PLA Samples Research Articles

A facile strategy for preparation of strong tough poly(lactic acid) foam with a unique microfibrillated bimodal micro/nano cellular structure

This work reports the design and fabrication of strong tough poly(lactic acid) (PLA) foam by combining pressure-induced-flow (PIF) processing with supercritical CO2 foaming. PIF processing widened the foaming window of PLA to 40–120 °C, while supercritical CO2 foaming released the undesired internal stress of PLA samples with PIF processing (P-PLA). The prepared PLA foams displayed a unique microfibrillated bimodal micro/nano cellular structure which is strongly affected by saturation temperature (Ts). Both micron and nano cells showed decreasing cells size and increasing cell density as Ts elevated. The orientation factor as well as internal stress of PLA foams decreased with increased Ts. Compared with P-PLA samples, PLA foam prepared at Ts of 40 °C showed negligible reduction of orientation from 0.45 to 0.41 and release of internal stress characterized by the rightward shift of Raman peak (stretching vibration of CO bond from 1763 to 1766 cm−1). Furthermore, PLA foam prepared at Ts of 40 °C presented excellent impact strength (32.3 kJ/m2), tensile strength (42.0 MPa), and ductility (14.2%). The combination of PIF processing and supercritical CO2 foaming provides a facile and effective method to prepare strong tough PLA foam that has immense potential in biomedical, aerospace, automotive, and other structural applications.

Magnetic field assisted 3D printing of short carbon fibre-reinforced polymer composites

This paper investigates and discusses the outcomes from an ongoing feasibility research being conducted at Advanced Composites Research Focused Group on 3D printing polymers and carbon composites subjected to localised magnetic field force lines. Magnetic equipped composite processes are starting to become an important new development for structural applications. Specific to this paper, in-situ alignment of short carbon fibres (∼1 mm length) in thermoplastic polymer filaments (Onyx FR, a Nylon base with micro carbon-fibres with a flame retardant additive supplied by Markforged) during a fused deposition modelling (FDM) based 3D printing (MakerBot Replicator 2). An experiment took place in which samples of PLA and onyx were printed, both with and without a magnetic field present. This was done to see what effects, if any, the magnetic field had on the flow orientation of these materials when printed. The results from using a high-resolution optical microscopy and scanning electron microscopy showed that while carbon fibres within the Onyx had aligned in response to the magnetic field, the PLA samples were visibly unchanged by the magnetic field. The observations have been partially supported by theoretical calculations utilizing Multiphysics constitutive equations.

Additive manufacturing of 3D reinforced structures: effects of process parameters on mechanical properties

Three dimensional (3D) printing or Rapid Prototyping (RP) provides an innovative additive manufacturing method for prototypes and functional components. Fused deposition modeling (FDM) is a fast growing rapid prototyping technology for fabricating thermoplastic parts due to its ability to build functional parts having complex geometrical shapes in reasonable time periods with the advantages of low cost, minimal wastage, and no tooling or touch labour. The quality of a built part (surface finish, dimensional accuracy or mechanical properties) depends on several process variables. Assessing the influence of these process parameters on mechanical properties is vital for understanding the performance of 3D printed materials, and to determine the needs for further research. The aim of this study is to characterize and assess of different process parameters on the mechanical performance of PLA and ABS samples manufactured with low cost 3D printing. Tensile and three-point bending tests series were carried out to determine the mechanical response of the printed specimens with different process parameters. Finally, the practicality of the results was assessed by testing an evaluation structure as a case example.

