Study of disintegrability in compost and enzymatic degradation of PLA and PLA nanocomposites reinforced with cellulose nanocrystals extracted from Posidonia Oceanica

Sustainability in the green engineering of nanocomposites based on marine-derived polysaccharides and collagens: A review

Nanocomposites are sophisticated materials that incorporate nanostructures into matrix materials, such as polymers, ceramics and metals. Generally, the marine ecosystem exhibits severe variability in terms of light, temperature, pressure, and nutrient status, forcing the marine organisms to develop variable, complex and unique chemical structures to boost their competitiveness and chances of survival. Polymers sourced from marine creatures, such as chitin, chitosan, alginate, sugars, proteins, and collagen play a crucial role in the bioengineering field, contributing significantly to the development of nanostructures like nanoparticles, nanocomposites, nanotubes, quantum dots, etc. These nanostructures offer a wide array of features involving mechanical strength, thermal stability, electrical conductivity, barrier and optical characteristics compared to traditional composites. Notably, marine nanocomposites have distinctive roles in a wide spectrum of applications, among them anti-cancer, anti-microbial, antioxidant, cytotoxic, food packing, tissue engineering and catalytic actions. Sol-gel, hot pressing, chemical vapor deposition, catalytic decomposition, dispersion, melt intercalation, in situ intercalative polymerization, high-energy ball milling and template synthesis are common processes utilized in engineering nanocomposites. According to our literature survey and the Web of Science, chitosan, followed by cellulose, chitin and MAPs emerge as the most significant marine polymers utilized in the construction of nanocomposites. Taken together, the current manuscript underscores the biogenesis of nanocomposites, employing marine polymers using eco-friendly processes. Furthermore, significant emphasis in this area is needed to fully explore their capabilities and potential benefits. To the best of our knowledge, this manuscript stands as the first comprehensive review that discusses the role of marine-derived polymers in engineering nanocomposites for various applications.

Evaluation of PLA-Based Composite Films Filled with Cu2(OH)3NO3 Nanoparticles as an Active Material for the Food Industry: Biocidal Properties and Environmental Sustainability

The globalization of markets has diversified the food supply, but it has also made the distribution chain more difficult, increasing the risk of microbial contamination. One strategy to obtain safer food and extend its shelf life is to develop active packaging with antimicrobial properties that prevent the growth of pathogenic microorganisms or spoilage in food products. In this context, and in line with the growing social awareness about the environmental impact generated by plastic waste, this work evaluated the effectiveness of polylactic acid (PLA) films loaded with different concentrations of copper (II) hydroxynitrate nanoparticles (CuHS) against the microbiota of fresh foods (chicken, fish and cheese). The results showed that the developed films containing 1, 3 and 5% w/w of CuHS in the polymeric matrix caused a decrease in the microbial abundance equal to or higher than 3 logarithmic units in all foods tested. Moreover, the mechanical and thermal properties of the formulated composites showed that the added CuHS concentrations did not substantially modify these properties compared to the PLA films. Taking into account the results obtained for antimicrobial activity, Cu (II) migration levels and the cytotoxicity of the films formulated, the PLA composite loaded with 1% CuHS (w/w) was the most suitable for its potential use as food packaging material. In addition, the biodegradation of this composite film was studied under conditions simulating intensive aerobic composting, demonstrating that almost 100% disintegration after 14 days of testing was achieved. Therefore, the innovative PLA-based films developed represent a promising strategy for the fabrication of packaging and active surfaces to increase food shelf life while maintaining food safety. Moreover, their biodegradable character will contribute to efficient waste management, turning plastic residues into a valuable resource.

