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A full understanding on the relationships between weathering factors and deteriorations in the physical or mechanical properties of polymeric materials as well as their intercorrelations is critically important to forecast the durability of materials. In this work, the outdoor weathering behaviors of isotactic polypropylene (iPP) across a 1.5-year period under six typical climate scenarios in China are investigated. A wide sets of natural exposure conditions and test methods allow the establishment of the substantial correlations between chemical/physical structures and appearance/mechanical properties under simultaneous effects of multiple weathering factors (such as light, heat, oxygen etc.). The results under diverse natural environments suggest that the crystallinity and crack development depend largely on the molecular weight while the yellowing index correlates directly with the carbonyl index irrespective of the exposure conditions. The relationship between tensile strength and molecular weight is found to be in accord with an empirical linear model. Subsequently, using principal component analysis (PCA), a data reduction and visualization method, the degradation risk map of PP materials in China is established and the relative importance of relevant weathering factors is evaluated. Temperature is found to be the most dominant weathering factor on iPP aging under the climate scenarios investigated in the present work. [ABSTRACT FROM AUTHOR]

Waterborne polyurethane (WPU) has attracted significant attention recently, considering its advantages of sustainability and low toxicity. However, fabricating WPU with excellent initial performance as well as extraordinary long-term stability is extremely challenging. In this study, we demonstrated the potential of polydopamine-modified graphene oxide (DGO) in the preparation of strong, tough, and highly durable WPU materials via in-situ polymerization. With the addition of only 2.0 wt% DGO, the tensile strength, and Young's modulus of WPU increased from 17.6 ± 2.6 to 56.5 ± 3.1 MPa (by 221%) and from 8.5 ± 1.1 MPa to 22.0 ± 0.8 MPa (by 159%), respectively. Compared with WPU, the degree of surface oxidation of the UV-aged WPU/DGO composites was substantially reduced from 174.3 to 19.5 (by 88% at maximum). Based on the cross-sectional analysis, the oxidation depth of the WPU/DGO composites was significantly reduced from 11.25 μm to 3.75 μm (by 66%). These improved properties originated not only from stronger interactions between DGO and WPU via the interfacial PDA layers and better dispersion of DGO, but also from the unique ultraviolet light absorption ability and free radical trapping ability of DGO. This facile yet environment-friendly in-situ synthesis technique is eco-sustainable and expected to promote the commercial availability of high-quality WPU and conserve natural resources. [Display omitted] • WPU/DGO composites were synthesized successfully via in-situ polymerization. • PDA layer enhanced the UV absorption and free radical scavenging ability of GO. • Covalent bonding through urea groups between DGO and WPU matrix was verified. • Tensile strength and Young's modulus of WPU/DGO composites were simultaneously boosted. • Surface oxidation and oxidation depth of WPU/DGO were significantly suppressed. [ABSTRACT FROM AUTHOR]

The degradation behaviors under outdoor and accelerated laboratory weathering conditions of isotactic polypropylene (iPP) were compared, aiming to establish a correlation between both weathering types. Outdoor weathering experiments were performed at six national standard natural exposure stations which represent six typical climate types in China. The evolutions in the chemical/molecular structure, surface morphologies, mechanical and crystalline properties were compared and the results suggested that the accelerated weathering experiment is substantially capable to mimic the main outdoor weathering behaviors. The degradation mechanism for all weathering conditions is consistent according to the similarity in the species and proportions of the carbonyl products. An improved Arrhenius equation, which considered the multiple effects of temperature, irradiation and oxygen pressure, was proposed to correlate the outdoor weathering behavior of iPP with that of accelerated laboratory weathering. The predictions for the outdoor weathering behavior of iPP based on this approach were satisfactory compared with the experimental results. Depending on the outdoor exposure locations, the acceleration of laboratory weathering was found to range from 8 to 30 times in comparison to outdoor weathering. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a new approach for the creep lifetime prediction of polypropylene (PP)/organoclay nanocomposites. The creep failure of PP and its nanocomposites with and without PP grafted maleic anhydride (PP-g-MAH) is found to occur at a critical strain independent of the stress level investigated. This peculiar critical strain is combined with a time-strain superposition method to predict the creep failure lifetime of PP nanocomposites. In this method, a generalized creep compliance curves followed a relatively simple power law are generated from nonlinear creep data obtained by accelerated tests at high stresses. The creep lifetime under lower stresses is then predicted successfully by using the critical strain as the failure criterion. The lifetime predictions for the PP materials considered based on this approach are satisfactory compared with the experimental results. The approach proposed is intuitive and convenient, and has the potential to be extended to other polymeric materials which possess a critical failure strain behavior. [Copyright &y& Elsevier]

