Degradation Of Polylactide Research Articles

Open- and Closed-Loop Recycling: Highly Active Zinc Bisguanidine Polymerization Catalyst for the Depolymerization of Polyesters.

In this study, the aliphatic N,N-bisguanidine zinc complex [Zn(DMEG2ch)2](OTf)2 ⋅ THF is introduced as a promising candidate for the chemical recycling of (bio) polyesters. This catalyst is highly active in the ring-opening polymerization (ROP) of lactide (LA) and ϵ-caprolactone (CL). The combination of polymerization and depolymerization activity creates new pathways towards a sustainable circular economy. The catalytic activity of [Zn(DMEG2ch)2](OTf)2 ⋅ THF for the chemical recycling of polylactide (PLA) via alcoholysis was investigated by detailed kinetic and thermodynamic studies. It is shown that various high value-added alkyl lactates can be obtained efficiently under mild reaction conditions. Catalyst recycling was successfully tested using ethanol for the degradation of PLA. In addition, LA can be recovered directly from PLA, enabling either open- or closed-loop recycling. Selective PLA degradation from mixtures with polyethylene terephthalate (PET) and polymer blends are presented. For the first time, a cascade recycling reaction of a PLA/polycaprolactone (PCL) blend is tested with a zinc-based bisguanidine catalyst, whereby PLA is degraded selectively at first and subsequent modification of the reaction conditions leads to efficient degradation of the remaining PCL. The highly active, universally applicable benign zinc catalyst allows the implementation of a circular plastics economy and thus the reduction of plastic pollution in the environment.

Enhanced photocatalytic degradation of polylactide (PLA) through TiO2-based up-conversion nanoparticles

As a degradable polymer material, the regulation of the degradation rate of polylactide (PLA) under an actual light exposure environment is of significant importance for realizing its multifaceted applications. This study aims to enhance the photodegradation of PLA under irradiation with lower-energy wavelengths by using TiO2-based up-conversion nanoparticles (UCNPs). Two modification methods were employed: doping TiO2 with Yb3+/Er3+/Tm3+ ions integrated within the TiO2 lattice, and creating a composite photocatalyst by adhering Y2O3: Yb3+/Er3+/Tm3+ to the exterior of TiO2 grains. The study investigated the impact of these two different TiO2-based UCNPs on the photocatalytic degradation rate and mechanism of PLA under simulated sunlight irradiation. Research has found that the doped TiO2, due to its narrower bandgap and higher photon utilization efficiency during the up-conversion process, exhibited superior catalytic efficiency in catalyzing the photodegradation reactions of PLA compared to unmodified TiO2 and composite TiO2. This work proposes a novel strategy for preparing PLA composites with enhanced photodegradation speed provided by modified TiO2, efficient light energy utilization offered by the up-conversion process, and potential applications in more advanced packaging and agricultural fields.

An engineered enzyme embedded into PLA to make self-biodegradable plastic.

Plastic production reached 400 million tons in 2022 (ref. 1), with packaging and single-use plastics accounting for a substantial amount of this2. The resulting waste ends up in landfills, incineration or the environment, contributing to environmental pollution3. Shifting to biodegradable and compostable plastics is increasingly being considered as an efficient waste-management alternative4. Although polylactide (PLA) is the most widely used biosourced polymer5, its biodegradation rate under home-compost and soil conditions remains low6-8. Here we present a PLA-based plastic in which an optimized enzyme is embedded to ensure rapid biodegradation and compostability at room temperature, using a scalable industrial process. First, an 80-fold activity enhancement was achieved through structure-based rational engineering of a new hyperthermostable PLA hydrolase. Second, the enzyme was uniformly dispersed within the PLA matrix by means of a masterbatch-based melt extrusion process. The liquid enzyme formulation was incorporated in polycaprolactone, a low-melting-temperature polymer, through melt extrusion at 70 °C, forming an 'enzymated' polycaprolactone masterbatch. Masterbatch pellets were integrated into PLA by melt extrusion at 160 °C, producing an enzymated PLA film (0.02% w/w enzyme) that fully disintegrated under home-compost conditions within 20-24 weeks, meeting home-composting standards. The mechanical and degradation properties of the enzymated film were compatible with industrial packaging applications, and they remained intact during long-term storage. This innovative material not only opens new avenues for composters and biomethane production but also provides a feasible industrial solution for PLA degradation.