Acceleration of the biodegradation of cationic polyacrylamide by the coupling effect of thermophilic microorganisms and high temperature in hyperthermophilic composting

As a flocculant of sewage sludge, cationic polyacrylamide (CPAM) enters the environment with sludge and exists for a long time, posing serious threats to the environment. Due to the environmental friendliness and high efficiency in the process of organic solid waste treatment, hyperthermophilic composting (HTC) has received increasing attention. However, it is still unclear whether the HTC process can effectively remove CPAM from sludge. In this study, the effects of HTC and conventional thermophilic composting (CTC) on CPAM in sludge were compared and analyzed. At the end of HTC and CTC, the concentrations of CPAM were 278.96 mg kg-1 and 533.89 mg kg-1, respectively, and the removal rates were 72.17% and 46.61%, respectively. The coupling effect of thermophilic microorganisms and high temperature improved the efficiency of HTC and accelerated the biodegradation of CPAM. The diversity and composition of microbial community changed dramatically during HTC. Geobacillus, Thermobispora, Pseudomonas, Brevundimonas, and Bacillus were the dominant bacteria responsible for the high HTC efficiency. To our knowledge, this is the first study in which CPAM-containing sludge is treated using HTC. The ideal performance and the presence of key microorganisms revealed that HTC is feasible for the treatment of CPAM-containing sludge.

Biodegradability of PBAT/PLA coated paper and bioplastic bags under anaerobic digestion

Poly (lactic acid) (PLA) and Poly(butylene adipate-co-terephthalate) (PBAT) are two of biodegradable plastics with the highest production capacities in 2021. Bioplastic waste management can be easily integrated with organic waste management, especially when bioplastics are used as food packaging material, since they are potentially biodegradable. The aim of this study was to assess the biodegradability of biodegradable polymer-coated paper (BPCP) and bioplastic bags made from PBAT/PLA blend during mesophilic and thermophilic anaerobic digestion (AD) and to reveal the changes in the physicochemical properties of the bioplastics. BPCP obtained 155 NmL-CH4/g VS and 307.3 NmL-CH4/g VS under mesophilic and thermophilic conditions, respectively, but left bioplastic film residues. The bioplastic bags did not exhibit significant biodegradation during the AD processes. 1H NMR results indicated that the ratio of PLA to PBAT decreased significantly after AD of the BPCP film and that PLA monomers were formed from the bioplastic bags, leading to a decrease in the hydrophobicity on the surfaces of the materials. Methanoculleus was found to be enriched on the bioplastic surface after mesophilic AD. From the perspective of coupling bioplastic waste management with the food waste management, the incorporation of BPCP into the AD reactor not only enhances system stability and methane production to a greater extent than biodegradable plastic bags but also raises concerns regarding the residual biofilm when utilizing the digestate for direct land applications.

Fungal enzyme degradation of lignin-PLA composites: Insights from experiments and molecular docking simulations

Fungal enzymes are effective in degrading various polymeric materials. In this study, we assessed the initial degradation of composites consisting of lignin-poly(lactic acid) (PLA) with both unmodified lignin (LIG) and oxypropylated lignin (oLIG) incorporated at 10 % and 40 % weight within the PLA matrix in a fungal environment. Trametes versicolor fungi were used, and the samples were treated only for eight weeks. Although there was no significant difference in weight loss, the degradation process impacted the chemical and thermal properties of the composites, as shown by Fourier transform infrared spectroscopy (FTIR) and Differential scanning calorimetry (DSC) analyses. After the degradation process, the carbonyl index values decreased for all composites and the hydroxyl index values increased for LIG/PLA and a reverse trend was observed for oLIG/PLA composites. The first heating scan from DSC results showed that the melting peak and the cold crystallization peak disappeared after the degradation process. Microscopic analysis revealed that LIG/PLA exhibited higher roughness than oLIG/PLA. Molecular docking simulations were carried out using guaiacylglycerol-β-guaiacyl ether (GGE) and lactic acid (LA) as model compounds for lignin and PLA, respectively, with laccase (Lac) enzyme for Trametes versicolor. The docking results showed that GGE had the strongest binding interaction and affinity with Lac than lactic acid and oxypropylated GGE. The oxypropylated GGE formed a shorter hydrogen bonding with the Lac enzyme than GGE and LA. The trend associated with the degradation of composites from experimental and molecular docking findings was consistent. This combined approach provided insights into the degradation process using fungi and had the potential to be applied to different polymeric composites.

