Controlling the isothermal crystallization of isodimorphic PBS-ran-PCL random copolymers by varying composition and supercooling

In this work, we study for the first time, the isothermal crystallization behavior of isodimorphic random poly(butylene succinate)-ran-poly(e-caprolactone) copolyesters, PBS-ran-PCL, previously synthesized by us. We perform nucleation and spherulitic growth kinetics by polarized light optical microscopy (PLOM) and overall isothermal crystallization kinetics by differential scanning calorimetry (DSC). Selected samples were also studied by real-time wide angle X-ray diffraction (WAXS). Under isothermal conditions, only the PBS-rich phase or the PCL-rich phase could crystallize as long as the composition was away from the pseudo-eutectic point. In comparison with the parent homopolymers, as comonomer content increased, both PBS-rich and PCL-rich phases nucleated much faster, but their spherulitic growth rates were much slower. Therefore, the overall crystallization kinetics was a strong function of composition and supercooling. The only copolymer with the eutectic composition exhibited a remarkable behavior. By tuning the crystallization temperature, this copolyester could form either a single crystalline phase or both phases, with remarkably different thermal propertiesPeer ReviewedPostprint (published version

The effect of titanium dioxide surface modification on the dispersion, morphology, and mechanical properties of recycled PP/PET/TiO2 PBNANOs

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

Structure and properties of reactively extruded opaque post-consumer recycled PET

This article belongs to the Special Issue Recycling and Resource Recovery from Polymers.The recyclability of opaque PET, which contains TiO2 nanoparticles, has not been as well-studied as that of transparent PET. The objective of this work is to recycle post-consumer opaque PET through reactive extrusion with Joncryl. The effect of the reactive extrusion process on the molecular structure and on the thermal/mechanical/rheological properties of recycling post-consumer opaque PET (r-PET) has been analyzed. A 1% w/w Joncryl addition caused a moderate increase in the molecular weight. A moderate increase in chain length could not explain a decrease in the overall crystallization rate. This result is probably due to the presence of branches interrupting the crystallizable sequences in reactive extruded r-PET (REX-r-PET). A rheological investigation performed by SAOS/LAOS/elongational studies detected important structural modifications in REX-r-PET with respect to linear r-PET or a reference virgin PET. REX-r-PET is characterized by a slow relaxation process with enlarged elastic behaviors that are characteristic of a long-chain branched material. The mechanical properties of REX-r-PET increased because of the addition of the chain extender without a significant loss of elongation at the break. The reactive extrusion process is a suitable way to recycle opaque PET into a material with enhanced rheological properties (thanks to the production of a chain extension and long-chain branches) with mechanical properties that are comparable to those of a typical virgin PET sample.We would like to acknowledge funding by the EU Interreg H2020 program through project POCTEFA EFA329/19. This work also received funding from the Basque Government, grant IT1309-19.Peer reviewe

The effect of titanium dioxide surface modification on the dispersion, morphology, and mechanical properties of recycled PP/PET/TiO2 PBNANOs

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.Peer Reviewe

Tuning the thermal properties and morphology of isodimorphic poly[(butylene succinate)-ran-(e-caprolactone)] copolyesters by changing composition, molecular weight, and thermal history

High molecular weight poly[(butylene succinate)- ran-(e-caprolactone)] copolyesters (PBS-ran-PCL) were synthesized in a wide composition range and compared with significantly lower molecular weight samples synthesized previously. DSC and WAXS showed that these copolyesters are isodimorphic (i.e., each crystalline phase contains a small amount of the second comonomer) as they able to crystallize in the entire composition range and display a pseudoeutectic point, and their unit cell dimensions are a function of composition. Copolymers close or away from the pseudoeutectic point exhibited a single crystalline phase, i.e., PBS-rich or PCL-rich crystalline phase. At the pseudoeutectic point, both phases can crystallize in double crystalline banded spherulites, as demonstrated by polarized light optical microscopy (PLOM) studies. An increase in molecular weight of the copolyester does not influence Tm and Tc significantly, as their values are determined by the randomness of the comonomer distribution. However, crystallinity values are higher for lower Mw copolymers because of their faster crystallization rate. Copolymers with higher Mw exhibited higher Tg values as expected for random copolymers that are characterized by a single phase in the amorphous regions. Therefore, changing composition and molecular weight, a remarkable separate control over Tg and Tm values can be achieved in these copolyesters. SAXS results revealed that the lamellar thickness lc decreases with composition at each side of the eutectic point. Comonomer exclusion limits the length of crystallizable sequences; as a result, the lamellar thickness values do not significantly vary with Mw in the range studied here. At the pseudoeutectic copolyester compositions, the cooling rate determines for both series of samples (low and high Mw) if one or two crystalline phases can develop: only the PCL-rich crystalline phase, only the PBS-rich crystalline phase, or both crystalline phases. This behavior was studied in detail by DSC, in situ WAXS/SAXS, and PLOM. Our studies demonstrate that these biodegradable copolymers are versatile materials whose properties can be tuned by composition, molecular weight, and thermal history to better target specific applications.Peer Reviewe

