Polylactic Acid Coatings Research Articles

The effect of polylactic acid ordering on the long-term corrosion protection capacity of biodegradable magnesium alloys

The polylactic acid (PLA) coatings of different crystallinity were prepared on biodegradable Mg-2.2Zn-0.3Ca alloy wires to improve the long-term anti-corrosion properties. The composition characteristics and microstructure of the samples were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscope (FTIR), wide angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). The corrosion resistance of all samples was investigated by immersion tests and electrochemical techniques in vitro simulated body fluid (SBF). The results indicated heat treatment improved the crystallinity of PLA coating and heated-coating performed protective behaviors in the short and long-term immersion. The corrosion rate of heated samples was lower than that of unheated samples and exhibited superior long term protective effect for Mg alloy wires. The lifetime of heated sample (H2) increased significantly from 33 to 55 days. The initial electrochemical performance of unheated coating was better than heated coating, but it declined more rapidly during the long-term immersion. These results indicated that PLA coating could not ignore the effect of its crystallinity to anti-corrosion ability, and only the suit heat treatment makes PLA coating more ordering and achieves higher corrosion resistance in vitro immersion. Therefore, it has promising potential by controlling effectively the PLA ordering for surgical implant applications.

Enhancing mechanical performance and water resistance of Careya-Banana fiber epoxy hybrid composites through PLA coating and alkali treatment

The ongoing research focuses on exploring the potential of Careya arborea (CA) fiber, banana fiber (BF), and epoxy composites as sustainable alternatives to petroleum-based products and synthetic fibers. The aim is to enhance the interfacial bonding and overall performance of these composites while reducing reliance on traditional materials. The study investigates the adhesion between CA fiber, BF (both chemically treated), and epoxy with polylactic acid (PLA) coating. Specifically, it examined how the PLA coating affects the mechanical properties, including tensile strength, flexural strength, impact resistance, and water absorption behavior, of the fabricated composites. Mechanical characterizations of the composite specimens are conducted following ASTM standards. The PLA-coated and NaOH-treated specimens significantly improved their tensile strength (20.56%) and flexural strength (16.7%), and significantly reduced their water absorption capacity (by 47.6%) compared to the untreated ones. These findings highlight the promise of using treated natural fibers and PLA coatings to create more sustainable and high-performance composite materials.

Degradation of paper-based boxes for food delivery in composting and anaerobic digestion tests

This study evaluated the fate of food delivery boxes when subjected to biological treatments, reproducing at the lab-scale the conditions of full-scale plants. Four paper-based boxes were composted: two made of paper only, one coupled with polylactic acid (PLA), and one with a barrier coating. One paper only box and the box with PLA were also investigated for their anaerobic degradability with biochemical methane potential (BMP) and semi-continuous tests. During composting, the boxes were not recognisable inside the compost after four (paper only boxes), eight (box with PLA), and twelve (box with barrier coating) weeks. In BMP tests, the paper only box showed a degradability similar to that of food waste (92 %), while the box with PLA degraded only at 76 %. Furthermore, undigested pieces of PLA were found in semi-continuous tests. Accordingly, paper resulted suitable for biological treatments, while the presence of PLA or other barrier coatings can be critical.

Systematic characterization and enhanced corrosion resistance of novel β-type Ti-30Zr-5Mo biomedical alloys with halloysite nanotubes (HNTs) and zirconia (ZrO2)-reinforced polylactic acid (PLA) matrix coatings

This study investigates synthesis, the in-vitro corrosion resistance and adhesion performance of PLA-based composite coatings reinforced with halloysite nanotubes (HNT) and zirconia (ZrO2) on beta-type Ti-30Zr-5Mo biomedical alloys. The coatings were synthesized using the sol-gel method and characterized for their surface morphology, chemical composition, and electrochemical properties. SEM analysis revealed the presence of micropores and cracks, particularly in HNT and HNT/ZrO2 bilayer coatings. XPS and Raman spectroscopy confirmed the successful integration of HNT and ZrO2 into the PLA matrix. The potentiodynamic polarization scans and electrochemical impedance spectroscopy (EIS) showed enhanced corrosion resistance for coatings containing HNT and ZrO2, with the HNT/ZrO2 bilayer demonstrating the best performance. Contact angle measurements indicated hydrophilic properties, crucial for bioactive surfaces. Overall, the study demonstrates that HNT and ZrO2 reinforcements in PLA coatings significantly improve the corrosion resistance and bioactivity of Ti-30Zr-5Mo alloys, making them promising candidates for biomedical applications. Details are compared and discussed in the text.

