Polymer Degradation and Stability最新文献

Vinyl ester resin (VER) are widely used in various applications, including automotive parts, yachts, wind turbine blades, and cooling towers, due to their excellent properties. However, the high flammability of VER limits its application in fields requiring stringent fire resistance. In this work, we used ionic liquid containing phospholipid structures (VIDHP) in combination with lithium-containing polyhedral oligomeric phenyl sesquisiloxanes (Li-POSS) to improve the mechanical and flame retardant properties of VER. The coordination between the VIDHP and Li-POSS increases the thermal stability of VIDHP and improve the solubility of Li-POSS in VER. The experimental results show an increase in initial decomposition temperature of VIDHP4/POSS1/VER compared to VIDHP/VER, while the solubility of Li-POSS in VER is improved. The Cone calorimeter results show that the total heat and smoke release of VIDHP4/POSS1/VER are reduced by 29.37 % and 36.55 % compared with the pure VER. The investigation of the flame retardant mechanism shows that the combined use of VIDHP and Li-POSS exhibits flame-retardant activity in both the gas and condensed phases, effectively enhancing the flame-retardant property of VER.

Polyurethane adhesives have been widely used in industrial production and daily life for their excellent properties. With the urgent need for social progress, the intelligent responsiveness of polyurethane adhesives has become more and more important. Here, we demonstrate a stimulus-responsive polyurethane adhesive. Starting from the structural design, sulfur (S₈) is added into the polyurethane adhesive for the first time using the inverse vulcanized mechanism, and the controllable disassembly response of the polyurethane adhesive under the condition of thermal stimulation is realized. In addition, the stimulus response of the adhesive can also be activated through the permeation process of methoxide anion (CH₃O⁻), and the rapid disassembly response property is displayed in the methanol solution of CH₃ONa, to realize the recovery of the bonding substrate. Simultaneously, the implementation of the inverse vulcanized mechanism imparts the adhesive with a diminished water absorption swelling rate and heightened cross-link density. On the surface of the metal substrate, it shows excellent bonding properties, with a lap shear adhesion strength reaching 2.8 MPa. It is worth noting that the adhesive also exhibits excellent underwater durability. After 36 h of underwater soaking treatment, its adhesion can still be maintained at 2.4 MPa. This work reveals the mechanism of rapid disassembly of polyurethane adhesives at the molecular level. By density functional theory (DFT) calculation, it is found that the minimum bond energy of the S-S bond in a polyurethane adhesive system is 134 KJ·mol⁻¹, and the disassembly response can be triggered by heating to 53.79℃. At the same time, the mechanism of the disassembly response induced by CH₃O⁻ is further analyzed using an electrostatic potential (ESP) diagram. This work utilizes sulfur (S₈) and castor oil (CO) as raw materials, which can be sourced from industrial or agricultural by-products. It breaks away from traditional polyurethane adhesive preparation methods and offers a "green" strategy that can be synthesized through a solvent-free one-pot process, thus providing a new way of thinking about obtaining sustainable polymers from industrial and agricultural by-products.

To address the growing need for fire-safe single-component epoxy resin (EP) systems, this study introduced a phosphorus-containing copper complex (Cu-DA) as a multifunctional latent curing agent. The Cu-DA complex, synthesized by coordinating copper (II) chloride and a phosphorus-based imidazole, significantly improved the latency, thermal stability, and fire resistance of single-component EP. The obtained EP/Cu-DA-2 mixture with 15.3 wt% Cu-DA showed a 43-day shelf life and a rapid gel time of 22 min at 150 °C, highlighting its superb latency and fast curing. After curing, the resultant thermoset had a high glass transition temperature of 160.9 °C and increased crosslinking density, indicating superior thermal stability. The EP/Cu-DA-3 system with 17.4 wt% Cu-DA achieved a high limiting oxygen index (LOI) of 37.8 % and a UL-94 V-0 rating, reflecting its satisfactory flame retardancy. Furthermore, compared to the control EP system, the total smoke production (TSP) and maximum smoke density (MSD) of EP/Cu-DA-3 were reduced by approximately 28.4 % and 25.8 %, respectively, demonstrating significantly enhanced smoke suppression. The research offers a scalable strategy for developing single-component EP systems with rapid curing, high fire resistance, and great smoke suppression, meeting the demands of industrial applications.