Tuning the thermal properties and morphology of isodimorphic poly[(butylene succinate)-ran-(e-caprolactone)] copolyesters by changing composition, molecular weight, and thermal history

High molecular weight poly[(butylene succinate)- ran-(e-caprolactone)] copolyesters (PBS-ran-PCL) were synthesized in a wide composition range and compared with significantly lower molecular weight samples synthesized previously. DSC and WAXS showed that these copolyesters are isodimorphic (i.e., each crystalline phase contains a small amount of the second comonomer) as they able to crystallize in the entire composition range and display a pseudoeutectic point, and their unit cell dimensions are a function of composition. Copolymers close or away from the pseudoeutectic point exhibited a single crystalline phase, i.e., PBS-rich or PCL-rich crystalline phase. At the pseudoeutectic point, both phases can crystallize in double crystalline banded spherulites, as demonstrated by polarized light optical microscopy (PLOM) studies. An increase in molecular weight of the copolyester does not influence Tm and Tc significantly, as their values are determined by the randomness of the comonomer distribution. However, crystallinity values are higher for lower Mw copolymers because of their faster crystallization rate. Copolymers with higher Mw exhibited higher Tg values as expected for random copolymers that are characterized by a single phase in the amorphous regions. Therefore, changing composition and molecular weight, a remarkable separate control over Tg and Tm values can be achieved in these copolyesters. SAXS results revealed that the lamellar thickness lc decreases with composition at each side of the eutectic point. Comonomer exclusion limits the length of crystallizable sequences; as a result, the lamellar thickness values do not significantly vary with Mw in the range studied here. At the pseudoeutectic copolyester compositions, the cooling rate determines for both series of samples (low and high Mw) if one or two crystalline phases can develop: only the PCL-rich crystalline phase, only the PBS-rich crystalline phase, or both crystalline phases. This behavior was studied in detail by DSC, in situ WAXS/SAXS, and PLOM. Our studies demonstrate that these biodegradable copolymers are versatile materials whose properties can be tuned by composition, molecular weight, and thermal history to better target specific applications.Peer Reviewe

Controlling the isothermal crystallization of isodimorphic PBS-ran-PCL random copolymers by varying composition and supercooling

In this work, we study for the first time, the isothermal crystallization behavior of isodimorphic random poly(butylene succinate)-ran-poly(e-caprolactone) copolyesters, PBS-ran-PCL, previously synthesized by us. We perform nucleation and spherulitic growth kinetics by polarized light optical microscopy (PLOM) and overall isothermal crystallization kinetics by differential scanning calorimetry (DSC). Selected samples were also studied by real-time wide angle X-ray diffraction (WAXS). Under isothermal conditions, only the PBS-rich phase or the PCL-rich phase could crystallize as long as the composition was away from the pseudo-eutectic point. In comparison with the parent homopolymers, as comonomer content increased, both PBS-rich and PCL-rich phases nucleated much faster, but their spherulitic growth rates were much slower. Therefore, the overall crystallization kinetics was a strong function of composition and supercooling. The only copolymer with the eutectic composition exhibited a remarkable behavior. By tuning the crystallization temperature, this copolyester could form either a single crystalline phase or both phases, with remarkably different thermal propertiesPeer Reviewe