Polymer Degradation and Stability最新文献

Natural rubber/cellulose nanofiber (NR/CNF) composites exhibit improved dry tensile properties compared with neat NR sheets. However, the presence of hydrophilic CNFs in the composites causes low water resistance, resulting in high water content and low tensile strength when the composites are soaked in water at 70 °C for 7 d. Herein, water-resistant NR/CNF composites were developed by adding zinc methacrylate or aluminum acrylate, and the oven-dried NR/CNF/additive materials were counterion-exchanged with 0.1 M NH₄OH. X-ray fluorescence analysis of the composite sheets indicates the reasons and mechanisms for the improved water resistance of the composites prepared with the tested additives by post-counterion exchange.

Understanding the migration and transformation of polycarbonate (PC) plastic wastes in the natural environment is crucial for assessing their environmental impact and bioremediation. In this study, PC plastic degradation was modeled and traced in soil microcosm by investigating physiochemical properties changes of PC, the formation of microplastics, and changes in soil microbial communities. Notably, PC microplastics quantification method was also successfully devised by pyrolysis gas chromatography mass spectrometry and also applied herein. Through gel permeation chromatography analysis, the molecular weight of the naturally aged PC film obviously reduced, whereas no change for unaged ones. After 12 months of soil burial, the surface corrosion and holes formation were emerged on the surfaces of both PC films in the non-sterilized soil harboring indigenous microorganisms by scanning electron microscope. The worsened thermal stability of both PC films in non-sterilized soil was demonstrated by thermogravimetric analysis. Meanwhile, the presence of increased hydroxyl group absorption and decreased carbonyl peak highlighted molecular chain breakage in both PC films by Fourier transform infrared spectroscopy. In particular, all the changes were more significant in aged PC than unaged ones. Furthermore, the increase of quantified PC microplastics on the surface of PC film in the non-sterilized soil accompanied the decreasing of microbial diversity and the enrichment of potential functional microorganisms. These findings revealed that the combination of natural aging and indigenous microbes exhibited a noticeable performance in PC plastics degradation in soil microcosm, providing new insights into the degradation mechanism of PC plastic wastes in the natural environment.

Failures due to the degradation of polymeric insulation in components of electrical power systems are difficult to predict. Partial discharges (PDs) are one of the main phenomena that contribute to polymeric insulators’ aging. Therefore, a better understanding of the aging process due to PDs is crucial to develop effective models that predict degradation, optimize materials and propose diagnostic indicators. Here we present an experimental characterization, via Fourier-transform Infrared spectroscopy (FTIR), of a composite material exposed to PDs. The material consisted of cured epoxy resin mixed with silica (quartz). Aging tests with surface discharges, using a needle-plate configuration, were conducted considering two atmospheres (air and CO${}_2$) and four exposition times (6, 24, 72 and 120 hours). To aid the interpretation of spectroscopic data, we included a series of simulation results. The main effect observed was the erosion and removal of epoxy resin from the surface of the samples, proportionally to treatment time and distance from the needle. Along with erosion, new chemical species (possibly oxalate salts) were detected on the surface exposed to air-plasma. These species were likely formed and then removed due to plasma activity over time. On the other hand, samples aged in CO${}_2$ atmosphere underwent only epoxy resin erosion.

Natural rubber (NR), as a green and renewable industrial raw material, is applied in many fields. However, the relatively weak resistance originated from its unsaturated backbone structure restricts the further application in some harsh conditions. To incorporate the excellent resistance feature of the fluorinated components into NR, fluorinated natural rubber (FNR) was prepared with dodecafluoroheptyl methacrylate (DFHMA) via in situ melt extrusion reaction. The results indicated that fluorinated reaction of NR mainly happened at the α-H of double bond in backbone chain and that styrene could promote fluorination and increase the size of fluorinated side chain. The vulcanized FNR (VFNR) exhibited wonderful mechanical performance, remarkable hydrophobicity, and excellent resistance to ozone, organic solvent, acid and alkali. The water contact angles of VFNR increased from 89 ° to 104 °and the ozone aging cracking time of VFNR increased by one time longer than that of VNR. The swelling degree of VFNR in the full synthetic engine oil is only two-thirds that of VNR, and the retention of tensile strength after immersion in HCl, H₂SO₄, and NaOH solution was elevated by 13 %, 11 %, and 5 % compared to those of VNR, respectively. This work presents a simple and eco-friendly method to prepare the fluorinated natural rubber facilitating the industrial fabrication of green and high-performance NR via melt extrusion.

