Properties of lactic acid based polymers and their correlation with composition

Melt Compounding of Poly(lactic acid)-Based Composites: Blending Strategies, Process Conditions, and Mechanical Properties

Polylactic acid (PLA), derived from renewable resources, has the advantages of rigidity, thermoplasticity, biocompatibility, and biodegradability, and is widely used in many fields such as packaging, agriculture, and biomedicine. The excellent processability properties allow for melt processing treatments such as extrusion, injection molding, blow molding, and thermoforming in the preparation of PLA-based materials. However, the low toughness and poor thermal stability of PLA limit its practical applications. Compared with pure PLA, conditions such as processing technology, filler, and crystallinity affect the mechanical properties of PLA-based materials, including tensile strength, Young's modulus, and elongation at break. This review systematically summarizes various technical parameters for melt processing of PLA-based materials and further discusses the mechanical properties of PLA homopolymers, filler-reinforced PLA-based composites, PLA-based multiphase composites, and reactive composite strategies for PLA-based composites.

Toughening Polylactic Acid with Ultrafine Fully Vulcanized Powdered Natural Rubber Graft-Copolymerized with Poly(styrene-co-acrylonitrile): Tailoring the Styrene-Acrylonitrile Ratio for Enhanced Interfacial Interactions

This study investigated the sustainable toughening of polylactic acid (PLA) by incorporating ultrafine fully vulcanized powdered natural rubber graft-copolymerized with poly-styrene-co-acrylonitrile (UFPNR-SAN). We investigated the effect of the styrene-to-acrylonitrile ratio (ST:AN) used during the grafting process on the final UFPNR-SAN compatibility with PLA. The ST:AN ratio was systematically varied during the grafting reaction to prepare UFPNR-SAN with a range of different surface energies. The ST:AN ratio of 4:1 showed the highest compatibility with the PLA matrix, attributed to optimal interfacial interactions and improved dispersion, as indicated by contact angle measurements and SEM observations. This resulted in a remarkable toughening of the PLA/UFPNR-SAN composite. For instance, an obvious fully ductile behavior without crack formation and flexural strain of around 17.5% against 5% of the neat PLA was recorded. In addition, 3.5 times improvement in the impact strength of the composite at 25 wt% dosage of the UFPNR-SAN was also achieved without compromising thermal properties. Overall, this study established the suitable ST:AN ratio on the grafting onto natural rubber to enhance interfacial interactions with PLA and its effects on the properties of the resulting PLA/UFPNR-SAN bio-based composite.

Shelf Life of Minced Pork in Vacuum-Adsorbed Carvacrol@Natural Zeolite Nanohybrids and Poly-Lactic Acid/Triethyl Citrate/Carvacrol@Natural Zeolite Self-Healable Active Packaging Films

Enhancing food preservation and safety using environmentally friendly techniques is urgently needed. The aim of this study was to develop food packaging films using biodegradable poly-L-lactic acid (PLA) as biopolymer and carvacrol (CV) essential oil as an antioxidant/antibacterial agent for the replacement of chemical additives. CV was adsorbed onto natural zeolite (NZ) via a new vacuum adsorption method. The novel nanohybrid CV@NZ with a high CV content contained 61.7%wt. CV. Pure NZ and the CV@NZ nanohybrid were successfully dispersed in a PLA/triethyl citrate (TEC) matrix via a melt extrusion process to obtain PLA/TEC/xCV@NZ and PLA/TEC/xNZ nanocomposite films with 5, 10, and 15%wt CV@NZ or pure NZ content. The optimum resulting film PLA/TEC/10CV@NZ contained 10%wt. CV@NZ and exhibited self-healable properties, 22% higher tensile strength, 40% higher elongation at break, 45% higher water barrier, and 40% higher oxygen barrier than the pure PLA/TEC matrix. This film also had a high CV release content, high CV control release rate as well as 2.15 mg/L half maximal effective concentration (EC50) and 0.27 mm and 0.16 mm inhibition zones against Staphylococcus aureus and Salmonella enterica ssp. enterica serovar Typhimurium, respectively. This film not only succeeded in extending the shelf life of fresh minced pork, as shown by the total viable count measurements in four days but also prevented the lipid oxidation of fresh minced pork and provided higher nutritional values of the minced meat, as revealed by the heme iron content determination. It also had much better and acceptable sensory characteristics than the commercial packaging paper.

Strategy to Antibacterial, High-Mechanical, and Degradable Polylactic Acid/Chitosan Composite Film through Reactive Compatibilization via Epoxy Chain Extender

Research into the production of antibacterial, high strength, and environmentally friendly biobased films for use in food packaging is crucial due to growing concerns about food safety. Herein, the preparation of antibacterial, high mechanical, and degradable Polylactic acid/chitosan (PLA/CS) composite films with exceptional interfacial compatibility through reactive compatibilization via the epoxy chain extender ADR4468 is reported. A strong bond, in the form of a chemical bond between PLA and CS, is established by the cycloaddition opening reaction of ADR, which induces cross-linking between hydroxyl and carboxyl groups on the molecular chains. As a result, the elongation at break increased by 31.8% compared to the composite film without ADR. In addition, the composite films exhibited good compost degradability, with a mass reduction of 42-45% after 100 days of degradation.

The Effects of Nucleating Agents and Processing on the Crystallization and Mechanical Properties of Polylactic Acid: A Review

Polylactic acid (PLA) is a biobased, biodegradable, non-toxic polymer widely considered for replacing traditional petroleum-based polymer materials. Being a semi-crystalline material, PLA has great potential in many fields, such as medical implants, drug delivery systems, etc. However, the slow crystallization rate of PLA limited the application and efficient fabrication of highly crystallized PLA products. This review paper investigated and summarized the influence of formulation, compounding, and processing on PLA's crystallization behaviors and mechanical performances. The paper reviewed the literature from different studies regarding the impact of these factors on critical crystallization parameters, such as the degree of crystallinity, crystallization rate, crystalline morphology, and mechanical properties, such as tensile strength, modulus, elongation, and impact resistance. Understanding the impact of the factors on crystallization and mechanical properties is critical for PLA processing technology innovations to meet the requirements of various applications of PLA.

