Journal of Polymers and the Environment

This paper assesses the modifications in the properties of rotomolded polyethylene (PE) and polylactic acid (PLA) composites obtained with 5 and 10% giant reed fibers, mainly focusing on the alterations due to a bio-disintegration process. Thermal properties (melting temperature and crystallinity degree), morphology (via optical and scanning electron microscopy), and chemical changes (by Fourier Transformed Infrared spectroscopy) were studied. Composites with untreated and NaOH-treated fibers were obtained, finding that this treatment does not improve the mechanical performance of composites due to increased porosity. The introduction of natural fibers into a PE matrix does not significantly modify the thermal and bio-disintegration properties of the rotomolded material. Regarding mechanical properties, PE-composites show increased tensile modulus and reduced impact and tensile strength than the matrix. On the other hand, PLA composites show lower impact and flexural strength than neat PLA, remaining the rest of the mechanical properties unchanged regardless of the fibers' addition. The incorporation of Arundo fibers modifies to a great extent the thermal and degradation behavior of the PLA matrix.

Poly(lactic acid) (PLA) is one of the most important polyester bioplastics, produced from agricultural renewable resources and due to its excellent properties already has found applications in several industrial sectors, including packaging. Its amount, relative to PET, in the waste stream is continuously increasing. Although waste bioplastics are biodegradable, the process sometimes needs long degradation times. Therefore, sufficient recycling techniques should be developed in terms of sustainable chemistry. Hydrolysis of PLA under microwave irradiation in an alkaline solution was investigated aiming in the chemical recycling of this biodegradable polymer and the recovery of the monomer, lactic acid. Several process parameters were examined, including the presence or not of an alkali solution, its amount and concentration, the presence or not of methanol in the reaction medium, together with reaction temperature and time. Moreover, several phase transfer catalysts were employed at various relative amounts to PLA. Reaction temperature, pressure and microwave power did not change significantly during degradation. Optimum experimental conditions, leading to PLA degradation more than 90%, were achieved using hexadecyltrimethylammonium bromide as phase transfer catalyst in a 10% w/v NaOH medium at 100 °C for 10 min irradiation time. Using such low temperature and degradation times results in great environmental benefit since it does not consume significant amount of energy compared to other similar techniques proposed in literature and thus leads to the sustainability of the process. Therefore, it seems to be a very efficient method to be used in the recycling of large amounts of this polymer.

In this study, two novel functionalized silica nanocomposites were synthesized via covalent bonding with nanopolyaniline (NPANI) and crosslinked nanopolyaniline (CrossNPANI) to produce [NSi-NPANI] and [NSi-CrossNPANI], respectively. The two nanocomposites were portrayed by SEM, FT-IR, HR-TEM, BET-surface and TGA. The HR-TEM images of [NSi-NPANI] and [NSi-CrossNPANI] confirmed the particle size in the range 14.28–21.43 and 26.19–35.71 nm, respectively and these two nanocomposites were successfully applied to remove divalent cadmium and lead from solutions. As compared to nanosilica [NSi] sorbent, the maximum capacity values of the two nanocomposites for divalent cadmium and lead were identified to increase from 100–250 µmole g−1 (pH 1.0) to 750–800 µmole g−1 (pH 7.0) and from 400–1050 µmole g−1 (pH 1.0) to 650–1350 µmole g−1 (pH 6.0), at the optimum conditions. The adsorption data were compared using two and three parameter equations based on Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Redlish-Peterson and sips models. The kinetic study of [NSi-NPANI] and [NSi-CrossNPANI] revealed that the pseudo-second order kinetic was the best model to explain the kinetic data for cadmium(II) and lead(II). The free energy of sorption (ΔGo), enthalpy (ΔHo), and entropy (ΔSo) changes were calculated to portend the nature of adsorption. Adsorptive extraction of toxic lead and cadmium from tap water and wastewater was successfully accomplished with the range of percentage recovery values 98.5–100.0 and 91.9–93.0%, respectively.