Abstract: Thermal oxidation behavior of isotactic polypropylene (PP) films with and without nucleating agent was investigated at 100 °C in air. The crystal form of PP was modified with a specific aryl amide derivative as β-nucleating agent (β-NA). Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests were performed to determine the extent of chemical degradation and the variations of microstructure of the two kinds of PP films during thermal oxidation. It was found that the mechanism of thermal oxidation of PP films was not changed in the presence of β-NA, but the time to initiation and the rate of oxidation both declined. Moreover, during the thermal oxidation aging, the melting temperature of neat PP significantly decreased while only a slight decrease of the melting temperature occurred for β-PP. Overall, the investigation indicated that the thermal oxidative stability of β-PP was higher than that of neat PP. The underlying mechanism was further analyzed by considering the change in the physical structure, especially the crystalline and the amorphous structure, of PP in the presence of β-NA. [Copyright &y& Elsevier]

Trustworthy evaluation on the long-term reliability of PV backsheets depends largely on the estimation of ultraviolet (UV) damage from the ground reflection; however, current use of total UV irradiance can hardly provide precise estimation due to the spectral UV albedo of grounding materials and spectral sensitivity of backsheet degradation. In this work, effects of spectral UV albedo on the estimation of UV damage were evaluated theoretically through the combinations of 35 types of grounding materials and 4 types of common backsheet materials, including polypropylene (PP), polyethylene terephthalate (PET), polycarbonate (PC) and polyamide (PA). The results showed that, without considering the spectral reflectivity, overestimation of the UV damage for PV backsheets can happen. This work can provide the critical basis for developing more precise lifetime prediction model and designing more reliable accelerated aging tests. • Spectral albedo effects on the UV damage estimation for backsheets are evaluated. • Overestimation of UV damage for backsheets could happen using total UV irradiance. • Effective UV albedo shall be used to establish a more precise UV damage assessment model. [ABSTRACT FROM AUTHOR]

As the research for advanced materials suitable for high-temperature uses continues, the need for oxide ceramic micro-nanofibers with outstanding mechanical and thermal properties becomes increasingly important. By incorporating two types of magnesium sources, specifically Mg(CH 3 COO) 2 ·4H 2 O and MgCl 2 ·6H 2 O, into the precursor, a range of fibers made of magnesium silicate ceramics was produced through electrospinning. X-ray diffraction (XRD) analysis verified that the resulting multiple phases included MgO, MgSiO 3 , Mg 2 SiO 4 , and amorphous SiO 2 , with the phase composition being affected by the diffusion reaction of Mg ions. The fibers produced using the dual-precursor method maintained a stable morphology with a uniform and compact structure after undergoing high-temperature treatments ranging from 1000 to 1200 °C. This study is the first to report the tensile strength of magnesium silicate fibrous membranes, which was found to be 1.54 ± 0.27 MPa and 1.21 ± 0.73 MPa after heat treatment at 800 °C and 1000 °C, respectively. Furthermore, these fibrous membranes demonstrated dependable thermal insulation properties within the testing range of 500–1000 °C, along with a low thermal conductivity at room temperature of 0.0301–0.0306 W m−1·K−1. Characterized by their impressive mechanical strength and high temperature stability, magnesium silicate ceramic micro-nanofibers show significant potential for various applications in the targeted field. [ABSTRACT FROM AUTHOR]

With the increasingly serious issues of energy conservation and emission reduction, hollow fibers have attracted wide attention as materials that have structural advantages in terms of thermal insulation. Herein, we report the preparation of flexible hollow TiO 2 fibrous membranes via coaxial electrospinning. To optimize the thermal-insulation performance of the fibers, hollow fibers with different diameters and pore sizes were prepared by adjusting the feeding rate of the core spinning solution. Optimum conditions were achieved at a feeding rate of 2 mL/h for the shell solution and 0.4 mL/h for the core solution. The hollow fibers had a compact tube wall structure and good mechanical properties, and the tensile strength of the fibrous membranes reached 0.652 ± 0.119 MPa. In addition, the hollow fibrous membranes have excellent thermal insulation properties with an average reflectance of more than 89% and a room temperature thermal conductivity of less than 0.0294 ± 0.00015 W m−1K−1. In practical experiments, the temperature can be reduced from 1174.6 to below 273.6 °C using 15-mm-thick fibrous membranes, which confirms its excellent thermal insulation. Flexible hollow TiO 2 fibrous membranes have a wide range of insulation applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Failure risk of transparent backsheets for bifacial PV modules was systematically evaluated. • Single UV exposure caused pits and fish-scale craters on the surface. • Additional strain can induce surface cracking of aged transparent backsheets. • Cracking increases the oxygen/water vapor permeation rate significantly. • Current standard UV aging tests don't match field conditions, misleading lifetime estimates. Recently, bifacial photovoltaic (PV) modules have attracted more and more interest due to their potential advantage in energy yield. Transparent polymer backsheets are crucial for protecting the bifacial modules from environmental exposure to guarantee a service lifetime of PV modules of at least 25 years. However, harsh service environments often lead to the premature degradation of polymer backsheets and the loss of their protection performance. To date, understanding on the risk of failure of transparent PV backsheet is still very limited. In this study, commercial single-layer polyethylene terephthalate (PET) samples were used as the model transparent backsheet. A sequential UV exposure-fragmentation test was then conducted to evaluate their risk of failure. Changes in its key protection performance (including oxygen and water vapor barrier properties) were characterized before and after fragmentation tests. In addition, systematic characterizations of its chemical structures, crystalline structures, and mechanical properties were conducted. Moreover, to understand the correlation between their cracking patterns and barrier properties, finite element simulation was also performed. We hope that this work can provide a scientific basis for the reliability evaluation and optimization of transparent backsheets toward more durable bifacial PV modules. [ABSTRACT FROM AUTHOR]

