Additive manufacturing (AM), alternatively known as 3D printing is an emerging technology supported by Industry 4.0. When combined with a stimulus-responsive behavior, decorated with the fourth dimension of time, it results in a manufacturing technique known as 4D printing. Although 4D printing technique is currently in its infancy stage, it has attracted exponential rise in attention in last 5 years. 4D printed entities have a distinctive characteristic of property transformation, under the influence of a drafted stimulus, which can be cleverly engineered for the desired application. Currently, 4D printed constructs have been implemented in renewables, textiles, electronics, biomedicals, agriculture, aerospace, purification, etc. and is aggressively growing. The conventional stimuli-driven smart printing inks deployed in 4D printing are non-biodegradable polymers that pose a defiance to sustainability. Hence, it is imperative to appraise the utilization of sustainable raw-materials, comprising of natural and synthetic biodegradable polymers, such as polylactic acid, polyvinyl alcohol, polycaprolactone, etc. as feedstocks for 4D printing. Natural resources, such as carbon, starch, cellulose, alginate, chitosan, collagen, etc. have fluctuating properties, that fortunately make them receptive toward intelligent engineering. This review is an effort towards the implementation of sustainable feedstocks as printing inks for 4D printing, for eventual environmental benignity. It incorporates several sustainable raw materials used for 4D printing and the strategies to use them in conjunction with conventional inks, in order to bring down the volume of non-biodegradables. This article would serve as a reference for designers and engineers wishing to practice sustainable inks for 4D printing, thereby boosting the momentum needed to consolidate this next-generation technology in-line with the sustainable development goals.

The aim of this study was to enhance the flame-retardant properties of chicken-feather-reinforced thermoplastic polyurethane (TPU) composites by incorporating three different phosphorus-based flame retardants – namely, aluminum hypophosphite (AHP), ammonium polyphosphate (APP) and aluminum diethyl phosphinate (AlPi) – at concentrations of 5, 10 and 20 wt%. The effectiveness of the additives was evaluated through various tests, including limiting oxygen index test, vertical burning test (vertical UL 94), thermogravimetric analysis and mass loss calorimeter test. The results indicated that all three additives exhibited flame-retardant properties in both the condensed and gas phases, but APP and AHP performed better than AlPi due to their enhanced char-formation capabilities. The flame-retardant effectiveness of the additives decreased in the order of APP > AHP > AlPi.

Activated carbon has found key applications in the adsorption of polluted industrial dyes in water. In this work, macadamia husk biochar (MHC) was prepared using a household pyrolysis kiln before being activated with phosphoric acid (H3PO4) to obtain macadamia-husk-activated carbon (MHAC). A preliminary study was made on two activation conditions of MHC:phosphoric acid (w/v), 1:1 and 1:3, for the removal of malachite green (MG) dye. Analysis of experimental results revealed that the adsorption process was highly controlled by the time of contact, MHAC particle size, MHAC dosage and initial dye concentration. With the use of an MHAC particle size of 125–202 μm, an MHAC dosage of 6 g/l and a contact time of 120 min, the removal efficiency reached >99% at an MG concentration of 40 parts per million (ppm) before being degraded to around 75% at 70–80 ppm MG. Impregnation with zinc nitrate hexahydrate (Zn(NO3)2·6H2O) on the MHAC surface could maintain a removal efficiency of >99% at all initial dye concentrations (40–80 ppm), so the maximum removal capacity increased to ∼130 mg/g.

Interest in stimuli-responsive materials has increased rapidly, leading to a multitude of innovative applications in biomedical design. This study seeks to induce controlled shape memory effects through induction heating of magnetic polymer nanocomposites while retaining thermal consistency within attached hydrogel composites for various biomedical applications. Three commonly used polymer matrices were embedded with varying concentrations of magnetite nanoparticles to determine minimum and maximum loading effects on induction heating response and optimal shape memory effects. Thermal and morphological characterizations were performed to determine transition temperatures, followed by induction heating tests by way of an induction coil at different magnetic field strengths to determine heating rates, activation times and activation rates of shape memory effects for each polymer nanocomposite composition. Simultaneously, mechanically tunable sodium alginate and cellulose nanocrystal hydrogel composites were fabricated and characterized to determine hydrational, mechanical and thermal buffering properties. Induction heating tests revealed that all substrates exhibited a heating response; however, shape memory effects were observed only in poly(vinyl acetate) and Nylon 11. Moreover, all hydrogels displayed promising thermal dissipation, <1°C per 20 s of heating, preventing any potential thermal shock to biological components. These unique properties will allow for successful employment of these multi-composite scaffolds in a multitude of biological applications.

