Polymer Degradation and Stability最新文献

Polypropylene (PP) is widely used in the medical industry to produce syringes, vials, and numerous other single-use biopharmaceutical devices. The need to sterilize these products has led to intensive use of high-energy radiation, even though PP is known to undergo excessive oxidative degradation and deterioration in properties upon irradiation in air. In recent years, a shortage in ⁶⁰Co supply, as a main source for gamma sterilization, is pushing radiation sterilization of polymeric medical products to electron beam (EB) and/or X-ray modalities as preferable. Some questions related to the equivalence of these methods remain open and are mostly related to changes in the material structure caused by different types of radiation and processing conditions, such as dose rates.

This research compares electron beam and gamma irradiation modalities employed on the low crystalline (quenched) PP. In the case of EB irradiation, the typical dose rates are on the order of 10⁴ kGy/h, while in the case of gamma radiation dose rates are lower for three or more orders of magnitude. Since gamma irradiation covers a wide range of dose rates, the difference between samples gamma irradiated with relatively fast (8 kGy/h) and slow (0.08 kGy/h) dose rates was also analyzed in detail. Comparative investigation of crystallinity, oxidative degradation, thermal, dielectric, and mechanical properties provide a clearer picture of the impact of different modalities and dose rates on mesomorphic PP and are of interest in the practical application of ionizing radiation in the sterilization of PP-based medical devices.

A novel polyhedral oligomeric sesquisiloxane (POSS) antioxidant based on amide-linked hindered phenols (HPAm-POSS) was successfully synthesized via a nucleophilic substitution reaction. The chemical structure of HPAm-POSS was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), MALDI-TOF mass spectrometry (MS), and thermogravimetric analysis (TGA). The antioxidative efficiency of HPAm-POSS in polyamide 6,6 (PA66) was investigated by accelerated thermal aging tests, processing experiments, and extraction experiments and compared with a commercial hindered phenol antioxidant, Irganox 1098, at an equivalent concentration of active hindered phenolic stabilizer groups. The results showed that the thermal-oxidative stability of PA66 materials was significantly improved by the incorporation of either HPAm-POSS or Irganox 1098. Although the antioxidant efficiency of HPAm-POSS in the long-term accelerated thermal aging of PA66 at 150 °C in an air oven is slightly lower than that of Irganox 1098, HPAm-POSS is slightly more effective than Irganox 1098 in inhibiting the degradation of PA66 during multiple processing. Notably, HPAm-POSS exhibited higher anti-extraction properties in PA66 due to its higher molecular weight and lower migration ratio. Consequently, PA66/0.35 %HPAm maintains thermo-oxidative stability even after being extracted with organic media such as ethanol, toluene, or ethylene glycol, whereas PA66/0.30 %1098 is highly susceptible to thermo-oxidative degradation due to the physical loss of Irganox 1098 by extraction.

Four water-soluble α-amino acid-derived polyamidoamines (PAAs) obtained by reacting N,N’-methylenebisacrylamide with glycine, leucine, arginine and glutamic acid were studied as photostabilizers of cotton. Untreated and PAA-treated cotton strips with 10 % PAA add-on underwent accelerated photoaging by UV irradiation in air at temperature from 25 to 50°C and 30 % relative humidity. Irradiation was applied in consecutive 4 h cycles, after each of which samples were analyzed by different techniques. After 30 h irradiation, the whiteness index and colorimetric parameters indicated significant yellowing of cotton, which became slightly more intense after 100 h irradiation. On irradiation, PAA-treated samples showed only slow decrease in whiteness and increase in yellowing. After 100 h, yellowing achieved significantly lower levels than in untreated cotton. In no case did the infrared spectroscopy and electron microscopy reveal detectable structural and morphological alterations, even after 100 h of UV exposure. Thermogravimetric analysis showed only little changes of thermograms following photoaging. X-ray diffraction analysis revealed slight deformation of the cellulose crystalline structure following both PAA treatment and UV irradiation. Finally, the PAA coatings were extracted from the cotton strips and analyzed by ¹H-NMR analysis. Only the glutamic acid-derived PAA showed detectable structural changes that did not involve the main chain. The FT-IR spectra and white indexes of the washed cotton strips did not differ from those of untreated cotton. Overall, it was proven that α-amino acid-derived PAAs protect cotton from photo-oxidation. Their performance was attributed to the radical scavenging ability of tert-amine groups present in their repeat units.

