Polymer Degradation and Stability最新文献

The fabrication of ultralight high-performance flame-retardant composites significantly reduces fire risk for buildings. Flame retardation of porous polyvinyl alcohol (PVA) aerogels with directional arrangement is difficult. Herein, the polyvinyl alcohol/ 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivative/two-dimensional (2D) MXene (PVA/DiDOPO/MXene) composite aerogel was prepared by ice template one-way freezing process. PVA-DiDOPO4 composite aerogel with an oriented porous structure reaches the V-1 level at the UL-94 test. Moreover, the peak heat release rate (pHRR) value of PVA-DiDOPO4 reduces to 452.26 (W/g) from 482.88 (W/g) of pure PVA. In addition, PVA/DiDOPO/MXene composite aerogel has improved thermal decomposition properties such as the maximum decomposition temperature (T_max1) of the PVA-DiDOPO4 sample attains 319.92 °C from pure PVA of 302.90 °C. The design strategy of PVA combined 2D MXene nanosheet and DOPO derivatives construct oriented porous composite aerogel paves the way for the fabrication and customization of ultralight flame-retardant polymer composites, which can be expected to be applied in construction and reduce fire risk.

Thermoplastic polyurethane (TPU) has an extensive application in many different industries. However, serious fire hazards and smoke toxicity have been the main reason limiting its wide application. Therefore, it is necessary and urgent to perform flame retardant and smoke suppression treatment for TPU. In recent years, metal-organic framework compounds (MOFs) have very promising application prospects in the fields of flame-retardant polymer composites. However, there is a problem of low flame-retardant efficiency for the original MOFs alone in polymer composites. It is reported the multi-level and multi-structured flame-retardant system has better flame-retardant efficiency than the traditional structures. So, the dual MOF core-shell heterostructure may have more effective heat reduction and smoke suppression than any single component. In this paper, a core-shell 3D cross-heterostructures nanohybrid (ZIF-67H@PBA) was prepared using ZIF-67H as the host MOF and Prussian blue nanocubes (PBA) as the guest MOF. It has been found that TPU/ZIF-67H@PBA composites with ultra-low additions have excellent fire safety. Compared with those of pure TPU, the peak heat release rate (PHRR), total smoke release (TSP), and smoke factor (SF) of the samples with 0.5wt% ZIF-67H@PBA were reduced by 33.6 %, 47 %, and 61 %, respectively. At the same time, a cone calorimeter (CCT), a homemade soot sampling device and a gas chromatography-mass spectrometry (GC–MS) coupling with each other were constructed and used to demonstrate the most realistic effects of flame retardants in terms of smoke suppression and toxicity reduction. This work provides a new strategy to design TPU flame retardants.

Developing bio-based copolyesters with excellent mechanical properties, controlled degradation, and easy industrial production would significantly promote adopting disposable green products and advancing a circular economy. A series of poly(butylene adipate/terephthalate-isosorbide) (PBIAT) were successfully synthesized by introducing varying amounts of biologically derived isosorbide (IS) as the modifying monomer into cost-effective poly(butylene adipate-co-terephthalate) (PBAT). It was demonstrated that IS effectively enhances the rigidity of molecular chains, thereby the glass transition temperature of PBIAT increased almost linearly with IS content, while the tensile strength, elongation at break, and tensile toughness improved by up to 85 %, 69 %, and 42 %, respectively, compared to neat PBAT. Moreover, studies on the degradability of the copolyester demonstrated that PBIAT exhibits controlled degradation capability. The stability of PBIAT in a neutral solution is consistent with that of PBAT, whereas the degradation rate of PBIAT increased by up to 70 % in the enzyme solution. This work provides insights into the design of isosorbide-modified degradable polyesters for regulating the mechanical properties and degradation rate.

