Journal of Polymers and the Environment最新文献

ACETEM (E472a) and CITREM (E472c) are fatty acid esters used as additives in the food industry to improve quality, stability and sensory properties of food products due to their emulsifying, stabilizing properties, and antioxidant and antimicrobial activities. Herein, we have explored their use as active plasticizers in one of the most used biobased polymers, polylactic acid (PLA). Initially, different CITREMs (LR10, SP70, RO and VEG) and ACETEM (SOFT-NSAFE), with a variety of compositions and physical states at room temperature, were characterized. The studied fatty acid esters demonstrate good thermal stability and moderate to good antioxidant properties. Subsequently, PLA films containing 10% of the tested fatty acid esters were prepared by melt extrusion and posterior compression molding. The obtained films were analyzed by different characterization techniques to evaluate their role as active plasticizers. Raman confocal microscopy showed that SOFT-NSAFE is homogeneously distributed in the PLA films, whereas CITREMs form microdomains due to their immiscibility with PLA. The incorporation of these plasticizers decreases the tensile strength, Young’s modulus and glass transition temperature. However, only CITREM-LR10 is able to significantly enhance the elongation at break of PLA up to 42%, due to the elongation and orientation of the microdomains along the cracks formed during the tensile test. Additionally, their incorporation provides antioxidant properties to the PLA films, being CITREM LR10, SP70 and SOFT-NSAFE that impart higher activity. In terms of antimicrobial activity, CITREM-LR10 showed effectiveness against S. aureus, while SOFT-NSAFE was active against L. innocua bacteria. These results open the possibility to use such CITREM and ACETEM food additives as plasticizers in films for a variety of applications such as active food packaging.

This study investigates the dielectric effects of bidirectional stretching (BO), which involves both machine (MDO) and transverse (TDO) directions, on poly(lactic acid) and nano-silver coated microcrystalline cellulose. The experiments employed stretching ratios of 2 × 2, 3 × 3, and 4 × 4. Results indicate that BOPLA-Ag/MCC4, which underwent the highest biaxial stretching ratio, exhibited the most significant increase in dielectric constant. The BOPLA-MCC4 and BOPLA-Ag/MCC4 demonstrated the highest dielectric constants, measuring 48 and 53, respectively. This increase can be attributed to the reorganization of molecular chains, leading to higher structural order and crystallinity, which promotes dipole and interface polarization. Biaxial stretching also enhances the mobility of polar polymer chains, enabling a stronger response to electric fields. Conversely, unidirectional stretching can reduce polymer chain disruption, limiting the movement of polar polymers and leading to a drop in dielectric properties. Consequently, biocomposite films stretched in biaxial directions demonstrate superior dielectric properties, indicating their potential for dielectric applications and suitability as environmentally friendly, biodegradable films.

Graphical Abstract

Gelatin-chitosan-based (GL-CS) functional films were synthesized by incorporating a nanoemulsion (NE) containing the essential oil (EO) of Satureja kermanshahensis Jamzad, commonly referred to as “Marzeh Kermanshahi” (MK) in Persian. These films also incorporated different concentrations (1%, 2%, and 3%) of carbon dots (CDs) derived from citric acid and urea. The physical, mechanical, optical, structural, and barrier characteristics, alongside the assessment of antioxidant and antibacterial efficacy of the resultant films, were thoroughly characterized and examined. The sizes of MK-EONE and CDs, as measured by a Zetasizer, were determined to be 118 nm and 1.2 nm, respectively. Fourier-Transform Infrared (FTIR) spectra and Scanning Electron Microscopy (SEM) of the films indicated favorable compatibility between both polymers, MK-EONE, and 1% CD, with uniform dispersion within the polymer matrix. The composite film containing MK-EONE and 1% CD exhibited enhanced UV protection, mechanical properties, and glass transition temperature (T_g). However, certain characteristics, such as water solubility, water vapor permeability (WVP), hydrophobicity, and transparency, demonstrated a decrease. Furthermore, the films incorporating MK-EONE and CDs demonstrated strong antioxidant activity, assessed through the DPPH method, and potent antimicrobial effectiveness against foodborne pathogens like Staphylococcus aureus, Bacillus cereus, and Escherichia coli. Consequently, the GL-CS-MK-EONE-CDs film, characterized by its superior functional attributes, shows promise for applications in food packaging.

