Polyester Brush Coatings for Circularity: Grafting, Degradation, and Repeated Growth

Polymer brushes are widely used as versatile surface modifications. However, most of them are designed to be long-lasting by using nonbiodegradable materials. This generates additional plastic waste and hinders the reusability of substrates. To address this, we present a synthetic strategy for grafting degradable polymer brushes via organocatalytic surface-initiated ring-opening polymerization (SI-ROP) from stable PGMA-based macroinitiators. This yields polyester brush coatings (up to 50 nm in thickness) that hydrolyze with controlled patterns and can be regrown on the same substrate after degradation. We chose polyesters of different hydrolytic stability and degradation mechanism, i.e., poly(lactic acid) (PLA), polycaprolactone (PCL), and polyhydroxybutyrate (PHB), which are grown from poly(glycidyl methacrylate) (PGMA)-based macroinitiators for strong surface binding and initiating site reuse. Brush degradation is monitored via thickness changes in pH-varied buffer solutions and seawater with PHB brushes showing rapid degradation in all solutions. PLA and PCL brushes show higher stability in solutions of up to pH 8, while all coatings fully degrade after 14 days in seawater. These brushes offer surface modifications with well-defined degradation patterns that can be regrown after degradation, making them an interesting alternative to (meth)acrylate-based, nondegradable polymers brushes.

Long-Chain Branched Bio-Based Poly(butylene dodecanedioate) Copolyester Using Pentaerythritol as Branching Agent: Synthesis, Thermo-Mechanical, and Rheological Properties

The introduction of long-chain branched structures into biodegradable polyesters can effectively improve the melt strength and blow-molding properties of polyesters. In this study, pentaerythritol (PER) was used as a branching agent to synthesize branched poly(butylene dodecanedioate) (PBD), and the resulting polymers were characterized by Nuclear Magnetic Resonance Proton Spectra (1H NMR) and Fourier Transform Infrared spectroscopy (FT-IR). It was found that the introduction of a small amount of PER (0.25-0.5 mol%) can generate branching and even crosslinking structures. Both impact strength and tensile modulus can be greatly improved by the introduction of a branching agent. With the introduction of 1 mol% PER content in PBD, the notched impact strength of PBD has been increased by 85%, and the tensile modulus has been increased by 206%. Wide-angle X-ray diffraction and differential scanning calorimetry results showed that PER-branched PBDs exhibited improved crystallization ability compared with linear PBDs. Dynamic viscoelastics revealed that shear-thickening behaviors can be found for all branched PBD under low shear rates.

Biodegradable Polyesters and Low Molecular Weight Polyethylene in Soil: Interrelations of Material Properties, Soil Organic Matter Substances, and Microbial Community

Conventional and also biodegradable polymer microplastics have started to be broadly present in the environment, if they end up in soil, they may influence both abiotic and biotic soil properties. In this study, the interactions of polyethylene wax together with three biodegradable polyesters PLA, PHB and PBAT with a soil matrix were investigated over a 1-year incubation period. Soil organic matter content was measured using UV-VIS, the microbial biomass amount was measured using qPCR, the mineralisation of polymers was measured using UGA 3000, the surface of polymers was observed with SEM, live/dead microorganisms were determined by fluorescent microscopy and microbial consortia diversity was analyzed using NGS. The amount of humic substances was generally higher in incubations with slowly degrading polyesters, but the effect was temporary. The microbial biomass grew during the incubations; the addition of PHB enhanced fungal biomass whereas PE wax enhanced bacterial biomass. Fungal microbial consortia diversity was altered in incubations with PHB and PBAT. Interestingly, these two polyesters were also covered in biofilm, probably fungal. No such trend was observed in a metagenomic analysis of bacteria, although, bacterial biofilm was probably formed on the PE520 surface. Different methods confirmed the effect of certain polymers on the soil environment.

Achievements and Trends in Biocatalytic Synthesis of Specialty Polymers from Biomass-Derived Monomers Using Lipases

New technologies for the conversion of biomass into high-value chemicals, including polymers and plastics, is a must and a challenge. The development of green processes in the last decade involved a continuous increase of the interest towards the synthesis of polymers using in vitro biocatalysis. Among the remarkable diversity of new bio-based polymeric products meeting the criteria of sustainability, biocompatibility, and eco-friendliness, a wide range of polyesters with shorter chain length were obtained and characterized, targeting biomedical and cosmetic applications. In this review, selected examples of such specialty polymers are presented, highlighting the recent developments concerning the use of lipases, mostly in immobilized form, for the green synthesis of ε-caprolactone co-polymers, polyesters with itaconate or furan units, estolides, and polyesteramides. The significant process parameters influencing the average molecular weights and other characteristics are discussed, revealing the advantages and limitations of biocatalytic processes for the synthesis of these bio-based polymers.

