Substantial effect of water on radical melt crosslinking and rheological properties of poly(ε-caprolactone)

One-step reactive melt processing (REx) via radical reactions was evaluated with the aim of improving the rheological properties of poly(ε-caprolactone) (PCL). In particular, a waterassisted REx was designed under the hypothesis of increasing crosslinking efficiency with water as a low viscous medium in comparison with a slower PCL macroradicals diffusion in the melt state. To assess the effect of dry vs. water-assisted REx on PCL, its structural, thermo-mechanical and rheological properties were investigated. Water-assisted REx resulted in increased PCL gel fraction compared to dry REx (from 1–34%), proving the rationale under the formulated hypothesis. From dynamic mechanical analysis and tensile tests, the crosslink did not significantly affect the PCL mechanical performance. Dynamic rheological measurements showed that higher PCL viscosity was reached with increasing branching/crosslinking and the typical PCL Newtonian behavior was shifting towards a progressively more pronounced shear thinning. A complete transition from viscous-to solid-like PCL melt behavior was recorded, demonstrating that higher melt elasticity can be obtained as a function of gel content by controlled REx. Improvement in rheological properties offers the possibility of broadening PCL melt processability without hindering its recycling by melt processing

Reactive melt crosslinking of cellulose nanocrystals/poly(ε-caprolactone) for heat-shrinkable network

Focusing on the challenge of non-biodegradable plastics replacement, we propose a design for peroxide-initiated crosslinking of biodegradable poly(ε-caprolactone) (PCL) and renewable cellulose nanocrystals (CNCs) bionanocomposites. An industrially scalable water-assisted reactive melt-processing (REx) is studied to explore the hypothesis of synergy between simultaneous effects of water on improving CNC dispersion and boosting PCL branching/crosslinking. We demonstrate that the melt processing control enables the preparation of targeted thermoplastic/thermoset bionanocomposites with gel content up to ≈ 40 %, identified as the limit of their melt-processability. Structural characterization reveals that ≈ 70 wt% of the initial CNC content is irreversibly incorporated in a percolating network, enhancing the crosslinked bionanocomposites properties. The bionanocomposites\u27 complex viscosity and elastic character increase with the gel content, thus improving PCL melt performance. Furthermore, the irreversible entrapment of CNCs in the 3D percolating network provides heat-shrinkability, indicating a potential of the reacted bionanocomposites for heat-triggered shape-memory

Nanocluster-Based Drug Delivery and Theranostic Systems: Towards Cancer Therapy

Over the last decades, the global life expectancy of the population has increased, and so, consequently, has the risk of cancer development. Despite the improvement in cancer therapies (e.g., drug delivery systems (DDS) and theranostics), in many cases recurrence continues to be a challenging issue. In this matter, the development of nanotechnology has led to an array of possibilities for cancer treatment. One of the most promising therapies focuses on the assembly of hierarchical structures in the form of nanoclusters, as this approach involves preparing individual building blocks while avoiding handling toxic chemicals in the presence of biomolecules. This review aims at presenting an overview of the major advances made in developing nanoclusters based on polymeric nanoparticles (PNPs) and/or inorganic NPs. The preparation methods and the features of the NPs used in the construction of the nanoclusters were described. Afterwards, the design, fabrication and properties of the two main classes of nanoclusters, namely noble-metal nanoclusters and hybrid (i.e., hetero) nanoclusters and their mode of action in cancer therapy, were summarized

Development of Low-Viscosity and High-Performance Biobased Monobenzoxazine from Tyrosol and Furfurylamine

This work details the scalable and solventless synthesis of a potential fully biobased monobenzoxazine resin derived from tyrosol and furfurylamine. The structure of the monomer was studied by nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FTIR). The curing of the precursors was characterized by differential scanning calorimetry (DSC), rheological measurements, and thermogravimetric analysis (TGA). The properties of the resulting biobased polybenzoxazine were then determined by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMA). A thermally stable resin was obtained with 5% and 10% weight-reduction-temperature (Td5 and Td10) values of 349 and 395 °C, respectively, and a char yield of 53%. Moreover, the low melting temperature, low viscosity, and excellent thermomechanical behavior make this fully biobased resin a promising candidate for coating applications