Long-Term Thermal Stabilization of Poly(Lactic Acid)

To use polylactic acid in demanding technical applications, sufficient long-term thermal stability is required. In this work, the thermal aging of polylactic acid (PLA) in the solid phase at 100 °C and 150 °C is investigated. PLA has only limited aging stability without the addition of stabilizers. Therefore, the degradation mechanism in thermal aging was subsequently investigated in more detail to identify a suitable stabilization strategy. Investigations using nuclear magnetic resonance spectroscopy showed that, contrary to expectations, even under thermal aging conditions, hydrolytic degradation rather than oxidative degradation is the primary degradation mechanism. This was further confirmed by the investigation of suitable stabilizers. While the addition of phenols, phosphites and thioethers as antioxidants leads only to a limited improvement in aging stability, the addition of an additive composition to provide hydrolytic stabilization results in extended durability. Efficient compositions consist of an aziridine-based hydrolysis inhibitor and a hydrotalcite co-stabilizer. At an aging temperature of 100 °C, the time until significant polymer chain degradation occurs is extended from approx. 500 h for unstabilized polylactic acid to over 2000 h for stabilized polylactic acid.

In vitro and in vivo degradation profile, biocompatibility of poly-L-lactic acid porous microspheres

The objective of this study is to evaluate the in vitro and in vivo degradation profile and biocompatibility of poly-L-lactic acid (PLLA) porous microspheres (PMs) for their potential application as injectable microcarrier or micro-scaffolds materials in the research and clinical use of craniofacial cartilage repair. In this study, PLLA PMs prepared exhibited spherical shape and uniform surface pores followed by 24-week evaluations for degradation behavior and biocompatibility. In vitro degradation analysis encompassed morphological examination, pH monitoring, molecular weight analysis, thermodynamic assessment, and chemical structure analysis. After 12 weeks of in vitro degradation, PMs maintained a regular porous spherical structure. Molecular weight and glass transition temperature of PLLA PMs decreased over time, accompanying with an initial increase and subsequent decrease in crystallinity. Enzymatic degradation caused morphological changes and accelerated degradation in the in vitro studies. Finally, in vivo evaluations involved subcutaneous implantation of PLLA PMs in rats, demonstrating biocompatibility by enhancing type I and type III collagen regeneration as observed in histological analysis. The results demonstrated that PLLA PMs were able to maintain their spherical structure for 12 weeks, promoting the generation of collagen at the implantation site, meeting the time requirements for craniofacial cartilage repair.

Utilization of Silica Filler as Reinforcement Material of Polylactic Acid (PLA) in 3D Printing Applications: Thermal, Rheological, and Mechanical Performance

Glass was introduced as an additive to filaments used for the manufacturing of composite materials, employed by Additive Manufacturing applications. Glass accounts for a large waste electric and electronic equipment (WEEE) percentage, and its recovery and recycling can lead to the production of sustainable composite materials. In this work, poly(lactic acid) (PLA)/commercially available silicon oxide composite filaments were manufactured and their structural, thermal, rheological, and mechanical properties were assessed. Scanning Electron Microscopy confirmed the 1:2 ratio of silicon: oxygen, along with the relatively low adhesion between the filler and the matrix. Differential Scanning Calorimetry presented steady glass transition and melting temperatures of composites, whereas a crystallization temperature of 10% wt. and a crystallinity of 15% wt. composite slightly increased. Rheological analysis showcased that the viscosity of the composite filaments decreased compared to PLA (10-100 compared to 300-400 Pa·s), with a more shear-thinning behavior. Dynamic mechanical analysis exhibited increased elastic, flexural moduli, and flexural strength of composites (up to 16, 23, and 11%, respectively), whereas tensile strength and elongation decreased. The affordability of raw materials (with the future introduction of recycled ones) and the minimal processing steps can lead to the potential scaling up of the study.

Characterization of Polylactic Acid Biocomposites Filled with Native Starch Granules from Dioscorea remotiflora Tubers

Biocomposites were fabricated utilizing polylactic acid (PLA) combined with native starch sourced from mountain's yam (Dioscorea remotiflora Knuth), an underexplored tuber variety. Different starch compositions (7.5, 15.0, 22.5, and 30.0 wt.%) were blended with PLA in a batch mixer at 160 °C to produce PLA/starch biocomposites. The biocomposites were characterized by analyzing their morphology, particle size distribution, thermal, X-ray diffraction (XDR), mechanical, and dynamic mechanical (DMA) properties, water absorption behavior, and color. The results showed that the amylose content of Dioscorea remotiflora starch was 48.43 ± 1.4%, which corresponds to a high-amylose starch (>30% of amylose). Particle size analysis showed large z-average particle diameters (Dz0) of the starch granules (30.59 ± 3.44 μm). Scanning electron microscopy (SEM) images showed oval-shaped granules evenly distributed throughout the structure of the biocomposite, without observable agglomeration or damage to its structure. XDR and DMA analyses revealed an increase in the crystallinity of the biocomposites as the proportion of the starch increased. The tensile modulus (E) underwent a reduction, whereas the flexural modulus (Eflex) increased with the amount of starch incorporated. The biocomposites with the highest Eflex were those with a starch content of 22.5 wt.%, which increased by 8.7% compared to the neat PLA. The water absorption of the biocomposites demonstrated a higher uptake capacity as the starch content increased. The rate of water absorption in the biocomposites followed the principles of Fick's Law. The novelty of this work lies in its offering an alternative for the use of high-amylose mountain's yam starch to produce low-cost bioplastics for different applications.

Synthesis of L-Lactide from Lactic Acid and Production of PLA Pellets: Full-Cycle Laboratory-Scale Technology

Lactide is one of the most popular and promising monomers for the synthesis of biocompatible and biodegradable polylactide and its copolymers. The goal of this work was to carry out a full cycle of polylactide production from lactic acid. Process conditions and ratios of reagents were optimized, and the key properties of the synthesized polymers were investigated. The influence of synthesis conditions and the molecular weight of lactic acid oligomers on the yield of lactide was studied. Lactide polymerization was first carried out in a 500 mL flask and then scaled up and carried out in a 2000 mL laboratory reactor setup with a combined extruder. Initially, the lactic acid solution was concentrated to remove free water; then, the oligomerization and synthesis of lactide were carried out in one flask in the presence of various concentrations of tin octoate catalyst at temperatures from 150 to 210 °C. The yield of lactide was 67-69%. The resulting raw lactide was purified by recrystallization in solvents. The yield of lactide after recrystallization in butyl acetate (selected as the optimal solvent for laboratory purification) was 41.4%. Further, the polymerization of lactide was carried out in a reactor unit at a tin octoate catalyst concentration of 500 ppm. Conversion was 95%; Mw = 228 kDa; and PDI = 1.94. The resulting products were studied by differential scanning calorimetry, NMR spectroscopy and gel permeation chromatography. The resulting polylactide in the form of pellets was obtained using an extruder and a pelletizer.