The thermal properties and pyrolysis decomposition paths of cotton fibers modified by different chemical treatments, a conventional functionalization with silane and a novel sulphation-phosphorylation approach, were studied. The effects on the fibers thermal behavior and decomposition products were investigated. The cotton fibers were characterized before and after the surface treatments by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and pyrolysis/gas chromatography–mass spectrometry (Py/GC–MS). Morphological investigation was also performed by SEM/EDS analysis to assess the treatment effects on the cotton fibers’ surface. The silanization increases the cotton hydrophobicity and thermal stability, changing the pyrolysis mechanism, favoring depolymerization over dehydration and charring. On the contrary, sulphation-phosphorylation methods cause a decrease in the onset temperature and an increase of fire resistance, and charring yield. Thermal decomposition temperatures, weight losses, and pyrolysis mechanisms and products, were fully analyzed. The results can open the way on the use of modified cotton fibers in industrial fields where fireproofing is strongly desired.

Cellulose implementation as filler in polyurethane foams (PUF) often leads to an increased the fire risk associated to the prepared biocomposite. To address this problem, this paper presents a novel approach where the cellulose filler is coated by a nanostructured layer-by-layer (LbL) assembly with flame retardant characteristics before its addition to the biocomposite. During PUF production, the presence of cellulose led to a reduced cell size distribution with improved thermal insulation properties. By forced combustion tests, the use of neat cellulose produced a detrimental effect by increasing the PUF heat release rates (up to +21 %). Conversely, the coated cellulose simultaneously decreased the peak of heat release rate (-22 %) and the total smoke release (-32 %) if compared with the reference PUF. The proposed approach represents a viable strategy for the production of PUF biocomposites where sustainability and fire protection are optimized.

In order to satisfy the application of epoxy resin (EP) in high-end electronic packaging, phosphorus fluorine containing polymers were synthesized to simultaneously enhance the flame retardant, dielectric, and hydrophobic properties of EP. Through the reaction of 2-hydroxyethyl methacrylate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a monomer named HEMA-P was synthesized. By copolymerizing (2,2,2-trifluoroethyl methacrylate and 1H, 1H, 7H-dodecafluoroheptyl methacrylate) with HEMA-P through the typical reversible addition-fragmentation chain transfer (RAFT) polymerization, two phosphorus fluorine containing polymer modifiers named 3FOP and 12FOP with different lengths of fluorine side chain were obtained. The flame-retardant level of FOP/EP composites reached V-1 level. The limited oxygen index (LOI) values of 3FOP/EP and 12FOP/EP composites (10 wt% additive amount) increased to 33.6 ± 0.5 % and 32.8 ± 0.3 %, respectively, with corresponding peak heat release rates (pHRR) decreased by 37.8 % and 33.2 % compared with neat EP, suggesting the FOP modified EP composites have good flame retardant and smoke suppression effects. The mechanical properties of the FOP/EP composites can also be improved. Notably, with the 10 wt% addition of 12FOPs, the water contact angle of 12FOP/EP composite reached 116.5°, which was 40.7 % higher than that of EP. Moreover, the dielectric constant decreased with the increasing fluorine content. The thermal stability and possible thermal degradation pathways of 3FOP and 12FOP were characterized by TG-IR, Py-GC/MS, and Raman spectroscopy. Based on experimental results, we innovatively revealed a phosphorus fluorine synergistic flame retardancy mechanism.

The preparation of flame retardant PA56 material with superior thermal stability, melt-drop resistance, and mechanical properties has been challenging in industry. Herein, we prepared a core-shell MCA-based flame retardant (BP-MCA) for PA56 via the hydrogen bond self-assembly and solvent exchange strategies. The hydrogen bond self-assembly strategy modulates the morphology of MCA-based flame retardant. The solvent exchange strategy further improves the dispersion, and char-forming properties of flame retardant. Compared with PA56, PA56/BP-MCA achieves the UL-94 V-0 rating, LOI value of 32.5 % and THR value of 55.2 MJ/m². Besides, PA56/BP-MCA exhibits superior mechanical properties due to the larger aspect ratio and better dispersion of BP-MCA.