The feasibility of using thermally reduced graphene oxide (TrGO) to improve the antioxidative efficiency of commercial antioxidant (3,5-di-tert-butyl-4-hydroxycinnamic acid, AO) on unstabilized polypropylene (PP) was evaluated in terms of the oxidation induction time (OIT) and the initial degradation temperature ( T i ). It was found that a synergistic effect exist between AO and TrGO in retarding the degradation of PP in oxygen-containing atmosphere. Compared with that of PP/AO (100/0.5) sample, the OIT value of PP/AO/TrGO (100/0.5/1) composite was almost doubled at 180 °C and the value of T i in air was improved by 37.2 °C. As verified by using radical scavenging assay with the 1,1-diphenyl-2-picrylhydrazyl radical, the TrGO sheets exhibited a good radical scavenging capacity. The synergistic stabilization mechanism was attributed to the enhanced dispersion of TrGO sheets in the PP matrix in the presence of 0.5 wt.% AO, which could improve the oxygen barrier effect and radical scavenging efficiency of TrGO. This synergistic effect between AO and TrGO can efficiently reduce the concentrations of oxygen and peroxy radicals in the PP matrix, leading to the significant improvement in thermo-oxidative stability of PP/AO/TrG composite. [ABSTRACT FROM AUTHOR]

Optimizing the durability and degradability of polymers is essential for prolonging their useful life and minimizing their environmental footprint post-use, contributing to a sustainable world; however, durability in many cases conflicts with degradability. In this context, we developed lignin-based waterborne polyurethane (WPU) composites that bypass this dichotomy. Lignin nanoparticles (LNP), derived from enzymatic hydrolysis lignin (EHL), were synthesized using the anti-solvent method and incorporated into WPU emulsions through solution blending. The introduction of 5 wt% LNP notably improved the tensile strength of WPU composites, increasing it from 21.5 MPa to 29.7 MPa, a surge of up to 38 %. Moreover, 5 wt% of LNP significantly enhanced the durability of WPU by reducing creep strain (under a stress of 1 MPa for 3000 s) from 606 % to 70 % with an 88 % decrease, and by increasing molecular weight retention rate from 11 % to 87 % after 15 days of UV exposure. Concurrently, LNP notably accelerated the alkaline degradability of WPU/LNP composites, with weight loss rate increasing from 38 % to 92 % (a 142 % increase) and molecular weight loss from 17 % to 44 % (a 159 % increase), compared to pure WPU. The strategy employed in this study leverages the inherent properties of LNP to offer a promising approach to enhancing polymer sustainability, presenting an effective solution to the significant end-of-life challenge. [Display omitted] • WPU composite incorporating 5 wt% LNP was fabricated via solution blending. • Tensile strength and Young's modulus of WPU/LNP5 are enhanced concurrently. • Addition of 5 wt% LNP strongly suppressed the UV aging of WPU. • Alkaline hydrolysis degradation of WPU/LNP5 was significantly accelerated. • Natural inherent properties of LNP enhanced the durability and degradability of WPU. [ABSTRACT FROM AUTHOR]

Long chain branching (LCB) structures are efficiently introduced into polylactide (PLA) by employing sustainable soybean oil (SO) under the initiation of trace amount of cyclic peroxide, which displays robust foamability and heat resistance. It is discovered that with the introduction of 0.6 wt% SO, the expansion ratio and Vicat softening temperature of LCB PLA are sharply raised to 75.2-fold and 155.8 °C, respectively, which is about 17.9 and 2.6 times those of linear PLA. This is because that the amounts of LCB structures are significantly increased in LCB PLA by the addition of SO with low reactivity of internal C C bonds, which can avoid the oligomerization reaction, resulting in more dramatically improved melting strength and crystallization performance of LCB PLA. Moreover, the hydrolytic degradation of LCB PLA is largely expedited as compared to linear PLA, owing to the more rapid water permeation caused by the loose packing of LCB structures. Finally, the PLA foam tray with light weight and good heat resistance is successfully developed by using LCB PLA with 0.6 wt% SO through extrusion foaming with supercritical carbon oxide and thermoforming techniques. Hence, this research offers a green route to produce eco-friendly light-weight and high-heat-resistance LCB-PLA foam with full biodegradability, which is an ideal alternative to the non-degradable oil-based plastics in the field of disposable packaging products. [Display omitted] [ABSTRACT FROM AUTHOR]