Degradation of Polylactic Acid/Polypropylene Carbonate Films in Soil and Phosphate Buffer and Their Potential Usefulness in Agriculture and Agrochemistry

Blends of poly(lactic acid) (PLA) with poly(propylene carbonate) (PPC) are currently in the phase of intensive study due to their promising properties and environmentally friendly features. Intensive study and further commercialization of PPC-based polymers or their blends, as usual, will soon face the problem of their waste occurring in the environment, including soil. For this reason, it is worth comprehensively studying the degradation rate of these polymers over a long period of time in soil and, for comparison, in phosphate buffer to understand the difference in this process and evaluate the potential application of such materials toward agrochemical and agricultural purposes. The degradation rate of the samples was generally accompanied by weight loss and a decrease in molecular weight, which was facilitated by the presence of PPC. The incubation of the samples in the aqueous media yielded greater surface erosions compared to the degradation in soil, which was attributed to the leaching of the low molecular degradation species out of the foils. The phytotoxicity study confirmed the no toxic impact of the PPC on tested plants, indicating it as a "green" material, which is crucial information for further, more comprehensive study of this polymer toward any type of sustainable application.

Assessment of biodegradation of lignocellulosic fiber-based composites - A systematic review

Lignocellulosic fiber-reinforced polymer composites are the most extensively used modern-day materials with low density and better specific strength specifically developed to render better physical, mechanical, and thermal properties. Synthetic fiber-reinforced composites face some serious issues like low biodegradability, non-environmentally friendly, and low disposability. Lignocellulosic or natural fiber-reinforced composites, which are developed from various plant-based fibers and animal-based fibers are considered potential substitutes for synthetic fiber composites because they are characterized by lightweight, better biodegradability, and are available at low cost. It is very much essential to study end-of-life (EoL) conditions like biodegradability for the biocomposites which occur commonly after their service life. During biodegradation, the physicochemical arrangement of the natural fibers, the environmental conditions, and the microbial populations, to which the natural fiber composites are exposed, play the most influential factors. The current review focuses on a comprehensive discussion of the standards and assessment methods of biodegradation in aerobic and anaerobic conditions on a laboratory scale. This review is expected to serve the materialists and technologists who work on the EoL behaviour of various materials, particularly in natural fiber-reinforced polymer composites to apply these standards and test methods to various classes of biocomposites for developing sustainable materials.

Aging Process of Biocomposites with the PLA Matrix Modified with Different Types of Cellulose

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

Assessing the Effect of Cellulose Nanocrystal Content on the Biodegradation Kinetics of Multiscale Polylactic Acid Composites under Controlled Thermophilic Composting Conditions

This work studied the effect of cellulose nanocrystal (NCC) content on the biodegradation kinetics of PLA-based multiscale cellulosic biocomposites (PLAMCBs). To facilitate biodegradation, the materials were subjected to thermo-oxidation before composting. Biodegradation was carried out for 180 days under controlled thermophilic composting conditions according to the ASTM D 5338 standard. A first-order model based on Monod's kinetics under limiting substrate conditions was used to study the effect of cellulose nanocrystal (NCC) content on the biodegradation kinetics of multiscale composite materials. It was found that thermo-oxidation at 70 °C for 160 h increased the biodegradability of PLA. Also, it was found that the incorporation of cellulosic fibrous reinforcements increased the biodegradability of PLA by promoting hydrolysis during the first stage of composting. Likewise, it was found that partial substitution of micro cellulose (MFC) by cellulose nanocrystals (NCCs) increased the biodegradability of the biocomposite. This increase was more evident as the NCC content increased, which was attributed to the fact that the incorporation of cellulose nanocrystals facilitated the entry of water into the material and therefore promoted the hydrolytic degradation of the most recalcitrant fraction of PLA from the bulk and not only by surface erosion.

Polymer-Matrix Composites: Characterising the Impact of Environmental Factors on Their Lifetime