PREVENTING OF MIGRATION IN FOOD CONTACT POLYVINYL CHLORIDE-BASED STRETCH FILMS WITH POLYLACTIC ACID LAYER

In this study, the effectiveness of biodegradable polylactic acid (PLA) coatings for the prevention of residues migrating through polyvinyl chloride (PVC) films was investigated. PLA films prepared in chloroform at concentrations of 5, 10, 15 and 20 wt% were heat sealed to PVC film surfaces in a hot press (130 °C, 5 min, 5 tons). Physical, mechanical, FTIR and migration analyses were performed on these two-layer films. With PLA coating, the thickness of the films increased, mechanical properties decreased and some changes in color values occurred. It was determined by FTIR that there was no structural change on both surfaces of the films as a result of hot pressing. From the overall migration analysis, no migration was observed in the tests with aqueous food simulants, while migration was detected in fatty food simulants. In the specific migration analysis by GC-MS, di-2-ethylhexyl phthalate (DEHP) migration decreased by 50% with PLA coating. It is concluded that PLA coating of PVC stretch films may be a promising application to reduce migration.

Electrochemical investigations of PLA coatings deposited by fused filament fabrication on magnesium alloy in Ringer's solution

In this paper, polylactic acid (PLA) layers were printed on AM60 magnesium alloy through a fused filament fabrication-3D printing manufacturing method, as a low-cost and innovative technology. Then, the effect of coating thickness and anodized layer as a binder on the electrochemical behavior of Mg substrates was investigated in Ringer's solution. Electrochemical impedance spectroscopy, Tafel polarization, and weight loss investigations were performed at various exposure times for 28 days to achieve this purpose. Corroded surfaces were also analyzed through field emission scanning electron microscopy images and Fourier-transform infrared spectroscopy patterns. The obtained results showed that the higher thickness of the layer with a value of 400 µm was not effective in raising the PLA layer impedance without the anodized layer. However, the higher PLA thickness could have a key role in the corrosion rate reduction of PLA layers when printed on the anodized layer. The lowest corrosion rate with a value of 0.3 µA/cm2 was related to the PLA-printed layer with a lower thickness (200 µm) and without an anodized layer. This reduction range in corrosion current density was about 80.2–99.4 % compared to the Mg alloy. The weight loss behavior of PLA layers during a long time of exposure was followed by a logarithmic function. The range of corrosion rate decrease was 9.7–32.2 %. The PLA degradation mechanism was also suggested based on all obtained results.

Deposition and corrosion performance of phosphate-polylactic acid composite coatings on WE43 magnesium alloy

The degradation profile of Mg alloys in biomedical environments can be controlled by applying various types of surface coatings. Phosphate chemical conversion coatings (CaP) and polylactic acid (PLA) biopolymer coatings are biocompatible and promising for the corrosion protection of Mg alloys. The aim of this work was to investigate the physicochemical properties and corrosion performance of inorganic, organic, and mixed inorganic-organic coatings. Three types of surface modification, CaP, PLA, and a combined CaP-PLA coating were obtained on the surface of the magnesium alloy WE43. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and infrared spectroscopy were employed to characterize the surface and interfacial morphology, along with the composition of the coatings before and after corrosion experiments. The protective performance of obtained coatings was examined by electrochemical impedance spectroscopy and immersion testing in Hank's solution. Coated samples showed significantly improved corrosion resistance. The values of polarization resistance based on impedance measurements were 164; 8688; 69,410; and 228,369 Ω cm2 for WE43 alloy, CaP, PLA, and CaP-PLA coatings, respectively. The results allowed to propose the mechanism of the coatings growth and their further corrosion degradation. A two-component CaP-PLA coating provided reliable corrosion resistance in Hank's solution for 14 days.

Effects of Various Adhesive Layers on Electrochemical Characteristics of 3D-Printed Polylactic Acid Coatings on AM60 Magnesium Alloy

Effects of Various Adhesive Layers on Electrochemical Characteristics of 3D-Printed Polylactic Acid Coatings on AM60 Magnesium Alloy

