Publications

In the area of coating development, it is extremely difficult to find a substitute for bisphenol A diglycidyl ether (DGEBA), the classical petroleum-based raw material used for the formulation of epoxy thermosets. This epoxy resin offers fast curing reaction with several hardeners and the best thermal and chemical resistance properties for applications in coatings and adhesive technologies. In this work, a new biobased epoxy, derived from poly(limonene carbonate) oxide (PLCO), was combined with polyetheramine and polyamineamide curing agents, offering a spectrum of thermal and mechanical properties, superior to DGEBA-based thermosets. The best formulation was found to be a combination of PLCO and a commercial curing agent (Jeffamine) in a stoichiometric 1:1 ratio. Although PLCO is a solid due to its high molecular weight, it was possible to create a two-component partially biobased epoxy paint without the need of volatile organic compounds (i.e., solvent-free formulation), intended for use in coating technology to partially replace DGEBA-based thermosets.

JTD Keywords: acid, adhesion, epoxy thermoset, mechanical properties, monomer, polycarbonates, polymers, protection, resins, solvent-free paint, thermal properties, Adhesives, Biobased epoxy, Bisphenol-a-diglycidyl ethers, Carbonation, Coating development, Coating technologies, Curing, Curing agents, Epoxy coatings, Epoxy resins, Epoxy thermoset, Epoxy thermosets, Limonene oxide, Mechanical properties, Monoterpenes, Paint, Poly(limonene carbonate) oxide, Solvent free, Solvent-free paint, Thermal properties, Thermosets, Volatile organic compounds

Different copolymers incorporating terpene oxide units (e.g., limonene oxide) have been evaluated considering thermal properties, degradability, and biocompatibility. Thus, polycarbonates and polyesters derived from aromatic, monocyclic and bicyclic anhydrides have been considered. Furthermore, ring substitution with myrcene terpene has been evaluated. All polymers were amorphous when evaluated directly from synthesis. However, spherulites could be observed after the slow evaporation of diluted chloroform solutions of polylimonene carbonate, with all isopropene units possessing an R configuration. This feature was surprising considering the reported information that suggested only the racemic polymer was able to crystallize. All polymers were thermally stable and showed a dependence of the maximum degradation rate temperature (from 242 °C to 342 °C) with the type of terpene oxide. The graduation of glass transition temperatures (from 44 °C to 172 °C) was also observed, being higher than those corresponding to the unsubstituted polymers. The chain stiffness of the studied polymers hindered both hydrolytic and enzymatic degradation while a higher rate was detected when an oxidative medium was assayed (e.g., weight losses around 12% after 21 days of exposure). All samples were biocompatible according to the adhesion and proliferation tests performed with fibroblast cells. Hydrophobic and mechanically consistent films (i.e., contact angles between 90° and 110°) were obtained after the evaporation of chloroform from the solutions, having different ratios of the studied biobased polyterpenes and poly(butylene succinate) (PBS). The blend films were comparable in tensile modulus and tensile strength with the pure PBS (e.g., values of 330 MPa and 7 MPa were determined for samples incorporating 30 wt.% of poly(PA-LO), the copolyester derived from limonene oxide and phthalic anhydride. Blends were degradable, biocompatible and appropriate to produce oriented-pore and random-pore scaffolds via a thermally-induced phase separation (TIPS) method and using 1,4-dioxane as solvent. The best results were attained with the blend composed of 70 wt.% PBS and 30 wt.% poly(PA-LO). In summary, the studied biobased terpene derivatives showed promising properties to be used in a blended form for biomedical applications such as scaffolds for tissue engineering.

JTD Keywords: alternating copolymerization, biobased materials, biodegradability, composites, crystallization, cyclohexene oxide, induced phase-separation, limonene oxide, mechanical-properties, polyesters, scaffolds, spherulites, terpene derivatives, thermal properties, thermally-induced phase separation, Acetone, Bio-based, Bio-based materials, Biobased materials, Biocompatibility, Biodegradability, Butenes, Cell culture, Chlorine compounds, Degradation, Evaporation, Glass transition, Limonene oxide, Monoterpenes, Phase separation, Poly (butylenes succinate), Polybutylene succinate, Property, Ring-opening copolymerization, Scaffolds, Spheru-lites, Tensile strength, Terpene derivatives, Thermal properties, Thermally induced phase separation, Thermally-induced phase separation, Thermally?induced phase separation, Thermodynamic properties, Thermogravimetric analysis

© 2020 Hydrolytic degradation of poly(4-hydroxybutyrate) (P4HB) films has been studied considering media of different pH values (i.e., 3, 7 and 10) and temperatures (i.e., 37 and 55 °C). Enzymatic degradation has also been evaluated at physiological conditions using two different lipases: Pseudomonas cepacia and Rhizopus oryzae. Different bulk and surface erosion mechanisms with random chain scissions and successive removal of monomer units have been supported through weight loss measurements, molecular weight determinations by GPC and NMR spectroscopy and changes on thermal properties by DSC. Thermal annealing during exposure to different media and even degradation influenced on the melting temperature and crystallinity of samples, as well as on the lamellar geometrical parameters as evaluated by SAXS. Enzymatic degradation was ideal to selectively eliminate the amorphous regions and highlight the spherulitic morphology. Presence of ringed textures were therefore evident in bright field optical micrographs in addition to SEM images, namely observations under polarized light was not necessary to distinguish the presence of banded spherulites. Rhizopus oryzae was revealed to be the most suitable enzyme to crop out the P4HB spherulites that form part of the initial smooth surfaces of solvent casting films. After determining the appropriate activity and exposure time, the presence of rings constituted by cooperative C-shaped edge-on lamellae and flat-on lamellae was highlighted.

JTD Keywords: biodegradable polymers, enzymatic degradation, films, hydrolytic degradation, microstructure, thermal properties, Biodegradable polymers, Enzymatic degradation, Films, Hydrolytic degradation, Microstructure, Poly(4-hydroxybutyrate), Thermal properties

Blends with different ratios of polylactide and polyamide 6,10 (PA610) have been prepared by melt-mixing using a Brabender mixer equipment. Previously, a rheologically modified polylactide (PLAREx) was obtained through reactive extrusion using a multifunctional epoxide agent. It was expected that unreacted epoxy groups of PLAREx were able to improve the compatibility between the two polymers. SEM observations revealed a logical dependence of the morphology of immiscible phases with composition, and more interestingly a co-continuity at relatively low PA content (around 50%) was detected. This result contrasts with previous observations performed with non-modified PLA. Confined PA domains increased with the PA content and hardly crystallized at the typical crystallization temperature of the pure PA (195 °C). Synchrotron X-ray diffraction studies indicated that a PA crystallization at a lower temperature close to 120 °C was enhanced and led to a pseudohexagonal γ phase that differs from the characteristic layered structure of PA610. SAXS data revealed also that well differentiated lamellar entities could be assigned at both immiscible polymer phases. Clear differences were observed in the spherulitic morphologies attained under isothermal melt crystallization experiments. Results indicated that the texture of PLAREx spherulites was modified by the presence of PA. Compatibilization of PA molecules on the crystal lamellar boundaries of PLAREx led to an enhancement of the lamellar twisting frequency. Optical microscopy results also indicated that the crystal growth rate of PLAREx increased by the incorporation of PA, but in contrast this had an adverse effect on the nucleation process.

JTD Keywords: Crystal growth rate, Epoxy modified polylactide, Nucleation, Polyamide 6,10, Polyamide crystalline structure, Polyamide/polylactide blend morphology, Thermal properties