The integration of medium-frequency transformer design and the harsh service environment raise higher demands for the medium-frequency insulation performance of epoxy composites. As epoxy composite's frequency response characteristics and sensitivity to moisture intrusion are still unknown, its application as the insulation materials of medium-frequency transformers under hygrothermal conditions is limited. This paper investigates the mechanism of moisture intrusion damage to the molecular structure of the epoxy resin matrix and its cross-linking points with the curing agent. The regularity of medium-frequency insulation performance degradation of epoxy composites after hygrothermal aging is studied. Results indicate that after 40 days of hygrothermal aging, moisture together with high temperature damaged the main chain of the epoxy resin and its cross-linking points with the curing agent, resulting in a 23 °C decrease in the glass transition temperature and an 82 % decrease in cross-linking density of the epoxy composite. Moisture ionization and the increase of carriers due to epoxy resin hydrolysis lead to an increase in the amount of space charge. The temperature rise caused by dipole steering polarization facilitates the formation of internal conductive pathways in the epoxy composite, resulting in a 73 % decrease in the medium-frequency breakdown strength and a four-order magnitude decrease in the medium-frequency volume resistivity of the epoxy composite. This study can guide the insulation design of high-reliability medium-frequency transformers.

Polysiloxanes are modifiers that can enhance the fire safety and toughness of epoxy thermosets. However, the design of high-efficiency polysiloxane modifiers remains a formidable challenge, due to their indefinite structures as well as the complexity and high costs of the preparation process. A phosphorous-containing epoxy-functionalized polydimethylsiloxane (PDMS-DGE) has been prepared by a three-step process using octamethylcyclotetrasiloxane (D₄), 2,4,6,8-tetramethylcyclotetrasiloxane (D₄H), 1,1,3,3-tetramethyldisiloxane (TMDS), allyl glycidyl ether (AGE), and 9,10-dihydro-9-oxo-10-phosphaphenanthrene (DOPO). Incorporation of 15 wt% PDMS-DGE strongly improved the flame retardancy of epoxy thermosets. There was 38.2% increase in limiting oxygen index value (LOI), 54.4% decline in total heat release (THR), and 27.2% decrease in total smoke production (TSP) as compared to the same values for combustion of unmodified epoxy thermoset. This could be ascribed to the generation of phosphorus/silicon-containing char layers, which effectively reduced the formation of combustible gases, smoke, and heat during burning. Compared to neat EP thermoset, the flexural strength and impact strength of the 15 wt% PDMS-DGE modified epoxy thermoset was increased by 51.1% and 107.8%, respectively. This is due to the existence of epoxy groups, rigid phosphaphenanthrene structures, and flexible polydimethylsiloxane chains in PDMS-DGE. Further, the presence of PDMS-DGE provides epoxy thermosets with good moisture resistance. A facile strategy to develop polysiloxanes for epoxy thermosets with both flame retardant properties and toughness, which has vast potential for industrial applications has been proposed.

In this work, we synthesized a series of compounds, denoted as xCTAB@AMP, by incorporating varying different molar fractions of cetyltrimethylammonium bromide (CTAB) into ammonium phosphomolybdate (AMP). The effects of CTAB modification on the surface characteristics, morphology and hygroscopicity of AMP were studied. Moreover, we explored the combined flame-retardant impact between xCTAB@AMP and aluminum diethylphosphinate (ADP) when incorporated into epoxy resin (EP), as well as the resulting composite's mechanical properties, thermal stability and antibacterial properties. The EP composite containing 50 molar percent CTAB-modified AMP (EP/50CTAB@AMP/ADP) demonstrated remarkable flame retardancy, achieving a UL-94 V-0 rating and increasing limiting oxygen index (LOI) to 30.0%. This formulation significantly lowered the peak heat release rate (PHRR) to 452 kW/m², a 65% reduction to that of EP, and the total heat release (THR) to 68 MJ/m², a 24% decrease to that of EP. Additionally, compared to EP, the peak smoke production rate (PSPR) of this composite was decreased by 30% (0.28 m²/s), the total smoke production (TSP) was reduced by 25% (30.2 m²), and peak carbon monoxide release rate (PCOP) was diminished by 34% (0.038 g/s). The combination of 50CTAB@AMP and ADP in the EP matrix exhibited an exceptional synergistic flame-retardant effect. Concurrently, the CTAB modification bolstered the interfacial interactions between AMP and the EP matrix, which enhanced the mechanical properties of EP/AMP/ADP composites. As a result, the tensile strength and elongation at break of the EP/50CTAB@AMP/ADP composite increased by 13% and 15%, respectively, compared to the EP/AMP/ADP. Moreover, the 50CTAB@AMP maintained its inherent antibacterial activity, which endowed the EP/50CTAB@AMP/ADP composite with a potent inhibitory effect against Staphylococcus aureus, a common pathogenic bacterium.