Enhancing the Hydrolytic Stability of Poly(lactic acid) Using Novel Stabilizer Combinations

Commercially available poly(lactic acid) exhibits poor hydrolytic stability, which makes it impossible for use in durable applications. Therefore, a novel hydrolysis inhibitor based on an aziridine derivative as well as a novel stabilizer composition, containing an aziridine derivative and an acid scavenger, were investigated to improve the hydrolytic stability. To evaluate the stabilizing effect, the melt volume rate (MVR) and molecular weight were monitored during an accelerated hydrolytic aging in water at elevated temperatures. Temperatures were selected according to the glass transition temperature (~60 °C) of PLA. It was shown that the novel hydrolysis inhibitor as well as the novel stabilizer composition exhibited excellent performance during hydrolytic aging, exceeding commercially available alternatives, e.g., polymeric carbodiimides. A molecular weight analysis resulted in a molecular weight decrease of only 10% during approximately 850 h and up to 20% after 1200 h of hydrolytic aging, whereas poly(lactic acid) stabilized with a commercial polycarbodiimide revealed comparable molecular weight reductions after only 300 h. Furthermore, the stabilization mechanism of the aziridine derivative alone, as well as in the synergistic combination with the acid scavenger (calcium hydrotalcite), was investigated using nuclear magnetic resonance (NMR) spectroscopy. In addition to an improved hydrolytic stability, the thermal properties were also enhanced compared to polymeric carbodiimides.

Unexpected Periodicity in Cationic Group 5 Initiators for the Ring-Opening Polymerization of Lactones

ε-Caprolactone (ε-CL) adducts of cationic, amine tris(phenolate)-supported niobium(V) and tantalum(V) ethoxides initiate the ring-opening polymerization of lactones. The Ta(V) species prepared and applied catalytically herein exhibits higher activity in the ring-opening polymerization (ROP) of ε-caprolactone than the previously reported, isostructural Nb(V) complex, contradicting literature comparisons of Nb(V)- and Ta(V)-based protocols. Both systems also initiate the ROP of δ-valerolactone and rac-β-butyrolactone, kinetic studies confirming retention of higher activity by the Ta congener. Polymerizations of rac-β-butyrolactone and δ-valerolactone were previously unrealized under Group V- or Ta-mediated conditions, respectively, although the former has afforded only low molecular weight, cyclic poly-3-hydroxybutyrate. Cationic ethoxo-Nb(V) and -Ta(V) δ-valerolactone adducts are also reported, demonstrating the facility of δ-valerolactone as a ligand and the generality of the synthetic method. Both δ-valerolactone-bearing complexes initiate the ROP of ε-caprolactone, δ-valerolactone, and rac-β-butyrolactone. Accordingly, we have elucidated trends in reactivity and investigated the initiation mechanism for such systems, the insertion event being predicated upon intramolecular nucleophilic attack on the coordinated lactone by the adjacent alkoxide moiety. This mechanism enables quantitative, stoichiometric installation of a single monomer residue distinct from the bulk of the polymer chain, and permits modification of polymer properties via both manipulation of the molecular architecture and tuning of the polymerization kinetics, and thus dispersity, through hitherto inaccessible independent control of the initiation event.

Influence of polylactide coating stereochemistry on mechanical and in vitro degradation properties of porous bioactive glass scaffolds for bone regeneration

The mechanical properties of polylactide stereocomplexes (PLA SC) have been primarily studied through tensile testing, with inconsistent results, and the compressive properties of PLA SC compared to homocrystalline or amorphous PLA remain poorly understood. In this study, we coated porous bioactive glass 13-93 scaffolds with amorphous, homocrystalline, or stereocomplex PLA to investigate their mechanical and degradation properties before and after immersion in simulated body fluid. The glass scaffolds had interconnected pores and an average porosity of 76%. The PLA coatings, which were 10-100 μm thick and approximately 3% of the glass scaffold mass, covered the glass to a large extent. The compressive strength and toughness of all PLA-coated scaffolds were significantly higher than those of uncoated scaffolds, with approximately a fourfold increase before immersion and a twofold increase after immersion. The compressive strength and toughness of PLA SC-coated scaffolds were similar to those of scaffolds with homocrystalline PLA coating, and significantly higher than for scaffolds with amorphous PLA coating. All PLA coatings moderated the initial pH increase caused by the glass, which could benefit surrounding cells and bone tissue in vivo after implantation.

Enhancing biodegradation of PBAT through bio-stimulation using Pseudozyma jejuensis for effective plastic waste reduction

Polybutylene adipate-co-terephthalate (PBAT) is a flexible and biodegradable material that finds applications in mulching film and the food packaging industry. In this study, we aimed to address the global plastic waste problem by developing an improved biodegradation system for PBAT. Our focus was on utilizing the biodegradation capabilities of Pseudozyma jejuensis, a microorganism known for its ability to decompose Polycaprolactam (PCL). Through bio-stimulation, we aimed to enhance the growth mechanism of P. jejuensis and optimize PBAT biodegradation. Our results demonstrated significant structural changes in the PBAT film, as revealed by FT-IR analysis. Moreover, FE-SEM imaging exhibited evident surface erosion and pitting, indicating physical alterations due to biodegradation. These findings provide strong evidence for the efficiency of our developed biodegradation system. To fully harness the potential of this system and enable its practical implementation, further research is warranted to optimize and scale up the process. Our work contributes to the ongoing efforts to combat the global plastic waste crisis, offering a valuable solution for the efficient biodegradation of PBAT.