A lipase from Burkholderia cepacia was covalently linked to the surface of Laponite® layered silicate after its activation with glycidoxy moieties on two different routes. The modified silicate was embedded into poly-ε-caprolacton (PCL) for the preparation of self-degradable biopolymers. The activated silicate was characterized by thermogravimetry (TGA) and infrared spectroscopy (FTIR), the location of the linker among the silicate layers was determined by X-ray diffraction (XRD). The activity of the immobilized enzyme was tested in two model reactions, by transesterification in organic medium and hydrolysis in aqueous buffer. The immobilized enzyme was homogenized with the polymer and then films were compression molded at 70 °C. TGA and FTIR measurements verified the successful activation of the silicate but the number of available epoxy groups were limited on the surface. These functional groups linked enzyme molecules to the silicate surface. The enzyme retained its activity even after immobilization and had similar or better catalytic performance than the neat enzyme in both transesterification and hydrolysis. The supported enzyme degraded PCL efficiently, the rate of degradation depended on the type of the linker molecules and on the activated enzyme content of the polymer. The covalently linked enzyme catalyzes the degradation of a solid polymer matrix thus allowing the preparation of self-degradable composites with controlled lifetime and helping the reduction of environmental pollution.

The presented study was focused on the development of a sustainable type of composite characterized by improved flame retardance. Polyamide 6 (PA6) was modified with the addition of biocarbon (BC) and organic phosphorous flame retardant (OP). The initial part of the study was aimed at the evaluation of the OP:BC system efficiency, while the final part of the research focuses on the preparation of composites with basalt fibers (BF) reinforcement. Composite materials were modified using 20% of the OP:BC mixture at different ratios. The reinforced samples were modified with an additional 20% of the BF filler. Prepared samples were subjected to detailed analysis, mechanical properties evaluation, thermal analysis, microscopic observations, and burning tests. The results indicate that the application of the developed concept led to a large decrease in flammability for most of the investigated PA6-based materials; however, the most interesting results refer to materials containing a balanced OP:BC system.

A circular economy requires that plastic packaging should be recyclable or compostable as well as reusable. Compostable/biodegradable poly(lactic acid) (PLA) is an alternative to conventional packaging materials for films, bags, and containers. Packaging is not only for food and beverages but also for medicine, agricultural chemicals, industrial chemicals, and waste solvents such as chlorinated solvents, which sometimes contain water. This study determined that PLA films were completely soluble in dichloromethane and chloroform, insoluble but strongly swollen in trans-1,2-dichlorocycrohexane, o-dichlorobenzene, and carbon tetrachloride, and insoluble with retained film shape in tetrachloroethylene (TCE), 1,2,4-trichlorobenzene (1,2,4-TCB), and 1-bromonaphthalene (1-BN). The equilibrium mass uptake values of pure insoluble solvents in PLA films were 0.977 ± 0.219 wt% for TCE, 1.716 ± 0.631 wt% for 1,2,4-TCB, and 3.351 ± 1.936 wt% for 1-BN. After sorption of the three insoluble pure solvents, the α’-type crystals of PLA films changed to α-type crystals. This phenomenon was based on the molecular size and electrostatic potential value of the solvents. When insoluble solvents were mixed with water, the water-in-oil mixture enhanced the mass uptake for TCE and 1,2,4-TCB but reduced it for 1-BN. The oil-in-water mixture distinctly reduced the solubility for all solvents. The α-type crystal structure was stable in TCE and 1-BN. If an industrially appropriate method of α-type crystal structure formation could be realized selectively, then PLA could be used as packaging materials for films, bags, and containers for these solvents without any further modification.

Deconstruction of polyolefins into functionalized macromonomers presents a compelling strategy for polyolefin upcycling by creating macromonomers through dehydrogenation/depolymerization. We show that nitrous oxide (N₂O), a greenhouse gas waste product from the production of nylon, mediates the deconstruction of polycyclooctene (PCOE) and generates carbonyl-functionalized macromonomers. Carbonyl incorporation and macromonomer molar mass were well controlled by reaction time, and subsequent hydrogenation readily removed residual carbon-carbon double bonds. We also demonstrated that the reaction could progress efficiently with substrates of moderate levels of unsaturation, closely mimicking partially dehydrogenated polyethylene. Such carbonyl-functionalized macromonomers could serve as feedstock for preparing vitrimers and other functional polymers.