Wood flour and hazelnut shells polylactide‐based biocomposites for packaging applications: Characterization, photo‐oxidation, and compost burial degradation

AbstractIn this work, polylactide (PLA) was loaded with wood flour (WF) or hazelnut shells (HSs) (10% and 20% of fillers). The matrix and biocomposites were fully characterized from a mechanical and rheological point of view to test their processability and mechanical performance. Compost burial degradation test (30 days), with or without a prior photo‐oxidation step, assessed their biodegradability after an outdoor application, and was monitored by weight loss (WL). The viscosity of the biocomposites was lower than that of the matrix and this unusual result can be attributed to a limited adhesion between the PLA and fillers. Both fillers increased the elastic modulus but decreased the tensile strength and elongation at break. As for the weathering, the degradation of PLA was mostly due to hydrolytic chain scission due to the presence of humidity. Resistance of PLA to UV irradiation improved in presence of both the two fillers. Their lignocellulosic nature was responsible for this behavior. Both fillers induced a high resistance and lower degradation in compost: WL percentages of virgin PLA was about 26%, biocomposites with 20% of WF or HS showed WL of about 10% and 14%, respectively. Photo‐oxidation (36 h with condensation cycle) increased the compost degradation rate of both biocomposites and WL of PLA with 20% of WF or HS were about 15% and 21%, respectively, after 30 days.Highlights Poor adhesion between the matrix and fillers reduced the biocomposites viscosity. Fillers increased the elastic modulus but decreased the properties at break. Both fillers improved the resistance of PLA to UV irradiation. Biocomposites showed a lower susceptibility to compost degradation than PLA. Photo‐oxidation increased the compost degradation rate of biocomposites.

Structural subtleties and catalytic activity of sodium aminophenolate complexes in polylactide degradation: towards sustainable waste management solutions.

This study explores the intricate coordination chemistry of sodium aminophenolate species and their significant role in the depolymerization of polylactide (PLA), offering novel insights into catalytic degradation processes. By examining sodium coordination entities, including dimers and larger aggregates such as tetramers, we reveal how structural modifications, particularly the manipulation of steric hindrances, influence the formation and stability of these complexes. The dimers, characterized by a unique four-center core (Na-O-Na-O), serve as a foundational motif, which is further elaborated to obtain complexes with varied coordination environments through strategic ligand design. Our research delves into the lability of the amino arm in these complexes, a critical factor that facilitates the coordination of PLA to the sodium center, thereby initiating the depolymerization process. Moreover, DFT studies have been pivotal in identifying the most energetically favorable structures for catalysis, highlighting a distinct preference for an eight-membered ring motif stabilized by intramolecular hydrogen bonds. This motif not only enhances the catalyst's efficiency but also introduces a novel structural paradigm for sodium-based catalysis in PLA degradation. Experimental validation of the theoretical models was achieved through NMR spectroscopy, which confirmed the formation of the active catalyst forms and monitored the progress of PLA degradation. The study presents a comprehensive analysis of the influence of ligand structure on the catalytic activity, underscoring the importance of the eight-membered ring motif. Furthermore, we demonstrate how varying the steric bulk of substituents on the amino arm affects the catalyst's performance, with benzyl-substituted ligands exhibiting superior activity. Our findings offer a profound understanding of the structural factors governing the catalytic efficiency of sodium aminophenolate complexes in PLA degradation. This research not only advances the field of coordination chemistry but also presents a promising avenue for the development of efficient and environmentally friendly catalysts for polymer degradation.

Degradation of Structurally Modified Polylactide under the Controlled Composting of Food Waste.