A Green Conformable Thermoformed Printed Circuit Board Sourced from Renewable Materials

Printed circuit boards (PCBs) physically support and connect electronic components to the implementation of complex circuits. The most widespread insulating substrate that also acts as a mechanical support in PCBs is commercially known as FR4, and it is a glass-fiber-reinforced epoxy resin laminate. FR4 has exceptional dielectric, mechanical, and thermal properties. However, it was designed without considering sustainability and end-of-life aspects, heavily contributing to the accumulation of electronic waste in the environment. Thus, greener alternatives that can be reprocessed, reused, biodegraded, or composted at the end of their function are needed. This work presents the development and characterization of a PCB substrate based on poly(lactic acid) and cotton fabric, a compostable alternative to the conventional FR4. The substrate has been developed by compression molding, a process compatible with the polymer industry. We demonstrate that conductive silver ink can be additively printed on the substrate's surface, as its morphology and wettability are similar to those of FR4. For example, the compostable PCB's water contact angle is 72°, close to FR4's contact angle of 64°. The developed substrate can be thermoformed to curved surfaces at low temperatures while preserving the conductivity of the silver tracks. The green substrate has a dielectric constant comparable to that of the standard FR4, showing a value of 5.6 and 4.6 at 10 and 100 kHz, respectively, which is close to the constant value of 4.6 of FR4. The substrate is suitable for microdrilling, a fundamental process for integrating electronic components to the PCB. We implemented a proof-of-principle circuit to control the blinking of LEDs on top of the PCB, comprising resistors, capacitors, LEDs, and a dual in-line package circuit timer. The developed PCB substrate represents a sustainable alternative to standard FR4 and could contribute to the reduction of the overwhelming load of electronic waste in landfills.

Coordination of ε-Caprolactone to a Cationic Niobium(V) Alkoxide Complex: Fundamental Insight into Ring-Opening Polymerization via Coordination-Insertion

We report three niobium-based initiators for the catalytic ring-opening polymerization (ROP) of ε-caprolactone, exhibiting good activity and molecular weight control. In particular, we have prepared on the gram-scale and fully characterized a monometallic cationic alkoxo-Nb(V) ε-caprolactone adduct representing, to the best of our knowledge, an unprecedented example of a metal complex with an intact lactone monomer and a functional ROP-initiating group simultaneously coordinated at the metal center. At 80 °C, all three systems initiate the immortal solution-state ROP of ε-caprolactone via a coordination-insertion mechanism, which has been confirmed through experimental studies, and is supported by computational data. Natural bond orbital calculations further indicate that polymerization may necessitate isomerization about the metal center between the alkoxide chain and the coordinated monomer. The observations made in this work are expected to inform mechanistic understanding both of amine tris(phenolate)-supported metal alkoxide ROP initiators, including various highly stereoselective systems for the polymerization of lactides and of coordination-insertion-type ROP protocols more broadly.

A Review of Biodegradable Plastics: Chemistry, Applications, Properties, and Future Research Needs

Environmental concerns over waste plastics' effect on the environment are leading to the creation of biodegradable plastics. Biodegradable plastics may serve as a promising approach to manage the issue of environmental accumulation of plastic waste in the ocean and soil. Biodegradable plastics are the type of polymers that can be degraded by microorganisms into small molecules (e.g., H2O, CO2, and CH4). However, there are misconceptions surrounding biodegradable plastics. For example, the term "biodegradable" on product labeling can be misconstrued by the public to imply that the product will degrade under any environmental conditions. Such misleading information leads to consumer encouragement of excessive consumption of certain goods and increased littering of products labeled as "biodegradable". This review not only provides a comprehensive overview of the state-of-the-art biodegradable plastics but also clarifies the definitions and various terms associated with biodegradable plastics, including oxo-degradable plastics, enzyme-mediated plastics, and biodegradation agents. Analytical techniques and standard test methods to evaluate the biodegradability of polymeric materials in alignment with international standards are summarized. The review summarizes the properties and industrial applications of previously developed biodegradable plastics and then discusses how biomass-derived monomers can create new types of biodegradable polymers by utilizing their unique chemical properties from oxygen-containing functional groups. The terminology and methodologies covered in the paper provide a perspective on directions for the design of new biodegradable polymers that possess not only advanced performance for practical applications but also environmental benefits.

Biodegradable Polylactic Acid and Its Composites: Characteristics, Processing, and Sustainable Applications in Sports

Polylactic acid (PLA) is a biodegradable polyester polymer that is produced from renewable resources, such as corn or other carbohydrate sources. However, its poor toughness limits its commercialization. PLA composites can meet the growing performance needs of various fields, but limited research has focused on their sustainable applications in sports. This paper reviews the latest research on PLA and its composites by describing the characteristics, production, degradation process, and the latest modification methods of PLA. Then, it discusses the inherent advantages of PLA composites and expounds on different biodegradable materials and their relationship with the properties of PLA composites. Finally, the importance and application prospects of PLA composites in the field of sports are emphasized. Although PLA composites mixed with natural biomass materials have not been mass produced, they are expected to be sustainable materials used in various industries because of their simple process, nontoxicity, biodegradability, and low cost.

Bimetallic polymerization of lactide with binaphthol-derived bis-heteroscorpionate dizinc and dimagnesium complexes

Discrete bimetallic catalysts often provide enhanced reactivity and selectivity in lactone polymerization, making metal-metal cooperativity an important design principle for new catalyst development. However, the poor modularity of binucleating ligands limits structure-reactivity analysis and optimization. This report describes a modular, binucleating bis(pyrazolyl)alkane ligand series (1-R) bridged by a chiral binaphthol unit, prepared by nucleophile-catalyzed condensation between a dialdehyde and a bis(pyrazolyl)methanone. A bis(ethylzinc) complex was characterized by single-crystal X-ray diffraction, but in situ complexation with Zn(HMDS)₂ and Mg(HMDS)₂ provided more active catalysts for lactide polymerization (HMDS^- = hexamethyldisilazide). Structure-reactivity studies identified complexes of 1-Me₂ as the most active, and these catalysts show significant enhancements in rate compared to their monometallic analogues. Kinetic analysis resulted in first-order dependence on both mono- and bimetallic catalysts, suggesting metal-metal cooperativity as the basis for this rate enhancement. End-group analysis and low dispersity implicate a coordination-insertion mechanism through an alkoxide. Despite rapid transesterification observed by MALDI, we still demonstrated controlled polymerization in the block copolymerization of ε-caprolactone and L-lactide. Although we observed rate differences in the polymerization of L-lactide by opposite enantiomer catalysts, we did not observe catalyst-directed stereoselectivity in the polymerization of rac- or meso-lactide.