To develop a green drilling fluid additive, the modification and application of persimmon peel in a water-based drilling fluid was studied in this work. A natural product derivative, aluminium chloride–persimmon peel (ACPP), was prepared from aluminium chloride and persimmon peel and was assessed as a shale inhibitor. The clay-swelling ratio in 0.30% ACPP-3 solution was reduced to 28.10% from 69.50%. The rolling recovery tests and rheological evaluation of drilling fluids concluded that ACPP-3 has a high inhibition property to montmorillonite-hydrated expansion. ACPP-3 can adjust the particle size of montmorillonite to a large degree. ACPP-3 effectively reduces the apparent viscosity of carboxymethyl cellulose drilling fluids and the volume of filtration; furthermore, ACPP-3 can reduce the viscosity and the volume of filtration under high temperature, which means it can be used as an additive for deep drilling. The inhibition mechanism of ACPP-3 was investigated by thermogravimetric analysis and scanning electron microscopy. The results of this scientific research will be beneficial to the eco-friendly drilling fluid materials.

Epoxy is being extensively used in various engineering and structural applications. Epoxy is non-biodegradable, thus creating ecological problems. Apart from ecological problems, epoxy resin shows poor biofouling prevention in marine, freshwater and offshore environments. In the search for an eco-friendly solution to this problem, epoxy/chitosan/silver nanocomposites were devised. Chitosan was extracted from shrimp shells following deacetylation of chitin, and silver (Ag) nanoparticles synthesized using a chemical reduction process of silver salts. All the composite samples were prepared utilizing the solution casting method. The X-ray diffraction pattern and Fourier transform infrared analysis predict the successful creation of silver nanoparticles and chitosan, respectively. Different mechanical testings elaborate the fact that addition of chitosan into epoxy resin increases hardness, lowering tensile and flexural strength, whereas incorporation of silver nanoparticles reverses those properties, resulting in mechanical properties analogous with neat epoxy resin. Additionally, soil burial biodegradation testing ensured relatively greener characteristics of the final nanocomposites. Herein, the combined effect of chitosan and silver nanoparticles on an epoxy matrix is reported for the first time.

The interest and relevance of the present paper are in the current waste plastic valorisation scenario. The rapid depletion of fossil source carbon as crude oil and its ever-increasing costs have led to an intensive search for alternative fuels. An alternative or renewable green fuel (RGF) was obtained from waste low- and high-density polyethylene or polyolefins and computer body plastics through a pyrolysis process using cadmium carbonate (CdCO3) from 23 to 400°C. Five types of hydrocarbons were observed through two-dimensional gas chromatography and time-of-flight mass spectrometry (GC×GC-TOFMS): 7.621% paraffins, 53.668% branched/cyclic hydrocarbons, 14.083% aromatics, 0.327% phenanthrenes and 24.301% unclassified compounds. The research octane number of the RGF was 88.29. The bromine number of the RGF was 34.03%. The RGF was suitable for diesel engines and diesel furnaces without any upgrading. During the first, second and third pyrolysis experiments, 98, 95 and 100 g (wt%) waste granules with 2, 5 and 0 g (wt%) cadmium carbonate into RGFs were collected at 85, 89 and 80%; uncondensed gases were collected at 14.22, 10.15 and 19.52%; and the residue was collected at 0.78, 0.85 and 0.48%.

In the current study, three different types of biocomposites based on poly(lactic acid) (PLA) and short flax fiber were produced using extrusion. Alkali treatment was conducted on the flax fiber before the extrusion process in order to improve the interfacial adhesion between the flax fiber and the PLA matrix. The influence of the coupling agent and alkali treatment on the composite materials was investigated with regard to the mechanical, thermal and thermomechanical properties of the injected composites. The results show that the coupling agent has a favorable effect on the thermal, thermomechanical and mechanical properties of the composites. The flexural and tensile moduli of the composites were significantly enhanced compared with those of pure PLA samples. Dynamic mechanical thermal analysis and thermogravimetric analysis (TGA) results indicate that the loss and storage modulus of PLA/flax fiber composites are increased compared with those of both pure PLA and composites with the coupling agent. The TGA showed that the thermal stability of PLA improved with the addition of flax fiber into PLA. Additionally, the developed flax fiber content in PLA with the coupling agent improved the tensile, flexural strength and flexural modulus. The tensile strength of the alkali-treated flax fiber increased up to 50 MPa compared with that of the untreated flax fiber. The Fourier transform infrared spectroscopy method was carried out to examine the chemical composition of the composite and interaction of functional groups for both alkali-treated and untreated flax fibers.