In this study, MXene@Ag@PA hybrids were synthesized using radiation methods and chelation, aiming to enhance the key properties of EVA/MH composites, particularly their flame retardancy. The test results demonstrated that the addition of MXene@Ag@PA hybrids effectively reduced the amount of heat and smoke released during the combustion process of EVA composites. When 2 parts of MXene@Ag@PA hybrids were added, the peak heat release rate (pHRR) of the EVA/MH/2.0MXene@Ag@PA composite was reduced to 233 kW/m², representing a decrease of 78.5% and 63.3% compared to pure EVA and EVA/MH composites, respectively. Additionally, the time to reach the peak heat release rate was delayed to 300–400 s. Moreover, the MXene@Ag@PA hybrids further reduced the total smoke production (TSP) of the EVA composites to 3 m², which is 50% and 38.7% lower than that of pure EVA and EVA/MH composites, respectively. Besides providing significant flame-retardant enhancement to EVA/MH composites, the MXene@Ag@PA hybrids also acted as a radiation sensitizer. At an irradiation dose of 100 kGy, the addition of MXene@Ag@PA hybrids enhanced the cross-linking effect of EVA composites, thereby strengthening their mechanical properties.

In this study, we present an efficient and green extraction-pretreatment integrated approach for enhancing enzymatic conversion of chitinous wastes into N-acetyl-d-glucosamine (GlcNAc). Firstly, the enzyme cocktail containing a chitinase CmChi1 and a N-acetyl glucosaminase CmNAGase were constructed for hydrolyzing chitin into sole GlcNAc. Secondly, deep eutectic solvent (DES), consisting of choline chloride and glycollic acid was used to treat chitinous wastes. Under optimal conditions, chitin yield reach to 72 % with a purity of 98 %. Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction analysis revealed that the crystallinity and thermal stability of the obtained chitin decreased upon DES treatment without alteration of the chemical structure or deacetylation. Finally, the concentration of GlcNAc was increased 2–6 folds by enzymatic hydrolysis of DES-treated chitinous wastes (including shrimp shell, crab shell, ganoderma spores wall, and mycelium). The process provides a promising strategy for degrading chitinous wastes to produce high valued GlcNAc.

The most conspicuous problem regarding fire retardation of ethylene vinyl acetate (EVA) copolymer is that the flame-retardant efficiency of traditional fire retardants is very low. How to achieve high-efficient flame retardation has long been a big challenge. Herein, polyurea-modified microencapsulated expandable graphite (MEG) was synthesized through in-situ polymerization, and it was found that the proper combination of MEG and polyphosphoric acid (PPA) exhibits an unexpectedly high flame-retardant efficiency to EVA. The incorporation of just 5 wt% MEG/PPA enables EVA to achieve V-0 rating in UL-94 flammability test, increases its limiting oxygen index from 19.3 % to 25.7 %, and reduces its peak heat release rate by 72 % during combustion. The EVA/MEG/PPA composite, containing 5 wt% MEG/PPA, not only demonstrates improved fire retardancy, smoke suppression, and processability compared to virgin EVA, but also maintains good electrical insulation, water resistance, and mechanical properties. The high fire-retardant efficiency is ascribed to the larger expansion volume of MEG and the formation of high-quality intumescent char, which shield the polymer from burning. This work renders a simple and cheap approach for development of high-efficient flame-retarded EVA with good processability and mechanical property simultaneously.

Fused Deposition Modelling (FDM), a prevalent additive manufacturing technique utilising polymeric materials, facilitates intricate geometric customisation and rapid prototyping. The ongoing development of FDM technology emphasises the importance of the thermal characteristics of FDM-printed polymeric materials, which are essential for various applications, including aerospace and biomedical engineering. The thermal properties of FDM-printed polymeric materials, covering a wide range of thermoplastic polymers and composites, were examined in this review. Despite the versatility of FDM technology, thermal challenges persist in 3D printed parts, manifesting as anisotropy, voids, and sub-optimal conductivity, thereby impeding performance. Achieving precise control over printing parameters such as nozzle temperature, layer height, and speed is pivotal for optimising thermal properties. Additionally, controlled thermal treatments, like annealing, offer avenues for manipulating the crystalline structure of printed components to enhance the thermal conductivity. By elucidating the effects of reinforcements, this article aims to provide insights into potential enhancements and adjustments for developing thermally resistant FDM-based polymeric materials.