Review on the Degradation of Poly(lactic acid) during Melt Processing

This review paper presents an overview of the state of the art on process-induced degradation of poly(lactic acid) (PLA) and the relative importance of different processing variables. The sensitivity of PLA to degradation, especially during melt processing, is considered a significant challenge as it may result in deterioration of its properties. The focus of this review is on degradation during melt processing techniques such as injection molding and extrusion, and therefore it does not deal with biodegradation. Firstly, the general processing and fundamental variables that determine the degradation are discussed. Secondly, the material properties (for example rheological, thermal, and mechanical) are presented that can be used to monitor and quantify the degradation. Thirdly, the effects of different processing variables on the extent of degradation are reviewed. Fourthly, additives are discussed for melt stabilization of PLA. Although current literature reports the degradation reactions and clearly indicates the effect of degradation on PLA's properties, there are still knowledge gaps in how to select and predict the processing conditions that minimize process-induced degradation to save raw materials and time during production.

Ultra-stretchable and biodegradable elastomers for soft, transient electronics

As rubber-like elastomers have led to scientific breakthroughs in soft, stretchable characteristics-based wearable, implantable electronic devices or relevant research fields, developments of degradable elastomers with comparable mechanical properties could bring similar technological innovations in transient, bioresorbable electronics or expansion into unexplored areas. Here, we introduce ultra-stretchable, biodegradable elastomers capable of stretching up to ~1600% with outstanding properties in toughness, tear-tolerance, and storage stability, all of which are validated by comprehensive mechanical and biochemical studies. The facile formation of thin films enables the integration of almost any type of electronic device with tunable, suitable adhesive strengths. Conductive elastomers tolerant/sensitive to mechanical deformations highlight possibilities for versatile monitoring/sensing components, particularly the strain-tolerant composites retain high levels of conductivities even under tensile strains of ~550%. Demonstrations of soft electronic grippers and transient, suture-free cardiac jackets could be the cornerstone for sophisticated, multifunctional biodegradable electronics in the fields of soft robots and biomedical implants.

A review on biodegradable polylactic acid (PLA) production from fermentative food waste - Its applications and degradation

Due to its low carbon footprint and environmental friendliness, polylactic acid (PLA) is one of the most widely produced bioplastics in the world. Manufacturing attempts to partially replace petrochemical plastics with PLA are growing year over year. Although this polymer is typically used in high-end applications, its use will increase only if it can be produced at the lowest cost. As a result, food wastes rich in carbohydrates can be used as the primary raw material for the production of PLA. Lactic acid (LA) is typically produced through biological fermentation, but a suitable downstream separation process with low production costs and high product purity is also essential. The global PLA market has been steadily expanding with the increased demand, and PLA has now become the most widely used biopolymer across a range of industries, including packaging, agriculture, and transportation. Therefore, the necessity for an efficient manufacturing method with reduced production costs and a vital separation method is paramount. The primary goal of this study is to examine the various methods of lactic acid synthesis, together with their characteristics and the metabolic processes involved in producing lactic acid from food waste. In addition, the synthesis of PLA, possible difficulties in its biodegradation, and its application in diverse industries have also been discussed.

Recent advances in modified poly (lactic acid) as tissue engineering materials

As an emerging science, tissue engineering and regenerative medicine focus on developing materials to replace, restore or improve organs or tissues and enhancing the cellular capacity to proliferate, migrate and differentiate into different cell types and specific tissues. Renewable resources have been used to develop new materials, resulting in attempts to produce various environmentally friendly biomaterials. Poly (lactic acid) (PLA) is a biopolymer known to be biodegradable and it is produced from the fermentation of carbohydrates. PLA can be combined with other polymers to produce new biomaterials with suitable physicochemical properties for tissue engineering applications. Here, the advances in modified PLA as tissue engineering materials are discussed in light of its drawbacks, such as biological inertness, low cell adhesion, and low degradation rate, and the efforts conducted to address these challenges toward the design of new enhanced alternative biomaterials.

Medical-Grade Poly(Lactic Acid)/Hydroxyapatite Composite Films: Thermal and In Vitro Degradation Properties

Production of biocompatible composite scaffolds shifts towards additive manufacturing where thermoplastic biodegradable polymers such as poly(lactic acid) (PLA) are used as matrices. Differences between industrial- and medical-grade polymers are often overlooked although they may affect properties and degradation behaviour as significantly as the filler addition. In the present research, composite films based on medical-grade PLA and biogenic hydroxyapatite (HAp) with 0, 10, and 20 wt.% of HAp were prepared by solvent casting technique. The degradation of composites incubated in phosphate-buffered saline solution (PBS) at 37 °C after 10 weeks showed that the higher HAp content slowed down the hydrolytic PLA degradation and improved its thermal stability. Morphological nonuniformity after degradation was indicated by the different glass transition temperatures (T_g) throughout the film. The T_g of the inner part of the sample decreased significantly faster compared with the outer part. The decrease was observed prior to the weight loss of composite samples.

Anaerobic Biodegradability of Commercial Bioplastic Products: Systematic Bibliographic Analysis and Critical Assessment of the Latest Advances

Bioplastics have entered everyday life as a potential sustainable substitute for commodity plastics. However, still further progress should be made to clarify their degradation behavior under controlled and uncontrolled conditions. The wide array of biopolymers and commercial blends available make predicting the biodegradation degree and kinetics quite a complex issue that requires specific knowledge of the multiple factors affecting the degradation process. This paper summarizes the main scientific literature on anaerobic digestion of biodegradable plastics through a general bibliographic analysis and a more detailed discussion of specific results from relevant experimental studies. The critical analysis of literature data initially included 275 scientific references, which were then screened for duplication/pertinence/relevance. The screened references were analyzed to derive some general features of the research profile, trends, and evolution in the field of anaerobic biodegradation of bioplastics. The second stage of the analysis involved extracting detailed results about bioplastic degradability under anaerobic conditions by screening analytical and performance data on biodegradation performance for different types of bioplastic products and different anaerobic biodegradation conditions, with a particular emphasis on the most recent data. A critical overview of existing biopolymers is presented, along with their properties and degradation mechanisms and the operating parameters influencing/enhancing the degradation process under anaerobic conditions.

