Mechanical, thermal, and dielectric properties of poly(lactic acid)/chitosan nanocomposites

Spectroscopic investigation, dielectric and antimicrobial properties of chitin-cellulose@ZnO/CuO conductive nanocomposites

In this research, we fabricated a functional conductive nanocomposite with valuable properties through a chitin (CH) and cellulose (CE) polymerization process, incorporating ZnO/(0.1, 0.2, 0.3 mol.%) CuO bioactive nanoparticles. These bioactive nanoparticles, synthesized through sol-gel and polymerization interactions, greatly enhanced the structural, dielectric, and antimicrobial characteristics of CH-CE@ZnO/CuO conductive nanocomposites. The morphological analysis revealed that these nanoparticles, with diameters ranging from 11-25 nm, formed covalent bonds with the membrane matrix, bolstering the conductive nanocomposites ' structural integrity and dielectric performance. The dielectric properties of the conductive nanocomposites were significantly enhanced by the even distribution of ZnO/CuO nanoparticles within the CH-CE composite. Additionally, antimicrobial assessments demonstrated that the CH-CE@ZnO/CuO conductive nanocomposites displayed significant antibacterial properties against the Escherichia coli and Staphylococcus aureus, showcasing their potential as active packaging materials for electronic, biosensors, and sustainable applications.

Application of Natural Functional Additives for Improving Bioactivity and Structure of Biopolymer-Based Films for Food Packaging: A Review

The global trend towards conscious consumption plays an important role in consumer preferences regarding both the composition and quality of food and packaging materials, including sustainable ones. The development of biodegradable active packaging materials could reduce both the negative impact on the environment due to a decrease in the use of oil-based plastics and the amount of synthetic preservatives. This review discusses relevant functional additives for improving the bioactivity of biopolymer-based films. Addition of plant, microbial, animal and organic nanoparticles into bio-based films is discussed. Changes in mechanical, transparency, water and oxygen barrier properties are reviewed. Since microbial and oxidative deterioration are the main causes of food spoilage, antimicrobial and antioxidant properties of natural additives are discussed, including perspective ones for the development of biodegradable active packaging.

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.

Recent advancements in bio-based dielectric and piezoelectric polymers and their biomedical applications

The advent of polymer-based dielectrics marked a significant breakthrough in dielectric materials. However, despite their many advantages, they pose serious environmental threats. Therefore, in recent years, there has been growing interest in bio-based polymers as a sustainable alternative to traditional petroleum-based polymers. Their renewable nature and reduced environmental impact can fulfil the rising demand for eco-friendly substitutes. Beyond their ecological benefits, bio-based polymers also possess distinctive electrical properties that make them extremely attractive in a variety of applications. Considering these, herein, we present recent advancements in bio-based dielectric polymers and nanocomposites. First, the fundamental concepts of dielectric and polymer-based dielectric materials are covered. Then, we will delve into the discussion of recent advancements in the dielectric properties and thermal stability of bio-based polymers, including polylactic acid, polyhydroxyalkanoates, polybutylene succinate, starch, cellulose, chitosan, chitins, and alginates, and their nanocomposites. Other novel bio-based dielectric polymers and their distinct dielectric characteristics have also been pointed out. In an additional section, the piezoelectric properties of these polymers and their recent biomedical applications have been highlighted and discussed thoroughly. In conclusion, this paper thoroughly discusses the recent advances in bio-based dielectric polymers and their potential to revolutionize the biomedical industry while cultivating a more sustainable and greener future.

Effect of intermolecular hydrogen bonding strength on the dynamic fragility of amorphous polyamides

Small-molecular-induced intermolecular hydrogen bonding (inter-HB) interactions were reported to increase the glass transition temperature (Tg) while decrease the dynamic fragility (m) of polymers. Herein, enthalpy relaxation parameters heat capacity jump (ΔCp) at Tg and enthalpy hysteresis (ΔHR) were investigated to help clarify the effect of macromolecular-induced inter-HB on Tg and m using amorphous polyamides as model polymers. The inter-HB strength was weakened by random copolymerization with varied chain rigidity, but was enhanced by decreasing steric hindrance. It was found that Tg and m increased after copolymerization due to the increased chain rigidity. Nevertheless, increasing steric hindrance leads to an increased Tg while anomalously reduced m. Further results found that m can be well correlated to Tg·ΔCp/ΔHR. ΔCp increases more significantly than ΔHR in co-polyamides, and thus the entropy change dominates the activation free energy of cooperative rearrangement. By contrast, ΔHR increases more significantly than ΔCp with increasing steric hindrance, and thus it is reasonable that Tg increases while m decreases. Most importantly, ΔCp and ΔHR decrease with increasing inter-HB strength regardless of the variation of Tg. These results indicate that the inter-HB strength may be very strong and insensitive to temperature in polyamides, thus behaving like physical cross-linking.