Liquid silicone rubber (LSR) exhibits excellent thermal stability and has been selected for use in a variety of applications where thermal stability, chemical resistance and fire-retardant are required. The enhancement of the organic-to-inorganic conversion of LSR to improve their flame-retardant properties represents a significant area of research. The thermal stability of the platinum catalysts and the crosslinked network structure of the LSR have a considerable influence on the organic-to-organic conversion behavior of LSR. The present study demonstrates the efficacy of N-heterocyclic carbene (NHC) ligand-modified Karstedt's catalysts as catalysts for the curing of LSR by hydrosilylation at room temperature and for the organic-to-inorganic conversion of LSR at elevated temperatures. The catalyst was employed in the preparation of three LSRs with varying network structures, utilizing four polysiloxanes with differing degrees of functionality. The pyrolytic behavior and organic-to-organic conversion rate of these LSRs were investigated using a thermogravimetric analyzer (TG) coupled with a Fourier transform infrared spectrometer (FTIR). The findings indicated that LSRs with the highest crosslink density exhibited the highest organic-to-inorganic conversion rate; however, they demonstrated the lowest fire-resistance. The anomalous behavior has been subjected to further analysis with respect to the mechanical properties of the LSRs and the characteristics of their network structure. LSR coatings with enhanced hardness and fire-resistance are then produced by combining the advantageous properties of both LSRs in a layer-by-layer (LBL) assembly.

Atomic oxygen (AO) is the most common gas species in the Low-Earth-Orbit (LEO) and responsible for material degradation of the outer shell of spacecrafts within this space region. Due to their similar properties, low temperature oxygen plasmas are suited for material degradation studies taking place on earth instead of quite expensive space studies. Here we focus on the long-term degradation of Polytetrafluoroethylene (PTFE), which is often employed on the outside of spacecrafts. Up to date, there is no complete understanding of the degradation process on molecular level, which is necessary for materials improvement and new materials development.

For the degradation studies, a self-constructed capacitively driven 13.56 MHz RF reactor was used to generate an oxygen plasma for the simulation of LEO conditions. PTFE was characterised in the pristine state and after AO treatment at different times by ToF-SIMS, XPS and SEM. During plasma treatment, the samples show a linear mass loss behaviour. ToF-SIMS surface analysis reveal mass fragments which show a clear chemical reaction of oxygen species with PTFE. The presence of these molecular indicators was verified by XPS, where additional carbon species were found after plasma treatment. SEM micrographs showed an inhomogeneous degradation on the surface in the first hours similar to actual LEO exposure. For a complete understanding of the degradation progress, operando mass spectrometric studies of the plasma composition were carried out to detect volatile degradation products.

In summary, a steady degradation has been observed that leads to constant mass loss, defluorination, chain shortening and insertion of oxygen into the polymer.

In recent years, the excessive consumption of fossil energy leads to the depletion of petroleum resources and environmental pollution. Therefore, biomass which is renewable and easy availability has been exploited in the past few decades to replace petroleum resources and to design bio-based epoxy resins. Through molecular design and synthesis, alternative bio-based products with close properties to petroleum-based epoxy resins were exploited, and then bio-based epoxy resins with excellent and unique properties were developed. This present review mainly summarizes the synthetic strategies of bio-based epoxy resins through the chemical modification of various bio-based precursors, such as eugenol, vanillin, cardanol, furan, plant oil, and so forth. And then their inherent and superior properties relating to the unique structures and potential applications are discussed. Finally, the challenges and opportunities in the development of sustainable epoxy thermosets from renewable biomass are presented. It is hoped that this review will provide a framework for further design of bio-based epoxy thermosetting materials.