Effects of Modified Thermoplastic Starch on Crystallization Kinetics and Barrier Properties of PLA

This study reports on using reactive extrusion (REX) modified thermoplastic starch particles as a bio-based and biodegradable nucleating agent to increase the rate of crystallization, percent crystallinity and improve oxygen barrier properties while maintaining the biodegradability of PLA. Reactive blends of maleated thermoplastic starch (MTPS) and PLA were prepared using a ZSK-30 twin-screw extruder; 80% glycerol was grafted on the starch during the preparation of MTPS as determined by soxhlet extraction with acetone. The crystallinity of PLA was found to increase from 7.7% to 28.6% with 5% MTPS. The crystallization temperature of PLA reduced from 113 °C to 103 °C. Avrami analysis of the blends showed that the crystallization rate increased 98-fold and t1/2 was reduced drastically from 20 min to <1 min with the addition of 5% MTPS compared to neat PLA. Observation from POM confirmed that the presence of MTPS in the PLA matrix significantly increased the rate of formation and density of spherulites. Oxygen and water vapor permeabilities of the solvent-casted PLA/MTPS films were reduced by 33 and 19% respectively over neat PLA without causing any detrimental impacts on the mechanical properties (α = 0.05). The addition of MTPS to PLA did not impact the biodegradation of PLA in an aqueous environment.

Crystallization behavior of Zr62Al8Ni13Cu17 Metallic Glass

The crystallization behavior has been studied in Zr62Al8Ni13Cu17metallic glass alloy. The Zr62Al8Ni13Cu17metallic glass crystallized through two steps. The fcc Zr2Ni phase transformed from the amorphous matrix during first crystallization and then the Zr2Ni and residual amorphous matrix transformed into a mixture of tetragonal Zr2Cu and hexagonal Zr6Al2Ni phases. Johnson-Mehl-Avrami analysis of isothermal transformation data suggested that the formation of crystalline phase is primary crystallization by diffusion-controlled growth.

Effect of Organoclay Platelets on Crystallization of PTT/EVA-g-MA Blends: Non-Isothermal Melt Crystallization Kinetics

PTT/EVA-g-MA (80/20 w/w) nanocomposites were prepared by the melt mixing with different organoclay (OMMT) loading. The effect of OMMT on the non-isothermal crystallization kinetics of composites was investigated by DSC. The Avrami and Ozawa methods were used to describe the non-isothermal crystallization process of pure PTT and composites with various loading of OMMT. The Avrami analysis results show that the crystallization rate of 80/20 (w/w) PTT/EVA-g-MA blends with the OMMT is faster than that of pure PTT. The Ozawa analysis can describe the non-isothermal crystallization of pure PTT very well, but it was rather inapplicable for the 80/20 (w/w) PTT/EVA-g-MA blends with various amounts of the clay.

Crystallization Kinetics in Isotactic Polypropylene Films with Carbon Nanotubes

ABSTRACTPolymer nanocomposites are the largest commercial application for carbon nanotubes (CNTs) which determines the interest in their effect on crystallization processes of polymers. We chose Isotactic Polypropylene (iPP) as one of the most widely used polymers. Nanocomposites with multiwall carbon nanotubes (MWCNTs) 0-5% by weight were studied, using differential scanning Calorimetry to measure the crystal nucleation and kinetics effects of MWCNTs. Isothermal crystallization at 138°C was performed and the data were analyzed using Avrami analysis. We obtained results for the effect of MWCNTs on the crystallization kinetics. The Avrami analysis showed a dramatic increase in the crystallization rate constant and constancy of the Avrami exponent with increase of the CNTs concentration. The full width at half maximum (FWHM) of the heat flow exotherm and the peak time for crystallization (tp) change dramatically. The crystallinity shows a slight variation with the CNTs concentration dipping at 2% CNTs which can be explored further at higher concentrations.

Thermal Properties and Crystallization Behavior of Co67Fe4Cr7Si8B14 Amorphous Alloy

In order to investigate the crystallization behavior of the Co67Fe4Cr7Si8B14 amorphous metallic alloy, ribbons of this alloy were prepared by planar flow melt spinning process (PFMS). Differential scanning calorimetery (DSC) and differential thermal analyzer (DTA) were used to analyze the thermal properties and crystallization behavior of the samples at three heating rates of 10, 20 and 30º C/min. The experimental data were fitted to the Avrami model to determine the crystallization behavior. The results showed that the crystallization exotherm became wider and shifted toward a higher temperature range as the heating rate increased. The Avrami analysis also showed that n is about 1, which is related to the same transformation mechanism at different heating rates. The Kissinger method was used to determine the activation energy for the first crystallization peaks. The measured value is approximately 332.67 kJ/g.

Carbon Nanotube-Induced Changes of Crystal Growth In Polymer Films

Isotactic Polypropylene (iPP) nanocomposites with low concentrations of multiwall carbon nanotubes (CNTs) 0-1% were studied, using differential scanning calorimetry and Avrami analysis. The nanocomposites were isothermally crystallized at 135°C, in order to measure the effect of nanotubes on the kinetics of crystallization. In our study there is a great effect of the CNTs on the iPP crystallization kinetics. The Avrami analysis shows increase in the crystallization rate constant and constancy the Avrami exponent with increase of the CNTs concentration. The full width at half maximum (FWHM) of the heat flow exotherm and the peak time for crystallization (tp) change dramatically. For iPP, the carbon nanotubes serve as nucleation agents to speed up the crystallization process.

The effect of aliphatic chain length on thermal properties of poly(alkylene dicarboxylate)s

Some poly(alkylene dicarboxylate)s, derived from ethanediol or 1,4- butanediol and different diacids, have been synthesized and analyzed by DSC to determine the correlations existing between the thermal properties and the length of the aliphatic chain. The polymers show crystallization and melting temperatures and enthalpies which increase as the polymethylene segments lengthen, due to the formation of more stable crystals. The samples derived from ethanediol are peculiar; they show reorganization processes during the melting and the melting temperatures are notably higher with respect to those of the other polyesters. This behavior is discussed. Isothermal analysis highlights that poly(alkylene dicarboxylate)s are fast crystallizing polymers. The Avrami analysis suggests a crystallization mechanism characterized by heterogeneous nucleation and three dimensional growth; secondary crystallizations is present only in the samples characterized by short -(CH2)- sequences, due to the reorganization of less perfect crystalline forms. A comparative study between the crystallization rates as a function of the undercooling is reported.