Titanium dioxide (TiO2) nanoparticles have recently appeared in PET waste because of the introduction of opaque PET bottles. We prepare polymer blend nanocomposites (PBNANOs) by adding hydrophilic (hphi), hydrophobic (hpho), and hydrophobically modified (hphoM) titanium dioxide (TiO2) nanoparticles to 80rPP/20rPET recycled blends. Contact angle measurements show that the degree of hydrophilicity of TiO2 decreases in the order hphi > hpho > hphoM. A reduction of rPET droplet size occurs with the addition of TiO2 nanoparticles. The hydrophilic/hydrophobic balance controls the nanoparticles location. Transmission electron microscopy (TEM_ shows that hphi TiO2 preferentially locates inside the PET droplets and hpho at both the interface and PP matrix. HphoM also locates within the PP matrix and at the interface, but large loadings (12%) can completely cover the surfaces of the droplets forming a physical barrier that avoids coalescence, leading to the formation of smaller droplets. A good correlation is found between the crystallization rate of PET (determined by DSC) and nanoparticles location, where hphi TiO2 induces the highest PET crystallization rate. PET lamellar morphology (revealed by TEM) is also dependent on particle location. The mechanical behavior improves in the elastic regime with TiO2 addition, but the plastic deformation of the material is limited and strongly depends on the type of TiO2 employed.

We study the non-isothermal crystallization and morphology of two triblock terpolymers of practically perfect linear polyethylene (PE), poly­(ethylene oxide) (PEO) or poly­(ε-caprolactone) (PCL), and poly­(l-lactide) (PLLA) with three crystallizable blocks. The two triblock terpolymers PE21 2.6 -b-PEO32 4.0 -b-PLLA47 5.9 and PE21 7.1 -b-PCL12 4.2 -b-PLLA67 23.0 (subscripts indicate the composition in wt %, and superscripts refer to the number average molecular weights in kg/mol) were synthesized by a combination of polyhomologation and ring-opening polymerization techniques, using a “catalyst-switch” strategy. We have applied cooling ramps from the melt at 20 and 1 °C/min while simultaneously performing in situ SAXS/WAXS (small-angle X-ray scattering/wide-angle X-ray scattering) measurements. Parallel experiments performed by differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) at identical rates allowed us to unequivocally identify the crystallization sequence of the three blocks from the melt, as well as their superstructural morphology. SAXS indicated that the samples are weakly segregated in the melt as breakout occurs upon crystallization. WAXS and DSC results demonstrated that when the crystallization occurs at 20 °C/min, the blocks crystallize in the following peculiar sequence: PE first, then PLLA, and finally PEO or PCL depending on the triblock terpolymer. The faster crystallization kinetics of the PE block, in comparison with the PLLA block, is responsible for this crystallization sequence. Only when the cooling rate is reduced to 1 °C/min can the PLLA block crystallize first and only for the terpolymer with the highest amount of PLLA. The cooling conditions determine the morphology and properties of these fascinating materials.

Catechol-containing molecules have been recognized as versatile building blocks for polymer structures with tailormade functional properties. While catechol chemistry via metal− ligand coordination, boronate complexation, and oxidation-driven covalent bonds has been well examined in the past, the hydrogen bonding ability of these intriguing molecules has been dismissed. In this research, we investigated the gelation of poly(vinyl alcohol) (PVA) triggered by the crystallization of a 3,4-dihydroxy-catechol in water. Strong hydrogen bond interactions between PVA and catechol groups afforded supramolecular hydrogels with nearcovalent elastic moduli, yet dynamic, exhibiting reversible gel-tosol phase transitions around 50−60 °C. We studied the impact of the catechol derivative concentration on the gelation kinetics and physicochemical properties of these dynamic materials. Isothermal experiments revealed that heterogeneous crystallization governs the gelation kinetics. Moreover, because of the quasi-permanent cross-links within the supramolecular polymer network, these hydrogels benefit from ultrastretchability (∼600%) and high toughness (900 kJ•m −3 ). Our gelation approach is expected to expand the toolbox of catechol chemistry, opening up new avenues in designing dynamic soft materials with facile control over the phase transition, mechanics, and viscoelastic properties.