The degradation of polylactide (PLA) films of different structures under conditions of controlled composting has been studied. We have demonstrated that PLA underwent degradation within one month in a substrate that simulated standard industrial composting. Regardless of the initial structure of the samples, the number-average molecular weight (Mn) decreased to 4 kDa while the degree of crystallinity increased to about 70% after 21 days of composting. Addition of an inoculant to the standard substrate resulted in the accelerated degradation of the PLA samples for one week due to an abiotic hydrolysis. These findings have confirmed that industrial composting could solve the problem of plastic disposal at least for PLA.

Polylactide Degradation Activates Immune Cells by Metabolic Reprogramming.

Polylactide (PLA) is the most widely utilized biopolymer in medicine. However, chronic inflammation and excessive fibrosis resulting from its degradation remain significant obstacles to extended clinical use. Immune cell activation has been correlated to the acidity of breakdown products, yet methods to neutralize the pH have not significantly reduced adverse responses. Using a bioenergetic model, delayed cellular changes were observed that are not apparent in the short-term. Amorphous and semi-crystalline PLA degradation products, including monomeric l-lactic acid, mechanistically remodel metabolism in cells leading to a reactive immune microenvironment characterized by elevated proinflammatory cytokines. Selective inhibition of metabolic reprogramming and altered bioenergetics both reduce these undesirable high cytokine levels and stimulate anti-inflammatory signals. The results present a new biocompatibility paradigm by identifying metabolism as a target for immunomodulation to increase tolerance to biomaterials, ensuring safe clinical application of PLA-based implants for soft- and hard-tissue regeneration, and advancing nanomedicine and drug delivery.

Polylactide Degradation in the Presence of Members of the Genus Bacillus

Polylactide Degradation in the Presence of Members of the Genus Bacillus

Polylactide Degradation in the Presence of Members of the Genus <i>Bacillus</i>

Abstract—Microorganisms of the genus Bacillus were shown to have different effects on the degradation of polylactide packaging material. The degradation experiment was carried out on an agar medium at a temperature of 55°C and pH 5.9 for 14 days. This is the first report on the abiotic hydrolysis significantly slowing down during incubation with B. licheniformis S8 and occurring in parallel with the main process, enzymatic hydrolysis. The latter involved sequential cleavage of monomer units from the end of the macromolecule and the formation of low molecular weight products used by microorganisms as a substrate; it contributed to a decrease in the mass of polylactide by 5.1%, while maintaining its molecular weight and decreasing the dispersion of molecular weights. In the presence of bacteria B. amyloliquefaciens, B. subtilis subsp. spizizenii, and B. subtilis subsp. inaquosorum, the polymer weight did not decrease, but the molecular weight decreased significantly, similar to abiotic hydrolysis.

A Multitool for Circular Economy: Fast Ring-Opening Polymerization and Chemical Recycling of (Bio)polyesters Using a Single Aliphatic Guanidine Carboxy Zinc Catalyst.

A new aliphatic hybrid guanidine N,O-donor ligand (TMGeech) and its zinc chloride complex ([ZnCl2 (TMGeech)]) are presented. This complex displays high catalytic activity for the ring-opening polymerization (ROP) of lactide in toluene, exceeding the toxic industry standard tin octanoate by a factor of 10. The high catalytic activity of [ZnCl2 (TMGeech)] is further demonstrated under industrially preferred melt conditions, reaching high lactide conversions within seconds. To bridge the gap towards a sustainable circular (bio)economy, the catalytic activity of [ZnCl2 (TMGeech)] for the chemical recycling of polylactide (PLA) by alcoholysis in THF is investigated. Fast production of different value-added lactates at mild temperatures is demonstrated. Selective PLA degradation from mixtures with polyethylene terephthalate (PET) and a polymer blend, catalyst recycling, and a detailed kinetic analysis are presented. For the first time, chemical recycling of post-consumer PET producing different value-added materials is demonstrated using a guanidine-based zinc catalyst. Therefore, [ZnCl2 (TMGeech)] is a promising, highly active multitool, not only to implement a circular (bio)plastics economy, but also to tackle today's ongoing plastics pollution.

