Papers by Keyword: Poly(lactic acid) (PLA)

Abstract: Poly(lactic acid) (PLA) is a biodegradable thermoplastic polyester derived from renewable resources which may replace conventional polymers for some applications. To overcome some of its limitations such as poor gas barrier properties and low elongation at break, one method is to blend PLA with small amounts of other bio-based polymers. In this study, two processes, eg classical twin screw extrusion and a multilayer co-extrusion process have been used to combine PLA and poly(3-hydroxybutyrate-co-3-valerate) PHBV to obtain films with different blend morphologies. The effect of the morphology on the crystallinity has been studied and has hightlightned new behavior of PHBV. The addition of a nucleating agent in the PHBV to modify its crystallinity, has also been studied.

Abstract: Poly-(lactic acid) or PLA is a biodegradable polymer produced from renewable resources. Recently new polymerization routes have been discovered which allows increasing the produced quantity. Hence, PLA becomes of great interest to lessen the dependence on petroleum-based plastics. Due to its good mechanical properties, PLA is a potential substitute to some usual polymers such as PET. Nevertheless the kinetics of crystallization is relatively slow which can be an inconvenient in polymer processing. Thermomechanical history experienced by the polymer during processing affects drastically its relative crystallinity. For example, the flow is known to enhance the crystallization kinetics. Nevertheless, only a few studies were found in the literature about the crystallization of PLA under flow conditions. In the present work we investigate the crystallization of PLA under quiescent and flow conditions. A combination of DSC, rheological and optical measurements is used to identify the crystallization kinetic parameters. Thermal and flow-induced crystallization are then simulated using two sets of Schneider’s differential equations [1] based on a previously developed model Zinet & al [2]. Experimental results are analyzed and compared to the numerical model. New features about the influence of thermal and flow conditions on the crystallization of PLA are discussed.

Abstract: Poly (lactic acid) (PLA)/polyethylene oxide (PEO) bicomponent fibers werefabricated by co-electrospinning technique in a side by side configuration. Effect of PEO concentration, PLA and PEO solution flow rate and an applied voltage on formation, size and morphology of the fibers were investigated. The results showed that the fibers size increased with increasing PEO concentration, PEO flow rate ratio and applied voltage. The composition of the fibers was confirmed by IR spectrum. Additionally, by pairing PEO, which is a water soluble polymer, with PLA, follow by PEO phase removal in water, a C-shaped ultrafine fiber was prepared.

Abstract: Thermoplastic starch, polylactic acid glycerol and maleic anhydride (MA) were compounded with natural montmorillonite (MMT) through a twin screw extruder to investigate the effects of different loading of MMT on tensile properties and thermal behavior of the nanocomposites. Tensile results showed an increased in modulus, tensile strength and elongation at break. However, beyond 3phr of MMT the modulus of samples decreased because the MMT particles agglomerated. The thermal properties were characterized by using differential scanning calorimeter (DSC). The results showed that MMT increased melting temperature and crystallization temperature of matrix but reduction in glass transition temperature was observed.

Abstract: Recent work describes changes in polylactic acid samples with different crystallinity during microbiological degradation. We treated PLA at 93°C for different periods of time, which yielded samples with particular crystallinity. The fraction of crystalline phase was determined by differential scanning calorimetry, and the visual effect of crystallinity was measured by colorimetric method with black and white backgrounds. The medium for biological degradation process was living sludge under room temperature and normal atmospheric pressure. Furthermore, the change in mass was also measured. The results show that increased crystallinity reduces the rate of mass lost. The volumetric proportion of crystallinity is in direct correlation with opacity, so checking transparency is also a suitable possibility for estimating crystallinity. DSC, colorimetric method and visual observation experiments confirm that crystallinity has increased proportionally by the time of heat treatment and caused opacity. The experiments show that water uptake happened faster and in much higher volume in polymers having dominantly amorphous structure than in the case of samples with higher crystallinity. In the case of materials with only 2.43% crystallinity, weight lost began later because they had a greater water uptake during the first 7-12 days, while this period took only 7 days with a very low water uptake for samples containing approximately 35% crystalline phase. After swelling, weight loss of the crystalline samples was much slower than that of samples containing more amorphous parts, because crystalline phases inhibit the diffusion of small water molecules and the microbes with it.