Development of Stereocomplex Polylactide Nanocomposites as an Advanced Class of Biomaterials-A Review

This review paper analyzes the development of advanced class polylactide (PLA) materials through a combination of stereocomplexation and nanocomposites approaches. The similarities in these approaches provide the opportunity to generate an advanced stereocomplex PLA nanocomposite (stereo-nano PLA) material with various beneficial properties. As a potential "green" polymer with tunable characteristics (e.g., modifiable molecular structure and organic-inorganic miscibility), stereo-nano PLA could be used for various advanced applications. The molecular structure modification of PLA homopolymers and nanoparticles in stereo-nano PLA materials enables us to encounter stereocomplexation and nanocomposites constraints. The hydrogen bonding of D- and L-lactide fragments aids in the formation of stereococomplex crystallites, while the hetero-nucleation capabilities of nanofillers result in a synergism that improves the physical, thermal, and mechanical properties of materials, including stereocomplex memory (melt stability) and nanoparticle dispersion. The special properties of selected nanoparticles also allow the production of stereo-nano PLA materials with distinctive characteristics, such as electrical conductivity, anti-inflammatory, and anti-bacterial properties. The D- and L-lactide chains in PLA copolymers provide self-assembly capabilities to form stable nanocarrier micelles for encapsulating nanoparticles. This development of advanced stereo-nano PLA with biodegradability, biocompatibility, and tunability properties shows potential for use in wider and advanced applications as a high-performance material, in engineering field, electronic, medical device, biomedical, diagnosis, and therapeutic applications.

A Simple Method for Synthesis of Chitosan Nanoparticles with Ionic Gelation and Homogenization

Chitosan nanoparticles (CNPs) are known to have great utility in many fields (pharmaceutical, agricultural, food industry, wastewater treatment, etc.). In this study we aimed to synthesize sub-100 nm CNPs as a precursor of new biopolymer-based virus surrogates for water applications. We present a simple yet efficient synthesis procedure for obtaining high yield, monodisperse CNPs with size 68-77 nm. The CNPs were synthesized by ionic gelation using low molecular weight chitosan (deacetylation 75-85%) and tripolyphosphate as crosslinker, under rigorous homogenization to decrease size and increase uniformity, and purified by passing through 0.1 μm polyethersulfone syringe filters. The CNPs were characterized using dynamic light scattering, tunable resistive pulse sensing, and scanning electron microscopy. We demonstrate reproducibility of this method at two separate facilities. The effects of pH, ionic strength and three different purification methods on the size and polydispersity of CNP formation were examined. Larger CNPs (95-219) were produced under ionic strength and pH controls, and when purified using ultracentrifugation or size exclusion chromatography. Smaller CNPs (68-77 nm) were formulated using homogenization and filtration, and could readily interact with negatively charge proteins and DNA, making them an ideal precursor for the development of DNA-labelled, protein-coated virus surrogates for environmental water applications.

Chitosan as an Outstanding Polysaccharide Improving Health-Commodities of Humans and Environmental Protection

Public health, production and preservation of food, development of environmentally friendly (cosmeto-)textiles and plastics, synthesis processes using green technology, and improvement of water quality, among other domains, can be controlled with the help of chitosan. It has been demonstrated that this biopolymer exhibits advantageous properties, such as biocompatibility, biodegradability, antimicrobial effect, mucoadhesive properties, film-forming capacity, elicitor of plant defenses, coagulant-flocculant ability, synergistic effect and adjuvant along with other substances and materials. In part, its versatility is attributed to the presence of ionizable and reactive primary amino groups that provide strong chemical interactions with small inorganic and organic substances, macromolecules, ions, and cell membranes/walls. Hence, chitosan has been used either to create new materials or to modify the properties of conventional materials applied on an industrial scale. Considering the relevance of strategic topics around the world, this review integrates recent studies and key background information constructed by different researchers designing chitosan-based materials with potential applications in the aforementioned concerns.