Epoxy adhesives have been extensively used in the aerospace, marine, and automotive industries to join different components. A major concern with the use of epoxy adhesives is their viscoelastic behavior in aggressive service conditions such as hygrothermal ageing. Surveying the creep behavior of adhesives is of paramount importance to increase long-term durability. In this work, nanoindentation creep tests were performed on an epoxy adhesive exposed to distilled water and seawater at 55 °C for various ageing durations (0, 14, 38, 160, 251, 383, 582, and 800 h). The hardness, modulus, creep displacement, and creep rate sensitivity were quantitatively investigated to elucidate the effect of hygrothermal ageing. All the mechanical properties were found to decrease with the ageing time. The adhesive subjected to distilled water showed lower creep resistance due to higher absorption of moisture. In addition, linear relationships were observed between different mechanical properties and moisture contents irrespective of ageing conditions. Subsequently, the generalized Kelvin model was applied to investigate the creep compliance and the dependence of different deformation types (elastic, viscoelastic, and viscous deformation) on the ageing time and ageing conditions. The motion of molecular structures was also discussed. Finally, a modified creep model was proposed based on the generalized Kelvin model and continuum damage theories, which established the relationship between the dry and aged adhesive via the moisture-dependent degradation factors. The predicted creep displacements coincided well with the experimental results for the case, demonstrating the reliability of the creep model.

Epoxy amine coatings were subjected to hygrothermal ageing and accelerated weathering conditions that is comprised of neutral salt spray test and UV accelerated degradation condition. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Fourier Transform Infrared Spectroscopy (FTIR) were employed to study the surface responses and spectral variation of epoxy amine coatings subjected to different ageing conditions. As a result, principal component analysis (PCA) of ToF-SIMS positive ion spectra illustrated that principal component 1 (PC1) has collected information on a variation of surface responses caused by accelerated weathering and hygrothermal ageing conditions as compared to fresh epoxy amine coatings. On the other hand, principal component 2 (PC2) has distinguished the different surface responses generated on epoxy amine coatings that were subjected to UV accelerated degradation conditions and those that were not. FTIR analysis has demonstrated the hydrolysis and photooxidation of epoxy amine coatings from the growth of two absorption bands at 1709 cm⁻¹ and 1650 cm⁻¹, indicating the formation of carbonyl-containing groups such as ketones, aldehydes, phenyl formates, imine or tertiary amides. This comprehensive analysis provides significant insights into the degradation mechanisms of epoxy amine coatings subjected to corrosion under insulation (CUI) and/or artificial weathering (AW) environment. Understanding these mechanisms is pivotal for industries reliant on epoxy coatings, such as oil and gas, ensuring enhanced performance and extended lifespan of their products under varying environmental conditions. The findings also contribute to the broader field of materials science by offering methodologies and analytical approaches that can be applied to other polymeric coatings and materials.

As a degradable polymer material, the regulation of the degradation rate of polylactide (PLA) under an actual light exposure environment is of significant importance for realizing its multifaceted applications. This study aims to enhance the photodegradation of PLA under irradiation with lower-energy wavelengths by using TiO₂-based up-conversion nanoparticles (UCNPs). Two modification methods were employed: doping TiO₂ with Yb³⁺/Er³⁺/Tm³⁺ ions integrated within the TiO₂ lattice, and creating a composite photocatalyst by adhering Y₂O₃: Yb³⁺/Er³⁺/Tm³⁺ to the exterior of TiO₂ grains. The study investigated the impact of these two different TiO₂-based UCNPs on the photocatalytic degradation rate and mechanism of PLA under simulated sunlight irradiation. Research has found that the doped TiO₂, due to its narrower bandgap and higher photon utilization efficiency during the up-conversion process, exhibited superior catalytic efficiency in catalyzing the photodegradation reactions of PLA compared to unmodified TiO₂ and composite TiO₂. This work proposes a novel strategy for preparing PLA composites with enhanced photodegradation speed provided by modified TiO₂, efficient light energy utilization offered by the up-conversion process, and potential applications in more advanced packaging and agricultural fields.