Recent developments in the synthesis of poly(hydroxybutyrate) based biocomposites

Poly(hydroxybutyrate) (PHB) has become an attractive biomaterial in research and development for past few years. It is natural bio-based aliphatic polyester produced by many types of bacteria. Due to its biodegradable, biocompatible, and eco-friendly nature, PHB can be used in line with bioactive species. However, high production cost, thermal instability, and poor mechanical properties limit its desirable applications. So there is need to incorporate PHB with other materials or biopolymers for the development of some novel PHB based biocomposites for value addition. Many attempts have been employed to incorporate PHB with other biomaterials (or biopolymers) to develop sustainable biocomposites. In this review, some recent developments in the synthesis of PHB based biocomposites and their biomedical, packaging and tissue engineering applications have been focused. The development of biodegradable PHB based biocomposites with improved mechanical properties could be used to overcome its native limitations hence to open new possibilities for industrial applications.

Incorporation of Carbon Nanofillers Tunes Mechanical and Electrical Percolation in PHBV:PLA Blends

Biobased fillers, such as bio-derived cellulose, lignin byproducts, and biochar, can be used to modify the thermal, mechanical, and electrical properties of polymer composites. Biochar (BioC), in particular, is of interest for enhancing thermal and electrical conductivities in composites, and can potentially serve as a bio-derived graphitic carbon alternative for certain composite applications. In this work, we investigate a blended biopolymer system: poly(lactic acid) (PLA)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and addition of carbon black (CB), a commonly used functional filler as a comparison for Kraft lignin-derived BioC. We present calculations and experimental results for phase-separation and nanofiller phase affinity in this system, indicating that the CB localizes in the PHBV phase of the immiscible PHBV:PLA blends. The addition of BioC led to a deleterious reaction with the biopolymers, as indicated by blend morphology, differential scanning calorimetry showing significant melting peak reduction for the PLA phase, and a reduction in melt viscosity. For the CB nanofilled composites, electrical conductivity and dynamic mechanical analysis supported the ability to use phase separation in these blends to tune the percolation of mechanical and electrical properties, with a minimum percolation threshold found for the 80:20 blends of 1.6 wt.% CB. At 2% BioC (approximately the percolation threshold for CB), the 80:20 BioC nanocomposites had a resistance of 3.43 × 10 8 Ω as compared to 2.99 × 10 8 Ω for the CB, indicating that BioC could potentially perform comparably to CB as a conductive nanofiller if the processing challenges can be overcome for higher BioC loadings.

Modulating the Tg of Poly(alkylene succinate)s by Inserting Bio-Based Aromatic Units via Ring-Opening Copolymerization

Two series of aliphatic-aromatic copolyesters derived from succinic and 2,5-furandicarboxylic acids, and di-O-2-(hydroxyethyl) resorcinol as diol substituent of either 1,4-butanediol or ethylene glycol, respectively, were obtained by ring opening polymerization(ROP) performed in bulk and catalyzed by Sn(Oct)₂. Cyclic oligomers of furandicarboxylate of di-O-2-(hydroxyethyl) resorcinol were successfully synthesized by high-dilution condensation, and then copolymerized with cyclic oligomers of either butylene or ethylene succinate. The synthesized resorcinol-containing succinate-furanoatecopolyesters had M_w oscillating between 50,000 and 30,000 g·mol⁻¹ depending on composition, and they all displayed a nearly random microstructure. They showed an excellent thermal stability with onset decomposition temperatures near 300 °C. They are amorphous with T_g increasing monotonically with the content in resorcinol in both series with values ranging from −30 or −13 °C for butylene and ethylene-based copolyesters, respectively, up to around 45 °C. The resorcinol-containing succinate-furanoate copolyesters showed appreciable hydrolytic degradation when incubated for a few weeks in water under physiological conditions, a behavior that was notably enhanced in the presence of lipases.

Assessment of models for anaerobic biodegradation of a model bioplastic: Poly(hydroxybutyrate-co-hydroxyvalerate)

Kinetic models of anaerobic digestion (AD) are widely applied to soluble and particulate substrates, but have not been systematically evaluated for bioplastics. Here, five models are evaluated to determine their suitability for modeling of anaerobic biodegradation of the bioplastic poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV): (1) first-order kinetics with and without a lag phase, (2) two-step first-order, (3) Monod (4) Contois, and (5) Gompertz. Three models that couple biomass growth with substrate hydrolysis (Monod, Contois, and Gompertz) gave the best overall fits for the data (R²>0.98), with reasonable estimates of ultimate CH₄ production. The particle size limits of these models were then evaluated. Below a particle size of 0.8mm, rates of hydrolysis and acetogenesis exceeded rates of methanogenesis with accumulation of intermediates leading to a temporary inhibition of CH₄ production. Based on model fit and simplicity, the Gompertz model is recommended for applications in which particle size is greater than 0.8mm.