Chitosan Nanocomposites as Wound Healing Materials: Advances in Processing Techniques and Mechanical Properties

This review discusses the increasing potential of chitosan nanocomposites as viable materials capable of targeting these debilitating factors. This review focuses on various techniques used to process chitosan nanocomposites and their mechanical properties. Chitosan nanocomposites are regarded as highly effective antimicrobials for the treatment of chronic wounds. Chitosan nanocomposites, such as chitosan/polyethylene and oxide/silica/ciprofloxacin, demonstrate efficient antibacterial activity and exhibit no cytotoxicity against Human Foreskin Fibroblast Cell Lines (HFF2). Other studies have also showcased the capacity of chitosan nanocomposites to accelerate and improve tissue regeneration through increment in the number of fibroblast cells and angiogenesis and reduction of the inflammation phase. The layer-by-layer technique has benefits, ensuring its suitability in preparing chitosan nanocomposites for drug delivery and wound dressing applications. While the co-precipitation route requires a cross-linker to achieve stability during processing, the solution-casting route can produce stable chitosan nanocomposites without a cross-linker. By using the solution casting method, fillers such as multi-walled carbon nanotubes (MWCNTs) and halloysite nanotubes (HTs) can be uniformly distributed in the chitosan, leading to improved mechanical properties. The antibacterial effects can be achieved with the introduction of AgNPs or ZnO. With the increasing understanding of the biological mechanisms that control these diseases, there is an influx in the introduction of novel materials into the mainstream wound care market.

Enhancement of strength and toughness of bio-nanocomposites with good transparency and heat resistance by reactive processing

Growing concerns in addressing environmental challenges are driving the rapid advancement of both bio-based and environmental friendly materials. Biodegradable polymers have been compounded with various nanofillers to fulfill the multiple requirements in real applications. However, current technologies remain to be improved in terms of the intrinsic inferior performance and the lack of interfacial interactions. In this work, we employed a facile route to develop bio-nanocomposites integrating multiple functionalities by reactive processing of polylactide and reactive boehmite nanorods. The grafting of polymer chains onto the surface of the nanorods encourages fully homogeneous dispersion of nanofillers with even 30 wt% loadings. Such nanocomposites exhibit simultaneously enhanced tensile strength, modulus, ductility, and impact strength. Moreover, the bio-based nanocomposites present promising features such as high transparency, improved flame resistance, and heat resistance. This work demonstrates exciting opportunities to produce bio-plastics with diverse functionalities in versatile applications of sustainable packaging industry and engineering plastics.

Study on the Influence of Organic–Inorganic Interface Properties on Breakdown Strength and Thermal Properties of MgO/PLA Composites

Polylactic acid (PLA) is expected to be widely used in green power equipment manufacturing due to its good mechanical properties and biodegradability. In this paper, the effects of MgO with different particle sizes and mass fractions on the thermal and electrical properties of PLA composites were studied. The experiment found that with the increase in MgO particle sizes and mass fractions, the thermal conductivity of MgO/PLA composites showed a rising trend, which was up to 165.4% higher than that of pure PLA. However, the heat resistance first increases and then decreases. For the electrical properties of MgO/PLA composites, the breakdown strength and volume resistivity decrease with an increase in MgO particle size and mass fraction. In order to further study the influence mechanism of the introduction of MgO with different particle sizes and mass fractions on the thermal and electrical properties of MgO/PLA composites, molecular dynamics simulation was used to simulate the glass transition temperature (Tg) of PLA composites doped with MgO of different particle sizes, and it was found that MgO doping weakened the movement of the PLA molecular chain segment. Using density functional theory (DFT) calculations, it was found that in the MgO and PLA system, electrons have a tendency to migrate from the PLA matrix to MgO, which causes the formation of electron traps at the inorganic–organic interface and affects its electrical properties. The purpose of this study is to provide a theoretical reference for PLA composites in the manufacture of power equipment.

Influence of addition of organic fillers on the properties of mechanically recycled PLA

Poly(lactic acid) (PLA) is one of the most used biobased and biodegradable polymers. Due to their high stability, some of the newest grades of PLA are only degradable under severe industrial conditions. For these grades, mechanical recycling is a viable end-of-life option, with great environmental advantages. However, the polymer undergoes degradation during its service life and in the melt reprocessing, which leads to a decrease in properties that can compromise the recyclability of PLA. The goal of this work was to evaluate the usefulness of adding small amounts of two organic fillers, chitosan, and silk fibroin nanoparticles, during the recycling process for improving the properties of the recycled plastic. The degradation level of the aged polymer and the nature and amount of filler affect the performance of the recycled plastics. The fillers reduce the degradation during the melt reprocessing of PLA previously subjected to severe hydrolysis, thus increasing the intrinsic viscosity of the recycled plastic. A careful selection of the added organic filler lead to recycled plastics with improvements in some key mechanical, thermal, and barrier properties. Thus, the use of organic fillers represents a cost-effective and environmentally sound way for improving the mechanical recycling of bioplastics.