Biobased alginate treatments on flax fibre reinforced PLA and PHBV composites

This paper presents a novel study on the effect of alginates as a compatibilizer and flame retardant in natural fibre reinforced PLA and PHBV composites. Though alginates have been extensively studied for biomedical applications it's potential as a bio-based compatibilizer and flame retardant in biocomposites has not been investigated. In this study, flax nonwovens were treated with alginate solution and composites were prepared by casting technique and compression molding using chemically modified and unmodified flax nonwovens and biopolymers such as poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV). The developed composites were subjected to dynamic mechanical and thermal analysis. The fire resistance of the treated and untreated flax fibres were also tested using a cone calorimeter. Composites containing alginate modified flax fibres were found to exhibit improved viscoelastic and thermal properties. The storage modulus of alginate modified flax reinforced PLA samples exhibited a 60% increment compared to unmodified samples. Alginate modified flax fabrics exhibited reduced heat release rate values and smoke release rates when compared to untreated flax fabrics. Alginates showed potential for use as environmentally friendly compatibilizers and smoke suppressors in natural fibre composites for the development of completely sustainable and biodegradable composites.

Design of experiment analysis on tensile properties of PLA samples produced by fused filament fabrication

The fused filament fabrication (FFF) is one of the most common forms of 3D printing with many hobbyists and as well as professional printers adopting this technology. With numerous printing parameters available for each print, having the knowledge to optimize the printing process to obtain a custom mechanical properties is clearly advantageous. This paper aims to analyze the elastic mechanical properties of PLA specimens manufactured through FFF process. To reduce experimental runs, the L27 Taguchi orthogonal array was used to analyze the influence of seven parameters, (i) infill pattern, (ii) layer height, (iii) infill density, (iv) printing velocity, (v) raster orientation, (vi) outline overlap, and (vii) extruder temperature, and three interactions, (i) infill pattern/layer height, (ii) infill pattern/infill density and, (iii) layer height/infill density on both Young’s modulus (E) and yield strength (Rp0.2). To remove any doubt about certain parameters, a two-level fractional factorial design with four factors (24–1) was used to supplement Taguchi approach. Results show that the infill density, infill pattern, printing velocity, and printing orientation are the most influential parameters, whereas layer height, extruder temperature, and outline overlap have no significant influence on Young’s modulus and Yield strength. We show that the analysis of interactions could play a leading role in optimization parameters by removing doubt concerning some parameters. This work could be further developed to propose a model to help designers to obtain either tailor-made or a robust mechanical property with minimum variation and uncertainty in product.

Influence of biobased plasticizers on 3D printed polylactic acid composites filled with sustainable biofiller

Three-dimensional (3D) printing is extensively explored in scientific research and engineering applications; however, little is known about the feasibility of 3D printing multi-material composites. This paper investigates the effect of three different plasticizers including epoxidized soybean oil (ESO), polyethylene glycol (PEG), and glycerol on mechanical and thermal properties of PLA filled with distillers dried grains with solubles (DDGS) filaments for 3D printing. The composite filaments were extruded using a twin-screw extruder equipped with a collector to achieve uniform diameter. The eco-friendly PLA-DDGS-plasticizer based filaments were then used to print dog-bone and flexural samples. The results showed that the PLA-DDGS blends plasticized with ESO have improved elongation at break compared to pure PLA and those plasticized with glycerol and PEG. These results were evidenced by SEM micrographs showing PLA-plasticizers phase separations and formation of voids in fracture surface of PLA-DDGS plasticized by PEG and glycerol. DMA and FT-IR measurements confirmed the compatibility between PLA and ESO. PLA-DDGS blend containing 10 % ESO exhibited 6 % higher storage modulus in comparison with PLA samples, while the addition of 12.5 % ESO reduced storage modulus by 27 %. Storage modulus in 3D printed samples plasticized by PEG and glycerol showed a reduction of 32 % and 89 %, respectively. The same trend was observed in the mechanical properties of 3D printed composite filaments. Among all samples, PLA-DDGS blends plasticized by 15 % ESO exhibited higher elongation at the break while a significant reduction of 21 % was observed in ultimate tensile strength. The study confirmed that the types and amounts of plasticizer dictates the morphology and mechanical properties of PLA-DDGS composite.

Properties of Mosquito Repellent-Plasticized Poly(lactic acid) Strands.

