Connie Ocando

Nonisocyanate polyurethanes are sustainable alternatives to conventional polyurethanes but often exhibit limited mechanical performance. Here, poly(hydroxyurethane) (PHU)–epoxy hybrid networks were prepared to tune matrix stiffness through covalent cross-linking and reinforced with wood- and tunicate-derived cellulose nanocrystals (CNCs). Increasing epoxy content enhanced Young’s modulus and tensile strength while reducing strain at break. In contrast, incorporation of CNCs into an intermediate PHU–epoxy matrix produced substantial mechanical enhancement at low loadings. Tunicate-derived CNCs, characterized by higher aspect ratios, provided greater reinforcement than wood-derived CNCs and achieved a maximum toughness of ∼27 MJ m–3 at 2 wt %, exceeding both wood-derived CNC nanocomposites (≤17 MJ m–3) and neat PHU–epoxy hybrids (≤16.5 MJ m–3). Scanning electron microscopy confirmed homogeneous CNC dispersion, while Fourier transform infrared spectroscopy indicated extensive hydrogen-bonding interactions. These results demonstrate that epoxy hybridization and high-aspect-ratio CNC reinforcement provide complementary routes to enhance the mechanical performance of biobased PHU materials.

Incorporating biobased nanofillers including cellulose nanocrystals (CNCs) and chitin nanocrystals (ChNCs) into nonisocyanate polyurethane (NIPU) offers a multifunctional approach to improving mechanical and thermal properties while promoting sustainability and green chemistry. Nanocomposites of segmented thermoplastic polyhydroxyurethane (PHU) from vanillyl alcohol bis(cyclocarbonate) (VABC), poly(tetramethylene oxide) diamine (PTMODA), and bis(aminomethyl) norbornane (NORB) reinforced with a low amount of CNCs and partially deacetylated ChNCs were prepared and characterized. Fourier transform infrared spectroscopy, atomic force microscopy, and small-angle X-ray scattering revealed that partially deacetylated ChNCs were covalently grafted to the PHU through aminolysis of carbonate end groups in the hard segment, while CNCs were mixed with the PHU without interfacial covalent bonding. Consequently, the PHU/ChNC nanocomposites showed nanophase separation with smaller hard domains compared to neat PHU, while the PHU/CNC nanocomposites exhibited a phase-mixed system with broader interface regions. Dynamic mechanical analysis and tensile tests further revealed that the PHU/ChNC nanocomposites demonstrated a 49-fold increase in Young's modulus, a 20-fold increase in ultimate tensile strength, and a three-order-of-magnitude enhancement in storage modulus in the rubbery state compared to the PHU/CNC nanocomposites, highlighting the profound influence of interfacial covalent linkages in enhancing the thermal mechanical performance of segmented PHU.

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.

It 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 (T_s), 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 T_s 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.

Furandicarboxylate-based polyesters are considered an interesting class of bio-based polymers, due to their improved properties with respect to the petrol-based terephthalate homologues. 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 °C leads to growth of a single crystal form (-form), whereas two different crystal forms ( and ) 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 -phase, which therefore becomes the kinetically favored modification at low crystallization temperatures in the presence of a higher amount of catalyst residues, has been considered as feasible explanation. Two concomitant different spherulitic morphologies were observed, and connected to the - and -phase, respectively. The association between polymorphism and melting behavior was studied. The peaks that compose the multiple melting endotherm recorded at conventional heating rates were assigned by means of 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 -crystals in comparison with the -form was thus demonstrated.