• Experiments and simulations uncovered the pyrolysis mechanisms of polycarbonate. • Density functional theory and experiments validated the applicability of ReaxFF. • ReaxFF simulations revealed available and new chemical reactions. • The pyrolysis kinetics of polycarbonate was investigated. • The reduction of carbon dioxide and isomerization of isopropylidene were revealed. The isothermal pyrolysis behavior of bisphenol-A polycarbonate under anoxic conditions at different temperatures was studied by using molecular dynamics simulations with a reactive force field (ReaxFF) and compared with experiment results. The main pyrolysis products of polycarbonate observed in the actual pyrolysis experiments were well reproduced by ReaxFF simulations. The applicability and reliability of the ReaxFF force field were validated by the density functional theory and experiments. Kinetics study showed that the pyrolysis of polycarbonate was predominated by random chain scission and carbonate groups were more vulnerable to high temperatures than isopropylidene groups. The reaction routes of various pyrolysis products and related secondary reactions were revealed by ReaxFF simulations. The ether linkages can be formed by a concerted process or a radical process based on different reaction mechanisms. Cyclic oligomers, hydrolysis, and transesterification seldom took place at extremely high temperatures. Ultimately, the main thermolysis mechanisms of polycarbonate without oxygen were outlined. [ABSTRACT FROM AUTHOR]

• The role of bulk degradation and adhesion loss on the protection performance of coatings under UV irradiation is studied. • The degradation of polyurea and epoxy coatings under UV irradiation is compared. • The changes in chemical structure, water resistance and adhesion strength of coatings after UV irradiation are discussed. • The critical role of adhesion on the chloride ion penetration resistance of coatings after aging is identified. Organic coatings have been widely used to protect concrete structures from the aggressive environment and improve their reliability. However, there is a lack of clear understanding on how environmental stressors contribute to the degradation and, ultimately the loss of protection function of organic coatings. In this study, comparative degradation studies were carried out on two kinds of coatings, namely polyurea and epoxy coatings, with the major focus on the relationship between their bulk degradation, loss of adhesion and the deterioration of protection performance. Samples were all subjected to ultraviolet (UV)-condensation exposure up to about 1440 h. The changes in the surface morphology, internal pore structure, wettability and chemical structure of aged coating surface were characterized via scanning electronic microscopy (SEM) laser scanning confocal microscopy (LSCM), static contact angle measurements, and Fourier Transform Infrared Spectroscopy (FT-IR) respectively, while the water resistance and adhesion strength between coatings and concrete were studied by water sorption and pull-off tests separately. The results showed that UV irradiation induced significant morphological and chemical changes in the epoxy coatings, while the changes in the polyurea coating were minor. However, due to the higher loss in adhesion, it was interestingly found that the chloride resistance of polyurea coating was reduced even more pronouncedly than that of epoxy coating after aging. This study has clearly demonstrated the strong dependence of the protection performance of coatings for concrete on their adhesion loss besides the bulk degradation induced by the aging process. [ABSTRACT FROM AUTHOR]

A solvothermal deposition method using no TiO 2 seed layers was employed to grow a dense TiO 2 coating on ZrO 2 fibers as infrared opacifier. The crystal phase and microstructure of the obtained heterogeneous fibers were characterized by XRD, SEM, EDS and TEM. The mechanical stability and heat endurance of the TiO 2 coating were studied. The infrared shielding performance of the TiO 2 -coated ZrO 2 fibers was characterized by DRS and effective specific extinction (e*). In the infrared range of wavelengths from 2.5 to 10 μm, the TiO 2 coating on the fiber surface could increase the e* of the ZrO 2 fibers by 70%. The results suggest that the TiO 2 -coated ZrO 2 fibers are promising candidates as infrared opacifiers at high temperatures. • A uniform nano-TiO 2 coating was successfully fabricated on ZrO 2 fibers via a solvothermal method. • The coating thickness could be controlled by simply adjusting the hydrothermal time and temperature. • The coating had a strong binding force with the surface of ZrO 2 fibers and showed high thermal stability. • TiO 2 layer deposition provided barrier coating to reduce the infrared transmittance. [ABSTRACT FROM AUTHOR]

Successive self-nucleation and annealing (SSA) technique based on calorimetry is utilized to reveal the effect of uniaxial tensile stress on the photo-oxidation of high density polyethylene (HDPE). Stress-induced acceleratory and inhibitory effects on HDPE are confirmed by analyzing the newly formed melting peaks at low temperatures and the gradually disappeared melting peaks at high temperatures on the SSA curves. The formation of short chains due to chain scission contributes to both the new higher melting peaks (thick lamellae) and lower melting peaks (thin lamellae) because of high mobility and thermodynamic preference, respectively. Besides, chain crosslinking also gives rise to the formation of low melting peaks due to the decrease in the crystallizable sequence lengths and dynamical constraints. Compared with Fourier Transform Infrared Spectrometry, Scanning Electron Microscopy and Small Angle X-ray Scattering, the SSA technique can more precisely and sensitively reflect the early multi-scale aging behavior of HDPE subjected to stress. • SSA technique reveals the acceleratory and inhibitory effects of tensile stress on the photo-oxidation of HDPE. • Chain scission contributes to both the new higher melting peaks and lower melting peaks on SSA curves. • SSA technique is superior in detecting the early multi-scale degradation of HDPE under different stress levels. [ABSTRACT FROM AUTHOR]