Poly(lactic acid) (PLA) is an attractive candidate for replacing petrochemical polymers because it is fully biodegradable. This study investigated the potential of PLA as a sustainable and environmentally friendly alternative material that can be developed into commercially viable wearable mosquito repellent devices with desirable characteristics. PLA strands containing DEET and IR3535 were prepared by twin screw extrusion compounding and simultaneously functioned as plasticizers for the polymer. The plasticizing effect was investigated by thermal and rheological studies. DSC studies showed that the addition of DEET and IR3535 into PLA strands reduced the glass transition temperature consistent with predictions of the Fox equation, thus proving their efficiency as plasticizers. The rheology of molten samples of neat PLA and PLA/repellents blends, evaluated at 200 °C, was consistent with shear-thinning pseudoplastic behaviour. Raman studies revealed a nonlinear concentration gradient for DEET in the PLA strand, indicating non-Fickian Type II transport controlling the desorption process. Release data obtained at 50 °C showed initial rapid release followed by a slower, near constant rate at longer times. The release rate data were fitted to a novel modification of the Peppas-Sahlin desorption model.

Quality parameters and shelf-life of smoked Dalmatian dry-cured ham packed in bio-based and plastic bilayer pouches

Traditional Dalmatian dry-cured ham (prosciutto) was packaged under modified atmosphere, MAP (30%CO2/70%N2) and vacuum, in commercial polyamide/polyethylene (PA/PE) and biodegradable poly(lactic acid) (PLA) material. Samples were stored at 4 °C for 180 days and the effect of packaging materials and methods on various quality parameters was studied. The least changes were observed for PA/PE for both packaging methods. The pH, moisture content, colour parameters, TBARS and DNPH values of dry-cured ham packed in PLA were significantly affected already after 1 month in MAP and after 3 months in vacuum packaging. Similar changes in the above parameters were also observed in the control sample (packed in air-PA/PE) while vacuum-PA/PE and MAP-PA/PE showed significantly better results. The instrumental analyses agreed with the sensory panel results where appearance, taste, texture and overall acceptability of PLA samples decreased significantly already after 2 months of storage. For both, MAP-PA/PE and vacuum-PA/PE samples, the shelf-life was estimated to be 5 months.

Influence of FFF process parameters and macrostructure homogeneity on PLA impact strength

The article presents studies of the additive manufacturing printing parameters influence onthe impact strength of PLA samples obtained by the fused filament fabrication (FFF) method. Two processvariables were taken into account in the research program: the height of the printed layer andthe printing temperature. An optical microscope was used to analyze the cross-section image (breakthrough)of the samples. The impact strength was determined at −40°C and 23°C. Selected geometricfeatures of the macrostructure (uniformity and thickness of individual layers, voids) determined on thebasis of the sample cross-section image analysis, enhanced the possibility of assessing the PLA impactstrength, depending on the adopted process variables and the temperature at which the experiment wascarried out.

강화 단계가 PLA 매트릭스 나노 복합재의 기계적 및 생체 적합성 특성에 미치는 영향

In this study, it was aimed to obtain nanocomposite structure with poly(lactic acid) (PLA) matrix and to improve the mechanical and morphological properties of the PLA matrix nano-reinforced composites. Titanium dioxide (TiO₂) and hydroxyapatite (HA) nanoparticles were used as reinforcing elements. Solvent casting particle leaching method was used for the production of the composites. Thermal characterization and compression test of the composite samples were carried out. Microstructural properties and the phases formed on the surface of in vitro tested samples were examined. As a result of the study, it was observed that nano-reinforced composites with PLA matrix are biocompatible and apatite formation increases gradually every week. Also the highest compressive strength was obtained in PLA/HA samples, while the lowest was obtained in PLA sample. It was concluded that composites prepared within the scope of the study can be used as artificial tissue scaffolds in biomedical and medical applications.

