Search Results (20)

A deep learning strategy was exploited to learn and predict the deformation of stiffeners, 3D printed onto a pre-stretched soft membrane. The working process reads as follows: the membrane is stretched until a pre-defined level; a specific geometry of stiffeners is printed onto it; the membrane is finally released, and due to the presence of the printed stiffeners, the system undergoes an out-of-plane deformation due to buckling. Fused deposition modeling was specifically calibrated to print PLA (Polylactic acid or polylactide) on a Lycra fabric. To assess how the printed pattern affects the buckled configuration, samples featuring different dimensions and in-plane geometries of the stiffeners were printed and numerically modeled via finite elements (FEs). The calibrated model was next exploited to construct a larger training dataset of stiffener geometries. A pre-trained You Only Look Once (YOLO)-based digital model was finally trained to foresee the link between the in-plane dimensions of the stiffeners before the release and the out-of-plane displacements in the buckled configuration. By handling around 100 different patterns, a precision of 93% in terms of recognition of the in-plane dimensions of the stiffeners and a mean absolute percentage error of 5% at most in terms of an estimate of the features of the buckled configuration were attained. The reported results testify the capability of the proposed approach and its potential efficiency to optimize the shape of the 3D printed geometries. Full article

The aim of the work is to study the effect of the 3D printing process on the microstructural and hydrophilic properties of polylactic acid (PLA) samples with various model printing patterns obtained from the black filament PLA by sequentially applying polymer layers using the FDM (fused deposition modeling) method. X-ray phase analysis revealed the partial crystallization of PLA polymer chains in the printed samples, which occurs under thermal and mechanical action on the original amorphous PLA filament during 3D printing to varying degrees, depending on the geometry of the pattern and the morphology of its surface. At the same time, IR spectroscopy data indicate the preservation of all intrastructural chemical bonds of polylactide. Measured at the original installation, the values of the wetting edge angles on the surface of the printed samples are in the range φ = 50–60°, which is significantly less than the right angle. This indicates the hydrophilic properties of the whole sample’s surface. At the same time, the influence of different geometries of model drawings in printed samples was found not only on the morphology of the sample’s surface according to SEM data but also on its wettability. Full article

In the modern world, many products are disposable or have a very short lifespan, while at the same time, those products are made from materials that will remain in the environment in the form of waste for hundreds or even thousands of years. It is a serious problem; non-biodegradable polymer wastes are part of environmental pollution and generate microplastics, which accumulate in the organisms of living beings. One of the proposed solutions is biodegradable polymers and their composites. In our work, three types of polylactide-based composites with plant-derived fillers: microcellulose powder, short flax fibers, and wood flour at 2 wt.% were prepared. Poly(lactic acid) (PLA)-based biocomposite properties were characterized in terms of mechanical and surface properties together with microscopic analysis and Fourier-transform infrared spectroscopy (FTIR), before and after a UV (ultraviolet)-light-aging process to determine the effects of each cellulose-based additive on the UV-induced degradation process. This research shows that the addition of a cellulose additive can improve the properties of the material in terms of the UV-aging process, but the form of the chosen cellulose form plays a crucial role in this case. The testing of physicochemical properties demonstrated that not only can mechanical properties be improved, but also the time of degradation under UV light exposure can be controlled by the proper selection of the reinforcing phase and the parameters of the extrusion and injection molding process. The obtained results turned out to be very interesting, not only in terms of the cost reduction of the biocomposites themselves, as mainly the waste from the wood industry was used as a low-cost filler, but also that the additive delays the aging process occurring during UV light exposure. Even a small, 2 wt.% addition of some of the tested forms of cellulose delayed surface degradation, which is one of the most important factors affecting the biodegradation process. Full article

Biocomposites based on polylactic acid (PLA), tall wheatgrass (TWG), and hemp (H) were made by injection molding. The article discusses the impact of the agrofiller content on the composite properties, including thermal (DSC, DMA, and TG) and mechanical characteristics (tensile modulus, tensile strength, and impact strength). Generally, the introduction of a plant filler into the polylactide matrix reduced the thermal resistance of the resulting composites. Plant fillers influenced primarily the cold crystallization process, probably due to their nucleating properties. The addition of fillers to the PLA matrix resulted in an increased storage modulus across all tested temperatures compared to pure PLA. In the case of a composite with 50% of plant fillers, it was almost 118%. The mechanical properties of the tested composites depended significantly on the amount of plant filler used. It was observed that adding 50% of plant filler to PLA led to a twofold increase in tensile modulus and a decrease in tensile strength and impact strength by an average of 23 and 70%, respectively. It was determined that composites incorporating tall wheatgrass (TWG) particles exhibited a slightly elevated tensile modulus while showcasing a marginally reduced strength and impact resistance in comparison to composites containing hemp (H) components. Full article