A lysine-derived flame retardant for improved flame retardancy, crystallinity, and aqueous-phase degradation of polylactide

Polylactide (PLA) as one of the excellent representative bioplastics had attracted attention worldwide. However, high flammability and poor crystallization behavior of PLA limit its further application. Moreover, the aqueous degradation rate of the pure PLA has been reported extremely low in natural environment (e.g. in water or soil). To solve these problems, the bio-based flame retardant DL was designed and prepared in water phase without any organic solvent by using lysine (Lys), derived from animals and beans, and diethylenetriamine penta-(methylenephosphonic) acid (DTPMPA), a non-toxic scale inhibitor for water treatment, as raw materials. The combination of the flame retardant DL and polyethylene glycol (PEG) endowed PLA with UL94 V-0 rating and limited oxygen index (LOI) value of 29.4%. The crystallinity degree of PLA with 4 wt% PEG and 6 wt% DL were improved to 39.0%. Moreover, the aqueous degradation of PLA in the purified water at the ambient temperature was accelerated by the addition of DL and PEG, manifested by the 38% decrease in Mw of PLA. It is interested in the analysis of the degradation solution that the release of the oligomers of degraded PLA and the flame retardant DL was found during the aqueous degradation process, which further clarified the degradation mechanism.

Degradative polylactide nanofibers promote M2 macrophage polarization via STAT6 pathway in peritendinous adhesion

Biodegradability has been considered a future trend in the development of medical biomaterials, with polylactide (PLA) and its derivatives regarded as the essential representatives. However, along with post-implantation degradation, the complications, such as in-stent restenosis and postoperative adhesion, are increasingly evident, which can significantly hamper its clinical application. With high plasticity and heterogeneity, macrophages can switch from the pro-inflammatory to the anti-inflammatory microenvironment. Macrophage M2 polarization is closely related to postoperative adhesion and occurs mainly in the late stages of injury, which overlaps with the period of PLA degradation. The STAT6 pathway plays a regulatory role in this process. Therefore, we speculated that STAT6 participates in M2 polarization caused by PLA degradation. Macrophages were grown on esterase-degraded PLA membranes to mimic in vivo degradation. We identified that PLA degradation promotes STAT6 phosphorylation-mediated excessive M2 polarization in macrophages, resulting in a pro-adhesion microenvironment. Furthermore, the in vivo results revealed the dynamic changes in the macrophage status mediated by PLA degradation from proliferation to the remodeling phase. Consistent with the in vitro results, we demonstrated that STAT6 phosphorylation is the vital promoter of peritendinous M2 macrophages polarization promoted by PLA degradation. The released pro-adhesion cytokines, such as TGF-β, accelerate the myofibroblast state transition from rest-state to activation-state. Together with MMP2 and Col III release, they lead to peritendinous adhesion. Our study reveals the regulatory mechanisms underlying PLA degradation and reduced anti-adhesion efficacy and provides a novel direction for optimizing PLA anti-adhesion membranes.

Degradability of Polylactide in Natural Aqueous Environments

This study aims to estimate the degradation process of polylactide (PLA) in natural aqueous environments. The biological degradation of PLA took place in the Baltic Sea and in the natural pond over a period of 1 to 16 months. The characteristic abiotic parameters of both environments were monitored during incubation time, and their influence on the PLA degradation was discussed. The changes in weight, chemical structure, mechanical properties and surface morphology of investigated samples were also tested during incubation. The obtained results indicate that polylactide is not very susceptible to an enzymatic attack of microorganisms present in natural aqueous environments.

Degradation of Polylactide and Polycaprolactone as a Result of Biofilm Formation Assessed under Experimental Conditions Simulating the Oral Cavity Environment.