Abstract Although a great deal of work has been dedicated to revealing the annealing-induced structure and mechanical changes in isotactic polypropylene (iPP), its effect on the photo-degradation behavior is seldom investigated so far. In this work, the correlation between microstructure induced by annealing in vacuum and photo-oxidative degradation behavior of iPP is studied. Lamellae thickening and perfection with increasing crystallinity are observed upon increasing annealing temperature. Besides, the formation of looser amorphous phase due to descendant chain segment concentration and decreased mechanical coupling between crystalline and amorphous regions are also corroborated. Annealing under elevated temperatures leads to decreased solubility coefficient of oxygen, improved radical scavenging ability of crystals and inhibited chain scission, which all synergistically contribute to an enhanced resistance to the photo-oxidation of iPP. However, the UV light absorption is not significantly changed by annealing before photo-oxidation. Electron Paramagnetic Resonance (EPR) results suggest that an effective removal of reactive sites by annealing can also be probably ruled out. In addition, EPR confirms that the total free radical concentration of annealed iPP is lower than that of unannealed samples after chain initiation step during photo-oxidation. Highlights • iPP exhibits an enhanced resistance to photo-oxidation after thermal annealing in vacuum. • The result is suggested to be related with the multi-level changes in the microstructure of iPP tuned by annealing. • Thermal annealing in vacuum is a promising strategy in improving the comprehensive performance of semicrystalline polymers. [ABSTRACT FROM AUTHOR]

The photo-oxidation behavior of high density polyethylene (HDPE) subjected to uniaxial tensile stress is investigated at various temperatures, tensile stress levels and time durations. The effect of stress on the photo-oxidation rate of HDPE is found to be non-monotonous. Tensile stress is found to play distinctly different roles, namely showing acceleratory or inhibitory effect, with the elapse of aging time and at different temperatures. Stress-induced aging inhibition is prone to occur at low temperatures and high stresses within an appropriate aging duration. With elevating temperature, however, this inhibition effect disappears gradually and the stress is found to accelerate the aging process. Microstructural analysis reveals that the effect of stress is closely related to the interplay between the changes in the surface morphology as well as amorphous aggregation structure of materials and the photochemical degradation during aging, which is induced by the variation of molecular orientation and packing state in amorphous region, stress transfer efficiency, thermodynamic and kinetic aspects of photochemical reaction process. [ABSTRACT FROM AUTHOR]

Polyaceticzirconium (PEZ) sol, which is the precursor of zirconia (ZrO 2 ) continuous fibers, has been synthesized by means of the reaction between zirconium oxychloride octahydrate (ZrOCl 2 ·8H 2 O) and potassium acetate (CH 3 COOK) in methanol. The polymeric structures and the rheological behaviors of the sols with different molar ratios of ZrOCl 2 ·8H 2 O/CH 3 COOK are different and would affect the spinnability and stability significantly. Herein, the polymeric structures and rheological behaviors of the PEZ sols with the molar ratios of 1:1, 1:1.5, 1:1.8 and 1:2 were investigated by Fourier transform infrared (FT-IR), 1 H nuclear magnetic resonance spectrum ( 1 H-NMR), thermogravimetry and differential thermal analysis (TG/DTA) and rheological measurements. The results showed the carboxyl group acted as a chelating ligand instead of bidentate ligand, and the water molecule coordinated to Zr 4+ was deprotoned gradually with the decrease of the molecular ratios. The different polymeric structures lead to a different rheological behaviors of the sols. It is divided into three types, the Newton fluid with a low viscosity produced by the charged linear polymeric structures, the shear thinning fluid with a high viscosity produced by the three-dimensional polymeric structures and the shear thinning fluids with a proper viscosity produced by the linear twining polymeric structures. Through the experimental guidance, we successfully synthesized a sol with suitable viscosity and stability, and used it to fabricate high quality ZrO 2 fibers. [ABSTRACT FROM AUTHOR]

• Properties of two types of CPI films under the photo-oxidation are investigated. • The yellowness index, thermal stability and mechanical properties are degraded. • The microstructure evolution of CPI films under the photo-oxidation are studied. • The content of the C O with the depth under the photo-oxidation is studied. • The relationship between properties and the microstructure has been revealed. Colorless transparent polyimide (CPI) films with high thermal stability, superior mechanical and dielectric properties are widely used in optoelectronic devices, in which the properties are degraded in service. In this work, the degradation in properties and molecular mechanisms of the CPI-L film with the trifluoromethyl group and CPI-T film with the alicyclic group under photo-oxidation are revealed. It is found that for CPI-L and CPI-T films after 168 h photo-oxidation, the mechanical properties and thermal stability are decreased, especially the yellowness index is increased by 740% and 530%, respectively. Consequently, the degradation of the CPI-L film is more severe than the CPI-T film after photo-oxidation. This is because that the transmission at 365 nm of CPI-L and CPI-T films before photo-oxidation is 51% and 64%, respectively. After photo-oxidation, the ether bond, imide ring and phenyl of both CPI films are broken, and the rearrangement of C N in the CPI-L film is observed. And eroded voids and/or microcracks caused by off-gassing appear at 120 h and 72 h, respectively. Furthermore, possible molecular mechanisms of CPI films during photo-oxidation are proposed, and the relationship between molecular mechanisms and properties degradation is elucidated. Moreover, the content of the C O is decreased with the increased depth of CPI-L and CPI-T films, indicating the enrichment of the C O on the surface. It is mainly because free radicals generated during photo-oxidation can combine with the atmospheric O 2. [ABSTRACT FROM AUTHOR]

