Polymers are essential materials in our daily life. The synthesis of value-added polymers is mainly performed from fossil fuel-derived monomers. However, the adoption of the circular economy model based on the bioeconomy will reduce the dependence on fossil fuels. In this context, biorefineries have emerged to convert biomass into bioenergy and produce high value-added products, including molecules that can be further used as building blocks for the synthesis of biopolymers and bioplastics. The achievement of catalytic systems able to polymerize the natural monomer counterparts, such as terpenes or terpenoids, is still a challenge in the development of polymers with good mechanical, thermal, and chemical properties. This review describes the most common types of bioplastics and biopolymers and focuses specifically on the polymerization of terpenes and terpenoids, which represent a source of promising monomers to create bio-based polymers and copolymers.

Poly(lactic acid) (PLA) composites with 0.5 wt% lignin or nanolignin were prepared with two different techniques: (a) conventional melt-mixing and (b) in situ Ring Opening Polymerization (ROP) by reactive processing. The ROP process was monitored by measuring the torque. The composites were synthesized rapidly using reactive processing that took under 20 min. When the catalyst amount was doubled, the reaction time was reduced to under 15 min. The dispersion, thermal transitions, mechanical properties, antioxidant activity, and optical properties of the resulting PLA-based composites were evaluated with SEM, DSC, nanoindentation, DPPH assay, and DRS spectroscopy. All reactive processing-prepared composites were characterized by means of SEM, GPC, and NMR to assess their morphology, molecular weight, and free lactide content. The benefits of the size reduction of lignin and the use of in situ ROP by reactive processing were demonstrated, as the reactive processing-produced nanolignin-containing composites had superior crystallization, mechanical, and antioxidant properties. These improvements were attributed to the participation of nanolignin in the ROP of lactide as a macroinitiator, resulting in PLA-grafted nanolignin particles that improved its dispersion.

Poly(lactic acid) (PLA) is a biobased polyester with ever-growing applications in the fields of packaging and medicine. Despite its popularity, it suffers from inherent brittleness, a very slow degradation rate and a high production cost. To tune the properties of PLA, block copolymers with poly(propylene adipate) (PPAd) prepolymer were prepared by polymerizing L-lactide and PPAd oligomers via reactive extrusion (REX) in a torque rheometer. The effect of reaction temperature and composition on the molecular weight, chemical structure, and physicochemical properties of the copolymers was studied. The introduction of PPAd successfully increased the elongation and the biodegradation rate of PLA. REX is an efficient and economical alternative method for the fast and continuous synthesis of PLA-based copolymers with tunable properties.

Process design, techno-economic assessment and life cycle assessment have been employed for the evaluation of four biorefinery concepts using the organic fraction of municipal solid waste (OFMSW) for the production of biosurfactants together with lactic acid (LA), succinic acid (SA), hot melt adhesives (HMAs) or polyurethane urea dispersions (PUDs). LA and SA produced via fermentation using sugar-rich OFMSW enzymatic hydrolysates, while biosurfactants are produced from OFMSW-derived lipids and proteins and bacterial biomass remaining at the end of fermentation. OFMSW-derived SA replaces fossil-based SA and adipic acid in PUDs production. Process design was employed for equipment sizing and costing and the estimation of material and energy balances using experimental results obtained during the H2020 funded PERCAL project. HMAs and PUDs production could be profitable when biosurfactants are produced as co-product in OFMSW-based biorefineries, leading to minimum selling prices (MSP) of $2.92 per kg_HMAs and $1.95 per kg_PUDs when biosurfactants market price of $4.1 per kg, OFMSW management fees of $0.035 per kg and production capacities of SA and LA at economies of scale are considered. If LA or SA are considered as final products together with biosurfactants, then the corresponding MSPs are $1.58 per kg_LA and $2.14 per kg_SA. Five environmental indicators were estimated considering either conventional electricity production mix (grid) or renewable electricity usage from photovoltaics. The proposed biorefineries lead to 25–35% greenhouse gas emmission savings per kg main product (or 0.95–2.06 kg CO₂-eq per kg dry OFMSW) when compared to conventional production of end-products and two OFMSW management practices based on either landfilling alone or combined composting (37.45%) and landfilling (62.55%). The results demonstrate that OFMSW-based biorefineries could lead to profitable and sustainable production of bio-based products and OFMSW utilisation as feedstock.

Molecular dynamics investigations of block copolymers based on renewable polymers, PLA and PPAd, via broadband dielectric spectroscopy. Effects of composition, chain length, and interchain associations.

This work deals with molecular mobility in renewable block copolymers based on polylactide (PLA) and poly(propylene adipate) (PPAd). In particular, we assess non-trivial effects on the mobility arising from the implementation of crystallization. Differential scanning calorimetry, polarized light microscopy and broadband dielectric spectroscopy were employed in combination for this study. The materials were subjected to various thermal treatments aiming at the manipulation of crystallization, namely, fast and slow cooling, isothermal melt- and cold-crystallization. Subsequently, we evaluated the changes recorded in the overall thermal behavior, semicrystalline morphology and molecular mobility (segmental and local). The molecular dynamics map for neat PPAd is presented here for the first time. Unexpectedly, the glass transition temperature, T_g, in the amorphous state drops upon crystallization by 8–50 K. The drop becomes stronger with the increase in the PPAd fraction. Compared to the amorphous state, crystallization leads to significantly faster segmental dynamics with severely suppressed cooperativity. For the PLA/PPAd copolymers, the effects are systematically stronger in the cold- as compared to the melt-crystallization, whereas the opposite happens for neat PLA. The local β_PLA relaxation of PLA was, interestingly, recorded to almost vanish upon crystallization. This suggests that the corresponding molecular groups (carbonyl) are strongly involved and immobilized within the semicrystalline regions. The overall results suggest the involvement of either spatial nanoconfinement imposed on the mobile chains within the inter-crystal amorphous areas and/or a crystallization-driven effect of nanophase separation. The latter phase separation seems to be at the origins of the significant discrepancy recorded between the calorimetric and dielectric recordings on T_g in the copolymers. Once again, compared to more conventional techniques such as calorimetry, dielectric spectroscopy was proved a powerful and quite sensitive tool in recording such effects as well as in providing indirect indications for the polymer chains’ topology.