Production and characterization of two medium-chain-length polydroxyalkanoates by engineered strains of Yarrowia lipolytica

Background: The oleaginous yeast Yarrowia lipolytica is an organism of choice for the tailored production of various compounds such as biofuels or biopolymers. When properly engineered, it is capable of producing medium-chain-length polyhydroxyalkanoate (mcl-PHA), a biobased and biodegradable polymer that can be used as bioplastics or biopolymers for environmental and biomedical applications.Results: This study describes the bioproduction and the main properties of two different mcl-PHA polymers. We generated by metabolic engineering, strains of Y. lipolytica capable of accumulating more than 25% (g/g) of mcl-PHA polymers. Depending of the strain genetic background and the culture conditions, we produced (i) a mcl-PHA homopolymer of 3-hydroxydodecanoic acids, with a mass-average molar mass (M-w) of 316,000 g/mol, showing soft thermoplastic properties with potential applications in packaging and (ii) a mcl-PHA copolymer made of 3-hydroxyoctanoic (3HO), decanoic (3HD), dodecanoic (3HDD) and tetradecanoic (3TD) acids with a M-w of 128,000 g/mol, behaving like a thermoplastic elastomer with potential applications in biomedical material.Conclusion: The ability to engineer Y. lipolytica to produce tailored PHAs together with the range of possible applications regarding their biophysical and mechanical properties opens new perspectives in the field of PHA bioproduction

Emerging polyhydroxyurethanes as sustainable thermosets: a structure–property relationship

peer reviewedPolyhydroxyurethanes (PHU), obtained from CO2-based cyclic carbonates (CC) and polyamines, are known as greener and safer alternatives to conventional polyurethanes. Interestingly, the hydroxyurethane moieties present along the PHU’s backbone offer unexplored opportunities in terms of enhanced adhesion and mechanical properties that could be a major breakthrough in many structural applications. Furthermore, PHUs have shown thermomechanical recyclability arising from the ability of hydroxyurethane moieties to participate in reversible exchange reactions. However, the relationship between the macromolecular structure, the processability, and the final properties of these materials have not been evaluated to a sufficient extent to establish a comprehensive overview of these emerging thermosets. In this sense, this work aims to address this research gap by investigating the rheological and thermomechanical performances of PHU thermosets and opening an unexplored door for future sustainable engineered structural applications. A special emphasis was put on PHU thermosets formulated using potentially biobased monomers. The rheological behavior during cross-linking of the PHU formulations was studied and highlighted the importance of the number of CC functionalities in the viscosity and gel time, ranging from 10 min to nearly 3 h. Moduli superior to 2 GPa and glass transition over 50 °C were obtained for short multifunctional CC. Finally, the dynamic network behavior of these PHUs was also demonstrated through stress-relaxation and reprocessing. High temperatures (over 150 °C) and pressure lead to a good recovery of the thermomechanical properties. Such materials appear to be an interesting platform for structural applications, particularly fiber-reinforced polymers, that can overcome many sustainability challenges.The " Non-Isocyanate Polyurethanes - European Joint Doctorate " [ NIPU-EJD

Melt memory effects in poly(Butylene succinate) studied by differential fast scanning calorimetry

none4It is widely accepted that melt memory effect on polymer crystallization depends on thermal history of the material, however a systematic study of the different parameters involved in the process has been neglected, so far. In this work, poly(butylene succinate) has been selected to analyze the effect of short times and high cooling/heating rates that are relevant from an industrial point of view by taking advantage of fast scanning calorimetry (FSC). The FSC experiments reveal that the width of melt memory temperature range is reduced with the time spent at the self-nucleation temperature (Ts), since annealing of crystals occurs at higher temperatures. The effectiveness of self-nuclei to crystallize the sample is addressed by increasing the cooling rate from Ts temperature. The effect of previous standard state on melt memory is analyzed by (a) changing the cooling/heating rate and (b) applying successive self-nucleation and annealing (SSA) technique, observing a strong correlation between melting enthalpy or crystallinity degree and the extent of melt memory. The acquired knowledge can be extended to other semicrystalline polymers to control accurately the melt memory effect and therefore, the time needed to process the material and its final performance.noneSangroniz L.; Ocando C.; Cavallo D.; Muller A.J.Sangroniz, L.; Ocando, C.; Cavallo, D.; Muller, A. J

Towards sustainable reprocessable structural composites: benzoxazines as biobased matrices for natural fibers

In this work, we synthesized and investigated three fully biobased benzoxazine matrices containing exchangeable ester bonds for natural fiber composites. The thermoset properties were investigated and the transesterification behavior was assessed. The obtained polymers show high tunability. Using isosorbide as the starting building block, the thermoset exhibits a glass transition of 130 °C, a bending modulus of 2.5 GPa, and thermal stability leading to degradation occurring after 270 °C with 31% char at 800 °C. All formulations stress relax under catalyst-free conditions within an hour with properties recovery superior to 80%. Finally, flax composites were manufactured. We highlight strong affinities between the matrices and the fibers through high mechanical performances with a modulus over 30 GPa and stress at break of 400 MPa in the longitudinal direction. 5 GPa modulus and 47 MPa stress at break were found in the transverse direction. Excellent fire retardancy properties, with self-extinguishment and UL-94 V1 classification were obtained for the isosorbide-based/flax composite. The obtained composites were able to be welded with comparable results to glued ones, paving the way to processable laminates and stable cured prepreg perfectly suited for transportation-engineered applications