Polymer-matrix composites are widely used in engineering applications. Yet, environmental factors impact their macroscale fatigue and creep performances significantly, owing to several mechanisms acting at the microstructure level. Herein, we analyse the effects of water uptake that are responsible for swelling and, over time and in enough quantity, for hydrolysis. Seawater, due to a combination of high salinity and pressures, low temperature and biotic media present, also contributes to the acceleration of fatigue and creep damage. Similarly, other liquid corrosive agents penetrate into cracks induced by cyclic loading and cause dissolution of the resin and breakage of interfacial bonds. UV radiation either increases the crosslinking density or scissions chains, embrittling the surface layer of a given matrix. Temperature cycles close to the glass transition damage the fibre-matrix interface, promoting microcracking and hindering fatigue and creep performance. The microbial and enzymatic degradation of biopolymers is also studied, with the former responsible for metabolising specific matrices and changing their microstructure and/or chemical composition. The impact of these environmental factors is detailed for epoxy, vinyl ester and polyester (thermoset); polypropylene, polyamide and poly etheretherketone (thermoplastic); and for poly lactic acid, thermoplastic starch and polyhydroxyalkanoates (biopolymers). Overall, the environmental factors mentioned hamper the fatigue and creep performances, altering the mechanical properties of the composite or causing stress concentrations through microcracks, promoting earlier failure. Future studies should focus on other matrices beyond epoxy as well as on the development of standardised testing methods.

Posidonia oceanica (L.) Delile: A Mediterranean seagrass with potential applications but regularly and erroneously referred to as an algal species

Posidonia oceanica (L.) Delile is one of the most abundant aquatic vascular higher plants in the Mediterranean Sea belonging to Posidoniaceas family. It is considered as a valuable natural source for multiple uses either for ecological functions or industrial applications. Nevertheless, this marine phanerogam is commonly confused with macroalgae, or seaweeds, known also as cryptogams. The present note intends to discuss the mis-use of the associated terminology of P. oceanica as algae in the scientific literature in order to avoid the widespread of this issue in the future. Thus, an extensive assessment of some important published woks has been conducted. This note will certainly allow the accurate nomenclature of this promising endemic species, which will continue its valorizations' ascension in several potential applications.

Application of cellulose nanocrystals in water treatment membranes: A review

Nanomaterials have brought great changes to human society, and development has gradually shifted the focus to environmentally friendly applications. Cellulose nanocrystals (CNCs) are new one-dimensional nanomaterials that exhibit environmental friendliness and ensure the biological safety of water environment. CNCs have excellent physical and chemical properties, such as simple preparation process, nanoscale size, high specific surface area, high mechanical strength, good biocompatibility, high hydrophilicity and antifouling ability. Because of these characteristics, CNCs are widely used in ultrafiltration membranes, nanofiltration membranes and reverse osmosis membranes to solve the problems hindering development of membrane technology, such as insufficient interception and separation efficiency, low mechanical strength and poor antifouling performance. This review summarizes recent developments and uses of CNCs in water treatment membranes and discusses the challenges and development prospects of CNCs materials from the perspectives of ecological safety and human health by comparing them with traditional one-dimensional nanomaterials.

Rigid and film bioplastics degradation under suboptimal composting conditions: A kinetic study

The present research investigates the degradation rate of bioplastics under various composting conditions, including suboptimal ones. Lab-scale tests were carried out setting three variables: temperature (37°C-58°C), humidity (30%-60%) and duration of the thermophilic and the maturation phases (15-60 days). The composting tests were carried out following modified guideline ISO 20200:2015 and lasted for 60 days. Bioplastics in the synthetic waste matrix consisted of Mater-Bi^® film biobags and PLA rigid teaspoons. A kinetic study was performed, resulting in faster degradation rates for film bioplastics (first-order kinetics with k = 0.0850-0.1663 d^-1) than for rigid (0.0018-0.0136 d^-1). Moreover, film bioplastics reached a complete degradation within the 60 days of the test. Concerning the rigid products, 90% degradation would be achieved in 2-3 years for mesophilic conditions. Finally, in the undersieve of 0.5 mm some microplastics were identified with the ImageJ software, mainly relatable to rigid (PLA) bioplastics. Overall, the results disclosed that the combination of mesophilic temperatures and absence of moistening slowed down both the degradation and the disintegration process of bioplastics.