Comparison of the Dielectric Properties of Ecoflex® with L,D-Poly(Lactic Acid) or Polycaprolactone in the Presence of SWCN or 5CB

The main goal of this paper was to study the dielectric properties of hybrid binary and ternary composites based on biodegradable polymer Ecoflex®, single walled carbon nanotubes (SWCN), and liquid crystalline 4'-pentyl-4-biphenylcarbonitrile (5CB) compound. The obtained results were compared with other created analogically to Ecoflex®, hybrid layers based on biodegradable polymers such as L,D-polylactide (L,D-PLA) and polycaprolactone (PCL). Frequency domain dielectric spectroscopy (FDDS) results were analyzed taking into consideration the amount of SWCN, frequency, and temperature. For pure Ecoflex®, two relaxation processes (α and β) were identified. It was shown that the SWCN admixture (in the weight ratio 10:0.01) did not change the properties of the Ecoflex® layer, while in the case of PCL and L,D-PLA, the layers became conductive. The dielectric constant increased with an increase in the content of SWCN in the Ecoflex® matrix and the conductive behavior was not visible, even for the greatest concentration (10:0.06 weight ratio). In the case of the Ecoflex® polymer matrix, the conduction relaxation process at a frequency ca. several kilohertz appeared and became stronger with an increase in the SWCN admixture in the matrix. Addition of oleic acid to the polymer matrix had a smaller effect on the increase in the dielectric response than the addition of liquid crystal 5CB. Fourier transform infrared (FTIR) results revealed that the molecular structure and chemical character of the Ecoflex® and PCL matrixes remained unchanged upon the addition of SWCN or 5CB in a weight ratio of 10:0.01 and 10:1, respectively, while molecular interactions appeared between L,D-PLA and 5CB. Moreover, adding oleic acid to pure Ecoflex® as well as the binary and ternary hybrid layers with SWCN and/or 5CB in a weight ratio of Ecoflex®:oleic acid equal to 10:0.3 did not have an influence on the chemical bonding of these materials.

N, N’-sebacic bis(hydrocinnamic acid) dihydrazide: A crystallization accelerator for poly(L-lactic acid)

Developing more organic nucleating agent with different molecular structure is very instructive to improve the crystallization of poly(L-lactic acid) (PLLA) and explore the crystallization mechanism. In this study, N, N’-sebacic bis(hydrocinnamic acid) dihydrazide (HAD) was synthesized to serve as a nucleating agent for PLLA. The effects of HAD on the non-isothermal crystallization, melting behavior, thermal stability and optical performance of PLLA were investigated by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), and light transmittance meter. The melt crystallization behavior showed that HAD was able to promote the crystallization of PLLA via heterogenous nucleation in cooling, and it was found that, upon the cooling of 1°C/min, the incorporation of 1 wt% HAD made the crystallization temperature and non-isothermal crystallization enthalpy increase from 94.5°C and 0.1 J/g to 131.6°C and 48.5 J/g comparing with the pure PLLA. Additionally, the melt crystallization significantly depended on the cooling rate and the final melting temperature. For the cold crystallization, when the nucleation density from HAD and PLLA itself was saturated, the influence of the HAD concentration on the cold crystallization process of the PLLA/HAD samples is negligible. The melting behavior after isothermal or non-isothermal crystallization further confirmed the crystallization accelerating effect of HAD for PLLA, and the appearance of the double melting peaks was attributed to the melting-recrystallization. Unfortunately, the addition of HAD decreased the thermal stability and light transmittance of PLLA.

Non-isothermal Crystallization, Thermal Stability, and Mechanical Performance of Poly(L-lactic acid)/Barium Phenylphosphonate Systems

The introduction of a nucleating agent in semi-crystalline polymers is a frequently utilized way to improve the crystallization performance, and the use of a nucleating agent has a very great effect on the performance of the polymer in other areas including thermal stability and mechanical properties. In this investigation, barium phenylphosphonate (BaP) was prepared as a crystallization accelerator for Poly(L-lactic acid) (PLLA), and the non-isothermal crystallization behavior, thermal stability, and mechanical properties of PLLA modified by BaP were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and electronic tensile testing. Non-isothermal crystallization analysis showed that the BaP could significantly accelerate the crystallization of PLLA, and the non-isothermal crystallization peak shifted to a higher temperature with increasing concentration of BaP, however, the corresponding crystallization peak became wider. XRD results after non-isothermal crystallization confirmed the non-isothermal crystallization DSC results. Additionally, the addition of BaP did not change the crystal form of PLLA. A comparative study on thermal stability indicated that BaP decreased the onset decomposition temperature of PLLA, resulting from the formation of more tiny and imperfect crystals. Whereas the influence of BaP on the thermal decomposition profile of PLLA was negligible. In terms of mechanical properties, the tensile strength and elastic modulus of PLLA/BaP increased compared to the virgin PLLA, unfortunately, the elongation at break decreased.