Fabrication and properties of alginate-hydroxyapatite biocomposites as efficient biomaterials for bone regeneration

Restricted self-recovery that pursues a bone injury and the need of inexpensive and painless clinical treatments for tissue regeneration require new pathways developments to fabricate biocompatible and biodegradable scaffolding materials. For these requirements, covalent crosslinked alginate and alginate/Mg-doped hydroxyapatite (MgHAp) hydrogels are fabricated by "click" chemistry to mimic highly porous structures with the dimensional hierarchy of bone tissue. Cells viability, proliferation and cytotoxicity are reported. These scaffolds show high pore volume with adequate size and interconnectivity for osseous tissue regeneration. An uniform dispersion of low content of bioactive MgHAp nanoparticles on the surface of pore walls allows a good pre-osteoblast cell attachment and proliferation

A novel paradigm approach to design structural natural fiber composites from fully sustainable CO2-derived thermosets with outstanding interfacial strength and circular features

We herein propose capitalizing on strong hydrogen bonding from novel bio-CO2-derived dynamic thermosets to achieve high-performance natural fiber composites (NFC) with circular features. CO2- and biomass-derived polyhydroxyurethane (PHU) thermosets were selected, for the first time of our knowledge, as matrices for their ability to make strong H-bond, resulting in outstanding mechanical properties for NFC. Exploiting this H-bond key feature, exceptional interface bonding between flax and PHU was confirmed by atomic force microscopy and rationalized by atomistic simulation. Without any treatment, an increase of 30% of stiffness and strength was unveiled compared to an epoxy benchmark, reaching 35 GPa and 440 MPa respectively. Related to the thermoreversible nature of hydroxyurethane moieties, cured flax-PHU were successfully self-welded and displayed promising properties, together with recyclability features. This opens advanced opportunities that cannot be reached with epoxy-based composites. Implementing CO2-derived thermosets in NFC could lead to more circular materials, critical for achieving sustainability goals

Polymorphism and Multiple Melting Behavior of Bio-Based Poly(propylene 2,5-furandicarboxylate)

Furandicarboxylate-based polyesters are considered an interesting class of bio-based polymers due to their improved properties with respect to the petrol-based terephthalate homologs. An in-depth analysis of the crystal structure of poly(propylene 2,5-furandicarboxylate) (PPF), after maximum possible removal of the catalyst, was carried out. The study disclosed that purified PPF presents two different crystalline phases after crystallization from the melt. Crystallizations at temperatures lower than 120 \ub0C lead to growth of a single crystal form (\u3b2-form), whereas two different crystal forms (\u3b1 and \u3b2) were found to coexist at higher Tcs. This behavior is opposite to that previously observed for unpurified PPF. The possibility that the catalyst nucleates the \u3b1-phase, which therefore becomes the kinetically favored modification at low crystallization temperatures in the presence of a higher amount of catalyst residue, has been considered as a feasible explanation. Two concomitantly different spherulitic morphologies were observed and connected to the \u3b2- and \u3b1-phase, respectively. The association between polymorphism and melting behavior was studied. The origin of the peaks that compose the multiple melting endotherm recorded at conventional heating rates was determined by combined wide-angle X-ray scattering, differential scanning calorimetry, fast scanning chip calorimetry, and polarized light optical microscopy measurements. The higher thermal stability of the \u3b1-crystals in comparison with the \u3b2-form was thus demonstrated

Structure and properties of a semifluorinated diblock copolymer modified epoxy blend

Novel nanostructured thermosetting materials have been prepared by modification of an epoxy resin with a semifluorinated diblock copolymer, poly(heptadecafluorodecyl acrylate)-b-poly(caprolactone), PaF-b-PCL. In a first step, the phase behavior and linear viscoelasticity of PaF-b-PCL were investigated. According to the segregation regime, no order-order transitions were detected, being the order-disorder transition temperature beyond the degradation temperature. Atomic force microscopy (AFM) images of the block copolymer after different thermal treatments revealed that self-assembly takes place into spherical nanodomains, which is consistent with the copolymer composition. This block copolymer was further used to prepare a nanostructured thermoset blend with an epoxy resin. DSC and DMA analysis reveals microphase separation of PaF block from the epoxy-rich phase after curing. The PaF block self-assembled into wormlike and spherical micelles in the thermoset system. This nanostructured blend presented unique surface properties showing high hydrophobicity (upsilon = 109 degrees) and low surface energy (17 mN/m).NANOTRON project; MAT2003-08125; Nanostructured and functional polymer-based materials and nanocomposites (NANOFUN-POLY) projec