Carboxymethyl cellulose (CMC) can be extracted from agricultural waste and better employed in the formulation of bioplastics to promote sustainability. Zein, a hydrophobic prolamin protein that can be obtained from industrial wastes of the corn industry. It may be combined with hydrophilic CMC, resulting in composite materials where both functionalities are synergistically enhanced. In the zein/CMC systems studied in the present work, CMC was added directly in the mixing stage. Physical interactions take place as blends are formed, and the effect of the CMC concentration was studied from 5–30%. At the highest CMC concentration, those blend systems were compared to conjugated systems, where prior chemical conjugation of both biopolymers was carried out at 60°C for 48 h. The physical and chemical interactions between the biopolymers certainly affected the viscoelastic properties of the eventually obtained injection-moulded bioplastics. Thus, samples softened after the addition of CMC, independent of the procedure followed. Thus, the addition of CMC always resulted in a reduction in the viscoelastic moduli (i.e., E’ decreased from approximately 900 MPa in the absence of CMC to 265 MPa in the presence of 30% CMC, either blended or conjugated). Conversely, the samples presented much higher water uptake capacity (WUC) values when conjugation was carried out. Therefore, the WUC of zein bioplastics (approximately 200%) increased to 950% for 30% conjugated CMC, which is almost twice the value obtained when the same amount of CMC was added in the mixing stage. Biodegradable biocomposite materials obtained through conjugation could be of great interest for developing hydrophilic green materials.

Petroleum-based plastics are recalcitrant world-wide used materials that severely pollute the environment, thus biodegradable bioplastics are emerging as a viable alternative. From this group, the study of polyhydroxyalkanoates (PHAs) has stood out for their potential in diverse applications including medicine, packaging and agriculture. The enzyme responsible for PHAs synthesis inside the microbial cell is the PHA synthase (PhaC). PhaCs are present in a wide variety of microorganisms and are classified according to their substrate specificity and subunit composition into 4 classes. Class I, class III and class IV use the acyl-CoA as a precursor to synthesize short-chain-length PHAs while Class II enzymes use an intermediate of the β-oxidation pathways to synthesize medium-chain-length PHAs. Enzymes from this pathway that have been upregulated and downregulated to optimize PHAs production are described in this review. Another important enzyme is the PHA depolymerase (PhaZ) which is responsible for all PHA degradation inside and outside the cell. This review describes both enzymes in detail, including classification, structure, substrate specificity and proven protein engineering techniques for enzymatic rate enhancement and modified substrate specificity of the proteins. It also includes a mutation map for the class II PhaC sequence of Pseudomonas putida that suggest point mutations for future protein engineering work.

Exine, in the form of a natural microcapsule, refers to the outermost layer of the pollen grains and is composed of a complex mixture of sporopollenin, a highly resistant polymer, which makes it durable and able to withstand harsh conditions. Distinctive features of sporopollenin have attracted interest in the encapsulation of bioactive substances. Herein, we describe the pathway to producing sporopollenin microcapsules (SMCs) by exploiting bees and trapping common bee pollen pellets, offering a simple approach to acquiring substantial amounts of pollen grains for industrial application. Palynological results showed that separating bee pollen pellets by colour could lead to almost pure products ranging from 90 to 96%, depending on the pollen species. Subsequently, a single extraction technique removed around 82– 86% of the proteinaceous content, which could cause potential allergic reactions in humans. Detailed morphological analysis by scanning electron microscope (SEM), confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), and laser diffraction particle size (LDPS) analysis proved that the purified SMCs retained their 3D micro-structures, besides being hollow and uniform micron-scale size. Fourier-transform infrared spectroscopy (FTIR) findings point out that the sporopollenin biopolymer structure of the pollen grain comprises distinct aliphatic and aromatic domains, and the purification of the SMCs resulted in the loss of nitrogen-related peaks. The hydrophobic/hydrophilic properties of the SMCs, evaluated by contact angle measurements, showed variability between pollen, depending on the specificities of their chemical structure. Simultaneous thermal analysis (STA) confirmed SMCs thermal stability up to 451 °C. Altogether, we showed that green microcapsules with various morphological properties could be produced by simply processing Castanea spp., Cistus spp., Erica spp., Olea spp, and Rubus spp, all common bee pollen pellets available in large quantities in the northeast of Portugal, but also many other countries. These microcarriers promise applicability to various fields, from pharmaceuticals to the food industry.

The preparation of high-performance recyclable epoxy vitrimer from bio-based feedstocks is of great industrial significance. Based on the above considerations, in this paper, we report a reaction of curing a bio-based epoxy monomer, propanetriol triglycidyl ether (GTE), with vanillin-derived diphenol monomer (VD) and 3-aminophenylboronic acid (M-APBA) as a curing agent, which resulted in the preparation of epoxy vitrimer films (EVB-X) with acylhydrazone bonds and cyclic boroxine dual dynamic response. Among them, the diphenol monomer VD supplies the flexible structure of the film, while the film showed a gradual increase in the boroxine six-membered ring structure with the gradual increase in the ratio of M-APBA, and the thermal and mechanical properties of the films are also gradually improving. By varying the ratio of VD to M-APBA in the material, EVB-3 was the most thermally stable, while T_g was measured at 45 °C, the highest tensile strength (57.40 MPa), and the largest cross-linking density (3271 mol/m³) among the four groups of films obtained from EVB-X films. In addition, the EVB films had excellent triple memory and could be largely degraded in acidic DMF and DMSO, with a gel content of 86.74% measured with EVB-3. Notably, the EVB scratches were completely healed at 100 °C for 1 h, indicating that EVB have excellent self-repairing properties, while the tensile strength could be recovered up to 28.98 MPa after heat treatment, and the strain repair rate could reach up to 89.42%, which provides good reprocessability.

