Morphology and properties of biodegradable poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends with different viscosity ratio

Phase morphology exerts a tremendous influence on the properties of polymer blends. The development of the blend morphology depends not only on the intrinsic structure of the component polymers but also on extrinsic factors such as viscosity ratio, shearing force and temperature in the melt processing. In this study, various poly (butylene adipate-co-terephthalate) (PBAT) materials with different melt viscosity were prepared, and then poly (lactic acid) (PLA)/PBAT blends with different viscosity ratio were prepared in a counter-rotating twin-screw extruder under constant processing conditions. The influence of viscosity ratio on the morphology, mechanical, thermal and rheological properties of PLA/PBAT (70/30 w/w) blends was investigated. The experimental results showed that the morphology and properties of PLA/PBAT blends strongly depended on the viscosity ratio. Finer size PBAT phase were observed for viscosity ratio less than 1 (λ < 1) compared to samples with λ > 1. It was found that the interfacial tensions of PLA and PBAT were significantly different when the viscosity ratio was changed, the lowest interfacial tensions (0.12 mN/m) was obtained when the viscosity was 0.77. Additionally, the maximal tensile strength in PLA/PBAT blends were obtained when the viscosity ratio was 0.44, while the maximal impact properties were obtained when the viscosity ratio was 1.95.     

Physical blends of PLA with high vinyl acetate containing EVA and their rheological,thermo-mechanical and morphological responses

Rheological, morphological and thermo-mechanical responses of poly(lactic acid) (PLA)/ethylene-co-vinyl-acetate copolymer (EVA) blends at EVA volume fractions varying in the range of 0–0.35 were evaluated. The micro-structural analysis demonstrated dispersive mixing at low content and co-continuous morphology at 30 wt % of EVA in PLA. Dynamic rheology demonstrated enhanced storage modulus and complex viscosity (η*) with increase in frequency of the blends indicated strong phase interaction. Cole-Cole and Han plots indicated partial miscibility and incompatibility between the polymer matrix and the dispersed phase. Dynamic mechanical analysis (DMA) revealed slight increase in damping parameters which indicated interaction or reinforcement in the blends. Additionally, the thermogravimetric analysis (TGA) of the blends showed two step degradation and enhanced thermal stability.     

In-situ changes of thermo-mechanical properties of poly(lactic acid) film immersed in alcohol solutions

Poly (lactic acid) (PLA) has properties suitable for many applications. However, PLA's properties are affected by environmental conditions. In this study, the glass-rubber transition temperatures (T_g) of PLA films were measured during immersion (i.e., in-situ) in pure alcohols and alcohol aqueous solutions using a dynamic mechanical analysis technique. The T_g of PLA decreased when immersed in alcohols. For pure aliphatic alcohols, the T_g reduction became smaller as the number of carbons (C1–C10) in the alcohol main chains increased. The Fox equation and the Hansen solubility parameters (HSP)/Flory-Huggins (FH) model were used to explain the T_g reduction. The relationships explained the interactions between PLA and pure alcohols with small molecules (C1–C8), but bigger pure alcohols (C9–C10) did not fit the prediction. The chemical isomerism in pure propanol (i.e., propan-1-ol and propan-2-ol) did not affect the T_g reduction. The T_g reduction in propan-2-ol aqueous solutions was concentration dependent although the partition coefficients based on the HSP and the FH parameters did not fit this relationship. The in-situ immersion of PLA in alcohol solutions could be used to evaluate the change in T_g from the T_g of dry PLA.     

