Bio-upcycling of multilayer materials and blends: closing the plastics loop

The urge to discover and develop new technologies for closing the plastic carbon cycle is motivating industries, governments, and academia to work closely together to find suitable solutions in a timely manner. In this review article, a combination of uprising breakthrough technologies is presented highlighting their potential and complementarity to be integrated one with the other, therefore providing a potential solution to efficiently solve the plastics problem. First, modern approaches for bio-exploration and engineering of polymer-active enzymes are presented to degrade polymers into valuable building blocks. Special focus is placed on the recovery of components from multilayered materials since these complex materials can only be recycled insufficiently or not at all by existing technologies. Then, the potential of microbes and enzymes for resynthesis of polymers and reuse of building blocks is summarized and discussed. Finally, examples for improvement of the bio-based content and enzymatic degradability and future perspectives are given.

Environmentally benign alginate extraction and fibres spinning from different European Brown algae species

Applications of natural fibres are expanding, and sustainable alternatives are needed to support this growing demand. We investigated the production of fibres using alginates from Saccharina latissima (SAC), Laminaria digitata (LAM), Sacchoriza polyschides (SACC), and Himanthalia spp. (HIM). After extraction (3 % w/v biomass) using a sustainable protocol based on citric acid, crude alginate represented 61-65 % of the biomass dry weight for SAC and LAM, and 34-41 % for SACC and HIM when experiments were performed at small scale (1.5 g of starting material). Interestingly, scaling-up extraction (60 g of starting material) decreased yields to 26-30 %. SAC and LAM alginates had the highest M/G (mannuronic acid/guluronic acid) ratios and molecular weights when compared to those from SACC and HIM (M/G:1.98 and 2.23, MW: 302 and 362 kDa, vs 1.83 and 1.86, 268 and 168 kDa). When the four types of alginates were tested for spinning fibres cross-linked with CaCl2, only SAC and LAM alginates produced fibres. These fibres showed no clumps or cracks under stretching action and presented a similar Young's modulus (2.4 and 2.0 GPa). We have demonstrated that alginate extracted from S. latissima and L. digitata can be successfully spun into functional fibres cross-linked with CaCl2.

Polymer Chemistry Applications of Cyrene and its Derivative Cygnet 0.0 as Safer Replacements for Polar Aprotic Solvents

This study explores a binary solvent system composed of biobased Cyrene and its derivative Cygnet 0.0 for application in membrane technology and in biocatalytic synthesis of polyesters. Cygnet-Cyrene blends could represent viable replacements for toxic polar aprotic solvents. The use of a 50 wt % Cygnet-Cyrene mixture makes a practical difference in the production of flat sheet membranes by nonsolvent-induced phase separation. New polymeric membranes from cellulose acetate, polysulfone, and polyimide are manufactured by using Cyrene, Cygnet 0.0, and their blend. The resultant membranes have different morphology when the solvent/mixture and temperature of the casting solution change. Moreover, Cyrene, Cygnet 0.0, and Cygnet-Cyrene are also explored for substituting diphenyl ether for the biocatalytic synthesis of polyesters. The results indicate that Cygnet 0.0 is a very promising candidate for the enzymatic synthesis of high molecular weight polyesters.

Characterization of Alginate from Sargassum duplicatum and the Antioxidant Effect of Alginate–Okra Fruit Extracts Combination for Wound Healing on Diabetic Mice

Diabetes mellitus is a group of metabolic disorders characterized by high blood-glucose levels over a prolonged period that causes complications when an open wound is present. Alginate is an antioxidant and a good absorbent of exudates. Okra fruit contains flavonoids that can act as antioxidants. The antioxidant properties of extracts combination reduce blood-glucose levels significantly to accelerate the activities of wound-healing processes on diabetic mice. Alginate was characterized by Size Exclusion Chromatography-Multiple Angle Laser Light Scattering (SEC-MALLS), thermal stability and Proton Nuclear Magnetic Resonance (1H-NMR). The evaluation of wound healing on 36 male mice were divided into 12 groups including normal control (NC), diabetics control (DC), alginate (DA) and alginate–okra (DAO) groups in three different times by histopathology test on skin tissue. The results of SEC-MALLS analysis showed that alginate as single and homogeneous polysaccharide. The 1H-NMR spectrum showed that the mannuronate/guluronate ratio of the used alginate was 0.91. Alginate, okra fruit extract and their combination were classified as moderate and strong antioxidants. The numbers of fibrocytes, fibroblasts, collagen densities had significantly increased from three to seven days. In contrast, wound width, neutrophil, macrophages had significantly decreased at 14 days. The administration of extracts combination increased the re-epithelization of the wound area and wound-healing process on diabetic mice.

Work-hardening Photopolymer from Renewable Photoactive 3,3'-(2,5-Furandiyl)bisacrylic Acid

The design of a photopolymer around a renewable furan-derived chromophore is presented herein. An optimised semi-continuous oxidation method using MnO2 affords 2,5-diformylfuran from 5-(hydroxymethyl)furfural in gram quantities, allowing the subsequent synthesis of 3,3'-(2,5-furandiyl)bisacrylic acid in good yield and excellent stereoselectivity. The photoactivity of the diester of this monomer is confirmed by reaction under UV irradiation, and the proposed [2+2] cycloaddition mechanism supported further by TD-DFT calculations. Oligoesters of the photoreactive furan diacid with various aliphatic diols are prepared via chemo- and enzyme-catalysed polycondensation. The latter enzyme-catalysed (Candida antarctica lipase B) method results in the highest Mn (3.6 kDa), suggesting milder conditions employed with this protocol minimised unwanted side reactions, including untimely [2+2] cycloadditions, whilst preserving the monomer's photoactivity and stereoisomerism. The photoreactive polyester is solvent cast into a film where subsequent initiator-free UV curing leads to an impressive increase in the material stiffness, with work-hardening characteristics observed during tensile strength testing.

Chemo-enzymatic synthesis of a levoglucosenone-derived bi-functional monomer and its ring-opening metathesis polymerization in the green solvent Cyrene™

The levoglucosenone-based norbornenes family was extended to include a new bi-functional methacrylate monomer that, upon ROMP in Cyrene™, leads to polymers with pendent methacrylate moieties which can be modified by post-polymerization reactions.