In this work, the feasibility of applying a digital twin combined with machine learning algorithms (convolutional neural network and random forest classifier) to predict the performance of PLA (polylactic acid or polylactide) parts is being investigated. These parts are printed using a low-cost desktop 3D printer based on the principle of fused filament fabrication. A digital twin of the extruder assembly has been created in this work. This is the component responsible for melting the thermoplastic material and depositing it on the print bed. The extruder assembly digital twin has been separated into three simulations, i.e., conjugate convective heat transfer, multiphase material melting, and non-Newtonian microchannel. The functionality of the physical extruder is controlled by a PID/PWM circuit, which has also been modelled within the digital twin to control the virtual extruder’s operation. The digital twin simulations were validated through experimentation and showed a good agreement. After validation, a variety of parts were printed using PLA at four different extrusion temperatures (180 °C, 190 °C, 200 °C, 210 °C) and ten different extrusion rates (ranging from 70% to 160%). Measurements of the surface roughness, hardness, and tensile strength of the printed parts were recorded. To predict the performance of the printed parts using the digital twin, a correlation was established between the temperature profile of the non-Newtonian microchannel simulation and the experimental results using the machine learning algorithms. To achieve this objective, a reduced order model (ROM) of the extruder assembly digital twin was developed to generate a training database. The database generated by the ROM (simulation results) was used as the input for the machine learning algorithms and experimental data were used as target values (classified into three categories) to establish the correlation between the digital twin output and performance of the physically printed parts. The results show that the random forest classifier has a higher accuracy compared to the convolutional neural network in categorising the printed parts based on the numerical simulations and experimental data. Full article

The present paper analyses the properties of printed polylactic acid (PLA) samples with admixtures of graphene nanopowder (GNP) at wt. 1%, 2% and 4%. The pure polylactide and admixed polylactide printed samples were examined to determine their chemical-physical properties, stiffness, and strength parameters. The tests of tensile, dynamic mechanical analysis (DMA), difference thermogravimetric (TG), and differential scanning calorimetry (DSC) were executed before and after UV (ultraviolet) treatment. The first part of the paper shows the process of manufacturing granulates and filaments mixed with graphene. The second part of the paper concerns the results of the tests made on printed samples. The analysed samples were printed using a Prusa i3 MK3 printer. It transpired that the content of graphene at 1% improved the mechanical parameters of the printed composite by organising its structure. Increasing the amount of graphene caused the values of the measured parameters to drop. This research indicates how important it is to determine the optimal values of nanoadditives in biopolymers. Full article

This study provides insight into the accelerated hydrolysis of polyester PLA through the addition of phosphites based on pentaerythritol. To control hydrolysis and ensure processing stability, different types of phosphites and combinations of phosphites with acid scavengers were studied. Therefore, commercially available PLA was compounded with selected additives on a twin-screw extruder, and hydrolysis experiments were performed at 23 °C, 35 °C and 58 °C in deionized water. Hydrolysis of PLA was evaluated by the melt volume rate (MVR) and size-exclusion chromatography (SEC). For example, after 4 days of water storage at 58 °C, the number average molecular weight of the PLA comparison sample was reduced by 31.3%, whereas PLA compounded with 0.8% phosphite P1 had a 57.7% lower molecular weight. The results are in good agreement with the expected and tested stability against hydrolysis of the investigated phosphite structures. ³¹P-NMR spectroscopy was utilized to elucidate the hydrolysis of phosphites in the presence of lactic acid. With the addition of phosphites based on pentaerythritol, the hydrolysis rate can be enhanced, and faster biodegradation behavior of biodegradable polyesters is expected. Accelerated biodegradation is beneficial for reducing the residence time of polymers in composting facilities or during home composting and as litter or microplastic residues. Full article

