Crosslinked polysaccharide sponges have been prepared by freeze-drying of amorphous alginate-oxidized nanocellulose in the presence of a Ca(2+) ionic crosslinking agent. The new carboxyl groups on the surface of nanocellulose induced by the chemical oxidization provided the possibility of participating in the construction of an alginate-based sponge's structure and played a fundamental role in the structural and mechanical stability of ensuing sponges. Furthermore, enhanced mechanical strength induced by oxidized cellulose nanocrystals and the formation of a semi-interpenetrating polymer network from oxidized microfibrillated cellulose were reported. Together with the facile and ionic crosslinking process, the ultrahigh porosity, promising water absorption and retention, as well as the improved compression strength of the crosslinked sponges should significantly extend the use of this soft material in diverse practical applications.

Summary: Different lignins were converted into polyols by a chain extension reaction with propylene oxide (PO). Thus, soda lignin from Alfa (Stipa tenacissima) (SL), organosolv lignin from hardwoods (OL), kraft lignin (KL) from softwood and oxidized organosolv lignin (OOL) were oxypropylated in a batch reactor at 180 °C in the presence of KOH as catalyst. The ensuing polyols were characterized by FTIR and 1H NMR spectroscopy, which showed that they had incorporated poly(propylene oxide) grafts into their structure. Their viscosity varied from 5 mPa · s to infinity, depending on the Lignin/PO ratio and their hydroxy index was in the range of 100–200, which made them suitable for rigid polyurethane foam (RPU) formulations. The RPUs thus obtained had a Tg of ca. 60 °C and a thermal conductivity of ≈20 mW/m · K before ageing and ≈25 mW/m · K after accelerated ageing for 10 d at 70 °C. The analyses of the gases inside the cells showed that these were mostly closed, since the partial pressure did not decrease significantly with ageing.

The hydrolysis of three alkoxy-silane coupling agents, gamma-methacryloxypropyl trimethoxy silane (MPS), gamma-aminopropyl triethoxy silane (APS), and gamma-diethylenetriaminopropyl trimethoxy silane (TAS), was carried out in ethanol/water solutions (80/20 w/w) at different pH values and followed by 1H, 13C and 29Si NMR spectroscopy. Acidic media were found to stabilize the hydrolyzed forms. As expected, the formation of silanol groups was followed by their self-condensation to generate oligomeric structures, yielding, ultimately, solid homopolycondensated structures, as analyzed by 29Si and 13C high-resolution solid-state NMR. Hydrolyzed MPS in acidic media was then successfully adsorbed onto a cellulose surface and the ensuing substrates submitted to thermal treatment at 110-120 degrees C under reduced pressure, in order to create covalent bonds between cellulose and the coupling agent.

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