Abstract: Nowadays, bio-plastic is the most popular in packaging field. Green chemistry and environmental responsibility has led it to develop the bio-plastic for use as packaging. Polylactic acid (PLA) is the well known staring material in this area. However, some properties of PLA films have to develop. Polymer blend is the interesting technique, in this work, PLA/Cellulose acetate (CA) blend films were prepare by casting solution at various compositions. Mixing solvent of Chloroform and acetone in acid condition were used, it was found that the mixing solvent can improved the compatibility and mechanical properties of the blend films. From this work CA can significantly increase PLA properties both the usefulness and the possible applications for bio-plastic material.

Abstract: In this work, biodegradable plastics were produced from different poly(lactic acid) (PLA)/ poly(butylene succinate) (PBS) blend ratios in the presence of a fix loading (1 phr) of a commercial epoxy functionalised polymeric chain extender (Joncryl ADR-4300-S). The effects of blend ratio and chain extender on the tensile properties, thermal stability and morphology were investigated by the tensile testing, thermogravimetric analysis (TGA) and scanning electron microscopy, respectively. The results show that the incorporation of PBS and Joncryl into PLA apparently reduced the tensile strength and tensile modulus, but increased the elongation at break of the blends in a dose-dependent manner. However, their blends provide interesting materials for industrial packaging applications, due to their enhanced ductility by decreasing the tensile modulus and increasing the elongation at break. TGA analysis showed that thermal stability of the blends was lower than that of the pure PLA and PBS. Moreover, the chain-extended products exhibit two stages of thermal decomposition, the first was due to the degradation of PBS, and the second was due to the degradation of PLA.

Abstract: In this study, polylactic acid(PLA)/ketoconazole(KCZ) composite microspheres were prepared by oil/water solvent evaporation method. Those drug-loaded microspheres were characterized in morphology using the scanning electron microscope (SEM). Fourier transform infrared spectroscopy (FT-IR) was used to determine the chemical functional groups in the sample and to analysis whether a chemical reaction occured between PLA and KCZ. The thermogravimetric spectra of PLA and PLA/KCZ microspheres were used to analyse the influence of KCZ on the thermal decomposition mechanism of PLA. Crystallinities of the KCZ and PLA/KCZ were analyzed by X-ray diffraction analysis (XRD).

Abstract: Polylactide (PLA) was plasticized by two types of plasticizers, glycerol and triacetin. These plasticized PLA were mixed with carboxymethylcellulose (CMC). It was found that with only small amount of CMC, 4.5 wt%, it is effectively to lower glass transition, cold crystallization and melting temperatures of glycerol-plasticized PLA (PLA-g) but not much affected on tensile properties. Moreover, increasing amount of CMC twice could not much affect thermal properties but largely reduced tensile strength, modulus and elongation. The melt flow index of the PLA-g increased largely with the amount of CMC. When 4.5 wt% CMC was added to the glycerol-triacetin plasticized PLA, only glass transition temperature became lower than that of 4.5 wt% CMC filled PLA-g but melting temperature and crystallinity were rather increased with poorer mechanical properties. Increasing amount of CMC tended to enhance melting temperature but still rather poor mechanical properties and high melt flow index. So, the CMC had strong positive effect on melt and negative effect on solid properties of plasticized PLA.

Abstract: The chitosan (CS) /poly-L-lactic (PLLA) acid blend scaffolds were prepared by two kinds of blend solutions through immersion precipitation phase inversion method. CS/PLLA blend scaffold was fabricated by mixing the CS-HAc solution and PLLA-DMF solution, CSP/PLLA blend scaffold was fabricated by mixing chitosan powder (CSP) and PLLA-DMF solution. The results revealed that CS content in CSP/PLLA scaffold was 126 times higher than that in CS/PLLA scaffold. The difference of CS content made the structures of CS/PLLA scaffold and CSP/PLLA scaffold exhibit an obvious discrepancy, which resulted from the different thermodynamics and phase separation behavior of two blend solutions. CS/PLLA scaffold with a higher porosity took on an unsymmetrical structure with a compact upper surface and a porous cross-section containing the fingerlike macrovoids, while CSP/PLLA scaffold displayed a symmetrical structure with a porous upper surface and the sponge-like cross-section. WVTR and equilibrium swelling of CSP/PLLA blend scaffold were higher than that of CS/PLLA blend scaffold. WAXD analysis revealed that PLLA and CS did not crystallize in the course of CS/PLLA scaffold formation, while there were the diffraction peaks of PLLA and CS in the CSP/PLLA scaffold.