More than one century ago, piezoelectricity and ferroelectricity were discovered using Rochelle salt crystals. Today, modern societies are invited to switch to a resilient and circular economic model. In this context, this work proposes a method to manufacture piezoelectric devices made from agro-resources such as tartaric acid and polylactide, thereby significantly reducing the energy budget without requiring any sophisticated equipment. These piezoelectric devices are manufactured by liquid-phase epitaxy-grown Rochelle salt (RS) crystals in a 3D-printed poly(Lactic acid) (PLA) matrix, which is an artificial squared mesh which mimics anatomy of natural wood. This composite material can easily be produced in any fablab with renewable materials and at low processing temperatures, which reduces the total energy consumed. Manufactured biodegradable samples are fully recyclable and have good piezoelectric properties without any poling step. The measured piezoelectric coefficients of manufactured samples are higher than many piezoelectric polymers such as PVDF-TrFE. Full article

The aim of this work was to verify the material properties of polylactic acid (PLA) with an addition of carbon nanotubes (CNTs) or graphene nanopowder (GNP). The pure polylactide and admixed polylactide samples were subjected to chemical–physical tests to determine their stiffness and strength parameters. The tensile and impact tests were performed on samples without UV (ultraviolet) treatment and after UV treatment, in a physiological saline solution. The investigations were composed of two stages. The first one was related to the examination of the properties of pure polylactide, denoted as the following: 3001D, 4032D, and 4043D. The second stage was based on an analysis of the properties of PLA 4032D with an admixture of GNP or CNTs, at 0.1 wt.% and 0.5 wt.%. By comparing the strength and the stiffness of pure samples with samples with the considered admixtures, an essential increase was not observed. However, it is stated that the presence of GNP and CNTs in the samples positively influenced the resistance of the materials to the ageing process. Full article

In the category of biopolymers, polylactide or polylactic acid (PLA) is one of the most promising candidates considered for future developments, as it is not only biodegradable under industrial composting conditions, but it is produced from renewable natural resources. The modification of PLA through the addition of nanofillers is considered as a modern approach to improve its main characteristic features (mechanical, thermal, barrier, etc.) and to obtain specific end-use properties. Iron oxide nanoparticles (NPs) of low dimension (10–20 nm) such as magnetite (Fe₃O₄), exhibit strong magnetization in magnetic field, are biocompatible and show low toxicity, and can be considered in the production of polymer nanocomposites requiring superparamagnetic properties. Accordingly, PLA was mixed by melt-compounding with 4–16 wt.% magnetite NPs. Surface treatment of NPs with a reactive polymethylhydrogensiloxane (MHX) was investigated to render the nanofiller water repellent, less sensitive to moisture and to reduce the catalytic effects at high temperature of iron (from magnetite) on PLA macromolecular chains. The characterization of nanocomposites was focused on the differences of the rheology and morphology, modification, and improvements in the thermal properties using surface treated NPs, while the superparamagnetic behavior was confirmed by VSM (vibrating sample magnetometer) measurements. The PLA−magnetite nanocomposites had strong magnetization properties at low magnetic field (values close to 70% of M_max at H = 0.2 T), while the maximum magnetic signal (M_max) was mainly determined by the loading of the nanofiller, without any significant differences linked to the surface treatment of MNPs. These bionanocomposites showing superparamagnetic properties, close to zero magnetic remanence, and coercivity, can be further produced at a larger scale by melt-compounding and can be designed for special end-use applications, going from biomedical to technical areas. Full article

Over the past few decades, long acting injectable (LAI) depots of polylactide-co-glycolide (PLGA) or polylactic acid (PLA) based microspheres have been developed for controlled drug delivery to reduce dosing frequency and to improve the therapeutic effects. Biopharmaceuticals such as proteins and peptides are encapsulated in the microspheres to increase their bioavailability and provide a long release period (days or months) with constant drug plasma concentration. The biodegradable and biocompatible properties of PLGA/PLA polymers, including but not limited to molecular weight, end group, lactide to glycolide ratio, and minor manufacturing changes, could greatly affect the quality attributes of microsphere formulations such as release profile, size, encapsulation efficiency, and bioactivity of biopharmaceuticals. Besides, the encapsulated proteins/peptides are susceptible to harsh processing conditions associated with microsphere fabrication methods, including exposure to organic solvent, shear stress, and temperature fluctuations. The protein/peptide containing LAI microspheres in clinical use is typically prepared by double emulsion, coacervation, and spray drying techniques. The purpose of this review is to provide an overview of the formulation attributes and conventional manufacturing techniques of LAI microspheres that are currently in clinical use for protein/peptides. Furthermore, the physicochemical characteristics of the microsphere formulations are deliberated. Full article