Polylactide (PLA) and polycaprolactone (PCL) are biodegradable and bioabsorbable thermoplastic polymers considered as promising materials for oral applications. However, any abiotic surface used, especially in areas naturally colonized by microorganisms, provides a favorable interface for microbial growth and biofilm development. In this study, we investigated the biofilm formation of C. krusei and S. mutans on the surface of PLA and PCL immersed in the artificial saliva. Using microscopic (AFM, CLSM) observations and spectrometric measurements, we assessed the mass and topography of biofilm that developed on PLA and PCL surfaces. Incubated up to 56 days in specially prepared saliva and microorganisms medium, solid polymer samples were examined for surface properties (wettability, roughness, elastic modulus of the surface layer), structure (molecular weight, crystallinity), and mechanical properties (hardness, tensile strength). It has been shown that biofilm, especially S. mutans, promotes polymer degradation. Our findings indicate the need for additional antimicrobial strategies for the effective oral applications of PLA and PCL.

Kinetics of Catalyzed Thermal Degradation of Polylactide and Its Application as Sacrificial Templates†

Comprehensive SummaryPolylactide (PLA) is an outstanding sacrificial template material for the manufacture of microchannels in a thermosetting matrix. However, the initial thermal degradation temperature of pure PLA is relatively high (about 280°C), which limits its use as a sacrificial template. In this report, we found that TBD, an organic base catalyst, can significantly reduce the thermal degradation temperature of PLA. TBD has higher catalytic activity for the thermal degradation of PLA compared with Tin(II) oxalate (Sn(Oxa)), one catalyst reported in the literature. Moreover, the gaseous products catalyzed by TBD for PLA thermal degradation are mainly lactide, and the formation temperature of the monomer is lower and the yield is higher, which may have potential value for PLA recycling. A combined catalyst, S8T2, was composed of 80% low activity catalyst Sn(Oxa) and 20% high activity catalyst TBD, which can catalyze the rapid degradation of PLA without greatly damaging the mechanical properties of PLA. PLA‐S8T2 sacrificial fibers can form high‐precision one‐dimensional microchannels in the epoxy resin matrix, and 3D‐printed PLA‐S8T2 sacrificial templates can be used to form three‐dimensional microchannels in a thermosetting matrix by vaporization of sacrificial components process (VaSC). These features highlight the great potential of PLA‐S8T2 as sacrificial template material for the preparation of the complicated microchannels in the thermosetting matrix.

Effects of Sterilization and Hydrolytic Degradation on the Structure, Morphology and Compressive Strength of Polylactide-Hydroxyapatite Composites.

Composites based on polylactide (PLA) and hydroxyapatite (HA) were prepared using a thermally induced phase separation method. In the experimental design, the PLA with low weight-average molar mass (Mw) and high Mw were tested with the inclusion of HA synthesized as whiskers or hexagonal rods. In addition, the structure of HA whiskers was doped with Zn, whereas hexagonal rods were mixed with Sr salt. The composites were sterilized and then incubated in phosphate-buffered saline for 12 weeks at 37 °C, followed by characterization of pore size distribution, molecular properties, density and mechanical strength. Results showed a substantial reduction of PLA Mw for both polymers due to the preparation of composites, their sterilization and incubation. The distribution of pore size effectively increased after the degradation process, whereas the sterilization, furthermore, had an impact on pore size distribution depending on HA added. The inclusion of HA reduced to some extent the degradation of PLA quantitatively in the weight loss in vitro compared to the control without HA. All produced materials showed no cytotoxicity when validated against L929 mouse skin fibroblasts and hFOB 1.19 human osteoblasts. The lack of cytotoxicity was accompanied by the immunocompatibility with human monocytic cells that were able to detect pyrogenic contaminants.

