Highly Unsaturated Microcrystalline Cellulose and Its Cross-Linked Soybean-Oil-Based Thermoset Composites

Development of sustainable composites from renewable cellulose and vegetable oil has been one of the focus topic for many researchers in the field of materials science. One of the common revelations that they have arrived at is that vegetable oil that consists of triglycerides has been fundamental to painting, lubrication, and in inks due to its high level of availability. Currently, acrylated epoxidized soybean oil (AESO) is one of the common soybean oil derivatives that polymerizes through radical reactions to generate the thermoset AESO. However, AESO faces serious challenges, such as poor mechanical strength due to its insufficient cross-linking density and weak interfacial adhesion with highly hydrophilic lignocellulosic fibers.

To this extent, Fujian Agriculture and Forestry University scientists: Tingting Chen (PhD candidate) and Dr. Wendi Liu. focused their efforts on unsaturation functionalization of microcrystalline cellulose (MCC) as well as its role both as a cross-linking agent and reinforcing agent. Their research is published in journal ACS Sustainable Chemistry and Engineering.

The initial step entailed preparing the unsaturated MCC through esterification with methacrylic anhydride with the assistance of ultrasonic treatment. Some of the key features of measuring the level of unsaturation in MCC entailed measurement of surface chemistry and hydrophobicity. This was followed by measuring the degrees of both substitution and unsaturation of MCC which were done quantitatively. In the manufacture of sustainable composites, the unsaturated MCC was used as the reactive reinforcing agent that was cross-linked with AESO. Finally, the researchers analyzed the dynamic and static mechanical properties as well as water resistance of the resulting sustainable biocomposites.

The findings of their research indicated that the MCC contains a high number of hydroxyl groups, and thus it is possible to verify the reaction between methacrylic anhydride and the MCC. As the concentration of methacrylic anhydride was increasing, the level of unsaturation on the MCC increased, indicating that it is possible to regulate the unsaturated degree of MCC via controlling the concentration of methacrylic anhydride. Cellulose cannot be penetrated by the methacrylic anhydride, considering that the esterification reaction between MCC and methacrylic anhydride takes place on the surface of the microcrystalline cellulose. Due to this reason, the non-polar components and the level of hydrophobicity on the MCC surface increases as the reaction proceeds.

In summary, the study of Chen and Liu showed that it is possible to manufacture unsaturated MCC through esterification and the assistance of the ultrasonic treatment. Further, they showed how the ratio between methacrylic anhydride and the MCC are essential when determining the degree of saturation level of the unsaturated MCC. Finally, the unsaturated MCC was verified to have great potential for reinforcing and cross-linking soybean oil thermoset for the development of sustainable biocomposites.