A Highly Active and Selective Zirconium-Based Catalyst System for the Industrial Production of Poly(lactic acid)

The biodegradable, aliphatic polyester poly(lactic acid), PLA, is a leading bio-based alternative to petrochemical-derived plastic materials across a range of applications. Widely reported in the available literature as a benchmark for PLA production via the bulk ring-opening polymerization of lactides is the use of divalent tin catalysts, and particularly tin(II) bis(2-ethylhexanoate). We present an alternative zirconium-based system that combines an inexpensive Group IV metal with the robustness, high activity, control, and designed compatibility with existing facilities and processes, that are required for industrial use. We have carried out a comprehensive kinetic study and applied a combined experimental and theoretical approach to understanding the mechanism by which the polymerization of lactide proceeds in the presence of this system. In the laboratory-scale (20 g) polymerization of recrystallized racemic d,l-lactide (rac-lactide), we have measured catalyst turnover frequencies up to at least 56,000 h-1, and confirmed the reported protocols' resistance toward undesirable epimerization, transesterification, and chain scission processes, deleterious to the properties of the polymer product. Further optimization and scale-up under industrial conditions have confirmed the relevance of the catalytic protocol to the commercial production of melt-polymerized PLA. We were able to undertake the efficient preparation of high-molecular-weight PLA on the 500-2000 g scale, via the selective and well-controlled polymerization of commercial polymer-grade l-lactide under challenging, industrially relevant conditions, and at metal concentrations as low as 8-12 ppm Zr by weight ([Zr] = 1.3 × 10-3 to 1.9 × 10-3 mol %). Under those conditions, a catalyst turnover number of at least 60,000 was attained, and the activity of the catalyst was comparable to that of tin(II) bis(2-ethylhexanoate).

Antimicrobial Poly (Lactic Acid)/Copper Nanocomposites for Food Packaging Materials

Composites based on polylactic acid (PLA) and copper for food packaging applications were obtained. Copper clusters were synthesized in polyethylene glycols 400 and 600, respectively, using ascorbic acid as a reducing agent, by reactive milling. Copper clusters were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR), and Ultraviolet-Visible (UV-VIS) spectroscopy. Copper/PLA composites containing Proviplast as plasticizer were characterized by FT-IR spectroscopy, mechanical tests, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), absorption of the saline solution, contact angle, and antibacterial properties. It was observed that the concentration of Copper/PEG influenced the investigated properties. The mechanical properties of the samples decreased with the increasing of Copper/PEG concentration. We recorded the phase transformation temperatures and identified the exothermic or endothermic processes. The lowest absorption values were recorded in the case of the sample containing 1% Cu. The contact angle decreases with the increase in the concentration of the PEG 600-Cu mixture in the recipes. The increase in the content of Cu clusters favors the decrease in the temperature, taking place 15% wt mass losses. The obtained composites showed antibacterial properties for all tested strains. These materials could be used as alternative materials for obtaining biodegradable food packaging.

Correlation between Processing Parameters, Morphology, and Properties of Injection-Molded Polylactid Acid (PLA) Specimens at Different Length Scales

Polylactic acid (PLA) is one of the most promising bioplastic representatives that finds application in many different areas, e.g., as single-use products in the packaging industry, in the form of mulch film for agriculture, or in medical devices. For the development of new areas, especially in terms of long-term applications and the production of recyclable products, the material properties controlled by processing must be known. The state of the art is investigations at the global scale (integral values) without consideration of local structure inhomogeneities and their influence on the material properties. In this work, morphological, thermal, and mechanical properties of injection-molded PLA tensile bars are investigated at different length scales (global and local) as a function of processing parameters. In addition to the processing parameters, such as melt temperature, mold temperature, and cooling time in the mold, the influence of the D-isomer content on the crystallization behavior and the resulting material properties are investigated. The material was found to form crystalline structures only when cooled in a mold tempered above T_g. In addition, PLA with a lower content of D-isomer was found to have a higher degree of crystallinity. Since the mechanical properties obtained by tensile tests could not be correlated with the degree of crystallinity, detailed analysis were performed showing a characteristic inhomogeneous morphology within the tensile bars. By means of micromechanical investigations on samples with different microstructure ranges, the relationship between local morphology and failure behavior could be explained.

Beeswax as a natural alternative to synthetic waxes for fabrication of PLA/diatomaceous earth composites

In this study, injection moulding was applied to produce biocomposites consisting of polylactide (PLA) and amorphous diatomaceous earth used as a filler at different concentrations. Natural wax and synthetic wax were added to improve processing properties, comparing the resulting biocomposites. The use of natural beeswax makes the composite environmentally friendly. The prepared composites contained 2.5, 5, 10 and 15% w/w filler. The test samples have been injection moulded. Rheological, mechanical, surface and other properties were assessed for the fabricated composites. The testing has shown that the use of wax additives has a significant influence on the mechanical properties (tensile strength, flexural strength, impact strength) and the hydrophilicity/hydrophobicity of composite surfaces. The addition of natural wax, especially at lower concentration, has a positive effect on the rheological properties of composites (melt flow rate, MFR), flexural modulus and impact strength. Different composite parameters are modified by different wax types so both natural and synthetic waxes, can be used interchangeably, depending on the required final material characteristics.