Development of Inherently Flame—Retardant Phosphorylated PLA by Combination of Ring-Opening Polymerization and Reactive Extrusion

In this study, a highly efficient flame-retardant bioplastic poly(lactide) was developed by covalently incorporating flame-retardant DOPO, that is, 9,10-dihydro-oxa-10-phosphaphenanthrene-10-oxide. To that end, a three-step strategy that combines the catalyzed ring-opening polymerization (ROP) of L,L-lactide (L,L-LA) in bulk from a pre-synthesized DOPO-diamine initiator, followed by bulk chain-coupling reaction by reactive extrusion of the so-obtained phosphorylated polylactide (PLA) oligomers (DOPO-PLA) with hexamethylene diisocyanate (HDI), is described. The flame retardancy of the phosphorylated PLA (DOPO-PLA-PU) was investigated by mass loss cone calorimetry and UL-94 tests. As compared with a commercially available PLA matrix, phosphorylated PLA shows superior flame-retardant properties, that is, (i) significant reduction of both the peak of heat release rate (pHRR) and total heat release (THR) by 35% and 36%, respectively, and (ii) V0 classification at UL-94 test. Comparisons between simple physical DOPO-diamine/PLA blends and a DOPO-PLA-PU material were also performed. The results evidenced the superior flame-retardant behavior of phosphorylated PLA obtained by a reactive pathway

Cold Sintering Process for developing hydroxyapatite ceramic and polymer composite

International audienceCold sintering process (CSP) is a non-conventional, low-energy sintering technique that promotes thedensification of ceramics in the presence of transient liquids under low temperatures (≤300°C) andpressures (≤500 MPa). Additionally, it provides a new strategy for the co-sintering of ceramic andpolymers into a single system which is not feasible through conventional methods. Exploiting theadvantages of cold sintering, this investigation has aimed to densify the hydroxyapatite (HA) atnanoscale as well as the co-sintering of HA/polylactic acid (PLA) based composite for boneregeneration applications. The importance of liquid phase chemistry in cold sintering of HA wasassessed using water, acetic acid, and phosphoric acid as liquids. The changes in relative density wasobserved with respect to the nature of liquid/ionic concentrations (0.5M, 1.0M, & 2M). In the case ofcomposites, the influence of different compatibilizers on the homogeneous integration of HA/PLAcomposite was examined. Eventually, this study contributes critical fundamental knowledge pertainingto the development of dense HA ceramics and polymer composites. Specifically, it underscores theimportance of liquid phase chemistry in the cold sintering of HA as well as the influence ofcompatibilizers in co-sintering of HA/PLA composites

The complex amorphous phase in poly(butylene succinate-ran-butylene azelate) isodimorphic copolyesters

Poly(butylene succinate-ran-butylene azelate) random copolyesters (PBS-ran PBAz) were studied using broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). These copolymers are characterized by being isodimorphic and by displaying a eutectic behavior. Depending on their composition, the PBS-rich phase, the PBAz-rich phase, or both phases can crystallize. The complex development of the amorphous phase, especially at compositions around the eutectic point was demonstrated by BDS results. The comonomer fraction included in the amorphous phase was quantified from the relaxation strength of the dielectric β relaxations, and thus the crystalline fraction can be calculated. The good agreement between the values determined from BDS and the crystallinity obtained from DSC experiments demonstrates that the degree of comonomer exclusion in these random copolymers during crystallization is far larger than comonomer inclusion. However, the glass transition temperatures determined from the dielectric α relaxation behavior are lower in most of the copolymers than those measured by DSC, whereas they are about the same in the homopolymers. This result is probably caused by a significant amount of amorphous phase in the copolymers that is not influenced by crystallinity. Furthermore, the crystallization behavior of these copolymers at different cooling protocols showed that the α relaxation depends not only on the crystalline fraction but also on the details of the crystallization process in these complex multiphasic copolymers.I.A. acknowledges the fellowship from the University of the Basque Country UPV/EHU. Financial support is acknowledged from UPV/EHU (UFI11/56), “UPV/EHU Infrastructure: INF 14/38”; “Mineco/FEDER: SINF 130I001726XV1/Ref: UNPV13-4E-1726” and “Mineco MAT2014-53437-C2-P”. R.M. gratefully acknowledges financial support from the Wallonia and European Commission in the frame of the BIOMAT/FEDER project and the Interuniversity Attraction Pole program of the Belgian Federal Science Policy Office (PAI 7/05). A.A. acknowledges financial support from the Projects MAT2015-63704-P (Spanish-MINECO and EU) and IT-654-13 (Basque Government).Peer Reviewe

