Vitrimers are thermally reversible crosslinked polymers that combine the performance of thermosets with the benefits of melt (re)processing. However, existing high-storage modulus vitrimers lack this ...melt-reprocessibility. This study reports on high storage modulus vitrimers obtained by grafting vinyltrimethoxysilane onto high-density polyethylene (HDPE) using silyl ether crosslinker, bis3-(trimethoxysilyl)propylamine. We also explored the effects of 2,2,6,6-tetramethyl-4-piperidinol and diethyl maleate on the performance of these vitrimers. All vitrimers reported herein are prepared in one step via melt-extrusion without the use of any solvent or catalyst. These vitrimers were characterized via differential scanning calorimetry, Fourier-transform infrared spectroscopy, thermogravimetric analysis, dynamic mechanical analysis and mechanical testing. Selected vitrimers were melt-reprocessed six times and assessed for changes in their storage modulus and mechanical strength by industry-relevant extrusion processing. This study is the first of its kind to offer a solvent-free, single-step approach for the synthesis of vitrimers from HDPE. These vitrimers exhibit an impact strength five times higher relative to that of conventional HDPE, a very high storage modulus (1.58 MPa) at 180oC, and full melt-reprocessability. Considering that extrusion and injection molding is used, the storage modulus achieved in this study is significantly higher than that of vitrimers generated by compression molding, which is commonly used in previous research.
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•Demonstrated high storage modulus silyl ether HDPE vitrimers.•Investigated TEMPO and diethyl maleate effect on vitrimers performance.•A solvent-free, single-step approach for preparing silyl ether-based HDPE vitrimers.
•Functionally graded syntactic foams (FGFs) are 3D printed for the first time.•Weight-saving potential of 3D printed graded foams of glass micro balloons in HDPE matrix is between 9.27 and ...14.56%.•Foams exhibited better specific compressive properties compared to neat HDPE.•FGF exhibited better specific compressive strength than all 3D printed samples and is 1.2 times of pure HDPE.•FGFs exhibited better energy absorption than other plain foams and is 35 to 50 % more than pure HDPE.
In this work, functionally graded foams (FGFs) of closed cell types are three-dimensionally printed (3DP) concurrently. These closed cell syntactic foams are manufactured by reinforcing 20, 40, and 60 vol% hollow glass microballoons (GMBs) in the high density polyethylene (HDPE) matrix and are investigated for their mechanical buckling and free vibration response. The critical buckling load (Pcr) of the FGFs are evaluated using the Double Tangent Method (DTM), Modified Budiansky Criteria (MBC), and Vibration Correlation Technique (VCT). It is observed that Pcr evaluated by all three methods are in good agreement. Among all FGFs, FGF-2 exhibited higher buckling strength with 22–26% higher than FGF-1 and FGF-3. Under no-load and uniaxial compressive loads, the first three natural frequency of FGFs and their corresponding damping factors are evaluated. At first mode, the natural frequency of FGFs decreases in the pre-buckling zone and started increasing in the post-buckling zone. Damping factor exhibited reverse trend compared to the trend shown by the natural frequencies. Among all FGFs, FGF-2 (20-40-60 GMB gradation) exhibited better natural frequency. Experimental results are compared with a finite element based simulation results.
The applications of 3D printing are rapidly increasing in aerospace and naval applications. Nonetheless, 3D printing (3DP) of graded foams exhibiting property variation along the thickness direction ...is yet to be explored. In the current work, the different volume fractions of hollow glass micro balloon (GMB) reinforced high-density polyethylene (HDPE) composite based graded foams are 3D printed using the fused deposition modelling (FDM) technique. The bonding between successive layers and porosity distribution of these graded configurations are studied using micro-CT scan. Further, the 3D Printed functionally graded foams (FGFs) are tested for flexural response, and results are compared with numerical values. The micro-CT results showed delamination absence between the layers. In neat HDPE layers, porosity is not evident, while minor porosity creeps in the layers having the highest GMB content. Experimental results of the flexural test showed that the graded sandwiches exhibited better strength than the graded core alone. Compared to neat HDPE, the modulus of FGF-2 (H20–H40–H60) increased by 33.83%, implying better mechanical stiffness. Among all the FGFs, FGF-2 exhibited a better specific modulus. A comparative study of experimental and numerical results showed a slight deviation due to neglecting the induced porosity.
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•Nonalternating preference yields carbonyl-functionalized polyethylene.•Pd catalyst with electron donating substituents affords a uniform carbonyl dispersion.•The unique polyethylene ...exhibits comparable tensile properties with conventional HDPE.•The incorporated carbonyls in polyethylene main chains impart photodegradability.•Ni/Pd complexes are versatile for generating both of polyketone and keto-polyethylene materials.