Synergistic effect of polylactic acid(PLA) and Poly(butylene succinate-co-adipate) (PBSA) based sustainable,reactive, super toughened eco-composite blown films for flexible packaging applications

Polylactic acid (PLA)/poly (butylene succinate-co-adipate) (PBSA) based blend films at variable compositions and fixed weight percentage of Epoxy functionalized styrene acrylate (ESA) were prepared using a single step blending process, followed by blown film extrusion process. The morphological studies revealed proper interaction between polymers by the interaction of chain extender (ESA) subsequently improved the mechanical properties of the prepared blown films. Similarly, the blend films showed a decrease in oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) in the order of 60% and 14% as compared with VPLA film. The optical and antislip properties of the blend films also increased considerably. The thermal analysis of the blend films depicted marginal enhancement in the stability of PLA along with heterogeneous nucleation effect in PLA matrix due to the presence of ESA and PBSA.     

Microanalysis of hybrid characterization of PLA/cHA polymer scaffolds for bone regeneration

Tissue engineering uses some engineering strategies for the reconstruction and repair of the compromised tissues, among which the use of biomaterials as an alternative to conventional transplants is significant. However, not many research has been developed on the use of biopolymer nanostructure microanalysis and calcium phosphate composites of carbon apatite in PLA as scaffolds for tissue regeneration. In this work, poly (lactic acid) filaments with 5% and 20%, carbon apatite (cHA) were microanalysis to produce a 3D printing scaffold. The scaffolds were characterised by the Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray (EDX) techniques, thereby making it possible to notice a good load dispersion. The microstructural analysis of the scaffolds was carried out by computerised micro-tomography to determine the roughness, morphological parameters of pore size distribution, porosity, as well as better visualisation of the distribution of particles. A computational in vitro and microanalysis tests to assess the biocompatibility viability of the PLA/cHA structure with a variation of scaffold geometry to evaluate their effects on morphological, physicochemical and mechanical properties were also carried out. The characterisation of Ca and P release assays were observed for longer incubation times and the dynamic condition control to simulate the stresses suffered by the biomaterial exerted by the flow of fluids was achieved. The results obtained indicated that the micrographs of the cross-sections of the scaffolds showed a flatness in the loaded material when compared to the 100/0 PLA. Furthermore, the apparent porosity of 5% and 20% of cHA scaffolds gave a porosity percentage of approximately 62% and 41% respectively. The reduced summit height, reduced valley depth and the percentage upper and lower bearing area difference of the samples are 16.33 nm, 9.62 nm and 75.07% respectively. The morphological characterisation surface roughness analysis and tolerance insertion gave a favourable reduced porosity result for the composite scaffolds with 5% of cHA. Hence, this work will assist biomaterial industries in the development of biomaterials which have been engineered with biological systems to meet medical purposes.     

A method for simultaneously improving the flame retardancy and toughness of PLA

In order to modify the brittleness and flame retardant properties of poly(lactic acid) (PLA), a series of flame retardant toughened PLA composites were prepared using poly(ethylene glycol) 6000 (PEG6000) as a toughening and charring agent together with ammonium polyphosphate (APP) as an acid source and blowing agent. The fire and thermal behavior of PLA/PEG/APP composites was evaluated by limiting oxygen index (LOI), UL‐94, cone calorimeter, and thermogravimetric analysis (TGA). The results showed that the PLA/PEG/APP system had good charring ability and could improve the flame retardancy of PLA. When the content of APP in the composites was more than 5 wt%, all samples could reach UL‐94 V‐0 rating. The results of mechanical property tests demonstrated that the brittleness of PLA was also improved after blended with PEG6000. All the PLA/PEG/APP composites with an APP content of less than 10 wt% showed an obvious neck and fracture behavior, that is, the tensile behavior of PLA was changed from brittle to ductile. Copyright © 2010 John Wiley & Sons, Ltd.     