The Impact of Diethyl Furan-2,5-dicarboxylate as an Aromatic Biobased Monomer toward Lipase-Catalyzed Synthesis of Semiaromatic Copolyesters

International audienceFuran-2,5-dicarboxylic acid has been introduced in recent years as a green aromatic monomer toward the design of aromatic (co)polyesters with enhanced properties, i.e., polyethylene furanoate (PEF) that can definitely compete with its petroleum-based counterpart, i.e., polyethylene terephthalate (PET). In an attempt to produce biobased semiaromatic copolyesters in an efficient eco-friendly approach, we report herein the polycondensation of diethyl furan-2,5-dicarboxylate (DEFDC) with different aliphatic diols and diesters of variable chain length catalyzed by an immobilized lipase from Candida antarctica using a two-step polymerization reaction carried out in diphenyl ether. The influence of diol and diester chain length, the molar concentration of DEFDC, and the effect of enzyme loading were assessed via nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and wide-angle X-ray scattering (WAXS). With high quantities of DEFDC, significant differences in terms of M̅n buildup were noticed. Only longer diols starting from octane-1,8-diol successfully reacted with up to 90% DEFDC as opposed to only 25% DEFDC reacting with short diols such as butane-1,4-diol. While varying the chain length of the diester, it was evident that shorter diols such as hexane-1,6-diol have better reactivity toward longer diesters, while dodecane-1,12-diol was reactive toward all tested diesters. The incorporation of long chain fatty dimer diols such as Pripol 2033 led to polyesters with higher M̅n and was successfully used to overcome the limitations of poor reactivity observed in the case of short diols in the presence of high furan content. The DSC results showed a pseudoeutectic behavior as a function of increasing the mol % of DEFDC, and a change in the crystalline phase was confirmed via WAXS analysis. Finally, this work showed the successful enzyme-catalyzed synthesis of several DEFDC biobased semiaromatic copolyesters with variable interesting properties that can be further optimized for possible applications in food packaging as well as other possibilities.L'acide furane-2,5-dicarboxylique a été introduit ces dernières années en tant que monomère aromatique vert pour la conception de (co)polyesters aromatiques aux propriétés améliorées, comme le polyéthylène furanoate (PEF) qui peut définitivement concurrencer son homologue issu du pétrole, le polyéthylène téréphtalate (PET). Dans le but de produire des copolyesters semi-aromatiques d'origine biologique par une approche efficace et respectueuse de l'environnement, nous rapportons ici la polycondensation du furan-2,5-dicarboxylate de diéthyle (DEFDC) avec différents diols et diesters aliphatiques de longueur de chaîne variable, catalysée par une lipase immobilisée de Candida antarctica, en utilisant une réaction de polymérisation en deux étapes réalisée dans de l'éther diphénylique. L'influence de la longueur de chaîne des diols et des diesters, la concentration molaire de DEFDC, ainsi que l'effet de la charge enzymatique ont été évalués par Résonance Magnétique Nucléaire (RMN), chromatographie par perméation de gel (CPG), calorimétrie différentielle à balayage (DSC) et diffusion des rayons X à angle large (WAXS). Sans DEFDC, ou à faible teneur, l'augmentation de la longueur du diol n'a pas eu d'effet négatif sur la masse moléculaire moyenne en nombre (Mn) des copolyesters aliphatiques préparés. En revanche, lorsque des quantités élevées de DEFDC (plus de 40 % molaire) ont été ajoutées dans le milieu réactionnel, des différences significatives en termes d'accumulation de Mn ont été remarquées. Seuls les diols plus longs à partir de l'octane-1,8-diol ont été mis en réaction avec succès avec jusqu'à 90% de DEFDC, par opposition à seulement 25% de DEFDC avec des diols courts tels que le butane-1,4-diol. Le Mn obtenu a montré une tendance à diminuer en fonction de l'augmentation du % d'alimentation en DEFDC, surtout avec les diols courts où la diminution du Mn était plus prononcée. En faisant varier la longueur de la chaîne du diester, il était évident que les diols plus courts tels que l'hexane-1,6-diol ont une meilleure réactivité vis-à-vis des diesters plus longs, tandis que le dodécane-1,12-diol était réactif vis-à-vis de tous les diesters testés. L'incorporation de diols dimères gras à longue chaîne tels que le Pripol 2033 dans le milieu réactionnel a conduit à des polyesters avec un Mn plus élevé et a été utilisé avec succès pour surmonter les limitations de la faible réactivité observée dans le cas des diols courts en présence d'une teneur élevée en furanes. Les résultats de la calorimétrie différentielle à balayage (DSC) ont montré un comportement pseudo-eutectique caractérisé par une diminution du point de fusion (Tm) en fonction de l'augmentation du % molaire de DEFDC, suivie d'une augmentation à un % molaire plus élevé deࣙࣙ DEFDC (≥ 50%) et un changement de la phase cristalline confirmé par une analyse de diffusion des rayons X à grand angle (WAXS). Enfin, ce travail a montré la synthèse réussie par catalyse enzymatique de plusieurs copolyesters semi-aromatiques biosourcés avec des propriétés intéressantes variables, à base de DEFDC