Mechanical and Thermal Properties of Bamboo Fiber–Reinforced PLA Polymer Composites: A Critical Study

In the past few years, a new passion for the growth of biodegradable polymers based on elements derived from natural sources has been getting much attention. Natural fiber-based polymer matrix composites offer weight loss, reduction in cost and carbon dioxide emission, and recyclability. In addition, natural fiber composites have a minimal impact on the environment in regards to global warming, health, and pollution. Polylactic acid (PLA) is one of the best natural resource polymers available among biodegradable polymers. Natural fiber–reinforced PLA polymer composites have been extensively researched by polymer researchers to compete with conventional polymers. The type of fiber used plays a massive part in fiber and matrix bonds and, thereby, influences the composite’s mechanical properties and thermal properties. Among the various natural fibers, low density, high strength bamboo fibers (BF) have attracted attention. PLA and bamboo fiber composites play a vital character in an extensive range of structural and non-structural applications. This review briefly discussed on currently developed PLA-based natural bamboo fiber–reinforced polymer composites concentrating on the property affiliation of fibers. PLA polymer–reinforced natural bamboo fiber used to establish composite materials, various composite fabrication methods, various pretreatment methods on fibers, their effect on mechanical properties, as well as thermal properties and applications on different fields of such composites are discussed in this study. This review also presents a summary of the issues in the fabrication of natural fiber composites.

Chemical Structures, Properties, and Applications of Selected Crude Oil-Based and Bio-Based Polymers

The growing perspective of running out of crude oil followed by increasing prices for all crude oil-based materials, e.g., crude oil-based polymers, which have a huge number of practical applications but are usually neither biodegradable nor environmentally friendly, has resulted in searching for their substitutes-namely, bio-based polymers. Currently, both these types of polymers are used in practice worldwide. Owing to the advantages and disadvantages occurring among plastics with different origin, in this current review data on selected popular crude oil-based and bio-based polymers has been collected in order to compare their practical applications resulting from their composition, chemical structure, and related physical and chemical properties. The main goal is to compare polymers in pairs, which have the same or similar practical applications, regardless of different origin and composition. It has been proven that many crude oil-based polymers can be effectively replaced by bio-based polymers without significant loss of properties that ensure practical applications. Additionally, biopolymers have higher potential than crude oil-based polymers in many modern applications. It is concluded that the future of polymers will belong to bio-based rather than crude oil-based polymers.

Bioresorbable Nonwoven Patches as Taxane Delivery Systems for Prostate Cancer Treatment

Prostate cancer is the second most common cancer in males. In the case of locally advanced prostate cancer radical prostatectomy is one of the first-line therapy. However, recurrence after resection of the tumor can appear. Drug-eluting bioresorbable implants acting locally in the area of the tumor or the resection margins, that reduce the risk of recurrence would be advantageous. Electrospinning offers many benefits in terms of local delivery so fiber-forming polyesters and polyestercarbonates which are suitable to be drug-loaded were used in the study to obtain CTX or DTX-loaded electrospun patches for local delivery. After a fast verification step, patches based on the blend of poly(glycolide-ε-caprolactone) and poly(lactide-glycolide) as well as patches obtained with poly(lactide-glycolide- ε-caprolactone) were chosen for long-term study. After three months, 60% of the drug was released from (PGCL/PLGA) + CTX and it was selected for final, anticancer activity analysis with the use of PC-3 and DU145 cells to establish its therapeutic potential. CTX-loaded patches reduced cell growth to 53% and 31% respectively, as compared to drug-free patches. Extracts from drug-free patches showed excellent biocompatibility with the PC-3 cell line. Cabazitaxel-loaded bioresorbable patches are a promising drug delivery system for prostate cancer therapy.

Marine-Derived Actinomycetes: Biodegradation of Plastics and Formation of PHA Bioplastics-A Circular Bioeconomy Approach

Plastics are present in the majority of daily-use products worldwide. Due to society's production and consumption patterns, plastics are accumulating in the environment, causing global pollution issues and intergenerational impacts. Our work aims to contribute to the development of solutions and sustainable methods to mitigate this pressing problem, focusing on the ability of marine-derived actinomycetes to accelerate plastics biodegradation and produce polyhydroxyalkanoates (PHAs), which are biodegradable bioplastics. The thin plastic films' biodegradation was monitored by weight loss, changes in the surface chemical structure (Infra-Red spectroscopy FTIR-ATR), and by mechanical properties (tensile strength tests). Thirty-six marine-derived actinomycete strains were screened for their plastic biodegradability potential. Among these, Streptomyces gougerotti, Micromonospora matsumotoense, and Nocardiopsis prasina revealed ability to degrade plastic films-low-density polyethylene (LDPE), polystyrene (PS) and polylactic acid (PLA) in varying conditions, namely upon the addition of yeast extract to the culture media and the use of UV pre-treated thin plastic films. Enhanced biodegradation by these bacteria was observed in both cases. S. gougerotti degraded 0.56% of LDPE films treated with UV radiation and 0.67% of PS films when inoculated with yeast extract. Additionally, N. prasina degraded 1.27% of PLA films when these were treated with UV radiation, and yeast extract was added to the culture medium. The main and most frequent differences observed in FTIR-ATR spectra during biodegradation occurred at 1740 cm^-1, indicating the formation of carbonyl groups and an increase in the intensity of the bands, which indicates oxidation. Young Modulus decreased by 30% on average. In addition, S. gougerotti and M. matsumotoense, besides biodegrading conventional plastics (LDPE and PS), were also able to use these as a carbon source to produce degradable PHA bioplastics in a circular economy concept.

Effective immobilization of lactate dehydrogenase onto mesoporous silica

This study presents that covalent immobilization technique has been utilized for the immobilization of l-lactate dehydrogenase (l-LDH) from porcine on mesoporous silica. To develop mesoporous silica as support material for use in l-LDH immobilization, the particle surfaces were functionalized with 3-aminopropyltrimethoxysilane and further conjugated with glutaraldehyde. The effect of some parameters such as glutaraldehyde concentration, immobilization pH, initial enzyme concentration, and immobilization time was investigated and the optimum conditions for these parameters were determined as 1% (w/v), pH 8.0, 1 mg/ml, and 120 min, respectively. The maximum working pH and temperature for the oxidation of lactate to pyruvate reaction were determined as 10.0 and 35°C for free and 9.0 and 40°C for immobilized l-LDH, respectively. The kinetic parameters (K_m and V_max ) of l-LDH for the oxidation of lactate to pyruvate reaction were examined as 1.02 mM and 7.58 U/mg protein for free and 0.635 mM and 1.7 U/mg protein for immobilized l-LDH, respectively. Moreover, the immobilized l-LDH was 1.3-fold more stable than free l-LDH at 25°C according to calculated t_1/2 values. The immobilized l-LDH retained 80% of its initial activity in a batch reactor after 14 reuses.