Effect of fill pattern and printing speed on friction characteristics of FDM printed polylactic acid polymer

ABSTRACT Fused Deposition Modelling is a three-dimensional printing technique used for making prototypes and rapid manufacturing of various parts ranging from commercial to biomedical applications. The FDM printed parts results in anisotropic mechanical properties due to weak bond formation between the rasters and the layers. It is possible to print a part with desired properties by optimising the tool path strategy and printing parameters. This paper investigates the friction properties of FDM-built PLA samples with three different fill patterns (Concentric, linear, and Hilbert) at two different printing speeds (20 mm/s and 50 mm/s). This study shows that printing parameters influence the friction coefficient and specific wear rate. The result shows that the fill pattern with a suitable printing speed provides good bonding between the rasters and the layers, and enhances the crystallinity for better wear resistance.

Fracture characterization and modeling of Gyroid filled 3D printed PLA structures

Abstract Polylactic acid (PLA) is a commonly used biodegradable material in medical and increasingly in industrial applications. These materials are often exposed to various flaws and faults due to working and production conditions, and increasing the demand for PLA for various applications requires a full understanding of its fracture behavior. In addition to ABS, PLA is a widely used polymeric material in 3D printing. The gyroid type of filling is advantageous for overcoming the relatively higher brittleness of PLA in comparison with conventional thermoplastic polymers. In this study, the effects of various filling ratios on the fracture toughness of 3D printed PLA samples with gyroid pattern were investigated numerically and experimentally for pure mode I, combined mode I/II, and pure mode II. Two-dimensional finite element modeling was created, and the two-dimensional functions of stress intensity coefficients were extracted in loading mode I, mode I/II, and mode II at varied filling ratios of the gyroid PLA samples. Mixed-mode fracture tests for 3D printed PLA samples with a gyroid pattern at various filling ratios were performed by using a specially developed fracture testing fixture. The results showed that the amount of fracture toughness of the samples under study in tensile mode was much higher than those values in shear mode. Also, as the percentages of the filling ratios in the samples increased, both tensile and shear fracture toughness improved.

Influence of fabrication parameters on the elastic modulus and characteristic stresses in 3D printed PLA samples produced via fused deposition modelling technique

Abstract Commonly used 3D printed samples are partially infilled to reduce time and cost of printing, with mechanical properties dependent on the infill. In this work, the influence of the percentage and pattern of infill in PLA printed samples on the elastic modulus and characteristic stresses was analyzed. The elastic modulus, E, and characteristic stresses (σ 0.2, σ 4 and the maximum tensile stress) were determined for each sample using impulse excitation technique, IET, and uniaxial tensile tests. An apparent density was calculated for each pattern and infill percentage, and the mechanical parameters were studied as a function of such density. The results of IET obtained in different modes of vibration were analyzed and an apparent value of E was calculated. FEM simulations were carried out and the results were compared with the experimental ones. The mechanical properties for different infill percentages and infill patterns were studied by comparing the specific values of E and the stresses. Samples with higher infill percentages exhibit the best specific values of maximum stress and E, but the sample with 20% infill has the highest specific yield stress and a good value of the specific E from flexural vibrations.

Mechanical Properties of FDM Printed PLA Parts before and after Thermal Treatment.

Fused deposition modeling (FDM) is one of the most often-used technologies in additive manufacturing. Several materials are used with this technology, such as poly(lactic acid) (PLA), which is most commonly applied. The mechanical properties of 3D-printed parts depend on the process parameters. This is why, in this study, three-point bending tests were carried out to characterize the influence of build orientation, layer thickness, printing temperature and printing speed on the mechanical properties of PLA samples. Not only the process parameters may affect the mechanical properties, but heat after-treatment also has an influence on them. For this reason, additional samples were printed with optimal process parameters and characterized after pure heat treatment as well as after deformation at a temperature above the glass transition temperature, cooling with applied deformation, and subsequent recovery under heat treatment. These findings are planned to be used in a future study on finger orthoses that could either be printed according to shape or in a flat shape and afterwards heated and bent around the finger.