Polyethylenes are currently the most prevalent synthetic polymers in the world, and the introduction of functional groups into polyethylene backbone can reduce problematic environmental persistence and enhance compatibility with other materials. This target can be addressed by transition-metal-catalyzed nonalternating copolymerization of ethylene with carbon monoxide, but it is generally impeded by the facile formation of alternating polyketones in kinetics. The reduction of carbonyl density in polyketones could weaken their inter-chain dipolar interaction, thus gradually approaching to polyethylene materials in term of crystalline and tensile properties. In this contribution, we communicate our continued efforts to investigate on the electronic and steric nature of Ni- and Pd-coordinated cationic P,O type catalysts, and they were used for nonalternating carbonylative copolymerization of ethylene, which resulted carbonyl functionalized polyethylenes with comparable molecular weight and desirable mechanistic property similar to those of commercial high-density polyethylene, and the incorporated carbonyls in polyethylene chains impart photodegradability. Notably, Pd complex 5 with an electron donating substituent on phosphine moiety yielded polyethylene products with a uniform dispersion of isolated carbonyls and a high molecular weight of ∼100 kg/mol.
The main focus of this investigation is to quantitatively analyze the opposing effect of filler on the desired properties of fabricated composite specimens. First, the high‐density polyethylene ...(HDPE) powders with proportions of 0, 2, 4, 6, 8, and 10 wt% of boron nitride (BN) are mixed by the ball mill processes and further hot molded to fabricate HDPE‐BN composites. The density and thermal conductivity of fabricated composites are then measured, and the variation of these properties with the added volume percent of BN is determined. The notions of multi‐objective optimization are employed to obtain the optimum BN content to maximize thermal conductivity while minimizing density. The relative importance of these properties is calculated by applying the entropy method to the variation of thermal conductivity and density with the BN content. It is observed that the positive effect of BN on the thermal conductivity has potentially the same importance as its negative effect on the density. In a more general consideration, various hypothetical fillers with a wide range of thermal conductivities and densities are studied by the same procedure. It is obtained that density has a more determinative rule in the efficiency of a particular filler in circumstances where both thermal conductivity and density have practical importance. While the results of this investigation are presented in terms of thermal conductivity and density, the procedure used here can be applied to any set of properties with practical significance.
High-density Polyethylene (HDPE) is widely used in industrial processes due to its excellent mechanical properties, solvent resistance and chemical stability. However, its surface usually shows high ...hydrophobicity and lipophilicity, which makes it ineffective in resisting contamination by oil pollution. In this study, Polyvinyl alcohols (PVA) were grafted onto the surface of the glycidyl methacrylate (GMA) grafted HDPE to improve the surface hydrophilization, furthermore, the surface structure of the PVA@GMA-HDPE and the factors affecting its hydrophilic modification were investigated. The introduction of the GMA in HDPE surface results in a large number of reactive sites on the inert surface of HDPE, which allows for further grafting of PVA onto the HDPE surface. Most importantly, the addition of PVA improves the water wettability, which reduced the water contact angle from 87.82° to 23.33° in the air and increased the oil contact angle from 107.30° to 156.90° under water. With the help of the significant improvements in resistance to oil contamination, the grease on the surface of the modified HDPE can be easily removed by washing with water after many repetitions. The low cost, simple manufacture and versatility of the PVA@GMA-HDPE with superior hydrophilicity and submerged superoleophobicity have significant application value for sewerage pipes and membranes.
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•Hydrophilic modified of high-density polyethylene (HDPE) by polyvinyl alcohol (PVA).•The optimal reaction time for PVA modified HDPE is 2 h.•The water contact angle (WCA) of PVA@GMA-HDPE sheet reached 23.33°.•The oil contact angle (OCA) of PVA@GMA-HDPE sheet reached 156.9° under water.•The PVA@GMA-HDPE sheet has superior resistance to oil adhesion.
To develop viable solutions for reducing plastic waste, spatially explicit data on the management of these materials are critical. Here we employ statistical and geospatial methods to present a ...comprehensive assessment of plastic waste in the United States by resin type at the state, county, and local levels. Of the estimated 44 Mt of plastic waste managed in 2019 domestically, approximately 86% was landfilled, 9% was combusted, and 5% was recycled. Landfilled plastics represented significant losses to the country's economy in 2019: an average of US$7.2 billion in market value, about 3.4 EJ as embodied energy (equivalent to 12% of energy consumption by the industrial sector), and 1.5 EJ as an energy source (equivalent to 5.5% and 5% of energy consumption by the industrial and transportation sectors, respectively). Lastly, we posit that substantial amount of landfilled plastic waste could be recovered through advanced sorting, existing, and emerging recycling processes.