Exploring the Size Effect of Graphene Oxide on Crystallization Kinetics and Barrier Properties of Poly(lactic acid)

Two different sizes of graphene oxide/poly(lactic acid) composites were prepared by the solution flocculation method, and the effect of the size effect of graphene oxide on the crystallization, barrier, and mechanical properties of poly(lactic acid) was investigated by various characterization methods. The results of the crystallization behavior test show that the size change of graphene oxide has little effect on the nucleation effect of poly(lactic acid). Increasing the size of graphene oxide can promote the crystal growth, so as to improve the crystallization ability of poly(lactic acid). The test results of mechanical properties and barrier properties show that increasing the size of graphene oxide can provide a larger interfacial surface area and transmit stress more effectively, which can greatly improve the modulus of poly(lactic acid). At the same time, because of this, the diffusion path of gas molecules in poly(lactic acid) can be longer and more tortuous, so as to improve the barrier performance of poly(lactic acid).

Effect of Epoxidized and Maleinized Corn Oil on Properties of Polylactic Acid (PLA) and Polyhydroxybutyrate (PHB) Blend

The present work analyzes the influence of modified, epoxidized and maleinized corn oil as a plasticizing and/or compatibilizing agent in the PLA-PHB blend (75% PLA and 25% PHB wt.%). The chemical modification processes of corn oil were successfully carried out and different quantities were used, between 0 and 10% wt.%. The different blends obtained were characterized by thermal, mechanical, morphological, and disintegration tests under composting conditions. It was observed that to achieve the same plasticizing effect, less maleinized corn oil (MCO) is needed than epoxidized corn oil (ECO). Both oils improve the ductile properties of the PLA-PHB blend, such as elongation at break and impact absorb energy, however, the strength properties decrease. The ones that show the highest ductility values are those that contain 10% ECO and 5% MCO, improving the elongation of the break of the PLA-PHB blend by more than 400% and by more than 800% for the sample PLA.

Stability Study of the Irradiated Poly(lactic acid)/Styrene Isoprene Styrene Reinforced with Silica Nanoparticles

In this paper, the stability improvement of poly(lactic acid) (PLA)/styrene-isoprene block copolymer (SIS) loaded with silica nanoparticles is characterized. The protection efficiency in the material of thermal stability is mainly studied by means of high accurate isothermal and nonisothermal chemiluminescence procedures. The oxidation induction times obtained in the isothermal CL determinations increase from 45 min to 312 min as the polymer is free of silica or the filler loading is about 10%, respectively. The nonisothermal measurements reveal the values of onset oxidation temperatures with about 15% when the concentration of SiO2 particles is enhanced from none to 10%. The curing assay and Charlesby-Pinner representation as well as the modifications that occurred in the FTIR carbonyl band at 1745 cm-1 are appropriate proofs for the delay of oxidation in hybrid samples. The improved efficiency of silica during the accelerated degradation of PLA/SIS 30/n-SiO2 composites is demonstrated by means of the increased values of activation energy in correlation with the augmentation of silica loading. While the pristine material is modified by the addition of 10% silica nanoparticles, the activation energy grows from 55 kJ mol-1 to 74 kJ mol-1 for nonirradiated samples and from 47 kJ mol-1 to 76 kJ mol-1 for γ-processed material at 25 kGy. The stabilizer features are associated with silica nanoparticles due to the protection of fragments generated by the scission of hydrocarbon structure of SIS, the minor component, whose degradation fragments are early converted into hydroperoxides rather than influencing depolymerization in the PLA phase. The reduction of the transmission values concerning the growing reinforcement is evidence of the capacity of SiO2 to minimize the changes in polymers subjected to high energy sterilization. The silica loading of 10 wt% may be considered a proper solution for attaining an extended lifespan under the accelerated degradation caused by the intense transfer of energy, such as radiation processing on the polymer hybrid.

A Review of Woven Tracheal Stents: Materials, Structures, and Application

The repair and reconstruction of tracheal defects is a challenging clinical problem. Due to the wide choice of materials and structures, weaving technology has shown unique advantages in simulating the multilayer structure of the trachea and providing reliable performance. Currently, most woven stent-based stents focus only on the effect of materials on stent performance while ignoring the direct effect of woven process parameters on stent performance, and the advantages of weaving technology in tissue regeneration have not been fully exploited. Therefore, this review will introduce the effects of stent materials and fabric construction on the performance of tracheal stents, focusing on the effects of weaving process parameters on stent performance. We will summarize the problems faced by woven stents and possible directions of development in the hope of broadening the technical field of artificial trachea preparation.

Mechanical and microbiological testing concept for activatable anti-infective biopolymer implant coatings

An anti-infective bilayer implant coating with selectively activatable properties was developed to prevent biofilm formation and to support the treatment of periprosthetic infection as a local adjunct to current treatment concepts. In a first step, Ti6Al4V discs were coated with a permanent layer of Poly(l-lactide) (PLLA) including silver ions. The PLLA could be optionally released by the application of extracorporeal shock waves. In a second step, a resorbable layer of triglyceride (TAG) with incorporated antibiotics was applied. The second layer is designed for resorption within weeks. Prior to approval and clinical application, a comprehensive evaluation process to determine mechanical/physical and microbiological properties is obligate. To date, none of the existing test standards covers both drug-releasing and activatable coatings for orthopedic implants. Therefore, a comprehensive test concept was developed to characterize the new coating in a pilot series. The coatings were homogeneously applied on the Ti6Al4V substrate, resulting in an adhesion strength sufficient for non-articulating surfaces for PLLA. Proof of the extracorporeal shockwave activation of PLLA was demonstrated both mechanically and microbiologically, with a simultaneous increase of biocompatibility compared to standard electroplated silver coating. Wettability was significantly reduced for both layers in comparison to the Ti6Al4V substrate. Thus, potentially inhibiting biofilm formation. Furthermore, the TAG coating promoted cell proliferation and bacterial eradication. In conclusion, the testing concept is applicable for similar biopolymer coating systems. Furthermore, the extracorporeal activation could represent a completely new supportive approach for the treatment of periprosthetic joint infections.