)3 in the polysaccharide solutions at pH ~ 8.5. Following this, they were characterized by powder X-ray diffraction (XRD), elemental and thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning and transmission electron microscopy (SEM and TEM). It was found that welan gum successfully intercalated into the Zn–Al–LDH structure, giving a d-spacing of 2.38 nm for the interlayer distance, while neutral scleroglucan failed to intercalate. Instead, the biopolymer was only surface adsorbed on inorganic CaAl–OH–LDH platelets, as was evidenced by de-washing experiments. These results indicate that the anionic functionality in the polysaccharide presents a main parameter for the intercalation ability of exopolysaccharides.
 
Diutan gum, a bulkier polysaccharide as compared to welan gum, and EPS I, a polysaccharide with similar constituents as xanthan gum but with its anionic charge along the trunk chain, will be studied next. We hope to understand and identify key factors such as the bulkiness of the biopolymer and the steric position of the anionic functionality which affect the intercalating ability. From which, a general understanding of the tendency of polysaccharides to incorporate into LDH structures as a function of their different physical and chemical properties is sought.