Morphology and thermal degradation studies of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) biodegradable polymer blend nanocomposites with TiO2 as filler

The morphology and thermal stability of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blend nanocomposites with small amounts of TiO2 nanoparticles were investigated. The nanoparticles were mostly located in the PLA phase, with good dispersion of individual particles, although significant aggregation was also visible. The thermal stability and degradation behaviour of the different samples were studied using thermogravimetric analysis (TGA) and TGA-Fourier-transform infrared (FTIR) spectroscopy. Neat PCL showed better thermal stability than PLA, but the degradation kinetics revealed that PLA had a higher activation energy of degradation than PCL, indicating its degradation rate more strongly depends on temperature, probably because of a more complex degradation mechanism based on chain scission and re-formation. Blending of PLA and PCL reduced the thermal stabilities of both polymers, but the presence of TiO2 nanoparticles improved their thermal stability. The nanoparticles also influenced the volatilization of the degradation products from the blend, acted as degradation catalyst and/or retarded the escape of volatile degradation products.The National Research Foundation (NRF) in South Afric

Morphology and thermal degradation studies of melt-mixed poly(hydroxybutyrate-co-valerate) (PHBV)/poly(ε-caprolactone) (PCL) biodegradable polymer blend nanocomposites with TiO2 as filler

The morphology, thermal stability and thermal degradation kinetics of melt-mixed poly(hydroxybutyrateco-valerate) (PHBV)/poly(e-caprolactone) (PCL) blends filled with small amounts of titanium(IV)oxide (TiO2) nanoparticles were investigated. The nanoparticles were mostly well dispersed in both phases of the PHBV/PCL blend, which showed a co-continuous morphology at a 50/50 w/w ratio, but some large agglomerates were also observed. The equal dispersion of the TiO2 nanoparticles in both polymers was attributed to the polymers having the same surface properties, polarities and viscosities. The thermal stability of PHBV was improved when blended with the more thermally stable PCL, but the PCL became less thermally stable when blended with PHBV. The introduction of only 1 wt% of TiO2 nanoparticles seems to have observably improved the thermal stabilities of both polymers in the blend, but the nanoparticles probably retarded the evolution of the degradation products through their interaction with these products. Further improvement in thermal stability at higher nanoparticle contents was insignificant because of the nanoparticles’ agglomeration which reduced their effectiveness. Changes in the activation energies of degradation, determined through the Flynn–Wall–Ozawa model from thermogravimetric analysis mass loss data, and differences between the Fourier transform infrared spectra of the degradation volatiles obtained during the degradation process, to a large extent support the other observations

Dynamic mechanical properties of PLA/PHBV, PLA/PCL, PHBV/PCL blends and their nanocomposites with TiO2 as nanofiller

The effect of blending and the addition of small amounts of TiO2 nanoparticles on the dynamic mechanical properties of PLA/PHBV, PLA/PCL and PHBV/PCL blends is reported in this paper. The storage modulus of the PLA/PHBV blends was higher than those of both PLA and PHBV in the temperature region below the glass transition of PHBV, but the PLA/PCL and PHBV/PCL bends did not show a similar feature. The E′ values between the glass transitions of PLA and PHBV depended on the blend compositions and morphologies. The presence of titania nanoparticles had little effect on the E′ values of all the investigated blends. The cold crystallization transition of PLA shifted to lower temperatures in the PLA/PHBV blends, and shifts in the Tgs of the two polymers indicated partial miscibility at the polymer-polymer interfaces. This partial miscibility reduced the chain mobilities of these polymers, which could be seen in a reduction in the damping during their respective glass transitions. Blending and nanoparticle addition had little influence on the glass transition temperatures of PLA and PCL in the PLA/PCL blends, but the glass transitions of PHBV and PCL in the PHBV/PCL blends were respectively at higher and lower temperatures than those of the neat polymers, which is a somewhat abnormal observation. The PCL glass transition peaks became broader as a result of blending, which was attributed to the incompatibility of the polymers in the blends, because blending had no influence on the PCL crystallinity

Effect of layered silicates on the thermal stability of PCL/PLA microfibrillar composites

This paper reports on an investigation of the influence of the presence of two different clays, Cloisite 15A and Cloisite 30B, and fibre drawing on the degradation behaviour and kinetics of PCL/PLA composites. It was found that the type of clay significantly influenced the mass loss behaviour of the composites because of physical interactions between the clay and the polymer chains and degradation volatiles. Melt drawing of the composite films, however, had little influence on the degradation behaviour of the investigated samples.This work was supported by Czech Science Foundation (Grant No 13-15255S)

Thermally conductive phase-change materials for energy storage based on low-density polyethylene, soft Fischer–Tropsch wax and graphite

Phase change materials based on graphite-filled wax/polyethylene blends could find application as thermal energy storage materials. Such compounds, comprising wax to polyethylene in a 3:2 proportion, were prepared by twin screw compounding. Two types of graphite were used in an attempt to improve the thermal conductivity of the compounds. Expanded graphite enhanced the thermal conductivity by more than 200% at a loading of 10 wt.%, compared to a ca. 60% improvement with natural graphite flakes at the same loading. The TGA results showed that all the compounds underwent a two-step degradation. In all cases the mass % ratios of the two degradation steps were roughly 3:2 for wax:LDPE, which confirms that the wax evaporated completely before the degradation of LDPE started. The DSC results suggest that the heat energy storing capacity of the wax is not influenced by the other components as long as heating is restricted to temperatures just above the melting point of the wax. It is also apparent that the presence of both forms of graphite enhanced the rate of heat transfer to the PCMs. The DMA results show that the presence of wax had a softening effect, while the presence of graphite opposed this softening effect by reinforcing the PCM composites.http://www.elsevier.com/locate/tc