Preparation, Characterization and Mechanical Properties of Bio-Based Polyurethane Adhesives from Isocyanate-Functionalized Cellulose Acetate and Castor Oil for Bonding Wood

Abstract

Nowadays, different types of natural carbohydrates such as sugars, starch, cellulose and their derivatives are widely used as renewable raw materials. Vegetable oils are also considered as promising raw materials to be used in the synthesis of high quality products in different applications, including in the adhesive field. According to this, several bio-based formulations with adhesion properties were synthesized first by inducing the functionalization of cellulose acetate with 1,6-hexamethylene diisocyanate and then mixing the resulting biopolymer with a variable amount of castor oil, from 20% to 70% (wt). These bio-based adhesives were mechanically characterized by means of small-amplitude oscillatory torsion measurements, at different temperatures, and standardized tests to evaluate tension loading (ASTM-D906) and peel strength (ASTM-D903). In addition, thermal properties and stability of the synthesized bio-polyurethane formulations were also analyzed through differential scanning calorimetry and thermal gravimetric analysis. As a result, the performance of these bio-polyurethane products as wood adhesives were compared and analyzed. Bio-polyurethane formulations exhibited a simple thermo-rheological behavior below a critical temperature of around 80-100 • C depending on the castor oil/cellulose acetate weight ratio. Formulation with medium castor oil/biopolymer weight ratio (50:50 % wt) showed the most suitable mechanical properties and adhesion performance for bonding wood.

Synthesis and properties of polyurethane elastomers based on renewable castor oil polyols

“…In the last few years, castor oil has been used widely to prepare polyurethane products, including rigid foams, flexible foams, elastomers, coatings, and adhesives . As castor oil and its derived polyols bear long hydrophobic hydrocarbon chains, they can increase the hydrophobicity of soft segment (SS) and enhance the water resistance of the as‐prepared polyurethane products.…”

High thermal stability of aliphatic polyurethanes prepared from sesame and peanut oil and their kinetic parameters

“…After the ring opening of the oxirane ring, the signals obtained at δ 71, 34 and 27 ppm corresponds to carbon atoms of -C-C-C=C-C-, respectively. Finally, after the reduction reaction, the diol of CaOD secondary hydroxyl (-OH) group overlapped with newly formed -OH group, the obtained peak at δ 74 ppm, the corresponding >C-O-C-CH2peak at δ 32 ppm longer observed [5][6][7][8][9][10][11][12][13]. It concludes that the SCOL and PCOL were successfully prepared and again confirmed.…”

“…The second step degradation of the PUs was observed in the range of 330 to 328 °C corresponding to 88% weight loss. The thermal degradation exerted in the second step may be observed due to the breakdown of the aliphatic alkyl group of fatty acid [1][2][3][4][5][6][7][8][9]23]. The third step thermal degradation reported in the temperature range 380 to 392 °C and weight loss in the range of 60 to 64 % and the major weight losses between 430 to 445 °C at 37% and 450 to 495 °C at 7 to 12 % are due to complete decomposition of cross-linker this is due to sluggish amongst both PUs formulations may be presence of secondary -OH groups in castor diol moiety of SCOL and PCOL polyol.…”

“…HMDI are the two most common commercially used aliphatic diisocyanates. Furthermore, the aliphatic diisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate (IPDI) are comparatively more reactive and produce polyurethanes with high strength and thermal stability [7,8]. The aliphatic diisocyanate-based polyurethanes possess superior retention of modulus, hydrolysis, resistance to water uptake, hardness, hydrolysis, and high thermal degradation compared to aromatic diisocyanate-based polyurethanes [1,[7][8][9][10][11][12][13].…”

“…Furthermore, the aliphatic diisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate (IPDI) are comparatively more reactive and produce polyurethanes with high strength and thermal stability [7,8]. The aliphatic diisocyanate-based polyurethanes possess superior retention of modulus, hydrolysis, resistance to water uptake, hardness, hydrolysis, and high thermal degradation compared to aromatic diisocyanate-based polyurethanes [1,[7][8][9][10][11][12][13]. Hence aliphatic diisocyanates find a wider use in elastomer and coating applications where color is an important consideration than their aromatic counterparts [14][15][16][17][18][19].…”