Nanoplastics from disposable paper cups and microwavable food containers

Nanoplastics (NPs, <1 µm) pose greater risks due to their increased absorption rates in biological systems. In this study, we investigated the release of NPs from paper cups and microwavable food containers coated with low-density polyethylene (LDPE) and polylactic acid (PLA). For disposable paper cups, we found that LDPE-coated cups released up to 26-fold more NPs (maximum 1.9 × 107 per cup) than PLA-coated ones. The NPs release from LDPE-coated cups was increased at high temperatures above 80 °C, and further increased by physical agitation. However, negligible NP release was observed when the inner coating thickness exceeded 1 mm. For microwavable food containers, those with PLA coatings were more susceptible to the effects of microwave. Depending on the cooking time, we noticed a significant difference (up to 40000 times) in the number of released NPs between LDPE and PLA coatings. Additionally, higher microwave power level led to an increase of NPs, even with constant total energy input. Considering the release of NP, PLA coatings for disposable paper cups and LDPE coatings for microwavable food containers seem more suitable. Furthermore, our results suggest that multi-use cups significantly reduce NPs release due to their material thickness, making them a safer alternative to disposable ones.

Impact of 3D-printed PLA coatings on the mechanical and adhesion properties of AM60 magnesium alloys

This article investigates the impact of PLA (Polylactic Acid), an emerging bioplastic coating, fabricated with an additive manufacturing method (3D printing) on AM60 magnesium alloys. In addition to tensile testing, the adhesion of PLA on magnesium alloys with two epoxy and polyvinyl pyrrolidone adhesives was checked with the pull-off experiment. The strength of the bond between PLA and AM60 magnesium alloy was tested using two different adhesives, polyvinyl pyrrolidone and epoxy glue. The polyvinyl pyrrolidone adhesive resulted in an adhesion strength of 0.3 ± 0.02 MPa, whereas the epoxy glue resulted in a much stronger adhesion strength of 4.29 ± 0.71. Coating the AM60 magnesium alloy with PLA led to enhancements of 5.26 % in the yield stress (Syt), 7.79 % in the ultimate stress (Sut), 2.40 % in the elongation, and 2.34 % in the elastic module, as compared to the uncoated specimen. The fracture surface was also checked with FESEM (field-emission scanning electron microscopy) images. It was found that the fracture type for AM60 magnesium alloys with and without PLA coatings was brittle under tensile loading.

Characterization of Two Types of Polylactic Acid Coating Loaded with Gentamicin Sulphate Deposed on AZ31 Alloy

This paper compares two types of polylactic acid (PLA) coating on AZ31 alloy obtained by dip coating and electrospinning. Both types of coating were loaded with gentamicin sulphate (GS) and the drug-loading efficiency and release were assessed. A higher encapsulation and release efficiency of GS was seen for dip coating (73% and 49.53%, respectively) compared to nanofiber coating (65% and 12.37%, respectively). Furthermore, the antibacterial effect of the samples with and without GS was assessed using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria, showing that the samples with the drug encapsulated are more resistant to bacteria than the other samples. The electrochemical data reveal a higher stability in the SBF of the surface obtained by dipping than that obtained by electrospinning. The PLA coating shows a porosity of 46% for the sample obtained through dip coating and 32% for nanofibers, which is in accordance with the BET analysis results. Moreover, a higher adhesion strength was obtained for AZ31-PLA-dip (4.99 MPa) than for the AZ31-PLA-nanofibers (1.66 MPa). All samples were structurally, morphologically, and topographically characterized.

Electrical-responsive biocompatible coatings for highly corrosion-resistance and self-healing performance on AZ31 Mg alloy

An electrically stimulated smart 8-hydroxyquinoline loaded poly(3,4-ethylenedioxythiophene) (8-HQ@PEDOT) nanocapsules are fabricated via emulsion polymerization. SEM and TEM images indicate that the 8-HQ@PEDOT nanocapsules display a hollow nanosphere structure with an average diameter of 300–500 nm. TGA results confirm the loading ratio of 8-HQ inhibitors in 8-HQ@PEDOT nanocapsules is approximately at about 8.2 %. Furthermore, increased concentrations of the 8-HQ inhibitors are achieved after applying higher negative voltages, reflecting its evident electrical-responsive features. Afterward, 8-HQ@PEDOT nanocapsules are incorporated into the polylactic acid (PLA) coatings and deposited on the AZ31 Mg alloy surface. The corrosion resistance and self-healing performance of the PDA/8-HQ@PEDOT/PLA coatings are explored by electrochemistry tests. The EIS tests and hydrogen evolution test indicate that the PDA/8-HQ@PEDOT/PLA coatings show enhanced corrosion protective performance and remarkable self-healing ability during the immersion period. In addition, a larger number of MG-63 cells can survive on the coating surface and the hemolysis rate value of 2.68 % confirms their indicating the excellent biocompatibility of PDA/8-HQ@PEDOT/PLA coatings. The designed PDA/8-HQ@PEDOT/PLA coatings possessed remarkable anti-corrosive, self-healing and biocompatibility, which has great potential in the bio-implant material applications field.