Despite the huge success of commercial stabilizers (antioxidants, UV absorbers, etc.) on the functionality enhancement and lifetime prolonging of polymers, their toxicity on the environment has been raising severe concerns. Therefore, producing environmentally benign stabilizers via green chemistry has been attracting researchers' attention. In this work, we demonstrated the potential of mussel-inspired polydopamine nanoparticles (PDA-NPs) with intrinsic biocompatibility for the enhancement of both thermo- and photo-oxidation stability of polypropylene (PP). The effects of PDA-NPs size on the antioxidative performance of PP were systematically explored. PDA-NPs with different sizes of 471 nm, 284 nm, and 98 nm were synthesized first by tuning the pH values of initial dopamine solutions. The antioxidation ability of PDA-NPs for PP increased remarkably with the decreasing size, which was attributed to a higher specific area and more available semiquinone structure of smaller PDA-NPs. Compared with pure PP, the oxidation induction time (OIT) and onset thermal decomposition temperature of optimized PP composites can be increased significantly from 9.8 min to 26.0‍‍ min by 165% with the addition of only 0.5 wt% PDA-NP (98 nm), while the thermo- and photo-oxidative degree (formation of carbonyl products) on the surface can be decreased by 53% and 92% at most, respectively. However, the dependence of UV protection ability of PDA-NPs for PP on their size is non-monotonic. As indicated by cross-sectional fluorescence and modulus imaging, the shallowest degradation depth was observed for PP composites with the PDA-NP size of 284 nm other than that of 98 nm. These results have demonstrated the feasibility of PDA-NPs as robust stabilizers and the importance of size design for optimizing the anti-aging efficiency of PDA-NPs, providing valuable insights into the development of multifunctional stabilizers for environmental sustainability. • Polydopamine nanoparticles (PDA-NPs) significantly improved both thermo- and photo-oxidation stability of polypropylene. • The antioxidation ability of PDA-NPs for PP increased remarkably with the decreasing size of PDA-NPs. • The dependence of UV protection ability of PDA-NPs for PP on their size is non-monotonic. [ABSTRACT FROM AUTHOR]

Environmental toxicity of conventional stabilizers for polymers and their degradation products is raising severe concerns. There is an urgent need for the development of environmental-friendly, high-efficiency, and multifunctional stabilizers for polymers. Herein, Lignin nanoparticles (LNP), which were produced from enzymatic hydrolysis lignin (EHL) isolated from corncob residue, were demonstrated as a multifunctional stabilizer for polypropylene (PP). LNP fabricated by the anti-solvent method has distinct surface properties from the raw EHL, which lends it a better dispersion state in PP, and a higher free radical scavenging and UV absorption ability. The addition of 1 wt% LNP significantly enhances the thermo- and photo-oxidation stability of PP. The oxidation induction time of PP increases from 6.1 min to 12.3 min by 102 % with the addition of 1 wt% EHL, while it further increases to 20.1 min by 230 % for PP/LNP. Compared with PP, the oxidation degree of PP/EHL during thermo-oxidation for 8d is reduced by 27 % while that of PP/LNP is reduced by 60%. In addition, the UV degradation diffusion from the surface to the inner part of PP/LNP is significantly suppressed. These results highlight the excellent stabilization effects of LNP on PP and provide a promising path for the high-value-added lignin. [Display omitted] • Lignin nanoparticles (LNP) were fabricated from enzymatic hydrolysis lignin via antisolvent method. • LNP significantly enhanced both thermo- and photo-oxidation stability of polypropylene (PP). • The stabilization roles of LNP were attributed to its better dispersibility in the PP matrix, enhanced free radical scavenging ability, and stronger UV shielding effect. [ABSTRACT FROM AUTHOR]

The wear damage and aging behavior of natural rubber (NR) nanocomposites are very complex under severe conditions (high load, high-speed wear, or ablation). Little is known about the influence of strong interfacial friction on the high-temperature aging mechanism in the internal of NR nanocomposites. In this study, a set of UMT-TriboLab wear tester was used to study the wear and aging of NR nanocomposites, and to reveal their influence on the internal aging of specimens under severe conditions. Sliding wear tests were carried out with rubber-metal tribopair using a Block-on-Ring configuration. Different from mild wear conditions, the wear mechanism of NR nanocomposites under severe conditions experienced a transition from abrasive wear to adhesive wear. The viscous film formed by the degradation products on the wear surface was found to strongly affect the subsequent wear and aging behavior (wear weight loss, friction coefficient, temperature rise, etc.) of specimens. Layer-by-layer analysis showed that the heat diffusion caused by surface wear resulted in noticeable post-crosslinking in the internal layer of specimens while the oxidation reaction was limited to occur only on the specimen surface. • The wear behavior of NR blocks was studied under high loads and high speeds. • The specimen surface underwent serious mechanical and oxidative degradation. • Viscous films formed at interface strongly affected the wear and aging behavior. • Diffusion of frictional heat led to post-crosslinking in the internal layer. [ABSTRACT FROM AUTHOR]