In this work, the Brazilian biomass – macaw palm oil, was reacted with tris(2-aminoethyl)amine to give a fatty amide derivative, which was further modified to obtain an epoxidised derivative. After that, the last derivative reacted with CO₂, providing a new carbonated compound. The vegetable oil-based products were analysed using spectroscopic techniques and showed fluorescence when exposed to UV light. The carbonated compound was polymerised with four different polyphenols (quercetin, curcumin, tannic acid, and gallic acid). This resulted in dark brown, thermosetting poly-hydroxycarbonates with a shiny and brittle appearance. Modified vegetable oil compounds and final polymers present bio-based and bio-based carbon contents above 88%, indicating their renewability. Polymers made with quercetin and gallic acid were hydrophobic (water-repellent). Thermal analysis confirmed that all polymers could withstand temperatures up to 195 °C before decomposing. In addition, they have resistance against acid solutions but are fully hydrolysed after 24 h in an alkaline solution. These new polymeric materials also present self-healing properties; therefore, they can be healed and recovered by simple heating using a red-light LED (660 nm) and hydraulic press, a greener, faster, and more straightforward method.

Polyurethane foam (PUF) is one of the most widely used polymers and accordingly large quantities of waste materials reveal globally. In this study, chemical recycling method based on acidolysis by dicarboxylic acids using a mixture of unsaturated maleic acid and saturated phthalic acid was used to cleave urethane bonds and produce recycled polyol (repolyol). Effects of the reaction temperature (190 °C, 220 °C), stirring speed (400 rpm, 500 rpm), and reaction time (6 h, 12 h) on the hydroxyl number, water content, viscosity, and acid number of the repolyols were tested. FTIR (Fourier Transform Infrared) and TGA (Thermogravimetric Analysis) techniques were employed to compare the properties of the obtained repolyols with reference polyol. The repolyols were then used at 10–50 wt% as substitute of reference polyol to produce flexible polyurethane foam (FPUF). The produced foams were analyzed by optical microscopy and TGA techniques, and the density, hardness, air permeability, compression set, resilience, and tensile strength characteristics were tested. The analysis results of the FPUFs containing repolyols were compared with those of the reference foam. It was concluded that the obtained polyol can be safely used up to 20 wt% to produce FPUFs. However, further increase in repolyol ratio led to reduction in air permeability, compression set, and resilience performance of the produced FPUFs.

In this study, a chitosan-based polymer composite hydrogel grafted with polyimidazolium was synthesized and evaluated as an adsorbent for nitrate removal from water. The synthesis began with the preparation of a dinitro compound, followed by the synthesis of a diamine monomer, which was then conjugated with chitosan in the presence of glyoxal and formaldehyde to form the final composite. The chemical structure of the synthetic monomers and the composite was characterized using FT-IR, ¹H-NMR, FE-SEM, EDX, and TGA analyses. The concentration of nitrate ions in aqueous solutions was quantified using a spectrophotometer at wavelengths of 220 nm and 275 nm. Various operational parameters, including pH, contact time, initial nitrate ion concentration, and adsorbent dosage, were optimized to maximize nitrate removal efficiency. At an initial nitrate concentration of 70 mg/L, a pH of 7, an adsorbent dosage of 40 mg, and a contact time of 40 min, the synthesized composite exhibited a maximum removal efficiency of 97.75% and an adsorption capacity of 85.53 mg/g. The selectivity of the composite for nitrate ions in the presence of competing ions such as sulfate, bicarbonate, chloride, and phosphate was also evaluated. The presence of competing ions reduced nitrate removal, with bicarbonate having the most significant inhibitory effect and phosphate the least. The adsorption kinetics was best described by a Pseudo-second-order model, while the equilibrium data conformed to the Langmuir isotherm model. The PCH reusability was checked by an adsorption/desorption experiment, and the results showed acceptable constant loading efficiency after five reuse cycles. In addition to the adsorption studies, the composite’s anti-cancer properties were assessed. Cytotoxicity tests were conducted in vitro against three cancer cell lines: A431 (skin carcinoma), HT29 (colorectal cancer), and MCF7 (breast cancer), using cisplatin as a reference standard. The results demonstrated a potent anti-cancer effect against the MCF7 cell line, with an IC50 value of 4.80 µM. Furthermore, the composite included a collapse in the mitochondrial membrane potential (MMP) in MCF7 cells, highlighting its potential as a therapeutic agent.

Graphical abstract