This study focuses for the first time on the investigation of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) permanent coatings on composite surfaces to enhance the electrical and surface properties of fiber-reinforced composite materials, particularly those commonly used in the aerospace sector, such as Kevlar® (aramid), carbon (C), and glass fiber-reinforced composites. One significant challenge encountered is the weak adhesion property between PEDOT:PSS and the composite surface, which poses some difficulties in coating durability in harsh environmental conditions. The resulting material comprises a three-component structure, consisting of composite surface modifications, PEDOT:PSS coating, and sulfonated poly(ether ketone) (SPEEK) primer. To address the primary issues of adhesion, delamination, stability, and electrical conductivity, this study adopts a novel approach to improve the permanence of PEDOT:PSS coatings on composite surfaces by utilizing a SPEEK primer under ultraviolet (UV) light exposure, deionized (DI) water, saltwater, and acidic environments. Tape-peeling and cross-cut adhesion tape tests were employed to evaluate the coating durability, while optical microscopic observations, water contact angle (WCA), and Fourier-transform infrared (FTIR) spectroscopy analyses assess physical, chemical, and physicochemical property changes. Test results indicated that the SPEEK/PEDOT:PSS-coated composite surfaces exhibited enhanced electrical conductivity, stability, and permanent adhesion properties. Overall, this study contributes to the development of next-generation materials for various industries (aviation, defense, energy, and manufacturing) by offering a promising solution to improve electrical, adhesion, and other surface properties in composite materials.

Thermal degradation of N, N'-dibutyladipamide and polyamide 66 (PA66) was carried out in a large-scale experimental setup with nitrogen sweeping in order to collect elusive degradation intermediates. At a high nitrogen flow rate, 1-butylazepane-2,7-dione was identified as a major degradation product from the thermal decomposition of N, N'-dibutyladipamide. Upon heating, 1-butylazepane-2,7-dione produced cyclopentanone and its derivatives, dibutylurea and a nitrile that constituted the majority of degradation products of N, N'-dibutyladipamide, proving that the 7-membered heterocycle compound is a crucial primary degradation product as well as a precursor for the secondary degradation products of N, N'-dibutyladipamide. Subsequently, chemistry concerning the generation and decomposition of 1-butylazepane-2,7-dione was developed for the thermal decomposition of DBA. On the other hand, hexamethylenediamine, 1,8-diazacyclotetradecane-2,7-dione, cyclopentanone and its derivatives were collected as important degradation products from the thermal decomposition of PA66. In view of the structural similarity between DBA and PA66 and their comparable degradation products, a mechanism centering on the generation and decomposition of a 7-membered ring has ultimately been established for thermal degradation of PA66.

One potential solution for reducing marine pollution from plastic waste is to replace conventional plastics with biodegradable alternatives. However, most chemosynthetically biodegradable aliphatic polyesters, such as poly(butylene succinate) (PBS), exhibit extremely slow biodegradation rates in marine environments. To address this problem, we present a novel method to enhance the marine biodegradability of PBS by blending it with 10 wt.% of 16-hydroxyhexadecanoic acid (16HHD) and poly(ε-caprolactone) (PCL). The weight loss rates of the PBS samples with 16HHD and PCL were 18.4- and 7.8-times faster than that of pristine PBS. Scanning electron micrographs of PBS blended with 16HHD and PCL after oceanic incubation for four months showed a rough surface, suggesting that enzymatic degradation occurred. Additionally, unlike pristine PBS, samples with 16HHD and PCL demonstrated biochemical oxygen demand (BOD) biodegradabilities of 90.4 % and 83.2 %, respectively, under marine conditions. Analysis of the microbial community of BOD testing using 16S ribosomal RNA gene sequencing indicated that the addition of 16HHD and PCL changed the microbial community compared to pristine PBS. These findings demonstrate how blending PBS with 16HHD and PCL enhances its marine biodegradability, thereby offering a promising avenue for addressing plastic pollution in marine ecosystems.