Biodegradation of sequentially surface treated lignocellulose reinforced polylactic acid composites: Carbon dioxide evolution and morphology

Maple fibres were treated with a variety of sequential treatments, namely sodium hydroxide (NaOH), NaOH followed by acetylation, or NaOH followed by silanation. These fibres were incorporated into a polylactic acid (PLA) composite and the biodegradation effects were investigated. After 124 days, all composites had exceeded 90% biodegradation with most close to 100%. The PLA composite with the NaOH-treated fibres had the quickest onset of degradation (4.9 days) and highest peak rate of degradation (1.77% biodegradation/day) of all composites studied. Neat PLA had a similarly high peak rate of degradation at 1.85% biodegradation/day, but had a later onset of 11 days. Gel permeation chromatography (GPC) analysis showed the earlier onset of degradation of the composites was caused by increased hydrolysis during composite fabrication as well as composting. GPC showed the formation of up to three molecular weight bands in the PLA during composting which were hypothesised to be occurring by surface hydrolysis, bulk hydrolysis and hydrolysis at the fibre interface. Analysing the remaining composite revealed the NaOH treatment not only caused an increased rate of degradation in the PLA through increase fibre porosity, but also caused an increased rate of degradation in the fibre from the lack of surface waxes and hemicellulose. Similar, yet slower, behaviours were also seen in the NaOH followed by acetylation and NaOH followed by silane treated composites with all composites degrading more rapidly than the neat PLA and neat maple fibre samples.     

Characteristics of X‐ray attenuation in electrospun bismuth oxide/polylactic acid nanofibre mats

The characteristics of the X‐ray attenuation in electrospun nano(n)‐ and micro(m)‐Bi₂O₃/polylactic acid (PLA) nanofibre mats with different Bi₂O₃ loadings were compared as a function of energy using mammography (i.e. tube voltages of 22–49 kV) and X‐ray absorption spectroscopy (XAS) (7–20 keV). Results indicate that X‐ray attenuation by electrospun n‐Bi₂O₃/PLA nanofibre mats is distinctly higher than that of m‐Bi₂O₃/PLA nanofibre mats at all energies investigated. In addition, with increasing filler loading (n‐Bi₂O₃ or m‐Bi₂O₃), the porosity of the nanofibre mats decreased, thus increasing the X‐ray attenuation, except for the sample containing 38 wt% Bi₂O₃ (the highest loading in the present study). The latter showed higher porosity, with some beads formed, thus resulting in a sudden decrease in the X‐ray attenuation.     

Preparation and in vitro evaluation of an ultrasound-triggered drug delivery system: 10-hydroxycamptothecin loaded PLA microbubbles

10-Hydroxycamptothecin (HCPT) loaded PLA microbubbles, used as an ultrasound-triggered drug delivery system, were fabricated by a double emulsion-solvent evaporation method. The obtained microbubbles were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and confocal laser scanning microscope (CLSM). In addition, the effect of diagnostic ultrasound exposure on BEL-7402 cells combined with HCPT-loaded PLA microbubbles was evaluated using cytotoxicity assay, CLSM and flow cytometry (FCM). It was found that the HCPT-loaded PLA microbubbles showed smooth surface and spherical shape, and the drug was amorphously dispersed within the shell and the drug loading content reached up to 1.69%. Nearly 20% of HCPT was released upon exposure to diagnostic ultrasound at frequency of 3.5 MHz for 10 min. Moreover, HCPT fluorescence in the cells treated only with the HCPT-loaded PLA microbubbles was discernible, but less intense, while those treated with the microbubbles in conjunction with ultrasound exposure was evident and intense, indicating an increased cellular uptake of HCPT by ultrasound exposure. Cytotoxicity test on BEL-7402 cells indicated that the HCPT-loaded PLA microbubbles combined with ultrasound exposure were more cytotoxic than the microbubbles alone. The results suggest that the combination of drug loaded PLA microbubbles and diagnostic ultrasound exposure exhibit an effective intracellular drug uptake by tumor cells, indicating their great potential for antitumor therapy.     

电纺丝法制备聚乳酸/多壁碳纳米管/羟基磷灰石杂化纳米纤维的研究

电纺丝是一种利用聚合物溶液或熔体在强电场中进行喷射纺丝的加工技术,所制得的纤维、直径一般在数十纳米至几微米之间,比传统方法制得的纤维直径小几个数量级,是获得纳米尺寸长纤维的有效方法之一．