The promiscuous potential of cellulase in degradation of polylactic acid and its jute composite

It has been suggested that cellulolytic enzymes can be effective on the degradation of PLA samples. The idea was investigated by examining the impact of cellulase on degradation of PLA and PLA-jute (64/36) composite in an aqueous medium. The obtained results demonstrated 55% and 61% thickness reduction in PLA and PLA-jute specimens after four months of treatment, respectively. Gel permeation chromatography (GPC) showed significant decline in the number average molecular weight (Mn) approximately equal to 85% and 80% for PLA and PLA-jute in comparison with their control. The poly dispersity index (PDI) of PLA and PLA-jute declined 41% and 49% that disclosed more homogenous distribution in molecular weight of the polymer after treatment with cellulase. The cellulase promiscuity effect on PLA degradation was further revealed by Fourier-transform infrared spectroscopy (FT-IR) analysis where substantial decrease in the peak intensities of the polymer related functional groups were observed. In addition, PLA biodegradation was studied in more detail by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) of control and cellulase treated specimens. The obtained results confirmed the promiscuous function of cellulase in the presence or the absence of jute as the specific substrate of cellulase. This can be considered as a major breakthrough to develop effective biodegradation processes for PLA products at the end of their life cycle.

Fractal characterization of conductive Ag/flexible 3D printed PLA

In this paper, thin and flexible PLA plates were prepared through FDM printing process. The traditional FDM process was adopted at predetermined optimal printing parameters of the 3D printer. The CAD designs of the samples were built on SpaceClaim modeler (ANSYS® 2019). The slicing and generation of the toolpath (gcodes) were undertaken in Cura software whereas the printing undertaken using a Desktop 3D printer (WANHAO Duplicator D10). The flexible PLA samples were designed for conductivity in smart devices; as such, they were coated with microfilms of highly conductive silver paint through a dipping method. The dipping was carefully undertaken in which the samples could soak inside the paint for 40 seconds and then removed and allowed to dry in vacuum desiccators for 12 hours. The samples were then heat treated at varying times (0, 10 and 20 minutes) in an oven at a constant temperature of 100°. The samples were then profiled using atomic force microscopy to obtain the microroughness characteristics of the Ag/PLA surfaces. The height features as well as spatial roughness characteristics were obtained through mono-fractal and multifractal approaches. The influence of heat treatment times at the reported temperature is shown to significantly shown to influence the spatial roughness characteristics of the 3D printed flexible samples.

Thermal and Environmentally Induced Degradation Behaviors of Amorphous and Semicrystalline PLAs Through Rheological Analysis

The degradation behaviors of an amorphous and a semicrystalline PLA (i.e., aPLA and cPLA) with similar molecular weights are compared at elevated temperatures and after being treated under various environmental conditions through using small amplitude oscillatory shear rheological experiments. The degradation behaviors are also studied by differential scanning calorimetry and Fourier-transform infrared spectroscopy analysis. Melt thermal degradation analysis shows that the d-lactic acid content does not affect the degradation behavior of PLAs. This is while the increase in temperature beyond 190 °C dramatically, but still similarly, increases the degradation rate of aPLA and cPLA samples. It is also shown that processing of aPLA through a twin-screw extruder at temperatures below 190 °C and at different screw speeds has a negligible effect on its thermal degradation. The degradation of the PLA samples treated under various humidity levels as well as when exposed to different environments such as tap and sea water, regular garden soil and commercial grade microbial fertilizer, is expedited more dramatically around and beyond the glass transition temperature. This is while the cPLA, with around 50% crystallinity, reveals a much less degradation under the aforementioned conditions. This is because the bulk diffusion of water molecules or micro-organisms is harder in cPLA with a compacted crystalline structure. It should, however, be emphasized that the fertilizer degrades the PLA samples much faster and more pronounced than other environments. The tap and sea water exhibits a similar effect on the degradation of PLA samples. Notably, the temperature is the most effective parameter in expediting the degradation rate of PLA, suggesting that the PLA degradation could gradually occur in the environments with extreme warm weather. The increase in humidity also accelerates such degradation.