Synthesis, characterization and stereocomplexation of polyamide 11/polylactide diblock copolymers

The present work deals with the building of novel, fully bio-based polyamide 11 (PA11)/polylactide (PLA) diblock copolymers (PA11xPLAy). The adopted two-step synthetic strategy involves first the preparation of an amino-terminated PA11 prepolymer (i.e., having the amino end-group available and the carboxylic one protected), to be employed subsequently as a macro-initiator in the ring-opening polymerization of D-lactide (or L-lactide). Upon tuning the lactide conversion, diblock copolymers with different PA11/PLA ratios are targeted and achieved, as demonstrated by1H NMR and TGA analysis. The thermal properties of these double-crystalline polymers are characterized by means of DSC. Finally, fast stereocomplexation is demonstrated upon mixing the enantiomeric PA11xPLAydiblock pairs. Indeed, the idea behind these systems is to conjugate the properties of PLA with those of the high-performance PA11, in a cumulative rather than intermediate fashion, as for widely reported random poly(ester amide)s, but without phase separation occurring, which is the case for PLA/PA11 immiscible blends. In addition, the presence of the stereocomplex, well-known for its improved chemical/thermal resistance over PLA homopolymer, could impart even further quality to the final materials

Chemical force microscopy of stimuli-responsive adhesive copolymers

Atomic force microscopy with chemically sensitive tips was used to investigate the hydrophobic and electrostatic interaction forces of a stimuli-responsive adhesive polymer, and their dynamic changes in response to water immersion and salt concentration. Block copolymer-filled coatings were obtained by incorporating an amphiphilic block copolymer containing a polydimethylsiloxane (PDMS) block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block in a PDMS matrix. Topographic images of fresh samples revealed the presence of nanoscale domains associated with the presence of copolymers,covered by a thin layer of PDMS. Prolonged (30 days) immersion in aqueous solution led to the exposure of the hydrophilic PDMAEMA chains on the surface. Using adhesion force mapping with hydrophobic tips, we showed that fresh samples were uniformly hydrophobic, while aged samples exhibited lower surface hydrophobicity and featured nanoscale hydrophilic copolymer domains. Force mapping with negatively charged tips revealed remarkable salt-dependent force plateau signatures reflecting desorption of polyelectrolyte copolymer chains. These nanoscale experiments show how solventinduced conformational changes of stimuli-responsive copolymers can be used to modulate surface adhesion