Quantitative analysis of factors determining the enzymatic degradation of poly(lactic acid)

The enzymatic degradation of poly(lactic acid) was catalyzed with Proteinase K and the effect of various factors on the rate of degradation was analyzed quantitatively with the help of appropriate kinetic models. The Michaelis-Menten model was modified for the purpose by considering the heterogeneous nature of the reaction and the denaturation of the enzyme. The results proved that Proteinase K degrades the polymer very efficiently. The rate of degradation increases considerably up to 0.1 mg/ml enzyme concentration, but remains constant at larger values. Temperature has an optimum at around 50 °C that is somewhat higher than the 37 °C extensively used in the literature as the most advantageous temperature. If degradation occurs in the same medium throughout the process, the formation of lactic acid results in the rapid decrease of pH and finally in the denaturation of the enzyme. The dropping of pH below 5 slows down and finally stops degradation completely. The daily change of the medium results in degradation with a constant rate and the entire amount of the polymer can be decomposed mainly into monomer or smaller oligomer fragments. Degradation rate decreases slightly with increasing molecular weight and increasing d-lactide content. The use of appropriate kinetic models allows quantitative analysis and the prediction of the rate of enzymatic degradation of PLA.

Starch Nanocomposite Films: Migration Studies of Nanoparticles to Food Simulants and Bio-Disintegration in Soil

In this work, films containing AgNPs were obtained by different green synthesis techniques (AgNP in situ and AgNP L). The inclusion of nanoparticles in the starch matrix improved both mechanical and barrier properties. The migration of AgNPs from the nanocomposite material to three food simulants (water, 3% v/v acetic acid and 15% v/v ethanol) was studied. The experimental data were fitted by using different widely accepted mathematical models (Fickian, Ritger and Peppas, and Weibull), indicating that the AgNP migration followed a complex mechanism. The silver concentration (mg Ag per kg of simulant) that was released from the nanocomposite films was higher for the samples with AgNPs in situ than for those containing AgNP L. Likewise, the maximum release value (0.141 mg/dm² for AgNPs in situ in acetic acid simulant) was lower than the limits proposed by the legislation (European Commission and MERCOSUR; 10 and 8 mg/dm², respectively). The replacement of conventional plastic materials by biodegradable ones requires the evaluation of bio-disintegration tests in soil. In this sense, a period of 90 days was necessary to obtain ≥50% weight loss in both nanocomposite films. Additionally, the bio-disintegration of the samples did not contribute with phytotoxic compounds to the soil, allowing the germination of fast-growing seeds.

Modification of Cellulose Micro- and Nanomaterials to Improve Properties of Aliphatic Polyesters/Cellulose Composites: A Review

Aliphatic polyesters/cellulose composites have attracted a lot attention due to the perspectives of their application in biomedicine and the production of disposable materials, food packaging, etc. Both aliphatic polyesters and cellulose are biocompatible and biodegradable polymers, which makes them highly promising for the production of “green” composite materials. However, the main challenge in obtaining composites with favorable properties is the poor compatibility of these polymers. Unlike cellulose, which is very hydrophilic, aliphatic polyesters exhibit strong hydrophobic properties. In recent times, the modification of cellulose micro- and nanomaterials is widely considered as a tool to enhance interfacial biocompatibility with aliphatic polyesters and, consequently, improve the properties of composites. This review summarizes the main types and properties of cellulose micro- and nanomaterials as well as aliphatic polyesters used to produce composites with cellulose. In addition, the methods for noncovalent and covalent modification of cellulose materials with small molecules, polymers and nanoparticles have been comprehensively overviewed and discussed. Composite fabrication techniques, as well as the effect of cellulose modification on the mechanical and thermal properties, rate of degradation, and biological compatibility have been also analyzed.

Evaluation of the Factors Affecting the Disintegration under a Composting Process of Poly(lactic acid)/Poly(3-hydroxybutyrate) (PLA/PHB) Blends

The overall migration behavior and the disintegration under composting conditions of films based on plasticized poly(lactic acid)/poly(3-hydroxybutyrate) (PLA-PHB) blends were studied, with the main aim of determining the feasibility of their application as biodegradable food packaging materials. The role of composition in the disintegration process was evaluated by monitoring the changes in physical and thermal properties that originated during the degradation process. PLA and PHB were blended in two weight ratios with 15 wt% of tributyrin, using a Haake mixer and then compression molded into ~150 μm films. We found that the migration level of all of the studied blends was below check intended meaning retained in non-polar simulants, while only plasticized blends could withstand the contact with polar solvents. The disintegration of all of the materials in compost at 58 °C was completed within 42 days; the plasticized PHB underwent the fastest degradation, taking only 14 days. The presence of the TB plasticizer speeded up the degradation process. Different degradation mechanisms were identified for PLA and PHB. To evaluate the annealing effect separately from bacteria degradation, the influence of temperature on materials in the absence of a compost environment was also studied. With the increasing time of degradation in compost, both melting temperature and maximum degradation temperature progressively decreased, while the crystallinity degree increased, indicating that the samples were definitely degrading and that the amorphous regions were preferentially eroded by bacteria.