Bio-polymer coatings fabricated on AM60 magnesium alloys by fused deposition modeling 3D-printing to investigate electrochemical behavior

In this paper, various bio-polymer coatings were applied on the surface of AM60 magnesium alloys through 3D-printing. These coatings were from different polymeric filaments of polylactic acid (PLA), polycaprolactone (PCL), acrylonitrile butadiene styrene (ABS), thermoplastic polyurethane (TPU), and polyethylene terephthalate glycol (PETG). Electrochemical impedance spectroscopy (EIS) was utilized to investigate the bio-degradation of fabricated coatings in the simulated body fluid. EIS measurements illustrated that the highest impedance was related to the PCL-T (transparent version) and PLA coatings. However, the increase in the impedance of all bio-coatings compared to the magnesium alloy was about 63.1–99.7%.

Poly-lactic acid coatings on the biomedical WE43 Mg alloy: Protection mechanism and ion permeation effects

Poly-lactic acid (PLA) coatings are deposited on the biomedical WE43 Mg alloy and the degradation behavior and mechanism are investigated during 504 h immersion in Hanks' solution. The protection mechanism is investigated by studying the ion permeation phenomenon and a custom in situ apparatus is constructed to evaluate the performance and elucidate the underlying principle. Na+ and Cl− penetrate the PLA membrane gradually and the different permeation effects stem from the different hydrated radii. Ion permeation can be separated into three stages. Penetration of Cl− is dominant in the first stage and Na+ dominates in the third stage. Penetration of Ca2+, PO43− along with other ions also take part in the third stage leading to the formation of Ca−P on the WE43 substrate. Based on the experimental results, models are established to describe the ion permeation behavior through the PLA membrane and predict the protection efficiency of the PLA coating. The results enrich our understanding of ion permeation in polymeric coatings and provide insights into the development of Mg-based biomedical implants.

Cu2+ Release from Polylactic Acid Coating on Titanium Reduces Bone Implant-Related Infection.

Implant-related infection (IRI) is a major problem in orthopedics. Copper (Cu) is an essential trace element with strong bactericidal activity and, thus, presents potential for reducing IRI. The present study explored a straightforward strategy for releasing Cu2+ from titanium (Ti) implants, and we conducted a preliminary study to assess the feasibility of this approach in clinical translation. Polylactic acid (PLA) coatings containing different concentrations of copper ions were prepared on Ti discs. The antibacterial activity and biocompatibility of the copper ion-incorporated Ti implants were evaluated using Staphylococcus aureus (S. aureus), bone marrow mesenchymal stem cells (BMSCs) and animal models. In vitro, the coatings produced burst release of Cu2+ in 12 h, and inhibited S. aureus growth in a dose-dependent manner. The coatings prepared from PLA solutions containing 0.5 or 1.0 mg/mL reduced the viability and osteogenic differentiation of BMSCs, but these effects were negated after the coatings were immersed in culture medium for 6 h. Four weeks after implantation, the Cu-free K-wires challenged with S. aureus had persistent infection and inferior fracture healing to the other three groups, while Cu-coated wires had no evidence of infection. Furthermore, the Cu-coated wires placed in rabbits without S. aureus challenge showed superior fracture healing to the other three groups. These results suggest that PLA coatings containing Cu2+ may be an effective design for reducing IRI without adversely affecting adjacent bone healing.

Polylactic acid and polyhydroxybutyrate coating on hemp fiber: Its effect on hemp fiber reinforced epoxy composites performance

The present research work investigated the influence of biodegradable polymer coatings of hemp fiber on the structural, water absorption, mechanical, and tribological properties of hemp fiber and hemp fiber reinforced epoxy composites (HFREC). Hemp fibers were initially treated with sodium hydrogen carbonate and then coated with biodegradable polymers like polyhydroxybutyrate (PHB) and polylactic acid (PLA). Scanning electron microscopy (SEM) images of the coated fibers showed a visible change in fiber surface and improvement in surface roughness, while; X-Ray diffraction (XRD) analysis indicated the improvement in crystallinity of the coated fibers resulting in enhanced interfacial adhesion between the coated fibers and the epoxy matrix. The experimental results also revealed that both PHB and PLA coatings of the fibers have resulted in improvement of water resistance and mechanical properties such as tensile strength, modulus, and impact strength of coated HFREC. Tribological test results also revealed that the coated HFREC have improved wear and frictional properties in comparison to uncoated HFREC. The best tribological and mechanical properties were exhibited by PLA coated HFREC, which was also confirmed through the SEM images of worn and fractured surfaces of the uncoated and coated hemp fiber composites.