Poly(lactic-co-glycolic acid)s (PLGAs) hold considerable significance for their biomedical applications. Biodegradation and mechanical properties of PLGAs and PLGA-based composites are strongly influenced by lactate/glycolate (L/G) ratio in copolymers, molecular weight characteristics and microstructure of PLGAs. The common approach to PLGAs is based on ring-opening copolymerization of lactides and glycolide, the products of which contain long (L)_n and (G)_n segments. An efficient but expensive approach to PLGAs with given l-G sequences is a segmer assembly polymerization that is hardly applicable for the synthesis of high-MW PLGAs. In the present work, for the first time we synthesized lactate-enriched PLGAs using ring-opening copolymerization of l-lactide (l-LA) with l-methylglycolide (l-MeGL) in 85:15 and 70:30 molar ratios, resulting in l-PLMG 85/15 and l-PLMG 70/30 copolymers. l-PLGA 85/15 with the same L/G ratio as in PLMG 70/30 was synthesized by ring-opening copolymerization of l-LA with glycolide as a sample for a comparison. According to ¹H and ¹³C NMR data and [α]_D measurements, l-MeGL-based PLGAs had a unique microstructure, e.g. macromolecules of l-PLMG 85/15 consisted of L_n sequences with single G insertions. Composites of PLLA and three samples of PLGAs with plate-like carbonated apatite (pCAp) containing 25 and 50 wt.% of the filler were prepared. Rectangular specimens from (co)polymers and (co)polymer composites were obtained by injection molding and studied. Due to the absence of highly reactive (G)_n fragments, l-PLMG 85/15 and PLMG 70/30-based materials demonstrated higher thermal and hydrolytic stability, mechanical testing showed that l-MeGL-based copolymers provide better maintaining of the bending strength in comparison with l-PLGA 85/15 matrix.

The degradation behaviors, mechanisms and compatibility are not well understood and hard to be harnessed for EPDM composite in the coupled gamma radiation-thermal environments. This contribution performs a thorough study accordingly with 0 ∼ 200 kGy dose under temperatures varying from room temperature to 90 °C in N₂/O₂ mixture atmosphere. Radiation-thermal aging leads to annealing effect and chemi-crystallization that rebuilds the semi-crystalline structure and invokes competitive filler migration, reconfiguration and loss. Crosslinking reactions prevail the scission during the investigated conditions. However, the surface oxidation and damage are not severe. In-situ nondestructive gas-phase FTIR sensitively find the formed various gaseous products, whose generation kinetics behaviors are temperature and dose dependent. Most surprisingly, the radiolysis caused carbonyl sulfide and carbon disulfide are discovered with indispensable gamma radiation, which manifest temperature reined conversion thermodynamics and kinetics behavior. The qualitative and quantitative analysis of gas products is also validated by GC and GC-MS tests. The evolved semi-crystalline structure, macromolecular chain network and filler network significantly impact the mechanical property, but the barrier property and hydrophobic property are slightly influenced. The inverse temperature effect occurred at 50 °C for the mechanical properties, which show abnormal rejuvenation behavior due to the counteraction between aging induced change in molecular structure, aggregation structure and filler reconfiguration, migration and loss. The multiscale structure-property-behavior relationships possess good interdependency, indicating the main aging mechanism and failure mode are almost invariant. By ReaxFF simulation, the complex degradation mechanism for EPDM composite at atomic scale is revealed for the first time.

The ecological risk assessment of a product released into the environment is a complex process that takes into account both its ecotoxicity and the Predicted Environmental Concentration (PEC) in the environment. The latter depends on the use, transport, fate (i.e. persistence) of the product. This article describes a model to determine the Predicted Environmental Concentration (PEC) of a biodegradable mulch film taking into account its characteristics, the frequency of application of the mulch film, its degradation rate, and the density of the soil to which it is applied. The effect of temperature on biodegradation kinetics was also taken into account to estimate the biodegradation rate achievable at a given temperature based on data obtained in the laboratory under standard conditions. Using the same approach as for pharmacokinetics, the model can calculate the average mulch film concentration at steady state and the maximum concentration applied. The PEC values can be compared with the Predicted No-Effect Concentration (PNEC) derived from ecotoxicity studies to characterise the risk associated with use of mulch film. The model, if validated by comparison of the calculated PECs with the Measured Environmental Concentrations (MECs), determined by detection and quantification of biodegradable mulch film residues in soil, may provide a valuable tool for the ecological risk assessment of biodegradable mulch films.