جستجوی مقالات مرتبط با کلیدواژه « Polylactic acid » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Hypothesis: 

Fused filament fabrication (FFF) method is widely used in additive manufacturing due to its benefits, such as ease of use, cost-effectiveness, and availability. The mechanical properties of polylactic acid (PLA) printed by the FFF method can be significantly improved by combining them with nanomaterials such as nanoclay and optimizing the printing process parameters such as printing temperature and raster angle.

In order to investigate and optimize the multi-objective 3D printing process of PLA nanocomposite samples reinforced by nanoclay, the response surface method (RSM) was used as one of the methods of design of experiments. Nozzle temperature (190, 210 and 230°C), raster angle (0, 45 and 90°) and nanoclay weight percentage (0, 2 and 4% by wt) were studied to optimize output responses. Melt mixing of PLA with nanoclay particles was done using a twin-screw extruder machine and a granulator machine. The composite granules of PLA were prepared with 2 and 4% (by wt) of nanoclay. The prepared composite granules were entered into a single-screw extruder and composite filaments were produced.

The analysis of parameter participation in the density data reveals that the weight percentage of nanoclay and the nozzle temperature exhibit the most substantial influence, while raster angle has the least impact. Conversely, when considering tensile strength results, the weight percentage of nanoclay is the dominant factor, while the interaction between the weight percentage of nanoclay and raster angle has the smallest influence among the parameters under investigation. The multi-objective optimization results revealed that the optimal process conditions to achieve maximum strength are a nanoclay weight percentage of 4% (by wt), a nozzle temperature of 230°C, and a raster angle of about 25.5°. The tensile strength of the parts produced is 33.78 MPa, and their density is at least 1.089 g/cm3.

Biodegradable compounds with high mechanical and thermal properties are one of the intersting research topics. Polylactic acid is an aliphatic polyester with high biodegradability and flexibility. It, however, suffers from several weaknesses such as high permeability to water vapor and gases, low glass transition temperature, poor thermal stability and brittleness which can be improved by the incorporation of nano-scale fillers giving rise to bionanocomposites. The aim of this study was to investigate the effect of the simultaneous incorporation of cellulose nanocrystals and nanosilver on the mechanical, thermal and water vapor permeability behavior of polylactic acid-based films.

Polylactic acid films and their bionanocomposites containing different levels of cellulose nanocrystals (0.01, 0.03 and 0.05 g) and nanosilver (0.01 g) were prepared by solution casting method. To improve compatibility and miscibility of the polymer, cellulose nanocrystals were reacted with acetic anhydride and modified. FTIR spectroscopy, tensile test, thermal properties (DSC), migration test and antibacterial properties were used to study the properties of the samples. The water vapor permeability of the samples were also measured.

The addition of cellulose nanocrystals, increased the glass transition temperature (Tg) and melting point (Tm) of the samples. The presence of cellulose nanocrystals increased the tensile strength and modulus of elasticity of the bionanocomposite relative to pure polylactic acid. With the addition of cellulose nanocrystals, permeability was reduced by about 25%. As the amount of cellulose nanocrystals increased, the swelling and water absorption of the samples increased significantly. The migration rate of the samples also decreased after the addition of nanocellulose.

Hypothesis: 

Nowadays, the use of mixtures of natural and synthetic polymers in the production of biological scaffolds has been considered by researchers because of their ability to achieve the desired properties.

Nanofibers from polylactic acid (PLA) and nanofibrillated chitosan/zinc oxide nanoparticles (CS/ZnO) with three different blend ratios of 1:1, 2:1 and 1:0 were fabricated by electrospinning method. In order to reduce the number of experiments and thus reduce the cost of materials and time, nine different experiments were performed using Taguchi test design method with three factors: PLA concentration (PLA 7, 9 and 11% by wt), CS/ZnO concentration (5, 10 and 20% by wt) and three different CS/ZnO ratios of 1:1, 2:1 and 1:0. The contact angle and morphology of the produced scaffolds were evaluated using scanning electron microscopy (SEM).

The results of scanning electron microscopy showed that with increasing PLA concentration, the beads and spindle-like morphologies are lost and the fibers are almost smooth and uniform. The results showed that by increasing the CS/ZnO concentration from 5% to 20%, the diameter of nanofibers first decreased and then slightly increased. The contact angle of fabricated samples decreased with increasing CS/ZnO concentration from 5% to 10%. Also from the samples obtained by Taguchi method, nanofiber sample containing PLA (7%, CS/ZnO 2: 1) with CS/ZnO concentration of 10%, due to having a smaller diameter (345±30 nm), very thin structure and lower contact angle (101°) was reported as the optimal sample. The contact angle, morphology and surface roughness for the optimum sample were examined and the surface roughness for the optimal sample was about 178 nm. Cell culture studies on the optimal sample was successfully performed.

Hypothesis: Among nanostructures, nanofibers and nanoparticles have a tremendous efficiency in tissue engineering and controlled release of drugs due to their high specific surface area and excellent biocompatibility. The production of nanofibrous scaffolds from polylactic acid (PLA), gelatin (Gel) and graphene (G) has been conducted in order to investigate their application in bone tissue engineering. The use of a combination of natural and synthetic polymers resulted in simultaneous use of the appropriate mechanical stability of PLA and the unique biological properties of Gel. The loading of graphene in the Gel/PLA structure caused the formation of nanofibrous mat with great resemblance to bone tissue. For the production of scaffolds from two mentioned polymers, the dual electrospinning method was applied. Gelatin solution was injected from a syringe and PLA or PLA-G solutions from another syringe. The morphological properties of the produced scaffolds showed that the addition of graphene to PLA solution reduced the diameter of the fabricated fibers, significantly. The addition of Gel to PLA and graphene to Gel/PLA decreased the contact angle of the samples. Gel/PLA-G hybrid nanofibers revealed good biocompatibility in the presence of human osteosarcoma cells, and no trace of cellular toxicity was observed. The cells grown on the scaffolds exhibited a spindle-like and broad morphology and almost uniformly covered the entire mat structure. The fabricated nanofibers due to smooth and nanofibrous morphology, good cellular behavior and higher hydrophilicity can be a good candidate for use in bone tissue.