• The evolution of performance and microstructure of aluminized colorless transparent polyimide films in the simulated vacuum ultraviolet (VUV) environment are systematically investigated. • The performance and microstructure for two types of aluminized colorless transparent polyimide films induced by the trifluoromethyl group and the alicyclic group are compared. • The optical performance of the aluminized colorless transparent polyimide film induced by the alicyclic group has better VUV resistance. • The Young's modulus, tensile strength, and the onset degradation temperature of aluminized colorless transparent polyimide films are slightly degraded after the VUV irradiation, whereas the elongation at break is significantly reduced. • Both the cross-linking and breakage of the molecular structure for aluminized colorless transparent polyimide films compete during irradiation, which determines the changes of properties. Aluminized colorless transparent polyimide (CPI/Al) film has a medium absorptivity emissivity ratio, which can keep a moderate equilibrium temperature for spacecraft, however, the property evolution and relative mechanisms under vacuum ultraviolet irradiation of CPI/Al films are rarely reported. In this work, the evolution of performance and microstructure of CPI/Al films in the simulated vacuum ultraviolet (VUV) environment is systematically investigated, in which two types of CPI films induced by the trifluoromethyl group (CPI-L/Al film) and the alicyclic group (CPI-T/Al film), respectively, are compared. It is found that the optical performance of the CPI-L/Al film is degraded more severely than that of the CPI-T/Al film, indicating better VUV resistance of the CPI-T/Al film. Specifically, for CPI-L/Al and CPI-T/Al films after 2000 ESH irradiation, the yellowness index and the solar absorptance are increased by 532.9% and 503.1%, and 157.0% and 126.7%, respectively, whereas the hemisphere emissivity is decreased by 20.8% and 6.1%, respectively. This is because the oxygen-ion escapes from the surface of CPI films and oxygen-ion vacancies are formed. Moreover, the Young's modulus, tensile strength, and the onset degradation temperature of CPI/Al films are slightly degraded after the VUV irradiation, whereas the elongation at break is significantly reduced especially for CPI-L/Al and CPI-T/Al after 2000 ESH irradiation it is decreased by 90.2% and 95.1%, respectively. This can be ascribed to the competition between the cross-linking and breakage of the molecular structure during irradiation, in which the breakage is dominant in the early stage of irradiation, leading to a great degradation in properties, and cross-linking structures are formed in the later stage of irradiation which can compensate for the degradation in properties. [ABSTRACT FROM AUTHOR]

• As a natural antioxidant, NRCs improved the thermo-oxidative stability of NR. • NRCs promoted the formation of mono- and disulfide bonds during vulcanization. • More monosulfide bonds were formed during the aging of vulcanized SHANR. • SHANR showed high thermal/mechanical stability against aging. Non-rubber components (NRCs) in natural rubber (NR), including proteins, phospholipids, fatty acids, etc., determine to a large extent the structure and properties of NR. In this study, the effects of NRCs on the network structure and thermo-oxidative aging behavior of unvulcanized and vulcanized NR were investigated. NRCs were found to form physically crosslinked networks in the unvulcanized NR and acted as a natural antioxidant to scavenge free radicals, which contributed to improved thermo-oxidative stability of the unvulcanized NR. Swell analysis, chemical probe analysis (DPPH), and XPS results showed that the NRCs accelerated the vulcanization reaction and increased the crosslink density, and promoted the formation of more mono- and disulfide bonds during vulcanization. When aged at high temperatures, more monosulfide bonds were formed in the vulcanized rubber with high contents of NRCs by cleaving and rearranging the poly- and disulfide bonds. NRCs were also found to increase the activation energy of thermal degradation and led to the better mechanical stability of vulcanized NR against thermal oxidation. [ABSTRACT FROM AUTHOR]

Polymer-based electromagnetic wave-absorbing (EWA) coatings that can effectively dissipate electromagnetic radiation are in high demand. While researchers on the development of lighter and more efficient EWA coatings have been carried out extensively, there is limited information on their durability and the underlying degradation mechanisms. In this work, epoxy (EP)/flake carbonyl iron powder (FCI) coatings were selected as the model EWA coating. UV aging experiments of specimens were conducted up to about 240 h to study the effects of additional FCI on the photo-oxidative behaviors of coatings. The evolutions in the surface topography, chemical structure, hydrophilicity of aged coatings were systematically studied by Scanning electron microscopy (SEM), Laser scanning confocal microscopy (LSCM), Fourier transform infrared spectroscopy (FTIR), and static contact angle measurement, and further combined with micro-FTIR to investigate the degradation diffusion behavior from the exposed surface to the bulk of coatings. The results showed that the addition of FCI significantly accelerated the photo-oxidation of EP coatings, which was attributed to the corrosion of FCI during aging and the concomitant photo-catalytic degradation effects of its corrosion products. Moreover, the cross-sectional analysis revealed a non-uniform distribution of EP degradation species across the thickness direction, while it is interesting to find that the degradation depth of EP/FCI coating was lowered compared with that of pure EP coating, which could be due to the UV blocking effect of FCI. This work clearly revealed the underlying mechanisms for the distinct dependence of surface and cross-sectional degradation of coatings on the incorporation of FCI, which has laid crucial groundwork for durability evaluation and performance optimization of EWA coatings. [Display omitted] • Paradox effects of FCI on the photodegradation behaviors of epoxy coatings • The addition of FCI accelerated the photo-oxidation on the surface of EP coatings • The degradation depth of EP/FCI coating was decreased due to UV blocking effects of FCI [ABSTRACT FROM AUTHOR]