In this study, three different combinations of essential oils (EO) of cinnamon, melaleuca and citronella were incorporated in polyhydroxybutyrate (PHB) films by conventional solution-casting method for food packaging applications. Although melaleuca and citronella EO films have been not demonstrated antimicrobial activity, they presented low UV transmission and high thermal stability. Films containing citronella and cinnamon EO or melaleuca and cinnamon EO, in turn, were active against all tested microorganisms and showed greater flexibility than pure PHB films. Aspergillus niger was the most sensitive microorganism to EO-based polymer films. Overall, the addition of EOs improved the thermal stability of films and reduced the polymer melting temperature as the result of its plasticization, affecting the elastic modulus and elongation at break of films. Taken together, these results suggest that EO-loaded PHB films could be used in designing of biodegradable active packaging for food products.

The removal of organic dyes from the aquatic system using modified Montmorillonite clay (MMT), one of the low cost adsorbent, was studied in this paper. Polyphosphoric acid (PPA) modified MMT (PMMT) with better surface area was used for adsorbing cationic dyes such as methylene blue(MB), rhodamine B (RB) and anionic dye Rose Bengal. The adsorption capacity of the PMMT clay for MB, RB and Rose Bengal dyes were 293.9 mg g−1, 244.77 mg g−1 and 296.13 mg g−1 respectively and all follows pseudo second order kinetics with Langmuir adsorption isotherm model. For better practical application polyvinyl alchohol (PVA) thin film composite with PMMT as filler was prepared and the adsorption studies were conducted. PVA composite film with 0.5 w/v% PMMT filler was found to be a good adsorbent for the cationic dye than anionic dyes and adsorbs 99% of MB dye from 30 mgL−1 dye solution. The composite film showed pseudo second order kinetics and better fit with the Langmuir model and the mono layer adsorption on the clay surface can be explained by electrostatic interaction between adsorbent and adsorbate. The introduction of the PMMT clay in the PVA matrix increases the thermal stability of neat PVA. Tensile strength of the composite was showing a gradual increase with the amount of PMMT filler and at 0.4% addition of PMMT in PVA, the tensile strength was increased up to 39% when compared to PVA film.

The feasibility of using alkyd-acrylic copolymers as a barrier material was studied. Copolymers of tall oil fatty acid or rapeseed oil-based alkyd resin and polyacrylates were synthesized and films of these copolymers were prepared. Nuclear magnetic resonance spectroscopy revealed that after copolymerization the proportion of double bonds in alkyd resin was diminished due to grafting reactions. The mechanical properties, such as strength and flexibility, of the copolymer films were tested, and the performance of the films as water, oil, and oxygen barrier was evaluated. An increased amount of alkyd resin made the films more brittle and increased their oxygen permeability, however, at the same time their hydrophobicity was increased.

Antimicrobial and biodegradable film-forming biopolymers are of tremendous interest for their possible use in food packaging applications. In this study, solvent casting and evaporation techniques were used to fabricate biodegradable active films from chitosan that contained Mustard oil (MO) at 0, 0.5, 1, and 2 Wt.% (v/v) concentrations. Then, it was evaluated if the chitosan films combined with MO could be employed as naturally biodegradable films for food application by examining the physical properties, mechanical, thermal, antibacterial, and antioxidant activities of various films. Potential interactions between the MO and chitosan were confirmed by Fourier- transform infrared spectroscopy (FT-IR). The elongation at break (EB) and the thickness of the films increased significantly because of the higher MO content. In contrast, there was a significant drop in water solubility, tensile strength (TS) and young’s modulus (YM), and moisture content. With the inclusion of MO, creases and tiny droplets were seen on the otherwise fine surface morphology of the films, which explained why TS and YM was reduced. The addition of MO enhanced the film's water vapor barrier properties while having slight improvement in their thermal stability. Moreover, the antibacterial and antioxidant characteristics of the chitosan films were evaluated and investigated, revealing a specific capacity to scavenge DPPH radicals while demonstrating a significant inhibitory effect against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The prepared composite films were 45–70% soil biodegradation after 21 days. In conclusion, the introduction of MO to chitosan-based films has shown significant promise for use in food packaging applications.