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

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

Nanoclay Effect into the Biodegradation and Processability of Poly(lactic acid) Nanocomposites for Food Packaging

One of the most promising expectations in the design of new materials for food packaging is focused on the development of biodegradable systems with improved barrier character. In this sense PLA reinforced with nanoclay is a potential alternative to the use of conventional oil-derivative polymers due to the synergetic effect of the biodegradable character of PLA and the barrier-induced effect derived from the dispersion of nanoparticles. In this work, composite materials based on PLA and reinforced with bentonite nanoparticles (up to 4% w/w) (NC) have been prepared to produce films with improved barrier character against water vapor transportation. Additionally, the biodegradable character of the composites depending on the crystallinity of the polymer and percentage of NC have been evaluated in the presence of an enzymatic active medium (proteinase K). Finally, a study of the capacity to film production of the composites has been performed to determine the viability of the proposals. The dispersion of the nanoparticles induced a tortuous pathway of water vapor crossing, reducing this diffusion by more than 22%. Moreover, the nanoclays materials were in all the cases acceptable for food packing in terms of migration. A migration lower than 1 mg/m2 was obtained in all the materials. Nonetheless, the presence of the nanoclays in decreased biodegradable capacity was observed. The time was enlarged to more than 15 days for the maximum content (4% w/w). On the other hand, the incorporation of NC does not avoid the processability of the material to obtain film-shaped processed materials.

Effect of Cellulose and Cellulose Nanocrystal Contents on the Biodegradation, under Composting Conditions, of Hierarchical PLA Biocomposites

In this work, the effect of microfibrillated cellulose (MFC) and cellulose nanocrystals (CNCs) on the biodegradation, under composting conditions, of hierarchical PLA biocomposites (HBCs) was studied using a full 2² factorial experimental design. The HBCs were prepared by extrusion processing and were composted for 180 days. At certain time intervals, the specimens were removed from the compost for their chemical, thermal and morphological characterizations. An ANOVA analysis was carried out at different composting times to study MFC and CNCs’ effects on biodegradation. The specimen’s mass loss and molecular weight loss were selected as independent variables. The results show that the presence of MFC enhances the PLA biodegradation, while with CNCs it decreases. However, when both cellulosic fibers are present, a synergistic effect was evident—i.e., in the presence of the MFC, the inclusion of the CNCs accelerates the HBCs biodegradation. Analysis of the ANOVA results confirms the relevance of the synergistic role between both cellulosic fibers over the HBC biodegradation under composting conditions. The results also suggest that during the first 90 days of incubation, the hydrolytic PLA degradation prevails, whereas, beyond that, the enzymatic microbial biodegradation dominates. The SEM results show MFC’s presence enhances the surface biodeterioration to a greater extent than the CNCs and that their simultaneous presence enhances PLA biodegradation. The SEM results also indicate that the biodegradation process begins from hydrophilic cellulosic fibers and promotes PLA biodegradation.

Biodegradable Antimicrobial Films for Food Packaging: Effect of Antimicrobials on Degradation

The environmental problem generated by the massive consumption of plastics makes necessary the developing of biodegradable antimicrobial materials that can extend food shelf-life without having a negative impact on the environment. The current situation regarding the availability of biodegradable food packaging materials has been analysed, as well as different studies where antimicrobial compounds have been incorporated into the polymer matrix to control the growth of pathogenic or spoilage bacteria. Thus, the antimicrobial activity of active films based on different biodegradable polymers and antimicrobial compounds has been discussed. Likewise, relevant information on biodegradation studies carried out with different biopolymers in different environments (compost, soil, aquatic), and the effect of some antimicrobials on this behavior, are reviewed. In most of the studies, no relevant effect of the incorporated antimicrobials on the degradation of the polymer were observed, but some antimicrobials can delay the process. The changes in biodegradation pattern due to the presence of the antimicrobial are attributed to its influence on the microorganism population responsible for the process. More studies are required to know the specific influence of the antimicrobial compounds on the biodegradation behavior of polymers in different environments. No studies have been carried out or marine media to this end.