Cold Crystallization Kinetics and Thermal Degradation of PLA Composites with Metal Oxide Nanofillers

Poly(lactic acid) (PLA) nanocomposites with antimicrobial fillers have been increasingly explored as food packaging materials that are made of a biobased matrix and can minimize food loss due to spoilage. Some of the most commonly studied fillers are zinc oxide (ZnO), titanium dioxide (TiO2), and silver nanoparticles (AgNPs). In this work, nanocomposites with 1 wt.% of each filler were prepared by melt mixing. An extensive study of thermally stimulated processes such as crystallization, nucleation, degradation, and their kinetics was carried out using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). In detail, non-isothermal cold crystallization studies were performed with DSC and polarized light microscopy (PLM), and kinetics were analyzed with multiple equations. The activation energy of the non-isothermal cold crystallization was calculated with the methods of Kissinger and Friedman. The latter was used to also determine the Hoffman–Lauritzen parameters (Kg and U*) by applying the Vyazovkin method. Additionally, effective activation energy and kinetic parameters of the thermal decomposition process were determined by applying the isoconversional differential method and multivariate non-linear regression method. According to TGA results, metal oxide nanofillers affected the thermal stability of PLA and caused a decrease in the activation energy values. Moreover, the fillers acted as heterogenous nucleating agents, accelerating the non-isothermal crystallization of PLA, thus reducing its activation energy. It can be concluded that metal oxide nanofillers catalytically affect the thermal degradation and crystallization of PLA samples.

Morphological and thermal properties of composites prepared with poly(lactic acid), poly(ethylene-alt-maleic anhydride), and biochar from microwave-pyrolyzed jatropha seeds

The morphological and thermal properties of composites containing a bioplastic blend and micro/nano-sized biochar from pyrolyzed jatropha seeds from microwave pyrolyzed jatropha seeds were investigated using scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The biocomposite samples exhibited a brittle structure with a slightly ductile chip-like appearance. The Fourier transform infrared spectroscopy results for the PLA/PEMA/BC bio-composites were comparable to the PLA/BC biocomposites. A lower bio-filler content had more pronounced peak intensities than the higher bio-filler content biocomposites. The added PEMA compatibilizer in the PLA/PEMA/BC biocomposite showed more pronounced peaks, which indicated slightly improved bonding/interaction between the bio-filler and the matrix. Overall, increasing bio-filler content did not drastically affect the functional groups of the biocomposites. Thermogravimetric and differential scanning calorimetry analysis showed the developed biocomposites had a slight improvement in thermal stability, in comparison to the PLA sample. Improvements in the thermal stability of the PLA/PEMA/BC biocomposite could be attributed to the additional hydroxyl group, which was due to the added PEMA in the PLA and PLA/BC. According to the results of the analysis of the developed biocomposites, the biocomposites were more brittle and had reasonable thermal stability.

Mechanical and thermal study of 3D printing composite filaments from wind turbine waste

AbstractThe subject of composite waste from the wind turbine blades has become more serious and challenging. Inspired by the recent popularity of the 3D printing industry, this work presents a step‐by‐step recycling solution to manufacture fiber reinforced filaments for fused filament fabrication. Polylactic acid filaments reinforced with 3, 5, and 10 wt% recyclate content are manufactured and tested using thermogravimetric analysis (TGA), and micro computed tomography (μCT). TGA results elucidate that an increase in the recyclate content translates into a reduction in the mean fiber length. Visualizing μCT results, it is confirmed that fibers are predominantly aligned along the filament length. Tensile specimens per ASTM D636 standard are manufactured and tested with results showing an improvement of, respectively, 20% and 28% in the specific tensile strength and modulus compared with pure PLA samples. The mechanical performance of the newly introduced recycled parts is also assessed through a coherent set of theoretical models, where an excellent agreement between the experiments and predictions is observed.