Production of sustainable thermoplastic composites from waste nitrogen fertilizer-grown marine filamentous cyanobacterium Geitlerinema sp

The global demand for petroleum-derived plastics continues to increase, as does pollution caused by plastic consumption and landfilling plastic waste. Recycling waste plastics by thermomechanical molding may be advantageous, but it alone cannot address the challenges associated with plastic demand and its widespread pollution. A more sustainable and cleaner approach for recycling plastic waste could be to produce thermoplastic composite blends of waste plastic and biobased alternative materials such as marine algal biomass. In this study, Geitlerinema sp., a marine cyanobacterium, was cultivated with waste nitrogen fertilizer as a nitrogen source, resulting in phycocyanin content and biomass density of 6.5% and 0.7 g/L, respectively. The minimum and maximum tensile strengths of thermoplastic blends containing Geitlerinema sp. biomass, recycled glycerol plasticizer, and waste plastic were 0.29-23.2 MPa, respectively. The tensile strength and Young's modulus of thermoplastic composites decreased as the Geitlerinema sp. biomass concentration increased. Furthermore, thermal analysis revealed that thermoplastics containing Geitlerinema sp. biomass have lower thermal onset and biomass degradation temperatures than waste polyethylene. Nevertheless, 35-50% of Geitlerinema sp. biomass could be a sustainable biobased alternative feedstock for producing thermoplastic blends, making the recycling of waste plastics more sustainable and environmentally friendly.

Microplastics encapsulation in aragonite: efficiency, detection and insight into potential environmental impacts

Plastic pollution in aquatic ecosystems has become a significant problem especially microplastics which can encapsulate into the skeletons of organisms that produce calcium carbonates, such as foraminifera, molluscs and corals. The encapsulation of microplastics into precipitated aragonite, which in nature builds the coral skeleton, has not yet been studied. It is also not known how the dissolved organic matter, to which microplastics are constantly exposed in aquatic ecosystems, affects the encapsulation of microplastics into aragonite and how such microplastics affect the mechanical properties of aragonite. We performed aragonite precipitation experiments in artificial seawater in the presence of polystyrene (PS) and polyethylene (PE) microspheres, untreated and treated with humic acid (HA). The results showed that the efficiency of encapsulating PE and PE-HA microspheres in aragonite was higher than that for PS and PS-HA microspheres. The mechanical properties of resulting aragonite changed after the encapsulation of microplastic particles. A decrease in the hardness and indentation modulus of the aragonite samples was observed, and the most substantial effect occurred in the case of PE-HA microspheres encapsulation. These findings raise concerns about possible changes in the mechanical properties of the exoskeleton and endoskeleton of calcifying marine organisms such as corals and molluscs due to the incorporation of pristine microplastics and microplastics exposed to dissolved organic matter.

Emergent Self-Assembly of Sustainable Plastics Based on Amino Acid Nanocrystals

Development of biodegradable plastic materials is of primary importance in view of acute environmental and health problems associated with the accumulation of plastic waste. We fabricated a biodegradable composite material based on hydroxyethyl cellulose polymer and tyrosine nanocrystals, which demonstrates enhanced strength and ductility (typically mutually excluding properties), superior to most biodegradable plastics. This emergent behavior results from an assembly pattern that leads to a uniform nanoscale morphology and strong interactions between the components. Water-resistant biodegradable composites encapsulated with hydrophobic polycaprolactone as a protection layer were also fabricated. Self-assembly of robust sustainable plastics with emergent properties by using readily available building blocks provides a valuable toolbox for creating sustainable materials.

Development of shelf life-extending packaging for vitamin C syrup based on high-density polyethylene and extracted lignin argan shells

Biobased packaging is an essential parameter in the pharmaceutical industry. In the present work, bio-composites consisting of high-density polyethylene (HDPE) as a matrix and lignin recovered from argan nut shells as filler were developed to investigate their potential use as packaging materials for vitamin C drugs. The lignin was extracted via alkali and klason processes, and the effects of the extraction method as well as the lignin content on the thermal, morphological, mechanical, and rheological properties of the produced composites, as well as their application for vitamin C packaging, were investigated. Among all the prepared packaging materials, the one with desirable results in pH, color stability, hardness, and mechanical characteristics was based on alkali lignin. It achieved its highest Young's modulus enhancement, 10.12 %, at 10 % alkali lignin loading, while the highest yield strain enhancement (4.65 %) was obtained with 2 % loading. When compared to neat HDPE and HDPE/klason lignin packaging materials, vitamin C solutions packed with this composite showed a lower oxidation rate, attributed to the extremely low pH variation and high color stability of the material, which decreased the rate of vitamin C degradation. According to these findings, HDPE/alkali lignin composite is a promising vitamin C syrup packaging material.

