Polyols and Polyurethane Foams Based on Water-Soluble Chitosan

Abstract

At present, majority of polyols used in the synthesis of polyurethane foams are of petrochemical origin. The decreasing availability of crude oil imposes the necessity to convert other naturally existing resources, such as plant oils, carbohydrates, starch, or cellulose, as substrates for polyols. Within these natural resources, chitosan is a promising candidate. In this paper, we have attempted to use biopolymeric chitosan to obtain polyols and rigid polyurethane foams. Four methods of polyol synthesis from water-soluble chitosan functionalized by reactions of hydroxyalkylation with glycidol and ethylene carbonate with variable environment were elaborated. The chitosan-derived polyols can be obtained in water in the presence of glycerol or in no-solvent conditions. The products were characterized by IR, 1H-NMR, and MALDI-TOF methods. Their properties, such as density, viscosity, surface tension, and hydroxyl numbers, were determined. Polyurethane foams were obtained from hydroxyalkylated chitosan. The foaming of hydroxyalkylated chitosan with 4,4′-diphenylmethane diisocyanate, water, and triethylamine as catalysts was optimized. The four types of foams obtained were characterized by physical parameters such as apparent density, water uptake, dimension stability, thermal conductivity coefficient, compressive strength, and heat resistance at 150 and 175 °C. It has been found that the obtained materials had most of the properties similar to those of classic rigid polyurethane foams, except for an increased thermal resistance up to 175 °C. The chitosan-based polyols and polyurethane foams obtained from them are biodegradable: the polyol is completely biodegraded, while the PUF obtained thereof is 52% biodegradable within 28 days in the soil biodegradation oxygen demand test.

Chitosan Oligomer as a Raw Material for Obtaining Polyurethane Foams

“…CSs with high molecular weights are not readily available substrates to obtain polyols. However, we previously described the methods of the polyol synthesis from a water-soluble CS WS [ 33 ]. Here, we replaced a chitosan with an oligomeric CSo which dissolves in water, although worse than the previously used CS WS .…”

“…The hydroxyalkylation of CS makes it possible to obtain polyols suitable for the production of PUFs similar to the results demonstrated in the case of the hydroxyalkylation of cellulose and starch [ 7 , 8 ]. Chitosan may be used as a source to obtain polyols, alternative to petrochemical sources, provided that it can be liquefied, which can be achieved be hydroxyalkylation [ 32 , 33 ]. The application of chitosan in the fabrication of polyurethane foams creates new directions for the use and management of readily available chitosan waste accompanying the food industry.…”

“…Their protocol required a burdensome CS-swelling step with the use of NaOH in alcohol. Another protocol leading to CS-derived polyols was established in our laboratory [ 33 ] by the hydroxyalkylation of CS with GL and ethylene carbonate (EC). It should be mentioned that generally the difficulty of the CS hydroxyalkylation is due to its low solubility in organic solvents and in water.…”

“…Therefore, a high-molecular-weight CS has not been hydroxyalkylated so far. In the work described in [ 33 ], we used the so-called water-soluble chitosan (CS WS ), which was characterized by a better solubility, and we subjected it to the hydroxyalkylation with GL and then EC to obtain the expected polyols. This time, we focused on another kind of the CS, the chitosan oligomer (CS O ).…”

“…We obtained polyols and then PUFs thereof based on an oligomeric CS. The properties of the obtained PUFs were compared to those of the PUFs previously obtained from a CS WS [ 33 ].…”