Preparation and characterization of bio‐based polyurethanes obtained from castor oil and poly (3‐hydroxybutyrate) and their nanocomposites

Abstract

Bio‐based polyurethanes (PUs) were synthesized from castor oil (CO) and poly(3‐hydroxybutyrate)‐diol (PHB‐diol) using 1,6‐hexamethylene diisocyanate, as nontoxic connecting agent. The PHB content in the obtained PUs was adjusted from 0 to 60.0 wt%. The synthesis was carried out by one pot solution polymerization. PUs nanocomposites loaded with different contents of cloisite®25A (C25A) were prepared by means of in situ solution polymerization. The molecular structure of the obtained PUs was confirmed by FT‐IR. The thermal properties of the neat PUs and the resulting nanocomposites were investigated using DSC and TGA. It was found that the cold crystallization of the PHB component was enhanced, while its melt crystallization was retarded with increasing its own content in the PUs. The incorporated C25A in the PU matrix shifted the cold crystallization peak to higher temperature. TGA studies reveal that neat PUs and nanocomposites exhibited three main decompositions steps. The thermal stability of the neat PUs decreased with increasing the PHB content and increased with increasing the C25A content. Tensile mechanical testing revealed that increasing the content of the PHB and C25A made the PUs rigid and strong. The elastic modulus and ultimate tensile strength of the neat PUs were found to increase with increasing the PHB content and enhanced with incorporation of C25A, while the elongation decreased with increasing the PHB and C25A content. The equilibrium swelling in 1,2‐dichloroethane decreased with increasing both the PHB and C25A content in PU matrix. POLYM. COMPOS., 39:E489–E499, 2018. © 2017 Society of Plastics Engineers

Biodegradable Polyurethanes Based on Castor Oil and Poly (3-hydroxybutyrate)

“…The second heating curves of the synthesized CO/PHBD PU 8h at different PHBD contents are shown in Figure 6 a. Regardless of the CO/PHBD ratio, only one T g was detected at the range of −5.1 to 2.7 °C [ 9 , 12 ]. Overall, T g increased upon the incorporation of PHB which may suggest a partial mixing between hard and soft segment phase [ 15 ].…”

“…As shown in Figure 6 a, crystallization and melting peaks appeared in the thermograms of the synthesized PUs upon the incorporation of PHBD. A slight shift in cold crystallization temperature (T cc ) to lower values was recorded as a result of increasing PHBD content, indicating an increase in the crystallization rate of PHBD component from the glassy state in the synthesized PUs [ 9 ]. This behavior can be attributed to the decrease in CO content which may decrease the chemical crosslinking degree in the PU matrix.…”

“…No evident shifts occurred in the melting peak of the synthesized PUs as a result of increasing PHBD content. Overall, the melting enthalpies of the synthesized PUs were lower than the pure PHBD (∆H m 63.1 J/g), which might be resulted from the disruption in PHB chain by soft CO dangling structure and phase mixing between CO and PHBD segments [ 9 , 36 ]. In fact, this phase mixing is expected to reduce the homogeneity of PHB chains.…”

“…Vegetable oils are mainly composed of triglyceride chains with a fatty acid triester of glycerol containing 12–22 carbon atoms and 0–3 carbon-carbon double bonds [ 5 ]. Among a variety of vegetable oils, castor oil (CO) has shown great potential in the green synthesis of PUs due to the presence of hydroxyl groups in its triglyceride chain [ 9 , 10 ]. Despite their good thermal stability, CO-based PUs exhibit poor mechanical properties and low biodegradation rate which may limit their application in many fields [ 10 , 11 ].…”

“…Poly(3-hydroxybutyrate) (PHB), an aliphatic polyester produced via bacterial fermentation, has drawn a considerable attention due to its biocompatibility and biodegradability [ 9 ]. However, due to its inherent brittleness, the use of PHB may be restricted in wide applications.…”