Mechanical and Tribological Performance of HDPE Matrix Reinforced by Hybrid Gr/TiO2 NPs for Hip Joint Replacement

Hip joint collapse is a very common health problem. Many cases need a joint replacement, so nano-polymeric composites are an ideal alternative solution. Due to its mechanical properties and wear resistance, HDPE might be considered a suitable alternative to frictional materials. The current research focuses on using hybrid nanofiller TiO2 NPs and nano-graphene with various loading compositions to evaluate the best loading amount. The compressive strength, modules of elasticity, and hardness were examined via experiments. The COF and wear resistance were evaluated via a pin-on-disk tribometer. The worn surfaces were analyzed based on 3D topography and SEM images. The HDPE samples with various compositions of 0.5%, 1.0%, 1.5%, and 2.0 wt.% filling content of TiO2 NPs and Gr (with a ratio of 1:1) were analyzed. Results revealed that hybrid nanofiller with a composition of 1.5 wt.% exhibits superior mechanical properties compared to other filling compositions. Moreover, the COF and wear rate decreased by 27.5% and 36.3%, respectively.

Enhancing mechanical properties of flash-spun filaments by pressure-induced phase separation control in supercritical high-density polyethylene solution

Flash-spun nonwoven (FS-NW) is gaining attention in the PPE field due to its excellent barrier and mechanical properties resulting from its non-uniform diameter distribution and unique filament morphology. The unique network structure of flash-spun filaments (FSF) comprising the FS-NW can be controlled by phase separation behavior in the supercritical fluid (SCF) process. This study proposes a simple method to control the microstructure of FSFs by controlling the pressure-induced phase separation (PIPS) process in polymer/SCF solution. This phase separation behavior of an HDPE/SCF solution was confirmed by using a high-pressure view cell. A multistage nozzle allowing for phase-separated pressure to form different phases was also designed. HDPE-FSFs were synthesized by flash-spinning, and their morphology, crystallinity, and mechanical properties were investigated. The results demonstrated that the filaments obtained by PSP control at 220 °C and with an HDPE concentration of 8 wt% showed a network structure composed of strands, wherein the diameters ranged from 1.39 to 40.9 μm. Optimal FSF was obtained at 76 bar, with a crystallinity of 64.0% and a tenacity of 2.88 g/d. The PIPS method can thus effectively control the microstructure more feasibly than temperature- or solvent-induced techniques and can allow the effective synthesis of various products.

Genipin-Crosslinked Gelatin/Chitosan-Based Functional Films Incorporated with Rosemary Essential Oil and Quercetin

Functional food packaging films were prepared using a binary mixture of chitosan and gelatin through crosslinking with genipin and hybridization with rosemary essential oil and quercetin. The mixture of chitosan and gelatin produced the compatible film, and the added fillers also showed good compatibility. The physical properties of the chitosan/gelatin film were not greatly affected by crosslinking with genipin, and the functionality of the composite film was increased by the addition of rosemary essential oil and quercetin. The bioactive additives did not significantly affect the hydrophobicity and water vapor barrier properties of the chitosan/gelatin film but significantly changed the color, while the mechanical and thermal properties were slightly affected. The addition of these functional fillers significantly improved the UV protection, antioxidant, and antibacterial properties of the chitosan/gelatin film. Therefore, the novel chitosan/gelatin film with genipin crosslinking and the integration of rosemary essential oil and quercetin is considered to have high potential for applications in active food packaging.

Synthesis of High Performance Thiophene-Aromatic Polyesters from Bio-Sourced Organic Acids and Polysaccharide-Derived Diol: Characterization and Degradability Studies

In this work, the feasibility of replacing petroleum-based poly(ethylene terephthalate) (PET) with fully bio-based copolyesters derived from dimethyl 2,5-thiophenedicarboxylate (DMTD), dimethyl 2,5-dimethoxyterephthalate (DMDMT), and polysaccharide-derived 1,6-hexanediol (HDO) was investigated. A systematic study of structure-property relationship revealed that the properties of these poly(thiophene-aromatic) copolyesters (PHS(20-90)) can be tailored by varying the ratio of diester monomers in the reaction, whereby an increase in DMTD content noticeably shortened the reaction time in the transesterification step due to its higher reactivity as compared with DMDMT. The copolyesters had weight-average molar masses (Mw) between 27,500 and 38,800 g/mol, and dispersity Đ of 2.0-2.5. The different polarity and stability of heterocyclic DMTD provided an efficient mean to tailor the crystallization ability of the copolyesters, which in turn affected the thermal and mechanical performance. The glass transition temperature (Tg) could be tuned from 70-100 °C, while the tensile strength was in a range of 23-80 MPa. The obtained results confirmed that the co-monomers were successfully inserted into the copolyester chains. As compared with commercial poly(ethylene terephthalate), the copolyesters displayed not only enhanced susceptibility to hydrolysis, but also appreciable biodegradability by lipases, with weight losses of up to 16% by weight after 28 weeks of incubation.

