Toughened poly(lactic acid)/thermoplastic polyurethane uncompatibilized blends

Poly(lactic acid), PLA, is a biodegradable polymer obtained from renewable sources with similar properties when compared with petroleum-based thermoplastics but with inherent brittleness. In this work, the use of thermoplastic polyurethane (TPU) as toughening agent was evaluated. PLA/TPU blends with 25 and 50 wt% of TPU were produced in an internal mixer without the use of compatibilizers. Their thermal, rheological, and mechanical properties were analyzed and correlated with the developed morphology. Immiscible blends with dispersed droplets morphology were obtained, and it was observed an inversion between the matrix and dispersed phases with the increase of the TPU content. The presence of TPU altered the elasticity and viscosity of the blends when compared to PLA, besides acting as a nucleating agent. Huge increments in impact resistance (up to 365%) were achieved, indicating a great potential of TPU to be used as a PLA toughening agent.

Blend Structure and n-Type Thermoelectric Performance of PA6/SAN and PA6/PMMA Blends Filled with Singlewalled Carbon Nanotubes

The present study investigates how the formation of melt-mixed immiscible blends based on PA6/SAN and PA6/PMMA filled with single walled nanotubes (SWCNTs) affects the thermoelectric (TE) properties. In addition to the detailed investigation of the blend morphology with compositions between 100/0 wt.% and 50/50 wt.%, the thermoelectric properties are investigated on blends with different SWCNT concentrations (0.25–3.0 wt.%). Both PA6 and the blend composites with the used type of SWCNTs showed negative Seebeck coefficients. It was shown that the PA6 matrix polymer, in which the SWCNTs are localized, mainly influenced the thermoelectric properties of blends with high SWCNT contents. By varying the blend composition, an increase in the absolute Seebeck coefficient, power factor (PF), and figure of merit (ZT) was achieved compared to the PA6 composite which is mainly related to the selective localization and enrichment of SWCNTs in the PA6 matrix at constant SWCNT loading. The maximum PFs achieved were 0.22 µW/m·K2 for PA6/SAN/SWCNT 70/30/3 wt.% and 0.13 µW/m·K2 for PA6/PMMA/SWCNT 60/40/3 wt.% compared to 0.09 µW/m·K2 for PA6/3 wt.% SWCNT which represent increases to 244% and 144%, respectively. At higher PMMA or SAN concentration, the change from matrix-droplet to a co-continuous morphology started, which, despite higher SWCNT enrichment in the PA6 matrix, disturbed the electrical conductivity, resulting in reduced PFs with still increasing Seebeck coefficients. At SWCNT contents between 0.5 and 3 wt.% the increase in the absolute Seebeck coefficient was compensated by lower electrical conductivity resulting in lower PF and ZT as compared to the PA6 composites.

Effect of the Incorporation of Polycaprolactone (PCL) on the Retrogradation of Binary Blends with Cassava Thermoplastic Starch (TPS)

The effects of incorporating polycaprolactone (PCL) in three binary blends with cassava thermoplastic starch (TPS) at TPS/PCL ratios of 60/40, 50/50, and 40/60 were studied. TPS previously obtained by single-screw extrusion was manually mixed with PCL and then transformed by extrusion. The results’ analysis focused mainly on monitoring the retrogradation phenomenon in TPS for different storage times at two relative humidities (29% and 54%) and constant temperature (25 °C). With the plasticization of the starch, a predominantly amorphous mass was generated, as evidenced by the scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) results. The results suggested that two opposite processes coexisted simultaneously: retrogradation, which stiffened the material, and plasticization, which softened it, with the latter mechanism predominating at short times and reversing at longer times. With the incorporation of PCL, immiscible blends were obtained in which TPS was the dispersed phase; the mechanical properties improved with the amount of PCL added. The properties of the binary blends as a function of time showed a trend similar to that observed for TPS alone; this finding indicated that the TPS/PCL interactions were not strong enough to affect the structural changes in the TPS, which continued to occur regardless of the PCL content. Finally, it was found that for the binary blend, the relative humidity during storage was more significant to the retrogradation phenomenon than the amount of PCL.

Preparation, Characterization and Processing of PCL/PHO Blends by 3D Bioplotting

Blends of polycaprolactone (PCL) and poly(3-hydroxyoctanoate) P(3HO) were prepared by melt compounding. These immiscible blends exhibited droplet-matrix morphology at compositions up to 30 wt% P(3HO). Even though the addition of amorphous P(3HO) decreased the crystallinity of PCL, the crystallization temperature of the blends increased by 6 to 7 8C. Blends containing up to 30 wt% P(3HO) had higher crystallization rates, and lower crystallization half-times compared to neat PCL. The viscosity of PCL decreased upon addition of P(3HO), making the blends suitable for processing using a 3D bioplotter. Compositions with 10 to 30 wt% P(3HO) were ideal for processing, because of their improved crystallization kinetics, reduced stickiness and good flow properties. Estimation of the interfacial tension by fitting the Palierne model to the linear viscoelastic properties of the blends revealed good compatibility, which gave rise to synergistic effects in the thermal and mechanical properties. The fibres prepared by 3D bioplotting maintained droplet matrix morphology, with finer particle size than the original compounded material. In addition to favourable viscosity and thermal properties, the extruded fibres containing 30 wt% P(3HO) had comparable modulus to the neat PCL, while exhibiting good ductility. These blends may be suitable alternatives to PCL for biomedical applications, because they provide a range of crystallinities, crystallization rates and viscosities.