Biopolymer electrolytes based on iota-carrageenan (I-carrageenan) with sodium trifluoromethanesulfonate (NaTf) were prepared by way of the conventional solution-casting technique. The biopolymer I-carrageenan was fixed as 1 g, and the concentration of NaTf was varied from 0.1 to 0.5 wt% in steps of 0.1 wt%. Distilled water was used as a solvent. Alternating current (AC) impedance measurements were carried out in the frequency window of 42 Hz–1 MHz. The same measurements were also carried out at different temperatures for all the prepared biopolymer samples. A maximum ionic conductivity of 2.6771 × 10−5 S/cm was obtained for the 0.3 wt% NaTf-added I-carrageenan system at room temperature. The temperature-dependent conductivity plot of the polymer electrolyte seemed to obey the Arrhenius relation. A low activation energy of 0.021 eV was observed for the sample with the highest ionic conductivity. From AC impedance data, dielectric parameters were obtained. The magnitude of the dielectric constant was found to increase with the increase in temperature. A low relaxation time was observed for the sample that possesses the maximum ionic conductivity.

Thermoplastic elastomers (TPEs) derived from sustainable cellulose and its derivatives have attracted a great deal of attention, because of their abundance, renewable nature, rigid backbone and good mechanical properties. To fabricate TPEs with tunable performance, a series of sustainable ethyl cellulose (EC)-grafted poly(methyl methacrylate (MMA)) (EC-g-P(MMA)) and poly(MMA-co-butyl methacrylate (BMA)) (EC-g-P(MMA-co-BMA)) were fabricated by way of atom-transfer radical polymerization (ATRP). By tuning the molar ratio of MMA/BMA in the copolymer side chains, tunable performance of TPEs with tunable glass transition temperatures (118–47.8°C) was achieved. The chemical structures of EC-bromide and EC graft copolymers were identifiable by Fourier transform infrared spectroscopy and hydrogen-1 (1H) nuclear magnetic resonance spectroscopy. The EC graft copolymers exhibited a higher molecular weight and good thermal stability and mechanical properties. These results suggested that these tunable-performance copolymers with a sustainable cellulose backbone and an acrylate side chain were potential candidates for service as TPEs in some applications.

Agar/cassava starch bioplastic film preparation using the extrusion technique was carried out to obtain a continuous production method that is more applicable to industrial production practices. Various ratios (w/w) of agar-and-cassava-starch blends were used in the bioplastic film formulations with glycerol as the plasticizer. All the ingredients were compounded using a single-screw extruder at 110°C. The extrudates were dried and chopped into bioplastic resin pellets, followed by hot compression into a film sheet. The bioplastic film samples were tested for their mechanical properties, water sensitivity, biodegradability and chemical structures. In general, the amount of agar in film formulations was prominently associated with superior mechanical properties, such as the tensile strength, elongation at break and water resistance of the samples. On the other hand, cassava starch contributed to faster film degradation in soil and water. These results, in general, could be explained by the inherent properties of each biopolymer constituent and the number of hydroxyl groups (OH) in the chemical structure of each film sample, which was observed by Fourier transform infrared spectroscopy. This investigation showed that agar/cassava starch bioplastic production using the hot-melt extrusion method was promising for further implementation on a commercial production scale.

Since the 1940s, bisphenol A (BPA) has been used in the plastic industry, reaching production of 10 Mt in 2022. More than 30% of the produced BPA is used in the production of epoxy resins. Decades of research has now provided enough evidence that BPA has endocrine-disrupting activity. Hence, it is an urgent matter to replace BPA in the production of epoxy resins. In the past years, considerable efforts have been put into finding alternatives to the toxic BPA. However, not only does the diglycidyl ether of BPA exhibit high polymerization reactivity, but also the presence of aromatic rings confers interesting thermomechanical resistance to epoxy networks therefrom. Hence, these properties are also expected from potential alternatives to BPA. In this review, first, the elements leading to toxicity of BPA are explained and then thorough accounts of possible bio-sourced aromatic alternatives to BPA are gathered. The reported synthetic routes for each of these alternatives and their toxicity are described. Also, their use in synthesis of epoxy resins and how the new alternatives influence the mechanical properties are discussed. This is a concise summary of the structure–property and structure–toxicity relationship for possible bio-sourced substitutes of BPA in synthesis of epoxy resins.

