Thermal Properties and Thermodynamics of Poly(l-lactic acid)

Degradation of Polylactic Acid/Polypropylene Carbonate Films in Soil and Phosphate Buffer and Their Potential Usefulness in Agriculture and Agrochemistry

Blends of poly(lactic acid) (PLA) with poly(propylene carbonate) (PPC) are currently in the phase of intensive study due to their promising properties and environmentally friendly features. Intensive study and further commercialization of PPC-based polymers or their blends, as usual, will soon face the problem of their waste occurring in the environment, including soil. For this reason, it is worth comprehensively studying the degradation rate of these polymers over a long period of time in soil and, for comparison, in phosphate buffer to understand the difference in this process and evaluate the potential application of such materials toward agrochemical and agricultural purposes. The degradation rate of the samples was generally accompanied by weight loss and a decrease in molecular weight, which was facilitated by the presence of PPC. The incubation of the samples in the aqueous media yielded greater surface erosions compared to the degradation in soil, which was attributed to the leaching of the low molecular degradation species out of the foils. The phytotoxicity study confirmed the no toxic impact of the PPC on tested plants, indicating it as a "green" material, which is crucial information for further, more comprehensive study of this polymer toward any type of sustainable application.

Role of Inorganic Fillers on the Physical Aging and Toughness Loss of PLLA/BaSO4 Composites

The addition of inorganic fillers has been reported to increase the toughness of poly(l-lactide) (PLLA), but the effect of physical aging in such composites has been neglected. The present work discusses the effect of the still ongoing segmental relaxation in PLLA-based composites filled with BaSO4 inorganic particles in regard of the filler quantity. By means of differential scanning calorimetry, X-ray diffraction, and tensile testing of progressively aged PLLA filled with particles ranging from 0.5-10 wt %, we observed an increase in the mechanical energy required to activate the plastic flow of the primary structure in the PLLA matrix, which resulted in the embrittlement of the majority of composites upon enough aging. Results further clarify the role of debonding in the activation process of PLLA, and the behavior of the composite is described at the segmental level. Only an addition of 10% of particles has effectively preserved a ductile behavior of the samples beyond 150 aging days; therefore, we strongly remark the significance of studying the effect of physical aging in such composites.

Synthesis and Characterization of Functional Cellulose-Ether-Based PCL- and PLA-Grafts-Copolymers

The use of biodegradable materials such as cellulose and polyesters can be extended through the combination, as well as modification, of these biopolymers. By controlling the molecular structure and composition of copolymers of these components, it should also be possible to tailor their material properties. We hereby report on the synthesis and characterization of cellulose-based graft copolymers with a precise molecular composition and copolymer architecture. To prepare such materials, we initially modified cellulose through the regioselective protection of the 6-OH group using trityl chloride. The 6-O protected compound was then alkylated, and deprotection at the 6-OH group provided the desired 2,3-di-O-alkyl cellulose compounds that were used as macroinitiators for ring opening polymerization. Regioselective modification was hereby necessary to obtain compounds with an exact molecular composition. Ring opening polymerization, catalyzed by Sn(Oct)₂, at the primary 6-OH group of the cellulose macroinitiator, using L-lactide or ε-caprolactone, resulted in graft copolymers with the desired functionalization pattern. The materials were characterized using Fourier-transform infrared spectroscopy, ¹H- and ¹³C- nuclear magnetic resonance spectroscopy, size exclusion chromatography as well as X-ray diffraction, and differential scanning calorimetry. PCL-based copolymers exhibited distinct melting point as well as a crystalline phase of up to 47%, while copolymers with PLA segments were highly amorphous, showing a broad amorphous reflex in the XRD spectra, and no melting or crystallization points were discernible using differential scanning calorimetry.

Bulk enthalpy of melting of poly (l-lactic acid) (PLLA) determined by fast scanning chip calorimetry

The bulk enthalpy of melting of α-crystals of poly (l-lactic acid) (PLLA) has been evaluated by fast scanning chip calorimetry (FSC), by analysis of the correlation between the measured enthalpy of melting of sets of samples of different crystallinity and the corresponding heat capacity at 90°C, that is at a temperature higher than the glass transition temperature of the bulk amorphous phase and lower than the melting temperature. Extrapolation of this relationship for crystals formed at 140°C towards the heat capacity of fully solid PLLA yields a value of about 104.5±6 J/g when melting occurs at 180-200°C. The analysis is based on the presence of a two-phase structure, that is, absence of a vitrified rigid amorphous fraction (RAF) at the temperature of analysis of the solid fraction of the material (90°C). Formation and vitrification of an RAF was suppressed by avoiding both continuation of primary crystallization and secondary crystallization during cooling the system from the crystallization temperature of 140°C to 90°C, making use of the high cooling capacity of FSC. Small-angle X-ray scattering (SAXS) confirmed distinct thickening of initially grown lamellae which only is possible if these lamellae are not surrounded by a glassy RAF. Linear crystallinity values obtained by SAXS and calorimetrically determined enthalpy-based crystallinities agree close to each other. This article is protected by copyright. All rights reserved.

Syntheses of polylactides by means of tin catalysts

Reaction mechanisms and synthetic methods used for the preparation of homo- and copolylactides based on tin(ii) and tin(iv) catalysts are reviewed.