Migration and Degradation in Composting Environment of Active Polylactic Acid Bilayer Nanocomposites Films: Combined Role of Umbelliferone, Lignin and Cellulose Nanostructures

This study was dedicated to the functional characterization of innovative poly(lactic acid) (PLA)-based bilayer films containing lignocellulosic nanostructures (cellulose nanocrystals (CNCs) or lignin nanoparticles (LNPs)) and umbelliferone (UMB) as active ingredients (AIs), prepared to be used as active food packaging. Materials proved to have active properties associated with the antioxidant action of UMB and LNPs, as the combination of both ingredients in the bilayer formulations produced a positive synergic effect inducing the highest antioxidant capacity. The results of overall migration for the PLA bilayer systems combining CNCs or LNPs and UMB revealed that none of these samples exceeded the overall migration limit required by the current normative for food packaging materials in both non-polar and polar simulants. Finally, all the hydrophobic monolayer and bilayer films were completely disintegrated in composting conditions in less than 18 days of incubation, providing a good insight on the potential use of these materials for application as active and compostable food packaging.

Poly(lactic acid)-Based Ink for Biodegradable Printed Electronics With Conductivity Enhanced through Solvent Aging

Biodegradable electronics is a rapidly growing field, and the development of controllably biodegradable, high-conductivity materials suitable for additive manufacturing under ambient conditions remains a challenge. In this report, printable conductive pastes that employ poly(lactic acid) (PLA) as a binder and tungsten as a conductor are demonstrated. These composite conductors can provide enhanced stability in applications where moisture may be present, such as environmental monitoring or agriculture. Post-processing the printed traces using a solvent-aging technique increases their conductivity by up to 2 orders of magnitude, with final conductivities approaching 5000 S/m. Such techniques could prove useful when thermal processes including heating or laser sintering are limited by the temperature constraints of typical biodegradable substrates. Both accelerated oxidative and hydrolytic degradation of the printed composite conductors are examined, and a fully biodegradable capacitive soil moisture sensor is fabricated and tested.

Environmental Degradation of Plastic Composites with Natural Fillers-A Review

Polymer composites are widely used modern-day materials, specially designed to combine good mechanical properties and low density, resulting in a high tensile strength-to-weight ratio. However, materials for outdoor use suffer from the negative effects of environmental factors, loosing properties in various degrees. In particular, natural fillers (particulates or fibers) or components induce biodegradability in the otherwise bio inert matrix of usual commodity plastics. Here we present some aspects found in recent literature related to the effect of aggressive factors such as temperature, mechanical forces, solar radiation, humidity, and biological attack on the properties of plastic composites containing natural fillers.

Methodologies to assess biodegradation of bioplastics during aerobic composting and anaerobic digestion: A review

Bioplastics are emerging on the market as sustainable materials which rise to the challenge to improve the lifecycle of plastics from the perspective of the circular economy. The article aims at providing a critical insight of research studies carried out in the last 20 years on the degradation of bioplastics under aerobic composting and anaerobic digestion conditions. It mainly focuses on the various and different methodologies which have been proposed and developed to monitor the process of biodegradation of several bioplastic materials: CO₂ and CH₄ measurements, mass loss and disintegration degree, spectroscopy, visual analysis and scanning electron microscopy. Moreover, across the wide range of studies, the process conditions of the experimental setup, such as temperature, test duration and waste composition, often vary from author to author and in accordance with the international standard followed for the test. The different approaches, in terms of process conditions and monitoring methodologies, are pointed out in the review and highlighted to find significant correlations between the results obtained and the experimental procedures. These observed correlations allow critical considerations to be reached about the efficiency of the methodologies and the influence of the main abiotic factors on the process of biodegradation of bioplastics.