Bacteriostatic Polylactic Acid Coatings Enriched with Zinc Oxide and Silica Nanoparticles for Titanium Pedicle Screws

Bacteriostatic Polylactic Acid Coatings Enriched with Zinc Oxide and Silica Nanoparticles for Titanium Pedicle Screws

Design and development of Schiff’s base (SB)-modified polylactic acid (PLA) antimicrobial film for packaging applications

SB compounds were synthesized from (para, ortho, meta)-phenylenediamine as a cross-linking agent through vanillin. The chemical structure of the formed SB complexes is confirmed by FT-IR spectroscopy. Among the three complexes, para-phenylenediamine (p-SB), possessing a stable resonance structure with the lowest steric repulsion, was obtained in the highest yield of 87%. Hence, the present work focused on reducing the brittle behavior and improving the antimicrobial activity of PLA by reacting it with p-SB. FT-IR investigation revealed the existence of an intermolecular hydrogen bonding between PLA and SB, which led to an increased toughness in the PLA–p-SB complex. This is further confirmed through SEM analysis. The tensile and contact angle measurements determined an improvement in mechanical properties and hydrophobic nature of the PLA–p-SB film. DSC results demonstrated an increase in flexibility, which indicated a 10 °C reduction in glass transition temperature (Tg) of PLA–p-SB films. The antimicrobial activity of the PLA–p-SB films had a maximum of 15 mm zone of inhibition, which was found to be more effective than the neat PLA film. PLA–p-SB coating on Kraft paper showed improved mechanical and barrier properties than neat PLA coatings and could be tried as a possible replacement for conventional synthetic packaging materials.Graphic abstract

Zein films with porous polylactic acid coatings via cold plasma pre-treatment

In this study, a two-step strategy is proposed to form a porous polylactic acid (PLA) coating on zein films aimed at improving their function. The effect of cold plasma (CP) pre-treatment on the structure and the properties of the films were evaluated. The CP pre-treatment augmented the compatibility and adhesiveness between the zein and PLA layers. The subsequent breath-figure assembly compacted and ordered the porous morphology structure of the PLA layer. Analysis by attenuated total reflectance Fourier transform infrared spectroscopy confirmed that the CP pre-treatment led to a change in the protein conformation and promoted hydrogen bonding interactions between zein and PLA. Exposure of the zein to the CP for 60 s before PLA coating improved the surface hydrophobicity by 24.11 %, the tensile strength by 50.47 %, the elongation at the break by 29.67 %, and water vapor barrier by 44.34 % compared with the untreated zein film. Moreover, the modified coating films exhibited a high UV barrier and excellent biodegradable performances. The strategy of adding a porous PLA coating on the zein films achieved the properties enhancement of zein and expanded its application scope, especially in the field of biodegradable packaging.

Biodegradable polyester thin films and coatings in the line of fire: the time of polyhydroxyalkanoate (PHA)?

From sustainability standpoint, bio-based resins are of crucial importance nowadays rather than fossil-based resins, but the former suffers from low flame retardancy. Bio-based thin films and coatings are in their early stage of development; hence, a long way must be paved to make them resistant against flame/fire. Polylactic acid (PLA)-based biocompatible (timesand some biodegradable) coatings have been in the core of attention, but even among available works one can rarely find a comprehensive report on flame retardancy of PLA thin films and coatings. Attention should also be paid to the fact that first-generation biodegradable polyesters, PLAs, are not fully biodegradable. Moreover, synthesis of PLAs is hooked on crop consumption. On the other hand, polyhydroxyalkanoates (PHAs) with more or less similar structure, but different physical properties due to their lower glass transition temperature compared with PLAs, are known as the second-generation of bio-polyester. Overall, we highlight here that PHAs might be a better candidate for thin film manufacturing thanks to their synthesis by microorganism as well as significant variability of their microstructure that provides a wide range of properties, and notably their full biodegradability compared with PLAs. Though mass production of PHAs is not cost-effective these days and their market just entered into the growth phase, we suggest study on flame retardancy of PHA-based resins, thin films, and coatings for near future. This short communication deals with the current status and future ahead of PHA-based flame retardant thin films and coatings.