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This study examined the effects of Ni loading on different types of alumina (γ-Al2O3, mesoporous Al2O3, 13 nm-sized Al2O3, and <50 nm-sized Al2O3) for high-density polyethylene gasification for ...enhanced hydrogen generation. The catalytic activity of Ni loaded alumina was observed in the order of 13 nm-sized Al2O3> mesoporous Al2O3> (<50 nm-sized Al2O3) > γ-Al2O3 for the gas yield and γ-Al2O3> (<50 nm Al2O3) > mesoporous Al2O3 > 13 nm Al2O3 for the oil yield, respectively. In addition, the production of hydrogen from Ni loaded alumina showed an increasing trend in the order of (<50 nm-sized Al2O3) > γ-Al2O3> 13 nm-sized Al2O3.> mesoporous Al2O3. In contrast, CO showed the trend as Ni/mesoporous Al2O3> Ni/13 nm-sized Al2O3> Ni/γ-Al2O3> (Ni/<50 nm Al2O3). The highest level of hydrogen production from the Ni/<50 nm-sized Al2O3 catalyst might be because of its highest Ni dispersion and surface area. The use of Ni-loaded nm-sized alumina could be an excellent method for increased hydrogen production compared to other types of alumina available.
•4 different Ni/alumina catalysts were applied to HDPE gasification.•γ-Al2O3, mesoporous Al2O3, 13 nm-sized Al2O3, and (<50 nm-sized Al2O3) were used.•The highest level of hydrogen was produced from the Ni/<50 nm-sized Al2O3 catalyst.•Ni/<50 nm-sized Al2O3 catalyst showed highest Ni dispersion and surface area.
•Chemical recycling of non-degradable polymers to functional materials to achieve a circular economy.•Hydrothermal nitric acid oxidation to convert HDPE waste to its small-sized value-added ...chemicals.•Optimization of reaction conditions: temperature, time, filling capacity, nitric acid concentration and HDPE/nitric acid ratio, to enhance product yields and diacid compositions.•Potential use as crosslinkers for UV-curable acrylate/ester-based adhesives.
Plastic waste has become a serious pollution problem due to the material's high consumption volume and durability. Therefore, effective waste treatment and conversion technology are urgently required. In this work, a chemical recycling process has been developed to convert high-density polyethylene (HDPE) from post-consumer milk bottles to value-added chemicals, especially mixed diacids with high succinic acid content, via hydrothermal nitric acid oxidation. The results reveal that HDPE can be completely recycled into water-soluble compounds with a yield ranging from 15 to 70% (∼8–36% carbon recovery) at 180–200 °C for 2–4 h. The oxidized products examined by 1H NMR spectroscopy are a mixture of succinic acid (C4), glutaric acid (C5), and adipic acid (C6), whose compositions are strongly governed by the reaction temperature, reaction time, filling capacity, nitric acid concentration and the HDPE/nitric acid ratio. With 20 ml of 0.18 g/ml nitric acid solution (1/7.2 HDPE/nitric acid ratio), a maximum product yield (%carbon recovery) of 69% (35%) with C4:C5:C6+ ratio of 55:30:15 (mol%) is achieved at 180 °C for 3 h. When the filling capacity was increased from 40 to 60% by adding extra water at the same HDPE: nitric acid ratio, prolonging the reaction time for 1 h resulted in the products with a high succinic acid composition (>94%) and 75% yield (36% carbon recovery). The benefits of employing dilute nitric acid solutions with the same HDPE: nitric acid ratio on the selectivity of succinic acid is also confirmed by a reaction at 200 °C for 2 h. As oxidation typically occurs at a higher rate at a higher temperature, the maximum product yield (∼53–56%) is received at 200 °C for 2 h. This lower optimum yield obtained at higher reaction temperature and higher nitric acid concentration implies heterogeneous degradation due to limited diffusion of reactive molecules. By adjusting the HDPE: nitric acid ratio (1:3.6 to 1:10.8), the optimum content of nitric acid is in a range of 3.6x–5.4x. The as-received products are successfully developed as UV-curable acrylate precursors by esterifying their carboxylic groups with hydroxyethyl acrylate, using 5 mol% p-toluene sulfonic acid as a catalyst. UV-cured sheets obtained after irradiating under a UV lamp for 10 min have a gel fraction of 80–90% tested in toluene, chloroform, and ethanol.
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