Numerical-Experimental Analysis of Polyethylene Pipe Deformation at Different Load Values

Polymer pipes are used in the construction of underground gas, water, and sewage networks. During exploitation, various external forces work on the pipeline, which cause its deformation. In the paper, numerical analysis and experimental investigations of polyethylene pipe deformation at different external load values (500, 1000, 1500, and 2000 N) were performed. The authors measured strains of the lower and upper surface of the pipe during its loading moment using resistance strain gauges, which were located on the pipe at equal intervals. The results obtained from computer simulation and experimental studies were comparable. An innovative element of the research presented in the article is recognition of the impact of the proposed values of the load of polyethylene pipe on the change in its deformation.

Design of a Reconfigurable THz Filter Based on Metamaterial Wire Resonators with Applications on Sensor Devices

A study on the design, simulation and characterization of a reconfigurable terahertz (THz) filter, composed of two frequency-selective surfaces (FSSs) with applications on sensor devices in general and highly sensitive stress sensors, is presented in this paper. Using the developed theoretical model, we found out that by careful tuning the wire parameters, it is possible to control the filter sensitivity and also the energy transmission and reflection that passes through the structure. Numerical modelling of both the mechanical and electromagnetic components (using the elasticity equation and Maxwell’s equations, respectively) has been undertaken for two types of the device assemblies based on different thermoplastic polymers transparent to the THz radiation, namely: high-density polyethylene (HDPE) and polytetrafluoroethylene (PTFE), operating in a THz window from 395 to 455 GHz. The numerical results allowed us to characterize the relation between the reflectance/transmittance and the amount of force required to obtain a specific frequency shift along that window. It was found that the device assembled with HDPE presents a more linear response and it is able to pass from a full transparency to almost full opacity using only its linear operating zone. Due to its characteristics, this THz filter might be an interesting solution not only for THz sensors based on reconfigurable filters but also for optical modulators for the THz domain.

Effective reinforcements for thermoplastics based on carbon nanotubes of oil fly ash

Carbon nanotubes (CNTs) are widely investigated for preparing polymer nanocomposites, owing to their unique mechanical properties. However, dispersing CNTs uniformly in a polymer matrix and controlling their entanglement/agglomeration are still big technical challenges to be overcome. The costs of their raw materials and production are also still high. In this work, we propose the use of CNTs grown on oil fly ash to solve these issues. The CNTs of oil fly ash were evaluated as reinforcing materials for some common thermoplastics. High-density polyethylene (HDPE) was mainly reinforced with various weight fractions of CNTs. Xylene was used as a solvent to dissolve HDPE and to uniformly disperse the CNTs. Significantly enhanced mechanical properties of HDPE reinforced at a low weight fraction of these CNTs (1–2 wt.%), mainly the tensile strength, Young’s modulus, stiffness, and hardness, were observed. The tensile strength and Young’s modulus were enhanced by ~20 and 38%, respectively. Moreover, the nanoindentation results were found to be in support to these findings. Polycarbonate, polypropylene, and polystyrene were also preliminarily evaluated after reinforcement with 1 wt.% CNTs. The tensile strength and Young’s Modulus were increased after reinforcement with CNTs. These results demonstrate that the CNTs of the solid waste, oil fly ash, might serve as an appropriate reinforcing material for different thermoplastics polymers.

Enhancing the potential of employing thermosetting powder recyclates as filler in LLDPE by structural modifications

Potential of using powder coating recyclates as filler material for polyethylene compounds was investigated. Due to their strong adhesion to the metal surface during compounding at extrusion temperatures higher than 100°C, the coating powder recyclates were chemically modified to facilitate its processing by extrusion and injection molding at higher temperatures. For this purpose, the coating powder recyclates were first hydrolyzed with addition of an alcohol as swelling agent. The deactivated recyclates were mixed at different ratios with the matrix polymer, a linear low-density polyethylene (LLDPE). The mixtures obtained were then compounded by extrusion and subsequently injection molded to plates to produce specimens for testing. The resulting samples were characterized mechanically by tensile, bending, and impact strength tests. In summary, the powder coatings recyclates can be processed as filler for thermoplastic material, without any adhesion problems up to 160°C and 180°C in the extruder and in the injection molding machine, respectively.