Publisher DOI: 10.1021/acsapm.0c00162
Title: Mechanically Strong Polyurea/Polyurethane-Cross-Linked Alginate Aerogels
Authors: Paraskevopoulou, Patrina 
Smirnova, Irina  
Athamneh, Tamara 
Papastergiou, Maria
Chriti, Despoina
Mali, Gregor 
Čendak, Tomaž 
Chatzichristidi, Margarita 
Raptopoulos, Grigorios 
Gurikov, Pavel 
Keywords: acoustic insulation; alginate aerogels; hydrophobic materials; mechanical strength; polymer-cross-linked aerogels; polyurea
Issue Date: 8-May-2020
Source: ACS Applied Polymer Materials 2 (5): 1974-1988 (2020-05-08)
Abstract (english): 
Two types of preformed alginate wet gels, one with a low (30-35%) and the other with a high (65-75%) content of glucuronic acid, were reacted with an aliphatic triisocyanate that was priorly allowed to diffuse in the pores. This reaction formed urethane groups on the surface of the alginate framework and also formed a polyurea (PUA) network connecting these urethane groups via respective reactions of the triisocyanate with alginate surface -OH groups or with gelation water remaining adsorbed on the inner surfaces of the wet gels. These processes formed a conformal nanothin film of PUA around the alginate network. After drying the wet gels with the supercritical fluid CO2, we obtained PUA/polyurethane-cross-linked alginate (X-alginate) aerogels. Although X-alginate aerogels are essentially copolymers, unlike all copolymers mentioned in previous literature reports, the relative topology of the alginate and the cross-linker is defined at the nanoscopic scale rather than at the molecular level. For the systematic study of X-alginate aerogels as a function of synthetic conditions, the experimental protocol was designed according to the central circumscribed rotatory design model using the alginate and the triisocyanate concentration as independent variables. Empirical models were derived for all relevant material properties by fitting experimental data to the two independent variables. The chemical identity of all samples was confirmed with attenuated total reflectance-Fourier transform infrared spectroscopy and solid-state 13C and 15N cross-polarization magic angle spinning NMR spectroscopy. The percentage of PUA uptake in X-alginate aerogels (58-98%) was calculated from skeletal density data. Scanning electron microscopy showed that all samples were nanofibrous, indicating that PUA coated conformally the skeletal network of both alginates, and the micromorphology remained the same as in the native (non-cross-linked) samples. X-alginate aerogels are mechanically strong materials, in contrast to their native counterparts, which are extremely weak mechanically. Compared to various organic aerogels from the literature, X-alginate aerogels can be as stiff as many other polymeric aerogels with 2 or 3 times higher densities. In addition, X-alginate aerogels are good candidates for sound insulation applications, as the speed of sound in most samples was estimated to be significantly lower than the speed of sound in dry air.
ISSN: 2637-6105
Journal: ACS applied polymer materials 
Institute: Thermische Verfahrenstechnik V-8 
Document Type: Article
Project: New generation of nanoporous organic and hybrid aerogels for industrial applications: from the lab to pilot scale production - NanoHybrids 
Advanced Engineering and Research of aeroGels for Environment and Life Sciences 
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