Polymer Degradation and Stability最新文献

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, 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.

In this study, multifunctional polyester-cotton fabrics (PTCO) were constructed by gradually assembling polyethyleneimine phenyl phosphonate (POI) and different hydrophobic agents, respectively. The effect of different hydrophobic agents including tetraethyl orthosilicate, perfluorooctyltriethoxysilane (PFDTES), and hexadecyltrimethoxysilane on the thermal stability, flame retardancy, hydrophobic property, UV resistance and antibacterial property of PTCO/POI was investigated in detail. PTCO/POI-SiF had better flame retardancy due to the flame-retardant effect of PFDTES and POI, and the limiting oxygen index increased from 29.8 % to 31.2 %. The thermal oxidation stability of PTCO/POI-SiH and PTCO/POI-SiF was significantly improved in high temperatures, and the char residues at 700 °C were increased from 4.1 % to 7.6 % and 7.4 %. And PTCO/POI-SiH and PTCO/POI-SiF had excellent superhydrophobic properties with water contact angles of 151° and 162° and sliding angles of 4° and 3°. The ultraviolet protection factors of them were increased to 56.9 and 63.3, respectively, which had a good UV resistance. And both PTCO/POI-SiH and PTCO/POI-SiF had excellent antibacterial effects for E. coli and S. aureus. The breaking force, whiteness and moisture permeability of the finished fabrics had not been changed. Therefore, it is believed that PTCO/POI-SiH and PTCO/POI-SiF are promising for application in multifunctional fabrics.

The development of high-quality thermal insulation material with exceptional flame-retardant qualities is crucial to reducing energy consumption in buildings and minimizing the risk of fire. Herein, we report the preparation of organic-inorganic composite aerogel by coating Mg/Al-LDH and phytic acid onto the exterior of hollow glass microspheres to obtain PLHGM, mixing PLHGM with the solution of sodium alginate and carboxymethyl cellulose to prepare the SA/CMC-PLHGM aerogel. The synthetic aerogel has exceptional thermal insulation with a thermal conductivity of 0.046 Wm⁻¹K⁻¹. Meanwhile, SA/CMC-PLHGM aerogel has a high limiting oxygen index value is greater than 90%, reaching the UL-94 test V-0 rating. In the cone calorimetry test, the peak heat release rate (pHRR) is 32.97 kW/m², a 55.19% reduction from the sodium alginate/carboxymethyl cellulose aerogel (SA/CMC aerogel), and the SA/CMC-PLHGM aerogel has lower CO and CO₂ production rates compared to the SA/CMC aerogel. The SA/CMC-PLHGM aerogel has properties of lightweight, porous, thermally stable, flame-retardant properties, and superior thermal insulating properties which provide a novel strategy for the practical use of aerogel in the field of modern building construction thermal insulation materials with flame-retardant properties.

The nature of the functional groups on the filler surface is one of the key influences on the interfacial interaction in the aging of polymer composites. However, the characteristics of this interfacial effect and its relation with functional groups remain unclear. In this study, we investigated the effects of interfacial interactions on the photooxidative aging of silica-filled polypropylene (PP) composites in which the interfaces comprise functional groups possessing different photooxidative properties. Results showed that the effects of interfacial interactions on the photooxidative aging of the silica-filled PP composites were closely related to the composition of the interfacial functional groups. Since the effect of interfacial interactions on the PP oxidation rate was correlated with the concentration of the interfacial functional groups, an aging kinetic model of interfacial effects could be constructed for determining the role of interfacial functional groups in the photooxidative aging of PP composites. This study will provide new ideas for developing interfacial antioxidant strategies for polymer composites.