Melt processability and thermomechanical properties of blends based on polyhydroxyalkanoates and poly(butylene adipate-co-terephthalate)

Polyhydroxyalkanoates were first greatly stabilized by an acid wash, and then reaction extruded to produce blends with enhanced interfacial adhesion.

Efficient Synthesis of Amides and Esters from Alcohols under Aerobic Ambient Conditions Catalyzed by a Au/Mesoporous Al2 O3 Nanocatalyst

An efficient heterogeneous Au/mesoporous alumina nanocatalyst has been successfully developed for the synthesis of amides and esters from simple building blocks of readily available alcohols and amines. The processes were simple and were performed at room temperature and atmospheric pressure of O2 to form the desired products with up to 97 % isolated yield. The ability of Au/mesoporous alumina to catalyze these reactions under ambient conditions further enhances the sustainability of these chemical processes. Furthermore, the nanocatalyst was stable to air and water and could be recovered and reused easily. The enhanced catalytic activity of Au/mesoporous alumina might be attributed to the presence of negatively charged Au nanoparticles that could promote oxidation processes as well as the stability of the mesoporous alumina support calcined at a high temperature of 800 °C.

Production of high levels of poly-3-hydroxybutyrate in plastids of Camelina sativa seeds

Poly-3-hydroxybutyrate (PHB) production in plastids of Camelina sativa seeds was investigated by comparing levels of polymer produced upon transformation of plants with five different binary vectors containing combinations of five seed-specific promoters for expression of transgenes. Genes encoding PHB biosynthetic enzymes were modified at the N-terminus to encode a plastid targeting signal. PHB levels of up to 15% of the mature seed weight were measured in single sacrificed T1 seeds with a genetic construct containing the oleosin and glycinin promoters. A more detailed analysis of the PHB production potential of two of the best performing binary vectors in a Camelina line bred for larger seed size yielded lines containing up to 15% polymer in mature T2 seeds. Transmission electron microscopy showed the presence of distinct granules of PHB in the seeds. PHB production had varying effects on germination, emergence and survival of seedlings. Once true leaves formed, plants grew normally and were able to set seeds. PHB synthesis lowered the total oil but not the protein content of engineered seeds. A change in the oil fatty acid profile was also observed. High molecular weight polymer was produced with weight-averaged molecular weights varying between 600 000 and 1 500 000, depending on the line. Select lines were advanced to later generations yielding a line with 13.7% PHB in T4 seeds. The levels of polymer produced in this study are the highest reported to date in a seed and are an important step forward for commercializing an oilseed-based platform for PHB production.

Biobased copolyesters from renewable resources: synthesis and crystallization behavior of poly(decamethylene sebacate-co-isosorbide sebacate)

A series of biobased copolyesters poly(decamethylene sebacate-co-isosorbide sebacate) are synthesized and their crystallization behavior is explored.

Poly(lactide)-block-poly(ε-caprolactone-co-ε-decalactone)-block-poly(lactide) copolymer elastomers

The midblock composition of poly(lactide)-block-poly(ε-caprolactone-co-ε-decalactone)-block-poly(lactide) is used to tune block polymer melting point, crystallinity, segregation strength and tensile properties.

Diglycerol-based polyesters: melt polymerization with hydrophobic anhydrides

The melt polymerization of diglycerol with bicyclic anhydride monomers derived from a naturally occurring monoterpene provides an avenue for polyesters with a high degree of sustainability. The hydrophobic anhydrides are synthesized at ambient temperature via a solvent-free Diels-Alder reaction of α-phellandrene with maleic anhydride. Subsequent melt polymerizations with tetra-functional diglycerol are effective under a range of [diglycerol]/[anhydride] ratios. The hydrophobicity of α-phellandrene directly impacts the swelling behavior of the resulting polyesters. The low E factors (<2), large amount of bio-based content (>75%), ambient temperature monomer synthesis, and polymer degradability represent key factors in the design of these sustainable polyesters.

Scalable production of mechanically tunable block polymers from sugar

Development of sustainable and biodegradable materials is essential for future growth of the chemical industry. For a renewable product to be commercially competitive, it must be economically viable on an industrial scale and possess properties akin or superior to existing petroleum-derived analogs. Few biobased polymers have met this formidable challenge. To address this challenge, we describe an efficient biobased route to the branched lactone, β-methyl-δ-valerolactone (βMδVL), which can be transformed into a rubbery (i.e., low glass transition temperature) polymer. We further demonstrate that block copolymerization of βMδVL and lactide leads to a new class of high-performance polyesters with tunable mechanical properties. Key features of this work include the creation of a total biosynthetic route to produce βMδVL, an efficient semisynthetic approach that employs high-yielding chemical reactions to transform mevalonate to βMδVL, and the use of controlled polymerization techniques to produce well-defined PLA-PβMδVL-PLA triblock polymers, where PLA stands for poly(lactide). This comprehensive strategy offers an economically viable approach to sustainable plastics and elastomers for a broad range of applications.