The main objective of this study was to evaluate the dynamic mechanical thermal analysis (DMTA), mechanical, physical and wettability properties of hybrid composites developed from sustainable green materials, jute fiber and wood particles that were manufactured by using the vacuum-assisted resin transfer molding technique. The storage modulus, loss modulus and tan δ values of the hybrid composites were also determined to evaluate the DMTA performance. The results showed that the storage modulus of jute/polyester resin is superior to those of the jute–wood/polyester hybrid and wood/polyester up to the glass transition temperature (T g). However, for temperature ranges higher than T g, the stiffness of hybrid composites increased relatively. The T g values from loss modulus and tan δ peaks support this effect of hybridization. Tests on mechanical properties showed that the jute/polyester specimens had a significant increase in tensile strength compared with the jute–wood/polyester hybrid and wood/polyester specimens. The results of tests of physical properties showed that the wood/polyester specimen had the lowest values of thickness swelling, water absorption and moisture content compared with the jute/polyester and jute–wood/polyester composites. The highest contact angle was obtained from composites made of wood/polyester. It could be concluded that the composites with enhanced performance could be used as novel green composites in various sectors.

In this research, a copper ferrite (CuFe2O4) nanocatalyst stabilized on clinoptilolite (CP) was prepared using green tea (Camellia sinensis) leaf extract. Fourier transform infrared spectra, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray analysis, transmission electron microscopy (TEM), the Brunauer–Emmett–Teller (BET) method, thermogravimetric analysis and differential thermal analysis were used to characterize copper ferrite/CP. After fixation on CP, the crystallite size of copper ferrite was determined to be 48.7 nm using an XRD pattern and the Debye–Scherrer equation. Copper ferrite nanoparticles were successfully placed on CP as evidenced by FESEM and TEM images. Using the Barrett–Joyner–Halenda method, the average diameter of the catalyst pores was found to be 22.2 nm. Using the BET method, the catalyst surface area was estimated to be 43.7 m2/g. The catalytic activity of copper ferrite/CP in the production of benzodiazepine (the reaction of o-phenylenediamine with ketones) was examined. The experimental results showed that this catalyst performs well under mild reaction conditions. Using an external magnetic field, copper ferrite/CP was easily separated from the reaction product and can be reused without appreciably decreasing its catalytic activity.

The present work aims to contribute to finding more recycling routes for phosphogypsum (PG) and its potential uptake in the material construction industry as paving blocks. Laboratory testing was conducted to formulate mixes using PG as fine sand replacement. An optimal 20% substitution rate was proved. Industrially processed paving blocks were made for high-quality experimental investigation. The most interesting testing results of PG paving blocks are the low water absorption coefficient of 5.7% and excellent mechanical properties, including high compressive and flexural strengths at early age (20.7 and 4.65 MPa at 7 days, respectively). Compressive strength evolves with respect to the curing period: 26% increase at 28 days and 36% increase at 90 days; flexural strength evolves from 6% at 28 days to 10% at 90 days. The leaching test showed low levels of heavy metals released, and their concentrations were lower in the mix than in the raw PG. For all the aforementioned results, PG waste from a phosphate plant in Gabès, Tunisia was proved to have high potential for reuse in the manufacturing of paving blocks with low health risks and excellent properties. Reusing PG waste in paving blocks would thus contribute to solving an environmental issue and reduce the use of sand, which is prone to depletion as a non-renewable resource.

This paper aims to investigate the influence of the grain size and the alkali metal hydride (AH, where A = lithium (Li), sodium (Na) or potassium (K))/carbon dioxide (CO2) mole ratio on carbon dioxide reduction-conversion to methane (CH4) through alkali metal hydrides at an intermediate temperature. The result of this investigation shows that the grain size and AH (A = Li, Na or K)/carbon dioxide mole ratio have a considerable effect on the methane mole percentage and output. Compared with the original sample, when the lithium or potassium hydride sample is milled for 2 h, the mole percentage and output of methane increase. When the time for which the lithium or potassium hydride sample is milled is increased from 2 to 48 h, the mole percentage and output of methane change very little. For the sodium hydride and carbon dioxide system, the grain size of the sample has little effect on the methane mole percentage and output. In brief, alkali metal hydride milled for 2 h is enough for the methanation reaction. In consideration of the AH/carbon dioxide mole ratio, the effects on different reaction systems are not consistent. Activated alkali metal hydrides can effectively convert carbon dioxide to methane under various AH/carbon dioxide mole ratios, and the higher the mole ratio of AH/carbon dioxide, the better the methanation of alkali metal hydride with carbon dioxide.

