Green Pathways for the Enzymatic Synthesis of Furan-Based Polyesters and Polyamides

The attention towards the utilization of sustainable feedstocks for polymer synthesis has grown exponentially in recent years. One of the spotlighted monomers derived from renewable resources is 2,5-furandicarboxylic acid (FDCA), one of the most promising bio-based monomers, due to its resemblance to petroleum-based terephthalic acid. Very interesting synthetic routes using this monomer have been reported in the last two decades. Combining the use of bio-based monomers and non-toxic chemicals via enzymatic polymerizations can lead to a robust and favorable approach towards a greener technology of bio-based polymer production. In this chapter, a brief introduction to FDCA-based monomers and enzymatic polymerizations is given, particularly focusing on furan-based polymers and their polymerization. In addition, an outline of the recent developments in the field of enzymatic polymerizations is discussed. </p

Thermoplastic PLA-LCP Composites: A Route toward Sustainable, Reprocessable, and Recyclable Reinforced Materials

Reprocessing of reinforced composites is generally accompanied by loss of value and performance, as normally the reinforcing phase is damaged, or the matrix is lost in the process. In the search for more sustainable recyclable composite materials, we identify blends based on poly(L-lactide) (PLA) and thermotropic liquid crystalline polymers (LCP) as highly promising self-reinforced thermoplastic composites that can be recycled several times without loss in mechanical properties. For example, irrespective of the thermal history of the blend, injection molded bars of PLA containing 30 wt % LCP exhibit a tensile modulus of 6.4 GPa and tensile strength around 110 MPa, as long as the PLA matrix has a molecular weight of 170 kg mol(-1) or higher. However, after several mechanical reprocessing steps, with the gradual decrease in the molecular weight of the PLA matrix, deterioration of the mechanical performance is observed. The origin of this behavior is found in the increasing LCP to PLA viscosity ratio: at a viscosity ratio below unity, the dispersed LCP droplets are effectively deformed into the desired fibrillar morphology during injection molding. However, deformation of LCP droplets becomes increasingly challenging when the viscosity ratio exceeds unity (i.e., when the PLA matrix viscosity decreases during consecutive reprocessing), eventually resulting in a nodular morphology, a poor molecular orientation of the LCP phase, and deterioration of the mechanical performance. This molecular weight dependency effectively places a limit on the maximum number of mechanical reprocessing steps before chemical upgrading of the PLA phase is required. Therefore, a feasible route to maintain or enhance the mechanical properties of the blend, independent of the number of reprocessing cycles, is proposed.</p