Four different plastics were tested: potato starch based plastic (TPS-P)–BIOPLAST GF 106/02; corn starch based plastic (TPS-C)–BioComp BF 01HP; polylactic acid (polylactide) plastic (PLA)—BioComp BF 7210 and low density polyethylene, trade name Malen E FABS 23-D022; as a petrochemical reference sample. Using the blown film extrusion method and various screw rotational speeds, films were obtained and tested, as a result of which the following were determined: breaking stress, strain at break, static and dynamic friction coefficient of film in longitudinal and transverse direction, puncture resistance and strain at break, color, brightness and gloss of film, surface roughness, barrier properties and microstructure. The biodegradable plastics tested are characterized by comparable or even better mechanical strength than petrochemical polyethylene for the range of film blowing processing parameters used here. The effect of the screw rotational speed on the mechanical characteristics of the films obtained was also demonstrated. With the increase in the screw rotational speed, the decrease of barrier properties was also observed. No correlation between roughness and permeability of gases and water vapor was shown. It was indicated that biodegradable plastics might be competitive for conventional petrochemical materials used in film blowing niche applications where cost, recyclability, optical and water vapor barrier properties are not critical. Full article

Over the past few decades, with the development of science and technology, the field of biomedicine has rapidly developed, especially with respect to biomedical materials. Low toxicity and good biocompatibility have always been key targets in the development and application of biomedical materials. As a degradable and environmentally friendly polymer, polylactic acid, also known as polylactide, is favored by researchers and has been used as a commercial material in various studies. Lactic acid, as a synthetic raw material of polylactic acid, can only be obtained by sugar fermentation. Good biocompatibility and biodegradability have led it to be approved by the U.S. Food and Drug Administration (FDA) as a biomedical material. Polylactic acid has good physical properties, and its modification can optimize its properties to a certain extent. Polylactic acid blocks and blends play significant roles in drug delivery, implants, and tissue engineering to great effect. This article describes the synthesis of polylactic acid (PLA) and its raw materials, physical properties, degradation, modification, and applications in the field of biomedicine. It aims to contribute to the important knowledge and development of PLA in biomedical applications. Full article

Surface-treated fumed silica nanoparticles were added at various concentrations (from 1 to 24 vol%) to a commercial poly(lactide) or poly(lactic acid) (PLA) matrix specifically designed for packaging applications. Thermo-mechanical behavior of the resulting nanocomposites was investigated. Field Emission Scanning Electron Microscopy (FESEM) micrographs revealed how a homogeneous nanofiller dispersion was obtained even at elevated filler amounts, with a positive influence of the thermal degradation stability of the materials. Modelization of Differential Scanning Calorimetry (DSC) curves through the Avrami–Ozawa model demonstrated that fumed silica nanoparticles did not substantially affect the crystallization behavior of the material. On the other hand, nanosilica addition was responsible for significant improvements of the storage modulus (E′) above the glass transition temperature and of the Vicat grade. Multifrequency DMTA tests showed that the stabilizing effect due to nanosilica introduction could be effective over the whole range of testing frequencies. Sumita model was used to evaluate the level of filler dispersion. The obtained results demonstrated the potential of functionalized silica nanoparticles in improving the thermo-mechanical stability of biodegradable matrices for packaging applications, especially at elevated service temperatures. Full article

End functionalized polylactides are prepared by ring opening polymerization of L-lactide in the presence of stannous octoate (Sn(Oct)₂). Three chromophores, 9H-carbazol-ethanol (CA), 9-fluorenyl-methanol (FM), and 2-(4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino)ethanol (Disperse Red 13, DR), are for the first time used as co-initiators in the polymerization process. The polymerization reaction is initiated by conventional thermal treatment, but in the case of FM, microwave-assisted polymerization is also carried out. CA and FM absorb and emit in the UV portion of the electromagnetic spectrum, whereas DR absorbs in the visible part. The obtained end-capped polylactides derivatives show the same photophysical properties as the initiator, so they are “macromolecular dyes” (MDs) that can be used “as synthesized” or can be blended with commercial poly(lactic acid) (PLA). The blends of PLA with MDs have ultraviolet-visible (UV-Vis) absorption and fluorescence emission features similar to that of MDs and thermal properties typical of PLA. Finally, migration tests, carried out onto the blends of PLA with MDs and PLA with free chromophores, show that MDs are less released than free chromophores both in solution and in the solid phase. Full article