Incorporation of betel leaf extract (BE) into chitosan and chitosan/vanillin (CH/Vn) blend films was carried out in order to improve the mechanical, thermal and antimicrobial properties of chitosan films. The influence of morphology, crystallinity and glass transition temperature (T g) on the mechanical properties of chitosan/betel leaf extract (CH/BE) and chitosan/vanillin/betel leaf extract (CH/Vn/BE) films was analyzed. The smooth homogeneous morphology, decreased crystallinity and shift of T g to a higher value resulted in improved mechanical properties. Scanning electron microscopy, atomic force microscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and Fourier transform infrared studies indicated that inclusion of BE into CH/Vn led to enhanced physicochemical properties. The results of antimicrobial activity, oxygen gas permeability and contact angle measurements confirmed the significantly improved activity and hydrophilic nature of the blend films compared with those of pure chitosan. The authors confirmed that the plant-extract-doped polymer material can be a novel antimicrobial agent for food-packaging application. Addition of BE at a higher weight percentage is a major limitation that has a major influence on the properties of the blend films.

Poly(3-hydroxybutyrate) (PHB) is a well-known member of the polyhydroxyalkanoate family of biopolymers, and it has been extensively investigated as an environmentally benign replacement for petrochemical-based polymers. The practical application of PHB in the biomedical field and in packaging has been limited because of its relatively narrow processing window, high brittleness and low thermal stability. In this study, a melt flow extrusion plastometer was used to investigate the processability of PHB by evaluating its melt flow rate and the mechanical properties of its monofilament extrudates. The monofilament extrudates were collected after exposure to different processing temperatures (180 and 190°C) and heating times, as well as after blending the biopolymer with different fractions of ground raw wool. The melt flow rate of PHB was not significantly affected when blended with different amounts of wool fiber. However, the melt flow rate increased significantly with the increase in heat duration and temperature. The mechanical properties of the monofilament extrudates from the parental PHB and PHB/wool blends were influenced by the fraction of wool, temperature and heat duration. The results of this study will be useful in selecting appropriate conditions for producing PHB-based blends/composites with desirable properties for a wide range of applications.

N-Methyl imines, as simple Schiff bases, could be prepared using a more sustainable and greener system, including a 33 wt.% solution of methylamine in absolute ethanol, and poly(N-vinylimidazole) (PVIm) at room temperature within 45–60 min. PVIm is a biocompatible, biodegradable and water-soluble synthetic solid functional polymer. It was indicated that PVIm can act as a reagent with multiple tasks in this reaction, including (a) reducing activation energy and stabilizing the transition states through hydrogen bond acceptor sites and low acidity of C(2)–H and (b) dehydrating activity through trapping of the released water molecules as the association phase. Inexperienced chemists can handle it easily because it is solid and less toxic than conventional catalysts – that is, piperidine, pyridine or metal- or halogen-containing salts. Additionally, ethanol and PVIm could be recycled and reused in subsequent runs without any further purification. The regenerated PVIm demonstrated stable activity after several recycle runs. No changes were detected in its chemical structure, as confirmed by Fourier transform infrared and nuclear magnetic resonance spectrum analyses.

Pressure-sensitive adhesive (PSA) is a kind of viscoelastic material with the viscous properties of liquids and the elastic properties of solids that can adhere to the surfaces of various substrates only under light pressure without phase change. PSAs derived from petroleum-based materials are generally non-biodegradable and disposable; therefore, a large amount of waste is generated from PSA products. Preparation of PSAs using renewable vegetable oil as raw material is an effective way to reduce dependence on petrochemical resources and environmental pollution. This paper summarizes the recent progress on vegetable-oil-based PSAs. Vegetable-oil-based PSAs mainly include epoxy resin, acrylic resin, fatty acid derivatives, polyester and polyurethane according to the chemical structures of vegetable-oil-based polymers. The design ideas and modification methods of vegetable-oil-based PSAs are introduced, including the development of functional vegetable oil monomers and the optimization of the polymer structure, so as to provide theory and reference for the design and development of new bio-based PSAs.