Effect of Cellulosic Waste Derived Filler on the Biodegradation and Thermal Properties of HDPE and PLA Composites

Composites with high density polyethylene (HDPE) and poly(lactic) acid (PLA) matrix have been tested to analyze the effect of natural fillers (wood flour, recycled wastepaper and a mix of both fillers) and temperature on polymer degradation. Composting tests have been performed in both mesophilic (35 °C) and thermophilic (58 °C) conditions. Degradation development has been evaluated through mass variation, thermogravimetric analysis and differential scanning calorimetry. HDPE, as expected, did not display any relevant variation, confirming its stability under our composting conditions. PLA is sensibly influenced by temperature and humidity, with higher reduction of Mw when composting is performed at 58 °C. Natural fillers seem to influence degradation process of composites, already at 35 °C. In fact, degradation of fillers at 35 °C allows a mass reduction during composting of composites, while neat PLA do not display any variation.

Combined effect of cellulose nanocrystals, carvacrol and oligomeric lactic acid in PLA_PHB polymeric films

Biodegradable multicomponent films based on poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) plasticized with oligomeric lactic acid (OLA), reinforced with synthetized cellulose nanocrystals (CNC) and modified by a natural additive with antimicrobial activity (carvacrol) were formulated and processed by extrusion. Morphological, mechanical, thermal, migration and barrier properties were tested to determine the effect of different components in comparison with neat poly(lactic acid). Results showed the positive effect of CNC in the five components based films, with the increase of the Young's modulus of the PLA_PHB_10Carv_15OLA, associated with an increase in the elongation at break (from 150% to 410%), by showing an OTR reduction of 67%. Disintegrability in compost conditions and enzymatic degradation were tested to evaluate the post-use of these films. All formulations disintegrated in less than 17 days, while proteinase K preferentially degraded the amorphous regions, and crystallinity degree of the nanocomposite films increased as a consequence of enzyme action.

Nanocomposites Based on Biodegradable Polymers

In the present review paper, our main results on nanocomposites based on biodegradable polymers (on a time scale from 2010 to 2018) are reported. We mainly focused our attention on commercial biodegradable polymers, which we mixed with different nanofillers and/or additives with the final aim of developing new materials with tunable specific properties. A wide list of nanofillers have been considered according to their shape, properties, and functionalization routes, and the results have been discussed looking at their roles on the basis of different adopted processing routes (solvent-based or melt-mixing processes). Two main application fields of nanocomposite based on biodegradable polymers have been considered: the specific interaction with stem cells in the regenerative medicine applications or as antimicrobial materials and the active role of selected nanofillers in food packaging applications have been critically revised, with the main aim of providing an overview of the authors' contribution to the state of the art in the field of biodegradable polymeric nanocomposites.

Enhanced in Vitro Mineralization and in Vivo Osteogenesis of Composite Scaffolds through Controlled Surface Grafting of L-Lactic Acid Oligomer on Nanohydroxyapatite

Nanocomposite of hydroxyapatite (HA) surface grafted with L-lactic acid oligomer (LAc oligomer) (op-HA) showed improved interface compatibility, mechanical property, and biocompatibility in our previous study. In this paper, composite scaffolds of op-HA with controlled grafting different amounts of LAc oligomer (1.1, 5.2, and 9.1 wt %) were fabricated and implanted to repair rabbit radius defects. The dispersion of op-HA nanoparticles was more uniform than n-HA in chloroform and nanocomposites scaffold. Calcium and phosphorus exposure, in vitro biomineralization ability, and cell proliferation were much higher in the op-HA1.1 wt %/PLGA scaffolds than the other groups. The osteodifferentiation and bone fusion in animal tests were significantly enhanced for op-HA5.2 wt %/PLGA scaffolds. The results indicated that the grafted LAc oligomer of 5.2 or 9.1 wt %, which formed a barrier layer on the HA surface, prevented the exposure of nucleation sites. The shielded nucleation sites of op-HA particles (5.2 wt %) might be easily exposed as the grafted LAc oligomer was decomposed easily by enzyme systems in vivo. Findings from this study have revealed that grafting 1.1 wt % amount of LAc oligomer on hydroxyapatite could improve in vitro mineralization, and 5.2 wt % could promote in vivo osteogenesis capacity of composite scaffolds.

Recycling of spodumene slag: preparation of green polymer composites

The recycling of spodumene slag is studied in this work, with the objective of exploring the possibility of using spodumene slag as a common polymer filler.