The utilization of captured CO2 as a part of the CO2 capture and storage system to produce biopolymers could address current environmental issues such as global warming and depletion of resources. In this study, the effect of feeding strategies of CO2 and valeric acid on cell growth and synthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] in Cupriavidus necator was investigated to determine the optimal conditions for microbial growth and biopolymer accumulation. Among the studied CO2 concentrations (1–20 %), microbial growth and poly(3-hydroxybutyrate) accumulation were optimal at 1 % CO2 using a gas mixture at H2:O2:N2 = 7:1:91 % (v/v). When valeric acid was fed together with 1 % CO2, (R)-3-hydroxyvalerate synthesis increased with increasing valeric acid concentration up to 0.1 %, but (R)-3-hydroxybutyrate synthesis was inhibited at >0.05 % valeric acid. Sequential addition of valeric acid (0.05 % at Day 0 followed by 0.025 % at Day 2) showed an increase in 3HV fraction without inhibitory effects on 3HB synthesis during 4 d accumulation period. The resulting P(3HB-co-3HV) with 17–32 mol  % of 3HV is likely to be biocompatible. The optimal concentrations and feeding strategies of CO2 and valeric acid determined in this study for microbial P(3HB-co-3HV) synthesis can be used to produce biocompatible P(3HB-co-3HV).

A novel sodium alginate-grafted poly(acrylic acid)/graphene oxide (NaAlg-g-PAA/GO) composite hydrogel was prepared via ultraviolet irradiation, and characterized by infrared spectroscopy spectrometer. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. It was employed to adsorb NH4+ from aqueous solution and used as slow-release nitrogen fertilizers (SNFs). Result indicated that the adsorption process for NH4+ reached equilibrium within 50 min, with the adsorption capacity of 6.6 mmol g−1 even if 30 wt% GO was incorporated. The results of adsorption kinetic and isotherm were well described by the pseudo-second-order and Freundlich model. The thermodynamics analysis showed the adsorption process was spontaneous. The study indicated excellent water-holding ratio of soil with 2 wt% SNFs was 81.2%, and nitrogen release was up to 55.1% within 40 days in soil. Overall, NaAlg-g-PAA/GO could be considered as an efficient adsorbent for the recovery of nitrogen with the agronomic reuse as a fertilizer.

Many natural living tissues, such as ligaments, muscles, tendons, and corneas, have anisotropic structural features that afford superior mechanical performance and functionalities. The development of hydrogels with structures and mechanical properties similar to those of natural living tissues for practical applications is urgently needed. In this study, a series of anisotropic Ca-alginate hydrogels are systematically fabricated via a facile prestretching and drying method. The resulting hydrogels exhibit highly ordered structures, which endow them with extraordinary mechanical properties and high mechanical anisotropy. The gels with a water content of ~ 54–60 wt%, similar to that of natural tissues such as cartilage, skin, and ligament, have the highest Young’s modulus, tensile strength, work of extension, and fracture energy of 258.40 ± 21.19 MPa, 28.54 ± 1.18 MPa, 11.79 ± 1.65 MJ/m3, and 4323 ± 224 J/m2, respectively. The highest degrees of anisotropy, or the ratio of the mean property between the parallel and perpendicular directions to the clamping direction, of those properties of the hydrogels are 11.08, 4.49, 1.47, and 4.01, respectively. Moreover, they are highly stable in distilled, domestic, and river water. With these remarkable characteristics, the developed anisotropic Ca-alginate hydrogels are expected to have numerous applications.