[Display omitted] • The branched PLA simultaneously exhibits extremely robust melt strength and low shear viscosity. • The long-chain branches are uniformly dispersed on the backbone of PLA. • The branched PLA shows super-robust foamability with volume expansion ratio of 72.9-fold. • The branched PLA displays super-high heat resistance up to 155.1 °C. Poor melt strength and crystalline properties are the key barrier for polylactide (PLA) toward broader applications. Long chain branched PLA (LCB-PLA) with high foamability and heat resistance are prepared by employing dual-functional 4-vinylbenzyl glycidyl ether (VBGE) as branching coagent with cyclic peroxide. As a result, the branched chains with same length of original PLA chains are uniformly dispersed on PLA backbones via both the free-radical grafting reaction of the vinyl group in VBGE with one PLA backbone and end-group reaction of the epoxy group in VBGE with the carboxyl group of the other PLA chain. Not only the significantly enhanced foamability and heat resistance of LCB-PLA induced by the largely improved melt strength and crystallization performance but also the excellent processing flowability due to a relatively slight increase in the shear viscosity are found. Specifically, as compared to the pure PLA, the expansion ratio of LCB-PLA with 0.6 wt% VBGE is increased by 17.4 times, and the Vicat softening temperature is enhanced by 95.5 °C. Thus, this study paves a novel one-step continuous strategy to design LCB-PLA with ultrahigh foamability and heat resistance, which is valuable for the large-scale popularization of foamed PLA packaging products. [ABSTRACT FROM AUTHOR]

• Acetone-induced crystallization roughened up the surface of polycarbonate (PC) substrates. • Fluorinated silica nanoparticles/epoxy superhydrophobic coating adhered firmly to the roughened PC surface. • The coating showed excellent anti-icing performance and resistance to mechanical and corrosive damages. • The coating exhibited good durability against photo-oxidative and hygrothermal aging. In this study, we designed mechanically and chemically robust superhydrophobic coatings with strong interfacial adhesion with polycarbonate (PC) substrates by dripping an acetone solution containing fluorinated silica (F-SiO 2) nanoparticles and epoxy resin. It was found that the acetone-induced crystallization and roughening of PC leading to a firm bonding of superhydrophobic F-SiO 2 /epoxy coatings onto the surface of PC substrates. The coatings prepared under the optimal condition showed an excellent superhydrophobic property with a water contact angle (CA) larger than 160° and a sliding angle (SA) smaller than 2°, together with superior anti-icing performance. The coatings retained their excellent superhydrophobicity after various external mechanical damages (such as tape adhesion, knife scratch, finger wiping, and sandpaper wear) and in different corrosive environments (acidic, alkaline, and salinity solutions). Furthermore, the new coatings exhibited outstanding ability against photo-oxidative and hygrothermal aging. Therefore, it is believed that the superhydrophobic coatings prepared have the potential to satisfy the imperative requirements in many harsh outdoor applications based on PC materials. [ABSTRACT FROM AUTHOR]

In this work, acrylates with various functionalities are employed as the branching coagent for improving the properties of long chain branched polylactide (LCB-PLA) induced by reactive extrusion with low content of cyclic organic peroxide (COP). It is discovered that the heat resistance and foaming performance of COP-initiated LCB-PLA are remarkably improved by the coagent. Specifically, the Vicat softening temperature and expansion ratio of 0.3 wt% COP-initiated LCB-PLA with 0.3 wt% coagent are sharply increased to above 150 °C and 27.0-fold, respectively (60 °C and 9.8-fold for 0.3 wt% COP modified PLA). This is due to the simultaneously enhanced melt strength and crystallization properties of LCB-PLA induced by the obviously enhanced branching degree by the coagent. Moreover, the branch-promotion efficiency of various coagents is found to be independent of the functionality due to the steric hindrance. The possible mechanisms on the formation of topological structures of COP modified PLA with coagents are proposed. Image 1 • Branched PLA is induced by cyclic peroxide and multifunctional acrylate coagents. • The branching degree of LCB-PLA is distinctly promoted by adding acrylate coagents. • The crystallization and melt strength of LCB-PLA are markedly improved by the addition of coagents. • Heat resistance and foaming performance of LCB-PLA are largely enhanced by coagents. • The branch-promotion efficiency of various acrylate coagents is independent of functionality. [ABSTRACT FROM AUTHOR]