Segmental Relaxation Dynamics in Amorphous Polylactide Exposed to UV Light

AbstractThe degradation of polylactide (PLA) under UV exposure is investigated in terms of cooperativity and kinetic fragility at the glass transition. In the first part, possibly coexisting degradation mechanisms are evoked from the interpretation of the infrared spectroscopy analyses. Furthermore, the reduction of PLA chain length, owing to photolytic scissions predominant over local crosslinks, is assessed from chromatography, and confirmed by the shift of the glass transition temperature toward lower temperature. Modulated temperature thermogravimetric analysis (MT‐TGA) also shows that the activation energy needed to initiate thermal degradation falls after UV exposure. In the second part, the impact of UV‐induced degradation on the cooperative rearranging region (CRR) size and the kinetic fragility, respectively, calculated thanks to calorimetric and dielectric measurements, is discussed. Despite the assumed concomitance of several degradation mechanisms, it is observed that the glass transition, the kinetic fragility, and the CRR size decrease together with the exposure time. Moreover, it is found that the data align well on another trend depicting the change in the relaxation properties caused by plasticization of PLA. Thus, the variations of segmental relaxation properties caused by UV may be related to the increase of free volume linked to the damaging of the PLA structure.

Zinc and magnesium catalysts for the synthesis for PLA and its degradation: Clues for catalyst design

Homoleptic and heteroleptic zinc and magnesium complexes bearing phenoxy-imine pyridine ligands were synthetized and characterized. Several structural parameters such as the structure of the ancillary ligand, the nature of the metal centre and the coordination geometry were investigated for identifying design elements purposeful to improve the catalytic activity in the ring opening polymerization (ROP) of lactide and in the reverse reaction of degradation of polylactide by alcoholysis. High efficiency and control degree were reached with zinc catalysts while magnesium ones showed lower activity and a weak control degree. NMR studies demonstrated that, for the homoleptic zinc complex, an activated-monomer mechanism was active. Differently, a coordination/insertion mechanism was observed for the related homoleptic zinc complex. Significantly, the complexes that showed the best activity in the ROP of lactide revealed to be the most efficient also in the degradation reaction.

Functionalization of polylactide with multibranched poly(ethyleneimine) by in situ reactive extrusion

Polylactide (PLA) was functionalized with multibranched polyethyleneimine (PEI) for the addition of active functional groups along the molecular chain by in situ reactive extrusion. The synthesis of PLA-PEI was performed in two steps through a PLA-maleate (PLA-MA) precursor varying the proportion of maleic anhydride (MA) at 1, 2, 3, or 4%(w/w) and the free radical initiator, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, at 0.1, 0.25, or 0.5% (w/w). The effects of the amount of initiator and MA on the degree of maleate grafting was investigated in terms of the acid value by titration. The %MA was found to depend on the amount of initiator, but not on the amount of MA. Next, two different molecular weights of PEI at different proportions [PEI800 at 1–4% (w/w) and PEI25k at 1–2% (w/w)] were modified onto the PLA-MA by the ring opening reaction of the anhydride group and the amino groups of PEI during extrusion. The amount of amino groups was quantitatively determined using the ninhydrin method. The structure of the obtained PLA-MA and PLA-PEI were characterized by Fourier transformed infrared spectroscopy and nuclear magnetic resonance analyses. Thermal properties were analyzed by differential scanning colorimetry. The molecular weight determination and melt flow index results implied the degradation of PLA during synthesis of the PLA-MA precursor, or substitution of PEI for PLA-PEI. Antibacterial properties of PLA-PEI were investigated against Escherichia coli and Staphylococcus aureus. The multibranched PLA-PEI800 showed a higher crystallization than neat PLA. The PLA modified with a PEI800 content of more than 1% (w/w) and PEI25k showed antibacterial activities against S. aureus in 24 h, but not against E. coli. The % reduction in the number of viable cells (colonies) was proportional to the amino group contents.

The influence of chain‐end functionalization and stereocomplexation on the degradation stability under alkaline condition

AbstractHydrolytic degradation of polylactides (PLAs) bearing cinnamic acid derivatives was conducted and their thermal degradation temperature at 10% weight loss (T10) and melting point temperature (Tm) were measured, to confirm that a PLA stereocomplex could be modified for use in a wide range of application. The improved T10 values of PLA films by chain end modification were maintained after the alkaline degradation. The increase in Tm by stereocomplex formation was also maintained after degradation with a slight change in the melting point of the attached homopolymer. The present results indicate the suitability of chain end modification for the additional functionality of PLA stereocomplex films.