Chitosan Oligomer as a Raw Material for Obtaining Polyurethane Foams

Abstract

Decreasing oil extraction stimulates attempts to use biologically available sources to produce polyols, which are the basic components for obtaining polyurethane foams. Plants are inexhaustible source of oils, sugars, starches, and cellulose. Similar substrates to obtain polyols are chitosans. Commercially available modified chitosans are soluble in water, which gives them the possibility to react with hydroxyalkylating agents. We used a water-soluble chitosan previously to obtain polyols suitable for producing rigid polyurethane foams. Here, we described hydroxyalkylation of a low-molecular-weight chitosan (oligomeric chitosan) with glycidol and ethylene carbonate to obtain polyols. The polyols were isolated and studied in detail by IR, 1H-NMR, and MALDI–ToF methods. Their properties, such as density, viscosity, surface tension, and hydroxyl numbers, were determined. The progress of the hydroxyalkylation reaction of water-soluble chitosan and chitosan oligomer with glycidol was compared in order to characterize the reactivity and mechanism of the process. We found that the hydroxyalkylation of chitosan with glycidol in glycerol resulted in the formation of a multifunctional product suitable for further conversion to polyurethane foams with favorable properties. The straightforward hydroxyalkylation of chitosan with glycidol was accompanied by the oligomerization of glycidol. The hydroxyalkylation of chitosan with glycidol in the presence of ethylene carbonate was accompanied by minor hydroxyalkylation of chitosan with ethylene carbonate. The chosen polyols were used to obtain rigid polyurethane foams which were characterized by physical parameters such as apparent density, water uptake, dimension stability, heat conductance, compressive strength, and heat resistance at 150 and 175 °C. The properties of polyurethane foams obtained from chitosan-oligomer and water-soluble-chitosan sources were compared. Polyurethane foams obtained from polyols synthesized in the presence of glycerol had advantageous properties such as low thermal conductivity, enhanced thermal resistance, dimensional stability, low water uptake, and high compressive strength, growing remarkably upon thermal exposure.

Polyols and polyurethane foams based on chitosans of various molecular weights

“…39 The valence and deformation hydroxyl bands were observed at 3400 cm À1 and within 770-650 cm À1 . The 1 H-NMR spectra of obtained polyols from CS L , CS M , and CS H (Figure 7) analyzed earlier for CS O and CS WS 4,5 overlapped on pristine CS substrate protons. 4 The new OH group proton resonances at 4.5-4.9 ppm in the spectra of polyols were attributed to hydroxyl groups formed upon EC and GL ring opening.…”

“…Recently we have tested the applicability of low molecular weight CS to obtain polyols. 4,5 We have used water soluble CS WS and oligomeric CS O of 141,250 and 8700 Da molecular mass, respectively. Here we extended our studies into higher molecular weight CS, namely into: low molecular weight (CS L ), medium (CS M ) and high (CS H ) molecular weight, and defined deacetylation degree (Table 1).…”

“…The PUFs obtained here were compared with those obtained from CS WS and CS O -based polyols, described before. 4,5 The results are presented in Table 12. The notation of (CS + GL) + EC indicates that polyol was obtained first by reaction of CS with GL followed by reaction with EC.…”

“…Such potential substrates are polysaccharides like starch, cellulose, and chitosan. [1][2][3][4][5] The latter can be obtained by N-deacetylation of chitin, 6,7 which is obtained mainly from waste, which is the shells of crustaceans, especially crabs and shrimps 6 (Figure 1).…”

“…Previously we have described the synthesis of polyols based on oligomeric CS (CS O ) and water soluble CS (CS WS ). 4,5 Four various synthetic protocols were successfully tested. In first method, the CS WS was hydroxyalkylated with glycidol (GL) in water, then unreacted water was removed and the residue was reacted with ethylene carbonate (EC).…”